Method of coating surface

Abstract

The method of forming relatively thick deposits of polymeric material on a surface of small threaded articles which comprises forming a thin coating on the surface of a solution of the polymeric material, at least partly drying the coating to eliminate some or all of the solvent for the polymeric material, applying a barrier coating to the polymeric material to protect it from attack by solvent, and applying a second thin coating of a solution of the polymeric material. The operation may be repeated as necessary to build up the required thickness of deposit. Coating is by successive immersions in baths of the polymeric solution separated by immersion in baths of the barrier material, or by other bulk treatment therewith, followed by partial drying before subsequent immersions and final drying after the last immersion.

Description

Claims

1. The method of building up a deposit of predetermined thickness of a friction producing resinous organic polymer on the thread surface of a threaded article which comprises preparing a solution of the polymer in a volatile organic solvent of a consistency such that application of an excess of the solution, draining and subsequent drying will provide a deposit of less than said predetermined thickness, applying an excess of the solution to the thread surface, draining the excess solution from the article, partly drying the deposit by evaporation of solvent to produce a substantially non-tacky outer surface on the partly dried deposit of polymer, applying a mixture of a barrier material in water to the surface of the partly dried deposit of polymer, partly drying the mixture to leave a coating of barrier material having a thickness only sufficient to protect the previous deposit of polymer from re-dissolving in the solvent, again applying an excess of the solution to the article, draining the excess solution from the article, and at least partly drying the last deposit by evaporation of solvent to produce a substantially non-tacky outer surface on the last deposit of polymer.

2. The method of claim 1 in which the polymer is essentially acrylic.

3. The method of claim 2 in which the solvent is methyl-ethyl-ketone.

4. The method of claim 3 in which the mixture is polyvinyl alcohol in a water solution.

5. The method of claim 1 in which the mixture is gelatin in a water solution.

6. The method of claim 1 in which the mixture is polyvinyl alcohol in a water solution.

7. The method of simultaneously building up a deposit of predetermined thickness of a friction producing resinous organic polymer on the surface of a multiplicity of small threaded articles which comprises preparing a solution of the polymer in a volatile organic solvent of a consistency such that application of an excess of the solution, draining, and subsequent drying will provide a deposit of polymer of less than said predetermined thickness, substantially simultaneously applying an excess of the solution to a multiplicity of such articles, draining the excess solution from the articles, supporting the articles in separated condition from each other, substantially simultaneously applying to the articles an excess of a mixture of barrier forming material in water, draining excess mixture therefrom, drying the mixture applied to the articles to leave a barrier coating of barrier material of a thickness only sufficient to protect the previous deposit of polymer from re-dissolving in organic solvent, again substantially simultaneously applying an excess of the solution to the multiplicity of articles, draining excess solution, separating the articles from each other, and drying the articles to provide a non-tacky outer surface.

8. The method as defined in claim 7 in which the application of the excess of solution to the articles is accomplished simultaneously for all articles making up the said multiplicity by immersing the multiplicity of articles in the solution.

9. The method as defined in claim 8 in which the steps of immersion, and draining are accomplished by placing the multiplicity of articles in a screen basket having openings through which solution and the mixture can drain, immersing the basket with the articles therein alternately in baths of the solution and the mixture, lifting the baskets above the baths, and permitting drainage through the openings back into the respective baths.

10. The method as defined in claim 7 in which the polymer comprises a major proportion of acrylic resin.

11. The method as defined in claim 10 in which the solvent is essentially methyl-ethyl-ketone.

12. The method as defined in claim 7 in which the mixture is animal gelatin or polyvinyl alcohol in a water solution.

13. The method as defined in claim 7 in which the mixture is a solution of about 20% animal gelatin in water.

14. The method as defined in claim 7 in which the mixture is a solution of polyvinyl alcohol in water with the polyvinyl alcohol provided in an effective amount up to 10% by weight of the solution.

15. The method as defined in claim 7 in which the mixture is a solution of polyvinyl alcohol in water with the polyvinyl alcohol provided in an amount of 3-4% by weight of the solution.

16. The method as defined in claim 7 in which the steps of applying the excesses of the solution comprise advancing the articles on a screen conveyor, and providing a continuous falling curtain of the solution to extend across the conveyor through which the articles advance.

17. The method as defined in claim 16 in which the polymer is essentially acrylic.

18. The method as defined in claim 17 in which the solvent is methyl-ethyl-ketone.

19. The method as defined in claim 18 in which the mixture is polyvinyl alcohol in a water solution.

20. The method as defined in claim 16 in which the mixture is gelatin in a water solution.

21. The method as defined in claim 16 in which the mixture is polyvinyl alcohol in a water solution.