WO2004045779A1

WO2004045779A1 - Coating process

Info

Publication number: WO2004045779A1
Application number: PCT/GB2003/005025
Authority: WO
Inventors: Roger Walter Britton
Original assignee: Ward, Aylis, Haviland
Priority date: 2002-11-19
Filing date: 2003-11-19
Publication date: 2004-06-03
Also published as: AU2003283610A1; GB2395451A; GB0326885D0; GB0226916D0

Abstract

The present invention provides a process for coating an article which process includes the steps of.- (i) forming a thermosetting powder comprising an intimate mixture of finely ground 5 particles of thermosetting resin and one or more additives; (ii) electrostatically charging the powder mixture; (iii) spraying the electrostatically charged powder mixture onto a part or all of the surface of the article to be coated and (iv) curing the coated article. The powder is sprayed onto the surface of the article in a pulsed manner and in the method further comprises the step of exposing the article to an electrostatic field containing ions of the opposite polarity to the charge of the powder mixture between pulses.

Description

COATING PROCESS

The present invention relates to an improved process for coating an article and to an article coated by this process. The process is suitable for coatmg both metallic and non-metallic articles.

It is known to use thermosetting powders in an electrostatic deposition process, in which a thermosetting powder comprising an mtimate mixture of finely ground particles of mermosetting resin and one or more additives is electrostatically charged and sprayed onto a part or all of the surface of the article to be coated and the coated article is cured. Known thermosetting resins include polyesters, epoxyresins andpolyester/ epoxy copolymers. It is known to mix these resins with additives to impart to the finished material a desired texture, colour or other special effect, for example a metallic effect. Such electrostatic powder deposition processes are in general only suitable for the coating of metal articles or for the coating of very simply shaped non-metal articles.

For the coating of more complex shaped non-metallic articles, for example articles of tableware such as mugs or cups, a wet method of coating such as coating with inks, lacquers or paints using a spray gun is generally used. Where it is desired to apply a printed pattern to the article after coatmg, a transfer with a graphic image maybe applied to the article , typically by sublimation printing, and the print is then volatilised so that it transfers to the coated surface of the ceramic article.

It is a disadvantage of such processes that the spray guns conventionally used are not precise, so that a large excess of coating material has to be used and this cannot be reused, causing significant wastage and environmental problems in disposal. This wastage is aparticular disadvantage where the coating material being used is an expensive material. Coating materials where this is aparticular problem mcludememιochromic,photochromic ortexturisingcoatingmaterials. These materials include in particular thermochromic coating materials which change colour, either reversibly or irreversibly, when warmed, and are available in a variety of colours and different temperature response types, for example from -5°C to 60°C for reversible thermochromic coating materials and from 110°C to 120°C for irreversible thermochromic coating materials.

Thermochromic coating materials have been used in a number of applications, including in the manufacture of articles of tableware such as ceramic mugs, in particular for advertising purposes or for the production of novelty articles. Theiruseis described and claimed in EP-A-0920357.

There are a number of problems associated with this process. The thermochromic coating material is very expensive so that a high yield is essential. Since the only practical way to apply the thermochromic coating material is by a spray gun, it is necessary to use very precise and expensive spraying equipment in order to reduce as far as possible the wastage.

Attempts have been made to use an electrostatic powder deposition process to coat non-metal articles. Since the non-metal articles are insulators, they become charged electrostatically during the powder deposition process. Areas of acomplex shaped non-metal article, for example a mug, such as return edges, for example near to the handle of the mug cannot be coated because of the charge density which produces a Faraday cage effect. It is very difficult to get an even coating unless a high excess of material is used, and this is very expensive.

It is an obj ect of the present invention to provide a process in which the above disadvantages are reduced or substantially obviated.

The present invention provides a process for coating an article which process includes the steps of :- (i) forrrimgathermosettmgpowdercomprismganintimater ground particles of thermosetting resin and one or more additives; (iip electrostatically charging the powder mixture; (iii) spraying the electrostatically charged powder mixture onto a part or all of the surface of the article to be coated and (iv) curing the coated article,

characterised in that the powder is sprayed onto the surface of the article in a pulsed manner and in the method further comprises the step of exposing the article to an electrostatic field containing ions of the opposite polarity to the charge of the powder mixture between pulses.

In apreferred embodiment of the process according to the invention, the article is anon-metallic article, in particular an article of glazed or unglazed tableware.

In aparticularly preferred embodiment of the process accordingto the invention, the thermosetting powder comprises a thermosensitive material, in particular a thermochromic or photochromic material or a texturising material.

The thermochromic powder described and claimed in our co-pending UK Patent Application No 0226917.3 is particularly suitable for use in the electrostatic powder deposition process of the present invention .

The electrostatic powder deposition process of the present invention will now be described with reference to the following specific Examples.

Example 1

A mug was presented to a spraying system within a ventilated enclo sure designed to reclaim the o verspray material for re-use. The mug was held in an attitude which enabled the spray application system sight of all of the surfaces during the spraying operation The mug was also held on a jig which was earthed. The attitude of the mug could be vertical or horizontal and the mug could be rotated. The spray application head was capable of delivering an air powder mix towards the mug. Manipulation of the powder nozzle was by conventional means, conducive with forming a cloud of powder around the mug. Over aperiod of time the powder migrated to the mug. The mug then became charged and repelled the powder. More powder was deposited on the mug by reversing the polarity of the sprayed powder .The surface of the mug then accepted more powder because the Faraday cage effect had been controlled. The mug then exited the spray area and entered a curing section where the mug and coating were subjected to temperatures between 150 and220° C until curing was complete. The thermocliromic powder in the cured state was then able to accept printing by the sublimation process or by other means if desired

Example 2

Example 1 was repeated, with the variation that an oppositely charged ionised air flow was produced over the mug, instead of reversing the polarity of the sprayed powder.

Claims

1. A process for coating an article which process includes the steps of:-

(i) forming a themiosetting powder comprising an intimate mixture of finely ground particles of thermosetting resin and one or more additives;

(iϊβ electrostatically charging the powder mixture;

(iii) spraying the electrostatically charged powder mixture onto a part or all of the surface of the article to be coated and

(iv) curing the coated article,

characterised in that the powder is sprayed onto the surface of the article in a pulsed 10 manner and in the method further comprises the step of exposing the article to an electrostatic field containing ions of the opposite polarity to the charge of the powder mixture between pulses.

2. A process according to claim 1 characterised in that the article is a non-metallic article.

3. A process according to claim 1 or claim 2 characterised in that the article is an article of glazed or unglazed tableware.

4. Aprocess accordingto any of claims 1 to 3 characterised in that the thermosetting powder comprises a thermochromic material.