JP2020121555A - Film manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a film having a uniform thickness by controlling a stretched state of a thermoplastic resin sheet in a stretching step even when a coating agent is applied to at least one surface of the thermoplastic resin sheet. A coating step of applying a coating agent to at least one surface of a thermoplastic resin sheet, a preheating drying step of raising the temperature of the thermoplastic resin sheet, and a stretching step of stretching the thermoplastic resin sheet in at least the width direction are provided in this order. In the film manufacturing method, at the start point of the stretching process, the temperature of the thermoplastic resin sheet at the center in the width direction is T (° C.), and the temperature of the thermoplastic resin sheet at each coated end is Tce1 (° C.) and Tce2 (Tce2), respectively. When the glass transition temperature of the thermoplastic resin sheet is Tg (° C.), T is [Tg + 15] or more and [Tg + 40] or less, and both Tce1 and Tce2 are [Tg-10] or more and Tg or less. A method for producing a film, which is characterized by being present. [Selection diagram] Fig. 2

Description

The present invention relates to a film manufacturing method capable of reducing thickness unevenness.

With the growth of the IT field in recent years, development of films for optical applications such as antireflection films for electronic device products such as displays, base films for touch panels, process papers for optical members such as optical displays and liquid crystal retarders. Is progressing. In such a base film, a hard coat layer or the like is often laminated on the film, and in that case, in order to improve the adhesion between the film and the hard coat layer or reduce the interference unevenness. In some cases, the film is coated with a resin layer having an easy adhesive property (also referred to as an easy adhesive layer).

In such fields, demands for reduction of optical defects are further increasing along with higher performance and higher quality of electronic device products, and in particular, it is one of the causes for causing optical interference unevenness in film lamination processing. There is a strong demand to reduce the uneven thickness. Further, in the case of a film in which an easy-adhesion layer is laminated, it is necessary to reduce not only the thickness unevenness of the base film but also the thickness unevenness of the easy-adhesion layer.

Generally, a uniaxially or biaxially oriented film having an easily adhesive layer is a non-oriented sheet or a uniaxially oriented sheet which is uniaxially stretched in the longitudinal direction. It can be produced by heating and drying with hot air or the like while gripping it with a plurality of running clips and the like, stretching in the width direction and/or the longitudinal direction, and then heat-treating at high temperature and cooling. That is, the uniaxially or biaxially oriented film having the easy-adhesion layer is manufactured through a coating step, a preheating drying step, a stretching step, a heat treatment step, and a cooling step. In each successive process after the coating process, a hot air circulation path is mainly provided, and an apparatus capable of controlling the temperature of the circulating hot air is used for each process.

This device is generally called a tenter oven. The tenter oven blows temperature-controlled air from the top and bottom of a sheet (film after the stretching process) that is continuously fed horizontally, and the sheet or film is processed in each process. By heating or cooling to a desired temperature, the sheet or film is subjected to treatments such as preheating drying, stretching, heat treatment, and cooling.

In order to reduce the film thickness unevenness, it is necessary to uniformly stretch the sheet in the width direction in the stretching step. Therefore, as shown in Patent Document 1, a method has been proposed in which the temperature of the sheet end portion is made higher by 1° C. to 30° C. than that of the central portion and the sheet is stretched in the width direction. Further, in Patent Documents 2 and 3, by making the temperature at a specific position higher than the temperature at other positions or by providing a temperature difference in the plane of the sheet, the neck stretching of the sheet is started from the specific position. , A method of obtaining a stretched film excellent in thickness accuracy has been proposed.

JP, 2002-301763, A JP, 2009-51161, A JP, 2005-147334, A

However, when a coating agent is applied to at least one surface of a non-oriented sheet or a uniaxially oriented sheet that is uniaxially stretched in the longitudinal direction, in the method described in Patent Document 1, the temperature rise in the sheet application section is the edge of the uncoated sheet. Since it is delayed compared with the above, the crystallization of the sheet end portion progresses and the sheet is easily broken at the stretched portion. In addition, when the sheet coating section is heated to a uniform temperature in the width direction, sufficient heating is required, so that the length in the longitudinal direction of the preheating drying process becomes long, and the thickness unevenness and foreign matter caused by increasing the wind speed Is a problem. Further, the methods disclosed in Patent Documents 2 and 3 cannot sufficiently control the thickness unevenness.

The present invention improves the drawbacks of the prior art, and even when a coating agent is applied to at least one surface of a thermoplastic resin sheet, by controlling the stretched state of the sheet in the stretching step, production of a film having a uniform thickness The task is to provide a method.

In order to solve the above problems, the present invention has the following configurations.
(1) A film having a coating step of coating a coating agent on at least one surface of a thermoplastic resin sheet, a preheating drying step of raising the temperature of the thermoplastic resin sheet, and a stretching step of stretching the thermoplastic resin sheet at least in the width direction in this order. At the starting point of the stretching step, the temperature of the thermoplastic resin sheet at the central portion in the width direction is T (° C.), and the temperature of the thermoplastic resin sheet at each coating end is Tce ₁ (° C.), Tce _{2 respectively.} (C) and the glass transition temperature of the thermoplastic resin sheet is Tg (°C), T is [Tg+15] or more and [Tg+40] or less, and both Tce ₁ and Tce ₂ are [Tg-10] or more. A method for producing a film, which is Tg or less.
(2) The method for producing a film as described in (1), wherein T is [Tg+20] or more and [Tg+30] or less.
(3) There are uncoated portions of the coating agent on both ends in the width direction of the thermoplastic resin sheet, and the temperatures of the uncoated portions at the starting point of the stretching step are Tne ₁ (°C) and Tne ₂ (°C), respectively. At times, Tne ₁ is [Tg-10] or more and Tce ₁ or less, and Tne ₂ is [Tg-10] or more and Tce ₂ or less, in the film according to (1) or (2). Production method.
(4) The T is the maximum when the temperature of the thermoplastic resin sheet is measured in parallel with the width direction at the starting point of the stretching step, and the T is the maximum, according to any one of (1) to (3). Film manufacturing method.
(5) When the preheating drying step and the stretching step are performed by a tenter having a plurality of chambers, the section length of the preheating drying step is L (m), and the longitudinal transport speed is V (m/min), 0.07≦[L/V]≦0.15, The method for producing a film according to any one of (1) to (4), wherein
(6) The surface on which the coating agent is applied in the coating step is one surface, the surface on which the coating agent is applied is the X surface, the surface on the opposite side is the Y surface, and the temperature of the air blown to the X surface in the preheating drying step is Tx (°C), the temperature of the air blown onto the Y surface is Ty (°C), the velocity of the air blown onto the X face is Vx (m/sec), and the velocity of the air blown onto the Y face is Vy (m/sec). And satisfying at least one of 1<Tx-Ty<10 and Vx>Vy. 7. The method for producing a film according to any one of (1) to (5), wherein

According to the present invention, even when a coating agent is applied to at least one surface of a thermoplastic resin sheet, it is possible to obtain a film having a uniform thickness by controlling the stretched state of the thermoplastic resin sheet in the stretching step. A method for manufacturing a film can be provided.

It is a schematic plan view which shows the coating process which concerns on one embodiment of this invention, and the whole tenter oven structure. FIG. 2 is an enlarged plan view of a preheating drying step and a stretching step in FIG. 1.

The method for producing a film of the present invention includes a coating step of applying a coating agent on at least one surface of a thermoplastic resin sheet, a preheating drying step of heating the thermoplastic resin sheet, and a stretching step of stretching the thermoplastic resin sheet at least in the width direction. A method for producing a film having steps in this order, wherein at the starting point of the stretching step, the temperature of the thermoplastic resin sheet at the center in the width direction is T (° C.), and the temperature of the thermoplastic resin sheet at each coating end is Tce _1. (C) and Tce ₂ (°C), and Tg (°C) is the glass transition temperature of the thermoplastic resin sheet, T is [Tg+15] or more and [Tg+40] or less, and both Tce ₁ and Tce ₂ are [Tg-10] or more and Tg or less. In the method for producing a film of the present invention, the sheet-shaped material before the stretching step is called a sheet, and the sheet-shaped material after the stretching step is called a film. Hereinafter, the method for producing the film of the present invention will be specifically described.

In the method for producing a film of the present invention, the thermoplastic resin sheet refers to a sheet containing a thermoplastic resin as a main component, and the phrase “containing a thermoplastic resin as a main component” means that all components constituting the sheet are 100 mass. % Means that the total amount of the thermoplastic resin is more than 50% by mass. The thermoplastic resin sheet may be a non-oriented sheet obtained by cooling and solidifying a molten thermoplastic resin or a uniaxially oriented sheet obtained by uniaxially stretching the molten thermoplastic resin as long as the effects of the present invention are not impaired.

The thermoplastic resin forming the thermoplastic resin sheet is not particularly limited as long as the effects of the present invention are not impaired, and examples thereof include polyolefin resins such as polyethylene, polypropylene and polymethylpentene, polyamide resins such as nylon 6 and nylon 66, and polyethylene terephthalate. (Hereinafter, it may be abbreviated as PET. The same applies in the following parentheses.), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), polybutylene naphthalate (PBN), polytrimethylene terephthalate ( PPT), polyethylene-p-oxybenzoate, polyester resin such as poly-1,4-cyclohexylene dimethylene terephthalate (PCT), polycarbonate resin, PET as a copolymerization component, for example, diethylene glycol, neopentyl glycol, polyalkylene glycol. Polyester resin obtained by copolymerizing a diol component such as and a dicarboxylic acid component such as adipic acid, sebacic acid, phthalic acid, isophthalic acid, and 2,6-naphthalenedicarboxylic acid, and other polyacetal resin and polyphenylene sulfide resin. .. Further, when using the method for producing a film of the present invention in a film for optical applications in which control of retardation and thickness unevenness is strictly required, an amorphous material such as a polycarbonate resin, a polyolefin resin, a cyclic polyolefin resin, or a polyacrylic resin is used. It is also possible to use the above resin as a constituent component. These thermoplastic resins may be used alone or in combination of two or more as long as the effects of the present invention are not impaired.

Further, these thermoplastic resins may contain various additives depending on the purpose. Examples of such additives include colloidal silica for imparting lubricity, alumina, calcium carbonate, organic silicones, and inert particles such as polydivinylbenzenesulfonic acid, as well as antistatic agents and antioxidants. Can be mentioned. Note that these additives may be used alone or in combination of two or more kinds as long as the effects of the present invention are not impaired.

In the method for producing a film of the present invention, the coating agent means a polymer solution or a polymer dispersion applied to at least one surface of the thermoplastic resin sheet in the step of producing the film, and the coating agent is applied to form a layer. As a result, easy adhesion, gas barrier properties, heat sealing properties, surface lubricity, antistatic properties, etc. can be improved. The polymer component of the coating agent can be selected according to the purpose without impairing the effects of the present invention, and specific examples include polyester resins, polyamide resins, polyvinylidene chloride resins, polyolefin resins, ionomer resins, polyvinyls. Thermoplastic resins such as alcohol resins, polyacrylic acid resins and polyalkylene glycol resins, aminoalkyd resins, aminoacrylic acid resins, melamine resins, urea resins, epoxy resins, polyurethane resins, silicone resins and the like, and these And the like. Further, the coating agent may appropriately contain various additives such as an emulsifier, an antiblocking agent, an antistatic agent, a leveling agent, and a viscosity adjusting agent according to the purpose within a range not impairing the effects of the present invention.

The thermoplastic resin sheet in the film manufacturing method of the present invention can be obtained by a known method, but the melt film forming method can be preferably applied from the viewpoint of cost and productivity. The melt film forming method can be classified into a straight die method, a cross head die method, a flat die method, a special die method and the like depending on the shape of the die used, but the flat die method is preferably used.

In the melt film-forming method, when a thermoplastic resin composition as a raw material (hereinafter, sometimes simply referred to as a resin raw material) is melt-extruded, the resin raw material is dried in advance with a dryer such as a hopper dryer or a paddle dryer, or a vacuum. It is preferable to dry using a dryer. The dried resin raw material is melted by a melt extruder or the like, measured by a gear pump, and continuously sent to a die. The die may have any design as long as the molten resin does not stay therein, and in the flat die method, any type such as a manifold die, a coat hanger die and a fish tail die that are commonly used may be used. A non-oriented sheet can be obtained by cooling and solidifying a molten resin extruded in a sheet form from a die on a cooling medium such as a drum. In melt film formation by the flat die method, the thickness of the non-oriented sheet can be adjusted by adjusting the extrusion temperature, the take-up speed at the time of take-up, and the lip gap of the die.

The non-oriented sheet thus obtained may be uniaxially stretched in the running direction of the sheet (hereinafter sometimes referred to as the longitudinal direction) to give a uniaxially oriented sheet. As a method of uniaxially stretching, for example, a method of contacting several rolls whose temperature is controlled, a method of heating by radiant heat of a heater such as an infrared heater, or the like, is heated to a temperature not lower than the glass transition temperature of the non-oriented sheet. And a method of stretching by using the peripheral speed difference between the front and rear rolls. The uniaxial stretching ratio in this case is appropriately selected according to the purpose, but is generally 1.2 times or more for the purpose of improving toughness and flexibility, and 1.5 times or more for the purpose of expressing strength and retardation. A range of 5 times or less is selected. Uniaxial stretching of the non-oriented sheet may be carried out in one step or in two or more steps as long as the effect of the present invention is not impaired, but defects such as surface scratches and sticking marks on the roll occur. It is preferable to select a difficult stretching method.

The thickness of the thermoplastic resin sheet in the method for producing a film of the present invention can be appropriately selected according to the purpose unless the effects of the present invention are impaired, but from the viewpoint of productivity and the like, it is 5 to 1,500 μm. It is preferable. When the thickness of the thermoplastic resin sheet is 5 μm or more, the yield due to breakage in the stretching step can be reduced, and when it is 1,500 μm or less, it is possible to reduce the decrease in transparency of the obtained film. It is possible to prevent the thickness from becoming excessively large.

The thickness unevenness in the longitudinal direction and the width direction of the thermoplastic resin sheet in the production method of the present invention is 0% or more and 2.5% or less of the thickness of the thermoplastic resin sheet from the viewpoint of making the physical properties of the obtained film uniform. For example, when the thickness of the thermoplastic resin sheet is 1,000 μm, it is desirable that the thickness unevenness is 0 μm or more and 25 μm or less in both the longitudinal direction and the width direction of the thermoplastic resin sheet. By controlling the thickness unevenness to be 2.5% or less, it is possible to suppress the occurrence of unevenness in the physical properties in the width direction and the longitudinal direction due to local stretching of a portion having a small thickness during stretching.

The method for producing a film of the present invention includes a coating step of applying a coating agent on at least one surface of a thermoplastic resin sheet, a preheating drying step of heating the thermoplastic resin sheet, and a stretching step of stretching the thermoplastic resin sheet at least in the width direction. It has steps in this order. The coating method in the coating step is not particularly limited as long as it does not impair the effects of the present invention, for example, a gravure roll method, a reverse roll method, an air knife method, a reverse gravure method, a Meyer bar method, an inverse roll method, and these. Various coating methods by combination can be adopted and can be appropriately selected depending on the characteristics of the coating agent and the target coating thickness. However, it is preferable that the coating can be applied as uniformly as possible in order to improve the efficiency of the drying performed in the subsequent step.

In the preheat drying step, the thermoplastic resin sheet is preheated and the coating portion formed of the coating agent is dried. The preheating drying step and the stretching step to be described later can be performed in a tenter oven which is mainly provided with a hot air circulation path and in which the temperature of the circulating hot air can be controlled for each step (in FIG. 1, the entire tenter oven is shown). An example of a schematic plan view showing the configuration is shown). The temperature of the thermoplastic resin sheet in the preheating drying step is preferably a temperature not lower than the glass transition temperature of the thermoplastic resin sheet and not higher than the crystallization temperature. When the thermoplastic resin sheet is a PET sheet, its glass transition temperature is about 70 to 90° C. and its crystallization temperature is about 140 to 170° C. Therefore, it depends on the heat transfer efficiency in the preheating drying step and the length in the longitudinal direction. However, it is preferable to heat at 80° C. or higher and 140° C. or lower in the preheat drying step. When the temperature of the thermoplastic resin sheet in the preheat drying step exceeds 140° C., crystallization of PET partially proceeds, and the thermoplastic resin sheet being stretched may be broken in the subsequent stretching step.

In the stretching step, the thermoplastic resin sheet is stretched at least in the width direction. In this stretching step, stretching may be performed at least in the width direction, and stretching may be performed only in the width direction or simultaneously in the width direction and the longitudinal direction. The draw ratio in the width direction and/or the longitudinal direction is appropriately selected according to the purpose, but generally 1.2 times or more for the purpose of improving toughness and flexibility, and 1 for the purpose of expressing strength and phase difference. A range of 5 to 5 times is selected. In addition, it is preferable to control the temperature of the thermoplastic resin sheet in the stretching step to the same extent as in the preheating drying step from the viewpoint of film-forming stability. When the thermoplastic resin sheet is a PET sheet, the temperature is 80°C or higher and 140°C or lower. It is preferable to heat. When the temperature of the thermoplastic resin sheet is 140° C. or higher, crystallization of PET partially proceeds, and the thermoplastic resin sheet may be broken without being stretched.

In the method for producing a film of the present invention, from the viewpoint of reducing the thickness unevenness of the film, at the starting point of the stretching process, the temperature of the thermoplastic resin sheet at the center in the width direction is T (° C.), and the thermoplasticity at each coating end is thermoplastic. When the resin sheet temperatures are Tce ₁ (° C.) and Tce ₂ (° C.) and the glass transition temperature of the thermoplastic resin sheet is Tg (° C.), T is [Tg+15] or more and [Tg+40] or less, and It is important that both Tce ₁ and Tce ₂ are not less than [Tg-10] and not more than Tg. When T is higher than Tce ₁ and Tce ₂ , tension propagation from the clip that grips both ends of the thermoplastic resin sheet is uniformly transmitted from both ends toward the center, and Tce ₁ and Tce ₂ are [Tg-10]. When it is at least Tg, the stretching can be started from both ends of the coating. It should be noted that which of the coating end portions has a temperature of Tce ₁ or Tce ₂ is arbitrary.

Here, the starting point of the stretching step means a point at which the stretching of the thermoplastic resin sheet in the width direction is started, and more specifically, a point at which the interval between the clip rails of the tenter oven begins to widen. The glass transition temperature Tg (° C.) of the thermoplastic resin sheet is 20° C./min in a range of 25° C. to 200° C. under a nitrogen atmosphere using a differential scanning calorimeter (Seiko Denshi Kogyo RDC220 type). It can be determined according to the method for determining the midpoint glass transition temperature of JIS-K-7121 (1987) from the chart when measured at the heating rate. When there are a plurality of stepwise change parts on the chart, the lower value in the measurement range is adopted. The differential scanning calorimeter used for measuring Tg (° C.) can be appropriately selected from known ones, and for example, RDC220 type manufactured by Seiko Instruments Inc. can be used. Moreover, T(° C.), Tce ₁ (° C.), and Tce ₂ (° C.) can be measured by a radiation thermometer installed below the thermoplastic resin sheet.

When T is lower than [Tg+15] and the difference between T and Tce _{1 and} the difference between T and Tce ₂ are small, local stretching occurs near the coated end of the thermoplastic resin sheet, and the thickness unevenness is deteriorated. On the other hand, when T is higher than [Tg+40], crystallization of the central portion of the thermoplastic resin sheet progresses, which causes uneven thickness and breakage. From the above viewpoint, T is preferably [Tg+15] or more and [Tg+30] or less, and more preferably [Tg+20] or more and [Tg+30] or less.

When at least one of Tce ₁ and Tce ₂ is lower than [Tg-10], the stretching starts not from the both ends of the coating but from the portion close to the central portion exceeding the glass transition temperature. Tension propagation may become non-uniform, resulting in uneven thickness, or breakage of the thermoplastic resin sheet. On the other hand, when at least one of Tce ₁ and Tce ₂ is higher than Tg, local stretching occurs near the application end of the thermoplastic resin sheet to deteriorate thickness unevenness, and the crystal of the end of the thermoplastic resin sheet. There is a case where the thermoplastic resin sheet is broken due to progress of chemical conversion.

In general, a thermoplastic resin sheet has a thicker thickness at both widthwise end portions due to neck-in when extruded into a sheet shape from a die or width shrinkage caused when uniaxially stretched in the longitudinal direction, and uneven thickness. May be large, and both ends in the width direction become uncoated portions of the coating agent. In the method for producing a film of the present invention, from the viewpoint of improving the uniformity of stretching and securing the film-forming stability, there are uncoated portions of the coating agent at both ends in the width direction of the thermoplastic resin sheet, and at the starting point of the stretching step. When the temperature of each uncoated portion is Tne ₁ (° C.) and Tne ₂ (° C.), Tne ₁ is [Tg-10] or more and Tce ₁ or less, and Tne ₂ is [Tg-10] or more and Tce ₂ The following is preferable. Tne ₁ (° C.) and Tne ₂ (° C.) can also be measured by a radiation thermometer installed below the thermoplastic resin sheet, similarly to T (° C.) and the like. The measurement point of Tne ₁ is an uncoated end portion outside the measurement point of Tce ₁ in the width direction, and the measurement point of Tne ₂ is an uncoated end portion outside the measurement point of Tce ₂ in the width direction.

By setting Tne ₁ to Tce ₁ or less and Tne ₂ to Tce ₂ or less, it is possible to prevent the uncoated portion having large thickness unevenness from becoming the stretching start point, so that the stretching start point becomes stable in the width direction. The thickness unevenness in the width direction and the length direction and the breakage of the thermoplastic resin sheet due to the progress of crystallization of the uncoated portion can be reduced. Further, by setting Tne ₁ and Tne ₂ to be [Tg-10] or more, it is possible to easily secure the amount of heat necessary for stretching, and thus it is possible to reduce breakage of the thermoplastic resin sheet.

The method of controlling the temperature (T, Tce ₁ , Tce ₂ , Tne ₁ , Tne _2, etc.) in the width direction of the thermoplastic resin sheet at the stretching start point is not particularly limited as long as the effect of the present invention is not impaired. There is a method of changing the temperature and the amount of air in the nozzle width direction for supplying heated air to the thermoplastic resin sheet, and a method of installing a cover or the like at the nozzle end to limit the amount of heat at both ends of the thermoplastic resin sheet. Considering application to existing production equipment, it is easy to install a cover or the like at the nozzle end to limit the amount of heat at the widthwise ends of the thermoplastic resin sheet. By installing a cover at the end of the nozzle, the air volume in the uncovered part increases, and by adjusting the cover position in the width direction, it is possible to adjust the temperature of the central part of the thermoplastic resin sheet and both ends of the width direction. Become.

In the method for producing a film of the present invention, T is the maximum when the temperature of the thermoplastic resin sheet is measured in parallel with the width direction at the starting point of the stretching step from the viewpoint of reducing the thickness unevenness of the obtained film. preferable. When the temperature of the thermoplastic resin sheet is measured in parallel with the width direction at the starting point of the stretching step, T is the maximum, and T, Tce ₁ , Tce ₂ , Tne ₁ , Tne ₂ , and the measurement point of Tce and Tce. It means that T is the maximum of the temperature at the midpoint of the measurement point of ₁ and the temperature at the midpoint of the measurement point of T and Tce ₂ . However, when there is no uncoated portion, it is possible to make a determination with all 5 points excluding Tne ₁ and Tne ₂ on both sides in the width direction.

When T is the maximum, the tension is propagated in one direction from both ends of the thermoplastic resin sheet toward the central portion, and stretching can be performed from both ends of the coating to the central portion along the widening of the film width in the stretching step. it can. Therefore, stretching unevenness is reduced, and the physical properties of the obtained film become more uniform. The method of maximizing T at the starting point of the stretching step is also the method of changing the temperature and the air volume in the nozzle width direction for supplying the heating air to the thermoplastic resin sheet in the preheating drying step as described above, or the nozzle end portion. A method of installing a cover or the like to limit the amount of heat at both ends of the thermoplastic resin sheet in the width direction can be used.

In the film production method of the present invention, when the productivity of the film is taken into consideration, 0.07≦ when the section length of the preheating drying step is L (m) and the longitudinal transport speed is V (m/min). It is preferable that [L/V]≦0.15. When [L/V] is 0.07 or more, it is not necessary to excessively increase the nozzle wind speed or temperature in order to secure the amount of heat required for preheat drying. Therefore, it is included in the nozzle air by increasing the nozzle wind speed. It is possible to suppress the occurrence of defects caused by foreign matter adhering to the coating portion and to suppress the occurrence of thickness unevenness due to temperature unevenness in the width direction of the thermoplastic resin sheet by raising the temperature. On the other hand, when [L/V] is 0.15 or less, the length of the section that can be uniformly preheated and dried in the width direction does not become excessively long, and it is possible to avoid a decrease in productivity and the occurrence of uneven thickness. it can. From the above viewpoint, [L/V] is more preferably 0.07≦[L/V]≦0.14.

The method for producing a film of the present invention, when the surface to which the coating agent is applied in the coating step is one side, from the viewpoint of simultaneously achieving reduction of coating agent drying and thickness unevenness, air blown onto each surface with a tenter oven. It is preferable to adjust the temperature and speed of. More specifically, the surface on which the coating agent is applied in the coating step is one surface, the surface on which the coating agent is applied is the X surface, the opposite surface is the Y surface, and the temperature of the air blown to the X surface in the preheat drying step. Is Tx (° C.), the temperature of the air blown onto the Y surface is Ty (° C.), the velocity of the air blown onto the X face is Vx (m/sec), and the velocity of the air blown onto the Y face is Vy (m/sec). At least one of 1<Tx-Ty<10 and Vx>Vy is sometimes preferable.

By setting 1<Tx−Ty or Vx>Vy, the Y surface is excessively heated while the coating agent applied to the X surface is dried, or the Y surface is heated to an appropriate temperature while the X surface is Since insufficient heating can be reduced, deterioration of thickness unevenness and breakage due to progress of crystallization of the sheet surface can be suppressed in the subsequent stretching step. On the other hand, by setting Tx-Ty<10, excessive preheat drying of the X-plane can be suppressed, and in the subsequent stretching step, deterioration of thickness unevenness and breakage due to crystallization progress of the sheet surface can be suppressed. From the above viewpoint, it is more preferable that at least one of 3<Ta-Tb<8 and Va>Vb is satisfied, and it is further preferable that at least one of 4<Ta-Tb<6 and Va>Vb is satisfied.

Tx (°C) and Ty (°C) can be measured by the following method. First, a total of six chambers (three on the upper surface side and three on the lower surface side) arranged at the widthwise central portion and at the midpoint between the widthwise central portion and each coating end without contacting the thermoplastic resin sheet. The temperature is measured at 1 second intervals for 60 seconds with a thermometer (the arrangement on the upper surface side is shown in FIG. 2. Reference numerals 4A, 4C-1 and 4C-2 are indoor thermometers). Then, the average value of all the measured values of the upper room thermometer and the average value of all the measured values of the lower room thermometer are calculated, and they are set as Tx (°C) and Ty (°C), respectively.

Hereinafter, the method for producing the film of the present invention will be specifically described with reference to the drawings, but the method for producing the film of the present invention is not limited to the following embodiments.

In the method for producing a film of the present invention, a coating step of applying a coating agent to at least one surface of a thermoplastic resin sheet obtained by a melt film-forming method, a preheating drying step of raising the temperature of the thermoplastic resin sheet, and thermoplasticity A film can be manufactured by going through a stretching step of stretching the resin sheet at least in the width direction in this order. FIG. 1 is a schematic plan view showing a general coating process and the entire configuration of a tenter oven, and FIG. 2 is an enlarged plan view of a preheating drying process and a stretching process in FIG.

The coating method in the coating step is not particularly limited as long as it does not impair the effects of the present invention, for example, a gravure roll method, a reverse roll method, an air knife method, a reverse gravure method, a Meyer bar method, an inverse roll method, and these. Various coating methods by combination can be adopted, and the preheating drying step and the stretching step can be performed by a tenter oven installed downstream of the coating step. As shown in FIG. 1, the tenter oven preferably has a plurality of chambers continuous in the running direction of the thermoplastic resin sheet, and at least one chamber in which the temperature of the supplied air is different is preferable. By adopting such a mode, in addition to preheating drying and stretching of the thermoplastic resin sheet, subsequent heat treatment and cooling can be continuously and easily performed.

Hereinafter, a specific flow of the process for producing a film from a thermoplastic resin sheet will be specifically described with reference to the drawings. First, in the coating step 1, the coating agent is applied to at least one surface of the thermoplastic resin sheet 2 to be stretched. At this time, since the thickness and the thickness unevenness of the widthwise both end portions of the thermoplastic resin sheet 2 are increased due to neck-in and the like when extruded from the die into a sheet shape, the widthwise both end portions of the thermoplastic resin sheet 2 are It is preferable to use the uncoated portion 3 of the coating agent (shown only in FIG. 2). Further, by providing the uncoated portion 3, the clip does not come into contact with the portion coated with the coating agent, so that troubles such as contamination of the clip due to the undried coating agent and sheet breakage due to detachment of the clip can be avoided.

After that, the thermoplastic resin sheet 2 coated with the coating agent is subjected to the preheating drying step 4 in the tenter oven by gripping the uncoated portions 3 on both sides in the width direction with a clip (not shown) continuously running in the tenter oven. Lead. In this preheating drying step 4, the thermoplastic resin sheet 2 is heated to a temperature not lower than the glass transition temperature and not higher than the crystallization temperature in preparation for the subsequent stretching step 5, and at the same time, the liquid component of the coating agent is removed by drying.

Further, in the case where the surface to be coated with the coating agent in the coating step is one side, the temperature and speed of the air blown to each surface in the tenter oven are adjusted from the viewpoint of achieving both drying of the coating agent and reduction of thickness unevenness. It is preferable.

The method of controlling the air blowing temperature of the surface to which the coating agent is applied (X surface) and the surface to which the coating agent is not applied (Y surface) is not particularly limited as long as the present invention is not impaired. For example, a thermoplastic resin using a heat exchanger or the like is used. Methods include changing the temperature of the air blown by the upper and lower nozzles of the resin sheet, and changing the amount of room temperature air supplied by the upper and lower nozzles of the thermoplastic resin sheet. To be More specifically, the temperature of the air can be lowered by using a heat exchanger or by increasing the amount of air mixed at room temperature. The method of controlling the air blowing speeds on the X-side and the Y-side is not particularly limited as long as the present invention is not impaired, but a method of controlling the air speed by the upper nozzle and the lower nozzle of the thermoplastic resin sheet is not limited. Examples include a method of changing the rotation speed and a method of adjusting a damper attached to a duct upstream of the nozzle. More specifically, the air blowing speed can be reduced by lowering the rotation speed of the motor, narrowing the damper, or the like. In addition, a method of controlling preheat drying by adjusting the heat transfer coefficient of the surface of the thermoplastic resin sheet by changing the balance of the exhaust amount and air circulation amount of the upper nozzle and the lower nozzle of the thermoplastic resin sheet Can also be used. Note that the air circulation means that a part or all of the air blown on the thermoplastic resin sheet is recovered and the air is circulated by a tenter oven having a structure capable of being blown again to the thermoplastic resin sheet. Say.

From the above viewpoint, the surface on which the coating agent is applied in the coating step is one surface, the surface on which the coating agent is applied is the X surface, the opposite surface is the Y surface, and the temperature of the air blown to the X surface in the preheat drying step. Is Tx (° C.), the temperature of the air blown onto the Y surface is Ty (° C.), the velocity of the air blown onto the X face is Vx (m/sec), and the velocity of the air blown onto the Y face is Vy (m/sec). At times, it is preferable that at least one of 1<Tx-Ty<10 and Vx>Vy is satisfied, and it is more preferable that at least one of 3<Ta-Tb<8 and Va>Vb is satisfied, and 4<Ta-Tb<. More preferably, at least one of 6 and Va>Vb is satisfied.

The thermoplastic resin sheet 2 that has undergone the preheating drying step 4 is sent to the stretching step 5 in the tenter oven. In this stretching step 5, the thermoplastic resin sheet 2 is stretched at least in the width direction to form the film 6 by changing the distance between the clips facing each other with the thermoplastic resin sheet 2 interposed therebetween. In addition, in the stretching step 5, stretching in the width direction may be performed simultaneously with stretching in the longitudinal direction by changing the speed of the clip that continuously runs.

In the stretching step 5, at the starting point 7 of the stretching step, the temperature of the thermoplastic resin sheet at the center in the width direction is T (° C.), and the temperature of the thermoplastic resin sheet at each coated end is Tce ₁ (° C.) and Tce _{2 respectively.} (C) and the glass transition temperature of the thermoplastic resin sheet is Tg (°C), T is [Tg+15] or more and [Tg+40] or less, and Tce ₁ and Tce ₂ are both [Tg-10] or more Tg. Below. The method of controlling the temperature in the width direction of the thermoplastic resin sheet at the starting point 7 of the stretching step is not particularly limited as long as the effect of the present invention is not impaired, but a nozzle for supplying heated air to the thermoplastic resin sheet 2 in the preheating drying step. There are a method of changing the temperature and the amount of air in the width direction, a method of installing a cover or the like at the end of the nozzle to limit the amount of heat at both ends of the thermoplastic resin sheet 2 in the width direction.

Further, the temperature distribution in the width direction of the thermoplastic resin sheet 2 at the starting point 6 of the stretching step can be measured by installing a radiation thermometer 8 below the thermoplastic resin sheet 2 as shown in FIG.

The film 6 obtained in the stretching step is then gripped and held in the intermediate step A9 in which the exhaust amount is larger than the air supply amount, while the film is heated at a temperature higher than the maximum temperature in the stretching process 5. /Or heat treatment step 10 to relax, intermediate step B11 in which the exhaust amount is larger than the supply amount, film 6 is gripped and/or relaxed while cooling the film 6 to a temperature lower than the minimum temperature in the heat treatment step 10. After the cooling step 12 is sequentially performed, the grip by the clip is released outside the tenter oven.

The intermediate step A9 is an optional step between the stretching step 5 and the heat treatment step 10, and the intermediate step B11 is an optional step between the heat treatment step 10 and the cooling step 12, both of which have a larger exhaust amount than the supply amount. By providing such an intermediate step, it is possible to prevent air at different temperatures from entering the stretching step, the heat treatment step, and the cooling step, and to keep the temperature in each step uniform, thereby improving the uniformity of physical properties in the width direction. An excellent film can be obtained. The supply air temperature in the intermediate step A9 is preferably equal to the circulation temperature at the outlet of the adjacent stretching step so as not to give a sudden change to the film 6. Similarly, the supply air temperature in the intermediate step B11 is preferably equal to the circulation temperature at the inlet of the adjacent cooling step so as not to make a sudden change in the film 6.

The heat treatment step 10 means a step of gripping and/or relaxing the film 6 while heating the film 6 at a temperature higher than the maximum temperature during the stretching step. The temperature of the heat treatment step 10 can be appropriately set according to the type of resin constituting the film 6, etc., and when the film 6 is a PET film, it is preferably 180° C. or higher and 250° C. or lower. Providing the heat treatment step 10 improves the dimensional stability when exposed to a high temperature during the subsequent processing step or when the product is used as a final product. In addition, in the heat treatment step 10, it is possible to narrow the clip gap in the width direction and the longitudinal direction, whereby the film 6 is relaxed and thermally shrunk, and the dimensional stability and the thickness uniformity can be further improved.

The cooling step 12 means a step of gripping and/or relaxing the film 6 while cooling the film 6 at a temperature lower than the minimum temperature in the heat treatment step 10. Then, as in the heat treatment step 10, it is possible to narrow the clip gap in the width direction and the longitudinal direction also in the cooling step 12, whereby the film 6 is relaxed and thermally contracted, and further the dimensional stability and the thickness uniformity are obtained. Can be improved.

The film 6, which has been released from gripping by the clip outside the tenter oven, is cooled in a subsequent conveying step and once wound into a wide roll by a wide winder. Then, the film roll 6 can be obtained by unwinding the film 6 from the wide roll, cutting and removing the uncoated portion 3 with a slitter, cutting the film 6 into a required width and length, and rewinding.

Hereinafter, the present invention will be described based on examples, but the present invention is not limited to the following examples. Prior to the description of each example, the measuring method of various physical properties and the like adopted in the example will be described.

(1) Glass transition temperature (Tg)
Approximately 5 mg of a sample (thermoplastic resin sheet) was sampled, and using a differential scanning calorimeter (RDC220 type manufactured by Seiko Denshi Kogyo Co., Ltd.), in a range of 25° C. to 200° C., at 20° C./min. It measured at the temperature rising rate and determined based on the measurement result of 1stRun. The glass transition temperature is determined according to JIS-K-7121 (1987), which is the midpoint glass transition temperature. The temperature at the point where the curve of the stepwise change part of intersects. When there are a plurality of stepwise changes, the lower value in the measurement range was adopted.

(2) Temperature of the thermoplastic resin sheet at the starting point of the stretching step (T, Tce ₁ , Tce ₂ , Tne ₁ , Tne _2, etc.)
Referring to FIG. 2, at the starting point of the stretching step, the temperature of the thermoplastic resin sheet at the starting point of the stretching step (T (° C.), Tce ₁ (° C.), Tce ₂ (° C.), Tne ₁ (° C.), And Tne ₂ (° C.) and the like) will be described. As shown in FIG. 2, a radiation thermometer 8A is provided below the widthwise central portion of the thermoplastic resin sheet 2 and at a position of ±400 mm in the widthwise direction from the widthwise central portion of the thermoplastic resin sheet 2 (corresponding to the coating end portion). The radiation thermometers 8B-1 and 8B-2 on the lower side, and the radiation thermometers 8C-1 and 8C-2 on the lower side at a position of ±200 mm in the width direction from the center in the width direction of the thermoplastic resin sheet 2, Radiation thermometers 8D-1 and 8D-2 are installed below the position (corresponding to the uncoated portion) ±450 mm in the width direction from the center of the thermoplastic resin sheet 2 in the width direction. The temperature of the thermoplastic resin sheet 2 was measured for a second. The average values of the temperatures obtained by measurement with the radiation thermometers 8A, 8B-1, 8B-2, 8D-1, and 8D-2 are T (°C), Tce ₁ (°C), and Tce ₂ (°C, respectively). ), Tne ₁ (° C.), and Tne ₂ (° C.). In addition, in order to evaluate whether T was the maximum, the average value of the temperatures obtained by measuring with the radiation thermometers 8C-1 and 8C-2 was also calculated.

(3) Average Thickness of Thermoplastic Resin Sheet and Film Regarding the thermoplastic resin sheet before coating in the coating step, both ends in the width direction of 200 mm are removed in order to eliminate the influence of thickness unevenness, and then the width is parallel to the width direction. Ten points were taken so that the straight line was divided into 11 equal parts, which were used as measurement points. Thereafter, the thickness at each measurement point was measured using a digital micrometer (MDC-25MJ type manufactured by Mitsutoyo), and the average value was used as the average thickness of the thermoplastic resin sheet. In addition, the same measurement was performed on the stretched film in a tenter oven, and the obtained value was used as the average thickness of the film.

(4) Thickness unevenness Rs of the thermoplastic resin sheet, thickness unevenness Rf of the film
The thermoplastic resin sheet before coating in the coating step is cut into a width of 50 mm in each of the longitudinal direction and the width direction, and a film thickness tester (manufactured by Anritsu Co., Ltd.) is used to measure a load of 0.15 g and a load of 1.5 m/ The thickness was continuously measured while traveling at a speed of min. Then, in the range of the length of 1 m of the central portion of the thermoplastic resin sheet in the longitudinal direction, and in the width direction in the entire range excluding 200 mm at both ends, the [difference between the maximum value and the minimum value] of the thickness chart is obtained, and the [maximum value] is calculated. And the minimum value difference] is divided by the average thickness of the thermoplastic resin sheet measured by the method (3) and expressed as a percentage, to obtain the longitudinal direction (MD) and the width direction (TD) of the thermoplastic resin sheet. The thickness unevenness Rs (%) was obtained. Further, the same measurement was performed on the film after stretched by a tenter oven, and the obtained values were defined as the thickness unevenness Rf (%) in the longitudinal direction (MD) and the width direction (TD) of the film. The smaller the thickness unevenness, the better. The thickness unevenness Rf (%) in both the longitudinal direction (MD) and the width direction (TD) was judged to be good when it was 2.0% or less.

(5) Thickness Rc of coating layer
The thickness of the coating layer was measured by observing the cross section of the film using a transmission electron microscope (TEM) at 10 measurement points determined as described in (3). The thickness of the coating layer was read from an image taken with a TEM at a magnification of 200,000 times. From the obtained measurement results, the average thickness and the [difference between the maximum value and the minimum value] are obtained, and the [difference between the maximum value and the minimum value] is divided by the average thickness to calculate the thickness unevenness Rc (%) of the coating layer. did. The smaller the thickness unevenness of the coat layer, the better, and it was determined that the thickness unevenness Rc (%) was 2.5% or less. In addition, when it has a coating layer on both sides, it was decided that at least one of the coating layers satisfied the requirement.

(6) Temperature of air blown in the preheat drying step (Tx, Ty)
In the preheat drying step, the indoor thermometer 4A is located at the central position in the width direction on the upper and lower sides of the thermoplastic resin sheet, and the indoor thermometer is located at a position ±200 mm from the central part in the width direction, without contacting the thermoplastic resin sheet. 4C-1 and 4C-2 were installed respectively (FIG. 2). After that, the temperature is measured at 1-second intervals for 60 seconds with each thermometer, and the average value of all the measured values of the upper room thermometer is the temperature of the air blown by the upper nozzle (°C), and the temperature of the lower room thermometer. The average value of all measured values was taken as the temperature (°C) of the air blown by the lower nozzle. When the coating agent was applied on one side (Examples 2, 12, and 13), the average value of all the measured values of the indoor thermometer on the applied side was Tx (° C.), and the indoor side on the opposite side was measured. The average value of all the measured values of the thermometer was defined as Ty (°C).

(Method for manufacturing PET sheet uniaxially oriented in the longitudinal direction)
As the thermoplastic resin, polyethylene terephthalate (PET) pellets having an intrinsic viscosity of 0.65 dl/g and a Tg of 75° C. were used. The pellets were dried at a temperature of 180° C. for 5 hours under a reduced pressure of 3 torr, then melted and extruded at 285° C. by a single-screw extruder, filtered by a gear pump with a constant discharge amount, and filtered with a filter accuracy of 5 μm, and then width 1 , 1,050 mm, average thickness 450 μm, density 1.34 g/cm ³ , thickness variation in the longitudinal direction and width direction by discharging in a sheet form from a 100 mm flat die and cooling and solidifying in a cooling drum at a temperature of 20° C. : 2.4-2.5% of non-oriented PET sheet was obtained. Subsequently, the non-oriented PET sheet was conveyed at a conveying speed of 23.3 m/min and preheated by a metal roll group having a roll temperature of 70° C., and then an infrared heater having a wavelength of 1.1 μm (600 V, 24 kW/m). Was stretched to 3.0 times due to the difference in speed between a pair of rolls provided in between. Then, it is cooled with a metal roll group at a roll temperature of 25° C. at a conveyance speed of 70 m/min, and has a width of 1,000 mm, an average thickness of 150 μm, and a thickness unevenness Rs in the longitudinal direction and the width direction Rs: 1.9 to 2.1%. A uniaxially oriented PET sheet was obtained. When the glass transition temperature (Tg) of the obtained uniaxially oriented PET sheet was measured by the method described in (1), it was 75°C.

(Prescription of coating agent)
A coating agent was prepared by adding 5 parts by mass of the following melamine-based crosslinking agent liquid and 1 part by mass of colloidal silica particles having an average particle diameter of 0.1 μm to 100 parts by mass of the following polyester resin emulsion.
[Polyester resin]
An emulsion of a polyester copolymer obtained by copolymerizing an acid component and a diol component having the following composition.
<Acid component>
・Terephthalic acid 50 mol%
・Isophthalic acid 40 mol%
*5-sodium sulfoisophthalic acid 10 mol%
<diol component>
・Ethylene glycol 96 mol%
・Neopentyl glycol 3 mol%
・Diethylene glycol 1 mol%
[Melamine-based cross-linking agent]
A liquid obtained by diluting imino group-type methylated melamine 2.5 times (mass ratio) with a mixed solvent of isopropyl alcohol and water (10/90 (mass ratio)).

(Example 1)
Using a coating step and a tenter oven as shown in FIG. 1, a uniaxially oriented PET sheet obtained by the method described in the section "Method for producing PET sheet uniaxially oriented in the longitudinal direction" has a conveying speed of 70 m/ After applying the above coating agent with a width of 850 mm in min, grip both ends of the sheet with 20 mm of continuous running clips and blow 125°C air from a nozzle limited to a width of 900 mm in the preheating drying process (section length 6 m) Was preheated and dried in the stretching step, and was stretched 3.0 times in the width direction while blowing air at 120 to 130° C. in the stretching step. Then, after passing through the intermediate step A, in the heat treatment step, air is blown at 210 to 230° C. to perform the heat treatment, and 4% of the stretched film width is applied at the center of the heat treatment step to the inlet of the cooling step. After passing through the intermediate step B, the film was cooled with air at 60° C. to 160° C. in the cooling step. After that, the film exiting the tenter oven was released from the grip of the clip, and both ends 150 mm in the film width direction including the part gripped by the clip were cut with a blade fixed to the exit of the tenter oven to obtain an average thickness of 50 μm and a density of 1 A biaxially oriented PET film of 0.40 g/cm ³ was obtained. In the preheating drying step, the temperature and speed of the air blown by the upper nozzle and the lower nozzle of the sheet were made equal to each other. Table 1 shows various conditions and measurement results of each item.

(Example 2)
A biaxially oriented PET film was obtained in the same manner as in Example 1 except that the coating in the coating step was performed only on the lower surface of the uniaxially oriented PET sheet and the temperature of the air in the preheating and drying step was 120°C. Table 1 shows various conditions and measurement results of each item.

(Comparative Example 1)
A biaxially oriented PET film was prepared in the same manner as in Example 1 except that the uniaxially oriented PET sheet was not applied in the applying step, the air temperature in the preheating drying step was 115° C., and the nozzle width was 1,000 mm. Got Table 1 shows various conditions and measurement results of each item.

(Examples 3 to 10, Comparative Examples 2 to 5)
A biaxially oriented PET film was obtained in the same manner as in Example 1 except that the conveying speed, the temperature of air in the preheat drying step and the width of the nozzle were as shown in Table 1. Table 1 shows various conditions and measurement results. In Comparative Example 5, film breakage occurred immediately after the conditions were reached, and a film required for measuring thickness unevenness could not be obtained and measurement could not be performed.

(Example 11)
A biaxially oriented PET film was obtained in the same manner as in Example 6 except that a nozzle having a width of 50 mm was inserted in the central portion of the nozzle in the first half of the preheating drying step (section length 3 m) to make the nozzle width substantially 850 mm. .. Table 1 shows various conditions and measurement results.

(Example 12)
In the preheat drying step, the temperature of the air blown to the coating agent application surface (lower side) (=120°C) is -5°C (=115°C) to the coating agent non-application surface (upper side). A biaxially oriented PET film was obtained in the same manner as in Example 2 except for the above. The temperature difference of the sprayed air was adjusted by increasing the outside air supply amount of the nozzle on the surface not coated with the coating agent. Table 1 shows various conditions and measurement results of each item.

(Example 13)
In the preheat drying step, the same as Example 2 except that the speed of the air blown to the coating agent non-applied surface (upper side) was -10% with respect to the speed of the air blown to the coating agent applied surface (lower side). To obtain a biaxially oriented PET film. The adjustment of the speed difference of the air to be blown was performed by squeezing the damper attached to the duct upstream of the nozzle on the side not coated with the coating agent. Table 1 shows various conditions and measurement results of each item.

In the table, MD means the longitudinal direction and TD means the width direction. The nozzle in the preheating drying step was arranged such that the widthwise central portion thereof overlaps the widthwise central portion of the thermoplastic resin sheet in any of the Examples and Comparative Examples (that is, the widthwise end portion of the thermoplastic resin sheet). The part that is not hit by the air is evenly arranged on both sides.). Further, in each of Examples and Comparative Examples except Examples 12 and 13, the temperatures of the air blown by the upper nozzle and the lower nozzle of the sheet in the preheating drying process were made equal to each other.

According to the present invention, it is possible to provide a method for producing a film capable of reducing thickness unevenness in the longitudinal direction and the width direction even when a coating agent is applied to at least one surface of a thermoplastic resin sheet. The film obtained by the method for producing a film of the present invention can be suitably used for optical applications where there is a particularly severe demand for uneven thickness. Further, depending on the coating layer on the upper and lower surfaces, the film is an antireflection film or a hard coat film, a base film such as a light diffusing plate, a base film of a near infrared absorbing film or an electromagnetic wave absorbing film used for the front plate of a plasma display, It can be suitably used for a touch panel, a base film of a transparent conductive film, and the like.

1: Coating step 2: Thermoplastic resin sheet 3: Uncoated part 4: Preheat drying step 4A: Indoor thermometers 4C-1 and 4C-2 at the center of the thermoplastic resin sheet in the preheat drying step: Thermoplasticity in the preheat drying step Indoor thermometer 5 between the central part of the resin sheet and the coating end part: Drawing process 6: Film 7: Starting point of the drawing process 8: Radiation thermometer 8A: Radiation temperature of the central part of the thermoplastic resin sheet at the starting point of the drawing process Total 8B-1, 8B-2: Radiation thermometer of the thermoplastic resin sheet coating end portion at the starting point of the stretching step 8C-1, 8C-2: Thermoplastic resin sheet central portion and coating edge portion at the starting point of the stretching step Between the radiation thermometers 8D-1 and 8D-2: Radiation thermometer of the uncoated portion of the thermoplastic resin sheet at the starting point of the stretching step 9: Intermediate step A
10: Heat treatment step 11: Intermediate step B
12: Cooling process

Claims (6)

Method for producing a film having a coating step of applying a coating agent on at least one surface of a thermoplastic resin sheet, a preheating drying step of raising the temperature of the thermoplastic resin sheet, and a stretching step of stretching the thermoplastic resin sheet in at least the width direction in this order. At the starting point of the stretching step, the temperature of the thermoplastic resin sheet at the center in the width direction is T (° C.), and the temperature of the thermoplastic resin sheet at each coating end is Tce ₁ (° C.) and Tce ₂ (° C.), respectively. When the glass transition temperature of the thermoplastic resin sheet is Tg (° C.), T is [Tg+15] or more and [Tg+40] or less, and Tce ₁ and Tce ₂ are both [Tg-10] or more and Tg or less. A method for producing a film, characterized in that The method for producing a film according to claim 1, wherein the T is [Tg+20] or more and [Tg+30] or less. When there are uncoated portions of the coating agent on both ends of the thermoplastic resin sheet in the width direction, and the temperatures of the uncoated portions at the starting point of the stretching step are Tne ₁ (° C.) and Tne ₂ (° C.), respectively, Tne ₁ is [Tg-10] or more and Tce ₁ or less, and Tne ₂ is [Tg-10] or more and Tce ₂ or less, The manufacturing method of the film of Claim 1 or 2 characterized by the above-mentioned. The method for producing a film according to claim 1, wherein the T is the maximum when the temperature of the thermoplastic resin sheet is measured in parallel with the width direction at the starting point of the stretching step. When the preheat drying step and the stretching step are performed by a tenter having a plurality of chambers, the section length of the preheat drying step is L (m), and the longitudinal transport speed is V (m/min), 0.07 <=[L/V]<=0.15, The manufacturing method of the film in any one of Claims 1-4 characterized by the above-mentioned. The surface on which the coating agent is applied in the coating step is one surface, the surface on which the coating agent is applied is the X surface, the opposite surface is the Y surface, and the temperature of the air blown to the X surface in the preheating drying step is Tx (°C. ), the temperature of the air blown onto the Y surface is Ty (° C.), the velocity of the air blown onto the X surface is Vx (m/sec), and the velocity of the air blown onto the Y surface is Vy (m/sec), 1 At least one of <Tx-Ty<10 and Vx>Vy is satisfy|filled, The manufacturing method of the film in any one of Claims 1-5 characterized by the above-mentioned.

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