TW201629541A - Method for producing phase-difference film and method for producing laminated polarizing plate - Google Patents

Abstract

In a method for producing a phase-difference film according to the present invention, when an elongate support film that comprises a bi-axially oriented film is conveyed in a lengthwise direction, a resin solution is coated on the support film, where the resin solution on the support is heated to dry so as to form a laminate comprising the coated film laminated on the support film. After drying, the laminate is stretched in at least one direction to impart optical anisotropy to the coated film. Before the resin solution is coated, heating treatment is conducted on the support film. The heating treatment is conducted in a condition that the support film is applied with tension in the lengthwise direction. With the present invention, a phase-difference film having less nonhomogeneous orientation angle of an optical axis in a width direction can be obtained.

Description

Method for producing retardation film and method for producing laminated polarizing plate

The present invention relates to a method of producing a retardation film. Further, the present invention relates to a method of manufacturing a laminated polarizing plate comprising a laminated polarizing element and a retardation film.

In a display such as a liquid crystal display device, a retardation film is used for the purpose of improving contrast or enlarging optical compensation such as a viewing angle (see, for example, Patent Document 1). For the retardation film used in optical compensation, uniformity of film thickness or optical characteristics is required. Therefore, in the film formation of the retardation film, a solution film forming method is widely used. In the solution film forming method, a resin solution (coating) in which a polymer is dissolved in a solvent is applied onto a support, and then the solvent is removed by heat drying or the like to form a laminate having a coating film adhered to the support. .

As described in Patent Document 2, a coating film (film) formed by a solution film forming method can be directly used as a retardation film. Further, various coating optical anisotropies can be imparted by extending the coating film formed by the solution film forming method in at least one direction. In the case where the coating film formed by the solution film forming method is stretched to produce a retardation film, generally, a method of peeling off the support from the laminate of the support and the coating film and separately stretching the coating film is employed.

On the other hand, when a support such as a resin film is used as the support for forming a solution for a solution, the laminate of the support and the coating film may be extended to impart optical anisotropy. In particular, when the film thickness of the coating film is small (for example, 30 μm or less) or when a less ductile (brittle) resin material is used, since the coating film is low in self-supporting and difficult to handle, Therefore, the laminate of the support and the coating film used in the film formation is extended. The method of stretching. In this case, as disclosed in Patent Document 3, there is a method in which the support is not peeled off from the laminate, and the laminate of the support and the coating film is directly used as a laminated retardation film, and the laminate is self-extended. The support is peeled off from the body, and only the stretched coating film is used as a retardation film for practical use. Further, Patent Document 4 discloses a method of forming a coating film by using a film formed by a heat shrinkable film as a support, heating and shrinking the laminate, and then peeling off the support, thereby forming nx>nz>ny. An optically anisotropic retardation film.

For the support used in the solution film formation, solvent resistance to a solvent or heat resistance at the time of heat drying is required. Further, when the support body and the coating film are not peeled off and the stretched laminated body is directly used as the retardation film, the support is required to be optically uniform. On the other hand, when the support is peeled off from the laminate after stretching, and only the coated film after stretching is used as the retardation film, the support system is not included in the step member which is the retardation film of the final product. In this case, the support does not necessarily need to be optically uniform, and it is preferable to have a range of solvent resistance or heat resistance which can withstand processing such as film formation or stretching.

[Previous Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open Publication No. 2009-139747

[Patent Document 2] Japanese Patent Laid-Open Publication No. 2009-80440

[Patent Document 3] Japanese Patent Laid-Open Publication No. 2004-46068

[Patent Document 4] Japanese Patent Laid-Open Publication No. 2011-227430

In recent years, with the advancement of high image quality of displays, and the performance required for retardation films have also increased. At the same time, the demand for lighter weight or thinner display has also increased, and a phase difference film having a smaller film thickness than before has been used. For films containing a small film thickness, or In the production of a film containing a resin material having a small mechanical strength, as described above, it is suitable to use a method in which a coating material is applied onto a resin film support, and after a coating film is formed on the support, the support and the coating film are used. The laminate is integrally extended to peel off the support.

As the support, a material which is inexpensive and has high mechanical strength is preferable, and in general, a biaxially oriented stretch film comprising a general-purpose resin such as polyethylene terephthalate (PET) or polypropylene (PP) is used. . However, according to the study by the inventors of the present invention, when the support body including the biaxially oriented film and the laminate of the coating film formed thereon are integrally extended, the film after stretching is a phase difference. The unevenness in the width direction of the alignment angle of the optical axis of the film becomes large.

In addition, as a problem in the case of using a general-purpose biaxially stretched PET film or the like as a support, the elongation workability when the laminate of the coating film and the support is stretched is insufficient, so that stretching or inability to form an appearance such as waviness may occur. bad. The present inventors have found that the use of a support having a high workability at a heating temperature (for example, in the vicinity of 140 ° C) when the laminate of the support and the coating film is subjected to elongation processing can solve the above-described extension processing. Sexual problem. However, in the case of using a support having a high workability, it has been found that the unevenness of the alignment angle of the optical axis of the retardation film tends to be larger.

In view of the above, an object of the present invention is to improve the phase difference after stretching in a method of manufacturing a retardation film in which a biaxially oriented support film and a laminate of a coating film formed thereon are integrally extended. The accuracy of the alignment angle of the optical axis of the film.

In the method for producing a retardation film of the present invention, the resin film is applied onto the support film while the support film is transported in the longitudinal direction (coating step), and the resin coated on the support film is heated by heating. The solution is dried (drying step). By these steps, a laminate having a coating film formed on the support film is formed. The film thickness of the coating film after drying is preferably 30 μm or less.

In the production method of the present invention, before the resin solution is applied onto the support, the support is carried out. Heat treatment of the body film. According to the study by the inventors of the present invention, it has been found that by heating the support before the formation of the coating film, the alignment angle of the optical axis of the extended retardation film becomes uniform. The heat treatment is carried out in a state where tension is applied in the longitudinal direction of the support film.

The laminate is coated with a coating film on the support film at least in one direction to impart optical anisotropy to the coating film (extension step) to obtain a retardation film. In one embodiment, in the extending step, the laminated body is extended in any one of the longitudinal direction and the width direction, and is contracted in a direction orthogonal to the extending direction. For example, by uniaxially extending (longitudinally extending) the free end in the longitudinal direction without holding both end portions in the width direction of the laminated body, the laminated body can be contracted in a direction orthogonal to the extending direction. In addition, the laminate body is contracted in the direction orthogonal to the extending direction by extending in the width direction without holding both end portions in the width direction of the laminated body and shrinking the laminated body in the longitudinal direction.

As the support film, a biaxial alignment film is used. The support film is preferably a biaxially stretched film. When the polyester film is used as the support film, the glass transition temperature Tg of the support film is preferably 110 ° C or less from the viewpoint of improving the workability at the time of stretching. Further, the tensile modulus at 140 ° C of the support film is preferably 1000 MPa or less. The support film may also be a heat shrink film.

The heating temperature T _H in the heat treatment is preferably 80 ° C or higher, and the heating time t _{H is} preferably 8 seconds or longer. Further, even when the heating temperature is less than 80 ° C, the same effect as in the case of heat treatment at 80 ° C or higher is obtained by prolonging the heating time. The temperature of the heat treatment can also be set based on the glass transition temperature of the film.

Further, the present invention relates to a method of manufacturing a laminated polarizing plate. A laminated polarizing plate can be obtained by laminating an optical film including a polarizing element on a retardation film obtained by the above-described manufacturing method.

According to the present invention, by performing the heat treatment of the support film before the film formation, the unevenness of the alignment angle of the optical axis of the retardation film obtained by the extension of the laminate of the support and the coating film can be reduced. In particular, in the case of using a support film having a low elongation elastic modulus which is excellent in workability at the time of stretching, the effect of reducing the unevenness of the alignment angle is large. Thereby, a retardation film having a small film thickness and excellent uniformity in optical characteristics can be produced with high yield.

1, 2, 7‧‧‧ Support

3, 4, 6‧‧ ‧ laminated body

5‧‧‧ phase difference film

10‧‧‧Support body winding body

20‧‧‧Layered body winding

50‧‧‧ phase difference film laminate wound body

11, 22‧‧‧Extracted Department

21, 51‧‧‧ Winding Department

101‧‧‧heating furnace

110‧‧‧Mask department

120‧‧‧ drying oven

130‧‧‧Extension

139‧‧‧heating furnace (extension furnace)

160‧‧‧ peeling department

170‧‧ ‧ Inspection Department

171‧‧‧ phase difference meter

172‧‧‧Defect Detection Department

190‧‧‧Fitting Department

TD‧‧‧width direction

MD‧‧‧ length direction

Fig. 1 is a view schematically showing an embodiment in which a coating step and a drying step are continuously performed after a heat treatment.

Fig. 2 is a view schematically showing an embodiment in which an extending step, a peeling step, and a bonding step are continuously performed.

Fig. 3 is a view schematically showing an embodiment in which a bonding step and a peeling step are continuously performed after the stretching step.

Fig. 4 is a view for explaining the study of the cause of the misalignment of the retardation film in the width direction. Fig. 4A schematically shows the line drawn in the support before heating (lower stage) and the alignment angle (upper stage) in the support before heating. 4B1 and B2 are photographs showing the dimensional change behavior of the support after heating.

Fig. 5 is a distribution in the width direction of the alignment angle of the optical axis of the coating film (after stretching) of Production Example A.

(A): Production Example A1 (140 ° C extension elastic modulus of the support: 800 MPa)

(B): Production Example A2 (140 ° C extension elastic modulus of the support: 600 MPa)

(C): Production Example A3 (140 ° C extension elastic modulus of the support: 200 MPa)

Fig. 6 is a distribution in the width direction of the alignment angle of the optical axis of the retardation film of Production Example B, (A) before stretching and (B) after stretching.

As the resin material constituting the retardation film, a polymer excellent in transparency, mechanical strength, and thermal stability is preferably used. As a specific example of such a polymer, acetaminophen fiber is exemplified. Cellulose resin, polyester resin, polycarbonate resin, polyamido resin, polyimide resin, maleic imine resin, polyolefin resin, or (meth)acrylic acid Resin, cyclic polyolefin resin (norbornene resin), polyarylate resin, polystyrene resin, polyvinyl alcohol resin, polyfluorene resin, and mixtures or copolymers thereof.

The above polymers may have positive intrinsic birefringence and may also have negative intrinsic birefringence. When manufacturing a retardation film in which the refractive index nz in the thickness direction of the retardation film is smaller than the refractive index nx in the retardation axis direction in the plane, that is, manufacturing a positive A sheet (nx>ny=nz) and a negative B sheet ( When nx>ny>nz), a polymer having a positive intrinsic birefringence is preferably used. On the other hand, when the retardation film nz in the thickness direction of the retardation film is larger than the retardation film of the refractive index ny in the in-plane direction of the in-plane, that is, the negative A-sheet is produced (nz=nx>ny), and In the case of a positive B sheet (nz>nx>ny), a polymer having a negative intrinsic birefringence is preferably used.

Here, nx and ny are respectively the refractive index in the direction of the slow axis and the direction of the phase in the plane of the coating film, and the refractive index in the thickness direction of the nz coating film. The in-plane birefringence Δn _in , the in-plane retardation Re, the thickness direction birefringence Δn _out , the thickness direction retardation Rth, and the Nz coefficient have the following relationships, respectively.

Re=△n _in ×d=(nx-ny)×d

Rth=△n _out ×d=(np-nz)×d

NZ=(nx-nz)/(nx-ny)

Among them, the difference between nx and ny and nz is set to np.

In the production method of the present invention, a solution (coating) of a resin material constituting the retardation film is applied onto the support film (coating step). The coating applied to the support film is dried by heating to form a laminate having a coating film of a resin material adhered to the support film (drying step). The coating film is imparted with optical anisotropy by extending at least one direction in the laminate in which the coating film is formed on the support film (extension step).

Applying along the length of the support film before applying the coating to the support film The heat treatment is performed under tension. By performing the heat treatment of the support film before the formation of the coating film, a retardation film having a small unevenness of the alignment angle can be obtained.

Further, the term "extending in at least one direction" in the extending step means that the distance between the two points is increased in at least one direction in the plane, including the extension in the length direction (MD) of the film ( Longitudinal extension), extension in the width direction (TD) of the film (lateral extension), extension in both the longitudinal direction and the width direction (biaxial extension), and extension in the oblique direction. In the longitudinal extension and the lateral extension, the film may also be contracted in a direction orthogonal to the direction of extension.

For example, when the longitudinal direction is extended (the longitudinal end of the free end) in a state where the both end portions in the width direction of the film are not held, the film is shrunk in the width direction. In general, in the longitudinal extension of the free end, the shrinkage ratio in the width direction is equal to the shrinkage ratio in the thickness direction, and the refractive index in the width direction is equal to the decrease rate (or increase rate) of the refractive index in the thickness direction. On the other hand, by using a heat shrinkable film as a support film, the shrinkage force of the heat shrinkable film can be used to reduce the rate of decrease (or increase rate) of the refractive index in the width direction from the decrease rate of the refractive index in the thickness direction (or increase). rate). By thus actively contracting in the direction orthogonal to the extending direction, a retardation film having optical anisotropy of nx>nz>ny can also be obtained.

In the case where the end portions in the width direction of the film are gripped by a tenter jig or the like, and the width direction is extended (the fixed end is laterally extended), the width can also be along the width if a simultaneous biaxial stretching machine is used. The film is stretched in the direction and the length direction, or the film is stretched in the longitudinal direction while extending in the width direction. Further, in the above-mentioned Patent Document 4 (Japanese Laid-Open Patent Publication No. 2011-227430), it is also described that by using a heat shrinkable film as a support film, the shrinkage force of the heat shrinkable film can also increase the shrinkage in the longitudinal direction. The retardation film having an optical anisotropy of nx>nz>ny was obtained by lateral stretching.

The laminated body after stretching can be directly used as a retardation film. It is preferable that the support film is peeled off from the laminated body after stretching (peeling step), and the peeled coating film is used as a retardation film.

From the viewpoint of improving the productivity of the retardation film, the above-described heating, coating, and drying are preferably carried out by a roll-to-roll method. In the roll-to-roll method, a long strip of support film is used. Further, the stretching and the peeling of the coating film from the extended support are also preferably carried out in a roll-to-roll manner. Hereinafter, the manufacturing method of the present invention will be described in order of steps based on the embodiment of the roll-to-roll.

Fig. 1 is a conceptual view schematically showing an example of a form in which a heat treatment, a film forming step, and a drying step are continuously performed by a roll-to-roll method. As shown in FIG. 1, the wound body 10 of the elongated support body 1 is accommodated in the extraction part 11. The support body 1 which is wound up from the winding body 10 is sequentially conveyed from the drawing unit 11 to the heating furnace 101, the film forming unit 110, and the drying furnace 120 located on the downstream side of the conveying path, and is formed on the support.

[Support body film]

In the roll-to-roll method, a film is formed while conveying a support film along the longitudinal direction. Thus, as the support film, a wound body (rolled) of a long film was used. Hereinafter, the support film may be abbreviated as "support".

In the production method of the present invention, after the coating film is formed on the support by the solution film forming method, the laminate of the support and the coating film is supplied to the stretching step. Therefore, the support preferably has flexibility and is excellent in thermal stability and mechanical strength. From this point of view, a biaxial alignment film is used as the support. In particular, when the material constituting the support is a crystalline polymer, the crystallinity of the polymer is improved by imparting biaxial orientation to the film, and mechanical strength, heat resistance, solvent resistance, and the like can be improved. .

The biaxially oriented film can be obtained, for example, by biaxially stretching the film. Examples of the biaxial stretching include longitudinal and lateral sequential biaxial stretching, and vertical and horizontal simultaneous biaxial stretching. In the longitudinal and transverse biaxial stretching, the width direction (TD) of the film is not fixedly extended in the longitudinal direction (MD) by longitudinal stretching or the like (longitudinal extension), and then the width direction of the film is held by a tenter or the like. The extension in the width direction (lateral extension) is performed in the state of both ends. In the simultaneous biaxial stretching, in the state in which both ends of the width direction of the film are held by a tenter jig or the like, linear electric power is used. In the drive mode such as the machine mode, the pantograph method, and the motor chain mode, the distance between the clamps in the width direction is increased while the distance between the clamps in the width direction is increased, thereby performing longitudinal extension and lateral extension at the same time.

In addition, a method of performing extension (longitudinal extension) in the longitudinal direction (MD) while holding both end portions of the film in the width direction by a tenter jig or the like, and contacting the film with a heat roller or the like to suppress the width direction A biaxially oriented film can also be obtained by a method of performing longitudinal stretching in a state of contraction. The biaxially oriented film may also be a film (or a film of shrinkage) that further extends the stretched film.

The resin material constituting the support is not particularly limited, and examples thereof include polyester, polyolefin, polycycloolefin, polyamine, polycarbonate, polyvinyl chloride, polyvinylidene chloride, ruthenium-based polymer, and ruthenium. It is a polymer or the like. A material which is insoluble in a solvent at the time of film formation of a solution can be suitably used from among these. Among them, as the resin material having high solvent resistance, a crystalline polyester resin is preferably used.

Examples of the crystalline polyester resin include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), which will constitute the polyester. The diol component of the monomer unit and/or one or all of the dicarboxylic acid is partially or completely replaced with a polyester of another monomer component.

The support is preferably a material excellent in elongation workability at a heating temperature (for example, in the vicinity of 140 ° C) in the stretching step after the formation of the coating film. For example, the universal biaxially stretched PET film has an elongation modulus of elasticity of about 1200 MPa at 140 °C. When a film having a high modulus of elasticity at such a high temperature is used as a support, the elongation workability in the case of extending the laminate of the coating film and the support is insufficient, so that stretching cannot be performed or appearance defects such as waviness are generated.

The elongation elastic modulus at 140 ° C of the support is preferably 1000 MPa or less from the viewpoint of elongation processability. When the tensile modulus at 140 ° C of the support is 1000 MPa or less, the workability at the time of stretching is excellent, and the appearance of the occurrence of waviness in the extending direction can be suppressed. bad. From the viewpoint of improving the elongation processability, the elongation elastic modulus at 140 ° C of the support is more preferably 900 MPa or less, further preferably 800 MPa or less.

The lower limit of the extension elastic modulus of the support is not particularly limited. If the extension elastic modulus of the support is too small, the optical anisotropy of the coating film may be insufficiently extended, or the alignment angle of the optical axis of the coating film (retardation film) after stretching (hereinafter sometimes abbreviated as The "alignment angle" becomes uneven. Therefore, the elongation elastic modulus at 140 ° C of the support is preferably 100 MPa or more, more preferably 200 MPa or more, and still more preferably 300 MPa or more.

The biaxially oriented film may have an anisotropy in the extension elastic modulus due to the difference in the stretching ratio in the longitudinal direction (MD) and the width direction (TD). In the case where the MD of the support differs from the extended elastic modulus of TD, the elongation elastic modulus at 140 ° C of the MD is preferably in the above range. More preferably, the elastic modulus at 140 ° C for both MD and TD is within the above range.

Further, from the viewpoint of improving the elongation processability, the glass transition temperature Tg of the support is preferably lower than the heating temperature (extension temperature) in the stretching step. When the support is a polyester film, the glass transition temperature Tg is preferably 110 ° C or lower, more preferably 105 ° C or lower, and still more preferably 100 ° C or lower. The lower limit of the glass transition temperature Tg of the support is not particularly limited. However, if the glass transition temperature is too low, the elastic modulus of the support during stretching is small, so that the extension of the optical anisotropy of the coating film is not The alignment angle of the coating film which is sufficient, or extended, becomes uneven. When the support is a polyester film, the glass transition temperature Tg is preferably 50 ° C or higher, more preferably 60 ° C or higher. The glass transition temperature is a measured value obtained by a thermogravimetric analysis (TMA) load extension mode.

As the crystalline polyester film having the above-mentioned extended elastic modulus and glass transition temperature, it is preferred to replace part or all of the diol component and/or one of the dicarboxylic acid constituting the monomer unit of the polyester with another monomer. A biaxially stretched film of crystalline polyester of the composition. Examples of the polyester which replaces the diol component include a part of a linear diol such as ethylene glycol of PET or 1,4-butanediol of PBT, which is substituted with 1,2-cyclohexanedimethanol or 1,4. a diol-modified polyester such as cyclohexanedimethanol or the like. Further, as the polyester which replaces the dicarboxylic acid component, PET is mentioned The terephthalic acid or PEN 2,6-naphthalenedicarboxylic acid is replaced by isophthalic acid, phthalic acid, 2,5-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, 1,5- A dicarboxylic acid-modified polyester such as naphthalene dicarboxylic acid.

Among the above, a polyethylene terephthalate/polyethylene isophthalate copolymer in which a part of PET terephthalic acid is replaced with isophthalic acid is preferably used. Poly(p-phenylene terephthalate)/ethylene isophthalate copolymer can adjust mechanical properties such as elastic modulus or thermal properties by changing the ratio of terephthalic acid component to isophthalic acid component. By increasing the ratio of isophthalic acid components, the modulus of elasticity at 140 ° C can be made smaller than PET. Further, since the polyethylene terephthalate/polyethylene isophthalate copolymer can be crystallized by stretching in the same manner as PET, it is excellent in mechanical strength and has high solvent resistance, and thus is suitable for use. As a support for solution film formation.

The support may be a colorless and transparent material, or may be a colored or opaque material. The surface of the support can also be subjected to easy bonding treatment, mold release treatment, antistatic treatment, anti-adhesion treatment, and the like. In addition, it is also possible to perform embossing (knurling) or the like on the end portion in the width direction of the support for the purpose of preventing adhesion or the like.

The thickness of the support is not particularly limited as long as it is a material having both self-supporting properties and flexibility. The thickness of the support is generally from about 20 μm to about 200 μm, preferably from 30 μm to 150 μm, more preferably from 35 μm to 100 μm. The width of the support is not particularly limited, but is preferably 300 mm or more, more preferably 500 mm or more, further preferably 700 mm or more, and particularly preferably 1000 mm or more. By increasing the width of the support, the mass production of the retardation film can be improved, and it can be applied to a large-screen display.

[heat treatment]

In the manufacturing method of the present invention, the heat treatment of the support 1 is performed before the coating material is applied onto the support 1 in the film forming unit 110. By performing the heat treatment, it is possible to reduce the unevenness in the width direction of the alignment angle of the retardation film obtained by extending the coating film formed on the support together with the support.

The heat treatment is performed in a state where tension is applied along the longitudinal direction of the support. For example, a method in which the support 1 is wound out from the wound body 10 of the elongated support, and the support 1 is continuously conveyed toward the downstream side, and the support is heated in the heating furnace 101; or The heating roller is heated in contact with it. The conveyance tension, that is, the tension in the longitudinal direction, can be imparted by transporting the support in the longitudinal direction.

The heating of the support is preferably carried out in a state where the tension is applied in the longitudinal direction of the support and the dimensional change in the width direction of the support is allowed. Therefore, it is preferable to carry out heating while conveying the support in the longitudinal direction without using the roll conveyance method, the float transfer method, or the like in the state in which both ends of the support body are not in the width direction.

The tension at the time of the heat treatment is not particularly limited as long as the support can be transported in the longitudinal direction, and an appropriate value may be set depending on the thickness of the support, the modulus of elongation, the coefficient of linear expansion, and the like. For example, when the support is a biaxially stretched film of a crystalline polyester, the tension per unit width of the support is set to a range of about 25 N/m to 500 N/m. When the tension in the longitudinal direction is too small, the film transport during the heat treatment becomes difficult, or the effect of reducing the unevenness of the alignment angle of the applied film is insufficient. On the other hand, if the tension in the longitudinal direction during the heat treatment is too large, the elongation becomes large, and scratches or wrinkles are formed in the support, and the appearance of the coating film formed thereon may be poor. The dimensional change rate in the longitudinal direction of the support before and after the heat treatment is preferably within 10%, more preferably within 5%, still more preferably within 3%.

It is presumed that the unevenness of the alignment angle of the retardation film is reduced by the heat treatment of the support before the coating of the coating material, and it is presumed that the size of the support after heat-drying after coating application or the extension after the coating is applied Behavior is related to homogenization.

The outline of the study on the cause of the unevenness of the alignment angle of the retardation film obtained by the extension of the laminate of the support and the coating film in the width direction will be described with reference to FIG. 4B1 and B2 are photographs showing the results of confirming the dimensional change behavior of the biaxially stretched polyester film by heating. In this experiment, the biaxially stretched film is divided into a plurality of tests in the width direction. For the test piece, a straight line extending along MD and TD and a circle centered on the intersection of the straight lines (refer to the lower side of FIG. 4A) were drawn in each test piece, and heated in an oven at 140 ° C for 5 minutes. Fig. 4B1 is a photograph of the test piece after the end portion in the width direction, and Fig. 4B2 is a photograph of the heated test piece of the center portion in the width direction. In Figs. 4B1 and B2, straight lines and circles in the MD direction in the test piece before heating are drawn by broken lines, and the direction of shrinkage by heating is indicated by arrows in the figure.

In the sample in the center in the width direction (Fig. 4B2), slight shrinkage was observed in the MD due to heating, but the angle of the straight line of MD before and after heating was substantially unchanged. On the other hand, in the sample (Fig. 4B1) at the end in the width direction, it was found that shrinkage occurred in the oblique direction due to heating, and the angle of the straight line of the MD changed after heating. From these results, it is understood that in the biaxially oriented film, the shrinkage direction of the film by heating is schematically shown in the upper portion of FIG. 4A, and is distributed in the width direction (so-called "bow bending").

Thus, when the dimensional change behavior by heating is different in the width direction of the support, the dimensional change behavior of the support differs in the width direction during heating or stretching during drying after application of the coating. From this, it is considered that the alignment angle of the retardation film stretched together with the support tends to be uneven in the width direction. On the other hand, in the present invention, the heat treatment of the support is performed, and the dimensional change of the support as shown in FIG. 4 is generated in advance, and then the application and drying of the coating (formation of the coating film) and stretching are performed. It is considered that by performing the heat treatment in advance, the substrate is dimensionally changed to alleviate the bow-bending, and the unevenness of the dimensional change behavior of the support during drying after the coating is applied and thereafter is reduced. The uniformity of the alignment angle of the retardation film can be improved.

In the manufacture of the universal biaxially stretched film, in order to suppress the dimensional change caused by heating, or to alleviate the bow bending, sometimes in the state in which the width direction of the film is always held after extending through the lateral direction of the tenter Heating is performed, thereby performing heat setting. However, in a general-purpose film, since a high alignment angle accuracy such as an optical film such as a retardation film is not required, a biaxial alignment film which suppresses dimensional change behavior by heat fixation is used as a support. In the case of the use of the body, the unevenness of the alignment angle in the width direction of the retardation film formed thereon is also likely to become large. On the other hand, in the present invention, since the tension is applied in the longitudinal direction and the heat treatment of the support is performed in the state of being contractible in the width direction, it is considered that the heat fixation treatment in the manufacture of the biaxially stretched film can be made more precise. The dimensional change behavior is uniformized, and the alignment angle of the retardation film formed on the support becomes uniform in the width direction.

The temperature and time of the heat treatment are not particularly limited as long as the material of the support, the glass transition temperature, the orientation (stretching ratio, or the alignment precision) are considered, so that the misalignment angle of the retardation film after the extension is It can be adjusted in a specific range. The higher the temperature at which the heat treatment is performed, the longer the heating time is, and the unevenness of the alignment angle of the retardation film after stretching tends to be smaller.

The heating temperature T _{H of the} support is preferably 60 ° C or higher, more preferably 80 ° C or higher, further preferably 90 ° C or higher, and particularly preferably 100 ° C or higher. By increasing the heating temperature, the heating time required to increase the uniformity of the alignment angle of the retardation film can be shortened. Further, the heating temperature T _{H of the} support may be set according to the glass transition temperature Tg of the support. The heating temperature T _{H is} preferably Tg - 15 ° C or more, more preferably Tg - 5 ° C or more, and still more preferably Tg or more. For example, since the glass transition temperature of polyethylene terephthalate or polyethylene terephthalate/polyethylene isophthalate copolymer is about 75 ° C to 80 ° C, the heating temperature is preferably 60 ° C or more, more preferably 80 ° C or more. In particular, when the heating temperature T _H is Tg + 15 ° C or more, there is a tendency that the heating time can be shortened.

On the other hand, when the heating temperature is too high, melting of the film, reduction in dimensional stability, reduction in strength, and the like occur. Further, when the polyester film is heated at a high temperature, the oligomer is precipitated, and the appearance of the coating film formed on the support is poor. Therefore, the heating temperature T _{H is} preferably 180 ° C or lower, more preferably 160 ° C or lower, and still more preferably 150 ° C or lower.

The heating temperature can be adjusted by an appropriate method. For example, when the support body is heated by contact with the support by the heat roller, the heat supply to the heat roller can be changed by changing The temperature is adjusted to adjust the heating temperature. In the case of heating by the support in the heating furnace, an air circulating type thermostat oven which can be circulated by hot air or cold air, a heater using microwave or far infrared ray, a roller heated to adjust the temperature, and a heat pipe A suitable heating mechanism such as a roller is used to adjust the heating temperature. The heating temperature does not need to be fixed in the furnace, and the temperature profile can be temperature-increased or cooled stepwise.

As described above, as long as the heating time t _H is set depending on the type of support, or the heating temperature T _H. For example, when the heating temperature T _H is 80 ° C or higher, the heating time t _{H is} preferably 8 seconds or longer, more preferably 12 seconds or longer, and still more preferably 15 seconds or longer. When the heating temperature T _H is 60 ° C or more and less than 80 ° C, the heating time t _{H is} preferably 23 seconds or longer, more preferably 30 seconds or longer, and still more preferably 40 seconds or longer.

The heating time can also be set based on the relationship between the glass transition temperature Tg of the support and the heating temperature T _H . For example, when the heating temperature T _H is Tg + 15 ° C or more, the heating time t _{H is} preferably 8 seconds or longer, more preferably 12 seconds or longer, and still more preferably 15 seconds or longer. In the range where the heating temperature T _H is Tg-15 ° C or more and less than Tg + 15 ° C, the heating time t _{H is} preferably {(Tg - T _H ) × 2 + 38} seconds or more, more preferably {(Tg) -T _H ) × 2 + 45} seconds or more, and further preferably {(Tg - T _H ) × 2 + 45} seconds or more.

The heating time is obtained by dividing the length of the heating furnace (the length of the film conveying path in the heating furnace) or the outer circumferential length of the heat roller (the length of the contact portion of the roller and the support in the circumferential direction of the roller) by the conveying speed of the support. The value. In the case of using the same equipment, since the length of the heating furnace or the length of the outer circumference of the heating roller is constant, in order to lengthen the heating time t _H , it is necessary to reduce the conveying speed of the support. As shown in Fig. 1, when the heating treatment of the support and the application and drying of the coating are continuously performed on-line, if the conveying speed of the support is decreased for the extension of the heating time t _H , the film forming step is continued. And the efficiency of the drying step is also reduced. On the other hand, even if the heating time is excessively extended, the effect of suppressing the unevenness of the alignment angle is also within a certain range. Therefore, from the viewpoint of improving productivity, it is preferable that the heating time is shorter in a range in which the desired effect of equalizing the alignment angle can be obtained. In the case where the heat treatment and the coating step are continuously performed, the heating time is preferably 300 seconds or shorter, more preferably 150 seconds or shorter, and still more preferably 100 seconds or shorter.

[Other steps before the coating step]

Other steps may be carried out before the heat treatment or before the heat treatment treatment step. For example, the surface of the support may be subjected to activation treatment such as corona treatment, plasma treatment, alkalization treatment, or low-pressure UV treatment for the purpose of improving the adhesion between the support and the coating film. Further, the cleaning treatment of the support may be performed for the purpose of removing foreign matter adhering to the support or the like.

<Cleaning treatment>

Examples of the cleaning method of the support include a non-contact method of ejecting ultrasonic air or a cleaning gas, a contact with a cleaning roller such as an adhesive roller, and a contact with a liquid. The cleaning of the support before coating can be carried out on either the coated side or the back side of the coating, or both sides of the support can be cleaned. By washing the coated surface of the coating material, it is possible to reduce the entry of foreign matter or the like adhering to the support into the film, and thus a retardation film having less optical defects can be obtained. Further, by cleaning the back surface of the support, it is possible to suppress the biting of foreign matter between the support roller and the support at the time of film formation.

When foreign matter is present between the support roller and the support at the time of film formation, the film formation surface side of the support is deformed into a convex shape by the pressing, and the support is deformed by coating the coating thereon. The coating thickness of the portion is locally small, and defects such as dot-shaped interference grooves (hereinafter sometimes referred to as "plotted lines") are generated. In particular, when the film thickness of the coating film is small, there is a tendency that the speckle pattern caused by the reduction in the local film thickness is easily observed as a defect. By extracting the support from the support to the coating material, the surface of the support opposite to the film formation surface (back surface) is cleaned on-line, thereby reducing the occurrence of speckle. In particular, when the back surface of the support is brought into contact with the cleaning roller via the cleaning liquid and wet-cleaned, the effect of reducing the speckle tends to be conspicuous.

The cleaning roller is preferably a roller having a concave-convex pattern on the surface, wherein the unevenness is preferably used. A roller in which the convex portion of the pattern does not extend in parallel with the circumferential direction of the roller. Examples of the roller having a convex portion extending in a direction not parallel to the circumferential direction include a gravure roll, a Meyer bar roll, an embossing roll, and the like. Since the cleaning liquid can be applied to the back surface of the support without damaging the support, it is particularly preferable to use a gravure roll and a Meyer bar as the cleaning roll. By performing the wet cleaning while the cleaning roller and the back surface of the support are in contact with each other via the cleaning liquid, foreign matter adhering to the back surface of the support can be efficiently removed, and generation of speckles can be suppressed.

The cleaning liquid supplied between the cleaning roller and the support is not particularly limited as long as it is liquid and does not dissolve the support, and water, an organic solvent, a mixture of water and an organic solvent, or the like can be used. From the viewpoint of efficient in-line cleaning, as the cleaning liquid, a liquid having a boiling point lower than water is suitably used. Further, for the purpose of improving the cleaning power and the like, a surfactant or a hydrophilic organic compound may be added to the cleaning liquid. Examples of the hydrophilic organic compound include a hydroxyl group, an amine group, a decylamino group, an imido group, a quinone imine group, a nitro group, a cyano group, an isocyanate group, a carboxyl group, an ester group, an ether group, a carbonyl group, a sulfonic acid group, and the like. An organic compound such as a SO group.

The support which has been cleaned by contact with the cleaning liquid can also be dried by the cleaning liquid adhering to the surface before the coating is applied. The drying method is not particularly limited, and examples thereof include a method of spraying clean air or a method of heating an oven. Further, the above-described heat treatment may be performed by drying the cleaning liquid which also serves as a surface adhering to the support. Since the heat treatment is performed by drying after washing, the production process can be simplified. Therefore, a retardation film which reduces the unevenness in the width direction of the alignment angle and suppresses the occurrence of speckle can be obtained with high productivity.

[film forming step and drying step]

In the film forming step, the heat-treated support 2 is conveyed along the longitudinal direction (MD), and a resin solution (coating material) is applied thereon. Thereafter, the resin solution is dried by heating to form a long laminated body having a coating film adhered to the support.

In the embodiment shown in Fig. 1, the support 2 subjected to heat treatment in the heating furnace 101 is via The guide roller 207 is conveyed to the film forming unit 110 provided on the downstream side to form a film. In addition, FIG. 1 shows a form in which film formation is continuously performed in the film forming unit 110 after the heat treatment in the heating furnace 101, but the heat treatment and the film formation are not necessarily required to be continuously performed. For example, the heat-treated support may be temporarily wound into a roll shape, and the support may be wound up in the wound body of the heat-treated support and transported to the downstream side to form a film.

In the film forming unit 110, the coating material 118 is spread on the support 2, and film formation is carried out in accordance with a usual method. In Fig. 1, a doctor roll coater is illustrated. In the roll coater, the support 2 is brought into contact with the coating material 118 in the liquid reservoir 117 while being in contact with the support roller 112, and the coating liquid is discharged by the doctor roll 111 to adjust the thickness of the coating film. The film forming method in the film forming unit 110 is not limited to the doctor roll coating method, and may be a kiss roll coating method, a gravure coating method, a reverse coating method, a spray coating method, a Meyer bar coating method, or a gas. Various methods such as a knife coating method, a curtain coating method, a lip mold coating method, and a die coating method.

The coating material 118 is a solution for forming a resin material of a retardation film, and contains a resin material (polymer) and a solvent. In the coating, if necessary, additives such as a leveling agent, a plasticizer, a UV absorber, and an anti-aging agent may be contained. As the resin material for forming the retardation film, any one of a polymer having positive intrinsic birefringence and a polymer having negative intrinsic birefringence can be used depending on the optical anisotropy of the desired retardation film. Further, a plurality of resin materials may be used in combination depending on the optical characteristics of the desired retardation film and the like. The type of the solvent is not particularly limited as long as it dissolves the resin material and does not dissolve the solvent of the support, and various solvents generally used in the solution film formation can be used. The solid content, viscosity, and the like of the coating material can be appropriately set depending on the type or molecular weight of the resin, the thickness of the retardation film, the film forming method, and the like.

The film thickness can be set, for example, such that the film thickness after drying is about 1 μm to 100 μm, depending on the optical characteristics (hysteresis value) required for the retardation film. In the present invention, since the laminate of the support film and the coating film formed thereon is extended, even when the film thickness is small and it is difficult to handle the film alone, the processing such as stretching can be easily performed. . by When the film thickness of the coating film is 30 μm or less, the retardation film having a small film thickness and excellent uniformity of the alignment angle can be easily obtained by using the production method of the present invention.

The coating layer applied to the support 2 is conveyed to the drying furnace 120 together with the support, and the solvent is removed, and the laminated body 3 in which the coating film is formed on the support 2 is obtained. The laminated body 3 is conveyed from the drying furnace 120 to the downstream side, and is wound by the winding portion 21 via the guide rolls 211 to 215 to obtain the wound body 20 of the laminated body 3 of the support and the coating film.

The heating temperature (drying temperature) or the drying time in the drying step is not particularly limited. In general, drying is carried out at a temperature near the boiling point of the solvent constituting the coating or at a temperature higher than the boiling point of the solvent. From the viewpoint of shortening the drying time and improving the production process, the drying temperature is preferably higher in the range where appearance defects such as bubbles are not generated. Specifically, the drying temperature is preferably 70 ° C or higher, more preferably 80 ° C or higher, further preferably 90 ° C or higher, and particularly preferably 100 ° C or higher. On the other hand, if the drying temperature is too high, bubbles may be generated in the coating film due to sudden boiling of the solvent, or dimensional changes of the support may occur. Therefore, the drying temperature is preferably 230 ° C or lower, more preferably 200 ° C or lower, and still more preferably 180 ° C or lower.

In the conventional production method, when the drying temperature after coating the coating on the biaxially oriented support is increased, the unevenness in the width direction of the alignment angle of the retardation film tends to become large. In the production method of the present invention, by performing the heat treatment in advance, the unevenness of the dimensional change of the support in the drying step can be eliminated, and even when the drying temperature is high, the alignment angle of the retardation film can be made uniform. Chemical.

The heating temperature in the drying step can be adjusted by the same method as described above for the heat treatment. The temperature in the furnace does not necessarily need to be fixed in the entire furnace, and may also have a temperature profile that gradually increases or decreases in temperature. For example, the furnace interior may be divided into a plurality of zones, and the set temperature is changed for each zone. In addition, from the viewpoint of suppressing the sharp dimensional change of the support due to the temperature change at the inlet or the outlet of the heating furnace, a preheating zone or a cooling zone may be provided to bring the temperature near the inlet and the outlet of the heating furnace. The change becomes soft.

Further, when the temperature in the entire drying furnace is not necessarily the case, the so-called drying temperature means the temperature in the furnace at the highest temperature (i.e., the temperature in the furnace). In the drying step, the heating time in the above temperature range is preferably 10 seconds or longer, more preferably 20 seconds or longer, and still more preferably 30 seconds or longer. The heating time can be adjusted by the length of the conveying path of the support in the heating furnace (the length of the furnace) or the conveying speed of the support.

When the coating film on the support is dried, the molecular chains of the polymer tend to align in the in-plane direction. If the polymer having positive intrinsic birefringence is aligned in the plane, the refractive index nz in the thickness direction of the coating film becomes relatively larger with respect to the in-plane refractive index (nx and ny), and the coating film exhibits nx=ny>nz Negative C-plate characteristics of refractive index anisotropy (Rth is a positive value). If the polymer having a negative intrinsic birefringence is aligned in the plane, the refractive index nz in the thickness direction of the coating film becomes relatively small with respect to the in-plane refractive index, exhibiting an index anisotropy with nx=ny<nz ( The positive C slice characteristic of Rth is a negative value.

Since the dimensional change rate of the biaxially oriented film differs depending on the direction during heating, if the coating film formed on the support is dried at a high temperature, the anisotropy of the dimensional change of the support is caused. The coating film produces an in-plane refractive index anisotropy. When the support is contracted in the oblique direction as shown in FIG. 4B1 by heating during drying, the coating film formed thereon is also shrunk in the oblique direction, and has an optical axis in the oblique direction. Therefore, when the shrinkage ratio of the support or the shrinkage direction is not uniform in the width direction, the optical axis of the coating film becomes uneven in the width direction. On the other hand, in the present invention, as described above, since the heat treatment of the support is performed in advance, the dimensional change behavior of the support is uniform in the width direction, and the optical axis of the coating film formed thereon is accompanied. The alignment angle also becomes uniform in the width direction.

[Extension step]

The layered body 3 on which the coating film is formed on the support 2 after the heat treatment is extended in at least one direction in the extending step. Fig. 2 is a view schematically showing one embodiment of an extending step and a peeling step. In the form shown in Fig. 2, in the extraction portion 22 of the extension device The wound body 20 of the layer body 3 is discharged. The laminated body 3 wound out from the wound body 20 is continuously conveyed from the drawing unit 22 to the heating furnace 139 of the extending portion 130 on the downstream side via the guide rolls 221 and 222. In addition, in FIG. 1 and FIG. 2, the winding body 20 of the laminated body 3 is temporarily wound in the winding part 21 of the film forming apparatus, and the laminated body 3 of the laminated body 3 is wound. It is placed in the take-out portion 22 of the stretching device and is unwound therefrom. However, the laminated body may be directly supplied to the stretching step without winding the laminated body after the film forming and drying steps.

In the form shown in Fig. 2, an example in which the free end uniaxially extends (longitudinal extension) in the longitudinal direction (MD) by the float method in the extending portion 130 is illustrated. The extension portion 130 includes a heating furnace 139, and nip rollers 231 and 232 are provided on the upstream side (inlet) of the heating furnace 139, and nip rollers 236 and 237 are provided on the downstream side (outlet). In the uniaxial stretching at the free end, the end portion in the width direction of the laminated body is not held, and the film is extended in the longitudinal direction. In the embodiment shown in Fig. 2, the laminated body 3 is extended in the longitudinal direction by making the circumferential speed of the nip rollers 236, 237 on the downstream side of the heating furnace 139 larger than the circumferential speeds of the upstream nip rollers 231, 232.

In the embodiment shown in FIG. 2, hot air discharge nozzles (floating nozzles) 131 to 137 are arranged in a zigzag manner in the heating furnace 139 in a zigzag manner, and are extended by heating by hot air. The film transfer method in the heating furnace (extension furnace) 139 is not limited to the float method, and a suitable transfer method such as a roll transfer method or a tenter transfer method may be employed. It is also possible to carry out the film in the longitudinal direction (MD) while being conveyed by a tenter, and to extend in the width direction (TD). Further, the heating furnace 139 may be biaxially extended or extended in the longitudinal direction in the longitudinal direction and the width direction. Further, it may be extended in the longitudinal direction in the heating furnace 139, and then extended in the width direction in another heating furnace (not shown) to perform sequential biaxial stretching.

The heating temperature (extension temperature) in the stretching step is not particularly limited, but is preferably a temperature at which the support can be extended together with the coating film formed thereon, and can be based on the polymer constituting the coating film (retardation film). Set the type, or the thermal characteristics of the support. The extension temperature is generally from about 100 ° C to about 220 ° C, preferably from about 120 ° C to about 200 ° C. Will be formed in support When the glass transition temperature of the coating film on the body is tg, the stretching temperature is preferably (tg - 100) ° C or more, more preferably (tg - 90) ° C or more, and further preferably (tg - 80) ° C. the above. If the stretching temperature is too low, peeling of the coating film from the support may occur, or the hysteresis may become uneven, or appearance defects such as an increase in turbidity may occur. On the other hand, if the stretching temperature is too high, the alignment property of the polymer constituting the coating film is lowered, and the desired retardation cannot be obtained.

The temperature in the heating furnace 139 does not necessarily have to be constant in the entire furnace, and may have a temperature profile in which the temperature is raised or lowered stepwise. For example, the furnace can be divided into a plurality of zones, and the set temperature is changed for each zone. In addition, from the viewpoint of suppressing the temperature change of the inlet or the outlet of the heating furnace 139 and causing a sharp dimensional change of the laminated body to cause wrinkles or poor conveyance, a preheating zone may be provided. Or a cooling zone, or a heating roller or a cooling roller, to make the temperature change near the inlet and the outlet of the furnace gentle.

In the uniaxial stretching at the free end, as the laminated body is extended in the longitudinal direction, shrinkage occurs in the width direction and the thickness direction. Therefore, when the polymer constituting the coating film has positive intrinsic birefringence, the refractive index (nx) in the longitudinal direction becomes large, and the refractive index (ny) in the width direction and the refractive index (nz) in the thickness direction become small. On the other hand, when the polymer constituting the coating film has a negative intrinsic birefringence, the refractive index (ny) in the longitudinal direction becomes small, and the refractive index (nx) in the width direction and the refractive index (nz) in the thickness direction become Big. In the uniaxial stretching at the free end, generally, the shrinkage ratio in the width direction is equal to the shrinkage ratio in the thickness direction, and the refractive index in the width direction is equivalent to the decrease rate (or increase rate) in the refractive index in the thickness direction. Therefore, when a polymer having positive intrinsic birefringence is used as the material of the retardation film, the retardation film obtained by the uniaxial stretching at the free end becomes positive in refractive index anisotropy with nx>ny=nz. PORN. On the other hand, in the case of using a polymer having a negative intrinsic birefringence, a retardation film obtained by uniaxial stretching at the free end becomes a negative A sheet having refractive index anisotropy of nz = nx > ny.

Moreover, a laminate having a coating film formed on the support body is used for the free end In the case where the shaft is extended, since the shrinkage ratio in the width direction of the laminate is largely affected by the mechanical properties or thermal properties of the support, the shrinkage ratio in the width direction of the coating film is different from the shrinkage ratio in the thickness direction. Further, when the coating film on the support is dried, the molecular chains of the polymer are aligned in the in-plane direction, whereby the refractive index nz in the thickness direction of the coating film is relatively large or smaller with respect to the in-plane refractive index, and is coated. The film has a negative C-plate characteristic, that is, a refractive index anisotropy having nx=ny>nz (Rth is a positive value), or a positive C-plate characteristic, that is, a refractive index anisotropy having nx=ny<nz ( Rth is a negative value). Therefore, when the coating film comprising the polymer having positive intrinsic birefringence formed on the support has a refractive index anisotropy of nx=ny>nz, the refractive index anisotropy of ny>nz is extended. It was maintained before and after, and a negative B piece having a refractive index anisotropy of nx>ny>nz was obtained. According to the same principle, when a polymer having a negative intrinsic birefringence is used as a material of a retardation film, a positive B piece having a refractive index anisotropy of nz>nx>ny is obtained by uniaxial stretching at the free end. .

As described above, in the uniaxial stretching at the free end, the shrinkage in the width direction is caused by the extension of the support to be stretched and the coating film, and optical anisotropy is imparted. In the present invention, by performing the heat treatment of the support before the formation of the coating film on the support, not only the dimensional change behavior during drying becomes uniform, but also the dimensional change behavior during stretching becomes uniform, so that the retardation film can be made. The alignment angle of the optical axis is uniformed in the width direction.

The stretching ratio in the stretching step is preferably 1.01 times or more, more preferably 1.03 times or more. In the uniaxial stretching at the free end, there is a tendency that the _in- plane birefringence (Δn _in ) tends to increase as the stretching ratio increases. If the stretching ratio is too large, breakage of the coating film or uneven optical properties may occur. Therefore, the stretching ratio is preferably 3 times or less, more preferably 2.5 times or less, and still more preferably 2 times or less. The stretching method in the stretching step, or the stretching ratio, can be adjusted according to the desired optical characteristics. The in-plane retardation Re of the retardation film is, for example, about 15 nm to 400 nm. The optical characteristics such as the retardation Rth and the NZ coefficient in the thickness direction of the retardation film can be appropriately set depending on the use of the retardation film or the like.

[Peeling step]

The laminated body 4 after stretching can be directly used as a retardation film. It is preferable that the support body 7 after the extension is peeled off from the laminated body 4 after stretching, and the coating film 5 after peeling off the support is used as a retardation film. In this case, the support system is not included in the step member as the retardation film of the final product. Thus, the support does not necessarily need to be optically uniform, and an inexpensive support can be used.

The stretched laminated body 4 may be temporarily wound into a roll shape, or may be continuously supplied to the peeling step from the stretching step. In FIG. 2, the form in which the peeling step is continuously performed in the peeling portion 160 after the stretching step is illustrated. The peeling method of the support 7 and the coating film (retardation film 5) after the extension is not particularly limited, but from the viewpoint of uniform peeling, it is preferable to sandwich the laminated body 4 with the nip rolls 261 and 262. On the downstream side, the support 7 and the retardation film 5 are conveyed along the upper roll 261 and the lower roll 262, respectively, and are peeled off. The peeled support 7 is wound around the winding portion 71 in a suitable manner.

[Other steps after the extension step]

The retardation film may be further supplied to the other steps after the stretching step or after the stripping step. For example, in the embodiment shown in FIG. 2, the retardation film 5 after peeling off the support 7 is inspected in the inspection portion 170, and then bonded to the other film 9 in the bonding portion 190, and then the retardation film 5 is The laminated body 6 of the film 9 is wound in the winding portion 51 to form a wound body 50.

<check step>

The inspection unit includes an inspection device for inspecting the retardation film. In the embodiment shown in FIG. 2, the inspection unit 170 includes a phase difference meter 171 and a defect detecting unit 172. The phase difference meter 171 detects the hysteresis of the retardation film 5 or the alignment angle of the slow phase axis. The hysteresis can be kept constant by feeding back the measured hysteresis value to the circumferential speed of the roller of the extending portion 130 or the like. From the viewpoint of accurately measuring the hysteresis of the retardation film 5, it is preferable to measure the phase difference after peeling off the support 7.

The defect detecting unit is configured to detect defects such as foreign matter existing on the inside or the surface of the retardation film, or irregularities such as scratches, scratches, and the like. By supporting the body After the defect is detected after the peeling, the defect of the retardation film 5 can be selectively detected without detecting the defect contained only in the support 7, and thus the defect detection accuracy can be improved.

<Fitting step>

In the bonding unit 190, the retardation film 5 is bonded to the other film 9 to form the laminated body 6. The film 9 may, for example, be a protective film (separator) temporarily attached to the retardation film 5 or another optical film (a retardation film, a polarizing element, or the like). The laminate of the retardation film and other films is preferably carried out via a suitable adhesive.

By laminating the polarizing element on the retardation film, a laminated polarizing plate having a retardation film can be formed. Further, a polarizing element may be separately laminated on the retardation film, or a member in which a transparent protective film or another retardation film is bonded to the polarizing element may be laminated.

The thickness of the polarizing element laminated on the retardation film is not particularly limited, but is generally about 1 μm to 50 μm. In particular, the thickness of the polarizing element is preferably 25 μm or less, more preferably 15 μm or less, and still more preferably 8 μm or less from the viewpoint of obtaining a thin laminated polarizing plate. By reducing the thickness of the polarizing element, it is possible to reduce the influence of the stress generated by the dimensional change of the polarizing element due to environmental changes such as heat or humidity on the adjacent retardation film and the like. Thus, by reducing the thickness of the polarizing element laminated on the retardation film, even when the thickness of the retardation film is small, a laminate having a small change in optical characteristics due to environmental changes in the surroundings can be obtained. Polarizer.

An adhesive layer for bonding to another optical film, a liquid crystal cell or the like may be laminated on the surface of the retardation film 5. For example, an adhesive layer can be laminated on the retardation film by bonding the surface of the adhesive layer side of the adhesive sheet having the adhesive layer to a suitable separator to the retardation film.

When the thickness of the retardation film 5 after peeling off the support 7 from the laminate 3 is 30 μm or less, the self-supporting property is small and the handleability is insufficient. Other film or adhesive layers can be laminated to improve handling. Further, in Fig. 2, the form of the single-sided bonding film 9 of only the retardation film 5 is illustrated, but it is also possible to have a phase difference. A film or an adhesive layer or the like is bonded to both surfaces of the film 5.

Further, before the support 7 is peeled from the laminate 3 in the peeling portion 160, another film or an adhesive layer may be bonded to the surface of the laminate 3 on the retardation film 5 side. By laminating the other film or the adhesive layer or the like on the retardation film 5 before peeling off the support 7, it is not necessary to separately transport the retardation film. Thereby, even when the thickness of the retardation film is small, the handleability can be improved. After laminating another film or an adhesive layer on the surface of the retardation film 5 of the laminate 3, the support 7 is peeled off, and another film is laminated on the exposed surface of the retardation film 5 after the support is peeled off. Adhesive layer.

<winding step>

The retardation film 5 after peeling off the support 7 is supplied to the inspection step or the bonding step as needed, and is wound in the winding portion 51 to form a wound body of the retardation film. As shown in FIG. 2, the retardation film 5 can also be wound in the winding portion 51 as a laminate 6 (for example, a laminated polarizing plate) laminated with another film 9. Further, the retardation film 5 after the support 7 is peeled off may be directly cut into a single sheet without being supplied to the winding step.

FIG. 2 is a view showing a state in which the laminate 3 having a coating film adhered to the support is stretched, and the support 7 is peeled off in the peeling portion 160 without being wound into a wound body. After the stretched laminated body 4 is temporarily wound into a wound body, a peeling step is performed in a device different from the stretching step. Further, it is also possible to bond with other films before peeling off the support from the laminate.

For example, after the stretched laminated body 4 is temporarily wound into a roll shape, as shown in FIG. 3, the wound body 340 of the laminated body is taken up and conveyed from the take-up portion 342 of the bonding-disbonding device. The bonding with the other film 309 and the peeling of the support 307 are sequentially performed. In the embodiment shown in Fig. 3, the laminated body 304 which has been wound up from the wound body 340 is pulled out from the drawing portion 342 via the guide rolls 321 and 322 in the bonding portion 390 on the downstream side, and is formed in the laminated body 304. On the opposite side of the support, another film 309 (for example, a polarizing plate) is bonded to form a laminated body 308. In the peeling portion 360 on the further downstream side, the support 307 is peeled off from the laminated body, and A laminate 306 (for example, a laminated polarizer) in which a retardation film and other films are bonded together is obtained. The laminate 306 in which the retardation film and the other film are bonded together is inspected in the inspection portion 470 as needed, and then wound in the winding portion 351 to form the wound body 350.

In this embodiment, after the retardation film is bonded to another film, the support is peeled off, and the retardation film formed on the support is transferred onto another film. If the bonding to other films is performed before peeling off the support from the laminated body, it is not necessary to separately treat the retardation film. Therefore, even when the film thickness of the coating film formed on the support is small and it is difficult to handle the separate coating film, the productivity of the laminated optical film in which the laminated retardation film and other films are formed can be improved or Yield.

[Embodiment using heat shrinkable support]

The example in which the A piece or the B piece is formed by stretching is mainly described, but the refractive index anisotropy of nx>nz>ny may be produced by using a heat shrinkable film as a support (the NZ coefficient is greater than 0 and Less than 1) retardation film. In the case where a heat shrinkable film is used as the support, the laminate of the support and the coating film is extended in one direction by the stretching step, and is contracted by the contraction force of the support in a direction orthogonal to the extending direction. The rate of decrease (or increase rate) of the refractive index in the direction orthogonal to the extending direction (shrinking direction) can be made larger than the rate of decrease (or increase rate) of the refractive index in the thickness direction.

The heat shrinkable film as the support is not particularly limited as long as it has biaxial orientation and is thermally contracted in the direction orthogonal to the extending direction in the stretching step. The shrinkage ratio (length after shrinkage/length before shrinkage) of the heat shrinkable film in the stretching step (for example, in the vicinity of 140 ° C) in the direction in which the laminate shrinks is preferably from 0.50 to 0.99, more preferably from 0.60 to 0.98. Further preferably, it is 0.70 to 0.95.

The heat shrinkable film may also be a material having a different stretching ratio in the extending direction from the shrinking direction in the stretching step. For example, in the case where the laminate body is extended in the width direction and contracted in the longitudinal direction in the stretching step, a heat shrinkable film which is more easily contracted in the longitudinal direction can also be used. As an example, in the production of a heat shrinkable film, two of the film are held by a tenter or the like. At the end, the heat shrinkable film which is easily contracted in the longitudinal direction can be obtained by moving the jig so as to increase the interval between the tenter clips in the longitudinal direction while maintaining the distance between the jigs in the width direction.

The material constituting the heat shrinkable film as the support is not particularly limited, and the material described above can be used as the material of the support. Among them, the above polyester, or a polyolefin such as polyethylene or polypropylene is preferably used.

In the case where a heat shrinkable film is used as the support, the heat treatment of the support and the application and drying of the paint onto the support may be carried out in the same manner as described above. The heating temperature T _H at the time of heat treatment is preferably 60° C. or higher, more preferably 80° C. or higher, still more preferably 90° C. or higher, and particularly preferably 100° C. or higher. By increasing the heating temperature, the unevenness of the shrinkage behavior of the support can be alleviated, and the alignment angle of the coating film formed thereon becomes uniform. Therefore, the retardation film after stretching tends to have a uniform alignment angle. On the other hand, if the temperature of the heat treatment is too high, the support body is thermally contracted or thermally fixed during the heat treatment, so that shrinkage in the stretching step is difficult to occur. Thus, the heating temperature T _{H is} preferably lower than the heating temperature in the extending step. Similarly, the drying temperature after coating the coating on the support is also preferably lower than the heating temperature in the stretching step.

In the extending step, the laminate of the support and the coating film is extended in one direction, and the laminated body is shrunk in a direction orthogonal to the extending direction. The extension and contraction can be carried out separately, but are preferably carried out simultaneously. By implementing both at the same time, it is possible to maintain the alignment due to shrinkage and elongation without easing it. By using a heat shrinkable film as a support, the heat shrinkable film shrinks in a direction orthogonal to the extending direction by heating during stretching, so that stretching and shrinking can be simultaneously performed, and it can be formed on a support (heat shrinkable film). The upper coating film extends in one direction and contracts in a direction orthogonal to the extending direction. As described above, in the extension method such as the uniaxial stretching at the free end, the contraction in the longitudinal direction (the direction orthogonal to the extending direction) is caused by the extension in the longitudinal direction, but the same shrinkage occurs in the thickness direction. In contrast, in the case of using a heat shrinkable film, it is orthogonal to the extending direction. Since the amount of shrinkage in the direction is larger than the amount of shrinkage in the thickness direction, a retardation film having optical anisotropy of nx>nz>ny can be produced.

The method of contracting in the direction orthogonal to the extending direction simultaneously with the stretching is preferably a method of shrinking the width direction (TD) simultaneously with the extension in the longitudinal direction (MD), or a width direction (TD) The method of extending the length direction (MD) at the same time. Among them, from the viewpoint of ensuring the retardation film width, the retardation film is easily applied to a large-screen display, or improving the area efficiency when the retardation film is cut in accordance with the screen size, it is preferable to have a width direction. The method of extending the length direction at the same time.

In order to contract in the width direction simultaneously with the extension in the longitudinal direction, for example, a free end uniaxial extension (longitudinal extension) may be used using a roll stretcher. Further, a biaxial stretching machine can be used to hold both ends in the width direction while controlling the shrinkage ratio in the width direction while extending in the longitudinal direction. In the case of contracting in the longitudinal direction simultaneously with the extension in the width direction, both ends in the width direction may be gripped, and the shrinkage ratio in the width direction may be controlled while extending in the longitudinal direction. In order to contract in the longitudinal direction at the same time as the extension in the width direction, for example, a double-axis stretching machine is used, and both ends of the width direction of the film are held by a tenter jig or the like in the width direction. The jig can be moved in such a manner that the distance between the jigs in the longitudinal direction becomes smaller.

[Use and optical characteristics of retardation film]

The use of the retardation film is not particularly limited, but is suitable for optical compensation of a liquid crystal display device. When the retardation film is used for optical compensation of a liquid crystal display device, a retardation film is disposed between the liquid crystal cell and the polarizing element.

The optical characteristics such as the in-plane retardation Re of the retardation film or the retardation Rth in the thickness direction can be appropriately selected depending on the driving method of the liquid crystal cell or the hysteresis value of the cell. For example, in the liquid crystal display device of the planar conversion (IPS) type, the black luminance becomes large when the image is viewed from the oblique direction of the azimuth angle of 45° with respect to the absorption axis direction of the polarizing plate, but by the liquid crystal cell and A retardation film is disposed between the polarizing elements to reduce black brightness in the oblique direction and improve contrast. In the optical compensation of the liquid crystal display device of the IPS type, for example, two or more retardation films may be used in combination as disclosed in the above-mentioned Patent Document 1 (Japanese Laid-Open Patent Publication No. 2009-139747). When two or more retardation films are used for optical compensation of a liquid crystal display device, a retardation film based on the production method of the present invention is used in at least one retardation film.

Further, the number of retardation films used for optical compensation of the liquid crystal display device is not limited to two, and may be one or three or more. For example, when a retardation film having a refractive index anisotropy of nx>nz>ny obtained by shrinking a laminate in a direction orthogonal to the extending direction is used as a support, one sheet is used. The retardation film can perform optical compensation of the IPS liquid crystal display device.

The liquid crystal display device can be manufactured, for example, by appropriately assembling an optical member such as a retardation film of the present invention, another optical film such as a polarizing element, a liquid crystal cell, and a backlight, and mounting the same in a driving circuit. When the retardation film and the liquid crystal cell are bonded together, it is preferable to laminate the retardation film and the polarizing element from the viewpoint of improving the uniformity of the alignment axis direction or simplifying the manufacturing process. The laminated polarizing plate and the liquid crystal cell are bonded via a suitable adhesive layer such as an adhesive.

[Examples]

Hereinafter, the present invention will be described in more detail by way of examples, but the invention is not limited to the examples described below.

[test methods]

The elastic modulus of the film was measured in accordance with JIS K7127 under the conditions of a temperature of 140 ° C and an elongation speed of 10 mm/min using an autoclave equipped with a thermostat (manufactured by Shimadzu Corporation). The hysteresis of the retardation film and the alignment direction of the optical axis were measured in a 23 ° C environment using a polarization-phase difference measurement system (product name "AxoScan" manufactured by Axometrics) (measurement wavelength: 590 nm).

The glass transition temperature of the support is measured in accordance with the TMA method described in JIS C6481 (1996 edition).

[Synthesis Example A: Synthesis of fumarate-based resin (polymer with negative birefringence) and formulation of coating]

To an autoclave equipped with a stirrer, a cooling tube, a nitrogen inlet tube, and a thermometer, 48 parts by weight of hydroxypropylmethylcellulose (manufactured by Shin-Etsu Chemical Co., trade name METOLOSE 60SH-50), 15601 parts by weight of distilled water, and fumaric acid II were added. 8161 parts by weight of isopropyl ester, 240 parts by weight of 3-ethyl-3-oxetanylmethyl acrylate, and 45 parts by weight of a third butyl peroxypivalate as a polymerization initiator, for 1 hour After bubbling with nitrogen, the mixture was stirred at 49 ° C for 24 hours while stirring, thereby performing radical suspension polymerization. Then, it was cooled to room temperature, and the suspension containing the produced polymer particles was centrifuged. The obtained polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure.

The obtained fumarate-based resin was dissolved in a toluene-methyl ethyl ketone mixed solution (toluene/methyl ethyl ketone 50% by weight/50% by weight) to prepare a 20% solution. Then, 5 parts by weight of tributyl trimellitate as a plasticizer was added to 100 parts by weight of the fumarate-based resin to prepare a coating material.

[Retardation film production examples A1 to A3]

In the retardation film production example A, a biaxially stretched film of polyester (polyethylene terephthalate/polyethylene isophthalate copolymer) (thickness: 75 μm, width: 1350 mm) was used as the support film. . Using three kinds of supports having different terephthalate/isophthalate content ratios in the polyester, changing the heat treatment conditions of the respective supports, and performing the alignment angle of the optical axes of the extended retardation film Evaluation. The elongation elastic modulus (MD) at 140 ° C of the support used in Production Examples A1, A2, and A3 was 800 MPa, 600 MPa, and 200 MPa, respectively.

<heat treatment, coating, drying>

The wound body supporting the body film is placed in the extraction portion of the film forming device, and the support is taken out The film is conveyed to the downstream side and heat-treated in a heating furnace. The temperature of the heat treatment is adjusted by changing the temperature of the atmosphere in the heating furnace. The heating time is adjusted by changing the conveying speed of the support. The coating prepared in Synthesis Example A was applied to the support after the heat treatment so that the film thickness after drying was 6 μm, and dried at 140 °C. The dried coating film is wound together with the support as a laminate.

<Extension and peeling>

The laminated body was placed in the drawing portion of the stretching device, and the laminated body was taken out and conveyed to the downstream side, and the free end was uniaxially stretched in a furnace having a temperature of 140 °C. The support was peeled off from the laminate after stretching to obtain a retardation film. The stretching ratio was adjusted so that the in-plane retardation of the retardation film after peeling off the support was 35 nm.

The alignment angle of the optical axis of the retardation film obtained in the above operation was measured at intervals of 10 mm in the width direction (measurement range: center 1230 mm in the width direction), and the difference between the maximum value and the minimum value was defined as the non-uniform range of the optical axis. Table 1 shows the non-uniform range of the alignment angle (°) of the optical axis with respect to the heat treatment time of the support and the heat treatment temperature in Production Example A1 (140 ° C extension elastic modulus: 800 MPa). In addition, the results of Production Example A2 (140 ° C extension elastic modulus: 600 MPa of the support) and Production Example A3 (140 ° C extension elastic modulus: 200 MPa of the support) are shown in Tables 2 and 3, respectively. Further, in Tables 1 to 3, the time 0 seconds indicates a non-uniform range of the alignment angle when the heating furnace 101 is set to room temperature without heat treatment. Further, the measurement results (extracted portions) of the alignment angles of the retardation films of Production Examples A1 to A3 are shown in Figs. 5(A) to (C), respectively.

<evaluation result>

As is clear from the production examples A1, A2, and A3, as the temperature of the heat treatment of the support is increased and the heat treatment time is prolonged, the unevenness of the alignment angle of the retardation film is smaller. In Production Example A3 (Table 3) in which the elongation modulus of the support at 140 ° C was 200 MPa, it was found that the unevenness of the alignment angle was 20° in the case where the heat treatment of the support was not performed, and the relative angle was 20°. By increasing the temperature of the heat treatment and prolonging the heating time, the unevenness can be made 1 or less. From this result, it is understood that when the extension elastic modulus of the support is small, the uniformity of the alignment angle by the heat treatment of the support is particularly large.

[Synthesis Example B: Synthesis of a polyarylate resin (polymer having a positive birefringence) and preparation of a coating]

In a reaction vessel equipped with a stirring device, 54.0 g of 2,2-bis(4-hydroxyphenyl)-4-methylpentane and 12 parts by weight of benzyltriethylammonium chloride were dissolved in 1 M sodium hydroxide solution. in. To the solution, a solution of 406 parts by weight of p-xylylene chloride dissolved in chloroform was added in one portion while stirring, and the mixture was stirred at room temperature for 90 minutes. Thereafter, the polymerization solution is allowed to stand. The chloroform solution containing the polymer was separated, washed with acetic acid water, washed with ion-exchanged water, and poured into methanol to precipitate a polymer. The precipitated polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure.

The obtained polyarylate-based resin was dissolved in cyclopentanone to prepare a coating having a solid concentration of 20%.

[Retardation film production example B]

In the retardation film production examples B1 and B2, a heat shrink film was used as the support film. As the heat shrinkable film, a film obtained by simultaneously holding both end portions in the width direction of the unstretched polypropylene film by a tenter jig of a biaxial stretching machine while maintaining the distance between the jigs in the width direction is used. Extending in the length direction to make it biaxially aligned.

<heat treatment, coating, drying>

In Production Example B1, the wound body 10 of the heat-shrinkable support film (width: 600 mm) was placed in the drawing portion 11 of the film forming apparatus schematically shown in Fig. 1, and the support film 1 was taken out, one side facing the downstream side. The transfer was carried out in a heating furnace at 110 ° C for 60 seconds. The coating prepared in Synthesis Example B was applied to the support after the heat treatment so that the film thickness after drying was 15 μm, and dried at 100 °C. The dried coating film is wound together with the support as a laminate. In Production Example B2, coating and drying of the coating onto the support were carried out in the same manner as in Production Example B1 except that the heating furnace was set to room temperature (that is, heating was not performed). The support was peeled off from the obtained laminate, and the alignment angle of the optical axis of the coating film was measured at intervals of 2 mm in the width direction (measurement range: 530 mm in the center in the width direction). The measurement results of the alignment angles of the heat treatment (Production Example B1) and the non-heat treatment (Production Example B2) are shown in Fig. 6(A).

<Extension and peeling>

The above laminated body was stretched 1.2 times in the width direction at a temperature of 145 ° C using a biaxial stretching machine, and the distance between the jigs in the longitudinal direction was reduced to shrink to 0.75 times. The in-plane retardation of the retardation film after peeling off the support was 270 nm and NZ = 0.5. In width The optical axis of the retardation film was measured at an interval of 2 mm upward (measurement range: 150 mm in the center in the width direction). The measurement results of the alignment angles of the retardation film having heat treatment (Production Example B1) and no heat treatment (Production Example B2) are shown in Fig. 6(B). In addition, the unevenness of the alignment angle (°) of the optical axes before and after the extension of the production examples B1 and B2 is shown in Table 4.

From the comparison between Fig. 6(A) and Fig. 6(B), in the production example B1 (with heat treatment) and the production example B2 (without heat treatment), the unevenness of the alignment angle tends to be small due to the elongation. In the production example B2 in which the heat treatment of the support was not performed, the unevenness of the alignment angle of the coating film after the coating was applied and dried was large (Fig. 6(A)), and therefore it was considered that the tendency remained after the stretching. The unevenness of the alignment angle of the retardation film becomes large (Fig. 6(B)). On the other hand, in Production Example B1, since the coating material was applied and dried after the heat treatment of the support, the unevenness of the alignment angle of the coating film was small, and the unevenness of the alignment angle was further reduced by the stretching. According to these results, when the heat shrinkable film is used as the support, the support may be subjected to heat treatment before film formation to obtain a retardation film having a small unevenness in the width direction.

TD‧‧‧width direction

MD‧‧‧ length direction

Claims (14)

A method for producing a retardation film, comprising: a coating step of applying a resin solution on the support film while transferring a long support film containing a biaxially oriented film in a longitudinal direction; a drying step of drying the resin solution by heating to form a laminate having a coating film adhered to the support film; and an extending step of extending the laminate in at least one direction after the drying step To the coating film, optical anisotropy is applied, and before the coating step, heat treatment of the support film is performed, and the heat treatment is performed in a state where tension is applied along the longitudinal direction of the support film. The method for producing a retardation film according to claim 1, wherein the heating temperature T _H in the heat treatment is 80 ° C or higher, and the heating time t _H is 8 seconds or longer. The method for producing a retardation film according to claim 1, wherein the heating temperature T _H in the heat treatment is 60 ° C or higher and less than 80 ° C, and the heating time t _H is 23 seconds or longer. A method of producing a retardation film according to claim 1, wherein the support film is a biaxially stretched film. The method for manufacturing a retardation film of the request 1, wherein the glass transition temperature of the above-described support to a Tg of the TMA measurement, the above-described heat treatment the heating temperature T _H of less than Tg-15 ℃. The method for producing a retardation film according to claim 5, wherein in the heat treatment, the heating temperature T _H is Tg + 15 ° C or more and the heat treatment time t _H is 8 seconds or more, or the heating temperature T _H is Tg - 15 ° C. Above and below Tg + 15 ° C, the heat treatment time t _H is {(Tg - T _H ) × 2 + 38} seconds or more. The method for producing a retardation film according to claim 1, wherein the support film is utilized A polyester film having a glass transition temperature Tg of 110 ° C or less as measured by TMA. The method for producing a retardation film according to claim 1, wherein the support film has a tensile modulus of at least 1000 MPa at 140 ° C before the heat treatment. The method for producing a retardation film according to claim 1, wherein the film thickness of the coating film after drying in the drying step is 30 μm or less. The method for producing a retardation film according to claim 1, wherein the in-plane retardation of the film after the stretching is 15 nm to 400 nm. The method for producing a retardation film according to any one of claims 1 to 10, wherein in the extending step, the laminated body is stretched in any one of a longitudinal direction and a width direction, and is in a direction of extension The laminated body is shrunk in the direction orthogonal to the direction. The method of producing a retardation film according to claim 11, wherein in the extending step, the free end is uniaxially stretched in the longitudinal direction without holding both end portions in the width direction of the laminated body. The method of producing a retardation film according to claim 11, wherein in the extending step, in a state in which both ends of the laminated body in the width direction are gripped, the width direction is extended and the length direction is made. The above laminated body shrinks. A method for producing a laminated polarizing plate, which comprises a method of producing a laminated polarizing plate comprising a layered polarizing element and a retardation film, wherein the retardation film is produced by the method according to any one of claims 1 to 13, An optical film including a polarizing element is laminated on the retardation film.