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...
Reexamination Certificate
2001-04-26
2004-12-07
Yoon, Tae H. (Department: 1714)
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...
C524S599000, C524S845000, C528S361000, C427S256000
Reexamination Certificate
active
06828376
ABSTRACT:
This invention relates to an aqueous coating composition which on application to a surface gives a coating which on drying has improved early hardness and tack-resistance. It especially relates to a paint or varnish of the type suitable for application at ambient temperatures (usually 0 to 40° C.) to surfaces found on buildings or vehicles or on their fittings or furnishings or on metal or plastics containers. This invention also relates to a method of painting and varnishing a building or vehicle or its fittings or furnishings or a metal or plastics container by applying the paint or varnish to a surface by means of a conventional decorating tool or technique such as a brush, roller, pad or spray. The invention further relates to the use of the paint or varnish in providing a coating supported on a non-fibrous surface, for example a surface provided by plaster, masonry, (including brick, stone or concrete), metal or plastics.
Aqueous paints or varnishes comprise a film-forming polymer (including copolymers) dispersed or dissolved in a so-called aqueous vehicle which comprises water and optionally also water-miscible organic solvents. One of the difficulties with aqueous paints or varnishes is the relative slowness with which a dried coat of the paint or varnish becomes fully hard and tack-resistant even after substantially all of the aqueous vehicle has been removed by evaporation. Any delay in achieving hardness increases the risk of the dried coating being damaged by scuffing or scoring. The lack of early tack-resistance means that opposed contiguous freshly painted surfaces are liable to stick together or “block”, to use the British trade term. Opposed contiguous surfaces are found for example when a freshly painted door or window frame is closed against its freshly painted enclosing frame, or when freshly painted containers are packed together. Hence a lack of early tack-resistance delays the time when freshly painted doors and windows can be safely closed or when freshly painted containers can be packed.
It is known that the onset of hardness and tack-resistance can be accelerated by chemically cross-linking an unsaturated film-forming polymer. This occurs for example when traditional alkyd resins are autoxidised by atmospheric oxygen in the presence of an autoxidation promoter or “drying agent” such as cobalt octoate. The problem with autoxidation is that it continues (albeit slowly) throughout the life of the dried coat of paint and eventually increases hardness to such an extent that the coating becomes too brittle to withstand thermal expansion and contraction and so flakes off the painted surface. In addition, most of the film-forming polymers used commercially in aqueous paints suitable for application at ambient temperatures comprise polymerised acrylic or vinyl monomers containing no residual unsaturation after polymerisation so that cross-linking by autoxidation is not possible.
Aqueous latexes of either crystalline or moderately non-crystalline naturally occurring thermoplastic polyester particles obtainable from renewable agricultural feedstocks are known to form cohesive coatings on non-fibrous substrates if they are heated to temperatures of 100° C. of more. Such polyesters contain polyhydroxyalkanoates and are exemplified by copolymers of poly(3-hydroxy)butyrate (PHB) and poly(3-hydroxy)valerate (PHV). Similar biodegradable polyester of long-chain 3-hydroxyalkanoates and of 4- and 5-hydroxyalkanoates are also known. When all of the polyester particle is fully crystalline, the density of the polyester reaches its maximum which will be called the “crystalline density”, D
max
of the polyester. Conversely, when all of the polyester particle is fully non-crystalline, the density of the polyester reaches its minimum which will be called the non-crystalline density of the polyester, D
min
. If the particles are only partially crystalline, they will have an intermediate density lying between the non-crystalline and crystalline densities and the amount by which their density falls below D
max
(the crystalline density) is indicative of the amount of non-crystalline structure present in the polyester.
The polyesters may be produced microbially—via known micro-organism-induced fermentations of aqueous substrates as described for example in the article “Biopol Polyester” by J M Liddell in the book “The Chemical Industry—Friend to the Environment” edited by J A G Drake and published in 1992 by the Royal Society of Chemistry of London, see page 1 et seq. The contents of this article are herein incorporated by reference. The aqueous fermentation medium contains both nutrients and carbon source or sources which together support growth. The carbon sources also provide energy. Suitable micro-organisms include bacteria such as Bacillus megaterium, Cyanobacteria, Alcaligenes latus, Pseudomonas pseudoflava, Pseudomonas cepacia and preferably Pseudomonas oleovorans or Alcaligenes eutrophus. Alcaligenes eutrophus has the advantage of being ubiquitous in nature but it is only capable of forming polyesters whose repeating units contain 3 to 5 carbon atoms. Pseudomonas cepacia offers a much wider range of carbon chains. The nutrients should provide elements needed for cell multiplication such as nitrogen, phosphorous, sulphur, sodium, potassium, magnesium, calcium, zinc, iron and copper. The carbon sources may be carbohydrates such as starch, sucrose, and preferably glucose, or its salts, natural oils, alkanoic acids, preferably acetic, propionic or valeric (i.e. pentanoic) acids or alcohols such as methanol, ethanol, propanol or pentanol.
The fermentation is usually performed in two stages. Firstly, enough micro-organism is grown to provide a practicable concentration of the micro-organism. The amount grown is conveniently controllable by selecting an appropriate concentration of nutrient for use in the fermentation medium. On exhaustion of the nutrient, the organism ceases to grow and the second stage begins.
In the second stage of the fermentation, more carbon source is added to the substrate and the synthesis of the polyester either begins or more usually greatly accelerates. In nature, the polyester serves as a food store for the organism and it accumulates as discrete particles in the cytoplasm of the micro-organism.
A proportion of moderately non-crystalline polyester particles may be extracted as an aqueous dispersion from the micro-organism cells by a process such as that described in European Patent Specification EP 0 145 233A or its corresponding United States Patent Specification U.S. Pat. No. 4,910,145 (the contents of which are herein incorporated by reference) provided the process stops short of any oxidation treatment or of any attempt to separate the particles from the dispersion and dry them. Briefly a useful process comprises heating the aqueous suspension of cells obtained from the fermentation to at least 80° C. and the digesting the cells with proteolytic enzyme and/or surfactant which dissolves most of the non-polymeric cell material leaving the polyester as a dispersed particulate solid which can be recovered by filtration or centrifugation. The proteolytic enzyme may be for example at least one of pepsia, trypsia, bromelain, papain, ficin, rennin, chymotripsin or bacterial or fungal proteolytic enzymes. The surfactant may be an anionic surfactant such as a sulphated or sulphonated fatty acid and in particular it may be sodium dodecyl sulphate.
Unfortunately, coating compositions formed from aqueous dispersions of crystalline or moderately non-crystalline polyester particles do not form cohesive coatings on non-fibrous substrates at ambient temperatures (i.e. 0 to 40° C.) and so they are unsuitable for use in aqueous paints or varnishes of the type suitable for application to plaster, masonry, wooden or metal surfaces or any previously painted surfaces found on buildings or vehicles or their fittings or furnishings or on metal containers.
An object of the invention is to provide an aqueous coating composition which on application to a surface gives a coatin
Imperial Chemical Industries PLC
Pabst Patent Group LLP
Yoon Tae H.
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