GB2194178A

GB2194178A - Coating surfaces

Info

Publication number: GB2194178A
Application number: GB08629661A
Authority: GB
Inventors: Geoffrey John Landon-Browne
Original assignee: Smith Meters Ltd
Current assignee: Smith Meters Ltd
Priority date: 1986-04-25
Filing date: 1986-12-11
Publication date: 1988-03-02
Also published as: GB8629661D0

Abstract

A surface of a material such as a smooth plastics material or a ceramic is painted with a coating material such as an epoxy or polyester resin. This material normally has poor adhesion to such surfaces. The coating material in dry powder form is mixed with fine consistency abrasive such as aluminium oxide powder, the aluminium oxide comprising preferably 1 DIVIDED 2%-2% by volume of the mixture. This is then directed in a jet of air at the surface by means of an air gun using a pressurized air source at e.g. 30 to 90 lbs/square inch. The abrasive material makes a mechanical key to which the paint adheres.

Description

SPECIFICATION Coating surfaces This invention relates to coating surfaces with materials which have poor adhesion thereto.

The invention provides a method of coating a surface with a fusible material which has poor adhesion thereto, comprising bombarding the surface with a mixture of abrasive material and the powdered coating material at pressures high enough to cause the abrasive material to make a mechanical key to which the coating material may adhere.

The said mixture may be projected at the surface from a gas or air gun using pressures of between 30 Ibs per square inch and 90 Ibs per square inch.

The mixture may comprise a minor proportion by volume of the abrasive material. The abrasive material may be of fine consistency like that of flour. Typically the abrasive material may be of 360 mesh.

The mixture may be between 2-2% by volume of aluminium oxide powder, the remainder being polyester or epoxy powder paint.

The method may include a second step of conventional painting over the base formed as set out above.

The invention also extends to objects coated by the above method; to the mixture used in the method; and to the machine for use in coating the surface.

A specific examples of the invention is described with reference to the accompanying drawing, which shows diagrammatically a machine in the process of painting.

The Item (11) being painted has a surface of a material which is difficult to paint because of either the lack of a mechanical key or chemical resistance. The surface may for instance be a smooth plastics material, or a ceramic, or a lead or metal alloy plate. The item may be a container formed of a plastics material onto which it is desired to paint a design or lettering. A stencil (12) formed into a negative of the design is placed in front of the container and a jet (13) is directed through the stencil to impinge on the container.

The jet (13) is produced by an air gun apparatus (14) in which pressurised air (arrow A) is directed over a nozzle (15) leading from a reservoir (16). Material from the reservoir is entrained into the air stream which emerges from mixing nozzle (17) as the jet.

Reservoir (16) contains a dry, powdery mixture comprising 99% powdered paint of the kind used in known powder coating techniques. The paint comprises polyester or epoxy resin base with a pigment. The other 1% of the mixture is 360 mesh powdered carborundum (aluminium oxide).

When the mixture impinges on the container (11) its surface is slightly roughened by the abrasive carborundum. The paint particles when striking the surface are heated by the impact and fuse into the crevices of the roughened surface. Thus a mechanical bond is formed.

It may be desired to apply another layer of paint in order to obtain a better surface finish or to overlay a different design. This may be done by the same or similar apparatus using a mixture in reservoir (16) from which the abrasive has been omitted. Alternatively, other known painting techniques can be used once the first layer has been bonded, if the new layers of paint are compatible with the first layer. The mixture used in the reservoir (16) may vary, for instance by the use of different abrasive material or by the omission of the paint pigment so that a clear coating is produced. Surfaces having different properties of hardness may be accommodated by using different abrasive grits, of larger or smaller particle size, the optimum sizes being ascertained by experimentation.

The air pressure used determines the speed at which the particles impinge on the surface.

The example described here uses an air pressure of 30 Ibs per square inch, but pressures up to 90 Ibs per square inch may be used.

Harder surfaces may require higher pressures.

The painting process may be fully automated, the containers being presented in turn to the painting station and the jet being timed.

1. A method of coating a surface with a fusible material which has poor adhesion thereto, comprising bombarding the surface with a mixture of abrasive material and the powdered coating material at pressures high enough to cause the abrasive material to make a mechanical key to which the coating material adheres.

2. A method as claimed in claim 1, in which the mixture comprises a minor proportion by volume of the abrasive material.

3. A method as claimed in claim 1 or claim 2, wherein the abrasive material is aluminium oxide powder.

4. A method as claimed in any of claims 1 to 3, in which the coating material is polyester or epoxy powder paint.

5. A method as claimed in any of claims 1 to 4, in which the mixture is projected at the surfaces from a gas or air gun using pressures of between 30 and 90 Ibs per square inch.

6. A method of coating a ceramic surface with a paint comprising bombarding the ceramic surface with a mixture of epoxy powder, paint and %-2% by volume of aluminium oxide powder in a jet of air using air pressures of between 30 and 901bs per square inch.

7. A method as claimed in any of claims 1 to 6, in which the abrasive material is of a fine consistency like that of flour.

8. A method as claimed in claim 7, in which the abrasive material is of 360 mesh.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Coating surfaces This invention relates to coating surfaces with materials which have poor adhesion thereto. The invention provides a method of coating a surface with a fusible material which has poor adhesion thereto, comprising bombarding the surface with a mixture of abrasive material and the powdered coating material at pressures high enough to cause the abrasive material to make a mechanical key to which the coating material may adhere. The said mixture may be projected at the surface from a gas or air gun using pressures of between 30 Ibs per square inch and 90 Ibs per square inch. The mixture may comprise a minor proportion by volume of the abrasive material. The abrasive material may be of fine consistency like that of flour. Typically the abrasive material may be of 360 mesh. The mixture may be between 2-2% by volume of aluminium oxide powder, the remainder being polyester or epoxy powder paint. The method may include a second step of conventional painting over the base formed as set out above. The invention also extends to objects coated by the above method; to the mixture used in the method; and to the machine for use in coating the surface. A specific examples of the invention is described with reference to the accompanying drawing, which shows diagrammatically a machine in the process of painting. The Item (11) being painted has a surface of a material which is difficult to paint because of either the lack of a mechanical key or chemical resistance. The surface may for instance be a smooth plastics material, or a ceramic, or a lead or metal alloy plate. The item may be a container formed of a plastics material onto which it is desired to paint a design or lettering. A stencil (12) formed into a negative of the design is placed in front of the container and a jet (13) is directed through the stencil to impinge on the container. The jet (13) is produced by an air gun apparatus (14) in which pressurised air (arrow A) is directed over a nozzle (15) leading from a reservoir (16). Material from the reservoir is entrained into the air stream which emerges from mixing nozzle (17) as the jet. Reservoir (16) contains a dry, powdery mixture comprising 99% powdered paint of the kind used in known powder coating techniques. The paint comprises polyester or epoxy resin base with a pigment. The other 1% of the mixture is 360 mesh powdered carborundum (aluminium oxide). When the mixture impinges on the container (11) its surface is slightly roughened by the abrasive carborundum. The paint particles when striking the surface are heated by the impact and fuse into the crevices of the roughened surface. Thus a mechanical bond is formed. It may be desired to apply another layer of paint in order to obtain a better surface finish or to overlay a different design. This may be done by the same or similar apparatus using a mixture in reservoir (16) from which the abrasive has been omitted. Alternatively, other known painting techniques can be used once the first layer has been bonded, if the new layers of paint are compatible with the first layer. The mixture used in the reservoir (16) may vary, for instance by the use of different abrasive material or by the omission of the paint pigment so that a clear coating is produced. Surfaces having different properties of hardness may be accommodated by using different abrasive grits, of larger or smaller particle size, the optimum sizes being ascertained by experimentation. The air pressure used determines the speed at which the particles impinge on the surface. The example described here uses an air pressure of 30 Ibs per square inch, but pressures up to 90 Ibs per square inch may be used. Harder surfaces may require higher pressures. The painting process may be fully automated, the containers being presented in turn to the painting station and the jet being timed. CLAIMS

9. A method of coating a surface substantially as described hereinbefore with reference to the accompanying drawing.

10. An article having a surface of smooth plastics material or a ceramic painted by the method as set forth in any of claims 1 to 9.

11. An article having a surface of lead or metal alloy plate painted by the method as set forth in any of claims 1 to 9.

12. Apparatus adapted for carrying out the method claimed in any of claims 1 to 9.