Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1994-10-14
1997-09-02
Cain, Edward J.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
525223, C08L 3300
Patent
active
056632320
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a peelable polymer blend or compound, a method for making the blend or compound and films, sheets and lamination products made from the blend or compound.
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 must also be possible to open the package without destroying the integrity of the film itself. The seal must be easily openable with pulling by 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 (yoghurt, micro-oven food) or when whole product is not taken away instantly but is kept in the open 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 substrate and 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 foods, canned foods, meat and meat products, different snack and sweet packages. A very fast growing group is ready processed foods and canned foods which are heated mainly in a microwave oven. A great part of packed foods are heat-processed after packaging when the materials and seals must resist the processing conditions. On the other hand sterilisable packages are needed also elsewhere as in packaging medical instruments.
Aluminium films and metallised plastic films are now commonly used in closing the heat-processable packages, e.g. containers.
In peelable compositions, one of the most commonly used components has been polybutylene and another is ethylene polymer, most often ethylene-vinyl acetate 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 describes a polymer composition, where the main component is EVA (75-92 w-%) and minor mounts of polybutylene (6-25 w-%) and polypropylene (2-15 w-%) have been blended to it. Polyamide or polycarbonate are the most suitable substrates.
Published patent application EP 213,698 describes a composition, 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.
Peelable polymer compositions based on polybutylene can also be sterilizable. Patent publication EP 339,990 describes a composition of 8-49 w-% polybutylene and 92-51 w-% polyethylene, which may also be functinalised with e.g. maleic anhydride.
The purpose of this invention is to achieve a novel polymer composition, which is sealable, peelable and also heat-processable. The polymer composition according to the invention is characterized in that it is a blend of polyolefin and ethylene-hydroxy(meth)acrylate consisting of 20-80 w-% polyolefin and 80-20 w-% ethylene-hydroxy(meth)acrylate co- or terpolymer, having as one comonomer 5-30 w-% hydroxyacrylate and as the comonomer 0-40 w-% vinyl compound.
The use of ethylene-hydroxyacrylate copolymer in sealable and peelable polymer compositions is especially advantageous, because the adhesion and cohesion properties resulting from hy
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Mattsson Lars-.ANG.ke
Ora Marja
Sainio Markku
Seppanen Hanneli
Vestberg Torvald
Borealis Holding A/S
Cain Edward J.
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