GB2119390A

GB2119390A - Powder coating composition

Info

Publication number: GB2119390A
Application number: GB08310031A
Authority: GB
Inventors: David Martyn Mcrobbie
Original assignee: VALENTINE VARNISH AND LACQUER
Current assignee: VALENTINE VARNISH AND LACQUER
Priority date: 1982-04-14
Filing date: 1983-04-13
Publication date: 1983-11-16
Also published as: GB2119390B; GB8310031D0

Abstract

A curable powder coating composition suitable for electrostatic spraying to produce a "texture" finish comprises a polyester resin, an epoxy resin crosslinkable with the polyester resin, a natural or synthetic rubber or elastomer and, optionally, one or more of pigments, extenders and flow additives. The composition is produced by mixing, extruding and grinding the components.

Description

SPECIFICATION Powder coating composition This invention concerns powder coating composition such as are used to form "texture" finishes on, for example, metal surfaces by spraying the composition onto the surface and curing.

A "texture" finish is usually defined as being formed when the coating composition when cured has a definite base layer with upstanding ridges or lumps providing the texture.

Powder coating compositions are known which can be cured at relatively high temperatures, for example 1 800C. However, lower temperature curing systems are desirable for economy.

The object of this invention is to provide a powder coating composition suitable for producing a "texture" finish which is curable at relatively lower temperatures than hitherto.

According to this invention there is provided a curable powder coating composition comprising a polyester resin, an epoxy resin crossiinkable with the polyester resin and a natural or synthetic rubber or elastomer.

The compositions of this invention may also comprise one or more of pigments, extenders and flow agents.

The polyester resin may be a highly reactive carboxylic polyester such as that sold under the trade name SCADO P2980 which is a solid saturated carboxylic polyester resin.

The epoxy resin may be of the solid Bisphenol A epichlorohydrin type or of the diandiglycidyl ether type solid resin such as sold under the trade name EUROPEX 700 3 by Schering AG.

The rubber or elastomer may be an acrylonitrile/butadiene elastomer, such as that sold under the trade name CHEMIGUM.

Suitable extenders are calcium carbonate, say in the form of chalk and barium sulphate, say in the form of blanc fixe. The pigment will be chosen according to the desired colour but in any case inorganic compounds, usually oxides, are preferred to organic compounds.

The ratio of pigment to extender will depend on the colour required. For example a white composition will require very little extender say 35 parts pigment to 5 parts extender whilst on the other hand a black composition will require very little pigment, say 2 parts pigment to 38 parts extender.

The flow agent is preferably a silicone resin.

The composition of this invention preferably contains the following ingredients in the amounts given in parts by weight: Polyester resin 50-60 Epoxy resin 50 40

Pigment 040 Extenders J Rubber or Elastomer 3-1 5 Flow additive 0-0.2 The compositions of this invention may be made by any suitable means. Preferably the ingredients are mixed, extruded, ground and sieved so as to produce a powder having an average particle size of the order of 10-75 micron. The grinding is best carried out at a very low temperature so that usually the grinder will be cooled with liquid nitrogen.

The compositions of the invention are suitable for spraying onto most surfaces but are particularly suitable for electrostatic spraying onto steel and non-ferrous alloy surfaces. After spraying the composition may be cured by heat say at 1 600C for about 10 minutes. The cured composition has a "texture" finish.

This invention will now be further described by means of the following Examples: EXAMPLE 1 A white power coating composition was prepared by mixing the following ingredients in the amounts given in percent by weight: Diandiglycidylether type solid epoxy resin 19.0 (EUROPEX 700 3) Saturated carboxylic polyester solid resin 28.7 (SCADO P2980) Solid Bisphenol-A epoxy resin incorporating 0.2 10% of flow agent Calcitic calcium carbonate (MILLICARB) 28.7 Acrylonitrile/butadiene copolymer (CHEMIGUM) 5.8 Teflon modified micronised wax (TF1778) 0.5 Titanium dioxide (RTC-4) 17.1 The resultant mixture was extruded and ground in a grinder cooled with liguid nitrogen. The ground mixture was then sieved to leave a powder having an average particle size of from 10 to 75 microns.

The powder composition of this Example was sprayed onto a surface and found to cure satisfactorily at 1 600C in 10 minutes giving a "texture" finish.

EXAMPLE 2 A black powder coating composition was prepared by mixing the following ingredients in the amounts given in percent by weight: Diandiglycidylether type solid epoxy resin 19.0 (EUROPEX 700 3) Saturated carboxylic polyester solid resin 28.7 (SCADO P2980) Blanc fixe (precipitated barium sulphate) 1 5.6 Calcitic calcium carbonate (MlLLlCARB) 28.7 Solid Bisphenol-A epoxy resin incorporating 0.2 10% of flow agent Carbon black 1.5 Acrylonitrile/butadiene copolymer (CHEMIGUM) 5.8 Tefion modified micronised wax (TF1778) 0.5 The resultant mixture was extruded and ground in a grinder cooled with liquid nitrogen. The ground mixture was then sieved to leave a powder having an average particle size of from 10 to 75 microns.

Claims

1. A curable powder coating composition comprising a polyester resin, an epoxy resin crosslinkable with the polyester resin, and a natural or synthetic rubber or elastomer.

2. A composition as claimed in claim 1 wherein the polyester resin is a carboxylic polyester resin

3. A composition as claimed in claim 2 wherein the polyester resin is a solid saturated carboxylic polyester resin.

4. A composition as claimed in claim 1, 2 or 3 wherein the epoxy resin is of the solid Bisphenol A epichlorohydrin type or of the solid diandiglycidylether type.

5. A composition as claimed in any one of claims 1 to 4 wherein the rubber or elastomer is an acrylonitrile/butadiene elastomer.

6. A composition as claimed in any one of claims 1 to 5 further comprising one or more of pigments. extenders and flow agents.

7. A composition as claimed in claim 6 wherein the extender is calcium carbonate or barium sulphate.

8. A composition as claimed in claim 7 wherein the calcium carbonate is in the form of chalk.

9. A composition as claimed in claim 7 or 8 wherein the barium sulphate is in the form of blanc fixe.

10. A composition as claimed in any one of claims 6 to 9 wherein the pigment is an inorganic oxide.

11. A composition as claimed in any one of claims 6 to 10 wherein the flow agent is a silicone resin.

12. A composition as claimed in any one of claims 1 to 11 containing the following ingredients in the amounts given in parts by weight: Polyester resin 50-60 Epoxy resin 50-40 Pigment 0--40 Extender J Rubber or elastomer 3-1 5 Flow additive 0--0.2

1 3. A composition as claimed in any one of claims 1 to 12 having an average particle size of from 10-75 micron.

14. A method of preparing a composition as claimed in any one of claims 1 to 1 3 comprising mixing the ingredients, extruding the resultant mixture, grinding the extruded mixture and sieving the ground mixture.

1 5. A method as claimed in claim 1 4 wherein the grinding step is carried out in a grinder cooled with liquid nitrogen.

16. A curable powder coating composition substantially as hereinbefore described with reference to Example 1 or Example 2.

1 7. A method of preparing a curable powder coating composition substantially as hereinbefore described with reference to Example 1 or Example 2.