JP2930600B2 - Laminate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a laminate having good gas barrier properties suitable as a packaging material. More specifically, the present invention relates to a laminate in which the gas barrier property is less likely to decrease even by retort treatment.

[Prior Art] Ethylene / vinyl alcohol copolymers having a high vinyl alcohol content are widely used in the food packaging field because of their excellent gas barrier properties. However, there is a disadvantage that the gas barrier property is greatly reduced due to moisture absorption. Particularly in retort food applications, it takes a considerable amount of time for the moisture absorbed during retort treatment to decrease, so that its high gas barrier properties have not been fully utilized. For the purpose of improving the above points, various multilayer packaging materials having an ethylene / vinyl alcohol copolymer as a single layer have been proposed so far, but many of the above-mentioned problems are solved even by such multilayering. Not yet. For example, JP-A-61-179737 discloses a multilayer film of nylon and an ethylene / vinyl alcohol copolymer, and describes that it is suitable as a packaging material for retort pouches. However, even with such a multilayer film, the gas barrier property immediately after the retort treatment is reduced to a considerable extent. Further, such a multilayer film has a disadvantage that it is difficult to obtain a film having good transparency.

[Problems to be Solved by the Invention] In order to improve such a drawback, the present inventors first coextruded a nylon layer containing a partially aromatic polyamide with an ethylene / vinyl alcohol copolymer. Regarding the manufactured composite film, refer to Japanese Patent Application No. 62-31.
No. 2321 proposed. However, in this proposal, the content of the partially aromatic polyamide in the nylon layer was specified to be a certain amount or less from the viewpoint of simultaneously focusing on hot water whitening resistance and pinhole resistance, so that a large amount of partially aromatic polyamide was used. The compounding aspect was excluded.

However, subsequent studies have shown that in the case of partially aromatic polyamides or partially aromatic polyamide compositions containing less than 30% by weight of aliphatic polyamides, such polyamide layers may be coated with ethylene-vinyl alcohol copolymers. It was noted that when laminated on both sides of the layer, the reduction in gas barrier properties after retorting was further reduced. Also, regarding hot water whitening which is a problem depending on the application, it is not so much a problem depending on the heating conditions, and by further providing a polyolefin layer on the outer layer side of such a polyamide layer, the hot water whitening tendency is reduced. It has also been found that this can be reduced and that this method can solve the problems associated with hydrothermal treatment.

Accordingly, an object of the present invention is to provide a laminate which is particularly suitable for retort food packaging and has a small decrease in gas barrier performance even when exposed to a high-temperature humidified atmosphere.

[Means for Solving the Problems] According to the present invention, 10 to 40% of terephthalic acid and 10 to 40% of terephthalic acid are provided on both sides of a core layer made of an ethylene / vinyl alcohol copolymer having a vinyl alcohol content in the range of 40 to 85 mol%. Amorphous partially aromatic polyamide layer formed from aromatic dicarboxylic acid consisting of 60 to 90% isophthalic acid and aliphatic or alicyclic diamine, or partially aromatic containing aliphatic polyamide in a proportion of less than 30% by weight There is provided a laminate comprising a group-A polyamide composition layer, and a polyolefin layer further provided outside the partially aromatic polyamide or polyamide composition.

The ethylene / vinyl alcohol copolymer constituting the core layer of the present invention has a vinyl alcohol content of 40 to 85% by mole, preferably 50 to 70% by mole, and the other monomer contains 10% by mole. %, It may be contained as a copolymer component. An optimal method for producing such a copolymer is a method of saponifying an ethylene-vinyl acetate copolymer having a vinyl acetate content of about 40 to 95 mol% to a saponification degree of 90 to 100%. is there. If the vinyl alcohol content in the copolymer is more than the above range, heat resistance is poor, and if the amount is less than the above range, gas barrier properties and mechanical properties are undesirably reduced.
An additive which is usually added to the ethylene / vinyl alcohol copolymer may be blended. For the purpose of improving the processability of the ethylene / vinyl alcohol copolymer, a small amount of an ethylene / vinyl alcohol copolymer having a vinyl alcohol content lower than the above range may be blended.

In the present invention, the ethylene / vinyl alcohol copolymer layer is used as a core layer, and a partially aromatic polyamide or a partially aromatic polyamide containing less than 30% by weight of a fatty acid polyamide is directly or via an adhesive layer on both sides thereof. A layer made of polyamide is formed.

The partially aromatic polyamide is an amorphous polyamide formed from an aromatic digalvonic acid component composed of 10 to 40% of terephthalic acid and 60 to 90 mol% of isophthalic acid, and an aliphatic or alicyclic diamine. . Such partially aromatic polyamides include, for example, terephthalic acid and isophthalic acid, hexamethylene diamine, 2,2,4 and / or 2,4,4-
Polyamides formed from one or more aliphatic or alicyclic diamines such as trimethylhexamethylenediamine, octamethylenediamine, decamethylenediamine, dodecamethylenediamine, and bis- (4-aminocyclohexyl) methane Can be exemplified. These partially aromatic polyamides have a molecular weight sufficient to form a film.

In the polyamide layer used in the present invention, such a partially aromatic polyamide can be used alone, but an aliphatic polyamide may be blended in a proportion of less than 30% by weight based on the total amount of the polyamide.

Such an aliphatic polyamide refers to a polymer compound having an amide bond that does not contain a substantial amount of an aromatic group, and typical examples thereof include nylon 6, nylon 66, and nylon 6.
610, nylon 6-66, nylon 11, nylon 12, and the like. These have a molecular weight such that a film can be formed. Among these, from the viewpoints of heat resistance, toughness, and pinhole resistance, it is preferable to select from nylon 6, nylon 66, and the like.
The partially aromatic polyamide layer may, of course, contain a stabilizer and other additives.

The smaller the proportion of the fatty acid polyamide in the partially aromatic polyamide, the lower the adhesiveness with the ethylene / vinyl alcohol copolymer. Therefore, an adhesive may be used for laminating both. Examples of such an adhesive include a modified product obtained by graft-copolymerizing an unsaturated carboxylic acid, an anhydride thereof, or another derivative thereof with a polyolefin, or a product obtained by blending the modified product with a polyolefin, and further, such a modified product. Alternatively, a composition obtained by mixing a rubber component with the composition can be used.

In the present invention, a polyolefin layer is further formed on both sides of a laminate in which a partially aromatic polyamide layer is formed on both sides of an ethylene / vinyl alcohol copolymer layer, whereby heat sealability is improved. Further, the tendency of whitening due to hot water treatment or the like can be reduced.

Polyolefins include low density polyethylene (high pressure method), linear low density polyethylene, medium density polyethylene,
Examples thereof include high-density polyethylene, polypropylene, ethylene / vinyl acetate copolymer, ethylene / ethyl acrylate copolymer, ethylene / (meth) acrylic acid copolymer or a metal salt thereof. Such a polyolefin may be a modified product obtained by graft copolymerization of a polar vinyl monomer such as maleic anhydride, or may be a blended product of such a modified product.

An adhesive layer may be provided between the polyolefin layer and the partially aromatic polyamide layer. As the adhesive used for this purpose, the same adhesive as exemplified above can be used.

In order to produce the laminate of the present invention, coextrusion inflation film molding, coextrusion cast film molding, extrusion or coextrusion lamination molding, dry lamination molding, coextrusion hollow molding and the like can be employed. Further, the laminate extruded into a sheet shape can be reprocessed into a desired shape by thermoforming such as vacuum forming or pressure forming. Although the thickness of each layer is arbitrary, it is generally about 1 to 500 μm. Particularly, the ethylene / vinyl alcohol copolymer layer has a thickness of 3 to 120 μm, especially 5 to 70 μm, and the polyamide layer has a thickness of 5 to 70 μm.
~ 150μ, especially 10 ~ 100μ, polyolefin layer is 5 ~
It is preferably set to 150μ, especially 10 to 100μ.

EXAMPLES Example 1 Hexamethylenediamine as a diamine component and terephthalic acid / isophthalic acid = 30/7 as a dicarboxylic acid component
0 mol% of an amorphous partially aromatic polyamide and nylon-6 as an aliphatic polyamide (Toray: Amilan CM-
1021XF) to a 40mmφ extruder at a ratio of 75/25,
The mixture was granulated at a temperature of 240 ° C. to obtain a polyamide composition.

Next, two types of three-layer films were prepared according to the following recipe.

The above polyamide composition was placed in a 50 mmφ extruder of a two-type, three-layer co-extrusion casting apparatus having a die of 500 mm width and 45 mmφ.
Ethylene / vinyl alcohol copolymer (ethylene content: 30 mol%) was supplied to the extruder, and two or three layers were extruded using a feed block to obtain a cast film.
The layer configuration and molding conditions of the three-layer film are as follows.

Layer composition: polyamide composition / ethylene vinyl alcohol copolymer / polyamide composition = 10/25/10 μm Molding temperature: polyamide composition 250 ° C. ethylene vinyl alcohol copolymer 220 ° C. Film forming speed: 30 m / min 3 types, 3 layers The above-mentioned polyamide composition was cast into a 50 mmφ extruder of a casting machine, linear low density polyethylene (LLDPE, density 0.920) into a 45 mmφ extruder, and “Vinenel E” into a 40 mmφ extruder.
-205 "(registered trademark; manufactured by DuPont, LLDPE-based adhesive resin, MFR 4.0 g / 10 min) to obtain a three-layer co-extruded cast film. The layer configuration and molding conditions of the three-layer film are as follows.

Layer composition: LLDPE / Vinel / Polyamide composition = 20/10/15
μm Molding temperature: Polyamide composition 250 ° C Vinenel E-205 180 ° C LLDPE 180 ° C Film forming speed: 30m / min Film 2 obtained from the film obtained above
The sheets were sandwiched from the outside (the polyamide layer was inside) and pressed with a heating roll to obtain the following multilayer film.

(EVOH: Ethylene vinyl alcohol copolymer) LLDPE / Vinel / Polyamide composition / EVOH / Polyamide composition / Vinel / LLDPE = 20/10/25/25/25/10/20 μm Was measured.

The film was further placed in a steam can and left at 120 ° C. for 30 minutes. After 30 minutes, the film was taken out from the steam can and the surface moisture was removed, and then the oxygen permeability was evaluated. Table 1 shows the measurement results of the oxygen permeability. It can be seen that the oxygen permeability of the steam can treatment is significantly smaller than that of the comparative example.

Example 2 The following two types of films were prepared using a feed block in a cast molding machine.

Co-extrusion using the ethylene vinyl alcohol copolymer (EVOH) used in Example 1 as the central layer and an amorphous partially aromatic polyamide (hexamethylenediamine / terephthalic acid / isophthalic acid = 100/30/70 mol%) as the outer layer Using the adhesive resin, the following three types of five-layer films were prepared. At this time, as the co-extrusion adhesive resin, Vinel E-3048 (EVA-based adhesive resin, MFR 1.0 g / 10 min) was used.

Layer composition: Aromatic polyamide / Vinel / EVOH / Vinel /
Aromatic polyamide = 22/10/25/10 / 22μm Molding temperature: Aromatic polyamide 250 ℃ Vinel 220 ℃ EVOH 220 ℃ Same as LLDPE (density 0.920) and co-extruded adhesive resin (Vinel E-205) two-layer film Was prepared using a cast molding machine.

Layer composition: LLDPE / Vinel = 15/15 μm Molding temperature: LLDPE 180 ° C. Vineel 180 ° C. Film 2 obtained from the film obtained above
The sheets were sandwiched from the outside (with the veneel layer inside) and pressure-bonded with a hot press to obtain the following multilayer film.

LLDPE / Vinel-205 / Aromatic polyamide / Vinel E-
3048 / EVOH / Vinel E-3048 / Aromatic polyamide / Vinel E-205 / LLDPE = / 15/15/22/10/25/10/22/15 / 15μm Oxygen permeability of this multilayer film before and after steam can treatment Was measured in the same manner as in Example-1. The results are shown in Table 1.

Example 3 The amorphous polyamide composition obtained in Example 1 was mixed with polypropylene (PPF-650 manufactured by Mitsui Petrochemical) and coextruded adhesive resin Vinel E-305 using a three-type three-layer casting apparatus.
(Polypropylene adhesive resin, MFR 3.1 g / 10 min) to obtain a three-layer three-layer film. The layer configuration and molding temperature are as follows.

Layer composition: PP / Vinel / Polyamide composition = 50/15/10 μm Molding temperature: Resin temperature: 250 ° C. Each of these two three-layer films and one two-layer three-layer film of Example-1 were used. In the same manner as in Example 1, thermocompression bonding was performed using a heating roll to obtain the following multilayer film.

PP / Vinel / Polyamide composition / EVOH / Polyamide composition / Vinel / PP = 50/15/20/25/20/15/50 μm Put this multilayer film in a steam can at 110 ° C and 120 ° C.
The film was allowed to stand for a minute, and the whitening state of the film was evaluated. Table-
2 shows the haze value of the multilayer sheet before and after being put into the steam can. The rise in haze after placing in a steam can is relatively small.

Comparative Example -1 Using a cast film forming apparatus having a feed block for three types and five layers, using the same ethylene vinyl alcohol copolymer, LLDPE and Vinel E-205 as used in Example 1, the following: Three types of five-layer films were prepared.

LLDPE / Vinel / EVOH / Vinel / LLDPE = 40/15/25/15 / 40μm Molding temperature: LLDPE 180 ℃ Vinenel E-205 180 ℃ EVOH 220 ℃ 3 Oxygen permeability of this multilayer film
The oxygen permeability after leaving for 0 minutes was measured in the same manner as in Example-1. The results are shown in Table 1.

[Effects of the Invention] According to the present invention, a laminate excellent in transparency and gas barrier properties can be provided. In particular, even when exposed to hot and humid conditions such as hot water sterilization and retort sterilization, the gas barrier property does not decrease so much and the tendency to whiten is small. Therefore, it is particularly excellent as a food packaging material that performs high-temperature sterilization and high-temperature filling.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 1/00-35/00

Claims (1)

(57) [Claims] 1. A fragrance comprising 10-40% of terephthalic acid and 60-90% of isophthalic acid on both sides of a core layer comprising an ethylene / vinyl alcohol copolymer having a vinyl alcohol content in the range of 40-85 mol%. Amorphous partially aromatic polyamide layer formed from an aliphatic dicarboxylic acid and an aliphatic or alicyclic diamine, or an amorphous partially aromatic polyamide composition layer containing an aliphatic polyamide in a proportion of less than 30% by weight. Provided,
An unstretched laminate further comprising a polyolefin layer provided outside the partially aromatic polyamide or polyamide composition layer.