FI86872B - Gas-proof material which contains internally softened polyvinyl alcohol - Google Patents

Description

86872

Gas-tight material containing internally plasticized polyvinyl alcohol

The invention relates to a gas-tight material and to 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.

15 Polyolefins are widely used, for example, in the packaging industry in the manufacture of various 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-20 films is limited in the packaging of certain materials, 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 particular 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 a low oxygen permeability. This property has been most commonly exploited 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 softeners. When polyolefin and polyvinyl alcohol are mixed in the molten state, a mixture consisting of two phases, a continuous phase and a dispersed phase, is obtained. When the diameter of the particles in the dispersed phase is small enough, completely transparent films are obtained. The mixing is usually performed in a separate compounding step 10 before extruding the final product.

When PVA forms a continuous phase in a mixture of polyolefin and PVA, a good tightness is obtained for the product, for example oxygen tightness, and the product is clear and stable in both molten and solid states 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 carboxyl-containing poly-20 olefin, and a polyether-incompatible third polymer. 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. A mixture of polyethylene and PVA is not useful due to its brittleness and a mixture of polyethylene and polyamide is not useful due to insufficient barrier properties. If, instead, polyethylene is mixed with PVA and polyamide, the product is both dense and tough.

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Although polyolefin / PVA / PA blends generally have good oxygen tightness properties under dry conditions, under humid conditions their oxygen tightness decreases significantly, making them sensitive to moisture. In addition, melt blending of blends of polyolefins, PVA, and polyamide 35 results in partial decomposition of PVA and strong discoloration of the product. When plasticizers are used, their stability in the mixture is not the best possible, which is why there is a migration of 3,86872 plasticizers in the product. Another disadvantage of conventional PE / PVA / PA blends is that the melt index of the product is not low enough.

The present invention relates to a material comprising polyolefin, polyvinyl alcohol 5 and polyamide in which the sensitivity of the product to oxygen tightness to moisture is reduced, the brightness of the product is increased and the need for plasticizers is eliminated and the strength properties of films made

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According to the invention, it has surprisingly been found that the mixing of certain internally plasticized vinyl alcohol polymers and polyamides with polyolefins in the molten state results in products with a lighter color and a much less oxygen-sensitive oxygen density than conventional PVA. ordinary polyvinyl alcohol and polyamide.

Thus, the invention relates to a gas-tight material comprising a polyolefin, a vinyl alcohol polymer and a polyamide prepared by mixing in a molten state 3 to 60% by weight of a polyolefin, 10 to 96% by weight of an internally plasticized vinyl alcohol polymer and 1 to 50% by weight of a 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 that contains 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 a Vinex polymer (trade name, Air Products and Chemicals Inc.) in which the comonomer is an ester of methacrylic acid and polyethylene glycol.

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 is characterized by good water solubility 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, in the poly (alkyleneoxy) ester derivative used as a comonomer, the alkylene of the alcohol moiety 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 part 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.

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The polyolefin in the gas-tight material according to the invention can 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, for example, an ethylene-vinyl acetate copolymer, an ethylene-acrylate ester copolymer or an ethylene-methacrylate ester copolymer, or it may be a non-thermoplastic base such as EP.

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The amount of 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 according to the invention is polyamide. As polyamide, e.g. the following polyamide grades: polyamide 6, polyamide 8, polyamide 10, polyamide 11, polyamide 12, polyamide 6,6, polyamide 6,10 and polyamide 12 elastomers or mixtures thereof. The amount of polyamide in the material according to the invention can be selected from 1 to 50% by weight.

Polyamide improves the toughness and deep drawing properties of the blend of polyolefin and polyvinyl alcohol copolymer.

The gas-tight polyolefin / PVA / PA blend of the invention can be prepared by mixing the polyolefin component, the vinyl alcohol copolymer component and the 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.

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Various products can be made from the polyolefin / PVA / PA blend of the invention by combining the blend with polyolefins, other plastics or other materials, such as fiber-based materials. Multilayer products can be made by coextruding 25, (co) extrusion coating, (co) extrusion lamination, glue lamination, or other techniques, and these manufacturing methods can also be combined.

Suitable products 30 containing 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 and sheets, liquid packaging boards, etc. Dense multilayer products are generally used for food packaging. the tightness of carbon dioxide or some other gas 35 may also be considered. In addition, grease, chemical and odor tightness are desired in both food packaging and technical products.

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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 was measured with an OX-TRAN 1000 instrument (ASTM D 3985).

5 The polyolefins, vinyl alcohol polymers and polyamides used in the experiments of the examples are shown in the table below:

Polyolefins: 10 P01 - LDPE (low density polyethylene), melt index 1.8 g / 10 min (190 ° C)

Polyvinyl alcohol: 15 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% 20

Polyamides: PA1 - polyamide 6 PA2 - polyamide 11 25 PA3 - polyamide 12

Plasticizer: glycerol, 99% purity 30

Example 1

The polyolefin / PVA / polyamide blends 35 of the invention were prepared by mixing polyolefin, polyvinyl alcohol and polyamide in a 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. 1 45

The thickness of the obtained films was 120-170 μχη. Their compositions are shown in Table 1 A below. The properties of the films are shown in Table 1 B below. The oxygen permeabilities of the films have been calculated for a thickness of 25 μιτκη. The brightness of the films was measured by the so-called as a yellowness index according to ASTM D 1925-70 on Hunter Lab’s Ultra Scan.

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Table 1 A

5 Test Polyvinyl alcohol Polvolefin Polyamide type p-% type p-% type p-% 1 PVA1 60 P01 30 PA1 10 10 2 PVA1 60 POl 30 PA2 10 3 PVA1 60 POl 30 PA3 10 4 PVAl 30 POl 40 PA1 30 5 PVA2 60 POl 40 15 Note. In Experiment 5, the amount of polyvinyl alcohol includes 4.5% of the amount of glycerol in the PVA.

Table 1 B

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Test Oxygen permeability Yellowness_ Tensile strength_ (ml / m2x24hxbar) index thickness across the machine - 25 0% RH 90% RH / im direction direction MPa MPa 1 0.10 239 0.90 121 18.5 15.9 30 2 0.15 1.5 0.90 142 17.8 12.5 3 0.18 2.0 0.95 150 17.9 13.5 4 0.20 2.4 0.89 147 39.7 32.5 5 0.20 10, 0 10.9 172 10.0 7.0 35

Claims (7)

1. Gas-sealed material containing polyolefin, polyvinyl alcohol and polyamide, which material is prepared by melting in the molten state to mix 3-60 wt.% Polyolefin, 10-96 wt.% Internally softened vinyl alcohol polymer and 1-50 wt.% Polyamide. characterized in that the vinyl alcohol polymer chains have side groups of polyglycol (polyether groups). Gas-sealed 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. Gas-sealed material according to claim 2, characterized in that said alkylene is ethylene or propylene and the acid part of said ester is acrylic acid or methacrylic acid. Gas-tight mixture according to any of the preceding claims, characterized in that the polyvinyl alcohol comprises in the mixture unmodified polyvinyl alcohol and vinyl alcohol polymer according to claims 2-3. Gas-sealed material according to any 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 polybutene, or a copolymer of ethylene with propylene, butene, hexene and octene or an olefin ester copolymer such as, for example, ethylene-vinyl acetate copolymer, ethylene-acrylate ester copolymer or ethylene-methacrylate ester copolymer, EP-rubber, EPD-rubber or any other thermoplastic elastomer. Gas-tight material according to any of the preceding claims, characterized in that the polyamide is selected from the group of polyamide 6, polyamide 8, polyamide 10, polyamide 11, polyamide 12, polyamide 6,6, polyamide 6,10 and polyamide 12 elastomers or mixtures. of these. 7. Products containing a gas-tight material according to any of the preceding claims.