JP2711304B2 - Heat shrinkable multilayer film and food package thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a heat-shrinkable multilayer film and a retort food package using the multilayer film, and more particularly to high-temperature retort resistance, food resistance, and transparency. A heat-shrinkable multi-layer film and a heat-shrinkable multi-layer film having excellent heat resistance, tightness, pinhole resistance, deformation resistance of a package, and the like, which can be suitably used for shrink packaging of retort foods such as ham and sausages. The present invention relates to a retort food package.

[Conventional technology and problems] Processed meat and processed fish meat, such as ham and sausage, are packaged using an oxygen gas barrier film from the viewpoint of preservation, and then heat-sterilized. Conventionally, this sterilization temperature was 70-90 ° C. However, due to the use of sterilizers, restrictions on the amount of use, and the need for short-time processing, appropriate tightness and transparency even in high-temperature processing near 120 ° C Hold and
Development of a heat-shrinkable film free from appearance defects such as wrinkles and deformations is desired.

As conventional multilayer films for shrink wrapping of retort foods, for example, a shrink multilayer film composed of nylon / polyolefin (JP-A-59-212,261, JP-A-56-1)
No. 36,365, Japanese Patent Publication No. 60-35257), a multilayer film composed of nylon / polypropylene (JP-A-51-6).
No. 4,583, Japanese Patent Publication No. 61-23,110) are known, but the above-mentioned ones are suitable for pasteurization treatment at 80 to 90 ° C. (heat shrinkage is 20% or more). In addition, since the heat treatment temperature is 90 ° C. or less, a polyethylene resin is used as the polyolefin in terms of heat sealing.

However, using such conventional films, 12
When the retort treatment is performed at 0 ° C., there are problems such as whitening of the polyolefin, deterioration of the transparency, and concern about the sealing property of the sealing portion.

On the other hand, in the case of the above-mentioned multilayer film, the degree of stretching of the film is unknown, and when used for retort packaging, particularly when subjected to a high temperature treatment of 120 ° C., the tightness of the multilayer film, rupture-resistant bag However, there is a problem that the resistance and the deformation resistance cannot be secured.

Further, regarding the above films and films, there is no description of the shrinkage ratio when heated to 120 ° C., and both films are developed for low-temperature retort treatment.

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

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

[Means for Achieving the Object] As a result of intensive studies conducted by the present inventors to develop a heat-shrinkable multilayer film for food shrink wrapping suitable for high-temperature retort treatment, at least a specific resin, that is, A heat-shrinkable polyamide resin having a thickness of 5 to 50 μm and a polypropylene-based resin having a transparency of 5 to 100 μm while maintaining transparency in a heat treatment at 120 ° C. and having a specific heat shrinkage Even when subjected to high temperature retort processing at 120 ° C, the multi-layer film retains appropriate tension and transparency, does not have poor appearance or deformation, and is used for retort food packaging with oxygen gas barrier properties, moisture resistance, etc. Was found to be a multilayer film having excellent basic characteristics, and based on this finding, the first invention (the invention according to claim 1) was completed, and the heat recovery having the above-mentioned excellent characteristics was completed. It has been found that a food package using a shrinkable multilayer film is a practically excellent retort food shrink package suitable for a high-temperature retort treatment at 120 ° C., and the second invention (the invention according to claim 2) ) Was completed.

That is, the structure of the first invention of the present application is a polyamide resin layer (A) having a thickness of at least 5 to 50 μm;
A heat-shrinkable multi-layer film which is made of a polypropylene resin layer (B) having a thickness of 5 to 100 μm and having a heat shrinkage of 5 to 30% at 120 ° C. The structure of the second invention of the present application is a polyamide resin layer (A) having a thickness of at least 5 to 50 μm and a polypropylene that maintains transparency in a heat treatment at 120 ° C. and has a thickness of 5 to 100 μm. It consists of a base resin layer (B) and has a heat shrinkage at 120 ° C. of 5 to 30
% Is a retort food package using a heat-shrinkable multilayer film.

The heat-shrinkable multilayer film in the first invention and the second invention of the present application will be described in detail with reference to the drawings.

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

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

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

Although FIG. 1 shows an example in which the adhesive layer (D) is used between the (A) layer and the (B) layer, the (A) layer and the (B) The integration with the layer may be performed by laminating using a laminating adhesive.

As described above, the heat-shrinkable multilayer film of the first invention of the present application comprises at least the polypropylene resin layer (B) and the polyamide resin layer (A) as raw materials. ) Layer and (B) layer and further laminated with (E) an oxygen gas barrier resin layer interposed therebetween,
The heat resistant resin layer (C) may be further laminated and integrated on the outer surface of the layer (A).

As described above, the oxygen gas barrier property of the heat-shrinkable multilayer film can be further improved by using the layer (E), and the moisture-proof property and heat resistance of the multilayer film can be improved by using the layer (C). It can be further improved.

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

These may be used alone or in combination of two or more of them in the form of a composition or a multilayer structure.

As the polyamide resin, its number average molecular weight is
Usually, it is in the range of 10,000 to 100,000.

Further, as the polyamide resin, the melt viscosity measured using a descending flow tester at 230 ° C. under a shear rate measurement condition of 100 sec ⁻¹ is within a range of 5 × 10 ⁻³ to 50 × 10 ⁻³ poise. Certain ones are preferred, and those in the range of 10 × 10 ^{−3 to} 20 × 10 ⁻³ poise are particularly preferred. If the ratio is outside the above range, workability may be reduced.

The layer (A) is usually sufficient to be used as a single layer per se, but may be used in a multilayer structure of two or more layers if desired.

As the polypropylene resin used as the (B) layer, known resins such as H-PP (polypropylene homopolymer), R-PP (random copolymer of propylene and other olefins), B-PP ( Block copolymers of propylene and other olefins) or mixtures or blends thereof, or these polypropylene resins and other resins or elastomers (e.g., E-PR, ethylene-butene-1 copolymer, etc.) Low crystalline resin, polyethylene, linear low density polyethylene, etc.)
And the like.

The other olefin in the propylene copolymer includes, for example, ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1
-Pentene and the like.

When other components are added to the polypropylene resin for use, it is desirable that the added components be added within a range that does not cause whitening and decrease in transparency during retort treatment at 120 ° C.

As the heat-resistant resin of the layer (C) optionally used, for example, a heat-resistant polyester resin, the above-mentioned polypropylene resin, or the like can be suitably used.

As the oxygen gas barrier resin of the (E) layer optionally used, for example, polyvinylidene chloride, polyvinyl alcohol and the like can be suitably used.

In addition, this oxygen gas barrier resin layer is the same as the above (D)
It may be laminated and integrated by using the same adhesive or adhesive resin as described above, or may be provided by coextrusion stretching with the polyamide resin of the layer (A).

As the adhesive used for laminating and unifying the layers (A) and (B), etc., those used as ordinary multilayer films for retort food packaging, for example, laminate adhesives can be suitably used. As the adhesive resin, for example, maleic anhydride-modified polypropylene or the like can be preferably used.

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

The control of the shrinkage ratio within the above range is performed by a resin film used for each layer, or a manufacturing condition of a laminated integration of each film, that is, a manufacturing process of a multilayer film, for example,
By adjusting stretching conditions such as stretching ratio and stretching temperature in forming a film or a multilayer film, and heat treatment conditions of a stretched film or a stretched multilayer film, ie, tension, relaxation, temperature (for example, 50 to 230 ° C.), and processing time, etc. It can be carried out.

When the shrinkage rate is less than 5%, when used for retort food packaging and subjected to a high-temperature retort sterilization treatment at around 120 ° C., shrinkage is insufficient and tightness is poor,
The appearance of the food package is poor, and when used as a sausage package, for example, the texture is poor. On the other hand, if the shrinkage ratio exceeds 30%, when used in a food package as described above, the end of the film is deformed, and unnecessary force is applied to the seal portion, and it is insufficient to secure the sealing performance. Or pinholes may occur. In addition,
This shrinkage ratio is determined within an appropriate range based on the type of the packaged object, the filling ratio, and the like.

The thickness of the polyamide resin layer (A) to be used is 5 to 50 μm.
m, preferably 5 to 30 μm, more preferably 8 to
When the film thickness is less than 5 μm, the gas barrier property is low, and the pinhole resistance may be reduced.
If it exceeds 50 μm, there may be excessive physical properties.

The thick film of the polypropylene resin layer (B) has a thickness of 5 to 5.
It is 100 μm, preferably 5 to 60 μm.

If the film thickness is less than 5 μm, the sealing resistance is reduced, and the sealing performance may be insufficient.
Exceeding the same may result in excessive physical properties.

The thickness of the adhesive layer to be used is usually 0.5 to 20 μm
It is preferable to set the range.

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

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

For example, a biaxially stretched film of a polyamide resin having a predetermined shrinkability as a layer (A) and a non-stretched or stretched film of a polypropylene resin as a layer (B) are used, and a laminating adhesive is used as an adhesive layer. A method of bonding, laminating and integrating into a desired heat-shrinkable multilayer film having a predetermined shrinkage.

(A) Layer of polyamide resin and adhesive layer (D) and (B) Layer of adhesive resin containing adhesive resin such as maleic anhydride modified polypropylene resin, or (A) Layer of polyamide resin and anhydrous layer of adhesive layer (D) An unstretched multilayer film is obtained by co-extrusion of an adhesive resin such as maleic acid-modified polypropylene and a polypropylene resin as the layer (B) into a multilayer film, which is stretched, for example, by a factor of 2 to 5 and then at an appropriate temperature, for example, from 50 to 50%. A method in which a desired heat-shrinkable multilayer film is formed by heat treatment within a temperature range of 230 ° C. to control a shrinkage ratio.

The stretched polyamide resin film used above can be obtained, for example, by forming the film into a film or a sheet using the above-mentioned polyamide resin, and then stretching the film.

Examples of the above laminating method include methods such as dry lamination, non-solvent lamination, and extrusion.

As a method for producing the heat-shrinkable multilayer film having the layer (C), for example, in the above methods (1) and (2), the heat-resistant resin used as the layer (C) or the stretched film thereof is provided simultaneously with the lamination and integration. Alternatively, a method in which the layers are sequentially laminated and provided can be suitably applied.

In order to obtain a heat-shrinkable multilayer film having the layer (E), for example, in the above-mentioned method, an oxygen gas barrier resin is used as the (E) layer as a single film, or is co-extrusion-stretched with a polyamide resin in advance. A method of laminating in the same manner using a two-layer film formed by the above method. In the above method, a co-extruded film is similarly formed using a gas barrier resin as the (E) layer,
A method of performing a stretching treatment, a heat treatment, or the like can be suitably applied.

The heat-shrinkable multilayer film of the first invention of the present application obtained as described above has an appropriate shrinkage even when subjected to a high-temperature retort treatment of, for example, 120 ° C., has excellent tightness with contents, and has wrinkles. No defective appearance such as deformation, deformation, etc., excellent transparency, good sealability, no pinholes between film part and seal layer, and food packaging such as oxygen gas barrier property, moisture resistance, food resistance etc. Heat-shrinkable multi-layer film with excellent basic properties as a film for foods. Formed and processed into various shapes according to the shape of the food content to be used, for shrink wrapping of retort foods, especially for high temperature retort processing at around 120 ° C It is suitably used as a heat shrink wrapping film such as various food shrink wrapping films including retort food shrink wrapping.

The food package of the second invention of the present application is a food package obtained by shrink-wrapping food contents using the heat-shrinkable multilayer film of the first invention of the present application.

The type and shape of the food content are not particularly limited, but edible meats such as solid cooked meats, such as hams and sausages, are particularly preferred.

The method for producing the food package can be performed according to a known method. For example, the heat-shrinkable multilayer film of the first invention of the present application is formed into a shape suitable for the shape of the food to be the contents. After forming and processing into a tube or tube, sealing and packaging the food as a content, retorting at a predetermined temperature, and heat shrinking the used multilayer film to provide excellent retentivity, tightness, adhesion, etc. Examples of the method include a method of obtaining a shrinkable package of a food. The sealing method in this case may be welding using an ultrasonic seal or the like, or caulking with metal, so-called rocket packaging.

The temperature of the retort treatment is usually 100 to 140 ° C., preferably 110 to 130 ° C., and a high temperature treatment of around 120 ° C. can be applied without any problem.

The food package of the second invention is a specific heat-shrinkable multilayer film of the first invention of the present application, that is, a heat-shrinkable multilayer film having excellent retort food shrink wrapping properties suitable for high-temperature retort treatment at around 120 ° C. Because we use
In particular, it has high strength even when subjected to high-temperature retort treatment at around 120 ° C., and has good tension with food contents.
Excellent transparency of packaging film, no appearance defects and deformation, and excellent oxygen gas barrier properties, moisture permeability resistance, etc.
In addition, since the seal has excellent adhesion, there is no pinhole between the film and the seal, and there is no restriction on the selection of food preservative additives such as disinfectants. It is a food package excellent in practical use which can greatly reduce the sterilization treatment time.

[Examples] (Examples 1 to 6 and Comparative Example 1) Production Example of Biaxially Stretched Polyamide Film Nylon-6 was melt-kneaded, then extruded from a downward annular die, and solidified with water to obtain a tubular film. The obtained tubular film is stretched about three times in the length direction and the width direction using a tubular biaxial stretching apparatus, and then 207 ° C. (Example 1), 202 ° C. (Example 2), 197 ° C.
(Example 3), 189 ° C. (Example 4), 180 ° C. (Example 5), 192 ° C. (Example 6), 221 ° C. (Comparative Example 1), each film was placed in a tenter heat treatment machine. Thicknesses having different shrinkage rates of 25 μm (Examples 1 to 5), 15 μm (Example 6),
And a 25 μm (Comparative Example 1) biaxially stretched polyamide film.

Production Example of Heat-Shrinkable Multilayer Film Each of the biaxially stretched polyamide films obtained above and a polypropylene film having a thickness of 40 μm were laminated using a polyurethane adhesive to obtain a heat-shrinkable multilayer film.

120 ° C heating of each of the obtained multilayer films (30 minutes)
Table 1 shows the shrinkage ratio at the time.

Production example and evaluation of the shrinkable food packaging body, each heat-shrinkable multilayer film obtained above,
The polypropylene film was bent with the polypropylene layer inside, and the ends of the polypropylene layer were opposed to each other, and sealed by using ultrasonic waves to obtain a cylindrical film having an inner diameter of 35 mm. A sausage package (150 m) is filled with sausage in each tubular film and the open end is sealed using ultrasonic waves.
m length). Next, heat sterilization treatment (retort treatment) was performed at 120 ° C. for 30 minutes.

 Table 1 shows the evaluation results.

After the retort treatment, no decrease in the transparency of the film was observed in any case.

[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-based resin, and has a specific range of shrinkage. When used for applications, even when subjected to high-temperature retort treatment at around 120 ° C, it has good tightness or strength with the contents, has no appearance defects such as wrinkles and deformation, and has high transparency and sealing properties. Good, no pinhole between film part and seal layer,
Further, it is a heat-shrinkable multilayer film excellent in oxygen gas barrier properties, heat resistance, and the like, and also excellent in food resistance.

That is, according to the first aspect of the present invention, it is possible to provide a heat-shrinkable multilayer film having excellent properties as a material for shrink-bonding packaging such as the above for retort food shrinkage packaging.

According to the second aspect of the present invention, since the heat-shrinkable multilayer film having the excellent characteristics of the first aspect is used as a packaging material, even when a high-temperature retort treatment at about 120 ° C. is performed, the food content is reduced. Tension is suitable, there are no appearance defects such as wrinkles and deformation, and the transparency of the packaging film is excellent,
Good sealing performance, no pinholes between the film and the sealing layer, oxygen gas barrier, moisture resistance,
A food package excellent in food resistance and the like can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view conceptually showing an example of the layer configuration of the heat-shrinkable multilayer film of the present invention. A: polyamide resin, B: polypropylene resin layer, (C): heat-resistant resin layer, (E): oxygen gas barrier improving resin layer, (D): adhesive layer.

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location B29K 23:00 77:00 105: 02 B29L 9:00

Claims (2)

(57) [Claims] 1. A polyamide resin layer (A) having a thickness of at least 5 to 50 .mu.m and a polypropylene resin layer (B) having a transparency of 5 to 100 .mu.m while maintaining transparency in a heat treatment at 120.degree. ), Wherein the heat shrinkage ratio at 120 ° C is 5 to 30%. 2. A polyamide resin layer (A) having a thickness of at least 5 to 50 .mu.m and a polypropylene resin layer (B) having a transparency of 5 to 100 .mu.m while maintaining transparency at 120.degree. ), Wherein a heat-shrinkable multilayer film having a heat-shrinkage ratio at 120 ° C of 5 to 30% is used.