JPH0526652B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention provides heat-shrinkable packaging that does not cause bag breakage when processed meat products such as grilled pork chunks are heat-shrink-wrapped and has excellent tightness. The present invention relates to a heat-shrinkable packaging film and a package manufactured using the heat-shrinkable packaging film.

More specifically, it is a heat-shrink packaging film that has excellent mechanical strength and oxygen barrier properties, and has specific shrinkage characteristics and sealing strength, so when packaging contents with irregular shapes such as roasted pork chunks, It can be packaged regardless of the size of the contents, and the bag does not break from the seal part of the package when heated in hot water or when taken out from hot water and left to stand naturally. A heat-shrinkable packaging film that does not leave any unshrinkable film around the periphery, has excellent tightness, and provides a good-looking package, and a film produced using the heat-shrinkable packaging film. The present invention relates to a package that has excellent heat retention and preservation of contents.

(Prior art) Recently, a heat shrink packaging method has been used in which roasted pork chunks and the like are vacuum packaged in a bag made of a heat shrinkable film with oxygen barrier properties, and then heat shrinked and sterilized in hot water. Ta. This packaging method has the feature that it can be packaged even if the shape is not uniform, such as a lump of grilled pork, and the contents can be preserved for a long time. Moreover, when processed meat products such as grilled pork chunks are packaged using this packaging method, they are always strong, from the time they are heat-shrinked and sterilized in hot water to the time they are taken out of the hot water and left to naturally stand. Since the contents can be tightened with force, the main feature is that it can prevent the meat juices (referred to as drips) from accumulating between the package and the roasted pork chunks, etc. It can be done (this kind of property is called ``pursuability'').

However, when using conventional bags made of heat-shrinkable packaging film, the contents, such as chunks of grilled pork, come in various sizes and shapes, so a bag that is appropriate for the size and shape is used. If the size of the bag was too large for the size of the item, a lot of film would remain around the contents without being completely heat-shrinked, making it unsightly and lacking in tightness. Furthermore, if the size of the bag is too small compared to the size of the contents, not only will it be difficult to fill the bag with the contents, but it will also be difficult to fill the bag with the contents. When the bag was removed from the inside and left to stand, the bag sometimes broke at the seal.

In this way, when using conventional heat-shrinkable packaging film to heat-shrink-wrap contents of variable shape, such as chunks of grilled pork, the size and shape of the bag depend on the size and shape of the contents. However, unless the shape is appropriately selected, there is a complicated problem in that the bag will not break at the sealed portion during the heating process in hot water, etc., and it will not be possible to obtain a package with excellent tightness.

(Background of the Invention) The present inventors have discovered the conditions of a heat-shrinkable packaging film that provides tightness to a heat-shrinkable packaging, and the conditions when the heat-shrinkable packaging is heat-shrinked in hot water; We conducted various experiments to find out why the bag breaks at the sealed part when it is removed from hot water and left to stand.

First, regarding the tightness of the heat-shrinkable packaging body, the heat-shrinkage rate of the heat-shrinkable packaging film used in hot water, the heat-shrinkage stress, and the shrinkage when left naturally after being heated in hot water. I did a lot of research on the relationship with stress, etc. Next, the reason why the bag breaks at the seal part when heat-shrinking the heat-shrinkable packaging body in hot water is due to the relationship between the heat-shrinkage stress of the heat-shrinkable packaging film in hot water and the seal strength. I looked into it. In addition, when the heat-shrinkable packaging film is removed from hot water and left to naturally stand, the cause of the bag breaking at the seal part is when the heat-shrinkable packaging film is heated in hot water and left to stand naturally. The relationship between shrinkage stress and seal strength was investigated.

The heat shrinkage rate, heat shrinkage stress, and seal strength of a heat shrink packaging film in hot water, or the shrinkage stress and seal strength when left naturally after being heated in hot water, are as follows. It was measured as follows.

First, the heat shrinkage rate was determined by cutting a heat-shrinkable packaging film into a square of 100 mm in both the vertical and horizontal directions, immersing the obtained sample in hot water at 80°C for about 3.0 seconds to shrink it, and shrinking it in the vertical direction. , the amount of contraction in each lateral direction was determined as a 100% of the length before contraction. In addition, when measuring the heat shrinkage rate, it is important to note that practical heat shrink packaging is heat-shrinked in hot water in the range of 80℃ to 95℃, and that heat shrinkage is 80℃ in hot water of 80℃ or higher. The heat shrinkage rate at 80°C was determined because the heat shrinkage rate was higher than the heat shrinkage rate.

Thermal shrinkage stress was measured by holding a sample of heat-shrinkable packaging film cut into tanzag shapes with a width of 10mm in both the vertical and horizontal directions between chucks spaced at 30mm intervals without creating any tension or loosening. ,
The stress generated between the chucks when the chucks were immersed in a predetermined hot water for 5 minutes while fixed so that the distance between the chucks did not change was determined as the thermal shrinkage stress in each direction in the hot water in units of g/cm. In the above heat shrinkage stress measurement, it was found that the heat shrink packaging film exhibits stronger heat shrinkage stress when the temperature of the hot water is higher, and as mentioned above, the temperature of the hot water in practical packaging ranges from 80°C. 95
℃ range, in practical packaging, the thermal shrinkage stress shows the lowest value in hot water of 80℃ and the highest value in hot water of 95℃. Therefore, we determined the thermal shrinkage stress in hot water at 80℃ and 95℃.

In addition, the shrinkage stress when left to stand naturally after being heated in hot water is as follows: After measuring the heat shrinkage stress in hot water at 95°C as described above, the sample was taken out of the hot water without changing the chuck interval and was When the chuck was left in a natural state for about 2 hours, the stress between the chucks was determined in units of g/cm in both the longitudinal and lateral directions. In addition, the shrinkage stress of a heat-shrink packaging film when it is left to stand after being heated in hot water is higher than that when it is heated in high-temperature hot water. The shrinkage stress after being heated in water was determined.

When the seal part of the heat shrink packaging film is heated in hot water during bag making or vacuum packaging, or
The seal strength when left undisturbed after heating was determined by the following method. First, a sample for seal strength measurement is prepared, which is cut into a tanzag shape with a width of 10 mm, including the seal portion of the heat-shrinkable packaging film. Similar to the heat shrinkage stress measurement, the sample was held between chucks spaced at 30 mm intervals in a state that did not create tension or slack, and was fixed so that the chuck spacing did not change.
Immerse in hot water at 95℃ for 5 minutes. Then, open the chucks in hot water at a speed of about 100 mm/min.
The strength at the beginning of the seal was determined as the seal strength in hot water at 95°C in units of g/cm. In addition, the seal strength when left naturally after heating is as above.
Similar to the seal strength measurement in 95°C hot water, the sample was held between chucks and immersed in 95°C hot water for 5 minutes. After that, the chuck was taken out of the hot water without changing the chuck interval, and after being allowed to stand for about 2 hours, the chuck interval was opened at a speed of about 100 mm/min.
The strength at which the seal begins to break was determined in units of g/cm as the seal strength when the seal was heated in hot water at 95°C and then left to stand.

The reason why the seal strength after heating was determined in hot water at 95℃ is because the heating of practical heat shrink packaging is from 80℃ to 95℃.
Moreover, the seal strength decreases as the temperature of the hot water increases, so 95℃
This is because it shows the lowest seal strength. moreover,
The seal strength when left naturally after heating shows a weaker value after being heated at high temperature, so we determined the seal strength when left naturally after being heated in 95℃ hot water. .

Based on the results of various measurements of the properties of the heat-shrinkable packaging film based on the above conditions, we have determined the conditions that give the heat-shrinkable packaging the following properties and that the heat-shrinkable packaging can be heat-shrinked in hot water. The following describes the results that were found regarding the cause of the bag breaking at the sealed part when the bag was taken out from hot water and left to stand.

Regarding the tightness of heat-shrinkable packaging, the first condition is the heat-shrinkage rate of the heat-shrinkable packaging film used, which must shrink by 10% or more in both the vertical and horizontal directions in hot water at 80°C. It is. If the heat shrinkage rate is less than 10%, the diameter of the heat shrink packaging bag should be set to a size that makes it easier to insert the bag compared to the outer shape of the contents, so that the temperature is lower for practical packaging. In hot water at 80°C, the amount of shrinkage is insufficient and the contents cannot be held tightly, causing sag in the heat-shrinkable package and, in the case of roasted pork chunks, drippings accumulate.
In other words, the result is a heat-shrinkable package lacking in tightness. Furthermore, if an attempt is made to reduce the diameter of the bag and obtain a package with tightness through heat shrinkage in 80° C. hot water, it will become extremely difficult to insert the contents. However, if the heat shrinkage rate exceeds 10%, the bag has a diameter that makes it easy to insert the contents, and it also has sufficient heat shrinkage in hot water at 80°C, which is a low temperature for practical packaging. A heat-shrinkable package with excellent tightness can be obtained. In addition, when heat-shrinking in hot water of 80°C or higher, the heat-shrinkable packaging film exhibits a higher heat shrinkage rate than that in hot water of 80°C, so the above-mentioned
If the shrinkage rate conditions in hot water of 80°C are satisfied, a good heat-shrinkable package with excellent tightness can be obtained in hot water of 80°C or higher.

The second condition is the heat shrinkage stress of the heat shrink packaging film used, which must be 50 g/cm or more in both the longitudinal and transverse directions in hot water at 80°C. If the heat shrinkage stress is less than 50 g/cm, even if the heat shrinkage rate exceeds 10%, it will not be possible to tightly hold the contents during heat shrinkage in 80°C hot water. , an unshrinkable film remains around the contents, causing sagging in the package. The reason for this is that the heat-shrinkable packaging film is in close contact with the contents during vacuum packaging, and if the heat-shrinkable stress of the film is weak, the film will not be able to fully shrink. That is, it is thought that this is because the heat-shrinkable packaging film that has come into close contact with the contents due to vacuum packaging does not have the strength to pull the wrinkled film and try to further heat-shrink it. However, the heat shrinkage stress is 50g/cm
If the value exceeds , the film will not sag in the package due to heat shrinkage in hot water, and there will be no film remaining around the contents, resulting in heat-shrinkable packaging with excellent tightness. Becomes a body. This is because the heat-shrinkable packaging film has strong heat shrinkage stress, so the packaging material not only tightly tightens the contents, but also, as mentioned above, does not leave any film that cannot be completely heat-shrinked around the contents. It seems to have excellent tracking performance.

The third condition is that after the heat-shrink packaging body is heat-shrinked in hot water, when it is taken out from the hot water and left to stand naturally, the shrinkage stress of the heat-shrink packaging film is
It is necessary to make the stress stronger than the heat shrinkage stress in hot water in order to maintain the tightness of the package over time. That is, when the contents such as pieces of grilled pork are heated, they expand to some extent, and in this expanded state, the tightness during heating contraction is maintained. However, when the heat-shrinkable package is taken out of the hot water and cooled, the contents such as grilled pork chunks will shrink and the volume will become somewhat smaller. Therefore, if the heat-shrinkable packaging film has the ability to shrink as the volume of the contents decreases, the heat-shrinkable packaging can maintain its tightness even after cooling.

Regarding the causes of bag breakage at the sealed portion of a heat-shrinkable package, first, the causes of bag breakage when the heat-shrinkable package is heat-shrinked in hot water are considered to be as follows. That is, the seal strength of a heat-shrinkable packaging film decreases significantly when heated in hot water, and the higher the heating temperature, the more the seal strength decreases.
In particular, in hot water at a temperature higher than the melting point of the sealant material, the decrease is remarkable. When the heat-shrinkable packaging body is heat-shrinked in hot water, if the seal strength of the heat-shrinkable packaging body in hot water becomes weaker than the heat-shrinkage stress of the film, it will be torn at the sealed portion and the bag will break. This is thought to occur. Therefore, in order to prevent the bag from breaking at the sealed portion when the heat-shrinkable package is heated in hot water, it is necessary to meet the following conditions. In other words, in the temperature range of 80°C to 95°C hot water in which heat-shrinkable packaging of pieces of grilled pork etc. is actually carried out, the sealing strength is the lowest in the 95°C hot water. indicates the highest value. Therefore, we decided to increase the seal strength in hot water at 95℃.
It is necessary to make the stress stronger than the thermal shrinkage stress in hot water in order to prevent bag breakage in all hot water temperature ranges. However, as described above, the heat shrinkage stress of the heat shrink packaging film must satisfy the above conditions in order to provide tightness to the package.

Next, when the heat-shrinkable package that has been heat-shrinked in hot water is taken out from the hot water and left to stand, the reason why the bag breaks at the sealed portion is considered to be as follows. In other words, the seal strength of the heat-shrinkable packaging when placed under the same conditions is higher than the shrinkage stress when the heat-shrinkable packaging film is heated in hot water and then left to stand. It is thought that the rupture occurs due to the weakness of the The reasons for this are that the sealant layer of the heat-shrink packaging film has poor heat resistance and water resistance, and the seal strength decreases after heating in hot water, and that the heat-shrink packaging film is heated in hot water. After that, it is thought that the shrinkage stress gradually increases when the product is left alone. Due to the shrinkage stress, heating in high temperature hot water shows stronger shrinkage stress. On the other hand, the seal strength shows a weaker seal strength when heated in hot water at a higher temperature. From the above, in light of practical packaging, it is necessary to ensure that the shrinkage stress when heated in hot water at 95°C and left alone is not stronger than the seal strength under the above conditions. As mentioned above, the shrinkage stress gradually increases when a heat-shrinkable packaging film is heated in hot water and then taken out from the hot water and left to stand. This is a necessary characteristic from this point of view.

(Summary of the Invention) In the first invention of the present application, one of the outermost layers is a polyamide resin layer (A), at least one intermediate layer is a thermoplastic resin layer (B) having excellent oxygen barrier properties, and the other layer is a polyamide resin layer (A). The outermost layer is a heat-sealable thermoplastic resin layer.
(C) A coextruded biaxially stretched film consisting of 80
Thermal contraction rate in hot water at ℃ is 10 in both longitudinal and transverse directions.
% or more, the heat shrinkage stress in hot water at 80°C is 50 g/cm or more in both the longitudinal and lateral directions, and the seal strength of the film in hot water at 95°C is 95°C or more. In addition, the seal strength of the film when left to stand naturally after being heated in 95°C hot water is
This is a heat-shrinkable packaging film that is stronger than the shrinkage stress that occurs when it is left naturally after being heated in hot water at 95°C. Further, in the second invention of the present application, one of the outermost layers is a polyamide resin layer (A), and at least one intermediate layer is a thermoplastic resin layer with excellent oxygen barrier properties.
In (B), however, the other outermost layer is a coextruded biaxially stretched film consisting of a heat-sealable thermoplastic resin layer (C), and the heat shrinkage rate in hot water at 80°C is in the longitudinal direction. , 10% or more in both the transverse direction, a heat shrinkage stress of 50 g/cm or more in both the longitudinal and transverse directions in hot water at 80°C, and the seal strength of the film in hot water at 95°C, It is stronger than the heat shrinkage stress of the film in 95°C hot water, and the sealing strength of the film when left naturally after heating in 95°C hot water is higher than that of the film in 95°C hot water. After being heated in a vacuum, a bag is made using a heat-shrinkable packaging film that is stronger than the shrinkage stress when left alone, the bag is filled with the packaged item, and after vacuum packaging, it is heated and shrunk in hot water. This is a package characterized by being sterilized.

The heat-shrinkable packaging film of the first invention of the present application and the heat-shrinkable packaging film used for the package of the second invention of the present application (these films are collectively referred to hereinafter simply as "the heat-shrinkable packaging film of the present application") are: ,
In order to increase the mechanical strength and maintain the tightness even after being heat-shrink wrapped in hot water and left in a natural state, the heat-shrink stress of the present invention, each seal strength, etc. In order to easily satisfy the above conditions, a polyamide resin is used as the resin for one of the outermost layers. In this case, it is desirable to include a copolymer layer of nylon-6 and nylon-66 in order to further improve the heat shrinkage rate of the resulting heat-shrink packaging film. By providing a polyamide resin layer as one of the outermost layers, the unique phenomenon that shrinkage stress gradually increases when a heat-shrinkable packaging film is heated in hot water and then taken out from the hot water and left to stand naturally, can be avoided. It can be demonstrated. This phenomenon is particularly preferable from the viewpoint of maintaining tightness even when the heat-shrinkable packaging body is heated in hot water and then left to stand. This phenomenon in which shrinkage stress gradually increases when left alone is thought to be due to the surface polyamide resin layer evaporating moisture absorbed during heating in hot water and increasing shrinkage stress as it dries. .

In addition, the shrinkage stress that increases when left to stand naturally after heating in hot water and the heat shrinkage stress that occurs in hot water during heating can be reduced by changing the resin composition, thickness, etc. of the polyamide resin layer. You can change it in many ways.

Furthermore, the heat-shrinkable packaging film of the present invention has at least one oxygen-blocking resin layer (for example, a vinylidene chloride resin layer or a saponified ethylene-vinyl acetate copolymer layer) in order to preserve contents such as roast pork chunks for a long time. It is contained as an intermediate layer.

The sealing strength of the heat-shrink packaging film of the present invention in hot water is largely influenced by the type of sealant material. That is, it is preferable that the sealant material has excellent water resistance and has a high melting point, since this increases the sealing strength in hot water. In particular, if the temperature of the hot water exceeds the melting point of the sealant, the sealing strength will drop sharply, so it is preferable that the melting point of the sealant is higher than the temperature of the hot water. Therefore, since heat shrink packaging in practical use shrinks and sterilizes in hot water in the temperature range of 80°C to 95°C, it is necessary to use a resin with a melting point of 95°C or higher as the sealant material layer. It is. Based on the above, the resin used for the sealant layer is low-density polyethylene, linear low-density polyethylene, ethylene-vinyl acetate copolymer, or ionomer resin, which has excellent water resistance and has a melting point of 95°C or higher. Ru. Furthermore, since the heat-shrinkable packaging film of the present invention is coextruded and biaxially stretched, polar groups are graft-copolymerized in order to improve adhesion with the intermediate layer, a thermoplastic resin layer (B) with excellent oxygen barrier properties. It is preferable to use modified low-density polyethylene, modified linear low-density polyethylene, modified ethylene-vinyl acetate copolymer, or the like.

In addition, an adhesive layer made of the above-mentioned modified polyethylene is provided between the heat-sealable thermoplastic resin layer (C) made of the above-mentioned low-density polyethylene and the intermediate layer (B) of the thermoplastic resin layer with excellent oxygen barrier properties. This is a preferred method in terms of improving seal strength.

The heat shrinkage rate, heat shrinkage stress, shrinkage stress when left unused, etc. of the present heat-shrink packaging film can be changed depending on the type of polyamide resin, the thickness of the layer, etc. as described above, but production conditions ,for example,
It can also be changed by the stretching conditions such as the stretching ratio and stretching temperature, and the heat treatment conditions such as the heat treatment temperature and relaxation rate. Furthermore, it can also be changed depending on the type and thickness of the resin constituting layers other than the polyamide resin layer of the heat-shrink packaging film.

The heat-shrink packaging film of the present invention is produced by biaxially stretching a coextruded original film, and is produced by the following method. That is, a multilayer sheet having the structure of the heat-shrinkable packaging film of the present invention is coextruded from a laminated die using a plurality of extruders, and after the multilayer sheet is cooled and solidified, it is reheated to a temperature at which it can be stretched. Stretch at least 2.0 times or more in both the longitudinal and transverse directions. The stretching method can be either the tenter method or the inflation method, but it is preferable to make bags for packaging roasted pork chunks etc. from tube-shaped film, and it is also possible to use the tenter method or the inflation method. The inflation method is more preferable because it is easy to maintain the same amount of contraction. In view of the above, it is preferable that the multilayer sheet before stretching is extruded into a tube shape using a multilayer circular die and laminated so that the outermost layer is a polyamide resin layer. moreover,
It is natural from the viewpoint of bag manufacturing that the sealant material layer is the innermost layer. In addition, when saponified ethylene-vinyl acetate copolymer is used as the oxygen-barrier resin, the resin can be melt-bonded with polyamide resin, but low-density polyethylene resin, linear low-density polyethylene resin, or It is difficult to melt and bond with resins such as , ethylene-vinyl acetate copolymer. Therefore, modified low-density polyethylene resins, modified linear low-density polyethylene resins, modified ethylene-vinyl acetate copolymers, etc. in which polar groups are graft-copolymerized are used as the sealant material layer, or these modified resins are used as sealant material layers. The above-mentioned resin is provided as a sealant material layer via. Furthermore, if the stretched coextruded laminated stretched film is left to naturally stand, the natural shrinkage of the film will cause deformation and deterioration of the surface condition over time. Therefore, in order to prevent this, it is more preferable to reduce the amount of natural shrinkage by performing heat treatment to an extent that does not deviate from the range of heat shrinkage rate and heat shrinkage stress that are the requirements of the present application.

The total thickness of the heat shrink packaging film of the present application is as follows:
When used as packaging for processed meat products such as roasted pork chunks, 30μ to 100μ is appropriate.

The package using the heat-shrink packaging film of the second invention of the present application is preferably packaged by the following method. In other words, packaged items such as roasted pork chunks,
Using the heat-shrinkable packaging film of the present invention, the bag is filled with a polyamide resin layer on the outside and a heat-sealable thermoplastic resin layer on the inside, and after the inside is degassed, the opening is closed. Heat seal. Then, the package is immersed in hot water at 80° C. to 95° C. for 5 to 20 minutes to simultaneously perform heat shrinkage and heat sterilization, and then taken out from the hot water and cooled with water.

(Effects of the Invention) The heat-shrinkable packaging film of the present invention can easily heat-shrink-wrap roasted pork chunks or other contents that have a constant shape, and the heat-shrinkable packaging film can heat-shrink and wrap the contents. Since the film adheres closely and has no creases or creases, they are very small, resulting in a package with a good appearance. Furthermore, the shrink packaging film of the present invention has excellent oxygen barrier properties, and the contents are heat sterilized in the process of heating and shrinking the package in hot water, making it possible to preserve the contents for a long time. I can do it.

In particular, the packaging body using the heat-shrinkable packaging film of the present invention has excellent tightness after heat-shrinking, even if the packaging bag is made larger so that the contents can be easily filled. The main feature is that the unshrinked film does not easily remain around the contents, so it looks good. An even more significant feature is that the bag does not break at the sealing part of the package when it is shrinked after being heated in hot water, or when it is left to naturally stand after being heated and shrunk. There is no need to select various bag sizes, etc., and the packaging process can be carried out smoothly.

Example 1 Copolymer of nylon-6 and nylon-66 (Toray Co., Ltd.)
Amilan CM-6041 (manufactured by Mitsui Petrochemical Industries, Ltd.), saponified ethylene-vinyl acetate copolymer (Soarnol ET, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.), and modified linear low-density polyethylene (Admar NF550, manufactured by Mitsui Petrochemical Industries, Ltd.). )
Using three extruders, a multilayer circular die was used to obtain a laminated, unstretched tube in which the resin was placed in the order from the outermost layer to the outermost layer. The unstretched tube was laminated and stretched by the conventional inflation biaxial stretching method, and the thickness of each layer was 12 μ/8 μ/1 from the outermost layer.
A heat-shrinkable packaging film having a thickness of 20μ was obtained. The heat-shrink packaging film is made so that the outer layer is a polyamide resin layer made of a copolymer of nylon-6 and nylon-66, and the inner layer is a heat-sealable thermoplastic resin layer made of modified linear low-density polyethylene. Vacuum-pack roasted pork chunks in a bag and place them in hot water at 90℃ for 20 minutes.
A packaging test was conducted in which heat shrinkage and sterilization were performed for minutes. As a result, in the package, the heat-shrinkable packaging film and the contents are in close contact with each other, the film has no creases, and no film that has not been completely heat-shrinked remains around the contents, so that it can be kept under tight conditions in hot water. It was excellent not only in tracking performance but also in tracking performance when left in the wild. Furthermore, the package did not break at the sealed portion when it was heated in hot water or when it was taken out from hot water and left to stand.

The heat shrinkage rates of this heat-shrink packaging film in 80°C hot water in the longitudinal and transverse directions are 23% and 22%, respectively.
%, and the heat shrinkage stress in hot water at 80°C was 78 g/cm and 74 g/cm in the longitudinal and transverse directions, respectively. Furthermore, the sealing strength of the heat-shrink packaging film in hot water at 95°C is 176 g/cm, and the heat shrinkage stress in the longitudinal and lateral directions in hot water at 95°C is 125 g/cm.
It showed a value stronger than 117g/cm. In addition, the seal strength of the heat-shrinkable packaging film after heating in hot water at 95°C and when left naturally is 1740g/cm, 95
The shrinkage stress in the longitudinal and transverse directions was 360 g/cm, which was much stronger than the 340 g/cm when it was left to stand naturally after being heated in hot water at ℃.

Example 2 Nylon-6 (Amilan CM- manufactured by Toray Industries, Inc.)
1021), saponified ethylene-vinyl acetate copolymer,
Using four extruders, modified linear low-density polyethylene and further linear low-density polyethylene (Mitsui Petrochemical Industries, Ltd. Ultxex 2020L) were processed using a multilayer circular die in such a way that the above resins were placed in the order starting from the outermost layer. A laminated unstretched tube was obtained. The unstretched tube was laminated and stretched by the inflation biaxial stretching method in the same manner as in Example 1 to obtain a heat-shrinkable packaging film in which the thickness of each layer was 12μ/8μ/5μ/20μ from the outermost layer. Using the obtained heat-shrinkable packaging film, a heat-shrinkable packaging test was conducted on roasted pork chunks in hot water at 95°C for 5 minutes in the same manner as in Example 1. As a result, as in Example 1, a package with excellent tightness and good appearance was obtained. Even when the package was heated in hot water, or when it was taken out from hot water and left to stand, the package did not break at the sealed portion.

The heat shrinkage rates of the heat shrink packaging film in the longitudinal and transverse directions in hot water at 80°C are 16% and 14%, respectively.
%, and the heat shrinkage stress in hot water at 80°C was 63 g/cm and 58 g/cm in the longitudinal and transverse directions, respectively. Furthermore, the sealing strength of the heat-shrink packaging film in hot water at 95°C is 340g/cm, and the sealing strength at 95°C
Longitudinal and transverse thermal shrinkage stress in hot water of 108
g/cm, which was much stronger than 102 g/cm. In addition, the sealing strength of this heat-shrinkable packaging film is strong when it is left to stand after being heated in hot water at 95°C, with a seal strength of 2170g/cm, and when it is left to stand after being heated in hot water at 95°C. Shrinkage stress in longitudinal and transverse directions when
It showed a value of 240g/cm, which was much stronger than 240g/cm.

Comparative Example 1 A 15μ thick heat-shrinkable packaging film made of nylon-6, a 10μ thick unstretched ethylene-vinyl acetate copolymer saponified film, and a 35μ thick unstretched film.
A low-density polyethylene (Sumikasen F-208 manufactured by Sumitomo Chemical Co., Ltd.) film is laminated in the above film order by a conventional dry lamination method,
A heat-shrinkable packaging film was obtained. Using the obtained heat-shrinkable packaging film, a heat-shrinkable packaging test was conducted using roasted pork chunks in hot water at 80°C in the same manner as in Example 1. As a result, in the package, the heat-shrinkable packaging film does not adhere sufficiently to the contents, the film has many folds and wrinkles, and moreover, there is a lot of film that has not been completely heat-shrinked left around the contents, resulting in a poor appearance. It lacked urgency.

The heat shrinkage rates of the heat shrink packaging film in the longitudinal and transverse directions in hot water at 80°C are 8% and 7%, respectively.
%, and the heat shrinkage stress in hot water at 80° C. was 32 g/cm and 29 g/cm in the longitudinal and transverse directions, respectively, which did not satisfy the conditions of each invention of the present application. However, the seal strength in hot water at 95℃ is 280
g/cm, the thermal shrinkage stress in the longitudinal and transverse directions in 95℃ hot water is 52g/cm, which is stronger than 48g/cm, and after heating in 95℃ hot water, The seal strength when left alone is 1860 g/cm, and the shrinkage stress in the longitudinal and lateral directions under the same conditions is 177 g/cm and 165
g/cm, and both showed the same values as in each invention of the present application.

Comparative Example 2 A copolymer of nylon-6 and nylon-66, a saponified ethylene-vinyl acetate copolymer, and a modified ethylene-vinyl acetate copolymer (Novatec AP-112E manufactured by Mitsubishi Chemical Corporation) were used. A heat-shrinkable packaging film having a thickness of 15μ/8μ/17μ from the outermost layer was obtained by coextrusion and inflation in the same manner as in Example 1. Using the obtained heat-shrinkable packaging film, a heat-shrinkable packaging test was conducted on roasted pork chunks in hot water at 95°C and 90°C in the same manner as in Example 1. As a result, rupture occurred at the sealed portion during heat shrinkage not only at 95°C but also at 90°C.

The heat shrink stress of the heat shrink packaging film in the longitudinal and transverse directions in hot water at 95°C is 142 g/cm and 140 g/cm.
In terms of g/cm, the seal strength in hot water at 95°C was weaker than the heat shrinkage stress and could not be measured because it broke when immersed in hot water. Furthermore, even in hot water at 90°C, the seal strength was weaker than the heat shrinkage stress and could not be measured. However, the thermal shrinkage rates in the longitudinal and transverse directions in hot water at 80°C are 25% and 24%, and the thermal shrinkage stress in the longitudinal and transverse directions in hot water at 80°C is 88 g/ cm and 86 g/cm, both of which showed the same values as in each invention of the present application. Furthermore, after heating in hot water at 95℃, the shrinkage stress in the vertical and horizontal directions is 179, respectively.
g/cm and 172 g/cm, but the seal strength could not be measured because it broke when immersed in hot water.

Comparative Example 3 A copolymer of nylon-6 and nylon-66,
A saponified ethylene-vinyl acetate copolymer and a laminated heat-shrinkable film were obtained by an inflation biaxial stretching method. Then, a film of ethylene-vinyl acetate copolymer (Ebatate D-2021F manufactured by Sumitomo Chemical Co., Ltd.) was dry laminated on the saponified ethylene-vinyl acetate copolymer layer side of the laminated heat-shrinkable film, and polyamide resin was 15μ/5μ/ from layer side
A heat-shrinkable packaging film having a thickness of 20μ was obtained. Using the obtained heat shrink packaging film,
Similar to Example 1, a heat shrink packaging test was carried out using roasted pork chunks.
The experiments were carried out in hot water at ℃. As a result, as in Comparative Example 2, the bag broke at the sealed portion during heat shrinkage in hot water.

The melting point of the ethylene-vinyl acetate copolymer film used for the heat-shrink packaging film was 95°C or lower. In addition, the temperature of the heat shrink packaging film at 95℃
The longitudinal and transverse thermal shrinkage stress in hot water is 102
g/cm and 97 g/cm, the seal strength in hot water at 95°C was weaker than the heat shrinkage stress and could not be measured. However, the thermal shrinkage rates in the longitudinal and transverse directions in hot water at 80°C are 18% and 20%, and the thermal shrinkage stress in the longitudinal and transverse directions in hot water at 80°C is 68 g/ cm
and 71 g/cm, both of which show the same values as in each invention of the present application. Furthermore, after heating in hot water at 95°C, the shrinkage stress in the longitudinal and transverse directions when left to stand was 145 g/cm and 150 g/cm, respectively, but the seal strength could not be measured.

Comparative Example 4 An emulsion type vinyl acetate resin was part-coated as a sealant on the saponified ethylene-vinyl acetate copolymer layer side of the laminated heat-shrinkable film obtained in Comparative Example 3, and a heat-shrinkable packaging film was prepared. Obtained. Using the heat-shrinkable packaging film, a heat-shrinkable packaging test was conducted on roasted pork chunks in hot water at 95°C in the same manner as in Example 1. As a result, the bag did not break at the sealed part during heat shrinkage in hot water, but the bag did break at the sealed part when it was taken out of the hot water and left to stand.

The shrinkage stress in the longitudinal and lateral directions of the heat-shrinkable packaging film after heating in 95°C hot water and being left to stand naturally is 440 g/cm and 420 g/cm, and the sealing stress under the same conditions is 440 g/cm and 420 g/cm, respectively. The strength was weaker than the shrinkage stress and could not be measured because it would break when left alone. However, the thermal shrinkage rates in the longitudinal and transverse directions in hot water at 80°C are 27% and 28%, and the thermal shrinkage stress in the longitudinal and transverse directions in hot water at 80°C is 90g/
cm and 93 g/cm, both of which showed the same values as in each invention of the present application. Furthermore, the seal strength in hot water at 95°C was 220 g/cm, and the shrinkage stresses in the longitudinal and lateral directions were 186 g/cm and 191 g/cm, which are similar to the values in each invention. .

Comparative Example 5 Modified linear low-density polyethylene, a copolymer of nylon-6 and nylon-66, a saponified ethylene-vinyl acetate copolymer, and a modified linear low-density polyethylene were produced using four extruders. A multilayer circular die was used to obtain a laminated, unstretched tube in which the resins were stacked in the order of the outermost layer. The unstretched tube was laminated and stretched by the inflation biaxial stretching method in the same manner as in Example 1 to obtain a heat-shrinkable packaging film in which the thickness of each layer was 10μ/12μ/8μ/20μ from the outermost layer. Using the obtained heat-shrinkable packaging film, a heat-shrinkable packaging test was conducted in hot water at 95° C. using grilled pork chunks in the same manner as in Example 1. As a result, a good package was obtained that had good tensile properties immediately after heat-shrink packaging, but when the chunks of grilled pork that were packaged were left to stand for 5 hours and cooled, wrinkles appeared in the film and the film became tight. It was inferior in performance and looked bad.

In addition, the heat shrinkage rate and heat shrinkage stress of the heat shrinkable packaging film, the relationship between shrinkage stress and seal strength in hot water, and the relationship between shrinkage stress and seal strength when left naturally after heating, etc. Although the conditions of the present invention were satisfied, since the outside of the bag was not a polyamide resin layer, no increase in shrinkage stress was observed when the bag was left to stand naturally after heating, compared to the shrinkage stress during heating.

Claims (1)

[Claims] 1. One outermost layer is a polyamide resin layer (A), at least one intermediate layer is a thermoplastic resin layer (B) with excellent oxygen barrier properties, but the other outermost layer is A coextruded biaxially stretched film consisting of a sealable thermoplastic resin layer (C), which has a heat shrinkage rate of 10% or more in both longitudinal and transverse directions in hot water at 80°C. The heat shrinkage stress inside is 50 in both the vertical and horizontal directions.
g/cm or more, and furthermore, the sealing strength of the film in 95°C hot water is stronger than the heat shrinkage stress of the film in 95°C hot water, and further, the sealing strength of the film in 95°C hot water is Heat-shrink packaging characterized in that the sealing strength when the film is left to stand after being heated in water at 95°C is stronger than the shrinkage stress of the film when it is left to stand after being heated in hot water at 95°C. film for use. 2. Claim 1, wherein the polyamide resin layer (A) is a copolymer of nylon-6 and nylon-66.
Heat-shrinkable packaging film as described in Section 1. 3. The heat-shrinkable packaging according to claims 1 and 2, wherein the thermoplastic resin layer (B) with excellent oxygen barrier properties is a vinylidene chloride resin or a saponified ethylene-vinyl acetate copolymer. film for use. 4. Claim 1, wherein the heat-sealable thermoplastic resin layer (C) is low-density polyethylene with a melting point of 95°C or higher, linear low-density polyethylene, ethylene-vinyl acetate copolymer, or ionomer resin.
A heat-shrinkable packaging film according to items 1 to 3. 5 Low-density polyethylene, linear low-density polyethylene, or modified low-density polyethylene in which a polar group is graft-copolymerized with an ethylene-vinyl acetate copolymer, modified linear low-density polyethylene, Alternatively, the heat-shrinkable packaging film according to claims 1 to 4, which is a modified ethylene-vinyl acetate copolymer. 6 One outermost layer is a polyamide resin layer (A), at least one intermediate layer is a thermoplastic resin layer (B) with excellent oxygen barrier properties, and the other outermost layer is a heat-sealable thermoplastic resin. A coextruded biaxially stretched film consisting of layer (C), which has a heat shrinkage rate of 10% or more in both the longitudinal and transverse directions in hot water at 80°C, and has a heat shrinkage stress in hot water at 80°C. is 50 in both vertical and horizontal directions
g/cm or more, and the sealing strength of the film in 95°C hot water is stronger than the heat shrinkage stress of the film in 95°C hot water, and
A heat-shrinkable packaging film whose sealing strength when left in hot water at 95°C is stronger than the shrinkage stress when the film is left out after heating in hot water at 95°C. The bag is made with a polyamide resin layer (A) on the outside and a heat-sealable thermoplastic resin layer (C) on the inside, the bag is filled with the items to be packaged, and after vacuum packaging, it is placed in hot water. A packaging body characterized by being subjected to heat shrinkage and sterilization.