Apparatus for coating a surface with a transferable layer of thermoplastic particles, and related methods

Patent metadata

Field	Value
Publication number	US-10960432-B2
Application number	US-201615363615-A
Country	US
Kind code	B2
Filing date	Nov 29, 2016
Priority date	May 27, 2015
Publication date	Mar 30, 2021
Grant date	Mar 30, 2021

Abstract

An apparatus for coating a donor surface that is movable relative to the apparatus with a layer of thermoplastic particles, the particles adhering more strongly to the surface than to one another. The apparatus comprises an application device to apply to the donor surface a fluid stream within which the particles are suspended, a housing surrounds the application device forming an interior plenum for confining the fluid stream, the housing prevents egress of particles from a sealing gap defined between the rim of the housing and the surface to be coated, and a suction source connected to the housing to extract from the plenum excess fluid and particles. In operation, the suction source extracts substantially all particles that are not in direct contact with the donor surface, leaving substantially a single particle layer adhering to the donor surface upon exiting the apparatus.

First claim

The invention claimed is:

1. A coating apparatus comprising:
a coating station; and
an endless donor surface movable cyclically past the coating station and an impression station, the coating station serving to coat the donor surface or portions thereof during each passage of the donor surface past the coating station, with a layer of thermoplastic particles to form a particle coating that is substantially only a single particle deep, at least selected regions of the particle coating being transferable from the donor surface to a substrate at the impression station;
wherein the coating station comprises:
a) a supply system operative to supply thermoplastic particles suspended in a fluid, the fluid being a liquid that does not wet the donor surface or being a gas; the surface energies of the thermoplastic particles and of
the donor surface being selected such that the particles have a higher tendency to adhere to the donor surface than to one another;
b) an application device for applying the fluid to the donor surface in a manner to cause the particles suspended in the fluid to adhere to the donor surface, so as to form a substantially continuous particle coating on the donor surface;
c) a cooler disposed to operatively cool the donor surface prior to the applying of the fluid to the donor surface; and
d) a surplus extraction system operative to cause a fluid flow over the donor surface, the fluid flow being of sufficient magnitude to entrain particles not in direct contact with the donor surface and insufficient to entrain particles which are in direct contact with the donor surface, so that the particle coating that is left adhering to the donor surface is substantially only a single particle deep.

2. A coating apparatus as claimed in claim 1 , wherein the application device comprises a spray head for spraying the fluid and suspended particles directly onto the donor surface.

3. A coating apparatus as claimed in claim 1 , wherein the application device comprises a rotatable applicator operative to wipe the fluid and suspended particles onto the donor surface.

4. A coating apparatus as claimed in claim 3 , wherein the applicator is a cylindrical sponge.

5. A coating apparatus as claimed in claim 4 , wherein the sponge is formed of a closed-cell foam.

6. A coating apparatus as claimed in claim 3 , wherein the applicator has a plurality of flexible strips extending radially from a rotatable axle.

7. A coating apparatus as claimed in claim 6 , wherein the flexible strips are formed of a closed-cell foam.

8. A coating apparatus as claimed in claim 1 , wherein the application device and the surplus extraction system are each independently contained within an interior plenum of a housing having a rim adjacent to the donor surface, the rim being configured to prevent egress of particles from a sealing gap defined between the rim of the housing and the donor surface.

9. A coating apparatus as claimed in claim 8 , wherein the surplus extraction system comprises a suction source connected to the housing to cause the fluid flow.

10. A coating apparatus as claimed in claim 8 , further comprising a wiper blade disposed adjacent to the rim at an upstream side of the coating apparatus, for preventing egress of particles and/or fluid.

11. A coating apparatus as claimed in claim 10 , wherein the surplus extraction system comprises a suction source connected to the housing to extract from the plenum surplus fluid and particles suspended in the fluid.

12. A coating apparatus as claimed in claim 11 , further comprising a fluid flow passage disposed at the rim of the housing to enable fluid to be drawn from the vicinity of the sealing gap, the passage being coupled to the suction source.

13. A coating apparatus as claimed in claim 8 , further comprising fluid flow passage disposed at the rim of the housing to enable fluid to be drawn from, or introduced into, at least regions of the sealing gap disposed downstream of the application device.

14. A coating apparatus as claimed in claim 13 , wherein the fluid flow passage is coupled to a suction source.

15. A coating apparatus as claimed in claim 13 , wherein the fluid flow passage is coupled to a supply of a gas at above ambient pressure and devoid of suspended particles.

16. A coating apparatus as claimed in claim 1 , wherein the fluid within which the particles are suspended is a gas.

17. A coating apparatus as claimed in claim 16 , wherein the particles are entrained into a stream of the gas by a Venturi tube.

18. A coating apparatus as claimed in claim 1 , wherein the fluid within which the particles are suspended is a liquid.

19. A coating apparatus as claimed in claim 18 , wherein at least a portion of the liquid is extracted from the donor surface by the surplus extraction system such that the particle layer is at least partially dry or substantially dry on exiting the apparatus.

20. A coating apparatus as claimed in claim 1 , wherein particles extracted by the surplus extraction system are recycled to the application device.

21. A coating apparatus as claimed in claim 1 , wherein the particles comprise a thermoplastic polymer and a coloring agent.

22. A coating apparatus as claimed in claim 1 , wherein the particles are substantially spherical.

23. A coating apparatus as claimed in claim 1 , wherein the particles have the form of flat platelets.

24. A coating apparatus as claimed in claim 1 , further comprising a burnishing station for homogenizing at least one property of the particle coating.

25. A coating apparatus as claimed in claim 1 , wherein the application device and the surplus extraction system are contained within a single housing.

26. A coating apparatus as claimed in claim 1 , further comprising a heater disposed to operatively heat the single particle deep particle coating.

27. A coating apparatus as claimed in claim 1 , further comprising a burnishing station for homogenizing at least one property of the particle coating, wherein the application device, the surplus extraction system and the burnishing station are contained within a single housing.

28. A method of coating a donor surface with a layer of thermoplastic particles, the method comprising:
a) providing a supply of the thermoplastic particles suspended in a fluid, the fluid being a liquid that does not wet the donor surface or being a gas,
b) the surface energies of the thermoplastic particles and of the donor surface being selected such that the particles have a higher tendency to adhere to the donor surface than to one another;
c) applying the fluid to the donor surface, by a particle applicator, in a manner to cause the particles suspended in the fluid to adhere to the donor surface so as to form a substantially continuous particle coating on the surface as the surface is moved relative to the particle applicator, and
d) causing fluid flow over the donor surface, the fluid flow being of sufficient magnitude to entrain particles that are not in direct contact with the donor surface and insufficient to entrain particles that are in direct contact therewith, thus extracting fluid and surplus particles that are not in direct contact with the donor surface, so as to leave adhering to the surface a coating that is substantially only a single particle deep.

29. A coating station serving to coat an endless donor surface or port

Assignees

• Landa Labs 2012 Ltd

Inventors

• Landa Benzion
• Krassilnikov Anton
• Fahima Moshe
• Yakhel Vadim

Classifications

• B05B7/1481 Primary

  Spray pistols or apparatus for discharging particulate material · CPC title

• C23C24/04

  Impact or kinetic deposition of particles · CPC title

• C09D5/38

  Paints containing free metal not provided for above in groups C09D5/00 - C09D5/36 · CPC title

• C09D1/00

  Coating compositions, e.g. paints, varnishes or lacquers, based on inorganic substances · CPC title

• B44F9/10

  of metallic or oxidised metallic surfaces · CPC title