GB2114987A

GB2114987A - Paints

Info

Publication number: GB2114987A
Application number: GB08205013A
Authority: GB
Inventors: David Eager
Original assignee: MACPHERSON GROUP PLC DONALD
Current assignee: MACPHERSON GROUP PLC DONALD
Priority date: 1982-02-19
Filing date: 1982-02-19
Publication date: 1983-09-01
Also published as: GB2114987B

Abstract

A thixotropic paint for application to a surface, in order to cover the surface with a solid veneer, said paint comprising e.g. an oil modified film forming alkyd, a dispersion of non- metallic particles and a dispersion of metallic particles. The paint may impart an antique, wood grain or other similar appearance to a surface.

Description

SPECIFICATION Paints The present invention provides a thixotropic paint containing at least two pigments which tend to separate when the viscosity of the paint is lowered by shear thus producing regions of visibly different colour. Such paint may for instance produce a wood grain, antique or other similar appearance on a surface.

In one known process for producing a wood grain or similar appearance a base coat is applied which is followed, upon drying, by a coat which is applied in such a manner so as to impart the required visual effect. The application is known as scumbling. A liquid graining coat is given the required appearance by means of a scumbling applicator, which may consist, for example, of a nylon pad which has an arcuate surface and has a series of concentric circular patterns in the surface. The surface of the applicator is rolled over the liquid paint and a graining and knotting effect similar to that seen on a wooden surface is imparted to the paint. However, use of the scumbling applicator as described above in this two coat process requires a high degree of skill and experience for an acceptable finish to the surface.

A paint intended for a one coat application to produce a grained effect is disclosed in United States Patent Specification No. 3,600,346. This paint contains a primary pigment dispersion which is usually coloured and is usually based on a conventional alkyd resin and a secondary pigment dispersion which is usually black in colour and is usually based on a styrenated or vinyl toluenated alkyd resin which is mutually insoluble with the alkyd resin employed in the primary pigment dispersion. The resultant mixture of the two dispersions usually has poor storage stability and may either become very sticky or settle badly during storage prior to its use. Furthermore, the desired pattern achieved by the method of application of the substance to a surface may deteriorate in quality before the substance has dried to a solid veneer.

The present invention provides a thixotropic paint comprising a film forming polymer, a dispersion of relatively high density pigment particles and a dispersion of relatively low density pigment particles, said thixotropic paint having a viscosity at low stress such that at low stress said particles are maintained in random suspension in said paint, and a viscosity at high stress such that said high and low density pigment particles separate to give regions in said paint containing a high proportion of the high density pigment and regions in said paint containing a high proportion of the low density pigment, the differences in composition of the said regions providing a visible difference in colour between the said regions.

The invention includes a thixotropic paint comprising a medium comprising at least one film forming polymer and a solvent, a dispersion of a first pigment or pigment mixture and a dispersion of a second pigment or pigment mixture pigment particles, said thixotropic paint having a viscosity at low stress such that at low stress said first and second pigments are substantially maintained in random suspension in said paint, and a viscosity at high stress such that said second pigment separates to give regions in said paint containing a high proportion of the second pigment and regions in said paint containing a high proportion of the first pigment, the differences in composition of the said regions providing a visible difference in colour between the said regions, wherein the first pigment includes a metal.

In preferred embodiments of the invention as described hereinbelow, the paint will contain a medium including a solvent and film forming material, and a pigment mixture, in addition to other additives.

The medium may comprise a thixotropic urethane oil-modified alkyd resin. This resin may be used alone or in combination with the alkyd resin obtained by reacting phthalic anhydride with a polyhydric alcohol such as glycerol or sorbitol. The resin may be further modified with a natural drying oil such as linseed oil, soyabean oil, tall oil, castor oil, soya-tung oil or safflower oil. Alternatively, a conventional alkyd resin produced by reacting a polyhydric alcohol with a polybasic acid or a polybasic anhydride may be used alone. Preferably, the solids content or content of film forming material of the medium is between 40 and 50 per cent by weight.

The dispersion of relatively low density pigment preferably comprises non-metallic particles.

These non-metallic particles are of carbon black, lamp black or black iron oxide, these substances constituting up to 4 per cent by weight of the resulting paint. The pigment may also contain other light fast and chemically inert organic and inorganic pigments, in order to modify the colour of the paint, these pigments constituting up to 4 per cent by weight of the paint.

The dispersion of relatively high density pigment preferably comprises metallic particles. These particles are of copper, zinc, bronze, brass, aluminium, copper having an oxide layer on the surface of the particle, or bronze having an oxide layer on the surface of the particle, the metallic particles constituting between 5 and 1 2 per cent by weight of the paint. The particle size and thickness determine, either alone or in combination, the resulting colour of the paint. Preferably the particles are finely divided laminae e.g. having a mean particle diameter of between 14 and 1 8 microns and a mean particle thickness of approximately 0.5 microns. The pigment may also contain silica particles, being finely divided, up to a quantity of 3 per cent by weight of the paint, in order to reduce the sheen, and dull the brightness of, the metallic particles.

A solvent may be added to the paint, which may preferably be white spirit but also mineral spirit, turpentine substitute, distillate, VM or P solvent xylol, the solvent being added in a quantity up to 50 per cent by weight of the paint. Up to 5 per cent by weight of the paint may be dipentine, which is added to the paint in order to improve the wetting action and workability of the paint when coating large areas.

Further additions may be added to the paint to improve the properties of the paint when being employed as described herein or when being stored prior or subsequent to use.

Catalysts may be added which accelerate the drying of the paint to a solid veneer after application. These catalysts may be any of the octoates, naphthenates or tallates of cobalt, calcium, lead zirconium, magnesium or zinc, or may be iron in quantities of 0.002 to 1.0 weight per cent of the paint.

An anti-oxidant may be added to prevent a skin forming on the liquid paint in the can during storage. In a preferred embodiment of the present invention, methyl ethyl ketoxime is added as an antioxidant.

Further additives to the paint may also be salts of lead or cobalt, for example, to prevent the catalyst additives being absorbed into the carbon black particles; structuring agents such as clays or hydrogenated castor oil, for example, up to a quantity of 2 per cent by weight of the paint to modify the viscosity and improve the anti-settlement properties of the paint such that the properties of the paint do not deteriorate during storage, and pigment wetting agents, such as soya lecithin, for example, up to a level of 2 per cent by weight of the carbon black, lamp black or black iron oxide employed, in order to improve the degree of dispersion of the pigment particles.

Using the preferred embodiments of the present invention, a grain effect may be produced by a single application of the paint to a surface, although in certain instances (mainly when porous surfaces are to be coated), a second application may give a greater uniformity to the finish. The preferred embodiments of the present invention allow the grain effects to be achieved in an applied film by brushing the surface, either with a normal paint brush or preferably with a brush having bristles which are uneven in length.

In addition, the use of a scumbling applicator, subsequent to the application of the paint, in the manner described hereinbefore may combine the result of an excellent surface finish to the paint, to give the desired graining effect, with ease of application.

The graining effect achieved when employing preferred embodiments of the present invention is thought to be principally derived from the difference in specific gravity between the two types of pigment e.g. the metallic and the non-metallic particles in the paint. The alkyd medium is highly thixotropic, and thus prior to application the metallic and non-metallic particles are held in suspension as a uniform dispersion in the paint. During the application, the viscosity of the paint decreases substantially, such that the metallic particles sink under the effect of gravity in relation to the less dense non-metallic particles which tend to be displaced upwards towards the outer surface of the paint by the movement of the applicator.

However, it may be that there is some incompatibility between the metallic pigments, particularly metallic laminae and nodular particles such as carbon black which causes separation.

If the metallic particles are plate-like, they will orientate and enhance the formation of streaks in the paint. This formation of streaks is also enhanced by the method of application, either by brushing or by using a scumbling applicator. Similarly, the non-metallic particles tend to aggregate and agglomerate to give streaks in the surface of the paint.

The preferred embodiments of the present invention provide a paint having a low viscosity, typically 1.0-1.5 poise at 10,000 sec-' at 250C, but a highly thixotropic nature. Hence the paint may be easily applied, particularly by brush application or by using a scumbling applicator but subsequent to application and brushing to achieve the desired effect there is a rapid increase in viscosity of the paint, resulting in the desired effect being permanently retained in the surface of the film which will not deteriorate in appearance due to subsequent flowing of the paint.

In further embodiments of the present invention, the polymer medium is of such a low pH value that it may react with the metallic particles and form soaps on the surface of the metallic particles.

These soaps help to increase the incompatibility of the metallic particles with the carbon black particles and help to dull the brightness of the metallic particles.

In further embodiments of the present invention, polypropylene or polyethylene wax may be incorporated into the paint to give a water repellant, readily polished, smooth film on drying.

Examples of preferred embodiments of the present invention are shown in the accompanying Table í: Table I Paint A Paint B Paint C % by Wt. % by Wt. % by Wt.

Finely Divided Copper 4% Finely Divided Aluminium 2% Finely Divided Aluminium 6% Finely Divided Bronze 4% Finely Divided Bronze 8% Finely Divided Copper 5% Finely Divided Silica 2% Finely Divided Silica 1% Finely Divided Silica 3% Carbon Black Pigment 1.5% Lamp Black Pigment 1% Carbon Black Pigment 1% Cobalt Drier 0.8% Yellow Iron Oxide Pigment 1.270% Cobalt/Zirconium Driers 0.5% Calcium Drier 1.4% Cobalt Drier 0.5% Calcium Driers 0.2% Methyl Ethyl Ketoxime 0.1% Lead Drier 0.8% Methyl Ethyl Ketoxime 0.005% Silicone 0.006% Calcium Drier 1.4% AP/ MG Clay 6.7% Urethane Modified Alkyd 65.346% Methyl Ethyl Ketoxime 0.08% Soya Bean Oil Modified Alkyd 10% Dipentine 3% Hydrogenerated Castor Oil 1.5% Urethane Oil Modified Aldyd 42.6% White Spirit 17.348% Soya Lecithin 1% White Spirit 24.995% Urethane Oil Modified Alkyd 34.6% Linseed Oil Modified Alkyd 28.6% Dipentine 2% White Spirit 16.24%

Claims

1. A thixotropic paint comprising a film forming polymer, a dispersion of relatively high density pigment particles and a dispersion of relatively low density pigment particles, said thixotropic paint having a viscosity at low stress such that at low stress said particles are maintained in random suspension in said paint, and a viscosity at high stress such that said high and low density pigment particles separate to give regions in said paint containing a high proportion of the high density pigment and regions in said paint containing a high proportion of the low density pigment, the differences in composition of the said regions providing a visible difference in colour between the said regions.

2. A paint as claimed in Claim 1 wherein said polymer is an alkyd resin.

3. A paint as claimed in Claim 1 wherein said polymer is alkyd resin modified with urethane oil.

4. A paint as claimed in Claim 3 wherein said polymer further comprises an alkyd resin, which is the product of the reaction of phthalic anhydride and a polyhydric alcohol, said alkyd resin being modified with a natural oil.

5. A paint as claimed in Claim 4 wherein said natural oil may be linseed oil, soya bean oil, tall oil, castor oil, soya-tung oil or safflower oil, or any two or more of these in combination.

6. A paint as claimed in Claim 1 wherein said relatively low density pigment particles comprise non-metallic particles and said relatively high density pigment particles comprise metallic particles.

7. A paint as claimed in Claim 6 wherein said non-metallic particles are comprised of carbon black, lamp black or black iron oxide, or any two or more of these in combination.

8. A paint as claimed in Claim 7 wherein said non-metallic particles constitute up to 4 per cent by weight of the paint.

9. A paint as claimed in Claim 6 wherein said metallic particles are comprised of copper, zinc, bronze, brass, aluminium, copper having an oxide layer on the surface of the particles or bronze having an oxide layer on the surface of the particles, or any two or more of these in combination.

10. A paint as claimed in Claim 9 wherein said metallic particles constitute between 5 and 1 2 per cent by weight of the paint.

1 A paint as claimed in Claim 10 wherein said metallic particles have a laminar shape, and have a mean particle diameter of between 14 and 1 8 microns and a mean particle thickness of approximately 0.5 microns.

12. A paint as claimed in Claim 1 wherein said paint further comprises up to 3 per cent by weight of silica particles.

13. A paint as claimed in Claim 1 wherein said paint further comprises a solvent, said solvent being white spirit, mineral spirit, turpentine substitute, di stillate VM or P solvent xylol, or any two or more of these in combination.

14. A paint as claimed in Claim 13, wherein said solvent constitutes up to 50 per cent by weight of the paint.

1 5. A paint as claimed in Claim 1 wherein said paint further comprises up to 5 per cent by weight of dipentine as a wetting agent.

1 6. A paint as claimed in Claim 1 wherein said paint further comprises catalysts to accelerate the drying of the paint, said catalysts being any of the octoates, naphthenates or tallates of cobalt, calcium, lead, zirconium, magnesium or zinc.

1 7. A paint as claimed in Claim 1 wherein said paint further comprises between 0.002 and 1 per cent by weight of iron, as a catalyst to accelerate the drying of the paint.

18. A paint as claimed in Claim 1 wherein said paint further comprises methyl ethyl ketoxime as an antioxidant.

1 9. A paint substantially as hereinbefore described as paint "A", Paint "B" or Paint "C" in Table 1.

20. A thixotropic paint comprising a medium comprising at least one film forming polymer and a solvent, a dispersion of a first pigment or pigment mixture and a dispersion of a second pigment or pigment mixture pigment particles, said thixotropic paint having a viscosity at low stress such that a low stress said first and second pigments are substantially maintained in random suspension in said paint, and a viscosity at high stress such that said second pigment separates to give regions in said paint containing a high proportion of the second pigment and regions in said paint containing a high proportion of the first pigment, the differences in composition of the said regions providing a visible difference in colour between the said regions, wherein the first pigment includes a metal.