FI86874C - Gas-sealed material containing internally plasticized polyvinyl alcohol - Google Patents

Description

86874

Gas-tight material containing internally plasticized polyvinyl alcohol

The material of the present invention is a mixture of 5 polyvinyl alcohols

The invention relates to a gas-tight material and products containing a gas-tight material. In particular, the invention relates to a gas-tight material comprising polyolefin, polyvinyl alcohol and polyamide and products containing it.

Polyolefins are widely used, for example, in the packaging industry in the manufacture of 15 different film products. The advantages of polyolefins are particularly good strength and water resistance properties. Disadvantages include permeability to certain gases and liquids, especially oxygen and hydrocarbon solvents. For this reason, the usefulness of polyolefin films is limited in the packaging of certain substances, such as foodstuffs, where low oxygen permeability is required.

It is common in the packaging industry to use multilayer film structures in which the materials of the different layers are selected for a specific purpose. Thus, such multilayer structures may include layers that provide a good barrier to gases, e.g., oxygen, as well as layers that impart other properties to the product, e.g., strength properties. In addition, multilayer structures may include other layers that provide, for example, adhesion between different layers. However, such products are expensive to manufacture.

Polyvinyl alcohol is a polymer with low oxygen permeability. This property has been most commonly used in olefin-vinyl alcohol random copolymers and olefin-vinyl alcohol block copolymers. It is also known to prepare, as a mixture, products containing polyolefin and polyvinyl alcohol which have low oxygen permeability and which are therefore excellently suitable for the production of packaging films, for example. Finnish patent application 87-5772 discloses a mixture of polyolefin and polyvinyl alcohol, which optionally additionally contains plasticizers. Mixing the polyolefin and polyvinyl alcohol in the molten state gives a mixture consisting of two phases, a continuous phase and a dispersed phase. When the diameter of the particles in the dispersed phase is small enough, completely transparent films are obtained. Mixing is usually performed in a separate compounding step before extruding the final product.

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When PVA forms a continuous phase in a mixture of polyolefin and PVA, a good density is obtained for the product, for example oxygen tightness, and the product is clear and stable in both molten and solid state despite the two phases and is easy to soften by adding plasticizers.

EP 280455-A discloses oxygen-tight materials comprising a blend of polyethylene, a polyolefin containing carboxyl groups and a third poly-20 polymer incompatible with polyethylene. According to the publication, said third polymer may be polyamide (PA), ethylene-vinyl alcohol copolymer, polyvinyl alcohol (PVA), polyester or a mixture thereof, although no examples of mixtures, for example mixtures of polyamide and polyvinyl alcohol, are given. The blend of polyethylene and PVA is not usable due to its brittleness and the blend of polyethylene and polyamide is not usable due to insufficient barrier properties. If, instead, polyethylene is mixed with PVA and polyamide, the product is both dense and tough.

30 Although polyolefin / PVA / PA blends generally have good oxygen tightness properties under dry conditions, under wet conditions they have a significant decrease in oxygen tightness and are therefore sensitive to moisture. In addition, melt blending of blends of polyolefins, PVA, and polyamide results in partial decomposition of PVA and intense discoloration of the product. When plasticizers are used, their stability in the mixture is not the best, which is why migration of plasticizers occurs in the product. Another disadvantage of conventional PE / PVA / PA blends is 3 86874 that the melt index of the product is not low enough.

The present invention relates to a material comprising polyolefin, polyvinyl alcohol and polyamide in which the sensitivity of the product to the moisture tightness of moisture is reduced, the brightness of the product is increased and the need for plasticizers is eliminated and the strength properties of films made of the product are improved toughness, tensile strength and impact strength.

According to the invention, it has surprisingly been found that the blending in the molten state of certain internally plasticized vinyl alcohol polymers and amorphous polyamide with polyolefins copolymerized or grafted with a carboxylic acid provides products which are lighter in color and have an oxygen density of much less than 15 m. and in addition, the strength properties of the films made from the product are better than when using unmodified polyolefin, ordinary polyvinyl alcohol and polyamide.

Thus, the invention relates to a gas-tight material comprising a polyolefin, a vinyl alcohol polymer and a polyamide, which material is prepared by mixing in a molten state 3 to 60% by weight of a polyolefin copolymerized or grafted with 0.01 to 10% by weight of a carboxylic acid, 10 to 96% by weight. % internally plasticized vinyl alcohol polymer and 1-25 50 wt% amorphous polyamide. The gas-tight material according to the invention is characterized in that the vinyl alcohol polymer chains have polyglycol groups (polyether groups) as side groups.

By internally plasticized vinyl alcohol polymer is meant a vinyl alcohol polymer containing polyglycol groups (polyether groups) or other polyvinyl alcohol plasticizing groups in its side chains. These plasticizer groups are attached to the chain by copolymerization, grafting, or reactive compounding. One such internally plasticized polyvinyl alcohol is Vinex polymer 33 (trade name, Air Products and Chemicals Inc.) in which the comonomer is an ester of methacrylic acid and polyethylene glycol.

86874 ύ Such internally plasticized vinyl alcohol polymers can be prepared, for example, as disclosed in U.S. Patent 4,708,999.

This patent discloses that the product has good oxygen tightness and is suitable for casting, injection molding and extrusion products and that it is characterized by good solubility in water and is therefore particularly suitable for the production of films requiring water solubility.

The vinyl alcohol polymer used in the polyolefin-polyvinyl alcohol-polyamide mixture according to the invention is preferably one in which the alkylene of the alcohol moiety in the poly (alkyleneoxy) ester derivative used as a comonomer is ethylene or propylene and the acid moiety is acrylic acid or methacrylic acid. Such modified vinyl alcohol polymers can be prepared, for example, by polymerizing a vinyl acetate monomer and a poly (alkyleneoxy) acrylate comonomer and hydrolyzing the copolymer thus obtained to produce an internally plasticized vinyl alcohol polymer.

The amount of internally plasticized vinyl alcohol polymer in the polyethylene-polyvinyl alcohol / polyamide blend according to the invention may be between 10 and 96% by weight, preferably between 30 and 60% by weight. In some cases, it may be advantageous to replace a portion of the internally plasticized vinyl alcohol polymer used in the gas-tight material with unmodified polyvinyl alcohol, if the intended use of the product allows it.

The acid-modified polyolefin in the gas-tight material of the invention may be based on homo- or copolymers of olefins. Thus, it may be low density polyethylene (LDPE), medium density polyethylene (MDPE) or high density polyethylene (HDPE), polypropylene or polybutylene. The polyolefin may also be a copolymer of ethylene with other olefins such as propylene, butene, hexene and octene. The polyolefin may also be an olefin ester copolymer, such as an ethylene-vinyl acetate copolymer, an ethylene-acrylate ester copolymer or an ethylene-methacrylate ester copolymer, or it may be a thermoplastic olefin-based elastomer such as EP or EPD rubber.

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According to the invention, 0.01 to 10% by weight of carboxylic acid is copolymerized or grafted onto the olefin polymer. The carboxylic acid comprises any unsaturated carboxylic acid or carboxylic acid anhydride which can be grafted or copolymerized into a polyolefin. Pre-5 signs of such acids are e.g. acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, crotonic acid, sorbic acid and anhydrides of the above acids. One or more of the aforementioned acids may be used in the grafting or copolymerization. The carboxylic acid grafted or copolymerized polyolefin may also be a mixture of an acid-modified polyolefin and an unmodified polyolefin as mentioned above.

The amount of acid-modified polyolefin in the gas-tight material according to the invention may be between 3 and 60% by weight, but preferably between 30 and 60% by weight of the total mixture.

The third component in the gas-tight material of the invention is amorphous polyamide. The polyamide used is preferably one in which the degree of crystallinity varies between 1 and 10%, preferably between 1 and 5%.

The amount of amorphous polyamide in the material according to the invention can be selected from 1 to 50% by weight.

Amorphous polyamide improves the toughness and deep drawing properties of a mixture of an acid-modified polyolefin and a polyvinyl alcohol copolymer.

The gas-tight polyolefin / PVA / PA blend of the invention can be prepared by mixing an acid-modified polyolefin component, a vinyl alcohol copolymer component and a polyamide component in a melt blender simultaneously as a dry blend, premixed in a solid or molten state, or the various components can be added separately.

Various products can be prepared from the polyolefin / PVA / PA blend of the invention by combining the blend with polyolefins, other molds or other materials, such as fiber-based materials. Multilayer products can be made by coextrusion, (co) extrusion coating, (co) extrusion, by gluamination or other techniques and these methods of preparation 5 can also be combined.

Suitable products comprising the gas-tight material according to the invention are, for example, films, blow-molded bottles and containers, sheets, tubes, injection-molded containers, deep-drawn films 10 and sheets, liquid packaging boards, etc. Dense multilayer products are generally used for food packaging, but also in oxygen-tight conditions. the tightness of carbon dioxide or some other gas may also be considered. In addition, grease, chemical and odor tightness are desired in both food packaging and technical products.

The following non-limiting examples illustrate the preparation, properties and application of the polyolefin / vinyl alcohol polymer / polyamide blend of the invention in dense monolayer products. The oxygen permeability of the membranes 20 was measured with an OX-TRAN 1000 instrument (ASTM D 3985).

The polyolefins, vinyl alcohol polymers and polyamides used in the experiments of the examples are shown in the table below: Polyolefins: PO1 = LDPE (low density polyethylene), melt index 1.8 g / 10 min (190 ° C) PO2 - LLDPE (linear low density polyethylene) branches with 0.25 wt% fumaric acid, melt index 0.5 g / 10 min (190 ° C)

Polyvinyl alcohol: 35 PVAl - vinyl alcohol copolymer with comonomer of methacrylic acid and polyethylene glycol ester (Vinex 4004, trade name, Air Products and Chemicals Inc.) PVA2 - polyvinyl alcohol, viscosity 4, degree of hydrolysis 88% 40 7 86874

Polyamides: PA1 - amorphous polyamide, crystallinity 1-5%? PA2 = polyamide 6 5 PA3 - polyamide 11 PA4 - polyamide 12

Plasticizer: 10 glycerol, 99% pure

Example 1 Polyolefin / PVA / polyamide blends of the invention were prepared by mixing polyolefin, polyvinyl alcohol and polyamide in the molten state using a Berstorff mixer equipped with a flat film nozzle. The temperature profile was 130-190-200-210-210-210-220-220-215-210. The production rate was 10 kg / h.

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The thickness of the obtained films was 140-190 μπι. Their compositions are shown in Table 1 A below. The properties of the films are shown in Table 1 B below. The oxygen transmittances of the films have been calculated for a thickness of 25 μπι: η. The brightness of the films was measured by the so-called as a yellowness index according to standard 25 ASTM D 1925-70 on a Hunter Lab Ulyta Scan instrument.

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Table 1 A

5 Test Polyvinyl alcohol Polvoleflin Polyamide type p-% type p-% type p-% 1 PVAl 80 P02 10 PA1 10 10 2 PVAl 70 P02 3 PA1 27 3 PVAl 60 P02 30 PAl 10 4 PVAl 30 P02 20 PAl 50 5 PVAl 10 PO2 60 PAl 30 6 PVAl 60 P02 10 PAl 9 15 PA2 21 7 PVAl 60 P02 10 PAl 9 PA3 21 8 PVAl 60 PO2 10 PAl 9 PA4 21 20 9 PVA2 60 POl 40 10 PVA2 70 PO2 30

Note. In Experiments 9 and 10, the amount of polyvinyl alcohol includes 4.5% of the amount of glycerol in the PVA.

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Table 1 B

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Test Oxygen permeability Yellowness_ Tensile strength_ (ml / mzx24hxbar) index thickness cross-machine 0% RH 90% RH μτα direction direction 35 MPa MP a 1 2 3 4 5 6 7 8 9 10 50 0,1 2,9 0,80 142 19, 9 18.5 2 0.05 1.9 0.70 171 32.2 25.0 3 40 3 0.01 2.5 0.75 166 16.8 15.0 4 1.5 25 0.85 151 42 , 5 39.7 5 3.6 55 0.85 147 35.0 31.6 6 0.08 1.4 0.75 186 46.8 26.0 7 0.10 1.5 0.75 150 45, 2 27.8 8 45 8 0.10 1.5 0.75 141 44.5 25.5 9 0.20 10.0 10.9 172 10.0 7.0 10 0.20 9.6 11.5 162 14.0 11.0

Claims (10)

86874 Patent 1 Claims A gas-tight material containing polyolefin, polyvinyl alcohol and polyamide, which material is prepared by mixing in a molten state 3 to 60% by weight of polyolefin copolymerized or grafted with 0.01 to 10% by weight of carboxylic acid, 10 to 96% by weight. -% of internally plasticized vinyl alcohol polymer and 1-50% by weight of amorphous polyamide, characterized in that the vinyl alcohol polymer chains have polyglycol groups (polyether groups) as side groups. 10 Gas-tight material according to Claim 1, characterized in that the polyvinyl alcohol is a copolymer in which the comonomer is an unsaturated poly (alkyleneoxy) ester derivative. A gas-tight material according to claim 2, characterized in that said alkylene is ethylene or propylene and in that the acid moiety of said ester is acrylic acid or methacrylic acid. Gas-tight mixture according to one of the preceding claims, characterized in that the polyvinyl alcohol comprises, as a mixture, unmodified polyvinyl alcohol and a vinyl alcohol polymer according to claims 2-3. Gas-tight material according to one of the preceding claims, characterized in that the polyolefin is low-density polyethylene (LDPE), medium-density polyethylene (MDPE) or high-density polyethylene (HDPE), polypropylene or polybutylene, or a copolymer of ethylene with propylene, butene, hexene and with octene or an olefin ester copolymer such as an ethylene-vinyl acetate copolymer, an ethylene-acrylate ester copolymer or an ethylene-methacrylate ester copolymer, an EP rubber, an EPD rubber or another thermoplastic olefin-based elastomer. G. A gas-tight material according to claim 5, characterized in that the carboxylic acid is one or more unsaturated carboxylic acids selected from the group consisting of acrylic acid, methacrylic acid, maleic acid, fumaric acid, icaconic acid, crotonic acid, sorbic acid and the above-mentioned anhydric acid. Gas-tight material according to one of the preceding claims, characterized in that the polyolefin is a mixture of unmodified polyolefin and carboxylic acid-modified polyolefin. Gas-tight material according to one of the preceding claims, characterized in that the degree of crystallinity of the polyamide is between 1 and 5%. Products comprising a gas-tight material according to any one of the preceding claims. 15 n 86874