This invention relates to a composition for forming on a silicate substrate a layer under or over a precious metal layer, to a method of forming the layers on the substrate, to a transfer for use in the method, and to a silicate substrate bearing the two layers.

European patent specification 445537 A 1 discloses a composition comprising a mixture of boron silicate glass frit and metal oxide and an alkyd- resin-containing organic medium, for use in the production of matt precious metal decorations produced from bright precious metal formulations on silicate material, characterised in that it consists of 50-80weight% of a mixture of 30-80weight% boron silicate glass frit and 20-70weight% tin oxide, cerium oxide and/or zirconium

oxide as metal oxide and 20-50weight% of the organic medium and that the organic medium contains 20-50weight% of alkyd resin and 3-30weight% of an additive of naturally occurring resin, acrylic resin and/or plasticizer.

The present invention provides an improved composition. The invention provides a composition for forming on a silicate substrate a layer under or over a precious metal layer, which composition consists essentially by weight of

(A) 40-80% of a frit-pigmentary metal compound mixture, and (B) 20-60% of organic medium,

(A) being by weight 10-90% boron-silicate glass frit and 10-90% pigmentary metal compound, and

(B) being by weight 0.2-30% nitrocellulose resin with the remainder diluents and/or additives.

The invention provides also a method of forming on a silicate substrate a layer under or over a precious metal layer, which method comprises forming on the substrate a dried layer of precious metal formulation and under or over the precious metal layer, a dried layer of the present composition, firing the dried formulation and firing the dried composition.

The invention provides also a transfer for use in this method, which transfer comprises a carrier sheet on which is carried a layer of the present

composition which has been dried thereon and over or under that layer, a precious metal formulation which has been dried thereon.

The invention provides also a silicate substrate bearing a layer of fired, dried present composition and over or under that layer, a layer of fired, dried precious metal formulation.

The precious metal usually comprises at least one of gold, platinum

and palladium. The precious metal preferably comprises gold.

The present invention does not rely on an alkyd resin or on naturally occurring resin, acrylic resin or plasticizer, though one or more of these can be included as optional ingredients in the present composition. The present composition is easy to use. It has good stability and does not require the precious metal formulation to be applied soon afterwards. It produces attractively decorated substrates and its firing is reliably effective. It produces a range of types of finish, a range of colours, and can produce a smooth (rather than rough) finish.

It has been discovered that a nitrocellulose organic medium is remarkably good for the present use. A surprisingly small amount of nitrocellulose resin is effective. Nitrocellulose resins are readily available and known such resins can be employed. The nitrocellulose usually contains 2-4 nitrate groups per molecule. The present organic medium contains preferably 0.2-20, especially 1-7,

in particular 1-5, % nitrocellulose resin. Percentages in this specification are by

weight unless indicated otherwise.

Besides the nitrocellulose resin, the organic medium contains diluents and/or additives. Known such diluents and additives can be employed. The diluent

can be organic solvent, for instance at least one of an ester for example butyl lactate, hydrocarbon for example aromatic hydrocarbon, or alcohol for example mixed terpene alcohol.

The organic medium can contain additives. These can be alkyd resin, naturally occurring resin and/or acrylic resin, which can be those known from European specification 445537 A 1 mentioned above, though preferably they are present in smaller amounts in the present organic medium. Usually the present organic medium contains between 0 and 20% additive. In a particular embodiment, the organic medium contains between 0 and 20%, especially from 0.5 to 12%, alkyd resin.

The frit-metal compound mixture, (A), usually is 20-80% of the glass frit and 20-80% of the metal compound, preferably 40-75% of the glass frit

and 25-60% of the metal compound.

Known glass frits can be employed as the present glass frit. The frit preferably contains substantially no lead, though slight amounts may have been

picked up incidentally, for instance during its production. Thus, preferably the frit contains 0-1.5mol% lead oxide.

A preferred frit is that of our European patent specification 460863, the contents of which are hereby incorporated by reference into the present

specification. Thus, the frit preferably consists essentially in mol% of 3.0-13.0 lithium oxide, 0.5-3.5 potassium oxide, 2.5-7.0 sodium oxide, 0.5-2.5 zinc oxide, 2.0-8.0 aluminium oxide, 15-30 boron oxide, -44-68 silica, 1.0-7.0 zirconium oxide,

0-4.0 calcium oxide, 0-3.0 lanthanum oxide, 0-1.0 other rare earth metal oxide,

0-1.0 yttrium oxide, 0-4.0 magnesium oxide, 0-4.0 strontium oxide, 0-4.0 titanium oxide, 0-10 phosphorus pentoxide, 0-1.5 lead oxide and 0-13 fluoride. This frit preferably contains 7-10.2 mol% lithium oxide. Its potassium oxide content is preferably 1.5-1.8 mol%. Its sodium oxide content is preferably 3.4-4.0 mol%. Its

calcium oxide content is preferably 0.8-1.2 mol%. Its zinc oxide content is

preferably 1.0-1.3 mol%. Its aluminium oxide content is preferably 4.3-5.5 mol%.

Its boron oxide content is preferably 18.8-22.5 mol%. Its silica content is preferably 48-57 mol%. Its zirconium oxide content is preferably 1.8-3.4 mol%. It desirably contains 0.1-3.0, especially 0.2-0.6, mol% lanthanum oxide. Its content

of other rare earth metal oxide is preferably 0-0.4 mol%. Its content of yttrium oxide is preferably 0-0.6 mol%. Its content of magnesium oxide is preferably 0-1.5 mol%. Its content of strontium oxide is preferably 0-1.5 mol%. Its content of titanium oxide is preferably 0-3 mol%. Its content of phosphorus pentoxide is

preferably 0-6 mol%. It preferably contains 0-7 mol% fluoride; to avoid any possible pollution problem, however, fluoride is preferably avoided. Any rare earth

metal oxide other than lanthanum oxide is preferably one or more, usually one, of

praseodymium oxide, cerium oxide and neodymium oxide, especially neodymium

oxide.

Whatever the form of any cerium oxide (and in particular whether

it is CeO ₂ or Ce ₂ O ₃ ), its content in this specification is calculated as CeO ₂ .

Known pigmentary metal compounds can be employ-ed in the present composition, including metal oxides known for use in the present type of composition. The pigmentary metal compound is often a metal oxide, which may be a simple metal oxide such as tin oxide or a complex metal oxide such as chromium titanate. Alternatively, the metal compound is converted to the oxide in use. The metal compound is usually at least one compound selected from compounds of tin, cerium, antimony, cobalt, iron, chromium, titanium, aluminium, zirconium, zinc, boron and nickel.

The metal compound can be employed either singly or in admixture as pigments to give a wide range of colours to the precious metal layer. The colours can be across the colour spectrum and include white and black. In a particular embodiment, however, the precious metal comprises gold and the colour of its layer in the product is gold.

Preferably the metal compound comprises tin oxide and/or zirconia, especially tin oxide.

The present composition usually consists essentially of 55-75% of the fri* -metal compound mixture, (A), and 25-45% of the organic medium, (B), and preferaoly consists essentially of 62-75% of (A) and 25-38% of (B).

The composition consists essentially of the specified ingredients in their specified amounts. Ingredients which do not prevent the essential purpose of the composition of course can also be present. A content of 10-30% graphite

powder of 1-lOmu particle size - which is referred to in the WPI Abstract

Accession No 77-01078Y/01 of Japanese patent specification 51133312A as being

present in a certain composition for a different use - is preferably avoided in the present composition, as it tends to make the composition unworkable for the present purpose as being too solid. A significantly smaller amount of graphite

powder may be present, though this too is preferably avoided.

The present composition can conveniently be produced in a two component pack, for the components to be admixed to form the composition, one component being the frit-pigmentary metal compound mixture, (A) and the other

the organic medium, (B).

The invention provides the use of the present composition to form

a layer under or over, preferably under, a precious metal layer. This contrasts with

European specification 445537 mentioned above, which does not mention use of its frit-containing composition as an over-layer. The present composition is for use on a silicate substrate. The substrate can be glass, for instance architectural glass

or glass containers, but preferably it is ceramic, for instance tiles or tableware. The

ceramic is preferably china or porcelain, which can be hard or soft.

The precious metal layer is preferably produced from a bright precious metal formulation. The formulation can be based on an organic medium.

The precious metal layer is usually decorative.

The present composition can produce a substrate whose precious metal layer under or over the other layer is matt, and the European specification 445537 mentioned above refers only to a matt finish. The present composition, however, can produce a substrate whose precious metal layer under or over the other layer is gloss or silky. Particularly attractive coloured, silky, precious metal decorations can be produced. Where the present composition is over or under the precious metal layer, the composition modifies the appearance of the latter. Particularly beautiful designs can be produced by forming a layer of the present composition in a particular design, and forming the precious metal in an overlapping layer, so that in the overlapping area the composition modifies the appearance of the precious metal layer and in the non-overlapping area it does not. In this way, from a bright precious metal formulation, one can produce a design of matt precious metal in the overlap area and bright precious metal in the non- overlap area. Conversely, the precious metal layer can be in a particular design and the frit-containing composition overlap it.

The present composition and the precious metal formulation used to produce the precious metal layer can be applied, dried and fired in ways known in themselves. The present composition and precious metal formulation are preferably applied by screen printing. They can be applied directly to the silicate substrate, though one or both can be applied by means of a transfer. Preferably both are applied by means of a transfer. The transfer can be of known type and made in known way. Thus, the present composition or precious metal formulation can be

applied to a transfer carrier sheet, dried thereon, and the other one applied and

dried thereon; a protective covercoat is preferably employed. However, a

protective layer, as described for instance in UK patent specification 2099760 A, under the covercoat is unnecessary and preferably avoided. The dried formulation and dried composition can be applied from the transfer to the substrate in the usual way.

The present composition or precious metal formulation can be applied directly to the substrate, dried thereon, and the other one applied and dried thereon. Less preferably, one can be applied in this way and the other applied, either before or after, by means of a transfer.

The Technical Information sheet on the Heraeus Matt Silk gold system states that the frit-containing composition is to be allowed to become touch- dry, which at a 20°C ambient temperature takes about 3 hours, and that the precious metal composition should be applied before the under-print is completely bone dry, and that due to this it is impossible to delay printing the gold layer.

There is no such criticahty with the present composition. There can be for instance

between 3 and 60 hours, or even longer, at 20°C ambient temperature between

applications in the present invention. We have found that a gap of 24 hours results in a product which is not inferior to that made with a gap of 4 hours.

The dried present composition or dried precious metal formulation on the substrate can be fired before application of the other. Preferably, however, both are fired together. Each firing is preferably at a temperature of 500-1300°C, for instance fast firing to 830°C in the case of hard porcelain and to 750°C in the case of soft porcelain.

The invention is illustrated by the following Examples. In each case, the nitrocellulose resin was DHL 120/170 available from ICI, UK, the alkyd resin was Surkyd 410 available from Mitchanol International, UK, the ambient temperature was 20°C the frit employed had the following composition:

Mol% Weiεht%

A 4.5563 7.1857

B ₂ O ₃ 21.8852 23.5670

CaO 0.9613 0.8339

K ₂ O 1.5995 2.3308

LaA 0.3731 1.8806

Li ₂ O 9.5299 4.4041

MgO 0.0059 0.0037

Mol% Weisht%

Na ₂ O 3.8396 3.6810

Nd ₂ O ₃ 0.0005 0.0030

PbO 0.0012 0.0045

SiO ₂ 53.5152 49.7406

ZnO 1.1541 1.4527

ZrO ₂ 2.5773 4.9123

EXAMPLE 1

A composition was prepared by mixing through a triple roll mill until a uniform dispersion was obtained:

(A) 65% of a mixture of 43% of the frit and 57% tin oxide; and (B) 35% of an organic medium consisting of 3.6% nitrocellulose resin, 9.8% alkyd resin and 86.6% organic solvent (69.2% butyl lactate, 10.9% Pine

Oil [mixed terpene alcohol] and 6.5% Solvesso 150 [aromatic hydrocarbon available from Exxon Chemical Limited, UK], totalling the 86.6%).

EXAMPLE 2

A composition was prepared by mixing through a triple roll mill until a uniform dispersion was obtained:

(A) 65% of a mixture of 43% of the frit and 57% zirconium oxide;

and

(B) 35% of an organic medium consisting of 5.0% nitrocellulose resin and 95% butyl lactate.

EXAMPLE 3

A composition was prepared by mixing through a triple roll mill until a uniform dispersion was obtained:

(A) 65% of a mixture of 56% of the frit, 14% chromium titanate complex and 30% zirconium oxide; and

(B) 35% of an organic medium consisting of 5.0% nitrocellulose resin and 95% butyl lactate.

EXAMPLE 4

A composition was prepared by mixing through a triple roll mill until a uniform dispersion was obtained:

(A) 65% of a mixture of 48% of the frit, 12% cobalt iron chromium spinel and 40% zirconium oxide; and

(B) 35% of an organic medium consisting of 4.5% nitrocellulose resin, 3.2% alkyd resin, 86.4% butyl lactate, 3.7% Pine Oil (mixed terpene alcohol)

and 2.2% Solvesso 150 (aromatic hydrocarbon available from Exxon Chemical

Limited, UK).

EXAMPLES 5-8

The composition of Examples 1-4 were each screen printed onto transfer paper through 130T polyester mesh through a decorative design. After

drying at ambient temperature for 4 hours, the coloured flux design was over¬

printed with the bright gold organic-medium based formulation GBC 11265S

available from Johnson Matthey PLC, UK through HOT polyester mesh. After drying for 4 hours at ambient temperature, the design was over-printed with the over-print lacquer OPL 164 available from Johnson Matthey PLC, UK to form a covercoat. The resulting transfer was applied to hard porcelain and fast fir-ed to

830°C at 29°C per minute, to produce a coloured silky precious metal decoration without firing defects.

EXAMPLES 9-12

Examples 5-8 were repeated except for using a 150T screen instead of a 130T screen through which to print the composition. The same result was obtained.

EXAMPLE 13-20

Examples 5-12 were repeated except for using a 100T screen instead of a 110T screen through which to print the gold formulation. The same result was obtained.

EXAMPLES 21-32

Examples 5-16 were repeated except for drying the composition for 24 hours instead of 4 hours. The same result was obtained.

EXAMPLES 33-60

Examples 5-32 were repeated except for drying the gold formulation for 24 hours instead of 4 hours. The same result was obtained.

EXAMPLES 61-116

Examples 5-60 were repeated except that the transfer was applied to soft porcelain and fast fired to 750°C. The same result was obtained.