Composite Material Based on Perfluoroalkoxy Polymers for Coating Metallic Surfaces

Abstract

Described herein is a composite material including perfluoroalkoxy polymer powder, carbon black powder and a film-forming liquid, where the proportion by mass of the film-forming liquid is from 0.05% by weight to 1.0% by weight, the film-forming liquid at least partially wets the surfaces of the particles of the perfluoroalkoxy polymer powder, and the particles of the carbon black powder adhere to the film-forming liquid and/or the particles of the perfluoroalkoxy polymer powder. Also described herein are a production process for coating metallic surfaces, which uses the composite material as starting material, and further uses of the composite material.

Claims

1. A composite material comprising perfluoroalkoxy polymer powder, carbon black powder and a film-forming liquid, wherein the proportion by mass of the film-forming liquid is from 0.05% by weight to 1.0% by weight, the film-forming liquid at least partially wets the surfaces of the particles of the perfluoroalkoxy polymer powder, and the particles of the carbon black powder adhere to the film-forming liquid and/or the particles of the perfluoroalkoxy polymer powder.

2. The composite material according to claim 1, wherein the film-forming liquid is an unbranched or branched aliphatic hydrocarbon compound having a polar functional group.

3. The composite material according to claim 2, wherein the film-forming liquid is 1-octanol.

4. The composite material according to claim 1, wherein the carbon black powder is selected from the group consisting of pigment blacks, conductive carbon blacks, industrial blacks, carbon-comprising soot and carbon nanotubes.

5. The composite material according to claim 1, wherein the proportion by mass of the carbon black powder is from 1.0% by weight to 5.0% by weight.

6. The composite material according to claim 1, wherein the composite material further comprises at least one additive having a thermal conductivity higher than the thermal conductivity of the perfluoroalkoxy polymer.

7. The composite material according to claim 1, wherein the composite material is pulverulent and free-flowing.

8. A process for producing a composite material according to claim 1, wherein the particles of the perfluoroalkoxy polymer powder are mixed with the film-forming liquid in a first step and the resulting mixture is mixed with the particles of the carbon black powder in a second step.

9. A component having at least one metallic surface which is at least partly coated with a composite material according to claim 1.

10. The component according to claim 9, wherein the surface resistance of the coating of the component is less than 1 gigaohm.

11. A process for coating the surface of a component with a pulverulent composite material according to claim 1, comprising (a) heating a component surface to a temperature which is from 1° C. higher to 100° C. higher than the melting point of the perfluoroalkoxy polymer, (b) electrostatically charging the pulverulent composite material, and (c) spraying a grounded surface of the component.

12. A process for producing a film, comprising (a) applying the composite material according to claim 1 to a surface, (b) heating the surface to a temperature which is from 1° C. higher to 100° C. higher than the melting point of the perfluoroalkoxy polymer, (c) cooling and curing a film layer, and (d) pulling-off the film from the surface.

13. A process for producing a component by the rotational molding process, comprising (a) of introducing the pulverulent composite material according to claim 1 into a heatable cavity, (b) heating surfaces of the cavity to a temperature which is from 1° C. higher to 100° C. higher than the melting point of the perfluoroalkoxy polymer, (c) cooling and curing the filling, and (d) removing the filling, which represents the component.

14. A process for producing a molding, comprising (a) introducing the pulverulent composite material according to claim 1 between at least two heatable tool parts, (b) heating the tool parts to a temperature which is from 1° C. higher to 50° C. higher than the melting point of the perfluoroalkoxy polymer and pressing of the composite material to give a molding, (c) cooling and curing the molding, and (d) removing the molding from the mold.

15. The composite material according to claim 1, wherein the film-forming liquid is an aliphatic C.sub.3-C.sub.10 alcohol-functional group.

16. The composite material according to claim 1, wherein the film-forming liquid is octanol or heptanol.

Description

[0042] The subject matter of the invention will be illustrated below with the aid of working examples.

[0043] FIG. 1: PFA powder/carbon black mixture with and without film-forming liquid

Example 1

[0044] To produce a composite material according to the invention, 100 gram of a perfluoroalkoxy polymer (Chemours 532 G-5010 PFA Powder Clear) in powder form having an average particle size of about 43 μm, and having a melting point of 305° C. were mixed in a first step with 0.2 gram of liquid 1-octanol as film-forming liquid at room temperature for 20 minutes on a set of rollers. Here, the surfaces of the particles of the perfluoroalkoxy polymer powder were predominantly wetted by the film-forming liquid. In a second step, 3 gram of conductive carbon black (Orion Printex L) in powder form having a sieve residue value “45 microns in accordance with DIN ISO 787-18” of 12 ppm were subsequently added to the mixture obtained and mixed for a further 10 minutes at room temperature on the set of rollers. The particles of the carbon black powder adhered in agglomerate form to the film-forming liquid and/or the particles of the perfluoroalkoxy polymer powder.

[0045] The free-flowing composite material obtained in this way was used to coat a metal surface by the EPS process. For this purpose, the metal part was heated to 330° C. in an oven. After taking the heated metal part from the oven, it was electrically grounded. The composite material was subsequently sprayed by means of a spray gun “Opti Flex” from Gema Switzerland GmbH (St. Gallen, Switzerland, www.gemapowdercoating.com), in which it was electrostatically charged, onto the hot surface, and the metal part was then heated further in the oven where it melted to give a contiguous layer. This cycle of spraying outside the oven and melting in the oven was repeated twice more.

[0046] After cooling of the coated metal surface, the layer thickness and the electrical surface resistance at room temperature were determined. The layer thickness was on average 150 microns, measured using a layer thickness measuring instrument Dualscope MP4C from Helmut Fischer GmbH, 71069 Sindelfingen. Here and in the following, “on average” means that the layer thickness was measured at at least three randomly chosen places on the coating and the arithmetic mean was formed from the measured values obtained. The electrical surface resistance was in the range from 1 to 100 megaohm, measured using the Tera Ohmmeter TOM TF600, two-point electrode model 840 from Keinath Electronic GmbH, 72810 Gomaringen.

Comparative Example 1a

[0047] A composite material according to the prior art without film-forming liquid was produced by a method analogous to that for the inventive composite material of example 1. For this purpose, 97 gram of the perfluoroalkoxy polymer (Chemours 532 G-5010 PFA Powder Clear) in powder form were mixed with 3 gram of conductive carbon black (Orion Printex L) in powder form having a sieve residue value “45 microns in accordance with DIN ISO 787-18” of 12 ppm. This mixture could be electrostatically charged to only a small extent, if at all, in the EPS spray gun. The corresponding coating experiment using 97% by weight of PFA powder and 3% by weight of conductive carbon black Printex L failed; no layer could be produced on the metal surface.

[0048] FIG. 1 shows, in the left-hand half of the figure, which is annotated with “PFA 5010 without additive”, a micrograph of the powder mixture of comparative example 1a. The right-hand half of the figure, which is annotated with “PFA 5010 with additive”, depicts a micrograph of the pulverulent composite material according to the invention as per example 1. The scale bar is 10 microns and is in each case shown in the right-hand lower corner. Comparison of the two halves of the figure shows a significantly darker coloration of the particles as per the prior art. The PFA particles are virtually completely and uniformly coated with a layer of carbon black, which makes electrostatic charging in an EPS spray gun very difficult or impossible. In contrast, both carbon black agglomerates as black points and also largely carbon black-free regions can be seen in the particles of the composite material according to the invention. These particles according to the invention could be electrostatically charged very well in the EPS spray gun and led to a good layer buildup on the metal surface and at the same time to a layer capable of conducting away electrostatic charges on the metal component.

Comparative example 1b

[0049] In a further coating experiment, 100% PFA powder was applied to the metal surface in the three coating cycles. The layer thickness was on average 200 μm. The surface resistance was more than 2 teraohm. This layer is thus not capable of conducting away electrostatic charges.

Example 2

[0050] Using experimental conditions and ratios of amounts analogous to those in example 1, 1,4-butanediol was used instead of 1-octanol as film-forming liquid. The layer thickness of the coating on the metallic surface was on average 100 microns. The electrical surface resistance was in the region of 1 gigaohm.

Example 3

[0051] Using experimental conditions and ratios of amounts analogous to those in example 1, 1-heptanol was used instead of 1-octanol as film-forming liquid. The layer thickness of the coating on the metallic surface was on average 120 microns. The electrical surface resistance was in the range from 100 to 500 megaohm.

Example 4

[0052] Using the experimental conditions of example 1, the color black “Orion Printex 90” from Orion Engineered Carbons GmbH, Cologne, was used instead of the conductive carbon black “Printex L”. The ratios of amounts were: 100 gram of the perfluoroalkoxy polymer Chemours 532 G-5010 PFA Powder Clear, 0.6 gram of 1-octanol, 3 gram of color black “Orion Printex 90”. The layer thickness of the coating on the metallic surface was on average 150 microns. The electrical surface resistance was in the region of 100 megaohm.

Example 5

[0053] In a metal bucket with lid, a polyethylene bag was filled with 10 kg of Chemours 532 G-5010 PFA Powder Clear and 20 g of 1-octanol and closed. The lid of the bucket was subsequently closed and the contents were mixed in a standard tumble mixer for 20 minutes at 20 degrees Celsius. The lid of the bucket and then the PE bag were subsequently opened and 300 g of conductive carbon black “Orion Printex L” were added. Subsequently, first the PE bag and then the bucket were closed and the contents were mixed for a further 20 minutes at 20 degrees Celsius in the tumble mixer. A layer thickness of the layer capable of conducting away electricity of on average 150 microns at a surface resistance of from 1 to 10 megaohm could be achieved for this formulation in three spray cycles as per example 1 when using this mixing process according to the invention.

Example 6

[0054] A sensor housing having a flange and a cylindrical tube was coated in four spray cycles as per example 1 with the mixture according to the invention as per example 5. After the last spray cycle, the sensor housing was cooled from 335° C. to 220° C. over a period of 30 minutes in the oven. After cooling to a temperature of 220° C., which is significantly below the melting point of the perfluoroalkoxy polymer, further cooling was effected by taking the coated sensor housing from the oven and cooling to room temperature. After cooling to room temperature, a layer thickness of on average 200 microns and an electrical surface resistance of from 1 to 10 megaohm were measured. The measurement of the surface resistance on the coated sensor housing was carried out by means of a teraohm meter from Keinath Electronic GmbH in accordance with the standard DIN EN 61340-2-3:2016.