Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
1999-08-13
2001-03-20
Krynski, William (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S327000, C428S323000, C428S375000, C106S412000, C106S416000, C524S444000
Reexamination Certificate
active
06203906
ABSTRACT:
This invention concerns polymer formulations, particularly those which are curable to provide rigid or semi-rigid products. It also concerns paint formulations, as liquid paints or powder coating compositions. An object of the invention is to confer improved abrasion resistance on cured products or paint films derived from such formulations.
The majority of fillers and pigments used in polymer formulations and paints are relatively soft and do not by themselves provide good abrasion resistance. It is known that abrasion resistance can be improved by incorporating in the formulation a relatively small proportion of a harder material. Thus JP-A-7-179616 describes artificial marble containing 0.2-5% by volume of fused alumina. But fused alumina is formed by melting aluminium oxide by heating at a temperature above 2000° C. followed by crushing and grinding the resultant cooled fused alumina, and commands a premium price. This invention results from the discovery of cheaper materials which can provide excellent abrasion resistance.
It might appear easy to improve the abrasion resistance of a polymer formulation by adding to it a relatively hard filler in a relatively high concentration sufficient to provide the desired abrasion resistance. But various disadvantages result from the incorporation of too much hard filler into a polymer formulation: the mechanical properties of the polymer may be spoiled; the colour and appearance of the product may be spoiled; the shaped and cured product may be difficult or impossible to cut or machine; the mouldable polymer formulation or paint may itself be abrasive and may damage the equipment used to handle it. These problems may be solved by using only a small concentration of a suitable hard filler to provide the desired abrasion resistance without its attendant disadvantages. This invention results from the discovery of such materials.
In U.S. Pat. No. 3,928,706 are described wear-resistant decorative laminates formed by applying to fibrous sheets a layer based on a thermosetting resin and an abrasion-resistant additive which is, however, used in a rather high concentration.
In U.S. Pat. No. 4,713,138 are described abrasion-resistant decorative laminates formed by applying to fibrous sheets a composition containing a thermosetting resin and an abrasion-resistant powder as the major or only filler material.
In one aspect the invention provides a formulation comprising as the major component a polymerisable monomer or polymer and optional filler materials, wherein there is present as an abrasion-resistant additive from 0.05-5% by weight on the weight of the non-fugitive content of the formulation of silicon carbide or an &agr;-alumina selected from at least one of: calcined unground alumina, calcined and ground alumina, and tabular alumina.
These formulations may be solid or semi solid or fluid mixes of the kind which are cast, moulded or extruded to form shaped products, which term is used to include sheet. These products are preferably rigid or semi-rigid and have plastic rather than elastic properties. Examples of such products where abrasion resistance is important include worktops such as kitchen worktops and floor tiles. Other formulations according to the invention include paints, both liquid paints and powder coating compositions, particularly of the kind where an applied paint film is cured to provide an abrasion resistant coating. The invention also includes fibres and other articles, whose shape and nature are not material to the invention, whose surface is coated with a film derived from such a liquid paint or powder coating composition.
The formulation may be thermoplastic but is preferably thermosetting. The formulation may be converted to a shaped product simply by removal of water or other volatile component. More usually a step of polymerisation or cross linking or curing the shaped product will be included, which step may be effected by heat or radiation or chemicals or other conventional means. Thus in another aspect the invention provides a shaped product of the kind comprising a polymer and optional filler materials, wherein there is present as an abrasion-resistant additive from 0.05-5% by weight on the weight of the product of silicon carbide or an &agr;-alumina selected from at least one of: calcined unground alumina, calcined and ground alumina, and tabular alumina.
The polymer is preferably a synthetic resin and may for example be polyester, acrylic, epoxy, PVC, polyolefin, polystyrene, polyamide, polyurethane, alkyds, etc. Preferred are PVC and thermosetting polyester, acrylic and epoxy resin formulations. Or the formulation may contain a polymerisable monomer (or oligomer) such as for example methyl methacrylate. Thus methyl methacrylate monomer (or oligomer) might have been present in the formulation of Example 2 below, as well as or instead of the resin.
The formulation generally contains a filler. The nature of the filler is not material to the invention, and those conventional in the field may be used, including inorganic particulate fillers such as calcium carbonate, magnesium carbonate, talc, fibrous fillers e.g. wollastonite, titanium dioxide and other white and coloured pigments, aluminium trihydroxide, China clay, silica, etc. Such fillers generally have a hardness of less than about 7 on the Mohs' scale, in contrast to the abrasion resistant additives described herein which have a Mohs' hardness much greater than 7. The proportion of filler is up to 400 phr e.g. 10-400 phr or 50-300 phr preferably 100-250 phr (parts by weight per hundred parts by weight of resin). Of particular interest is aluminium trihydroxide which, by virtue of having a refractive index of 1.50-1.57 about the same as many synthetic resins, can be used as a flame-retardant filler which confers a translucent rather than a white appearance on the product.
The filler may be useful to control the colour or opacity of the polymer, or to provide fire-resistant properties, or may be present simply to reduce the cost of the product. In some cases a filler is not necessary. Example 4 below shows a rigid PVC formulation whose fire resistance was adequate, and which did not require a filler for any other reason. Formulations containing substantial proportions of plasticisers or other materials are likely to require a fire-resistant filler. Thus the flexible PVC formulation shown in Example 5 contained aluminium trihydroxide.
The formulation may also contain other conventional additives such as dyes, stabilisers, polymerisation regulators, anti-blocking agents, flame retardants, smoke suppressants, ultra violet absorbents, anti-static agents, titanates, zirco aluminates, organometallic compounds, surfactants, etc. Wetting agents and silanes may be included to improve initial wear resistance. Particularly in aqueous compositions, microcrystalline cellulose particles may be included. (See U.S. Reissue Pat. No. 32,152). Particulate PTFE or polyamide resin materials may be included as anti scuffing agents. All these conventional additives may be used in conventional concentrations. Preferably the non-fugitive part of the polymer formulation consists essentially of the polymerisable monomer or polymer and optional filler materials and the abrasion-resistant additive, as described above, together optionally with one or more of these conventional additives.
A distinction is made herein between fugitive components, which disappear, typically by volatilisation, during the conversion of the formulation to a shaped polymer product or coating; and non-fugitive components which remain in the shaped polymer product or coating. Water and volatile organic solvents are examples of fugitive components. Methyl methacrylate is an example of a non-fugitive component, which though to some extent volatile, substantially remains in the shaped polymer product or coating.
This invention is characterised by the use of 0.05-5% by weight, preferably 0.1% to 3% and particularly 0.2-1% or 2% by weight on the weight of the formulation, of silicon carbide or preferably a
Christie Robert Michael
Cowton Richard John
Evans Kenneth Arthur
Southern Jennifer Carolyn
Alcan International Limited
Cooper & Dunham LLP
Gray J. M.
Krynski William
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