Patent Grant
6887571
The present invention relates to the production of coated silicon carbide particles, in particular to pigment coated silicon carbide particles.
Silicon carbide, also known as carborundum is a synthetic solid material comprising silicon and carbon. The hardness of silicon carbide is similar to that of diamond. Silicon carbide is produced electrolytically from graphite and silica under the influence of extreme heat and the product is then crushed to give a wide range of particle sizes.
Silicon carbide is a particulate material which has a smooth surface making it reflective and angular edges making it useful in products requiring slip resistant properties. Silicon carbide is only available in two colours which are black and dark green.
Silicon carbide is used in a variety of industries from grinding wheel manufacture to flooring.
Silicon carbide, is used to confer slip resistance and wear resistance to a variety of floors including vinyl safety floors. Its efficacy in achieving slip resistance has meant that its use is very wide spread in slip resistant flooring manufacture.
In flooring it is preferred to use the black version of the silicon carbide although it is less pure.
Being black, and used on the surface of a safety flooring, silicon carbide tends to darken the overall tone of the finished flooring. This is particularly an issue when high levels are used. In order to avoid the tone being darkened excessively, attempts have been made to use larger particles of silicon carbide, the idea being that, with larger particles, for a given mass per unit area, fewer particles can be used to achieve a particular slip resistance. However, with large black particles on a light background, the product appears very “functional” and is considered less aesthetically acceptable. Also if lost from the surface, large particles leave large surface voids.
Some users dislike the high reflectivity of the silicon carbide which is considered undesirable for certain applications.
It would therefore be advantageous to provide silicon carbide particles in colours other than black or dark green for use in slip resistant flooring to achieve the desired slip resistance while obtaining improved aesthetic properties.
Accordingly from a first aspect the present invention provides silicon carbide particles coated with a pigmented coating.
The coating may be a pigmented organic coating. Alternatively the coating may be a pigmented inorganic coating.
Where the pigment is a pigmented organic coating it is preferably a two part epoxy system where the two parts are mixed together to provide the pigmented organic coating.
Alternatively the pigmented organic coating may be a water based or solvent based epoxy or two part solvent based polyurethane or waterborne polyurethane or acrylic.
Where the coating is an inorganic coating it is preferably a ceramic glaze.
The silicon carbide particles may be coated with a coupling agent beneath the pigmented coating to aid adhesion of the pigmented coating.
The coating of the silicon carbide particles with a pigmented resin allows a range of colours to be obtained whilst still maintaining the angular edges of the particles which provide the required slip resistance when used in safety flooring.
The pigment can be any colour and the colour can be solid or metallic.
The silicon carbide particle size range is preferably from 0.2 to 0.8 mm.
According to a second aspect the present invention provides a method of applying an organic pigmented coating to silicon carbide particles comprising the steps of:—
The coated particles are preferably sieved to remove any agglomerates. The organic system is preferably a two part system wherein the two parts are mixed together then mixing with the silicon carbide particles. The organic coating system is preferably applied at a rate of 90-140 g/m2 of silicon carbide surface area, most preferably 120 g/m2 silicon carbide surface area.
The method preferably further comprises coating the silicon carbide particle with a coupling agent before applying the organic coating system.
The coupling agent is used to maximise adhesion of the organic coating system to the silicon carbide particles.
More than one coating of the organic coating system can be applied
In a third aspect the present invention provides a method of applying an inorganic pigmented coating to silicon carbide particles comprising the steps of fusing an inorganic pigmented coating onto the silicon carbide particles.
The inorganic coating is preferably a ceramic glaze.
Preferably the ceramic glaze comprises:
The alkali metal oxides may include lithium oxide, sodium oxide or potassium oxide.
The alkaline earth metal oxides may include magnesium oxide, calcium oxide and barium oxide.
The glaze may be made by mixing and fusing the selected components in a high temperature furnace to form a glass. The glass is preferably milled to form a powder known as a frit.
To coat the silicon dioxide particles with the ceramic glaze the frit is preferably applied to the particles, the water is removed by drying at almost 100° C. and the coated particles are then fired at temperatures of from 800° C. to 1400° C., most preferably 1200° C. to remelt the powder and form a glaze.
The present invention further provides a safety flooring material including the coloured silicon carbide particles of the present invention.
The silicon carbide particles confer slip resistance of the safety flooring material owing to their angular edges.
The coloured silicon carbide particles may be the same colour as the flooring material or alternatively the coloured silicon carbide particles may be a contrasting colour. The use of coloured silicon carbide particles means that the desired aesthetic effects can be achieved.
The safety flooring material could be made from plasticised PVC, plasticised acrylic, rubber, epoxy or polyurethane flow applied resin systems.
The present invention will now be described in more detail with reference to the following examples.
General Particle Coating
1. Organic Coating
The silicon carbide particles are mixed under low shear in a liquid pigmented organic coating, usually after coating with a coupling agent to improve adhesion of the final coating. The organic coating can be a two component epoxy or alternatively it could be a water based or solvent based epoxy or two part solvent based polyurethane or waterborne polyurethane or acrylic.
The application of frictional heat and/or externally applied heat reduces the viscosity of the coating system, allowing good coverage before the onset of curing which is accompanied by a rise in the viscosity. With water based systems the water would first be removed at 100° C.
Full curing is achieved after the coating has fully hardened onto the silicon carbide and there is no evidence of residual coating liquid.
The resulting product is then sieved to give correct particle size distribution.
Particle agglomeration is avoided by optimising the ratio of coating material to silicon carbide and agitation by tumbling or stirring in a rotary action mixer.
2. Inorganic Coating
Inorganic pigmented coatings such as vitreous enamel can be fused onto the silicon carbide particle at high temperatures.
Specific Formulations and Method
1. Pre-treatment—The silicon carbide particles are coated with the following coupling agent to maximise adhesion of the final coating. The coupling agent solution is added to the silicon carbide at 0.3 parts per hundred of silicon carbide and blended in a low shear rotary action mixer before force drying if necessary.
2. Coating—A resin system is added to the dried, pre-treated silicon carbide whilst mixing. Mixing is continued until the coating is cured. The product is forced dry and post cured if necessary.
The resin is added at a rate of 120 g per m2 of silicon carbide surface area.
In each two part resin system the whole of part A is mixed with the whole of part B before application to the silicon carbide particles. Typically the particles are mixed with the two part resin system in a ribbon or other rotary low shear mixer for about 60 minutes after which time the coating on the silicon carbide particles should be hard enough to handle.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0007731 | Mar 2000 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCTGB01/01447 | 3/30/2001 | WO | 00 | 4/21/2003 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO0174951 | 10/11/2001 | WO | A |
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| Number | Date | Country | |
|---|---|---|---|
| 20030157329 A1 | Aug 2003 | US |
