JPS62134261A - Multilayer film for cover material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a multilayer film that is 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 bags, deep-drawn containers, and tray bags have been widely used for their fashion effects and ease of use at stores. Various types of lid materials have been introduced to seal the opening of the package.

However, when containers are sealed and packaged using these conventional lid materials, dents of varying sizes can be seen in the lid material, and these dents significantly impair the display effect of the product.Moreover, there are no barcodes on the lid material! Even if the printing is elaborately printed, it is difficult to read (it does not perform its function satisfactorily, and it also causes serious problems when stamping or labeling the lid material after sealing, among 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 observed in such conventional lid materials after sealed packaging, and its purpose is to The object of the present invention is to provide a novel multilayer film for a lid material which exhibits a sophisticated display function even after being sealed 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 lid materials 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 lid materials. As a result, in order to reliably prevent the denting phenomenon with good reproducibility regardless of the shape of the container,
The present invention was completed by reaching the conclusion that the best method is to seal the container mouth with a lid made of a multilayer film with appropriate heat shrinkability, and then heat-shrink the lid by an appropriate means.

That is, the present invention provides a multilayer film of two or more layers consisting of at least a polyester film and a heat-sealable resin layer,
The present invention relates to a multilayer film for a lid material, characterized in that the polyester film has a heat shrinkage of 3 to 20% in both the vertical and horizontal directions in a 120° C. glycerin bath.

(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 three components include isophthalic acid, orthophthalic acid, adipic acid, sepacic acid, butanediol, diethylene glycol, neopentyl glycol, It may be a polyester film copolymerized with a dibasic acid or dihydric alcohol such as cyclohexane dimetatool, or it may be a film containing various additives such as a matting agent and a coloring agent.

Furthermore, the heat-sealing resin may 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, or 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 include, for example, paper, metal foil, metal-deposited film, or a resin film or sheet of nylon, polypropylene, vinylidene chloride, ethylene vinyl alcohol, or the like. It is a multilayer structure of at least two or more layers in which these coating layers are laminated as necessary, and its composition consists of a polyester film as the outermost layer,
Further, although it is common to use the heat-sealable resin layer as the innermost layer, it is not limited thereto.

In the multilayer film of the present invention, the polyester film and the heat-sealable resin layer may be laminated by any of the commonly known methods such as dry lamination, extrusion lamination, coextrusion, or coating.

The polyester film used in the multilayer film of the present invention is also coated in a 120°C glycerin bath at 3°C in both the longitudinal and lateral directions.
It must have a heat shrinkage of 20% to 20%.

In other words, the present inventors have discovered that a polyester film that has heat resistance, aroma retention, ultraviolet absorption properties, etc., and extremely excellent automatic packaging suitability, which is indispensable as a container lid material, has a number of properties 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 as part of a multilayer film, in addition to the excellent properties mentioned above as a lid material, it will also be able to withstand moderate heat even after the container is sealed. The present invention was completed based on the discovery that the material has shrinkage properties. Therefore, if the heat shrinkage rate of the polyester film is less than 3% in a 120°C glycerin bath, the multilayer film as a whole will lack heat shrinkage.
The shrinkage caused by heating after sealing the container was insufficient, making it impossible to avoid the denting phenomenon.On the other hand, the heat shrinkage rate was 2.
If it is greater than 0%, the heat shrinkage rate is too large, causing an inconvenient problem of deformation of the container.

(Note) Method for measuring heat shrinkage stress Sample films with a width of 15 mm and a length of 50+ m are separated at intervals of 30 m.
After mounting on upper and lower chucks set at m, the sample was immersed in a 120° C. glycerin bath for 30 seconds, and the maximum shrinkage stress during that time was defined as heat shrinkage stress (unit: kg/c+a2).

Such a polyester film can be manufactured by a well-known method such as a tenter method or a tubular method, but in this case, the heat setting temperature after biaxial stretching must be selected in a slightly lower range, or the intrinsic viscosity of the raw material must be adjusted. 0.7 or more to delay crystallization, or by using a copolymerized polyester resin alone or in a blend.
A material whose heat shrinkage rate in a 0° C. glycerin bath is adjusted to 3 to 20% is used.

In addition, it is an essential requirement for the polyester film used in the present invention to have such heat shrinkability, but in addition, for example, a polyester film having the above-mentioned heat shrinkage stress of 90 kg/c12 or more and a tear strength of 7 kg/am or more, It is preferable from the viewpoints of effective heat shrinkability of the multilayer film, strength as a lid material, and protection of contents.

Furthermore, 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 explained in more detail based on Examples below.
Of course, the present invention is 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 in length and area parallel to the longitudinal direction of the polyester film was immersed in a 120°C glycerin bath for 30 seconds, and heat shrinkage was performed using the following formula. The rate was calculated.

However, A is the vertical or horizontal length after immersion [unit: am]
shows.

2. Amount of dent in lid material (unit layer 1): In a state where the multilayer film is heat-sealed to the flange of the container, the maximum gap length in the vertical direction between the horizontal surface of the flange and the multilayer film was defined as the amount of dent.

3. Barcode inspection Barcode printing is read using a pen checker, and those that pass 95% or more are (A), 80% or more 90%.
Those with a passing rate of less than 80% were expressed as (B), and those with a passing rate of less than 80% were expressed as (C).

4. Comprehensive evaluation In addition to the above-mentioned dent amount and barcode inspection, we comprehensively evaluated the required performance as a lid material such as display effect and labeling suitability. (Δ), and defective ones were marked (×).

(Examples 1 to 3, Comparative Examples 1 to 2) Polyethylene terephthalate chips having an intrinsic viscosity of 0.65 were extruded into a sheet using an extruder to create an unstretched sheet with a thickness of about 120 microns.

This unstretched sheet was stretched 3.1 times in the machine 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 stretched at a temperature of 135°C to 220°C. By heat setting at a temperature of 120° C., polyester films of 12 micron thickness were obtained with various heat shrinkage rates in a glycerin bath of 120° C. ranging from 1 to 25% in both the longitudinal and transverse directions.

Next, after corona discharge treatment was applied to one side of each of these polyester films, a 40 micron thick unstretched polypropylene film was applied onto the treated surface via an adhesive whose main ingredient was Takelac A-610 manufactured by Takeda Pharmaceutical Co., Ltd. By dry laminating, a two-layer film consisting of a polyester film and an unstretched polypropylene film was created.

When the lid material made of the two-layer film thus obtained was heat-sealed to the flange of a polypropylene tray container with a mouth diameter of 70 am to seal the container, approximately 31 dents were found in all of the lid materials after heat sealing. Since this was recognized, hot air at 120° C. was further blown from the top of the lid material for 10 seconds. 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 was confirmed that it has many excellent features, such as fewer checking errors and the ability to attach labels such as price display labels without any problems.

Table 2 (Examples 4 to 7, Comparative Examples 3 to 4) 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 were prepared using an extruder. 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 by 150
By heat setting at a temperature of 120°C to 210°C
Polyester films having various thicknesses of 20 microns were obtained with heat shrinkage rates in a glycerin bath of 2 to 24% in both the longitudinal and transverse directions.

On the other hand, after subjecting the polyester film used in Example 1 to double-sided corona discharge treatment, one side was vapor-deposited with aluminum and the other side was coated with polyester-based heat-sealable lacquer 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 a polyester film.

Subsequently, the opening size is 80 x 100, consisting of three layers of polypropylene, ethylene pinyl alcohol, and polypropylene.
After filling soup into the rectangular tray container of No. 1, the container was sealed by heat-sealing the lid material made of the three-layer film on the flange of the container.
Since dents were observed, these were further subjected to retort treatment at a temperature of 120°C to also sterilize the contents. As a result, as shown in Table 3, when the polyester film has a heat shrinkage rate within the range of the present invention, the lid material shrinks appropriately and has good tension. It was confirmed that the product has many features such as fewer code checking errors and excellent label pasting workability.

Table 3 (Effects of the Invention) The multilayer film for lid materials of the present invention as described above is partially composed of a polyester film with appropriate heat shrinkability, so that it can be used as a container lid 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 by printing, etc., and in recent years, the introduction of full-scale POS systems has been at a rapid pace in Japan. Judging from the current situation, the benefits will be enormous.

Claims (1)

[Claims] 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 is heated in a glycerin bath at 120° C. in both longitudinal and transverse directions.
A multilayer film for a lid material, characterized in that it has a heat shrinkage of 20% to 20%.