JPH0212750B2 - - Google Patents

Description

[Detailed description of the invention]

(Technical Field of the Invention) The present invention relates to a multilayer film particularly suitable as a lid material for molded containers such as portion packs or tray packs made of single or composite materials such as plastic, aluminum foil, and paper. (Prior art) In recent years, container filling packaging such as portion packs, deep-drawn containers, and tray packs have been widely used due to their fashionability and ease of use at stores. Various types of lid materials have been introduced to seal the mouth of the package. However, containers that are hermetically sealed using these conventional lids have dents of varying sizes in the lid, which significantly impairs the display effect of the product, and furthermore, there is a bar code on the lid. Even if elaborate printing is done, it is difficult to read and cannot perform its function satisfactorily.Furthermore, it significantly hinders operations such as stamping or labeling the lid material after sealing, and many other troublesome problems. Therefore, there was a strong desire for improvement. (Problems to be Solved by the Present Invention) The present invention relates to a multilayer film that can eliminate the so-called denting phenomenon that occurs in such conventional lid materials after sealed packaging, and its purpose is to An object of the present invention is to provide a novel multilayer film for a lid material which exhibits a sophisticated display function even after sealing and which can be easily stamped or labeled on the lid material and has an extremely excellent display effect. (Means for Solving the Problems) In order to prevent the denting phenomenon observed in the lids of conventional molded containers, the inventors of the present invention have conducted intensive studies on both the sealing method of the containers and the structure of the lids. As a result, in order to reliably prevent the denting phenomenon with good reproducibility regardless of the shape of the container, it is necessary to use a lid material that is made of polyester film, which is part of a multilayer film, and has an appropriate heat shrinkage rate and heat shrinkage stress. The present invention was completed based on the conclusion that the best method is to heat-shrink the lid material by an appropriate means after sealing the mouth part. That is, the present invention provides a multilayer film having two or more layers consisting of at least a polyester film and a heat-sealing resin layer, wherein the polyester film is heated at 120°C.
The present invention relates to a multilayer film for a lid material, characterized in that it has a heat shrinkage rate of 3 to 20% in both the longitudinal and transverse directions in a glycerin bath, and a heat shrinkage stress of 90 kg/cm ² or more. (Function) Hereinafter, the function and effects of the multilayer film for lid material in the present invention will be specifically explained. The multilayer film of the present invention is composed of two or more layers consisting of at least a polyester film and a heat-sealable resin layer. Here, the polyester film is a general term for a polyester or a copolymer film thereof obtained by an esterification reaction between a dibasic acid component and a dihydric alcohol component. A typical polyester film is polyethylene terephthalate film derived from terephthalic acid and ethylene glycol, but other third components include isophthalic acid, orthophthalic acid, adipic acid, sebacic acid,
It may be a polyester film copolymerized with dibasic acids or dihydric alcohols such as butanediol, diethylene glycol, neopentyl glycol, cyclohexanedimethanol, etc., and may also be formulated with various additives such as erasing agents and coloring agents. But that's fine. The heat-sealing resin can be any resin as long as it can be heat-sealed, but generally it is a film-like material made of polyolefin resin such as polyethylene, polypropylene, ethylene-vinyl acetate copolymer, ionomer, etc. Heat-sealable coating lacquers such as chlorinated polypropylene, polyester copolymers, and vinylidene chloride resins are preferably used. In addition to the polyester film and heat-sealable resin layer, the multilayer film of the present invention may also include, for example, paper, metal foil, metallized film, or a resin film or sheet of nylon, polypropylene, vinylidene chloride, ethylene vinyl alcohol, or the like. It is a multilayer structure consisting of at least two or more layers in which these coating layers are laminated as necessary, and the structure is generally a polyester film as the outermost layer and a heat-sealable resin layer as the innermost layer. However, it is not limited to these. In the multilayer film of the present invention, the polyester film and the heat-sealable resin layer may be laminated by dry lamination, extrusion lamination,
Any commonly known method such as a coextrusion method or a coating method may be used. The polyester film used in the multilayer film of the present invention can also be vertically heated in a 120°C glycerin bath.
It must have a heat shrinkage rate of 3 to 20% in both the transverse direction and a heat shrinkage stress of 90 kg/cm ² or more. In other words, the present inventors have discovered that a polyester film, which has heat resistance, aroma retention, ultraviolet absorption properties, etc., and extremely excellent automatic packaging suitability, which is indispensable as a container lid material, has been developed in a number of ways as shown in Table 1. We focused on the fact that it has a particularly strong heat shrinkage stress among certain resins, and if we use this polyester film to form part of a multilayer film, in addition to the excellent properties mentioned above as a lid material, the polyester film also maintains its properties even after the container is sealed. The present invention was completed based on the discovery that strong heat shrinkage stress causes the multilayer film including the heat-sealing resin layer to uniformly and appropriately shrink and tighten, thereby preventing the denting phenomenon without significantly deforming the container. This is what led to this. Therefore, the heat shrinkage rate of the polyester film is less than 3% in a 120°C glycerin bath, or the heat shrinkage stress is less than 3%.
If it is ^less than 90Kg/cm2, the heat shrinkability of the multilayer film as a whole will be poor, and the shrinkage will be insufficient due to heating after sealing the container, making it impossible to avoid the dent phenomenon. If it is greater than 20%, the heat shrinkage rate is too large, causing an inconvenient problem of deformation of the container.

【table】

[Table] Such a polyester film can be manufactured by a well-known method such as the tenter method or the tubular method, but in this case, the heat setting temperature after biaxial stretching must be selected in a slightly lower range, or the specific The heat shrinkage rate and heat shrinkage stress in a 120°C glycerin bath can be improved by delaying crystallization by setting the viscosity to 0.7 or more, or by using a copolymerized polyester resin alone or in a blend. The one adjusted to the range is used. It is essential for the polyester film used in the present invention to have such heat shrinkability, but it is also preferable that the polyester film has a tear strength of 7 kg/cm or more in terms of strength as a lid material and protection of contents. Further, the multilayer film for lidding material of the present invention may be provided with an appropriate printing layer or a coating layer for the purpose of improving adhesion, preventing ultraviolet rays, preventing oxidation, etc., if necessary. (Examples) The present invention will be described in more detail below based on Examples, but the present invention is of course not limited to these Examples. The methods for measuring and evaluating the physical properties of the multilayer film for lidding materials of the present invention are as follows. 1 Heat shrinkage rate (unit: %): A sample film cut into a square of 100 mm both vertically and horizontally parallel to the longitudinal direction of the polyester film is immersed in a 120°C glycerin bath for 30 seconds, and the heat shrinkage rate is calculated from the following formula. was calculated. 100-A/100×100 (unit: %) where A indicates the length in the vertical or horizontal direction [unit: mm] after immersion. 2 Amount of dent in lid material (unit: mm): In the state shown in Fig. 1 when the multilayer film is heat-sealed to the container flange, the maximum gap length a in the vertical direction between the horizontal surface of the flange and the multilayer film is defined as the amount of dent. did. 3 Barcode inspection Barcode printing is read using a pen checker, and those that pass 95% or more are A.
Those who passed % or more and less than 90% are B, and the passing rate is 80.
% was expressed as C. 4 Comprehensive evaluation In addition to the above-mentioned dent amount and barcode inspection, the required performance as a lid material such as display effect and labeling suitability is comprehensively evaluated, and those that are good as a lid material are 〇, those that are relatively good are △, and poor. Marked things as ×. (Examples 1 to 3, Comparative Examples 1 to 2) Polyethylene terephthalate chips with an intrinsic viscosity of 0.65 were extruded into a sheet using an extruder, and the thickness was approx.
A 120 micron unstretched sheet was prepared. This unstretched sheet was stretched 3.1 times in the longitudinal direction at a temperature of 85°C, then introduced into a tenter device, stretched 3.3 times in the transverse direction at a temperature of 93°C, and further heat-set at a temperature of 135°C to 220°C. As a result, polyester films having different thicknesses of 12 microns were obtained, with heat shrinkage rates in a 120° C. glycerin bath ranging from 1 to 25% in both the longitudinal and transverse directions. The heat shrinkage stress of these polyester films in a 120℃ glycerin bath is 120Kg/
It was more than cm ² . Next, one side of these polyester films was subjected to corona discharge treatment, and then Takeda Pharmaceutical Co., Ltd.
A two-layer film consisting of a polyester film and an unstretched polypropylene film was prepared by dry laminating unstretched polypropylene films each having a thickness of 40 microns through an adhesive containing Takerakku A-610 (manufactured by Takerakku Co., Ltd.) as the main ingredient. When the lid material made of the two-layer film obtained in this way was heat-sealed to the flange of a polypropylene tray container with a mouth diameter of 70 mm to seal the container, there was a dent of approximately 3 mm in the lid material after heat sealing. Since this was recognized, hot air at 120°C was further blown for 10 seconds from the top of the lid. As a result, as shown in Table 2, when the polyester film has a heat shrinkage rate within the range of the present invention, the lid material shrinks and tightens appropriately, has good tension, and has an excellent appearance. It has been confirmed that this product has many excellent features, such as fewer check errors and the ability to attach labels such as price display labels without any problems.

[Table] (Examples 4 to 7, Comparative Examples 3 to 4) Using an extruder, copolymerized polyester chips consisting of 90 mol% terephthalic acid and 10 mol% isophthalic acid as the acid component and ethylene glycol as the alcohol component It was extruded into a tube shape to create an unstretched tube with a thickness of about 250 microns. This unstretched tube was heated to a temperature of 88°C and expanded by blowing compressed air to perform simultaneous biaxial stretching of 3.5 times in the longitudinal direction and 3.6 times in the transverse direction, and then further stretched at a temperature of 150°C to 210°C. By heat-setting, polyester films of various thicknesses of 20 microns and different heat shrinkage rates in a 120° C. glycerin bath ranging from 2 to 24% in both the longitudinal and transverse directions were obtained. The heat shrinkage stress of these polyester films in a 120℃ glycerin bath is 100Kg/
It was more than cm ² . On the other hand, after the polyester film used in Comparative Example 1 was subjected to double-sided corona discharge treatment, aluminum was vapor-deposited on one side and a polyester heat-sealable lacquer was coated on the other side to create a single-sided vapor-deposited heat-sealable film. did. Next, the polyester films having various heat shrinkage rates and the single-sided vapor-deposited heat-sealable film were bonded together using an adhesive mainly composed of AD-330 manufactured by Toyo Morton Co., Ltd., so that the vapor-deposited surface was in contact with the polyester film side. A three-layer film consisting of a polyester film, a vapor-deposited film layer, and a heat-sealable lacquer layer was prepared by dry laminating using the above-mentioned polyester film. Subsequently, a rectangular tray container with a mouth size of 80 x 100 mm made of three layers of polypropylene-ethylene vinyl alcohol-polypropylene was filled with soup, and a lid material made of the three-layer film was heat-sealed on the flange of the container. When the containers were sealed, dents of about 5 mm were found in all of the lids after heat sealing, so these were further heated to 120°C to sterilize the contents.
The retort treatment was carried out at a temperature of . As a result, the third
As shown in the table, when the polyester film has a heat shrinkage rate within the range of the present invention, the lid material shrinks and tightens appropriately, has good tension, and has an excellent appearance, as well as fewer check errors with pre-printed barcodes. Moreover, it was confirmed that it has many characteristics such as excellent label pasting workability.

【table】

[Table] (Examples 8-9, Comparative Examples 5-6) Copolyester chips copolymerized with various molar ratios of terephthalic acid and isophthalic acid as the acid component and ethylene glycol as the alcohol component were run in an extruder. extruded into a sheet with a thickness of approx.
A 100 micron unstretched sheet was prepared. This unstretched sheet is introduced into a tenter device and stretched in the longitudinal direction.
After simultaneous stretching of 2.8 times and 3.0 times in the transverse direction, an additional 150
Polyester films with a thickness of 12 microns having various heat shrinkage rates and heat shrinkage stresses were obtained by heat setting at temperatures ranging from 200°C to 200°C. Subsequently, an unstretched polypropylene film was laminated onto these polyester films in the same manner as in Example 1 to produce a two-layer film. When the lid material made of the two-layer film obtained in this way was heat-sealed to the flange of a polypropylene tray container with a mouth diameter of 70 mm, the container was sealed.
Since a dent of approximately 3 mm was observed in all of the lids after heat sealing, hot air at 120°C was further blown from the top of the lid. As a result, as shown in Table 4, polyester films whose heat shrinkage rate and heat shrinkage stress are within the range of the present invention have a cover material that shrinks appropriately, has good tension, has an excellent appearance, and is pre-printed. It was confirmed that it has many excellent features, such as fewer errors when checking barcodes that have been stored, and the ability to attach labels and the like without any problems.

[Table] (Effects of the Invention) The multilayer film for lidding material of the present invention as described above is partially composed of a polyester film with appropriate heat shrinkability, so it can be used as a container lidding material after being sealed. This avoids the denting phenomenon that was previously seen. Therefore, the multilayer film of the present invention provides excellent display effects and suitability for labeling, and at the same time allows for sophisticated display through printing, etc., and in recent years, the introduction of full-scale POS systems has become urgent in Japan. Judging from the current situation, the benefits will be enormous.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the amount of denting when the container is sealed and packaged using a lid. In addition, the code|symbol 1 in a figure shows a container, and 2 shows a lid material.

Claims (1)

[Claims] 1 In a multilayer film of two or more layers consisting of at least a polyester film and a heat-sealable resin layer, the polyester film has a heat shrinkage rate of 3 to 20% in both the longitudinal and transverse directions in a 120°C glycerin bath and a heat shrinkage rate of 90%.
A multilayer film for lid material, characterized by having a heat shrinkage stress of Kg/cm ² or more.