JP3207500B2 - Laminated film for retort food packaging - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated film for retort food packaging which can be retorted at 120 DEG C. using a linear ethylene-.alpha.-olefin copolymer for a seal layer.

[0002]

2. Description of the Related Art Conventionally, for packaging of retort foods, laminated films comprising a base material layer such as a polyester resin film, a polyamide resin film, an ethylene-vinyl alcohol copolymer film, an aluminum foil and a polyolefin resin-based sealant layer have been widely used. Used. In particular, since the retort treatment sterilizes by heating at about 120 ° C. for about 30 minutes, the heat resistance of the sealant layer of the laminated film used for the above purpose is also required to be 120 ° C. or more. For this reason, as the sealant layer, a polypropylene resin or a high-density polyethylene resin having good heat resistance and heat sealing properties is used.

However, in the case of a laminated film for retort food packaging, the ratio of the sealant layer to the total thickness of the laminated film is large in order to obtain a certain degree of sealing strength. When a resin having low impact strength at the time is used as the sealant layer, there is a problem that the packaging bag is broken at the time of low-temperature transportation or the like.

[0004] In addition to the above problems, when a propylene-ethylene random copolymer is used as the sealant layer as the polypropylene resin, the heat of the retort treatment causes the sealant layers to be thermally fused to each other, resulting in poor openability. The disadvantage that it is difficult to remove the contents is that when a propylene-ethylene block copolymer or a high-density polyethylene resin is used as the sealant layer, the transparency is somewhat poor, so that it cannot be used for transparent packaging. .

On the other hand, linear ethylene-α-olefin copolymers are excellent in transparency, impact strength at low temperatures and seal strength, and have been conventionally used as sealant layers for sterilizing boil up to 100 ° C. . However, when the retort treatment is performed at a high temperature of as high as 120 ° C. because the melting point is as low as about 125 ° C., the sealant layers are more easily heat-sealed with each other than in the case of the propylene-ethylene random copolymer. Could not be used as.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a linear ethylene-α which cannot be used as a sealant layer of a laminated film for retort food packaging which can be conventionally used for a retort treatment at 120 ° C. -An object of the present invention is to provide a laminated film for retort food packaging having excellent impact resistance, heat-sealing resistance and transparency using an olefin copolymer.

[0007]

According to the present invention, the sealant layer comprises a linear ethylene-α-olefin copolymer having a density of 0.930 to 0.945 g / cm ³ containing an antiblocking agent of 0.4% by weight or more. A laminate film for retort food packaging, characterized in that the sealant layer has a multilayer structure, and the sealing surface layer of the sealant layer has a density of 0.930 to 0.945 g in which an antiblocking agent is added in an amount of 0.4% by weight or more. The present invention provides a laminated film for packaging a retort food, wherein the laminated film is made of a linear ethylene-α-olefin copolymer having a thickness of / cm ³ and the other layer is made of a polyolefin resin.

[0008] That is, linear ethylene-α-α which has been conventionally considered to be unusable due to thermal fusion during retort treatment.
The olefin copolymer has a specific density of linear ethylene-
It has been found that by adding a specific amount of an antiblocking agent to an α-olefin copolymer, it can be suitably used as a sealant layer of a laminated film for retort food packaging, and the present invention has been accomplished.

Further, when the sealant layer has a multilayer structure and a specific amount of an antiblocking agent is added to the sealing surface layer of the sealant layer, the antiblocking agent may be used only for the sealing surface layer. It has been found that the amount can be reduced and various functions can be imparted to the sealant layer, so that the transparency can be further improved.

The linear ethylene-α-olefin copolymer used in the present invention is not particularly limited. However, when impact resistance is particularly required, ethylene having 6 to 8 carbon atoms may be used.
-An olefin, for example, hexene-1, 4-methylpentene-1, octene-1 is preferably used. Linear ethylene-α-olefin copolymers of various densities are commercially available, but usually, the higher the density, the higher the melting point and the higher the heat-fusible property, but the lower the impact resistance and transparency. . Therefore, the density of the linear ethylene-α-olefin copolymer must be 0.930 to 0.94 in order to satisfy a good balance of heat fusion resistance, impact resistance and transparency.
It must be in the range of 5 g / cm ³ . Density 0.930
If the amount is less than g / cm ^{3, the} heat-fusing property cannot be improved even if an antiblocking agent is added in an amount described below, which is not preferable. Conversely, when the density exceeds 0.945 g / cm ³ , the impact resistance and transparency are lowered, and the heat sealability is deteriorated. Further, the linear ethylene-α
The melt flow rate of the olefin copolymer is from 0.5 to
The case of 3.0 g / 10min is preferred. Melt flow rate
If it is less than 0.5 g / 10min, there is a problem in moldability, and conversely
If it exceeds 3.0 g / 10min, the impact strength is undesirably reduced.

When the sealant layer has a multilayer structure, the polyolefin resin used for the other layer may be a resin selected from ethylene-based polymers or copolymers, or propylene-based polymers or copolymers. They can be used alone or as a mixture. In addition, the other layer may be composed of two or more layers for the purpose of exhibiting various characteristics. In such a configuration, it is most preferable to use the same linear ethylene-α-olefin copolymer as the seal surface layer as the other layer from the viewpoint of interlayer adhesion, seal strength, and impact resistance in the sealant layer.

As the antiblocking agent, silica, silicone, zeolite, talc and the like which are generally used can be used. The addition amount must be 0.4% by weight or more, but it is desirable to add 0.8 to 3.0% by weight. When the addition amount is less than 0.4% by weight (the addition amount of the antiblocking agent to the ordinary synthetic resin is 0.1 to 0.2% by weight), the heat-fusing property becomes insufficient. On the other hand, the upper limit of the addition amount is not particularly specified, but if the addition amount exceeds 5.0% by weight, transparency deteriorates, and it is difficult to use in applications requiring transparency, which is not preferable.

Further, within a range not to impair the object of the present invention,
Additives such as a lubricant and an antioxidant which are usually added to a polyolefin-based film may be added.

The laminated film for packaging a retort food of the present invention can be produced by the following various laminating methods. That is, dry lamination, sand lamination,
Coextrusion, extrusion lamination and the like. In the dry lamination method, it is manufactured by laminating various base films and a sealant film having the structure of the present invention using an adhesive represented by a urethane-based adhesive or the like. In the co-extrusion method, it is manufactured by a usual method except that the sealant layer has the constitution of the present invention.

In particular, when the above-mentioned dry laminating method is employed, the sealant film is obtained by subjecting an ethylene-α-olefin copolymer having the above-mentioned composition to which an anti-blocking agent has been added, to a conventional extrusion molding method such as an inflation method or a T-die method. Can be manufactured. When the sealant layer has a multi-layer structure, the density of the sealant film added with 0.4% by weight or more of an antiblocking agent is 0.930 to 0.945 g /.
It can be produced by co-extrusion of a linear ethylene-α-olefin copolymer having a cm ³ and a polyolefin resin.

The thickness of the sealant layer of the thus obtained laminated film for retort food packaging is from 40 to 1
About 00μ is preferable. When the thickness of the sealant layer is less than 40 μm, the sealing strength is weakened, which is not preferable. On the contrary, when the thickness exceeds 100 μm, the thickness of the entire laminated film is undesirably too large. When the sealant layer has a multilayer structure, the thickness of the sealing surface layer may be any thickness as long as it is within the range of the thickness of the entire sealant layer, but about 5 to 20 μm is sufficient.

[0017]

The present invention will be described in more detail with reference to the following examples. In addition, the evaluation method of the physical property value in an example and a comparative example is as follows. <Impact resistance> A sample (23 cm) obtained by filling and sealing a bag made of a laminated film with 800 cc of saturated saline solution and sealing.
× 18 cm) after retorting at 120 ° C for 30 minutes.
A 3.4 kg weight was dropped from a height of 22 cm in an atmosphere of 10 ° C., and the average number of times for each sample to break was determined. <Heat-resistant fusing property> A sample (23) obtained by vacuum-sealing a bag manufactured from a
(cm × 18 cm) was subjected to a retort treatment at 120 ° C. for 30 minutes to evaluate whether or not each sample had internal fusion. Evaluation criteria ○: Not fused. ×: Fused. <HAZE> Conforms to ASTM D 1003. The lower the value, the better the transparency. <Seal strength> Measured according to JIS-Z1707.

The raw materials used in the embodiments of the present invention are indicated by the following symbols. L-LDPE1: linear ethylene-α-olefin copolymer (α
-Olefin = octene-1, melt flow rate 1.0g
/ 10 min, density 0.940 g / cm ³ ) L-LDPE2: linear ethylene-α-olefin copolymer (α
-Olefin = octene-1, melt flow rate 1.0g
/ 10 min, density 0.935 g / cm ³ ) L-LDPE3: linear ethylene-α-olefin copolymer (α
- olefin = 4-methylpentene-1, melt flow rate 2.1 g / 10min, density 0.925 g / cm ³⁾ PP1: a propylene - ethylene random copolymer PP2: propylene - ethylene block copolymer

Example 1 L-LDPE1 was added to silica-based antiblocking agent (particle size: 5 μm)
The resin composition containing 1.0% by weight of the resin composition was processed at an inflation molding machine equipped with a die having a die diameter of 300 mm and a die lip of 3.0 mm at a processing temperature of 190 ° C., a blow-up ratio of 1.7 and a thickness of 60 μm
After laminating a sealant film for lamination, a surface serving as an adhesive surface during lamination was subjected to corona discharge treatment so that the surface tension became about 48 dyne / cm. Then, this sealant film is dry-laminated using a biaxially stretched polyamide resin film having a thickness of 15 μm and a urethane-based adhesive, and aged at 40 ° C. for 2 days to obtain a laminated film for packaging a retort food of the present invention. Was.
Table 1 shows the evaluation results.

Example 2 A resin composition obtained by adding 2.0% by weight of the same silica-based antiblocking agent as in Example 1 to L-LDPE2 was used as a sealing surface layer. Similarly, the die diameter was adjusted so that L-LDPE2 became another layer. 300 mm,
Inflation multilayer molding machine equipped with a multilayer die of 3.0 mm die lip, processing temperature 190 ° C, blow-up ratio 1.
7, a sealant film for lamination having a two-layer structure with a thickness of 60 μm was formed. In this case, the thickness composition ratio was 1: 6.
Met. The resulting sealant film was subjected to corona discharge treatment so that the surface to be the adhesive surface (the surface to which the silica-based antiblocking agent was not added) had a surface tension of about 48 dyne / cm. Next, this sealant film was dry-laminated in the same manner as in Example 1 to obtain a laminated film for packaging retort foods of the present invention. Table 1 shows the evaluation results.

Comparative Example 1 A laminated film for retort food packaging was obtained in the same manner as in Example 1 except that no antiblocking agent was added. Table 1 shows the evaluation results.

Comparative Example 2 The same anti-blocking agent as in Example 1 was added to L-LDPE2 for 0.2%.
A laminate film for retort food packaging was obtained in the same manner as in Example 1 except that the resin composition added in an amount of about 10% by weight was used. Table 1 shows the evaluation results.

Comparative Example 3 A retort food packaging laminate film was obtained in the same manner as in Example 1 except that the linear ethylene-α-olefin copolymer was changed to L-LDPE3. Table 1 shows the evaluation results.

Comparative Example 4 An unstretched polypropylene sealant film for retort having a thickness of 60 μm containing a propylene-ethylene random copolymer as a main component was dry-laminated in the same manner as in Example 1 to obtain a laminated film. Table 1 shows the evaluation results.
Shown in

Comparative Example 5 An unstretched polypropylene sealant film for retort having a thickness of 60 μm containing a propylene-ethylene block copolymer as a main component was dry-laminated in the same manner as in Example 1 to obtain a laminated film. Table 1 shows the evaluation results.
Shown in

[0026]

[Table 1]

From the results in Table 1, it can be seen that a polypropylene resin conventionally used was used for the sealant layer of the laminated film for retort food packaging (Comparative Example 4,
5) has poor impact resistance. The density is 0.930 ~ 0.945g / cm ³
Even when the linear ethylene-α-olefin copolymer of Comparative Example 1 was used as the sealant layer (Comparative Examples 1 and 2), the effect of improving the heat-fusible property was not obtained if the amount of the antiblocking agent was small. Further, linear ethylene having a density of less than 0.930 g / cm ³
In the case where the α-olefin copolymer (Comparative Example 3) was used as the sealant layer, it was found that even when an antiblocking agent was added, the heat-fusible property could not be improved.

[0028]

As a result of the present invention, a linear ethylene-α-olefin copolymer, which could not be used as a sealant layer of a laminated film for retort food packaging because of the problem of heat fusibility, was used as a sealant layer. You can now. Therefore, it is possible to easily provide a laminated film for retort food packaging excellent in all of heat resistance, heat resistance, and impact resistance, transparency, and seal strength that can be retorted at 120 ° C. for 30 minutes. Was.

Continuation of the front page (56) References JP-A-2-95849 (JP, A) JP-A-2-163143 (JP, A) JP-A-3-239741 (JP, A) JP-A-2-172737 (JP) JP-A-2-16108 (JP, A) JP-A-60-125622 (JP, A) JP-A-57-64550 (JP, A) JP-A-55-12008 (JP, A) 53-12971 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B32B 1/00-35/00

Claims (2)

(57) [Claims] 1. The sealant layer contains an anti-blocking agent.
A laminated film for food packaging having excellent heat-fusibility, comprising a linear ethylene-α-olefin copolymer having a density of 0.935 to 0.945 g / cm ³ added at 0.8 to 3.0% by weight . 2. The sealant layer has a multilayer structure,
The sealing surface layer of the sealant layer contains an anti-blocking agent.
0.8-3.0 % by weight added, made of a linear ethylene-α-olefin copolymer having a density of 0.935-0.945 g / cm ³ , and the other layer is made of a polyolefin resin. Laminated film for food packaging.