WO2003002484A1

WO2003002484A1 - Coating composition for a ceramic article and use in repairing defects in glazed ceramic articles

Info

Publication number: WO2003002484A1
Application number: PCT/CA2001/000940
Authority: WO
Inventors: Jens Johan Kortman; Jeff Brent Mitobe; Francois Armand Jossinet; John Kevin Crawley
Original assignee: Crane Canada Inc.
Priority date: 2001-06-29
Filing date: 2001-06-29
Publication date: 2003-01-09

Abstract

A coating composition for application to a ceramic substrate comprising an undercoat and a clear topcoat, wherein the undercoat comprises a radiation curable oligomer, an extender or filler, aluminum hydroxide and titanium dioxide. The topcoat comprises an urethane acrylate oligomer and an hydrocarbon acrylate diluent. A coating composition is also provided comprising an undercoat and a clear topcoat, wherein the undercoat comprises a radiation curable oligomer, an extender or filler, and a colourant. The topcoat comprises an urethane acrylate oligomer and an hydrocarbon acrylate diluent. A surface defect on a glazed ceramic article can be repaired by first coating or hiding the surface defect with either of the above-described undercoats, curing such undercoat with an energy source, applying the above-described topcoat to the cured undercoat, and curing the topcoat with an energy source.

Description

COATING COMPOSITION FOR A CERAMIC ARTICLE AND USE IN REPAIRING DEFECTS IN GLAZED CERAMIC

ARTICLES

Field of Invention

The present invention relates to coating compositions applied to ceramic substrates and the method by which they are applied.

B ackground of the Invention

Vitreous glazes are typically applied to ceramic articles to enhance their

aesthetic appearance. When in their green state, ceramic articles are coated with a slurry which forms a vitreous coating when fired. After application of the

slurry, the ceramic article is then subjected to a high temperature firing process,

one consequence of which is the curing of the glaze to the ceramic article.

Unfortunately, the resultant glazed coating may possess any one of several kinds of surface defects. For instance, the coating may contain voids and

pinholes caused by trapped air or gas formed from a spot contaminant in the film

and insufficient flow during levelling of the coating. In such cases, the

appearance of the glazed ceramic article may be unacceptable, requiring further

action to correct the defect.

U.S. Patent 2,826,508 discloses a method of repairing surface defects of

fired ceramic articles by applying an undercoating to the defect, applying a glaze

coating on the undercoating, and then baking the applied coatings to effect curing

and adherence to the ceramic substrate. Unfortunately, exposure to such cyclical

firing increases the risk of stress fracture in the ceramic article. Further, this manner of repair creates disruption of and introduces inefficiencies into the

manufacturing process. It is therefore desirable to provide a coating composition

for repairing of surface defects of fired ceramic articles which resembles ceramic

glaze upon application but does not requires elevated temperatures to effect curing and adherence to the ceramic substrate.

Summary of Invention

The present invention provides an improved coating composition for use

in repairing surface defects of fired ceramic articles In accordance with one aspect, the present invention provides a coating

composition for application to a ceramic substrate comprising: a radiation curable

oligomer, an extender, aluminum hydroxide and titanium dioxide. The aluminum

hydroxide can be refined from gibbsite. The aluminum hydroxide can be

characterized by a particle size of less than about 1.5 μ . The radiation curable oligomer can be a polyether acrylate or an urethane acrylate. Suitable polyether

acrylates include those characterized by a viscosity of greater than 220 mPa/s.

The coating composition can include substantially no monomer. Suitable fillers include aluminum oxide, barium sulfate, or magnesium silicate. Where the

coating composition is cured by ultraviolet light, a photoinitiator blend

comprising an aromatic ketone and phosphine oxide can further be provided.

In another aspect, the present invention provides a coating composition

for applications to a ceramic substrate comprising: a binder, having a radiation curable oligomer and an extender; and a pigment, having aluminum hydroxide and titanium dioxide, wherein the pigment and the binder are combined in a ratio

in the range of from about 3:1 to about 10:1 by volume.

In another aspect, the present invention provides a coating composition

for application to a ceramic substrate comprising:

from about 55 to about 65 percent by weight, based on the total weight of

the composition, of a polyether acrylate;

from about 0.25 to about 3.0 percent by weight, based on the total weight of the composition, of a dispersant;

from about 10 to about 20 percent by weight, based on the total weight of

the composition, of barium sulfate;

from about 10 to about 20 percent by weight, based on the total weight of

the composition, of magnesium silicate;

from about 0.5 to about 20 percent by weight, based on the total weight of the composition, of aluminum hydroxide;

from about 3 to about 6 percent by weight, based on the total weight of

the composition, of titanium dioxide;

from about 0.25 to about 2 percent by weight, based on the total weight of the composition, of phosphine oxide; and

from about 0.25 to about 2 percent by weight, based on the total weight

of the composition, of benzophenone.

In a further aspect, the present invention provides a coating composition

for application to a ceramic substrate comprising: a radiation curable oligomer, an extender, and a colourant. The colourant can be pearlescent pigment or tinting

paste. The radiation curable oligomer can be a polyether acrylate or an urethane acrylate. Suitable polyether acrylates, include those characterized by a viscosity

of greater than 220 mPa/s. The coating composition can include substantially no monomer. Suitable fillers include aluminum oxide, barium sulfate, or

magnesium silicate. Where the coating composition is cured by ultraviolet light,

a photoinitiator blend comprising an aromatic ketone and phosphine oxide can further be provided.

In even a further aspect, the present invention provides a coating composition for application to a ceramic substrate comprising: a binder, having

a radiation curable oligomer and an extender, and a pigment, having a colourant,

wherein the pigment and the binder are combined in a ratio in the range of from

about 3:1 to about 10:1 by volume.

In yet a further aspect, the present invention provides a coating

composition for application to a ceramic substrate comprising:

from about 55 to about 65 percent by weight, based on the total weight of

the composition, of a polyether acrylate;

from about 15 to about 20 percent by weight, based on the total weight of

the composition, of barium sulfate;

from about 15 to about 20 percent by weight, based on the total weight of the composition, of magnesium silicate;

from about 1 to about 10 percent by weight, based on the total weight of

the composition, of a colourant; from about 0.25 to about 2 percent by weight, based on the total weight of the composition, of phosphine oxide; and

from about 0.25 to about 2 percent by weight, based on the total weight

of the composition, of benzophenone.

In another aspect, the present invention provides a coating composition for application to a ceramic substrate comprising an undercoat and a clear

topcoat, wherein the undercoat comprises a radiation curable oligomer, an extender, aluminum hydroxide and titanium dioxide, and wherein the topcoat

comprises an urethane acrylate oligomer and hydrocarbon acrylate diluent.

In yet even a further aspect, the present invention provides a coating

composition for application to a ceramic substrate comprising an undercoat and

a clear topcoat, wherein the undercoat comprises a radiation curable oligomer, an

extender and a colourant, and wherein the topcoat comprises an urethane acrylate

oligomer and a hydrocarbon acrylate diluent.

In a further aspect, the present invention provides a method of repairing

a surface defect on a glazed ceramic article comprising the steps of coating or

hiding a surface defect of a glazed ceramic article with a coating composition

comprising a radiation curable oligomer, an extender; aluminum hydroxide and

titanium dioxide and curing the composition with an energy source.

In yet another aspect, the present invention provides a method of repairing a surface defect on a glazed ceramic article comprising the steps of coating or hiding the surface defect with an undercoat comprising a radiation curable

oligomer, an extender, aluminum hydroxide and titanium dioxide, curing the

undercoat with a first energy source, applying a topcoat to the cured undercoat, the topcoat including an urethane acrylate oligomer and a hydrocarbon acrylate dilment, and curing the topcoat with a second energy source. The first and second

energy sources can be ultraviolet light.

In a further aspect, the present invention provides a method of repairing

a surface defect on a glazed ceramic article comprising the steps of coating or

hiding the surface defect with an undercoat comprising a radiation curable oligomer, an extender and a colourant, curing the undercoat with a first energy

source, applying a topcoat to the undercoat, the topcoat including an urethane

acrylate oligomer and a hydrocarbon acrylate diluent, and curing the topcoat with

a second energy source. The first and second energy sources can be ultraviolet

light.

Detailed Description

The present invention provides a white coating composition comprising

a radiation curable oligomer, an extender or filler, aluminum hydroxide and

titanium dioxide.

In one embodiment, the radiation curable oligomer is a polyether acrylate

or an urethane acrylate. Preferably, the radiation curable oligomer is a polyether

acrylate having a viscosity greater than 220 mPa/s, and even more preferably

between 220 - 400 mPa/s. Although small amounts of monomer could be in the

coating composition, it is preferable that the coating composition includes

substantially no monomer. Suitable extenders or fillers include barium sulfate, magnesium silicate, and silica oxides. The extenders or fillers enhance the optical effect of the

coating composition.

Preferably, the aluminum hydroxide is refined from gibbsite. The

structure of gibbsite is analogous to the basic structure of micas. In particular, the gibbsite structure is formed of stacked sheets of linked octahedrons of aluminum

hydroxide. Preferably, the aluminum hydroxide is characterized by a particle size

less than 1.5 μm.

Preferably, the titanium dioxide is of the rutile grade. Titanium dioxide

is used to impart a white colour to the coating composition. Other compounds

which could be substituted for titanium dioxide and provide the desired whiteness

include lead oxide and zinc sulfide.

Where the white coating composition is to be cured by ultraviolet light,

a photoinitiator is provided. The photoinitiator includes a blend of an aromatic ketone and phosphine oxide. The aromatic ketone can include benzophenone,

methyl-o-benzoyl benzoate and 2-isopropyl thioxanthone. The aromatic ketone

is a surface curing agent. The phosphine oxide is provided to obtain desired

depth of cure. A cationic curing agent, comprising iodonium or sulfonium salts,

could also be used as a photoinitiator where the coating composition is cured by

ultraviolet light. Optionally, the coating composition could also be cured using excimer laser, requiring the coating composition to include excimer laser

sensitive photoinitiators such as benzoketals. Alternatively, the coating

composition can be cured using electron beam technology, which would altogether eliminate the necessity for a photoinitiator. Optionally, the coating composition could include a dispersant. A suitable

dispersant includes solutions of polycarboxylic acid salt of polyamine amides or

solutions of high molecular weight block co-polymers with pigment affinic

groups. The dispersant could also include any of solutions of alkyl-ammonium

salt of an acidic polymer, solutions of salt of unsaturated polyamine amide and lower molecular weight acid polymer, solutions of salt of polyamine amides and

a polar acidic ester, solutions of hydroxy-functional carboxylic acid ester with

pigment affinic group, solutions of unsaturated poly-carboxylic acid polymer,

solutions of alkylammonium salt of a poly-carboxylic acid, solutions of

alkanolammonium salt of an unsaturated fatty acid, and solutions of unsaturated acidic polycarboxylic acid polyester.

In a preferred embodiment, the white coating composition of the present

invention comprises from about 55 to about 65 percent by weight, based on the total weight of the composition, of a polyether acrylate, from about 0.25 to about

3.0 percent by weight, based on the total weight of the composition, of a

dispersant, from about 10 to about 20 percent by weight, based on the total weight

of the composition, of barium sulfate, from about 10 to about 20 percent by

weight, based on the total weight of the composition, of magnesium silicate, from about 0.5 to about 20 percent by weight, based on the total weight of the

composition, of aluminum hydroxide, from about 3 to about 6 percent by weight,

based on the total weight of the composition, of titanium dioxide, from about 0.25

to about 2 percent by weight, based on the total weight of the composition, of

phosphine oxide, and from about 0.25 to about 2 percent by weight, based on the

total weight of the composition, of benzophenone. In another embodiment, the white coating composition of the present

invention comprises a binder and a pigment. The pigment includes a radiation

curable oligomer and an extender or filler. The pigment includes aluminum

hydroxide and titanium dioxide. The binder can also include a photoinitiator

and/or a dispersant. The pigment and the binder of the white coating composition

can be combined in a ratio in the range of from about 3:1 to about 10:1 by

volume. More preferably, the pigment and the binder are combined in a ratio in

the range of from about 4: 1 to about 6: 1 by volume. Even more preferably, the pigment and the binder are combined in a ratio of about 4:1 by volume.

In another embodiment, a coloured coating composition is provided

comprising a radiation curable oligomer, an extender or filler, and a colourant. In

one embodiment, the radiation curable oligomer is a polyether acrylate or urethane acrylate. More preferably, the radiation curable oligomer is a polyether

acrylate having a viscosity greater than 220 mPa/s, and even more preferably

between 220 - 400 mPa/s. Although small amounts of monomer could be used

in the coating composition, it is preferable that the coating composition includes

substantially no monomer. Suitable extenders or fillers include barium sulfate, magnesium silicate, and silica oxides.

The colourant is used to impart colour to the coating composition.

Depending on the desired colour, different colourants can be used in the coating

composition to match the colour of the surrounding ceramic glaze. Colourants

include opaque pigments, semi-transparent pigments and dyes.

Acceptable colourants include pearlescent pigments. Suitable pearlescent

pigments are mica coated with an oxide from the group including TiO₂, ZrO₂, SnO₂, ZnO, Fe₂O₃, Cr₂O₃ and N₂O₅, or mixtures of two or more of said oxides.

Mica as used herein is an all encompassing term for a class of naturally occurring

minerals, all of which possess a scaly, plate-like crystal structure. Examples of mica include muscovite, phlogopite and biotite. Preferably, the mica particles are

characterized by a particle size within the range of from about 5 μm to about 200

μ . Acceptable pearlescent pigments include the AFFLAIR™ line of pearlescent

pigments manufactured by BDH Chemicals, including, AFFLAIR™ 120, AFFLAIR™ 121, AFFLAIR™ 163, AFFLAIR™ 205, AFFLATR™ 215 and

AFFLAIR™ 225. Other acceptable pearlescent pigments include the

MEARLΓΝ™ line of pearlescent pigments manufactured by Engelhard

Corporation such as MEARLIΝ™ Super Blue 6392. Other colourants which

could be used to obtain a pearlescent effect include bismuth oxychloride, lead

hydrogen arsenate, and lead carbonate.

Other acceptable colourants include tinting paste comprising pigments

such as aryl red or Pigment Red 170, carbon black or Pigment Black 7, medium

yellow or Pigment Yellow 151 or Pigment Yellow 83, phtalo blue or Pigment

Blue 15:1, and quinacridone red or Pigment Violet 19.

Where the white coating composition is to be cured by ultraviolet light,

a photoinitiator is provided. The photoinitiator includes a blend of an aromatic

ketone and phosphine oxide. The aromatic ketone can include benzophenone,

methyl-o-benzoyl benzoate and 2-isopropyl thioxanthone. The aromatic ketone is a surface curing agent. The phosphine oxide is provided to obtain desired

depth of cure. A cationic curing agent, comprising iodonium or sulfonium salts,

could also be used as a photoinitiator where the coating composition is cured by ultraviolet light. Optionally, the coating composition could also be cured using excimer laser, requiring the coating composition to include excimer laser

sensitive photoinitiators such as benzoketals. Alternatively, the coating

composition can be cured using electron beam technology, which would

altogether eliminate the necessity for a photoinitiator.

Optionally, the coating composition could include a dispersant. A

preferred dispersant includes solutions of polycarboxylic acid salt of polyamine amides or solutions of high molecular weight block co-polymers with pigment

affinic groups. A suitable dispersant could also include any of solutions of alkyl-

ammonium salt of an acidic polymer, solutions of salt of unsaturated polyamine

amide and lower molecular weight acid polymer, solutions of salt of polyamine

amides and a polar acidic ester, solutions of hydroxy- functional carboxylic acid ester with pigment affinic group, solutions of unsaturated poly-carboxylic acid

polymer, solutions of alkylammonium salt of a poly-carboxylic acid, solutions of

alkanolammonium salt of an unsaturated fatty acid and solutions of unsaturated

acidic polycarboxylic acid polyester.

In a preferred embodiment, the coloured coating composition of the

present invention comprises from about 55 to about 65 percent by weight, based

on the total weight of the composition, of a polyether acrylate, from about 0.25

to about 3.0 percent by weight, based on the total weight of the composition, of

a dispersant, from about 15 to about 20 percent by weight, based on the total weight of the composition, of barium sulfate, from about 15 to about 20 percent

by weight, based on the total weight of the composition, of magnesium silicate,

from about 1 to about 10 percent by weight, based on the total weight of the composition, of a colourant, from about 0.25 to about 2 percent by weight, based

on the total weight of the composition, of phosphine oxide, and from about 0.25 to about 2 percent by weight, based on the total weight of the composition, of

benzophenone.

In another embodiment, the coloured coating composition of the present invention comprises a binder and a pigment. The pigment includes a radiation

curable oligomer and an extender or filler. The pigment includes aluminum hydroxide and titanium dioxide. The binder can also include a photoinitiator

and/or a dispersant. The pigment and the binder of the coloured coating

composition can be combined in a ratio in the range of from about 3 : 1 to about

10: 1 by volume. More preferably, the pigment and the binder are combined in a ratio in the range of from about 4:1 to about 6:1 by volume. Even more

preferably, the pigment and the binder are combined in a ratio of about 4:1 by

volume. In a further embodiment, the coating composition comprises an undercoat,

of the white coating composition or the coloured coating composition described

above, and a clear topcoat. The clear topcoat, when applied on the associated

undercoat, enhances the aesthetic appearance of the coating composition. The

clear topcoat comprises an urethane acrylate oligomer and a hydrocarbon acrylate

diluent.

Where the coating composition having an undercoat and topcoat is to be

cured by ultraviolet light, a photoinitiator can be provided. The photoinitiator

includes a blend of an aromatic ketone and phosphine oxide. The aromatic

ketone can include benzophenone, methyl-o-benzoyl benzoate and 2-isopropyl thioxanthone. The aromatic ketone is a surface curing agent. The phosphine

oxide is provided to obtain desired depth of cure. A cationic curing agent, comprising iodonium or sulfonium salts, could also be used as a photoinitiator

where the coating composition is cured by ultraviolet light. Optionally, the

coating composition could also be cured using excimer laser, requiring the coating composition to include excimer laser compatible photoinitiator such as

benzoketals. Alternatively, the coating composition can be cured using electron

beam technology, which would altogether eliminate the necessity for a

photoinitiator.

In a preferred embodiment, the topcoat comprises from about 56 to about

95 percent by weight, based on the total weight of the composition, of an urethane

acrylate oligomer. The topcoat also comprises from about 5 to about 40 percent

by weight, based on the total weight of the composition, of an hydrocarbon acrylate diluent, from about 0.25 to about 2 percent by weight, based on the total

weight of the composition, of phosphine oxide, and from about 0.25 to about 2

percent by weight, based on the total weight of the composition, of

benzophenone.

Any of the embodiments of the coating composition of the present

invention can be applied to a surface defect of a fired ceramic substrate, and then

cured using ultraviolet light, an electron beam, or an excimer laser.

The present invention also provides a method of repairing surface defects

on glazed ceramic articles. In one embodiment, the glazed ceramic article has

been previously fired. The method comprises the steps of (i) coating or hiding a

surface defect of a glazed ceramic article with a white coating composition or a coloured coating composition, and (ii) curing the composition with an energy source. The white coating composition can comprise any of the previously

described embodiments of the white coating composition of the present invention.

Similarly, the coloured coating composition can comprise any of the previously

described embodiments of the coloured coating composition of the present

invention.

The energy source can be an ultraviolet light source, an electron beam, an

excimer laser, or a cationic curing agent. Where the energy source is an

ultraviolet light source, the white or coloured coating composition comprises a photoinitiator including a blend of an aromatic ketone and phosphine oxide.

Another suitable photoinitiator, in this case, is a catonic curing agent. Where the

energy source is an excimer laser, the white or coloured coating composition must

also comprise an excimer laser sensitive photoinitiator such as a benzoketal.

Where the energy source is an electron beam, the white or coloured coating composition requires no photoinitiator.

In another embodiment, the present invention provides a method of

repairing surface defects on glazed ceramic articles comprising the steps of (i)

coating or hiding a surface defect of a glazed ceramic article with an undercoat of a white coating composition or a coloured coating composition, (ii) curing the

undercoat with a first energy source, (iii) applying a topcoat to the cured

undercoat, and (iv) curing the topcoat with a second energy source. The white

coating composition can comprise any of the previously described embodiments

of the white coating composition of the present invention. Similarly, the coloured coating composition can comprise any of the previously described embodiments of the coloured coating composition of the present invention. Also, the clear

topcoat composition can comprise any of the previously described embodiments

of the topcoat composition of the present invention. The first and second energy

sources can be any of those mentioned above. In one embodiment, the glazed ceramic article has been previously fired.

The present invention will be described in further detail with reference to

the following non-limitative examples.

Example 1

A coating composition comprising the compounds identified in Table 1 was applied to surface imperfections on a glazed ceramic substrate.

Table 1

The coating composition was cured using a Fusion System Model 450

ultraviolet light source. It was observed that the resultant cured coating failed to adhere to the ceramic substrate. Further, it was observed that the monomers

tended to boil out, leaving a greasy residue on the coating surface.

Example 2

A coating composition was formulated comprising 98 percent by weight, based on the total weight of the composition, of an oligomer, 1 percent by weight,

based on the total weight of the composition, of phosphine oxide, and 1 percent by weight, based on the total weight of the composition, of alpha-hydroxy ketone.

Several oligomers were tested, namely: epoxy acrylate, methacrylate acid ester, polyester acrylates and polyether acrylates.

Each of the formulation coating compositions were applied to a ceramic

substrate and were cured using a Fusion System Model 450 ultraviolet light

source. The coatings were tested for adhesion, discolouration, thermal stability,

water soak, aesthetics, resistance to alcohol and chlorines, and resistance to staining from Fuchsin Basic. The adhesion characteristics and aesthetic

characteristics of each of the cured coatings containing the various oligomers

tested are described in Table 2.

Table 2

Of the oligomers tested above, a polyether acrylate would appear to be a suitable candidate. In particular, a polyether acrylate characterized by a viscosity

of greater than 220 cps would appear to be a suitable candidate. A polyether acrylate characterized by a viscosity between 220 cps and 400 cps would appear to be particularly suitable.

Based on similarities between polyether acrylates and urethane acrylates,

namely features of low viscosity, high elasticity and low shrinkage, an urethane

acrylate would also appear to be a suitable candidate for inclusion in the coating

composition of the present invention.

Example 3

A coating composition was formulated comprising 60 percent by weight,

based on the total weight of the composition, of polyether acrylate, 2.5 percent by

weight, based on the total weight of the composition, of dispersant, about 5 to about 20 percent by weight, based on the total weight of the composition, of a

filler, 1 percent by weight, based on the total weight of the composition, of

phosphine oxide, and 1 percent by weight, based on the total weight of the

composition, of alpha hydroxy ketone. Several fillers were tested, namely:

calcium carbonate, aluminum hydrate, anahydrous sodium potassium aluminum

silicate, hydrated aluminium silicate, aluminium oxide, barium sulfate, and

magnesium silicate.

Each of the coating compositions, containing the different fillers tested,

were applied to a ceramic substrate and were subjected to a Fusion System Model

450 ultraviolet light source. The adhesion characteristics and curing characteristics of each of the formulations having different fillers were evaluated.

The observations made regarding these characteristics are identified in Table 3. Table 3

Therefore, of the fillers tested, aluminum oxide, barium sulfate, and

magnesium silicate appear to be acceptable candidates for the coating composition of the present invention.

Example 4

A coating composition was formulated comprising 60 percent by weight,

weight, based on the total weight of the composition, of dispersant, 20 percent by

weight, based on the total weight of the composition of the barium sulphate, 20 percent by weight, based on the total weight of the composition, of magnesium

silicate, and 1.0 to 2.5 percent by weight, based on the total weight of the

composition, of a photoinitiator. Several photoinitiators were tested, including

blends of individual photoinitiators.

Each of the coating compositions, containing the different photoinitiators

tested, were applied to a ceramic substrate and were subjected to ultraviolet light

from an Novacure UV Spot Care EFOS 100 SS Lamp. The adhesion characteristics and curing characteristics of each of the different formulations having different photoinitiators were evaluated. The observations made regarding

these characteristics are identified in Table 4.

Table 4

Of the photoinitiators tested, it would appear that a photoinitiator

comprising a blend of phosphine oxide and benzophenone would be suitable for the coating composition of the present invention.

Example 5

White coating compositions were formulated comprising the compounds

identified in Table 5.

Table 5

The titanium dioxide used was of the rutile grade. The rutile titanium

dioxide was included with a view to imparting a white colour to the coating

composition and with a view to matching the aesthetic appearance of a glaze.

The coating compositions that were tested included varying levels of rutile

titanium dioxide, namely between 5 and 15 weight percent.

Each of the coating compositions, containing different levels of rutile

titanium dioxide, were applied to a ceramic substrate and cured using an

ultraviolet light source. It was observed that the rutile titanium dioxide did not

impart the desired optical effects characteristic of a ceramic glaze.

A second formulation was created, comprising the compounds identified

in Table 6. Table 6

The aluminum hydroxide was refined from gibbsite and was characterized

by a particle size distribution between 0.015 and 1.5 μm.

Each of the coating compositions was applied to a ceramic substrate and

cured using ultraviolet light. The cured coating compositions, containing the aluminum hydroxide, were found to resemble the appearance of ceramic glaze. In comparison to the compositions defined in Table 5, the coating compositions

having the aluminum hydroxide were found to impart superior overall whiteness.

Further, the cured coating compositions having aluminum hydroxide were able

to provide a three-dimensional appearance which was not able to be achieved

with the coating compositions defined in Table 5.

It would appear, therefore, that inclusion of an aluminum hydroxide in the

white coating composition is necessary to provide the appearance of a ceramic

glaze. It will be understood, of course, that modifications can be made in the embodiments of the invention described herein without departing from the scope and purview of the invention as defined by the appended claims.

Claims

We claim:

1. A coating composition for application to a ceramic substrate comprising

a radiation curable oligomer, an extender, aluminum hydroxide and

titanium dioxide.

2. The coating composition as claimed in claim 1 wherein the aluminum

hydroxide is refined from gibbsite.

3. The coating composition as claimed in claim 2 wherein the aluminum

hydroxide is characterized by a particle size of less than about 1.5 μm.

4. The coating composition as claimed in claim 1 wherein the radiation

curable oligomer is a polyether acrylate or an urethane acrylate.

5. The coating composition as claimed in claim 1 wherein the radiation

curable oligomer is a polyether acrylate characterized by a viscosity

greater than about 220 mPa/s.

6. The coating composition as claimed in claim 1 wherein the radiation

curable oligomer is a polyether acrylate characterized by a viscosity from

about 220 mPa/s to about 400 mPa/s.

7. The coating composition as claimed in claim 3 wherein the radiation curable oligomer is a polyether acrylate or an urethane acrylate.

8. The coating composition as claimed in claim 3 wherein the radiation

curable oligomer is a polyether acrylate characterized by a viscosity

greater than 220 mPa/s.

9. The coating composition as claimed in claim 3 wherein the radiation

curable oligomer is a polyether acrylate is characterized by a viscosity

from about 220 mPa/s to about 400 mPa/s.

10. The coating composition as claimed in claim 1 having substantially no monomer.

11. The coating composition as claimed in claim 10 further comprising a

photoinitiator blend of an aromatic ketone and phosphine oxide.

12. The coating composition as claimed in claim 11 wherein the filler is

selected from the group consisting of aluminum oxide, barium sulfate and

magnesium silicate.

13. A coating composition for application to a ceramic substrate comprising:

a binder, having a radiation curable oligomer and an extender; and

a pigment, having aluminum hydroxide and titanium dioxide;

wherein the pigment and the binder are combined in a ratio in the range

of from about 3:1 to about 10:1 by volume.

14. The coating composition as claimed in claim 13 wherein the pigment and

the binder are combined in a ratio in the range of from about 4: 1 to about

6:1 by volume.

15. The coating composition as claimed in claim 13 wherein the pigment and

the binder are combined in a ratio in the range of about 4:1 by volume.

16. A coating composition for application to a ceramic substrate comprising:

from about 55 to about 65 percent by weight, based on the total weight of

the composition, of a polyether acrylate;

from about 0.25 to about 3.0 percent by weight, based on the total weight

of the composition, of a dispersant;

from about 10 to about 20 percent by weight, based on the total weight of

the composition, of barium sulfate; from about 10 to about 20 percent by weight, based on the total weight of the composition, of magnesium silicate;

from about 0.5 to about 20 percent by weight, based on the total weight

of the composition, of aluminum hydroxide; from about 3 to about 6 percent by weight, based on the total weight of

the composition, of titanium dioxide;

from about 0.25 to about 2 percent by weight, based on the total weight of the composition, of benzophenone.

17. A coating composition for application to a ceramic substrate comprising

a binder, including a radiation curable oligomer and an extender, and a

pigment comprising a colourant.

18. The coating composition as claimed in claim 17 wherein the radiation

curable oligomer is a polyether acrylate or an urethane acrylate.

19. The coating composition as claimed in claim 17 wherein the radiation

curable oligomer is a polyether acrylate characterized by a viscosity

greater than about 220 mPa/s.

20. The coating composition as claimed in claim 17 wherein the radiation

curable oligomer is a polyether acrylate characterized by a viscosity from

about 220 mPa/s to about 400 mPa s.

21. The coating composition as claimed in claim 18 having substantially no

monomer.

22. The coating composition as claimed in claim 21 wherein the colourant is a pearlescent pigment.

23. The coating composition as claimed in claim 21 wherein the colourant is a tinting paste.

24. A coating composition for application to a ceramic substrate comprising:

a binder, having a radiation curable oligomer and an extender; and a pigment, having a colourant;

wherein the pigment and the binder are combined in a ratio in the range

of from about 3:1 to about 10:1 by volume.

25. The coating composition as claimed in claim 24 wherein the pigment and the binder are combined in a ratio in the range of from about 4: 1 to about

6:1 by volume.

26. The coating composition as claimed in claim 24 wherein the pigment and

the binder are combined in a ratio of about 4:1 by volume.

27. A coating composition for application to a ceramic substrate comprising: from about 55 to about 65 percent by weight, based on the total weight of

the composition, of a polyether acrylate;

from about 0.25 to about 3.0 percent by weight, based on the total weight

of the composition, of a dispersant;

from about 15 to about 20 percent by weight, based on the total weight of the composition, of barium sulfate;

from about 15 to about 20 percent by weight, based on the total weight of

the composition, of magnesium silicate; from about 1 to about 10 percent by weight, based on the total weight of

the composition, of a colourant;

from about 0.25 to about 2 percent by weight, based on the total weight

of the composition, of phosphine oxide; and from about 0.25 to about 2 percent by weight, based on the total weight

of the composition, of benzophenone.

28. A coating composition for application to a ceramic substrate comprising

an undercoat and a clear topcoat, wherein the undercoat comprises a radiation curable oligomer, an extender or filler, aluminum hydroxide and

titanium dioxide, and wherein the topcoat comprises an urethane acrylate

oligomer and an hydrocarbon acrylate diluent.

29. A coating composition for application to a ceramic substrate comprising

an undercoat and a clear topcoat, wherein the undercoat comprises a

radiation curable oligomer, an extender or filler, and a colourant, and

wherein the topcoat comprises an urethane acrylate oligomer and an

hydrocarbon acrylate diluent.

30. A method of repairing a surface defect on a glazed ceramic article comprising the steps of:

coating or hiding a surface defect of a glazed ceramic article with the

coating composition as claimed in claim 1 ; and

curing the composition with an energy source.

31. A method of repairing a surface defect on a glazed ceramic article comprising the steps of: coating or hiding the surface defect with an undercoat comprising a radiation curable oligomer, an extender, aluminum hydroxide and titanium dioxide;

curing the undercoat with a first energy source;

applying a topcoat to the cured undercoat, the topcoat including an urethane acrylate oligomer and an hydrocarbon acrylate diluent; and curing the topcoat with a second energy source.

32. The method as claimed in claim 31 wherein each of the undercoat and

topcoat further comprise a photoinitiator, and wherein each of the first

and second energy sources is ultraviolet light.

33. A method of repairing a surface defect on a glazed ceramic article comprising the steps of:

coating or binding the surface defect with an undercoat comprising a

radiation curable oligomer, an extender and a colourant;

curing the undercoat with a first energy source;

applying a topcoat to the cured undercoat, the topcoat including an

urethane acrylate oligomer and an hydrocarbon acrylate diluent; and

curing the topcoat with a second energy source.

34. The method as claimed in claim 33 wherein each of the undercoat and

topcoat further comprises a photoinitiator, and wherein each of the first and second energy sources is ultraviolet light.