JPH0536685Y2 - - Google Patents

Description

[Detailed explanation of the idea]

"Industrial Application Field" The present invention relates to a transparent laminated film with excellent gas barrier properties, and more specifically, to an excellent gas barrier film suitable for use in packaging materials that require a high degree of gas barrier property. The present invention relates to a transparent laminated plastic film having properties. "Prior Art" When packaging foods, medicines, chemicals, etc., in order to prevent the packaged contents from deteriorating, it is necessary to use packaging materials that have excellent gas barrier properties, that is, gas barrier properties against gases, especially water vapor and oxygen. is important. In the past, glass containers, metal cans, etc. were used for packaging for this purpose, but
In recent years, with the diversification of packaging forms, various packaging materials made of plastic film have come into use, taking advantage of the processability, flexibility, and other characteristics of plastic. Packaging materials made from plastic film with excellent gas barrier properties include (a) metal-deposited film in which aluminum or the like is deposited on the surface of plastic film, (b) polyvinylidene chloride resin film, and polyvinylidene chloride resin film. Polyvinylidene chloride films such as resin coated films, (c) polyvinyl alcohol films, and the like are known. However, although metallized films have excellent gas barrier properties, they are opaque and the contents cannot be seen from the outside, making them unsuitable as packaging materials. Furthermore, although polyvinylidene chloride films are transparent and have gas barrier properties, these gas barrier properties are not sufficient and are unsuitable for applications requiring a high degree of gas barrier. In addition, polyvinyl alcohol film is widely used as a packaging material due to its excellent oxygen barrier properties, but this film has insufficient water vapor barrier properties, and furthermore, under high humidity conditions, it The drawback is that the oxygen barrier properties also deteriorate over time. For this reason, polyvinyl alcohol film is usually used as a laminated film in which a film with water vapor barrier properties is laminated, but such laminated films are also suitable for packaging materials that require a high degree of gas barrier. It cannot be said that it accomplishes this. Therefore, when such a laminated film is used as a packaging material that requires a high degree of gas barrier property, the thickness of the laminated film must be increased. The drawback was that the transparency and flexibility of the film were impaired, resulting in loss of desirable properties as a packaging material. Furthermore, the inventors of the present invention have developed a polyvinyl alcohol-based transparent laminated film that has improved the above-mentioned drawbacks, and have filed a patent application (see JP-A-62-82030 and JP-A-62-158044). but,
After further investigation, we found that these laminated films were unable to maintain their initially low moisture permeability when used for long periods of time under high humidity conditions.
It was found that the water vapor permeability gradually increased, and at the same time, the oxygen permeability also increased, eventually reaching several times the initial value. ``Problems to be solved by the invention'' In view of the current situation, the inventors of the present invention have created a material that is transparent, has a high degree of gas barrier property, and is capable of maintaining this high degree of gas barrier property for a long period of time. As a result of extensive research in order to provide a laminated plastic film, we laminated a transparent plastic film with high water vapor barrier properties on one side of a specific polyvinyl alcohol film with excellent gas barrier properties, and a transparent plastic film with high water vapor barrier properties on the other side. The inventors discovered that a laminated plastic film made by laminating transparent perforated plastic films with high properties is suitable for this purpose, and thus completed the present invention. "Means for Solving the Problems" The gist of the present invention is to provide a film made of a polyvinyl alcohol resin containing 50 mol% or more of vinyl alcohol residue, which One side of a polyvinyl alcohol film that has been stretched within a range of 10 times and then heat-treated within a temperature range with the lower limit of the stretching temperature of the film and the upper limit of a temperature below the melting point of the raw material resin, A transparent plastic film with high water vapor barrier properties is laminated, and the other side has transparent holes with a water vapor permeability of 500 g/ ^m2・24hrs.20 μm or more under the conditions of a temperature of 40℃ and a relative humidity of 90%. The present invention relates to a transparent laminated film with excellent gas barrier properties, which is characterized by being formed by laminating plastic films. Hereinafter, the present invention will be explained in detail based on the drawings. FIG. 1 is a sectional view of a laminated film according to the present invention. As shown in FIG. 1, the transparent laminated film with excellent gas barrier properties according to the present invention has a polyvinyl alcohol film 1 as an intermediate layer, and a transparent plastic film 2 with high water vapor barrier properties on one side. A transparent perforated plastic film 3 with high water vapor permeability is layered on the other side.
It has a structure in which these are laminated. Polyvinyl alcohol film (hereinafter referred to as "PVA film") used in this invention.
is made of a polyvinyl alcohol resin containing 50 mol% or more, preferably 70 mol% or more of vinyl alcohol residue, and this PVA film is
It is stretched in at least one direction at a predetermined magnification described later, and then subjected to heat treatment under predetermined conditions described later. The PVA film 1 is manufactured from a polyvinyl alcohol resin having a vinyl alcohol residue content in the above range, and a typical example of a suitable polyvinyl alcohol resin is polyvinyl alcohol obtained by saponifying polyvinyl acetate. Examples include resins, ethylene-vinyl alcohol copolymers obtained by saponifying ethylene-vinyl acetate copolymers, and mixtures thereof. Such a polyvinyl alcohol resin is suitable because it is easy to form into a film, and furthermore, by stretching this unstretched film to a predetermined stretching ratio shown below, a film with low hygroscopicity and low water vapor permeability can be obtained. It is. At least in one axis direction, the PVA film is
It is necessary that the film be stretched within a range of 5 to 10 times. The present inventors conducted a detailed study on the relationship between the stretching ratio and the crystallinity of the stretched film, and the relationship between this crystallinity and water vapor transmission rate regarding PVA-based films, and found that the stretching ratio was less than 5 times. Sometimes, the crystallinity of the stretched film is approximately 50%, but when the stretching ratio is increased to 5 times or more, the crystallinity of the stretched film increases rapidly, reaching 50%.
It has been found that a PVA film stretched at a stretching ratio of 100% or higher has both low hygroscopicity and low water vapor permeability. PVA film with a stretching ratio of less than 5 times,
It is used in this invention because it has high hygroscopicity and the gas barrier rapidly decreases as moisture absorption progresses.
It is not suitable as a PVA film. PVA film with a stretching ratio of over 10 times,
It is not suitable as a PVA film used in the present invention because the thickness and stretching ratio tend to be non-uniform and it is difficult to stably obtain a practical product. The PVA film used in this invention is a film that has been stretched within the above stretching ratio range and is heat-treated within a temperature range with the lower limit being the stretching temperature of the film and the upper limit being a temperature below the melting point of the raw resin. It is necessary that This heat treatment is for fixing the crystallized state that occurs in the film during the film stretching process. If the heat treatment temperature is lower than the film stretching temperature (150 to 220°C), it is insufficient to fix the crystallized state formed in the film. On the other hand, if the heat treatment temperature is higher than the melting point (220 to 230°C) of the raw resin, not only will the crystallized state that has occurred in the film disappear;
In some cases, the film may partially shrink, so it is not practical. The PVA film used in the present invention includes all films that satisfy the above requirements regarding film composition, stretching ratio, and heat treatment conditions. In this invention, plastic film 2 with high water vapor barrier properties is defined as a plastic film 2 with a temperature of 40°C and a relative humidity of 90% (hereinafter referred to as 40°C x 90%) based on ASTM F372.
Display as RH. ) has a water vapor permeability of 2g/ ^m2・24hrs.20μm or less.
Examples of such films include films made of vinylidene chloride resins such as polyvinylidene chloride and vinylidene chloride-vinyl chloride copolymers, films made of polytetrafluoroethylene, polypropylene films, polyethylene films, polyethylene terephthalate films, and nylon films. Examples include vinylidene coated film, which is a film coated with vinylidene chloride resin. In the present invention, the transparent perforated plastic film 3 with high water vapor permeability is defined as a temperature of 40℃ and a relative humidity of 90% (40℃ x 90%) based on ASTM F372.
Water vapor transmission rate under the condition of RH) is 500g/
^m2・24hrs. Refers to a transparent perforated plastic film with a diameter of 20μm or more. For such a film, a large number of holes with a diameter of about 0.1 to 3 mm are uniformly formed on the entire surface of a transparent plastic film by punching with a blade, perforation with a laser beam, etc., and the water vapor permeability is preferably within the above range. 2000g/ ^m2・24hrs.20μ
m or more can be used. In order to make bags and use the laminated film according to the present invention, it is preferable that the transparent perforated plastic film be one that can be heat-sealed. - It is preferable to use a film made of vinyl acetate copolymer or ionomer in which pores with a diameter of 0.1 to 0.5 mm are formed in a square or triangular array with a porosity of about 1.5 to 10% on the entire surface. The above-mentioned water vapor permeability of the transparent perforated plastic film is 500g/ ^m2・24hrs.20μm or less,
The resulting laminated film does not maintain high gas barrier properties for a long period of time, and the object of the present invention cannot be achieved. The upper limit of the water vapor permeability of the transparent perforated plastic film is not particularly limited, but can be determined on a case-by-case basis depending on the usage of the laminated film and the heat sealability to be imparted. The transparent laminated film according to the present invention can be manufactured by an adhesive lamination method using an adhesive.
Adhesives that can be used in this case include urethane adhesives, acrylic adhesives, polyester adhesives, and the like. These are best used in the form dissolved in an organic solvent and form the intermediate layer.
An adhesive is applied to one side of the PVA film using a roll coating method or other known method, and the solvent is evaporated to form an adhesive-coated surface. The plastic film 2 is stacked, and the other side of the PVA film is covered with the adhesive-coated surface of the transparent perforated plastic film 3, which has an adhesive-coated surface formed by the same method as above, and then rolled. Press to laminate. In the above lamination method, a method can also be adopted in which an adhesive coated surface is formed on a transparent perforated plastic film, and this adhesive coated surface is overlapped with the PVA film. However, in this case, care must be taken not to block the pores of the perforated plastic film by applying the adhesive. The thickness of the laminated film according to the present invention is preferably selected within the range of 5 to 500 μm, taking into consideration gas barrier properties, strength, flexibility, economic efficiency, usage, etc. Among these, a thickness of 10 to 200 μm is preferred, and a thickness of 12 to 100 μm is more preferred. The thicknesses of the PVA film, the plastic film with high water vapor barrier properties, and the perforated plastic film with high water vapor permeability may be appropriately selected so that the thickness of the resulting laminated film falls within the above range. In the laminated film according to the present invention, the films laminated on both sides of the PVA film have different properties, so it is necessary to use them depending on the application. For example, when used as a bag, container, or container lid to store dry solids, isolate them from the outside air, and prevent gases such as oxygen and water vapor from entering, use The surface of the plastic film is the outside, and the surface of the perforated plastic film with high water vapor permeability is the inside, that is, the side of the stored solids. On the other hand, when using a bag, container, or container lid to store items with a high moisture content and to isolate the item from the outside air and prevent the intrusion of oxygen and the release of water vapor, a plastic film with a high water vapor barrier property is used. With the side facing inside,
The surface of the perforated plastic film with high water vapor permeability is the outside. By using the film properly depending on the application in this way, the excellent gas barrier properties of the laminated film according to the present invention can be effectively utilized. "Effects of the invention" The laminated film according to the invention has the following particularly remarkable effects, and its industrial utility value is extremely large. (1) The laminated film according to the present invention has excellent transparency and exhibits extremely excellent gas barrier properties,
Flexible, strong and economical,
It is extremely excellent. Therefore, food,
It is used in a wide range of applications, including packaging materials for pharmaceuticals and chemicals, as well as packaging materials that require a high degree of gas barrier properties. (2) When the laminated film according to the present invention is used as a packaging material with the side of the film with high water vapor barrier property on the high humidity side and the side of the perforated film with high water vapor permeability on the low humidity side, this laminated film , exhibits excellent water vapor barrier properties and oxygen barrier properties over a long period of time. (3) By using a transparent plastic film with heat-sealability as the perforated film with high water vapor permeability, the laminated film according to the present invention can be used as is for heat-seal packaging. "Examples" The present invention will be described in detail below based on Examples and in contrast with comparative examples, but the present invention is not limited to the following Examples unless the gist of the invention is exceeded. do not have. In addition, in the following example, the water vapor transmission rate is
Based on ASTM F372, under the conditions of 40℃ x 90% RH, the side of the laminated film with high water vapor barrier properties is located on the high humidity (90% RH) side, and the side with low water vapor barrier properties is placed on the bone dry side. The oxygen permeability was measured using Modern Control's
Using OX-TRAN100 type oxygen permeability measuring device,
Measured under the conditions of 30°C x 80% RH. In all examples, the lamination method was a dry lamination method using a urethane adhesive. The transparency of the laminated film was evaluated by observing the laminated film with the naked eye. Example 1 Content of vinyl alcohol residue 99 mol%, melting point
Melt polyvinyl alcohol at 220°C with an extruder, extrude it into a film through a T-die, biaxially stretch it 5x5 times using a tenter method at a temperature of 180°C, and then heat treat it at a temperature of 200°C. and average thickness
A PVA film of 18 μm was obtained. After applying a urethane adhesive (manufactured by Takeda Pharmaceutical Co., Ltd., a two-component adhesive of Takerak A-606 and Takenate A-7) to one side of this PVA film and evaporating the solvent, Biaxially oriented polypropylene film with a 2 μm thick polyvinylidene chloride coating layer (water vapor permeability 2.0 g/m ²
24hrs.20μm, stretching ratio 5x5, total thickness 20μ
m. Hereinafter, this (referred to as "K-OPP") was laminated with the polyvinylidene chloride coating layer being positioned in contact with the surface of the PVA film. In addition, the other side of the PVA film has an adhesive coating layer made of the same urethane adhesive as above, and has a thickness of 20 μm and a water vapor permeability of 500 g/m ² .
24hrs.20μm perforated low density polyethylene film (manufactured by Shin Nippon ALC Co., Ltd., Annapolis; pore size 0.5mm,
The hole arrangement was a square arrangement, and the hole pitch was 1.4 x 1.4 mm). The water vapor permeability of the laminated film prepared as above was measured with the K-OPP side positioned on the high humidity (90% RH) side and the perforated low density polyethylene film side positioned on the bone dry side. Also,
Oxygen permeability was measured by the method described above. These measurements were followed over time immediately after being placed under the respective measurement conditions, and continued for about 200 hours. The results are shown in Table 1 together with the transparency evaluation results. In addition, the time-dependent trace curve of the water vapor transmission rate is shown as A in FIG. In Table 1, the primary value is the value of water vapor permeability or oxygen permeability after 24 hours, and the secondary value is the value of water vapor permeability or oxygen permeability after 150 hours (hereinafter, the same applies to each Example and Comparative Example). ). Example 2 Polyvinyl alcohol of the same kind as that used in Example 1 was melted in the same extruder as used in the same example, extruded into a film through a T-die, and heated 3× by tenter method at a temperature of 180°C. It was biaxially stretched 3 times, and then uniaxially stretched 1.7 times by a roll method at a temperature of 180°C. The film was then heat treated at 200° C. for 1.5 minutes to obtain a PVA film with an average thickness of 18 μm. One side of this PVA film was coated with the same type of K-OPP as used in Example 1, and the other side was coated with the same type of perforated low-density polyethylene film as used in Example 1. Lamination was carried out in the same manner as above to obtain a laminated film. Regarding this laminated film, water vapor permeability and oxygen permeability were measured in the same manner as in Example 1 to evaluate transparency. The results are shown in Table 1. Example 3 Polyvinyl alcohol of the same kind as that used in Example 1 was melted in the same extruder as used in the same example, extruded into a film through a T-die, and heated 3× by tenter method at a temperature of 180°C. It was biaxially stretched 3 times, and then uniaxially stretched 3.3 times by a roll method at a temperature of 180°C. The film was then heat treated at 200° C. for 1.5 minutes to obtain a PVA film with an average thickness of 18 μm. One side of this PVA film was coated with the same type of K-OPP as used in Example 1, and the other side was coated with the same type of perforated low density polyethylene film as used in Example 1. Lamination was carried out in the same manner as above to obtain a laminated film. Regarding this laminated film, water vapor permeability and oxygen permeability were measured in the same manner as in Example 1 to evaluate transparency. The results are shown in Table 1. Example 4 One side of the PVA film obtained in Example 1 was coated with the same type of K-OPP used in the same example, and the other side was coated with the same type of K-OPP with a thickness of 20 μm as used in the same example.
Water vapor permeability 2000g/ ^m2・24hrs.20μm perforated low-density polyethylene film (Shin Nippon ALC Industries Co., Ltd.)
Made in Annapolis; hole diameter 0.4mm, hole arrangement square.
(hole pitch 1.4 x 1.4 mm) were laminated in the same manner as in the same example to obtain a laminated film. The water vapor permeability and oxygen permeability of this laminated film were measured in the same manner as in the same example, and the transparency was evaluated. The results are shown in Table 1. Example 5 One side of the PVA film obtained in Example 2 was coated with the same type of K-OPP as used in the same example, and the other side was coated with the same type of K-OPP with a thickness of 20 μm as used in the same example.
Water vapor permeability 500g/ ^m2・24hrs.20μm perforated low-density polyethylene film (Shin Nippon ALC Industries Co., Ltd.)
Made in Annapolis; hole diameter 0.1mm, hole arrangement square.
(hole pitch 0.7 x 0.7 mm) were laminated in the same manner as in the same example to obtain a laminated film. The water vapor permeability and oxygen permeability of this laminated film were measured in the same manner as in the same example, and the transparency was evaluated. The results are shown in Table 1. Comparative Example 1 One side of the PVA film obtained in Example 2 was coated with the same type of K-OPP as used in the same example, and the other side was coated with the same type of K-OPP with a thickness of 20 μm as used in the same example.
Non-porous low-density polyethylene films having a water vapor permeability of 32 g/m ² ·24 hrs.20 μm were laminated in the same manner as in the same example to obtain a laminated film. The water vapor permeability and oxygen permeability of this laminated film were measured in the same manner as in the same example, and the transparency was evaluated. The results are shown in Table 1. In addition, a time-dependent trace curve of water vapor transmission rate is shown as B in FIG. Comparative Example 2 Polyvinyl alcohol similar to that used in Example 1 was melted in the same extruder as used in the same example, extruded into a film from a T-die, and heated 3× by tenter method at a temperature of 180°C. The film was biaxially stretched 3 times to obtain a PVA film with an average thickness of 18 μm. One side of this PVA film was coated with the same type of K-OPP as used in Example 1, and the other side was coated with the same type of perforated low-density polyethylene film as used in the same example. A laminated film was obtained by laminating in accordance with the following procedure. Regarding this laminated film, water vapor permeability and oxygen permeability were measured in the same manner as in Example 1 to evaluate transparency. The results are shown in Table 1. Example 6 Content of vinyl alcohol residue 70 mol%, melting point
A saponified product of ethylene-vinyl acetate copolymer at 190°C was melted in an extruder, extruded into a film through a T-die, and then heated at 140°C by a tenter method.
Biaxially stretched 3 times, then at a temperature of 140℃,
It was uniaxially stretched 1.7 times by the roll method. Then,
Heat treated at 180℃ for 1.5 minutes, average thickness 18μm
A PVA film was obtained. Example 1 was applied to one side of this PVA film.
The same type of K-OPP used in the above was applied to the other side.
Perforated low-density polyethylene films of the same type used in the same example, having a thickness of 20 μm and a water vapor permeability of 5000 g/m ² ·24 hrs.20 μm, were laminated in the same manner as in the same example to obtain a laminated film. The water vapor permeability and oxygen permeability of this laminated film were measured in the same manner as in the same example, and the transparency was evaluated. The results are shown in Table 1. Comparative example 3 Vinyl alcohol residue content 40 mol%, melting point
A saponified product of ethylene-vinyl acetate copolymer at 140°C was melted in an extruder, extruded into a film through a T-die, and then heated at 100°C by a tenter method.
The film was biaxially stretched 3 times, and then uniaxially stretched 1.7 times at a temperature of 100°C. Then, at a temperature of 130℃, 1.5
A PVA film having an average thickness of 18 μm was obtained by heat treatment for 1 minute. Example 1 was applied to one side of this PVA film.
The same type of K-OPP used in the above was applied to the other side.
Perforated low-density polyethylene films of the same type used in the same example, having a thickness of 20 μm and a water vapor permeability of 5000 g/m ² ·24 hrs.20 μm, were laminated in the same manner as in the same example to obtain a laminated film. The water vapor permeability and oxygen permeability of this laminated film were measured in the same manner as in the same example, and the transparency was evaluated. The results are shown in Table 1. Comparative Example 4 In the example described in Example 2, one side of the PVA film was coated with the K-OPP used in the same example.
A laminated film was obtained in exactly the same manner as in the same example except that a biaxially oriented polypropylene film not coated with polyvinylidene chloride was used instead and laminated. The water vapor permeability and oxygen permeability of this laminated film were measured in the same manner as in the same example, and the transparency was evaluated. The results are shown in Table 1.

【table】

[Table] From Table 1, the following is clear: (1) The laminated film according to the present invention has a low water vapor transmission rate of 0.1 to 0.3 g/ ^m2 /24 hrs or less in terms of the primary value;
Moreover, the secondary value is low at 0.15 to 0.4 g/ ^m2 ·24 hrs or less, and the difference between the primary and secondary values is very small, so that the film exhibits excellent water vapor barrier properties over a long period of time. (2) In contrast, the laminated films of the comparative examples have low primary water vapor transmission rates but high secondary values (Comparative Examples 1 and 2), or both the primary and secondary values are high (Comparative Examples 3 and 4).

[Brief explanation of the drawing]

FIG. 1 is an enlarged cross-sectional view of the laminated film according to the present invention, and FIG. 2 is a temporal tracking curve of water vapor permeability for the laminated films obtained in Examples and Comparative Examples, and the horizontal axis is after the start of the test. elapsed time,
The vertical axis is the water vapor transmission rate. In Figure 1, 1 is a PVA film, 2 is a plastic film with high water vapor barrier properties, and 3 is a PVA film.
is a perforated plastic film with a high water vapor permeability, and in FIG. 2, A and B are the water vapor permeability tracing curves over time for the film of Example 1 and the film of Comparative Example 1, respectively. .

Claims (1)

[Claims for Utility Model Registration] (1) A film made of polyvinyl alcohol resin containing 50 mol% or more of vinyl alcohol residue, which is stretched in at least one direction within a range of 5 to 10 times, and then , one side of the polyvinyl alcohol film was heat-treated within a temperature range with the lower limit being the stretching temperature of the film and the upper limit being a temperature below the melting point of the raw resin.
A transparent plastic film with high water vapor barrier properties is laminated, and the other side has a water vapor transmission rate of 500 at a temperature of 40°C and relative humidity of 90%.
g/ ^m2・24hrs. A transparent laminated film with excellent gas barrier properties characterized by being laminated with transparent perforated plastic films having a diameter of 20μm or more. (2) A utility model in which the transparent plastic film with high water vapor barrier properties is selected from those with a water vapor permeability of 2 g/m ² 24 hrs.20 μm or less under conditions of a temperature of 40°C and a relative humidity of 90%. A transparent laminated film with excellent gas barrier properties according to registered claim (1). (3) Utility model registration claim No. 1, in which the transparent perforated plastic film is selected from films made of low density polyethylene, high density polyethylene, polypropylene, ethylene-vinyl acetate copolymer, and ionomer. A transparent laminated film with excellent gas barrier properties as described in item ) or item (2).