GB2301597A

GB2301597A - Aqueous sodium silicate paint composition

Info

Publication number: GB2301597A
Application number: GB9611525A
Authority: GB
Inventors: Geoffrey Crompton
Original assignee: CROMPTON GARLAND Ltd
Current assignee: CROMPTON GARLAND Ltd
Priority date: 1995-06-03
Filing date: 1996-06-03
Publication date: 1996-12-11
Also published as: GB9511241D0; GB9611525D0

Abstract

A paint composition comprises a mixture of aqueous sodium silicate solution and an aqueous silicone emulsion together with typical paint components such as pigments. Preferably, additional substances are included in the composition, such as silane to aid adhesion and powdered additives to inhibit burning and to minimise smoke production under fire conditions. A method of making a paint composition comprising adding sodium silicate, hydrochloric acid and water to aqueous sodium silicate followed by adding a powder containing one or more frits is also claimed.

Description

TITLE: Paint compositions.

DESCRIPTION This invention concerns paint compositions based on sodium silicate.

Sodium silicate is a versatile material in liquid form. It is available as aqueous solutions having a range of silica to sodium oxide ratios. Aqueous sodium silicate is well known as an adhesive. Typically sodium silicate adhesives have a relatively higher ratio of silica to sodium oxide. A typical analysis would be 8.9% by weight sodium oxide, 29.2% by weight silica and 61.9% by weight water giving a specific gravity of 1.39 and a viscosity of 350 at 200C.

An object of this invention is to provide useful paint compositions based on aqueous sodium silicate.

According to a first aspect of the invention there is provided a paint composition comprising a mixture of aqueous sodium silicate solution and an aqueous silicone emulsion.

The aqueous silicone emulsion is preferably a reactive amino functional silicone and is preferably one that cures on evaporation of water. The preferred emulsion is 35% active and preferably contains both nonionic and cationic emulsifiers. A typically useful emulsion for this aspect of the invention has a specific gravity of about 0.99 at 250C. Suitable silicone emulsions for use in the compositions of the invention are sold under the trade names Ambersil Emulsion 3005 and G E Silicone SM 2059E.

In order to improve adhesion of compositions of the first aspect of the invention it is desirable to include in the compositions a silane. The silane preferably has a formula RnSi (X)4-n wherein R represents a moiety which affects adhesive strength, adhesion and mechanical properties, X represents an alkoxy group and n is an integer from 1 to 4.

The alkoxy groups hydrolyze in the presence of moisture to form silanol. These groups can co-condense to effect cross-linking through a moisture cure mechanism. Silanes of this type have free molecular hooks which migrate to the paint substrate interface to aid adhesion to the substrate.

Compositions according to the first aspect of the invention also preferably include zinc oxide preferably in an amount of 5 to 15, especially about 10% by weight.

The addition of zinc oxide to compositions of the invention starts a chemical change to the composition which aids in rendering it insoluble in water over a period of weeks.

According to a second aspect of the invention, there is provided a paint composition prepared by mixing an aqueous sodium silicate solution with hydrochloric acid followed by dilution with aqueous sodium silicate solution.

Such paint compositions may be insoluble in water.

The compositions according to the second aspect preferably include an aqueous silicone emulsion and more preferably still include a silane.

Compositions according to the second aspect of the invention may also include zinc oxide preferably in an amount 5 to 15% by weight, especially about 10% by weight.

Compositions according to the invention have been found to produce flexible coatings. Paint compositions of the invention will also include other typical paint components, such as, for example, pigment.

Suitable pigments for use in compositions of the invention include lithophone, albolith, ultramarine (alkali proof), ochre, iron oxide, carbon black, watersoluble nigrosine, iron oxide yellow, chromium oxide green and chromium oxide.

Compositions according to either aspect of this invention may further comprise one or more powder additives to inhibit burning and to minimise smoke production under fire conditions. The preferred powder additives may be selected from substances that give up water under heat, such as hydrated magnesium, calcium carbonate, hydrated calcium carbonate and alumina trihydrate, substances that melt and fuse under heat, such as one or more silica frits, especially a combination of frits, for example, as sold under the trade name CEEPREE, and zinc borate. Preferably all three of these additives will be included in compositions according to the invention. Alternatively powdered melamine may be used instead of or with any of the above powder additives.

It may also be advantageous to include mica in the powder additives when frits are present as the mica flows under heat and renders the frits stickier.

A sodium silicate based paint may be produced by adding a mix of sodium silicate, hydrochloric acid and water to aqueous sodium silicate followed by a powder mix comprising one or more frits, optionally with mica.

Other fire retardant materials may be included in the paint as described above. A wetting agent or alkaline surfactant may also be added to these paints.

For a primer coat the powder mix preferably comprises about 20% by weight of the paint composition, whereas for other coats up to about 60% by weight of the powder mix may be used.

Sodium silicate paint compositions can be made less soluble in water by addition of a substance that aids conversion of silicate into silica over a period of time. It has been found that silica itself and zinc borate are suitable substances for this purpose.

Other substance that may render sodium silicate paint compositions less soluble in water and increase flexibility include china clay, ball clay and kaolin clay.

Sodium silicate paint compositions of the invention may also be rendered more flexible by addition of aqueous silicone emulsion, such as, for example to an amount of 10% by weight or even 20% or more by weight, possibly with the addition of about 2% by weight of aqueous amino alkyl silicone solution (trade name "SILANE") to aid adhesion to a substrate. The resultant alkali tolerant composition may be diluted with water to a desired viscosity and may be stabilised with addition of a small amount, of say about 5% by volume, of alkali, such as aqueous ammonia.

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

Example A paint composition was prepared as follows: A sodium silicate solution was prepared by diluting 32 parts of aqueous sodium silicate solution (79'Tw, Sio2: Na20 ratio 3.3.1) with 320 parts of water.

11 parts of 36% hydrochloric acid were added with rigorous stirring and then the whole was diluted with 352 parts of aqueous sodium silicate solution (79'Tw).

The resulting solution had a specific gravity of 36'Tw.

A suitable pigment was added for colour.

10% by weight of a single component reactive amino silicone-functional silicone aqueous emulsion and 2% by weight of aqueous amino alkyl silicone emulsion (silane) was added to the mix.

Claims

1. A paint composition comprising a mixture of aqueous sodium silicate solution and an aqueous silicone emulsion.

2. A paint composition as claimed in claim 1, wherein the aqueous silicone emulsion is a reactive amino functional silicone.

3. A paint composition as claimed in claim 2, wherein the aqueous silicone emulsion cures on evaporation of water.

4. A paint composition as claimed in claims 1, 2 or 3, wherein the silicone emulsion is 35% active.

5. A paint composition as claimed in any one of claims 1 to 4 wherein the silicone emulsion contains both non-ionic and cationic emulsifiers.

6. A paint composition as claimed in any one of the preceding claims wherein the silicone emulsion has a specific gravity of about 0.99 at 250C.

7. A paint composition as claimed in any one of the preceding claims further comprising a silane.

8. A paint composition as claimed in claim 7, wherein the silane has the general formula RnSi(X)4-n wherein R represents a moiety which affects adhesive strength, adhesion and mechanical properties, X represents an alkoxy group and n is an integer from 1 to 4.

9. A paint composition as claimed in any one of the preceding claims further comprising zinc oxide.

10. A paint composition as claimed in claim 9 wherein the zinc oxide is in an amount of 5% to 15% by weight.

11. A paint composition as claimed in claim 10, wherein the zinc oxide is in an amount of 10%.

12. A paint composition as claimed in any one of the preceding claims further comprising a pigment.

13. A paint composition as claimed in claim 12 wherein the pigment is selected from lithophone, albolith, ultramarine (alkali proof), ochre, iron oxide, carbon black, water-soluble nigrosine, iron oxide yellow, chromium oxide green and chromium oxide.

14. A paint composition as claimed in any one of the preceding claims further comprising one or more powder additives to inhibit burning and to minimise smoke production under fire conditions.

15. A paint composition as claimed in claim 14 wherein the powder additives are selected from substances that give up water under heat, substances that melt and fuse under heat and zinc borate.

16. A paint composition as claimed in claim 15, wherein the substances that give up water under heat are selected from hydrated magnesium, calcium carbonate, hydrated calcium carbonate and alumina trihydrate.

17. A paint composition as claimed in claim 15 or 16, wherein the substances that melt and fuse under heat are one or more silica frits.

18. A paint composition as claimed in claim 17, wherein mica is included with the frits.

19. A paint composition as claimed in any one of claims 14 to 18, further comprising powdered melamine as a powder additive.

20. A paint composition as claimed in claim 1 producing by adding a mix of sodium silicate, hydrochloric acid and water to aqueous sodium silicate followed by a powder mix comprising one or more frits.

21. A paint composition as claimed in claim 21 further comprising mica.

22. A paint composition as claimed in claim 20 or 21 further comprising a wetting agent or alkaline surfactant.

23. A paint composition as claimed in claims 20, 21 or 22 to which has been added a substance that aids conversion of silicate into silica.

24. A paint composition as claimed in claim 23 wherein said substance is selected from silica and zinc borate.

25. A paint composition as claimed in any one of dclaims 1 to 24 further comprising a substance selected from china clay, ball clay and kaolin clay.

26. A paint composition as claimed in any one of claims 14 to 25, wherein the powder mix comprises up to about 60% by weight of the paint composition.

27. A paint composition as claimed in any one of claims 14 to 25, wherein the powder mix comprises about 20% by weight of the paint composition.

28. A method of preparing a paint composition comprising adding a mix of sodium silicate, hydrochloric acid and water to aqueous sodium silicate followed by a powder mix comprising one or more frits.

29. A method as claimed in claim 28 further comprising the step of adding to the composition a substance that aids conversion of silicate into silica.

30. A method as claimed in claim 29, wherein silica is added to decrease the solubility of the paint composition in water.

31. A method as claimed in claim 29, wherein zinc borate is added to decrease the solubility of the paint composition in water.

32. A paint composition substantially as hereinbefore described with reference to the foregoing Example.

33. A method of preparing a paint composition substantially as hereinbefore described with reference to the foregoing Example.