Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Patent
1994-08-10
1996-10-01
Beck, Shrive
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
427185, 604367, B05D 106, B05D 124, A61F 1315
Patent
active
055609627
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
THIS INVENTION relates to a structure having controlled water resistance and in particular to a structure having a water-disintegrable core and a water-resistant biodegradable coating.
SUMMARY OF THE INVENTION
The invention provides a structure comprising a core of a material having mechanical strength when dry but not when water-wet and a coating comprising biodegradable water-resistant polymer.
It provides also compound structures in which two or more structures are laminated together or in which core material or other material is laminated to the structure.
The core can be for example a foam or assemblage of particles or assemblage of fibres or any combination of these. Such fibres are preferably naturally occurring, rather than man made. The core thus could be bread-like or paper or papier-mach e or felt or candyfloss-like. It may include one or more water-sensitive and/or biodegradable adhesives. There may be water-resistant material mixed in with water-disintegrable material, provided the proportion thereof is insufficient to decrease water-sensitivity below the level required for the intended use of the structure.
The coating can be, or can be convertible by heat treatment to, for example a smooth fused or sintered film covering the whole surface of the core, or a reticulated film following the contours of the core, or both. It can be limited, for example to the surfaces of the units (such as fibres) of which the core is composed, or to junctions between such units. The coating can be of thickness in the range 5 to 500 preferably 20 to 200 .mu.m, for example. The coating of biodegradable polymer can be additional to a coating of water-sensitive material.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In one form of the invention the structure has one dimension substantially less than the other two, so that it has two sides: then it can carry the coating on both sides or only one side. The polymer coating can be the working surface of the structure. Alternatively the core material can be the working surface, for example, in a structure required to absorb water or grease from one side while the other side maintains its mechanical integrity during absorption. Such structures are subject to disintegration thereafter in a microbially active environment.
The structure is when dry preferably rigid or to a required extent flexible and resilient, e.g. to permit rolling-up.
The coating is for example the product of applying the polymer in fine particulate form, followed by heating to fuse or sinter the polymer and, if appropriate, to increase its crystallinity.
The material of the core can be for example water-soluble, for example sugar, starch, polyvinyl alcohol or a water-sensitive ester or ether thereof or poly(meth) acrylic acid or a water-sensitive ester or amide thereof or a cationic vinyl or (meth)acrylic polymer. It may be slowly biodegradable, such as cellulose, eg wood pulp or paper, or non-delignified material such as wood shavings, sawdust, hay or straw. Very suitably it is paper or papier mach e, especially recycled. For practical purposes it is thus to be regarded as at least water-disintegradable.
The material of the coating preferably comprises at least one polyester, especially a polyhydroxyalkanoate. Particular examples of polyhydroxyalkanoates are those consisting of repeating units of formula O-R-CO where R is an aliphatic chain of 2 to 6 carbon atoms optionally carrying a lower alkyl (C.sub.1 -C.sub.4) branch particularly on the carbon atom next to oxygen in the chain. Their molecular weight Mw is preferably over 100,000, especially in the range 200,000 to 1.5 million. In particular examples, referred to hereinafter as HB(HV), the units are ##STR1## or both such units may be present in the polyester. The relative proportion of such units is preferably such as will give a polymer that is crystallisable e.g. on holding at 20.degree. to 100.degree. C. for 0.1 to 0.5 h or possibly up to 4 h. If copolymer is used it may contain for example at least 2, especially 3
REFERENCES:
patent: 3107172 (1963-10-01), Baptist et al.
patent: 3657044 (1972-04-01), Singer
patent: 4009313 (1977-02-01), Crawford et al.
patent: 4503098 (1985-03-01), Potts
patent: 4826493 (1989-05-01), Martini et al.
Brunger Peter M.
Kemmish David J.
Beck Shrive
Parker Fred J.
Zeneca Limited
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