GB1569709A - Method of glazing a surface - Google Patents

Description

(54) METHOD OF GLAZING A SURFACE (71) We, METAL BOX LIMITED, of Queens House, Forbury Road, Reading RG1 3JH, Berkshire, England, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to methods of glazing a surface of a body. In our British Patent Specifications numbered 1,370,288 and 1,492,532, a method of glazing a surface is described in which an article to be glazed is preheated and then immersed in a fluidised bed consisting of a mixture of powdered inorganic glazing material and powdered organic resin. During immersion in the fluidised bed the article becomes coated with a layer of the mixture.The coated article is then removed from the bed and fired to fuse the glaze. Whilst our prior disclosures give examples of suitable ratios of quantities of glaze and resin to be used, and in British Patent No. 1,492,532 reference is made to "the proportion of organic resin in the glaze being less than that arising from a theoretical consideration of the space surrounding stacked spherical particles", the present invention adds information concerning the improved results to be derived from the use of rounded particles of glazing material. In this specification the method described in British Patent Specification No. 1,370,288 is described as "a method of dry glazing of the kind described".

In one aspect this invention relates to a dry glazing process of the kind described wherein the glaze particles are substantially spherical.

In another, preferred, aspect this invention relates to a dry glazing process of the kind described wherein the resin particles are much finer than the glaze particles. A preferred ratio of the glaze particles diameter to the resin particles diameter is 10:1. A preferred ratio of resin to glaze in the fluidised mixture is in the range 0.25% to 2.5% by weight.

Various embodiments of the invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. I is a diagram of stacked spheres; Fig. 2 is a diagram of nested spheres; Fig. 3 is a photo-micrograph of a coating of glass beads applied by the method; and Fig. 4 is a photo-micrograph showing typical bridges of adhesive between the beads.

Figs. I and 2 show diagrammatically particles of glaze as deposited on a substrate by immersing the preheated substrate in a fluidised bed containing particles of inorganic glaze and particles of an organic resin.

Referring to Fig. lit will be seen that the substantially spherical particles of inorganic glazing material, such as 11, have a diameter D and the particles of organic resin, such as 12, have a diameter d. The ratio of D to d is of the order of 10:1. The particles of glazing material, such as 11, are shown stacked rectilinearly with a particle of organic resin, such as 12, joining adjacent particles of glaze to form a layer adhered, in like manner, to a surface 13 of a substrate. It will be seen that there are voids, such as 14, between the particles and the surface and further voids 15 between the particles. Whilst the organic resin particles, such as 12, have been drawn as single particles for simplicity they may be agglomerates of several particles.However, it will be understood that the function of the resin is to adhere the glaze particles to adjacent particles and the surface of a substrate. Resin in excess of that required for this localised adhesion would be largely wasted because it is simply burnt off during firing of the coating.

Referring to Fig. 2, the glaze particles such as 11 are in nested relationship and are shown adhered by organic resin particles 12. Whilst the voids 14 between the particles of glaze and the surface 13 are the same as in Fig. 1, the voids, such as 16, between the particles are smaller than in Fig. 1, but again the resin adheres the glaze particles to one another and the surface 13, at their adjacent portions.

Both the arrangement of Fig. 1 and that of Fig. 2 permit the driving off of the organic resin through the voids 15, 14, while the glaze is being fused at a high temperature. Fig. 1 represents a maximum spacing of the spheres without cracks and Fig. 2 represents the closest spacing of the beads in relation to one another.

Fig. 3 is a photomicrograph showing an array of glass beads and resin in a coating as deposited on a preheated substrate (such as a tile) immersed in a fluidised bed of glass beads and particulate organic resin. The scale is indicated in micrometres in the lower right hand corner of the photomicrograph.

Fig. 4 is a micrograph, on a scale larger than Fig. 3, which shows the resin bridging the space between the beads. The bridges are created by the fusion of the particles of resin.

The glass beads are made from a soda glass to be substantially spherical. Two grades of bead, available from Potter-Ballotini Ltd. were used to obtain the data tabulated as examples 1 and 2 in the Table. Although the soda glass used does not permit firing at an elevated temperature to create a glazed coating (as would be true glazing material) the "Ballotini Beads" are an ideal shape to demonstrate the advantageous behaviour of the spherical shape during coating in the fluidised bed.

By way of a reference, the results of two further tests are tabulated as examples 3 and 4. In these examples irregular shaped particles, such as are produced by a ball mill, were placed in the fluidised bed.

The particulate organic resin used to produce the coating of Fig. 3 was an epoxy resin supplied by the Armstrong Chemical Company as number E 7100. The resin particle size was mostly less than 10 m, used as 0.25% of resin by weight of mixture in the fluidised bed. Other organic resins could have been used.

The typical coating thicknesses of the coatings deposited is in the range 1 to 50 thousandths of an inch.

TABLE

%age by Wt of E7100 Quality of Particle epoxy powder Biscuit Unfired Example Glazing Size used (mostly preheat Powder Number Powder approx. 10 {urn) temp OC Coating 1 Ballotini 44-88 11 % to 1 200-250 Thick, well beads held grade AH 2 Ballotini 177-297 /1 to 1 200-250 Thick, well beads held grade All Ball milled 40-100 ,u to 1 200-250 Thick, but glass with (mainly) less well irregular held than particles 1 & 4 Ball milled 40-100 , 4 200-250 Coating of glass with (mainly) comparable irregular strength to particles 1 & From the Table it will be seen that the spherical beads of examples 1 and 2 gave coatings which were thick and well held onto the substrate in contrast to the less well held coating of example 3.

Also the spherical beads of examples 1 and 2 required less resin in the fluidised mixture than did the irregular particles as is shown by comparison of examples 1 and 2 with example 4.

The range of ratios of bead size to resin particle size extends from 20 to 1 (example 2) to about 4 to 1 (example 1); a preferred ratio being 10:1.

The preferred range of proportions of resin to glass particles extends from as little as 0.25% up to 2.5% by weight of resin in the fluidised bed of glass particles and resin particles.

A range of glaze particle sizes may be used, a preferred range being between 20 and 200 micrometres. A range of resin particle sizes may also be used, a preferred range of resin particle size being between 0.1 and 10 micrometres.

WHAT WE CLAIM IS: 1. A method of dry glazing as defined in any claim of our British Patent Number 1,370,288, wherein the particles of glazing material are substantially spherical.

2. A method according to Claim 1 wherein the ratio of the diameter of the particles of inorganic glazing material to the diameter of the particles of organic resin is within the range 20:1 to 4:1.

3. A method as claimed in Claim 2 wherein the ratio is 10:1.

4. A method according to any preceding Claim wherein the range of glaze particle size is within the range 20 to 200 micrometres and the particle size of the resin is in the range 0.1 to 10 micrometres.

5. A method according to any preceding Claim wherein the percentage of resin by weight of the mixture is in the range 0.25% to 2.5%.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. TABLE %age by Wt of E7100 Quality of Particle epoxy powder Biscuit Unfired Example Glazing Size used (mostly preheat Powder Number Powder approx. 10 {urn) temp OC Coating 1 Ballotini 44-88 11 % to 1 200-250 Thick, well beads held grade AH 2 Ballotini 177-297 /1 to 1 200-250 Thick, well beads held grade All Ball milled 40-100 ,u to 1 200-250 Thick, but glass with (mainly) less well irregular held than particles 1 & 4 Ball milled 40-100 , 4 200-250 Coating of glass with (mainly) comparable irregular strength to particles 1 & From the Table it will be seen that the spherical beads of examples 1 and 2 gave coatings which were thick and well held onto the substrate in contrast to the less well held coating of example 3. Also the spherical beads of examples 1 and 2 required less resin in the fluidised mixture than did the irregular particles as is shown by comparison of examples 1 and 2 with example 4. The range of ratios of bead size to resin particle size extends from 20 to 1 (example 2) to about 4 to 1 (example 1); a preferred ratio being 10:1. The preferred range of proportions of resin to glass particles extends from as little as 0.25% up to 2.5% by weight of resin in the fluidised bed of glass particles and resin particles. A range of glaze particle sizes may be used, a preferred range being between 20 and 200 micrometres. A range of resin particle sizes may also be used, a preferred range of resin particle size being between 0.1 and 10 micrometres. WHAT WE CLAIM IS:

1. A method of dry glazing as defined in any claim of our British Patent Number 1,370,288, wherein the particles of glazing material are substantially spherical.

2. A method according to Claim 1 wherein the ratio of the diameter of the particles of inorganic glazing material to the diameter of the particles of organic resin is within the range 20:1 to 4:1.

3. A method as claimed in Claim 2 wherein the ratio is 10:1.

4. A method according to any preceding Claim wherein the range of glaze particle size is within the range 20 to 200 micrometres and the particle size of the resin is in the range 0.1 to 10 micrometres.

5. A method according to any preceding Claim wherein the percentage of resin by weight of the mixture is in the range 0.25% to 2.5%.

6. A method as claimed in Claim 1, substantially as hereinbefore described

with reference to the accompanying drawings.