GB2118188A

GB2118188A - Powder coating compositions

Info

Publication number: GB2118188A
Application number: GB08310032A
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: 1983-10-26
Also published as: GB2118188B; GB8310032D0

Abstract

A curable powder coating composition suitable for electrostatic spraying to produce a "structure" finish is prepared from a ground, extruded mixture of an epoxy resin, a curing agent therefor and optionally one or more of pigments and extenders and a ground blend of a silicone flow additive and a portion of epoxy resin mixed together.

Description

SPECIFICATION Powder coating compositions This invention concerns powder coating compositions such as are used to form "structure" finishes on for example, metal surfaces by spraying the composition onto the surface and curing the sprayed composition. The invention also concerns a method of producing such compositions.

A "structure" finish is usually defined as one having a base layer of material which when cured has formed therein valleys and pits providing the structure.

"Structure" compositions are known which are based on silicones. One problem with these compositions is that when sprayed onto surfaces some of the composition enters the atmosphere and can settle on other surfaces to be coated. The silicone can reduce adhesion of other coatings, such as paint, to surfaces causing formation of socalled "fish-eyes" and other blemishes. Thus spraying of silicone based compositions can contaminate factories and workshops.

Also, such silicone based coating compositions can require relatively high temperatures of the order of 2000C for curing. Lower curing temperatures are desirable for economy.

The object of this invention is to provide a powder coating composition for producing a "structure" finish which causes little or no atmospheric contamination and which is curable at relatively lower temperatures than hitherto.

According to this invention there is provided a curable powder coating composition comprising a curable epoxy resin, a curing agent for the epoxy resin and a silicone flow addition, the silicone flow additive being added to the composition in ground form after grinding of the other components thereof.

The invention also provides a method of producing a powder coating composition comprising mixing, extruding and grinding a curable epoxy resin and a curing agent therefor, and adding to the ground mixture a ground silicane flow additive.

The compositions of the invention may also comprise one or more of pigments and extenders which will usually be mixed with the epoxy resin and curing agent.

The silicone flow additive is preferably first blended with a portion of epoxy resin to form a master-batch which is then ground to the same size as the mixture of the other components and mixed with the mixture of the other components.

The grinding is best carried out at very low temperatures so that usually the grinder is cooled with liquid nitrogen. An average particle size of the order of 10-75 microns is preferred.

The epoxy resin is preferably one which will cure at relatively low temperatures, say at or below 1 400C. and may be of the solid Bisphenol A epichlorohydrin type. Any suitable curing agent may be used such as an accelerated amine or a resinous phenolic compound.

The silicone flow additive may be a silicone oil, such as that sold under the trade name BAYSILONE by Bayer AG.

Suitable extenders are calcium carbonate, say in the form of chalk, barium sulphate say in the form of blanc fixe, and magnesium carbonate. 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 whilst on the other hand a black composition will require very little pigment.

The compositions of this 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 compositions may be cured by heat say at 1 400C for 10 minutes and gives a "structure" finish.

This invention will now be further described by means of the following Examples.

EXAMPLE 1 A white powder coating composition was prepared by mixing solid bisphenol A epichlorohydrin type epoxy resin of low molecular weight, solid resinous phenolic curing agent, a coprecipitate of calcium carbonate and magnesium carbonate and titanium dioxide. The mixture was extruded and then ground in a grinder cooled with liquid nitrogen. The ground mixture was sieved to leave a powder having an average particle size of from 10 to 75 microns.

Then, a mixture of solid bisphenol A epichlorohydrin type epoxy resin and silicone oil was extruded, ground in a grinder cooled by liquid nitrogen, and sieved to leave a powder also having an average particle size of from lotto 75 microns.

This powder was then mixed with first-mentioned powder to give the following composition in percent by weight: Solid bisphenol A epichlorohydrin 37.0 type epoxy resin (low molecular weight) Solid resinous phenolic curing 12.5 agent Co-precipitate of calcium sulphate 1 9.9 and barium sulphate (MICRODOLX) Titanium dioxide 30.0 Silicone oil (BAYSILONE) 0.6 The powder composition of this Example was sprayed onto a surface and found to cure satisfactorily at 1 40 C in 10 minutes giving a "structure" finish.

EXAMPLE 2 A black powder coating composition was prepared by mixing solid bisphenol A epichlorohydrin type epoxy resin (low molecular weight), solid resinous phenolic curing agent, coprecipitate of calcium carbonate and magnesium carbonate and carbon black. The mixture was extruded and then ground in a grinder cooled with liquid nitrogen. The ground mixture was sieved to leave a powder having an average particle size of from 10 to 75 microns.

Then, a mixture of solid bisphenol A epichlorohydrin type epoxy resin (low molecular weight) and silicone oil was extruded, ground in a grinder cooled with liquid nitrogen, and sieved to leave a powder having an average particle size of from 10 to 75 microns. This powder was then mixed with the first mentioned powder to give the following composition in percent by weight: Solid bisphenol A epichlorohydrin 37.0 type epoxy resin (low molecular weight) Solid resinous phenolic curing 1 2.5 agent Coprecipitate of calcium carbonate 48.4 and magnesium carbonate Silicone oil (BAYSILONE) 0.6 Carbon black 1.5 The powder composition of this Example was sprayed onto a surface and found to cure satisfactorily at 1 400C in 10 minutes giving a "structure" finish.

Claims

1. A curable powder coating composition comprising a curable epoxy resin, a curing agent for the epoxy resin and a silicone flow additive, the silicone flow additive having been added to the pomposition in ground form after grinding of the other components thereof.

2. A composition as claimed in claim 1 wherein the epoxy resin is curable at a relatively low temperature.

3. A composition as claimed in claim 2 wherein the epoxy resin is curable at or below 1400 C.

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

5. A composition as claimed in any one of claims 1 to 4 wherein the curing agent is an accelerated amine or a resinous phenolic compound.

6. A composition as claimed in any one of claims 1 to 5 wherein the flow additive comprises a silicone oil.

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

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

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

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

11 A composition as claimed in any one of claims 7 to 10 wherein the pigment is an inorganic oxide.

12. A composition as claimed in any one of claims 1 to 11 having an average particle size of from 10 to 75 microns.

13. A method of producing a curable powder coating composition comprising mixing, extruding and grinding a curable epoxy resin and a curing agent therefor, and adding to the ground mixture a ground silicone flow additive.

14. A method as claimed in claim 13 wherein one or more of pigments and extenders are mixed with the epoxy resin and curing agent prior to extruding.

15. A method as claimed in claim 13 or 14 wherein the silicone flow additive is first blended with a portion of epoxy resin before grinding and adding to the ground mixture of other components.

16. A method as claimed in claim 13, 14 or 15 wherein grinding is carried out in a grinder cooled with liquid nitrogen.

17. A method as claimed in any one of claims 13 to 1 6 wherein the components are ground to an average particle size of from 10 to 75 microns.

1 8. A method as claimed in any one of claims 13 to 1 7 wherein the epoxy resin is curable at a relatively low temperature.

19. A method as claimed in claim 18 wherein the epoxy resin is curable at or below 1400 C.

20. A method as claimed in claim 1 8 or 19 wherein the epoxy resin is of the solid Bisphenol A epichlorohydrin type.

21. A method as claimed in any one of claims 1 3 to 20 wherein the curing agent is an accelerated amine or a resinous phenolic compound.

22. A method as claimed in any one of claims 13 to 21 wherein the flow additive comprises a silicone oil.

23. A method as claimed in any one of claims 13 to 22 further comprising mixing one or more of pigments and extenders with the epoxy resin and curing agent.

24. A method as claimed in claim 23 wherein the extender is calcium carbonate, barium sulphate or magnesium carbonate.

25. A method as claimed in claim 24 wherein the calcium carbonate is in the form of chalk.

26. A method as claimed in claim 24 wherein the barium sulphate is in the form of blanc fixe.

27. A method as claimed in any one of claims 23 to 26 wherein the pigment is an inorganic oxide.

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

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