Patent GB-1380458-A (GB)
Title: Method for modifying plastic surfaces
IPC: C08J7/02
Filed: 1972-08-08
Abstract: 1380458 Treating polymer surfaces DOW CHEMICAL CO 8 Aug 1972 [9 Aug 1971] 37018/72 Heading B2E  A method for reflowing plastic surfaces comprising introducing an object which is made of plastic material or which has a plastic surface into a first zone of saturated vapours of the solvent, maintaining the object therein for a period of time sufficient for at least a sufficient amount of solvent to enable the surface to flow to be absorbed into the plastic surface, withdrawing the object from the zone and introducing it into a second zone of superheated vapours of the same solvent as is utilised in the first zone and maintaining the object in the second zone for a period of time sufficient at least to raise the surface temperature of the object to the temperature of the superheated vapours, withdrawing the object from the second zone into a third zone of saturated vapours of the same solvent and without delay removing the object into the ambient atmosphere. The process removes surface blemishes. In an embodiment there is a method of coating which comprises introducing the objected to be coated into the saturated vapour of the solvent, maintaining the object therein for a period of time sufficient to raise its surface temperature to the boiling point of the solvent from which the coating is to be applied, either withdrawing the object from the saturated vapours and introducing it into the superheated vapours of the same solvent as the solvent of the saturated vapours and while therein applying a solvent-soluble plastic coating to the object, or applying a solvent-soluble plastic coating to the object whilst in the saturated vapours of the solvent ducing the object to be coated into the superheated vapours of the same solvent, in either case maintaining the coated object in the superheated vapours for a period of time sufficient for substantially all the coating solvent to be vapourised, withdrawing the object from the superheated zone and treating it in the manner defined above as a method of reflowing plastic surfaces. Suitable solvents are chlorinated hydrocarbon solvents, fluorinated hydrocarbon solvents, hydrocarbon solvents. Suitable examples of dress materials are given. The plastics may be an epoxide, acrylate, urethane, polyester, polyether, natural resin or rosin. In the drawing is shown an apparatus for carrying out a coating and reflow process. The zone A contains saturated solvent vapours which raise the surface of a substrate to the atmospheric volume of the solvent. In the intermediate zone the substarte is painted or coated by spraying, padding or dipping and this zone may be either a saturated or superheated vapour zone. The object consists of zone B containing superheated vapours which cause the coating vapours to be driven when the coating dries. The object then passes to zone C containing saturated vapours which reflow the coating before passing to zone D containing superheated vapours which cause the vapours absorbed in the reflow process to be driven off and finally in the zone E containing saturated vapours as a vapour lock. In the Examples a metal panel is coated with an acrylic paint containing titanium dioxide in a vehicle of methylene chloride.