GAS-SEALED MATERIAL

Abstract: The present invention concerns a gas-sealed material, containing polyolefin, polyvinyl alcohol and amide. Said material is manufactured by mixing in molten state 3 to 60 per cent by weight of polyolefin, 10 to 96 per cent by weight of internally plasticized vinyl alcohol polymer, and 1 to 50 per cent by weight of polyamide.

Description: Gas-sealed material The present invention concerns a gas-sealed material and products containing gas-sealed material. In particular, the invention concerns a gas-sealed material containing polyolefin, polyvinyl alcohol, and polyamide, and products containing the same. Polyolefins are widely used, for instance, in packaging industry in manufacturing various film products. Advantages of polyolefins are in particular appropriate strength and water resistance properties. Among the drawbacks may be mentioned permeability to certain gases and liquids, concerning particularly oxygen and hydrocarbon dissolvents. Therefore, the usability of polyolefin films is limited to packaging certain substances, such as foodstuffs, in which minor oxygen perme¬ ability is required. It is customary to use in packaging industry multiple layer film structures in which materials of different layers are selected for a given purpose. Therefore, such multiple layer structures may contain layers which form a good barrier against gases, such as oxygen, and layers which provide other properties for the product, such as strength properties. In addition, multiple layer structures may contain other layers which generate, for instance, adhesion between different layers. Products of this kind are, however, expensive to manufacture. Polyvinyl alcohol is one of such polymers which has a low oxygen permeability property. Said property has most often been utilized in olefin-vinyl alcohol random-mixed polymers and in olefin-vinyl alcohol segment-mixed polymers. It is also known in the art to manufacture products containing polyolefin and polyvinyl alcohol in the form of mixtures, which have a low oxygen permeability and which therefore are exceedingly appropriate for manufacturing e.g. packaging films. In the Finnish patent application No. 87-5772 is disclosed a mixture of polyolefin and polyvinyl alcohol, moreover containing optionally plasticizers. When polyolefin and polyvinyl alcohol are mixed in molten state, a mixture is obtained which is composed of two phases, a continuous phase and a dispersed phase. When the diameter of the particles in the dispersed phase is small enough, totally transparent films are obtained. The mixing is usually carried out in a separate compounding phase prior to the extrusion of the end product. When the PVA in the mixture of polyolefin and PVA establishes a continuous phase, a good sealing is provided in the product, for instance oxygen sealing, and the product is bright and stable, in spite of two phases, both in molten and in solid state, and it is easy to soften by adding plasticizers. In the EP patent publicizing print No. 280455-A discloses oxygen- sealed materials containing polyethylene, a polyolefin containing carboxyl groups, and a third polymer which is incompatible with the polyethylene. Said third polymer may be, as stated in the publication, a polyamide (PA), ethylene-vinyl alcohol copolymer, polyvinyl alco¬ hol (PVA), polyester, or a mixture thereof, although no examples of mixtures, for instance mixtures of polyamide and polyvinyl alcohol, are presented. A mixture of polyethylene and PVA is not useful because of its brittleness, neither is the mixture of polyethylene and polyamide useful because of its barrier properties. If, instead, polyethylene is mixed with PVA and polyamide, the product is both sealed and viscous. Although polyolefin-PV -PA mixtures are generally speaking provided with good oxygen sealing properties in dry circumstances, in moist circumstances their oxygen sealing property reduces significantly, so that they are sensitive to moisture. In addition, when mixtures of polyolefins, PVA, and polyamide are mixed in molten state, partial dissolution of PVA and colouring of the product take place. When plasticizers are used, their stability in the mixture is not as good as possible because of which migration of plasticizers take place in the product. One more drawback in conventional PE/PVA/PA mixtures is that the melt index of the product is not low enough. The object of the present invention is a material containing polyolefin, polyvinyl alcohol, and polyamide, in which the moisture sensitivity of the product regarding oxygen sealing is reduced, the lightness of the product has increased, and the need for plasticizers has been eliminated, and, in addition, the strength properties of the films manufactured from the product, such as viscosity, tensile strength, impact tensile strength, and resistance to rupture, have improved. As taught by the invention, it has been surprisingly found that when certain internally plasticized polyvinyl alcohol copolymers and polyamide are mixed in molten state with polyolefins, such products are obtained which have a lighter colour and the oxygen sealing gained in which is considerably less sensitive to moisture than in using conventional polyvinyl alcohol, and in addition, the strength properties of the films manufactured from the product are better than in using ordinary polyvinyl alcohol and polyamide. Therefore, the invention concerns a gas-sealed material containing polyolefin, polyvinyl alcohol, and polyamide. The gas-sealed material of the invention is characterized in that said material is produced by mixing in molten state 3 to 60 per cent by weight of polyolefin, 10 to 96 per cent by weight of internally plasticized vinyl alcohol polymer, and 1 to 50 per cent by weight of polyamide. The term 'internally plasticized vinyl alcohol polymer' refers to a vinyl alcohol polymer which contains polyglycol groups (polyether groups) or other groups plasticizing polyvinyl alcohol in the side chains thereof. Said plasticizer groups are connected into a chain by copolymerizing, grafting or by means of reactive compounding. One such internally plastizied polyvinyl alcohol is Vinex polymer (trade name, Air Products and Chemicals Inc.) , in which for comonomer is used an ester of methacrylic acid and of polyethylene glycol. Said internally plasticized vinyl alcohol polymers may be manu¬ factured, for instance in the manner as disclosed in the US. patent No. 4,709,999. Said patent presents that the product is provided with good oxygen sealing and that it is appropriate for cast, in¬ jection moulding and extrusion products, and that it is characterized by good water solubility, and therefore, it is particularly well appropriate for manufacturing films which are required to possess water solubility. The vinyl alcohol polymer used in the polyolefin/polyvinyl alcohol/ polyamide mixture of the invention is advantageously such in which in the poly(alkyleneoxy)ester derivative for use as a comonomer the alkylene of the alcohol component is an ethylene or propylene, and the acid component is an acrylic acid or methacrylic acid. Said modified vinyl alcohol polymers may be manufactured, for instance, by poly¬ merizing vinyl acetate monomer and poly(alkyleneoxy)acrylate co¬ monomer, and hydrolyzing the copolymer thus obtained in order to produce an internally plasticized vinyl alcohol polymer. The quantity of the internally plasticized vinyl alcohol polymer in the polyethylene-polyvinyl alcohol-polyamide mixture of the invention may be in the range from 10 to 96 per cent by weight, preferably in the range of from 30 to 60 per cent by weight. In some instances, it may be preferable to substitute part of the internally plasticized vinyl alcohol polymer used in the gas-sealed material for unmodified polyvinyl alcohol if the purpose of the product allows. The polyolefin in a gas-sealed material of the invention may be based on homopolymers or copolymers of the olefins. Therefore, it may be low density polyethylene (LDPE) , medium density polyethylene (MDPE) or high density polyethylene (HDPE) , polypropylene, or poly- butene. The polyolefin may also be a copolymer of ethylene together with other olefins, such as propylene, butene, hexene and octene. The polyolefin may also be an olefin-ester copolymer, such as ethylene-vinyl acetate copolymer, ethylene-acrylate-ester copolymer, or ethylene-methacrylate ester copolymer, or it may be a thermoplastic olefin-based elastomer, such as EP or EPD rubber. The polyolefin in the process according to the invention may also be a homopolymer or a copolymer of the above-mentioned olefins which has been modified with the aid of carboxylic acid. To such a modified olefin polymer is copolymerized or grafted 0.1 to 10 per cent by weight of carboxylic acid. The carboxylic acid may comprise any unsaturated carboxylic acid or carboxylic acid anhydride which can be grafted or copolymerized in polyolefin. Examples of such acids are, for instance, acrylic acid, methacrylic acid, maleic acid fumaric acid, itaconic acid, crotonic acid, sorbic acid, and anhydrides of the afore-mentioned acids. In grafting or in copolymerizing one or several above acids may be used. The polyolefin grafted or copolymer- ized with carboxylic acid may also be a mixture containing a poly¬ olefin modified in the manner described above, and un unmodified polyolefin. The quantity of the polyolefin in the gas-sealed material of the invention may be in the range from 1 to 99 per cent by weight, but preferably in the range from 30 to 60 per cent by weight of the quantity of the entire mixture. A third component in a gas-sealed material of the invention is poly- amide. For the polyamide, for instance the following polyamides may be used: polyamide 6, polyamide 8, polyamide 10, polyamide 11, poly¬ amide 12, polyamide 6.6, polyamide 6.10, and polyamide 12-elastomers, or mixtures thereof. The quantity of polymer in the material of the invention may be selected from the range 1 to 50 per cent by weight. The polyamide enhances the viscosity and deep-drawing properties of the mixture of polyolefin and the polyvinyl alcohol copolymer. The gas-sealed polyolefin/PVA/PA mixture of the invention can be manufactured mixing the polyolefin component modified with the acid, the vinyl alcohol/copolymer component, and the polyamide component in a melt mixer simultaneously as a dry mixture, premixed in solid or in molten state, or then various components are added separately. From the polyolefin/PVA/PA mixture of the invention various products may be prepared by combining the mixture with polyolefins, other plastics or other materials, such as fibre-based materials. Multiple layer products may be manufactured by coextrusion, (co)extrusion coating, (co)extrusion lamination, adhesion lamination, or using other techniques, and these production procedures may also be combined. As products containing a gas-sealed material of the invention, e.g. films, moulded-blown bottles and containers, plates, tubes, injection moulded vessels, deep-drawn films and plates, liquid packaging card¬ board, .etc. may be mentioned. Sealed multiple-layer products are generally used for packaging foodstuffs, when oxygen sealing is desired also in moist circumstances, but the sealing of carbon dioxide or some other gas may be thought of. In addition, fat, chemical and odour sealing may be desired both in various foodstuff packages and technical products. In the following non-limiting examples the manufacturing, properties and application of the polyolefin/vinyl alcohol polymer/polyamide mixture of the invention in sealed one-layer products are described. The oxygen permeability of the films was measured with an OX-TRAN 1000 apparatus (ASTM D 3985). The polyolefins, the vinyl alcohol po- lymers and polyamides used in the tests of the examples are presented in the table below. Polyolefins P01 = LDPE (loy density polyethylene) , molten index (MI) 1.8 g/10 min (190°C) P02 - LLDPE (linear low density polyethylene) , grafted with 0.25 per cent by weight of fumaric acid, melt index 0.5 g/10 min (190°C) P03 - EAA (ethylene-acrylic acid copolymer) , acrylic acid content 6.5%, melt index 9.5 g/10 min (190°C) Polwinyl alcohol PVAl = vinyl alcohol copolymer wherein the comonomer is an ester of a methacrylic acid and a polyethy- lene glycol (Vinex 4004, trade name, Air Products and Chemicals Inc.) PVA2 - polyvinyl alcohol, viscosity 4, degree of hydro¬ lysis 88% Polyamides PA1 =- polyamide 6 PA2 = polyamide 11 PA3 = polyamide 12 Plasticizer glycerol, degree of purity 99% Example 1 Polyolefin/PVA/polyamide mixtures of the invention were prepared by mixing polyolefin, polyvinyl alcohol and polyamide, in molten state, with the aid of a Berstorff mixer which was provided with a flat film nozzle. The temperature profile was 130 to 190 to 200 to 210 to 210 to 210 to 220 to 215 to 210. The production rate was 10 kilograms per hour. The thicknesses of the obtained films were 120 to 170 μm. The com- pounds thereof are presented in the accompanying Table 1 A. The properties of the films are presented in the accompanying Table 1 B. The oxygen permeability values of the films are calculated for 25 μm thickness. The lightness of the films was measured as a so-called yellowness index conforming to the standard ASTM D 1925-70 with the Ultra Scan apparatus of Hunter Lab. TABLE 1 A Test Polwinyl alcohol Polyolefin Polyamide type % by weight type % by w. type % by w. 1 PVA1 60 P01 30 PA1 10 2 PVA1 60 P01 30 PA2 10 3 PVA1 60 P01 30 PA3 10 4 PVA1 30 P01 40 PA3 30 5 PVA2 60 POl 40 - - Note. In test 5 the quantity of polyvinyl alcohol includes 4.5% glycerol of the PVA quantity. TABLE 1 B Test Oxygen permeabil. Yellowness Tensile (ml/m^x24hxbar') inde , thick- strength 0%RH 90%RH ness μm mach./ 'trans dir. dir. MPa MPa 1 0.10 239 0.90 121 18.5 15.9 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 Example 2 Polyolefin/PVA/polyamide mixtures of the invention were prepared by mixing polyolefin, polyvinyl alcohol and polyamide, in molten state, with the aid of a Berstorff mixer which was provided with a flat film nozzle. The temperature profile was 130 to 190 to 200 to 210 to 210 to 210 to 220 to 220 to 215 to 210. The production rate was 10 kilograms per hour. The thicknesses of the obtained films were 130 to 210 μm. The com- pounds thereof are presented in the accompanying Table 2 A. The properties of the films are presented in the accompanying Table 2 B. The oxygen permeability values of the films are calculated for 25 μm thickness. The lightness of the films was measured as a so-called yellowness index conforming to the standard ASTM D 1925-70 with the Ultra Scan apparatus of Hunter Lab. TABLE 2 A Test Polyvinyl alcohol Polyolefin Polyamide type % by weight type % by w. type % by w. 1 PVA1 80 P02 10 PA1 10 2 PVA1 70 P02 3 PA1 27 3 PVA1 70 P02 3 PA2 27 4 PVA1 70 P02 3 PA3 27 5 PVA1 60 P02 30 PA1 10 6 PVA1 30 P02 20 PA1 50 7 PVA1 10 P02 60 PA1 30 8 PVA1 60 P01 30 PA1 10 9 PVA1 60 P03 30 PA1 10 10 PVA1 60 P02 30 PA1 10 11 PVA2 60 P01 40 - - 12 PVA2 70 P02 30 - - 13 PVA2 70 P01 20 PA1 10 14 PVA2 70 P01 20 PA1 10 15 PVA2 70 P01 30 - - Note. In tests 11, 12 and 14, the quantity of polyvinyl alcohol in¬ cludes 4.5% glycerol of the PVA quantity. TABLE 2 B Test Oxygen per eabil. Yellowness Tensile (ml/m«x24hxbar) index, thick- strength 0%RH 90%RH ness μm mach. /trans dir. dir. MPa MPa 1 0.2 0.8 0.80 140 20.4 19.0 2 1.0 3.4 0.70 130 33.9 27.5 3 1.1 3.8 0.70 131 31.2 25.5 4 1.2 3.5 0.70 145 30.4 23.2 5 1.1 1.5 0.53 170 22.8 24.8 6 5 20 0.85 172 39.1 27.2 7 3.5 50 0.90 186 31.5 30.1 8 1.2 1.6 0.76 192 21.4 20.8 9 0.9 2.2 0.82 171 20.9 19.7 10 1.1 8.8 30.1 164 23.6 21.0 11 0.2 10.0 10.9 211 10.0 7.0 12 0.2 9.6 11.5 198 14.0 11.0 13 0.8 7.6 11.2 172 17.7 12.3 14 0.8 8.1 11.0 145 17.8 8.4 15 0.2 9.7 11.0 163 10.3 8.7 The results indicate that by using vinyl alcohol copolymer for the polyvinyl alcohol in the mixture, in which the comonomer is an ester of methacrylic acid and polyethylene glycol (Vinex 4004) , a product is obtained the low oxygen permeability of which changes very little in a moist vicinity. The colour of the product (yellowness) is very low. Polyamide addition increases the tensile strength of the product both in machine and transversal direction.

Claims: 1 Claims 1. A gas-sealed material, containing polyolefin, polyvinyl alcohol, and polyamide, characterized in that said material is prepared by 5 mixing in molten state 3 to 60 per cent by weight of polyolefin, 10 to 96 per cent by weight of internally plasticized vinyl alcohol polymer, and 1 to 50 per cent by weight of polyamide. 2. Gas-sealed material according to claim 1, characterized in that ■ |0 i the vinyl alcohol polymer chains contain polyglycol groups (poly- ether groups) as side groups. 3. Gas-sealed material according to claim 1 or 2, characterized in that the polyvinyl alcohol is a copolymer in which the comonomer is 5 an unsaturated poly(alkyleneoxy)ester derivative. 4. Gas-sealed material according to claim 3, characterized in that said alkylene is an ethylene or propylene and that the acid component of said ester is an acrylic acid or methacrylic acid. 20 5. A gas-sealed mixture according to any one of the preceding claims, characterized in that the polyvinyl alcohol contains in a mixture an unmodified polyvinyl alcohol, and vinyl alcohol polymer according to claims 2 to 4. 25 6. A gas-sealed material according to any one of the preceding claims, characterized in that the polyolefin is a low density polyethylene (LDPE) , medium density polyethylene (MDPE) or high density poly¬ ethylene (HDPE) , polypropylene or polybutene, or ethylene copolymer 30 with propylene, butene, hexene and octene, or an olefin/ester co¬ polymer, such as ethylene-vinyl-acetate copolymer, ethylene-acrylate ester copolymer or ethylene methacrylate ester copolymer, EP rubber, EPD rubber, or other thermoplastic olefin-based elastomer. 35 7. A gas-sealed material according to any one of the preceding claims, characterized in that the polyolefin is modified by copolymerizing or grafting thereto 0.1 to 10 per cent by weight of carboxyl acid selected from the group of acrylic acid, methacrylic acid, maleic acid, fu aric acid, itaconic acid, crotonic acid, sorbic acid, and anhydrides of the afore-mentioned acids. 8. Gas-sealed material according to any one of the preceding claims, characterized in that the polyolefin is formed from a mixture of an unmodified polyolefin and a polyolefin modified with carboxyl acid. 9. Gas-sealed material according to any one of the preceding claims, characterized in that the polyamide has been selected from among the group of polyamide 6, polyamide 8, polyamide 10, polyamide 11, poly¬ amide 12, polyamide 6.6, polyamide 6.10, and polyamide 12 elastomers, or mixtures thereof. 10. Products containing gas-sealed material according to any one of the preceding claims.

Inventors: BERGSTROEM CHRISTER, KETTUNEN LEILA, LINDSTROEM HELGE, MATTSON LARS-AAKE, SEPPAENEN HANNELI, STJERNBERG MARIA, TUOMINEN OLLI, BERGSTROEM, CHRISTER, KETTUNEN, LEILA, LINDSTROEM, HELGE, MATTSON, LARS-AAKE, SEPPAENEN, HANNELI, STJERNBERG, MARIA, TUOMINEN, OLLI
Applicants: NESTE OY
Application year: 1990
Main classification: C08L77
IPC codes: C08L23, C08L29, C08L51, C08L77