Stock material or miscellaneous articles – Composite – Of polyamide
Patent
1990-12-11
1993-04-13
Buffalow, Edith
Stock material or miscellaneous articles
Composite
Of polyamide
428516, 428520, 525 74, 525 78, B32B 2708
Patent
active
052021920
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to polyolefin-containing adhesive blends and multi-layered structures comprising the adhesive blends.
Polyolefin-containing blends suitable for use as adhesive layers in multi-layered structures are known. For example, Published European Patent Application 0258990 discloses a polyolefin-containing adhesive blend comprising (a) 10 to 30 parts by weight of a graft copolymer of a polypropylene backbone grafted with 0.001 to 30% by weight of at least one polymerisable ethylenically unsaturated carboxylic acid or derivative thereof, (b) 10 to 50 parts by weight of a linear low density polyethylene and (c) 20 to 80 parts by weight of polypropylene, the sum of (a), (b) and (c) being 100 parts by weight. The adhesive blend is suitable for bonding polypropylene to polar materials such as ethylene vinyl alcohol copolymers.
It has now been found that the use of a very low density polyethylene (VLDPE) in place of the linear low density polyethylene (LLDPE) used in the compositions disclosed in EP 0258990 provides an unexpected improvement in adhesive strength when used to bond polypropylene to a polar substrate. This improvement in adhesion is particularly pronounced when the multi-layered structure is retorted.
Food containers are retorted in order to kill bacteria or organisms which may cause premature spoiling of the food. Generally, the process comprises introducing the food into the container, closing the container and heating the closed container in a mixture of steam and air for about half an hour at 121.degree. C. The gases in the free space above the food expand on heating resulting in an increase in pressure within the container, but the retorting is carried out under pressure to maintain equilibrium.
The present invention therefore provides an improved polyolefin-containing adhesive blend and in particular it provides an adhesive blend suitable for bonding polypropylene to a polar substrate which blend has improved adhesion to polypropylene while maintaining good adhesion to the polar substrate, especially when the multi-layered structure is retorted.
Thus, according to the present invention a polyolefin-containing adhesive blend comprises; backbone grafted with 0.001 to 30% by weight of at least one polymerisable ethylenically unsaturated carboxylic acid or derivative thereof (C) being 100 parts by weight.
The polypropylene used as the backbone of the graft copolymer (A) and the polypropylene blending component (C) can be the same or different and can be a homopolymer or a copolymer of propylene with ethylene, butene or other unsaturated aliphatic hydrocarbons. Such homopolymers and copolymers are known and any such polymer can be used. Blends of two or more polypropylenes can be used. Preferably, if the polypropylene is a copolymer it comprises at least 80% of polymerised propylene units. Preferably, a crystalline polypropylene is used.
Very low density polyethylenes, are known and are copolymers of ethylene with one or more alpha-olefin. Suitable alpha olefins include those having from 3 to 8 carbon atoms such as propylene, butene-1, n-hexene-1, 4-methyl pentene-1 and octene-1. Terpolymers, such as ethylene/propylene/butene copolymer, may be used in the adhesive blend according to the present invention. VLDPEs can be prepared by known processes. VLDPEs have a higher comonomer content and lower density than LLDPEs. Typically, the comonomer content of a VLDPE is from 10 to 25% by weight. The density of a VLDPE can be from 0.86 to 0.91, preferably 0.86 to 0.906 and most preferably 0.86 to 0.900. A mixture of two or more very low density polyethylenes can be used in the adhesive blend according to the present invention.
Polymerisable ethylenically unsaturated carboxylic acids and derivatives thereof include, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, citraconic acid, mesaconic acid, maleic anhydride, 4-methyl cyclohex-4-ene-1,2-dicarboxylic acid anhydride, bicyclo (2.2.2) oct-5-ene-2,3-dicarboxylic acid anhydride, 1,2,3,4,5,8,9,10-octahydronaphthale
REFERENCES:
Modern Plastics International, vol. 17, No. 2, Feb. 1987, A. Sternfield: "Versatile VLDPEs Offer Impressive Property Range for Processors", pp. 34-35.
Hope Philip S.
Malley Peter J.
BP Chemicals Limited
Buffalow Edith
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