JPH01196338A - Heat-shrinkable multilayered film and its food packaging material - Google Patents

Abstract

PURPOSE:To provide a food packaging material specially suitable to high- temperature retort treatment, by making a heat-shrinkable multilayered film composed of a polyamide resin layer and a polypropylene resin layer and having a specified value of heat-shrinking ratio at 120 deg.C. CONSTITUTION:A polypropylene resin layer A and a polyamide resin layer B are used as stock. In compliance with a request, an oxygen gas barrier resin layer E may be interlaid between said layers, A and B, to unify them, or a heat-resistant resin layer C may be further laminated on the outer surface of the layer A to unify them. This heat-shrinkable multilayered film has the heat-shrinking ratio at 120 deg.C being in the range of 5-30%, and preferably 7-20%.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention relates to a heat-shrinkable multilayer film and a retort food package using the multilayer film. A heat-shrinkable multilayer film that has excellent elasticity, tightness, pinhole resistance, packaging deformation resistance, etc., and can be suitably used for shrink-wrapping retort foods such as hams and sausages, and a heat-shrinkable multilayer film using the film. Regarding retort food packaging.

[Prior Art and Problems] Processed livestock meat and processed fish foods, such as hams and sausages, are packaged using an oxygen gas barrier film and then heat sterilized for preservation. Conventionally, this sterilization temperature was 70 to 90°C, but due to the use of disinfectants, regulations on the amount used, and demands for short processing times, the temperature has been increased to 120°C.
It is desired to develop a heat-shrinkable film that maintains appropriate tightness and transparency even during near-high-temperature processing, and does not cause appearance defects such as wrinkles and deformation.

Conventional multilayer films for shrink packaging retort foods include, for example: Shrink multilayer films made of nylon/polyolefin (Japanese Unexamined Patent Publications No. 59-212,261, No. 56-136,365, Japanese Patent Publication No. 1983) -3525
7), ■Multilayer film made of nylon/polypropylene (Japanese Patent Application Laid-open No. 51-64,583, Japanese Patent Publication No. 6
No. 1-23,110) is known, but the above item (■) is suitable for pasteurization treatment at 80 to 90°C (heat shrinkage rate is 20% or more), Since the heat treatment temperature is 90''Ci or less, polyethylene resin is used as the polyolefin from the viewpoint of heat sealing.

However, using such conventional films, 12
If the retort treatment is carried out at 0°C, there are problems such as the polyolefin becoming white, the transparency being deteriorated, and the sealing performance of the sealing part being unsatisfactory.

On the other hand, in the case of the multilayer film mentioned above, the degree of stretching of the film is unknown, and when used for retort packaging,
Particularly when subjected to high-temperature treatment at 120° C., there is a problem in that the multilayer film cannot maintain its tightness, bag tear resistance, and deformation resistance.

Furthermore, with regard to the above films ① and ②, there is no description of the shrinkage rate when heated to 120° C., and both were developed for low-temperature retort processing.

The present invention has been made based on the above circumstances.

The object of the first invention of the present application is to exhibit suitable shrinkage even when subjected to high-temperature retort treatment at 120°C, excellent tightness and transparency, no deformation in appearance, and have oxygen gas barrier properties, moisture permeation resistance, etc. It is an object of the second invention of the present application to provide a heat-shrinkable multilayer film that has excellent basic characteristics for retort food packaging and is particularly suitable for high-temperature retort processing. An object of the present invention is to provide a retort food package using a heat-shrinkable multilayer film having excellent properties.

[Means for Achieving the Aforesaid Problems] As a result of extensive research by the present inventors in order to develop a heat-shrinkable multilayer film for food shrink packaging that is also suitable for high-temperature retort processing, the inventors have developed a method using a specific resin, namely polyamide resin. A heat-shrinkable multilayer film made of polypropylene resin and having a specific heat shrinkage rate maintains appropriate tightness and transparency even when subjected to high-temperature retort treatment at 120°C, with no appearance defects or deformation. Furthermore, they discovered that the multilayer film has excellent basic properties such as oxygen gas barrier properties and moisture permeation resistance for use in retort food packaging, and based on this knowledge, the first invention (the invention claimed in claim 1) was developed. In addition, we have realized that the food packaging using the heat-shrinkable multilayer film having the above-mentioned excellent properties is a practically excellent retort food shrink packaging that is suitable for high-temperature retort processing at 120°C. Therefore, the second invention (invention according to claim 2) was completed.

That is, the configuration of the first invention of the present application includes at least the polyamide resin layer (A) and the polypropylene resin layer (B).
It is a heat-shrinkable multilayer film having a heat shrinkage rate of 5 to 30% at 120°C, and the structure of the second invention of the present application consists of at least a polyamide resin layer (A) and a polypropylene resin layer (B), This is a retort food packaging body using a heat-shrinkable multilayer film having a heat shrinkage rate of 5 to 30% at 120°C.

The heat-shrinkable multilayer films in the first and second inventions of the present application will be explained in detail with reference to the drawings.

FIG. 1 is a cross-sectional view conceptually showing an example of the layer structure of the heat-shrinkable multilayer film in the first invention and the second invention.

In the figure, (B) indicates a polypropylene resin layer, and (A
) indicates a polyamide resin layer.

The (A) layer and the (B) layer are usually bonded together using an adhesive or an adhesive resin, and can be laminated and integrated.

In addition, in FIG. 1, the adhesive layer (D) is a layer (A) and a layer (B).
) is used between layers, but as described later, the (A) layer and (B) layer may be integrated by laminating using a laminating adhesive. .

As mentioned above, the heat-shrinkable multilayer film of the first invention of the present application is made of at least the polypropylene resin layer (A) and the polyamide resin layer (B);
If desired, (E
) They may be laminated and integrally fixed with an oxygen gas barrier resin layer interposed therebetween, and (C)
Heat-resistant resin layers may be laminated and integrated.

Thus, by using the (E) layer, the oxygen gas barrier properties of the heat-shrinkable multilayer film can be further improved, and by using the (C) layer, the moisture resistance and heat resistance of the multilayer film can be improved. Further improvements can be made.

As the polyamide resin used for the layer (A), known ones such as nylon-6, nylon-66, nylon-11, nylon-12, nylon-610, nylon-6-12, nylon-6-6, nylon -6-
12-66 etc. can be mentioned.

Note that these may be used alone, or two or more of these may be used in combination in a composition or multilayer structure.

The polyamide resin usually has a number average molecular weight within the range of to, ooo to too, ooo (7).

In addition, the polyamide resin has a melt viscosity of 5 x 10-3 to 50
-3 voids is preferable, l0x10
It is particularly preferable that the voids be within the range of -3 to 20X 10-3 voids; if the voids are outside the range, workability may deteriorate.

It is usually sufficient for the layer (A) to be used as a single layer, but it is also possible to use it in a multilayer structure of two or more layers if desired.

The polypropylene resin used for the layer (B) includes known ones, such as H-PP (polypropylene homopolymer), R-PP (random copolymer of propylene and other olefins, etc.), B-PP ( block copolymers of propylene and other olefins, etc.) or mixtures or blend compositions thereof; Examples include blend compositions with high quality resins, polyethylene, linear low-density polyethylene, etc.).

Note that other olefins in the propylene copolymer include, for example, ethylene, l-butene, 1-pentene, l-hexene, l-octene, 4-methyl-1-
Examples include pentene.

Furthermore, when other components are added to the polypropylene resin, it is desirable to add the additional components within a range that does not cause whitening or deterioration of transparency during 120° C. retort treatment.

The heat-resistant resin of the layer (C) used as desired is as follows:
For example, heat-resistant polyester resins, the above-mentioned polypropylene resins, and the like can be suitably used.

As the oxygen gas barrier resin for layer (E) used as desired, for example, polyvinylidene chloride, polyvinyl alcohol, etc. can be suitably used.

Note that this oxygen gas barrier resin layer may be bonded using the same adhesive or adhesive resin as in (D) above, and may be integrally laminated, or may be coextruded with the polyamide resin of layer (A). It may be provided in a stretched manner.

As the adhesive used for laminating and integrating each layer such as the (A) layer and the (B) layer, it is preferable to use a laminating adhesive or the like that is used for ordinary multilayer films for packaging retort food. Furthermore, as the adhesive resin, for example, maleic anhydride-modified polypropylene or the like can be suitably used.

The heat-shrinkable multilayer film according to the first and second inventions of the present application has a shrinkage rate at 120° C. within a range of 5 to 30%, preferably within a range of 7 to 20%.

Controlling the shrinkage rate within the above range is possible by adjusting the resin film used for each layer or the manufacturing conditions in the laminate of each film, that is, the manufacturing process of a multilayer film, for example, the stretching ratio at the time of film formation or multilayer film formation. This can be carried out by adjusting the stretching conditions such as the stretching temperature and the stretching temperature, the heat treatment conditions of the stretched film or stretched multilayer film, that is, tension, relaxation, temperature (for example, 50 to 230° C.), treatment time, etc.

If the shrinkage rate is less than 5%, when used for retort food packaging and subjected to high temperature retort sterilization treatment at around 120°C, the shrinkage will be insufficient and the tightness will be poor.
The appearance of the food package becomes poor, and when used as a sausage package, for example, the texture becomes poor. On the other hand, if the shrinkage rate exceeds 30%, the edges of the film may be deformed or unnecessary force may be applied to the sealing part, resulting in insufficient sealing when used in food packaging as described above. or pinholes may occur. In addition,
This shrinkage rate is determined within an appropriate range based on the type of packaged item, filling rate, etc.

The layer thickness of the polyamide resin layer (A) used is usually 5 to 2
0 JL irises, preferably 5 to 50 JL, preferably 8 to 3
It is preferable to set it to about 0ILm.

If the film thickness is less than 5 μm, gas barrier properties may be low and pinhole resistance may also be reduced;
Exceeding 0 final layer may result in excessive physical properties.

Moreover, the thick film of the polypropylene resin layer (B) is usually
Suitably it is between 5 and 100 gm, preferably between 5 and 60 gm.

If this film thickness is less than 5 mm, the sealing resistance will decrease,
v, M property may be insufficient, - direction, 100 end■
Exceeding this may result in excessive physical properties as well.

The thickness of the adhesive layer used is usually 0.5~20u.
It is suitable that the range is about the size of the L seal.

The thickness of the heat-shrinkable multilayer film in the first invention and the second invention is preferably in the range of 10 to 200 μm, LLll, and preferably in the range of 20 to 120 μm for boat fishing.

The method for producing the heat-shrinkable multilayer film in the first and second inventions of the present application is not particularly limited, but examples include the following method.

■For example, a lamination method using a biaxially stretched polyamide resin film having a predetermined shrinkability as the layer (A), an unstretched or stretched film of a polypropylene resin as the layer B, and a lamination adhesive as the adhesive layer. A method of adhering and laminating them together to form a desired heat-shrinkable multilayer film having a predetermined shrinkage rate.

■Polyamide resin as layer (A) and polypropylene resin containing adhesive resin such as maleic anhydride-modified polypropylene resin as adhesive layer (D) and layer (B);
1.) A polyamide resin as a layer, an adhesive resin such as maleic anhydride-modified polypropylene as an adhesive layer CD), and a polypropylene resin as a (B) layer. Multilayer coextrusion is performed to obtain an unstretched multilayer film, which is stretched, for example, 2 to 5 times, and further heat treated at an appropriate temperature, for example, within a temperature range of 50 to 230°C to control the shrinkage rate and achieve the desired heat shrinkability. A method of making a multilayer film.

The polyamide resin stretched film used in the above (2) can be obtained, for example, by forming the polyamide resin described above into a film or sheet shape and then stretching it.

Examples of the lamination method in (2) above include dry lamination, non-solvent lamination, and extrusion.

In addition, as a method for producing a heat-shrinkable multilayer film having layer (C), for example, in the methods (1) and (2) above,
The method of providing the heat-resistant resin or its stretched film used as the layer (C) at the same time when the above-mentioned lamination is performed, or sequentially providing the heat-resistant resin or its stretched film in a sequential manner can be suitably applied.

In addition, when obtaining a heat-shrinkable multilayer film having the (E) layer, for example, in the method (2) above, an oxygen gas barrier resin may be used as a single film as the (E) layer, or may be coextruded with a polyamide resin in advance. Stretched 2
Preferred is a method in which the film is used as a layer film and laminated in the same manner as above, and a method in which a gas barrier resin is used as the (E) layer and the same method is used to form a coextrusion film, stretching treatment, heat treatment, etc. It can be applied to

The heat-shrinkable multilayer film of the first invention of the present application obtained as described above has appropriate shrinkability even when subjected to high-temperature retort treatment at, for example, 120°C, has excellent tightness with the contents, and has no wrinkles. Food packaging with no appearance defects such as deformation, excellent transparency, good sealing properties, no pinholes between the film part and the seal layer, and oxygen gas barrier properties, moisture resistance, food resistance, etc. It is a heat-shrinkable multilayer film that has excellent basic properties as a film for food use, and can be molded into various shapes according to the shape of the food contents to be used for shrink packaging of retort food, especially for high-temperature retort processing at around 120°C. It is suitably used as a heat shrink packaging film such as a variety of food shrink packaging films including retort food shrink packaging.

The food package according to the invention of Section 2 of the present application is a food package obtained by shrink-wrapping food contents using the heat-shrinkable multilayer film of the invention according to Section 1 of the present application.

There are no particular restrictions on the type or shape of the food contents, but suitable examples include edible meats such as solid cooked meats such as ham and sausages.

The method for manufacturing this food package can be carried out according to a known method. For example, the food is molded into a tube or cylinder, sealed and packaged with the food as its contents, and then retorted at a predetermined temperature to heat-shrink the multilayer film used to achieve excellent tightness, adhesion, etc. However, a method for obtaining shrink packaging for retort food can be mentioned. The sealing method in this case may be welding using an ultrasonic seal or the like, caulking with metal, or so-called rocket packaging.

The temperature of the above retort treatment is usually 100 to 140°C.
, preferably 110 to 130°C, especially 12
High-temperature treatment at around 0° C. can be applied without any problem.

The food packaging body of the second invention is a heat-shrinkable multilayer film having excellent retort food shrink packaging properties suitable for high-temperature retort processing at around 120° C. Since we are using
In particular, it has high strength even when subjected to high-temperature retort treatment at around 120°C, has good tightness with food contents, has excellent packaging film transparency, does not have poor appearance or deformation, and is free from oxygen. It has excellent gas barrier properties, moisture permeation resistance, etc., and also has excellent adhesion at the seal part, so there are no pinholes in the film part or between the seals.
This is a food package that is extremely excellent in practical use, since it is not limited in the selection of food preservation additives such as sterilizers, and can greatly shorten retort sterilization time.

[Examples] (Examples 1 to 6 and Comparative Example 1) Production example of biaxially stretched polyamide film Nylon-6 was melt-kneaded, then extruded through a downward annular gouer, and solidified by water cooling to obtain a tubular film. The obtained tubular film was stretched approximately three times in the length and width directions using a tubular biaxial stretching device, and then heat treated at 180 to 220°C under various conditions to produce different shrinkage rates. Thickness 25Bm (Examples 1 to 5)
A biaxially stretched polyamide film of 15 pm (Example 6) was obtained.

Production Example of Heat-Shrinkable Multilayer Film Each of the two-wheel stretched polyamide films obtained above and a 40 gm thick polypropylene film were laminated using a polyurethane adhesive to obtain a heat-shrinkable multilayer film.

Table 1 shows the shrinkage percentage of each of the obtained multilayer films when heated at 120° C. (30 minutes).

Production example and evaluation of shrinkable food packaging Each of the heat-shrinkable multilayer films obtained above was bent with the polypropylene layer inside, the ends of the polypropylene layers facing each other, and sealed using ultrasonic waves. A cylindrical film having an inner diameter of 35 layers and 1 layer was obtained. A sausage package (1
Then, heat sterilization treatment (retort treatment) was performed at 120° C. for 30 minutes.

The evaluation results are shown in Table 1.

In addition, after the above-mentioned retort treatment, no decrease in transparency of the film was observed in any case.

Table 1 (Unit %) Agricultural RH: J degree "Effect of the invention" The heat-shrinkable multilayer film of the invention of claim 1 is made of a specific resin, that is, a polyamide resin layer and a polypropylene resin layer, and has a shrinkage within a certain range. When used for shrink-sealing packaging of retort foods, etc., the tightness or strength with the contents is suitable even when subjected to high-temperature retort processing at around 120°C, and there is no appearance defect such as wrinkles or deformation. It is highly transparent, has good sealing properties, and has no pinholes between the film part and the sealing layer.
It is also a heat-shrinkable multilayer film with excellent oxygen gas barrier properties, heat resistance, etc., and also excellent food resistance.

That is, according to the first aspect of the invention, it is possible to provide a heat-shrinkable multilayer film having excellent properties as a shrinkable close-tight packaging material for shrink-wrapping retort food as described above.

Further, according to the invention of claim 2, since the heat-shrinkable multilayer film having the excellent characteristics of claim 1 is used as a packaging material, even when high-temperature retort treatment at around 120°C is performed, the food contents can be The tightness of the packaging film is suitable, there are no appearance defects such as wrinkles or deformation, and the packaging film has excellent transparency.
Good sealing properties, no pinholes between the film part and sealing layer, oxygen gas barrier properties, moisture resistance,
A food package with excellent food resistance and the like can be provided.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view conceptually showing an example of the layer structure of the heat-shrinkable multilayer film of the present invention. A: polypropylene resin, B@Φ: polyamide resin layer, (No. 011: heat-resistant resin layer, (E): oxygen gas barrier improving resin layer, (I): fist adhesive layer.

Claims (2)

[Claims] (1) A heat-shrinkable multilayer film comprising at least a polyamide resin layer (A) and a polypropylene resin layer (B), and having a heat shrinkage rate of 5 to 30% at 120°C. 2. A retort food packaging body characterized by using a heat-shrinkable multilayer film consisting of at least a polyamide resin layer (A) and a polypropylene resin layer (B) and having a heat shrinkage rate of 5 to 30% at 120°C.