JPH0338979B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to coextruded laminates. More specifically, it relates to a coextruded laminate of ethylene-α,β-unsaturated carboxylic acid copolymer resin or its metal ion crosslinked resin (ionomer resin) and polyamide resin, which has improved pinhole resistance and bag tear strength. . In recent years, consumer demands regarding various properties of packaging materials have become stricter, and there is a demand for the development of qualitatively advanced packaging films. In order to meet these demands, various types of laminates are on the market.
Among these, coextruded laminates of ethylene-α,β-unsaturated carboxylic acid copolymer resins or their metal ion crosslinked resins and polyamide resins are attracting the most attention from the viewpoint of economic efficiency (cost) and physical properties of the laminates. There is. The first feature of the coextruded laminate with such a layered structure is:
Ethylene-α,β-unsaturated carboxylic acid copolymer resin or its metal ion crosslinked resin (hereinafter collectively referred to as carboxylic acid copolymer resin), which has the compatibility of polyolefin resins with a wide molding temperature range, and a very wide molding temperature range. When coextruded with narrow polyamide resin,
The disadvantage of polyamide resins, which are poor processability when used alone, is compensated for by the good moldability of carboxylic acid copolymer resins, making it possible to mold laminates very easily and, as a result, coextrusion molding. As a result, manufacturing costs can also be reduced at the same time. The second feature is that the interlayer adhesive strength between the carboxylic acid copolymer resin layer and the polyamide resin layer is at the practically required adhesive strength level ( Approx. 0.4Kg/15mm
It is possible to point out that it has reached a point (more than the width). Thirdly, the characteristics of polyamide resin such as oxygen impermeability and mechanical strength, and the characteristics of carboxylic acid copolymer resin such as transparency and heat sealability (low temperature sealability, hot sealability, oil sealability, etc.) ) and deep drawability. In this way, compared to other lamination methods such as dry lamination, extrusion coating, etc., laminates shaped by coextrusion do not require laminators, adhesives, solvents, etc., and there is less product loss.
It has the economical advantage of lower manufacturing costs in terms of the number of steps, yield, and all other aspects.In particular, coextruded laminates of carboxylic acid copolymer resins and polyamide resins have excellent physical properties, so they are currently commercially available. widely used. However, as the production volume of such coextruded laminates has increased and the range of use has expanded, a drawback has also been recognized in this laminate, and a fundamental solution has been sought. In other words, this laminate does not generate pinholes when used in the summer, but in the winter, especially in cold regions during the bitterly cold season, when moving heavy items such as chilled beef for vacuum packaging, pinholes may occur. A drawback is that vacuum return is likely to occur due to the generation of holes. The first possible solution to this problem is to use a flexible carboxylic acid copolymer resin. Specifically, pinhole resistance is certainly improved by using ethylene-α,β-unsaturated carboxylic acid-α,β-unsaturated carboxylic acid ester ternary copolymer resin or its metal ion crosslinked resin. However, this material has significant blocking properties and requires a large amount of additives to provide good aperture, resulting in a loss of adhesion to the polyamide resin and the optical properties of the laminate. A second possible solution is to use elastomers such as highly elastic styrene-butadiene copolymer rubber, polyisoprene rubber, polychloroprene rubber, acrylonitrile-butadiene copolymer rubber, butyl rubber, or flexible ethylene-vinyl acetate copolymer resins. This is a method in which the following compounds are blended with a carboxylic acid copolymer resin. The present inventors actually tried a solution by blending various elastomers, but carboxylic acid copolymer resins generally have poor compatibility with other polymers, and they suffer from lower heat sealability, optical properties, etc. than blends. Notably, the laminate using the blend was extremely cloudy and could not be used in applications requiring transparency. Furthermore, when an ethylene-vinyl acetate copolymer resin was blended, although there was little decrease in transparency, there was a decrease in interlayer adhesion strength, heat seal strength, etc., and the effect of improving pinhole resistance was also small. Therefore, the present inventors sought a coextruded laminate that does not have these drawbacks and still retains the characteristics of carboxylic acid copolymer resin, and as a result of various studies, the carboxylic acid copolymer resin has a specific ethylene-α- It has been discovered that when an olefin copolymer is blended and coextruded with a polyamide resin, a coextruded laminate with good pinhole resistance and significantly improved bag tear strength can be obtained. . Accordingly, the present invention relates to a coextruded laminate, which comprises about 95 to 80% by weight of an ethylene-α,β-unsaturated carboxylic acid copolymer resin or its metal ion crosslinked resin (ionomer resin) and It consists of a blend layer (A) containing about 5 to 20% by weight of an amorphous to low crystalline ethylene-α-olefin copolymer and a polyamide resin (B). As the ethylene-α,β-unsaturated carboxylic acid copolymer resin, for example, ethylene and an unsaturated carboxylic acid having 3 to 8 carbon atoms such as acrylic acid, methacrylic acid, ethacrylic acid, itaconic acid, fumaric acid, etc.
~35% by weight, preferably approximately 3~21% by weight, of copolymerization is used. In addition, the ionomer resin, which is a metal ion crosslinked resin, is
Generally, the carboxylic acid groups in these ethylene-α,β-unsaturated carboxylic acid copolymer resins are neutralized with about 10 mol% or more, preferably about 15 to 80 mol%, of metals from groups of the periodic table. used. In particular, in order to obtain strong adhesion with polyamide resin, it is preferable to use an ionic copolymer neutralized with group metals, especially zinc, and its melt index is about 0.5 to 10 dg/min. It is desirable that it be within the range. The ethylene-α-olefin copolymer blended with such carboxylic acid copolymer resin has a density of
It has a weight of 0.85 to 0.90 g/cm ³ and is amorphous to low crystallinity (crystallinity determined by the specific solution method is approximately 20 to 0%). The copolymer is obtained by copolymerizing ethylene and α-olefin using a composite catalyst of a vanadium compound represented by vanadium trichloride, vanadium tetrachloride, etc. and an organic aluminum compound, etc. α− in the copolymer
Approximately 5 to 30 mol% of olefin is copolymerized. As the α-olefin, propylene, putene, etc. are used, but in particular, copolymerization with ethylene using putene-1 can be carried out using carboxylic acid copolymer resin,
In particular, it shows the most excellent effects in terms of compatibility with ionomer resins and the effect of improving interlayer adhesion. In addition, these copolymers are approximately 0.5 to 10 d
It is desirable to have a melt index of g/min. The carboxylic acid copolymer resin and the ethylene-α-olefin copolymer are used as a blend, with the former being about 95 to 80% by weight and the latter being about 5 to 20% by weight. If the mixing ratio of the ethylene-α-olefin copolymer is less than this, the effect of improving pinhole resistance will be insufficient, and if it is more than this, not only will the heat sealing strength decrease significantly, This results in a decrease in interlayer adhesion with the polyamide resin and in the optical properties of the laminate. Blending is performed by simultaneously or sequentially dry blending or melt blending the carboxylic acid copolymer resin and the ethylene-α-olefin copolymer. In the case of dry blending, the ethylene-α-olefin copolymer is easily and uniformly melt-mixed with the carboxylic acid copolymer resin at the stage where the carboxylic acid copolymer resin is melted and plasticized in the molding machine. In the case of a melt blend, melt mixing may be carried out using various mixers such as a single screw extruder, a twin screw extruder, a Babbury mixer, a roll, a kneader, etc., and there is no particular restriction on the order of mixing. Polyamide resins that can be coextruded with such blends include nylon 6, nylon 610, nylon 11, and even nylon 6-66, nylon 66-
610, nylon 6-11, nylon 66-610-6, etc. are used, and if necessary, so-called impact-resistant nylon is used, which is a blend of these polyamide resins with ionomer resin, ethylene-vinyl acetate copolymer, etc. The effect of improving pinhole resistance becomes even greater. Coextrusion laminates can be formed using the inflation method,
If a method such as a T-die method or a blow molding method is used in which a blend of a carboxylic acid copolymer resin and an ethylene-α-olefin copolymer is extruded as a layer in direct contact with a polyamide resin in a molten state, You can do it in any way you like. Regarding the thickness structure of each layer after coextrusion, the thickness of the blend layer is determined primarily from the viewpoint of strength, and is generally set to a thickness of about 10 to 100 μm. Regarding the polyamide resin layer, it is preferable to make it thinner from the point of view of pinhole resistance, but it needs to be thicker in order to obtain sufficient gas impermeability, so it is generally about 15 to 50 μm thick. is set to Further, the laminate may have a structure of three or more layers, such as polyamide resin/polyolefin layer/blend layer, polyamide layer/blend layer/polyolefin layer, blend layer/polyamide layer/blend layer, etc. It may also be a multilayer coextruded laminate. In this way, the blend layer (A) of the ethylene-α,β-unsaturated carboxylic acid copolymer resin or its metal ion crosslinked resin and the amorphous or crystalline ethylene-α-olefin copolymer and the polyamide resin The coextruded laminate with layer (B) has significantly improved not only pinhole resistance but also bag breakage strength, so it can be effectively used for all such coextruded laminate applications. Next, the present invention will be explained with reference to examples. Example 1 Ionomer resin (Mitsui Polychemical product Himilan 1650); ZN salt, melt index 1.5d
g/min, density 0.95 g/cm ³ ) 95% (weight, same below) and low crystalline ethylene-butene-1 copolymer (melt index 4 dg/min, density 0.88 g/cm 3 )
cm ³ ) 5% using a 65 mm diameter extruder at a resin temperature of 200
Melt mixed at °C. This braided material was used as the inner layer component, and polyamide resin (Toray product Amiran CM604IXF; density 1.13
g/cm ³ ) as the outer layer component, melt coextrusion is performed using two extruders, the inner and outer resin layers are brought into contact in a die, and then a two-layer inflation film is produced by a known air cooling method. It was filmed. The resulting coextruded laminate film has an outer layer of 2.5 μm and an inner layer of
Each has a thickness of 55 μm. This coextruded laminate film was subjected to a gelboflex test (MILB-1310) at 0°C, and the maximum number of reciprocations without pinholes (in increments of 20) was measured to determine pinhole resistance. did. The interlayer adhesion strength of this film was determined by cutting out a film with a width of 15 mm in the vertical direction from a sample film, peeling off a portion of the film, and using a tensile tester to determine the interlayer adhesion strength of 30 mm.
Measurements were made by peeling at a speed of mm/min. The heat-sealing strength was determined by heat-sealing the film in the horizontal direction using a 10mm-wide heat-sealing bar under the conditions of 110-180℃, 2Kg/cm ² (actual pressure), and 0.5 seconds. A test piece was cut out, and the sealed portion was peeled off at a speed of 300 mm/min using a tensile tester for measurement. The bag breakage strength of this film is determined from the sample film.
A small bag of 120 x 180 mm is made, 200 ml of water is sealed in it, and this is compressed at a speed of 100 mm/min using a press. A 720 g weight was repeatedly dropped from a height of 27 cm into the sachet containing the bag, and the number of times the bag broke was determined as the impact bag breaking strength. Comparative Example 1 In Example 1, an ionomer resin was used alone as an inner layer component. Examples 2 to 4, Comparative Examples 2 to 3 In Example 1, the blending ratio of each component of the inner layer was variously changed. The physical property measurement results of the coextruded laminate films obtained in each of the above Examples and Comparative Examples are shown in Table 1 below.

[Table] As is clear from the results in Table 1, pinhole resistance and bag breakage strength are significantly improved by blending a low-crystalline ethylene-butene-1 copolymer, but the blending ratio is When it exceeds 25%, not only do these effects reach a plateau, but the interlayer adhesion and heat sealing strength with polyamide also begin to drop significantly. Examples 5 to 8 In Examples 1 to 4, low crystalline ethylene-butene-1 copolymer was replaced with low crystalline ethylene-butene-1 copolymer.
Propylene copolymer (melt index 12d
g/min, density 0.88 g/cm ³ ) was used. Example 9 In Example 7, ethylene-methacrylic acid copolymer resin (Mitsui Polychemical product Himilan ACR0910; melt index 10 dg/min, density 0.93 g/cm ³ , methacrylic acid content 9% by weight) was used instead of the ionomer resin. ) was used. Comparative Examples 4 to 5 In Examples 2 and 4, ethylene-vinyl acetate copolymer (Mitsui Polychemical product Evaflex P-1905; Melt Index) was used instead of the low-crystalline ethylene-butene-1 copolymer.
2.5 dg/min, vinyl acetate content 19% by weight) was used. Comparative Example 6 In Example 2, L-LDPE (Mitsui Petrochemicals Neozex 2015M; density 0.920 g/cm ³ ,
A melt index of 1.5) was used. The physical property measurement results of the coextruded laminated films obtained in each of the above Examples and Comparative Examples are shown in Table 2 below.

[Table] As is clear from the results in Table 2, the same effects as the ionomer resin can be obtained with the ethylene-methacrylic acid copolymer resin. However, ethylene-vinyl acetate copolymer and L-LDPE
When used in place of a low-crystalline ethylene-butene-1 copolymer, the effect of improving pinhole resistance and bag breakage strength is small, and when the blending ratio is increased, interlayer adhesion and heat sealing The strength decreases significantly. In addition, low crystalline ethylene-
Low crystalline ethylene instead of butene-1 copolymer
When a propylene copolymer is used, although there is a drawback that the interlayer adhesion strength is lowered, a similar effect is observed in terms of improving pinhole resistance.

Claims (1)

[Scope of Claims] 1. Approximately 95 to 80% by weight of ethylene-α,β-unsaturated carboxylic acid copolymer resin or its metal ion crosslinked resin (ionomer resin) and amorphous to low crystalline ethylene-α-olefin. Polymer approx. 5-20
A coextruded laminate consisting of a blended layer (A) and a polyamide resin layer (B) in weight percent. 2. The coextrusion laminate according to claim 1, wherein the amorphous to low crystalline ethylene-α-olefin copolymer is an ethylene-butene-1 copolymer. 3. The coextrusion laminate according to claim 1, wherein the metal ion crosslinked resin of the ethylene-α,β-unsaturated carboxylic acid copolymer resin is a zinc ion crosslinked resin.