Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Patent
1995-05-12
1997-10-14
Seidleck, James J.
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
428100, 428515, 525 70, 525 73, 525 77, 525 80, 4273881, 4273899, 427391, 4273935, B32B 2730
Patent
active
056770693
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/FI93/00446 filed Nov. 3, 1993.
The present invention relates to a peelable polymer composition, a method for making the composition and films, sheets and lamination and coating products made from it.
In the packaging industry it is conventional that a product is packaged in a plastic film or a rigid plastic package and the package is heat sealed. The seal must possess a mechanical resistance sufficient to maintain the tight-seal properties during storage and transport. It is required that the package can be opened without destroying the product inside but to a growing extent it must also be possible to open the package without destroying the integrity of the film itself. The seal must be easily openable by pulling with hands without scissors or other instruments, the seal must be peelable. The package can also be used after opening for instance as a serving or heating disc (yoghurt, micro-oven food) or as a product holder where the product is kept in the opened package (candies, cereals).
The peelable seal can be defined to be the seal or joint between two films or sheets produced by heat sealing or impulse sealing, the joint thus formed having the property of being openable by pulling with hands. The seal can be between two films or two sheets or between a film or sheet and some substrate. Depending on the substrate, an adhesion layer may sometimes be needed between the layers in the sheet or film.
The use of peelable seals in different packages has become more common with the development of packaging techniques. There is a special need in the food processing industry, where there are applications in all sections, e.g. dairy products (cheeses, yoghurt), frozen food products, ready-processed food, canned food, meat and meat products, different snack and sweet packages. A very fast growing group is ready processed food and canned food which is heated mainly in a microwave oven.
In peelable compositions, the most commonly used component has been polybutylene and another has been ethylene polymer, most often ethylene-vinyl acetate copolymer (E/VA) or low density polyethylene (LDPE). Also polypropylene can be included in the compositions. For instance U.S. Pat. No. 4,759,984 describes a polymer composition, where the main component is E/VA (75-92 w-%) and minor amounts of polybutylene (6-25 w-%) and polypropylene (2-15 w-%) have been blended to it. Polyamide or polycarbonate are the most suitable substrates.
In the patent application EP 213.698, a composition is disclosed, which consists of more than 50 w-% of polybutylene and the rest is polypropylene and an ethylene polymer (EVA, HDPE, LDPE, LLDPE). European patent 178.061 describes a polymer blend containing 65-85 w-% homo- or copolymer of ethylene (preferably LDPE or EVA), 5-30 w-% polybutylene and 3-15 w-% propylene polymer.
In patent publication EP196,727 multilayer structure is described in which one layer is a polymer blend comprising 65-95 w-% linear low density polyethylene (LLDPE) and 5-35 w-% polypropylene and/or polyisobutylene.
The purpose of the present invention is to achieve a novel polymer composition, which is sealable and peelable. The polymer composition according to the invention comprises a blend of 5-35 weight-% ethylene copolymer modified with styrene and 95-65 weight-% ethylene butylacrylate copolymer. Preferably, the ethylene copolymer is ethylene butylacrylate or ethylene vinylacetate copolymer. The butylacrylate content of the ethylene butylacrylate copolymer can be 5-30 weight-%, preferably 16-18 weight-%. The vinyl acetate content in ethylene vinylacetate copolymer is 10-30 weight-%.
Ethylene copolymer can be modified with styrene by all conventional grafting methods or preferably by impregnating styrene and a free-radical initiator into the ethylene polymer and polymerising thereafter at a elevated temperature. Impregnation can be made without water, by addition of some water or by addition of water when more than half of the styrene has impregnated into polyolefin particles or all the time in th
REFERENCES:
patent: 4759984 (1988-07-01), Hwo
patent: 5164456 (1992-11-01), Vestberg et al.
patent: 5223311 (1993-06-01), Tsutsumi et al.
patent: 5300578 (1994-04-01), Vestberg et al.
patent: 5312872 (1994-05-01), Vestberg et al.
Mattsson Lars-.ANG.ke
Sainio Markku
Seppanen Hanneli
Vestberg Torvald
Borealis Holding A/S
Seidleck James J.
Truong Duc
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