GB2152841A - Method for producing a decorative finish on a substrate of heterogenous composition - Google Patents

Abstract

A method for producing a decorative finish on a substrate of heterogenous composition comprises applying a lyophilic dye in a liquid medium to the substrate and subsequently applying a pigmented liquid. The method produces a variegated colour effect which bears no resemblance to the surtace pattern of the underlying substrate and, in some cases, in reminiscent of certain naturally occurring marble stones.

Description

SPECIFICATION Method for Producing a Decorative Finish on a Substrate of Heterogeneous Composition This invention relates to a method for producing a decorative finish on 3 substrate of heterogeneous composition such as a wood-based or synthetic particle board, for instance, chipboard, MDF (medium density fibre board), bagass board or hardboard.

The conventional method of finishing wood involves the use of transparent lacquers and sealers in conjunction with propietary stains. First, the proprietary stains, which are commonly blends of primary colours of dyes and pigments in a liquid medium, are applied to the substrate. The proprietary stains may also incorporate a pore-filler in which case a further coat of proprietary stain will normally be applied to the filled surface to obtain a uniform colour. After the substrate has been stained, it is then finished by the application of transparent conventional sealers and lacquers, which may be colourless or slightly tinted.

However, unlike natural wood, particleboards have not been considered as materials possessing a decorative enough surface to be used with transparent finishes in the manufacture of furniture.

Furthermore since particleboards are produced from finely chopped particles and fibres of wood or synthetic materials which are cemented together with water-borne adhesives under pressure at a high temperature, the surface of a particleboard is coarse, pitted, generally porous and therefore highly absorptive to liquids such as lacquers and paints. Thus, uneconomic quantities of conventional liquid finishes would have to be applied to a particleboard to fill the pits and saturate the air spaces at the surface so that a smooth, protective film of finish could be obtained. Consequently, conventional finishing processes, as described above, have not been applied to particleboards.

For the above reasons, previous methods of finishing particleboards have generally involved surfacing the boards with printed paper or laminates, or sealing the boards with plain paper before applying a liquid finish such as paint.

However, it has now been surprisingly discovered that, when certain substances are applied directly to the surface of a particleboard, in a particular manner, an unexpected attractive variegated colour effect is produced of highly decorative appearance which bears no resemblance to the surface pattern of the underlying substrate.

According to the present invention there is provided a method for producing a decorative finish on a substrate of heterogeneous composition comprising applying a lyophilic dye in a liquid medium to the substrate and subsequently applying a pigmented liquid.

It is preferred that the lyophilic dye forms a solution or dispersion with the liquid medium, the active dye content of the solution or dispersion preferably being in the range from 0.1% to 10%, and typically 3% (weight/volume). The liquid medium is preferably an organic liquid or a mixture of organic liquids selected from the group consisting of alcohols (e.g. ethanol), ketones (e.g butanone), esters (e.g. butyl ethanoate), aliphatic hydrocarbons, aromatic hydrocarbons (e.g.

toluene), ethers, (e.g. diisopropylether), alkoxyalcohols (e.g. 2-ethoxyethanol) and their esters (e.g. 2-ethoxyethyl ethanoate).

The pigmented liquid may be opaque or translucent and preferably includes a pigment, a resin binder, a plasticiser, a flow agent, a stabiliser and an organic liquid.

The pigment is preferably an inorganic salt or oxide or mixture of inorganic salts and/or oxides selected from the group consisting of titanium dioxide, aluminium oxide, aluminium silicate, antimony sulphide, barium sulphate, cadmium sulphide, calcium silicate, china clay, chromium oxide, lead cabonate, lead oxide, magnesium oxide, magnesium carbonate, iron oxide, silica, talc, ultramarine, mercury sulphide, calcium carbonate, zinc carbonate, zinc oxide and zinc sulphide. Of these pigments, titanium dioxide is especially preferred.

The resin binder preferably consists of an alkyd, cellulose nitrate, acid-curing aminoplast, polyester, vinyl or acrylic resins or suitable blends of these and the plasticiser is preferably dibutyl phthalate. The organic liquid may be any of those listed above as suitable for forming the liquid medium or a mixture of any of these.

The pigmented liquid may also include dyes and/or organic pigments. However, the total amount of pigment must be in the range of 0.1% to 20% of the pigmented liquid and the resin binders must be in the range of 5% to 60% of the pigmented liquid.

The method of the invention may also include the additional step of applying a pore filler to the substrate prior to the application of the solution or dispersion of lyophilic dye and applying a protective lacquer subsequent to the application of the pigmented liquid.

The effects of applying the method of the invention to a heterogeneous substrate are illustrated by the accompanying Figures in which: Figure 1 shows the surface of a piece of chipboard to which a lyophilic dye and a transparent lacquer have been applied and is not according to the invention; Figure 2 shows the surface of a piece of chipboard to which the method of the invention has been applied according to the conditions of Example 1; and Figure 3 shows the surface of a piece of chipboard to which the method of the invention has been applied according to the conditions of Example 4.

Generally, the substrate to which the decorative finish is to be applied is first sanded to an acceptable standard of smoothness. A pore-filler may then be applied whose physico-chemical properties are such that, after a suitable interval of time following its application, it resists the action of common industrial solvents but does not prevent the absorption of dyes by the surface of the substrate.

A solution or dispersion of a lyophilic dye or mixture of lyophilic dyes is then applied to the substrate by any of a number of standard methods of application. Such methods include dipping, spraying, paint brush, sponge, cloth and curtaincoating machine.

Following application of the dye solution or dispersion, the liquid medium is allowed to evaporate and an opaque or translucent pigmented liquid is then applied to the substrate by any suitable method, for instance, spraying. A typical pigmented liquid has the composition: Titanium dioxide pigment 3 parts Resin binder(s) 25 parts Plasticisers 3 parts Flow agents, stabilisers etc. 2 parts Organic liquids 67 parts After application of the pigmented liquid, the substrate is left in a well ventilated place and the airflow above the surface is controlled at such a rate that, in combination with air temperature, organic liquid balance and wet film thickness, the pigmented liquid coat quickly increases in viscosity and ceases to flow within 5to 10 minutes.During this time, there is produced the variegated pattern or colour effect of the invention.

The cause of this surprising variegated effect is uncertain. As already stated, it bears no resemblance to the surface pattern of the underlying substrate. Consequently, on first consideration the effect of the invention seemed to be wholly independent of the structure of the surface of the substrate. However, tests showed that the variegated effect of the invention was not obtained if a substrate was used which had a homogeneous surface, such as a sheet of glass or steel. On further consideration, a theory has been worked out which may at least partly explain how the effect of the invention is produced. According to this theory, the variegated colour effects achieved by this method may be related to the variable affinities towards certain loosely-absorbing dyes exhibited by the heterogeneous particles at the surface of the substrate.Thus, when lyophilic dyes are applied to such non-uniform surfaces, differential absorption of the dyes may occur and hence uneven retention and partial release of the dyes may occur when a pigmented liquid, which contains solvents for the dyes, is applied after an appropriate interval of time subsequent to dyeing. This may explain how the dyes, resins and pigments are able to intermingle randomly to produce a variegated colour effect which is seen.

The nature of the variegation seems to be influenced by, amongst other factors, the quantity of dye applied, the drying time, the temperature during drying, the viscosity, surface tension and quantity of pigment in the pigmented liquid, the "flash-off time", that is, the time taken to remove excess organic liquid following application of the pigmented layer, the slit width and conveyor speed when the pigmented layer is applied by a curtain coater, and the natural characteristics of the surface of the substrate.

The effects of varying these factors are illustrated in the following examples.

EXAMPLE 1 A piece of chipboard was sanded to 150 grit and then filled with MDF edge filler, applied by cloth.

The board was then dried at 75"C for ten minutes and sanded again with 240 grit paper. A3% lyophilic dye solution in methylated spirit: butanone: Cellosolve (R.T.M.) (3:3:1) was then applied liberally by spray and the board was then oversprayed with an artificial blend of an acid-catalysed base coat lacquer and titanium dioxide-pigmented alkyd paint in appaorixmiately 5:1 ratio and methyl isobutyl ketone. This yielded a pigmented liquid of 17 seconds viscosity at 19"C (measured in a standard Ford cup). After 10 minutes fiash-off, the coat was dried at 50"C for 30 minutes, de-nibbed with 400 grit paper spray-coated with a clear conventional acidcatalysed lacquer. Drying conditions were as for the coat of pigmented liquid.

The final effect generally consisted of off-white irregular areas, with diffused margins, optically embedded in the coloured base, i.e. that of the dyed surface, which itself assumed a 'pastel' shade. The overall visual impact of the finish was reminiscent of certain naturally occurring marble stones, as shown in Figure 2.

EXAMPLE 2 A piece of chipboard was subjected to the same processes of surface preparation, dyeing etc., as described in Example 1 exceptthatthechipboard was heated to 75"C for 15 minutes between the application of the dye solution and the pigmerited liquid.

This increase in temperature resulted in an increase in the contrast of colours and hence a more pronounced variegation in the final decorative finish.

EXAMPLE 3 A piece of chipboard was subjected to the same processes of surface preparation, dyeing etc., as described in Example 1 except that the pigmented liquid was applied by a curtain coaterwhose conveyor speed and slit width were 60 metres per minute and 0.25 mm, respectively.

The resulting decorative finish was similarto that of Example 1.

EXAMPLE 4 A piece of chipboard was subjected to the same conditions as in Example 3 except that the conveyor speed and slit width of the curtain coater were 30 metres per minute and 0.35 mm, respectively.

The resulting decorative finish differed from those obtained in Examples 1 to 3 in that the dye tended to assume distorted circular shapes of approximately 5 mm diameter surrounded by white zones of irregular shape averaging approximately 1 mm in width, as shown in Figure 3.

The method described in Example 1 was also applied to hardboard, MDF and bagass board, the effects obtained being similar to that obtained with chipboard. However, the variegation was less distinct with these substrates than with chipboard.

Claims (21)

1.A A method for producing a decorative finish on a substrate of heterogeneous composition comprising applying a lyophilic dye in a liquid medium to the substrate and subsequently applying a pigmented liquid.

2. A method according to claim 1 in which the substrate is a particleboard.

3. A method according to claim 1 or claim 2 in which the substrate is chipboard, MDF, bagass board or hardboard.

4. A method according to any one of claims 1, 2 and 3 in which the liquid medium is an organic liquid or a mixture of organic liquids selected from the group consisting of alcohols, ketones, esters, aliphatic and aromatic hydrocarbons, ethers, alkoxyalcohols and their esters.

5. A method according to any preceding claim in which the lyophilic dye forms a solution or dispersion with the liquid medium.

6. A method according to claim 5 in which the active dye content of the solution or dispersion is 0.1% to 10% (weight/volume).

7. A method according to any preceding claim in which the pigmented liquid is opaque or translucent.

8. A method according to any preceding claim in which the pigmented liquid includes a pigment, a resin binder, a plasticiser, a rheological agent, a stabiliser and an organic liquid.

9. A method according to claim 8 in which the pigment is an inorganic salt of oxide or mixture of inorganic salts and/or oxides.

10. A method according to claim 8 or claim 9 in which the pigment comprises one or a mixture of compounds selected from the group consisting of titanium dioxide, aluminium oxide, aluminium silicate, antimony sulphide, barium sulphate, cadmium sulphate, calcium silicate, china clay, chromium oxide, lead carbonate, lead oxide, magnesium oxide, magnesium carbonate, iron oxide, silica, talc, ultramarine, mercury sulphide, calcium carbonate, zinc carbonate, zinc oxide and zinc sulphide.

11. A method according to claim 8 in which the resin binder is a compound or blend of compounds selected from the group consisting of an alkyd, cellulose nitrate, acid-curing aminoplast, polyester, vinyl and acrylic resins.

12. A method according to claim 8 in which the plasticiser is dibutyl phthalate.

13. A method according to claim 8 in which the organic liquid is a liquid or mixture of liquids selected from the group consisting of alcohols, ketones, esters, aliphatic and aromatic hydrocarbons, ethers, alkoxy-alcohols and their esters.

14. A method according to any preceding claim in which the pigmented liquid includes dyes and/or organic pigments.

15. A method according to any of claims 8 to 14 in which the pigment comprises 0.1% to 20% of the pigmented liquid.

16. A method according to any of claims 8 to 15 in which the resin binder comprises 5% to 60% of the pigmented liquid.

17. A method according to any preceding claim in which a pore-filler is applied to the substrate prior to the application of the lyophilic dye in a liquid medium.

18. A method according to any preceding claim in which a protective lacquer is applied to the substrate subsequent to the application of the pigmented liquid.

19. A decorative material produced by the method of any preceding claim.

20. A method for producing a decorative finish on a substrate of heterogeneous composition substantially as hereinbefore described and with reference to the Examples.

21. A decorative material substantially as herein before described and with reference to the Examples.