Process for plastic coating, and coating produced by the process

Claim 2

A process of powder coating a high temperature resistant surface with fluorothermoplastics material comprising: (a) applying to said surface a base layer of a powdered fluorothermoplastics material having a first melting temperature and sintering the base layer at a baking temperature of the first thermoplastics material selected, (b) then applying over the base layer a covering layer of a powdered second fluorothermoplastics material having a lower melting temperature and the same or increased flowability than said first melting temperature, and heating the covering layer to a temperature below said first melting temperature to fuse the coating.

Claim 3

The process according to claim 1, and the further steps of: (a) initially building up the base layer to a thickness which is below the run-off limit of the fluorothermoplastic material at the processing temperature of the first partial layer of the first covering layer, (b) then building up the first partial layer of the covering layer at a processing temperature at which the base layer and the first partial layer melt to a thickness which is slightly below the run-off limit, and (c) then building up at least one further partial layer of the covering layer at a processing temperature which is lower than that of step (b), but which ensures adequate film formation and bonding with the previously applied layer and which does not exceed the run-off limit due to gravity of the whole covering layer.

Claim 4

The process according to claim 1, in which the fluorothermoplastic material of the covering layer has a melting point which is at least 10° C. lower and a flowability which is higher than that of the fluorothermoplastic material of the layer below.

Claim 5

The process according to claim 1, in which the fluorothermoplastic material of the covering layer has a melting point which is at least 30° C. lower than that of the layer below.

Claim 6

The process according to claim 1, in which the fluorothermoplastic material applied as the base layer and covering layer is a copolymer which is processable from the melt and is comprised of tetrafluoroethylene and at least one additional ethylenically unsaturated monomer which is copolymerizable with tetrafluoroethylene.

Claim 7

The process according to claim 1, in which the fluorothermoplastic material applied as the base layer and covering layer is a copolymer which is processable from the melt and is comprised of tetrafluoroethylene and at least one ethylenically unsaturated comonomer which is copolymerizable with tetrafluoroethylene, wherein the copolymer is comprised of different comonomers from layer to layer.

Claim 8

The process according to claim 1, in which the fluorothermoplastic material applied as the base layer and covering layer is a copolymer which is processable from the melt and is comprised of tetrafluoroethylene and at least one ethylenically unsaturated comonomer which is copolymerizable with tetrafluoroethylene, wherein the copolymer comprising the upper layer has a higher flowability at the processing temperature than the copolymer comprising the layer below the upper layer.

Claim 9

The process according to claim 1, in which the fluorothermoplastic material applied as the base layer and covering layer is a copolymer which is processable from the melt and is comprised of tetrafluoroethylene and at least one additional ethylenically unsaturated monomer which is copolymerizable with tetrafluoroethylene, wherein the copolymer comprising the upper layer has a melting point that is lower than that of the copolymer comprising the layer below the upper layer.

Claim 10

The process according to claim 1 further comprising the steps of: (a) pretreating the surface to be coated, including heating the surface; (b) applying a first partial layer of the base layer to the hot surface; (c) sintering the first partial layer at the baking temperature of the fluorothermoplastic material selected for the base layer; (d) applying additional partial layers of the base layer step-wise on the hot surface of the previous partial layer and sintering each applied partial layer at the baking temperature of the fluorothermoplastic material selected for the base layer; (e) applying a first partial layer of the covering layer on the base layer, the melting point of the covering layer being lower than that of the base layer, and sintering at a temperature above the melting point of the base layer; and (f) applying at least one additional partial layer of the covering layer stepwise on the hot surface of the previous partial layer and after applying the additional partial layer, sintering at a temperature below the melting point of the base layer.

Claim 11

The method according to claim 1, in which the base layer is applied with additives which promote curing.

Claim 12

A process as claimed in claim 1, wherein applying further covering layers of powdered fluorothermoplastics materials over the covering layer which further covering layers comprise materials selected so that each has a lower melting point than the material of the preceding layer and heating each layer to a temperature below the melting point of the material of the preceding layer.