BRPI0611448A2 - powder coating base layer - Google Patents

Abstract

Powder Coating Base Layer. The present invention relates to a process for coating a substrate with a coating comprising sequential steps of coating the substrate with mixtures of fluoropolymer powders, thermoplastic polymers, perfluoropolymers and inorganic fillers of certain particle sizes. The coated substrate has the property of strongly adhering to a topcoat comprising a perfluoropolymer.

Description

Descriptive Report of the Invention Patent for "LAYER BASE OF POWDER COATING".

CROSS REFERENCE TO RELATED APPLICATIONS

The priority of this order is based on Provisional Order No. 60/678908, filed May 6, 2005, incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to the application of non-adherent coatings to a substrate.

Prior Art

Mixing fluoropolymer powders and thermoplastic polymers, as well as inorganic pigment fillers, followed by applying the powder mixture to a metal substrate and applying powder melt to form a uniform coating on the substrate is well known from publications. such as WO 2005/58389.

Multilayer application of various fluororesins and thermoplastic polymers is also known from such publications as WO 2003/015935.

The present invention is based on the discovery of a process which comprises a unique combination of sequential steps through which multiple layers of fluoropolymer and thermoplastic polymer mixtures, inorganic fillers and perfluoropolymers are applied to a substrate.

SUMMARY OF THE INVENTION

Accordingly, the present invention comprises a process of coating a substrate with a coating comprising a fluoropolymer. The process comprises the steps of:

The. preparing a solid mixture comprising one or more fluoropolymer and one or more thermally stable thermoplastic polymers at temperatures above 400 ° C;

B. melt and extrude the solid mixture at a temperature of about 250 ° C to about 400 ° C to obtain homogeneity;

ç. subjecting the extrudate to mechanical means to obtain a powder of up to about 100 microns average particle size;

d. mixing the resulting powder with an inorganic filler with an average particle size of between about 5 and 100 microns and a perfluoropolymer powder with an average particle size of between 5 and 100 microns at the mixture of step c. to obtain a powder coating; the inorganic filler and perfluoropolymer being mixed with the powder of step c. At the same time either the inorganic filler mixed before the perfluoropolymer or the perfluoropolymer mixed before the inorganic filler;

and. apply the powder coating on the substrate; and

f. heat the substrate to a temperature sufficient to cause partial coalescence of the powder.

Other embodiments of the invention relate to details concerning the process and materials employed.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention is based on the unique combination of steps, materials and conditions that result in a non-adherent demulticamate coating with excellent adhesion between the dabase coating and the surface.

The present invention advantageously provides a VOC free coating system. Liquid primers that are currently trading are solvent based and thus have an undesirable high VOC content. Even a water based system contains a considerable level of VOC.

The invention also reduces the process to one which is a complete powder process. In addition to reducing VOC, this reduces the amount and complexity of equipment that the coating applicator must maintain.

The powder primer for non-stick powder coatings of the present invention is based on fluoropolymer powders, thermoplastic polymers and perfluorinated polymers, as well as an inorganic filler. This differs from FEP (hexafluo-ropropylene copolymer and tetrafluoroethylene) or PFA (perfluoropropyl vinyl ether copolymer and tetrafluoroethylene) used commercially with solvents. The method of converting these materials of the invention into a powder coating is the mixture of materials followed by co-extrusion and then milling to the desired particle size.

With respect to base coating, and the use of fluoropolymers and thermoplastic polymers, the technology of this invention is similar but not the same as that described in US patent application 2004/0253387 A1, incorporated herein by reference. However, if the invention described in the patent application were used as a base coat for powder coatings, there would be a deficiency in intercoat adhesion between the base coat and a perfluoropolymer powder surface coat. Surface coating, typically PFA, FEP and / or MFA (a tetrafluoroethylene copolymer and perfluoromethyl vinyl ether) would generally delaminate when tested by cross-hatch enail adhesion tests.

The coating of the present invention may be used with a substrate of any desired hardness. The type of substrate to which the coating is applied and the shape in which it is molded does not limit the scope of the invention. In a preferred embodiment, the non-stick coating of the present invention is used to coat a metal substrate, such as steel or aluminum, which is pan-formed. It is highly preferable that the substrate be pretreated to improve adhesion of the base coat, such as by chemical corrosion or sand polishing. Sand polishing is better.

This invention uses two approaches to improve adhesion between coatings. One approach to improving adhesion between coatings is to create a rough surface over the base coat that creates a mechanical bond between the base coat (Primer) and the upper coat. The smaller the particle size, the less rough it will be. surface of the lower and poorer layer will be the adhesion between the coatings. This rough surface and improved mechanical adhesion can be achieved by mixing an inorganic filler, such as a pigment, which has a particle size that will result in a rough surface when the primer is applied and baked to the powder coating. ex-shaved and ground. An example of such a pigment is an aluminum flake that has been bonded to the base powder coating. Thus when the resulting powder primer is applied to a metal substrate and cured followed by application of the powdered and cured topcoat, the bond between the base and topcoats is strong enough to be subjected to the boiling water test, " cross hatch "and" adhesion tape ". However, by itself the coating prepared in this way will fail adhesion between coatings when tested by the standard nail adhesion test after boiling water.

The second approach to improving adhesion between coatings is to mix a powder that should comprise the base coat, which may comprise FEP1 PFA and MFA of a particle size similar to that of the top coat that should be applied to the base coat. . This promotes a much closer bond between the lower and upper layers through chemical and mechanical bonds. Adhesion to the base and top coat is improved to the extent that the resulting coating passes the boiling water test, the cross hatch test and the tape test, as well as the nail test, which is very important for most applications. such as coatings for commercial cooking

One or both of the above approaches may be employed, but the best adherence is obtained by using both approaches.

As used herein, the term "similar" with respect to particle size means that the average diameter of the particles in question is no more than 50% larger or smaller than the average diameter of the particles with which they are being compared.

To form the base coat, the present invention performs a melt mixture of a fluoropolymer and a thermoplastic polymer at a temperature of about 250 ° C to about 400 ° C to achieve homogeneity. It is preferred that the amount of fluoropolymer in the resulting solid mixture be from about 5 wt% to about 50 wt%, and the amount of thermoplastic polymer in the solid mixture is from about 50 wt% to about 95 wt%. by weight, the solid mixture is mixed and extruded with a twin screw extruder at a preferred temperature of about 250-400 ° C. The extrudate may be ground to a powder of up to about 100 microns of average particle size in air at a temperature of about -10-20 ° C.

The powder is then combined with an inorganic filler, such as a pigment, with an average particle size of between about 5 and 100 microns, and a perfluoropolymer powder with an average particle size of between about 5 and about 100 microns. a powder coating is obtained. The inorganic filler and perfluoropolymer may be mixed with the powder of the milled extrudate at the same time, or the inorganic filler mixed before the perfluoropolymer or the combined perfluoropolymer before the inorganic filler. It is preferred that the particle size of the inorganic filler powder be similar to the particle sizes of the powdered polymers.

The inorganic filler / polymer blend may be bonded prior to step e. In this manner, the blend is heated until the polymer particles become sticky enough to adhere to the inorganic filler particles.

Preferred fluoropolymers for use in the invention may be selected from the group consisting of PTFE (Polytetrafluoroethylene), TFE (Tetrafluoroethylene) copolymers such as comonomers such as PMVE (perfluoromethylvinylether), PPVE (perfluoropropyl vinylene), HFP (hemp) Ethylene, CTFE (Chlorotrifluoroethyl) and combinations of the above comonomers.

Preferred thermoplastic polymers for use in the invention may be selected from the group consisting of Polyether Sulfones (PES), Polyarylsulfones (PAS), Polyphenyl Sulphide (PPS), Polyetheretherketins (PEEK), Polymides (PI) and Polyamideimides (PAI) ). PPS is most preferred. Inorganic fillers that may be used in the invention include mica or volastonite metasilicate, talc and aluminum flakes. Aluminum floats are more preferred. An example is the aluminum flake produced by Alcon-Toya, known as PCF 7130. It is advantageous to coat the aluminum flakes with an acrylic resin.

It is preferred that the average particle size of the inorganic filler be equal to or greater than the thickness of the substrate coating following step f.

The powder mixture is then applied to the substrate, preferably electrostatically in a layer of about 20-60 microns thick, but may be up to 100 microns thick, depending on the application and the substrate heated to a temperature sufficient to cause coalescence. partial dryness of the powder (melting only for the particles to adhere to each other), generally between about 370 ° C to about 415 ° C.

To form the topcoat, the perfluoropolymer powder is then applied to the coated substrate, and the substrate is heated again, also generally at a temperature of about 370 ° C to about 415 ° C, to make the perfluoropolymer powder. become sufficiently fluid and attach to the first layer. As previously mentioned, the powder forming the topcoat is preferably of a particle size similar to that of the powders forming the basecoat.

Preferred perfluoropolymers for use in the invention, both in the bottom base coat and the top coat are PFA, FEP and MFA, PFA is most preferred because of their physical properties (strength, release properties, etc.).

Once the base coat is applied, it can be evaporated for 2-3 minutes at a temperature of about 370-400 ° C. The top coat can then be applied followed by a final cure at 400 ° C for about 10 minutes. If a spray is not employed, the final temperature can be done for 10 minutes at a temperature of about 400-425 ° C, preferably about 415 ° C.

In the following non-limiting examples, a substrate was coated with several base coatings, only one of which was prepared according to the present invention, and subjected to three tests to determine how an upper layer of perfluoropolymer could adhere to the base coatings. . The first test was a pencil test in which pencil graffiti of varying hardness was streaked over the coating surface and it was observed whether the top layer, when cut, could be sedimented from the base layer. In the second test, a ballpoint pen was pressed into the coating with various pressures to make the same determination. The third test was the nail test to determine if the upper layer could be peeled using the examiner's nails, first easily peeled with one nail and second peeled with one nail after coated panels were immersed for 30 minutes in boiling water.

Example 1

In this example, all requirements of the invention were met except that no filler was used and no perfluoropolymer was mixed with the powdered extrudate.

Example 2

In this example, all the requirements of the invention were met except that no perfluoropolymer was combined with the powder extrudate.

Example 3

This example illustrates the invention in every respect.

The following table summarizes the materials employed in the above Examples.

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GROSS Material Description:

Rytori V1 is a low viscosity polyphenylene sulfide produced by Chevron-Phillips from Bartlesville, Oklahoma.

PTFE TL 10 is a fluoropolymer, better known as Polyite-trafluoroethylene. It is produced by AGC Chemicals Americas, Inc of Downningtown, Pennsylvania.

Channel Carbon Black is a micro-powder channel carbon black marketed by Keystone Aniline Corp. from Chicago, Illinois, used for color only.

Neocryl BT-44 is a 45% solids water-based acrylic latex produced by NeoResins Inc., which is a commercial unit of DSM.

Silica fume, produced by Cabot Corp. or Degussa, is an additive used to improve spray application of powder coatings.

PCF 7130 is a non Ieafing aluminum flake pigment produced by Toyal America Inc. This pigment has a D50 particle size of 23 microns.

Hyflon® PFA 7010 is a tetrafluoroethylene and terperfluoropropyl vinyl ether copolymer that has a particle size with a D50 of 38 microns.

In Examples 1 to 3, the milled material produced after step c. had a D50 particle size (about 50% of the particle size of the specified diameter) of 22 microns, the extrusion temperature was 300 ° C, with an air temperature of -1 ° C. The size of the fluoropolymer particle comprising the layer top was about 20-25 microns.

Regarding the pencil test, the hardness of the graphite was B1HBeF, in ascending order of hardness.

Regarding the ballpoint pen test, the pressures employed were 137.896; 344.74 and 482.636 KPa (20, 50 and 70 psi).

The following table summarizes the results:

<table> table see original document page 10 </column> </row> <table>

Only the coating of Example 3 passed on all tests through which the top layer did not delaminate or peel.

Claims (9)

A process for coating a substrate with a coating comprising a fluoropolymer, said process comprising the sequential e-tapes of: a. preparing a solid mixture comprising one or more fluoropolymers and one or more thermally stable thermoplastic polymers at temperatures above 400 ° C; melt the mixture and extrude said solid mixture at a temperature of about 250 ° C to about 400 ° C to achieve homogeneity; subjecting the extrudate to mechanical means to obtain a powder of up to about 100 microns of average particle size; mixing the resulting powder with a common inorganic filler average particle size between about 5 and 100 microns and a perfluoropolymer powder having an average particle size between 5 and 100 microns to the mixture of step c. to obtain a powder coating; the inorganic filler and perfluoropolymer being mixed with the eta-pa powder c. at the same time either the inorganic filler mixed before the perfluoropolymer or the perfluoropolymer mixed before the inorganic filler; applying said powder coating to said substrate; ef. heating said substrate to a temperature sufficient to cause partial coalescence of said powder. A process according to claim 1, wherein the blend of inorganic filler powder and polymer powders of step d. is on. A process according to claim 1, wherein a perfluoropolymer powder coating is applied to the coated substrate of step 1; and said substrate is heated again to make the powder sufficiently fluid and bonded as a second layer to the first layer. A process according to claim 1, wherein said powder coating of the step is electrostatically applied to a layer about 20-100 microns thick. A process according to claim 4, wherein the average particle size of said inorganic filler is equal to or greater than the thickness of the coating on the substrate after step f. A process according to claim 1, wherein the inorganic diphenyl filler comprises a pigment. A process according to claim 6, wherein the dithopigment comprises aluminum flakes. A process according to claim 1, wherein the particle size of the powder of step c. is similar to the particle size of the inorganic pre-filler of step d. The process according to claim 3, wherein the particle size of the powder forming the second layer is similar to the particle size of the powders forming the first layer.