Plastic material for packaging

Details Plastic material for packaging Plastic material for packaging

1996-12-24

1999-07-06

Glass, Margaret W.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

525 80, 428523, 428516, 428500, C08L 3312, C08L 2308

Patent

active

059198630

DESCRIPTION:

BRIEF SUMMARY
The 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 disk (yogurt, micro-oven food) or the whole product is not taken away instantly but 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 come more common with the development of packaging technique. There is a special need in the food processing industry, where there are applications in all sections, e.g. dairy products (cheeses, fats, yogurt), 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 manly in microwave oven.
In peelable compositions has most commonly been used as one component polybutylene and as another ethylene polymer, most often ethylene/vinylacetate copolymer (EVA) or low density polyethylene (LDPE). Also polypropylene can be included in the compositions. For instance in U.S. Pat. No. 4,759,984 is given a polymer composition, where the main component is EVA (75-92 wt-%) and minor amounts of polybutylene (6-25 wt-%) and polypropylene (2-15 wt-%) have been blended to it. Polyamide or polycarbonate are the most suitable substrates.
In the patent application EP 213,698 is given a composition, which consists of more than 50 wt-% of polybutylene and the rest is polypropylene and an ethylene polymer (EVA, HDPE, LDPE, LLDPE). In the European patent 178,061 there is a polymer blend containing 65-85 wt-% homo- or copolymer of ethylene (preferably LDPE or EVA), 5-30 wt-% polybutylene and 3-15 wt-% propylene polymer.
In the patent publication EP 196,727 is given a multilayer structure in which one layer is of polymer blend comprising 65-95 wt-% linear low density polyethylene (LLDPE) and 5-35 wt-% polypropylene and/or polyisobutylene.
In our earlier patent application FI925182 is given a peelable polymer composition containing 65-95 wt-% etylene/butylacrylate copolymer and 35-5 wt-% styrene grafted ethylene polymer, which is preferably ethylene/butylacrylate- or ethylene/vinylacetate copolymer. The weak point has, however, been the relatively narrow and rather low peelable area.
The purpose of this invention is to achieve a novel polymer composition, which is sealable and peelable at a very wide temperature area. Characterising to the polymer composition according to the invention is that it contains 5-80 weight-% ethylene/alkyl(meth)acrylate copolymer modified with vinyl monomer, preferably styrene, and 95-20 weight-% ethylene copolymer. Most preferably ethylene copolymer is ethylene/methyl(meth)acrylate, ethylene/ethyl(meth)acrylate, ethylene/butylacrylate or ethylene/vinylacetate copolymer. The amount of styrene modified ethylene copolymer must, however, be more than 35 weight-% if the other component is ethylene/butylacrylate copolymer. Methylarylate content of ethylene

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Abstract of JP 58180549.

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