Fluoropolymer finishes having improved scratch resistance

(54) Title: Fluoropolymer coating composition and use thereof (56) Publications cited:

FR 2247517 (C09D 3/727)

FR 2244791 (C08L 27/12)

US 3970627 (260-29.6 F)

It., J.

iKllD L-rcri RrcLct n / mnm clip printern international document code

7608257-7

Cooking vessels coated with fluoropolymers, in particular polytetrafluoroethylene (PTFE), have found great use in recent years.

Many people prefer to use such pans because of the non-adhesive properties and because they are so easy to clean.

Although cookware of this type is relatively durable, the fluoropolymer coating tends to be scratched after prolonged use as it is slightly softer than the utensils used for stirring and turning the food in the vessel.

It has now been found that the scratch resistance of a fluoropolymer coating can be improved if the composition from which the coating is derived comprises (a) a fluoropolymer, (b) mica particles, mica particles coated with pigment or metal scaffold, (c) a polymer of monoethylene unsaturated monomers which are polymerized. and vaporized at a temperature near the melting point of the fluoropolymer, and (d) a liquid carrier.

Such coating also has excellent cracking resistance and blistering resistance, and has an aesthetically pleasing

7608257-7 appearance.

The fluoropolymers used in the compositions of the invention are homopolymers and copolymers (i.e., polymers containing two or more different monomer units) of monoethylene-unsaturated hydrocarbon monomers which are completely substituted by fluorine atoms or completely substituted by a combination of fluorine atoms and chlorine atoms. This group includes perfluorolefin polymers, such as e.g. polytetrafluoroethylene and copolymers of tetrafluoroethylene and hexafluoropropylene in all weight ratios of the monomer units, fluorochlorocarbon polymers such as e.g. polymonochlorotrifluoroethylene, and the usually solid copolymers of tetrafluoroethylene and perfluoroalkyl vinyl ethers (wherein the alkyl group has 1-5 carbon atoms). Mixtures of these can also be used. Polytetrafluoroethylene is preferred because of its thermal stability.

The fluoropolymer used is particulate. The particles are small enough to pass through the nozzle of a spray gun without clogging it and are also small enough to give the obtained film integrity.

The fluoropolymer preferably has a number average molecular weight of at least about 20,000, in particular at least about 200,000, since such fluoropolymers provide harder surface layers. The number average molecular weight of PTFE is measured by the method described by Suwa, Takehisa and Machi in Journal of Applied Polymer Science, volume 17, pages 3253-3257 (1973). The number average molecular weight of a tetrafluoroethylene / hexafluoropropene copolymer is measured by first determining its melt flow rate (MFR) according to ASTM D2116, and then using the MFR value to determine the melt viscosity (MV) according to the equation, etc. - P * ^{x anvan}t pressure (mm) x nozzle radius (mm) x MFR x nozzle length (mm) and the molecular weight (MW) is determined according to the equation

<img file="SE434516B_D0001.tif" />

MV

1.62 x 10&gt;³

The number average molecular weight of a fluorochlorine carbon polymer is measured by ASTM D1U30.

Although a fluoropolymer powder can be used and a carrier is added separately, a polymer in the form of a water dispersion is preferred because of its stability and because it is most readily available.

7608257-7 is obtained in this form.

The fluoropolymer is usually present in the composition having a concentration of about 80-99.8%, preferably about 85-98%, based on the total weight of fluoropolymer and mica particles, mica particles coated with pigments, or metal scales.

The mica particles, the coated mica particles, and metal scales used in the compositions of the invention may be any of the commercially available particles. These particles and scales have an average longest dimension of 10-100 yarns, preferably 15-50 with no particles or scales having a longest dimension exceeding about 200 µm. Particle and rock size are optically measured against a standard.

The preferred mica particles coated with pigments are those described in U.S. Patents Nos. 3,087,827, 3,087,828 and 3,087,829, which describe various types of coated mica particles and their preparation.

The mica particles described therein are coated with oxides or hydrate oxides of titanium, zirconium, aluminum, zinc, antimony, tin, iron, copper, nickel, cobalt, chromium or vanadium. Titanium dioxide-coated mica is preferred because of its easy accessibility. Mixtures of coated mica particles can also be used.

Examples of metal scales that can be used are aluminum scales, stainless steel scales, nickel scales and bronze scales. Blends of scales can also be used.

The mica, coated mica or metal scales are usually present in the composition of the invention at a concentration of about 0.2-20%, based on the total weight of fluoropolymer and mica, coated mica or metal scales, preferably about 2-15%, especially

8-12%.

The polymer of monoethylene unsaturated monomers used in the compositions of the invention may be any polymer or copolymer (in the sense that it is composed of two or more types of monomers) of ethylene unsaturated monomers which are depolymerized and whose depolymerization products are vaporized, in the temperature range exceeding about 150 ° C below the melting temperature of the fluoropolymer used up to about the decomposition temperature of the fluoropolymer. The closer the depolymerization and evaporation temperature is to the melting temperature of the fluoropolymer, the better results are obtained.

7608257-7 t

By the term depolymerization is meant degradation of the polymer to the point where the degradation products are volatile at the temperatures encountered in curing the finished film. These degradation products may be monomers, dimers or oligomers.

By evaporation is meant a transition to the volatile state of the degradation products and their evaporation from the film. Ideally, all degradation products pass from the film, but in practice a small but insignificant amount usually remains.

Examples of suitable polymers are those of monoethylene unsaturated monomers which contain one or more monoethylene unsaturated acid units.

Examples of such monoethylene unsaturated monomers are alkyl acrylates and methacrylates of 1-8 carbon atoms in the alkyl group, styrene, α-methylstyrene, vinyltoluene and glycidyl esters of 4-14 carbon atoms. Examples of the monoethylene unsaturated acids are acrylic acid, methacrylic acid, fumaric acid, itaconic acid and maleic acid (or anhydride). Mixtures of these polymers may also be used.

Due to the obtained density and gloss of the surface layers obtained in their use, the polymers of alkyl acrylates, alkyl methacrylates, acrylic acid, methacrylic acid and a glycidyl ester marketed by Shell Chemical Company as Cardura E-ester, which is a mixed ester, are preferred. formula

<td>z ° \</td><td>0 tt</td><td> /¹</td>

<td>H "C ----- CH - CH" -</td><td>0 - c</td><td>- C --- R</td>

<td> 2 2</td><td></td><td>X²</td>

<td></td><td></td><td> *3</td>

<td>wherein</td><td></td><td></td>

<td>R₁ is CH₃</td><td></td><td></td>

<td>and</td><td></td><td></td>

R₂ and Rg are lower alkyl groups, and wherein

R_l, R₂ and Rg together contain a total of 7-9 carbon atoms.

The particularly preferred polymers are for the same reason:

1st methyl methacrylate / 2-ethylhexyl acrylate / methacrylic acid terpolymers, preferably terpolymers in the weight ratio 40-50: 48-52: 1-4,

2nd butyl acrylate / methyl methacrylate / Cardura E / acrylic acid quadripolymers, preferably in the weight ratio of 23-27: 33-37: 21-25: 15-19,

7608257-7

3rd styrene / methyl methacrylate / Cardura E / acrylic acid quadripolymers, preferably in the weight ratio of 28-32: 8-32: 21-25: 15-19, and

4th methyl methacrylate / ethyl acrylate / methacrylic acid terpolymers, preferably in the weight ratio of 37-41: 55-59: 1-6.

Such a polymer is usually present in the composition of the invention at a concentration of about 2-300%, preferably 5-20%, by weight of the fluoropolymer. It can be prepared by the conventional free radical methods well known to any polymer chemist.

The carrier used in the composition of the invention may be any one of them which is normally used in compositions of this type. It constitutes an inert, non-reactive or functional component (in the sense of contributing to the function of the invention) and its nature is therefore of secondary importance. The carrier serves only to keep the composition homogeneous and acts as a mechanism for transferring the solid components to the substrate. After a coating has been deposited, the carrier evaporates. Therefore, it is only necessary that it be compatible with the other components of the composition and that it has no adverse effects on the coating itself.

Usually, the fluorocarbon polymer used in the composition is supplied in the form of an aqueous dispersion, and the water introduced into the composition together with the polymer also functions as all or part of the carrier for the composition. Organic liquids, such as alcohols, ketones, aliphatic and aromatic hydrocarbons, or mixtures thereof, may also be used.

The compositions of the invention may also contain such conventional additives as flow regulating agents, surfactants and plasticizers as needed or desired. These additives are supplied for the usual reasons, in the usual manner and in the usual amounts.

The total amount of solids in the coating composition is controlled by the substrate to which the composition is to be applied, the method of application, curing procedures and similar factors. In the usual case, the composition contains about 10-80% by weight of solids.

The compositions can be prepared by simply mixing together appropriate amounts of the components in question. Pigment can

7608257-7 is added, if desired by first preparing a suitable pigment dispersion in a conventional manner and then adding this dispersion to the composition.

The compositions may be applied in any of the conventional ways. Spraying, roll coating, dipping, papermaking with razors are all suitable, although spraying is usually chosen. The article to be coated is preferably pretreated by sand blasting, metal spraying or by enamel coating. The article is then grounded with a composition of the type described in U.S. Patent Nos. 3,655,604 or 3,694,392. From these publications, information has been transferred to the present description on how such foundational compositions are prepared and applied.

The compositions of the invention are usually applied to a thickness of about 20-30 _{, J}M. (dry) and the coated article are then cured at a temperature and for a time sufficient to melt the fluoropolymer used.

The compositions of the invention are very suitable for coating metal cookware, in particular frying pans, but the compositions can also be used for coating other articles which require scratch resistant fluoropolymer coatings. These other articles may be made of glass or other material which is capable of withstanding the curing temperatures used. For example, the compositions can be used for coating bearings, valves, trees, metal foil, steam boilers, pipes, vessel bottoms, oven liners, iron soles, waffle iron, ice boxes, snow blades and plows, funnels, conveyors, nozzles, tools such as saws, files and drills, other industrial containers and molds,

The following examples illustrate the invention, wherein all parts and percentages are by weight unless otherwise specifically stated.

Example 1

The following ingredients were mixed in the order indicated:

(i) FTFE dispersion 64.9 parts (60% solids in water, Teflon

ΪΕΕ-fluorocarbon resin, water dispersion,

T-30, from EI du Font de ITemours and Company)

<img file="SE434516B_D0002.tif" />

7608257-7 (A) 2d pigment base

<td colspan="3">(prepared, by painting in the ball mill of a mixture of</td>

<td>distressed iron oxide</td><td> 44,9</td><td>parts</td>

<td>Deionized water</td><td> 33,7</td><td>tt</td>

<td>Oljeoyra</td><td> 5,3</td><td>n</td>

<td>triethanolamine</td><td> 6,7</td><td>it</td>

<td>Eutylkarbitol</td><td> 2,9</td><td>d </td>

<td>toluene</td><td> 8,5</td><td> )</td>

<td>a mix of</td><td></td><td></td>

<td>triethanolamine</td><td> 0,92</td><td>parts</td>

<td>oleic acid</td><td> 0,75</td><td>II</td>

<td>toluene</td><td> 3,48</td><td>! l</td>

<td>carbitol</td><td> 1,3</td><td>II</td>

(G) Ethyl methacrylate / ethyl acrylate / methacrylic acid-39/57 / 4terpolymer dispersion (40% in water.)_£..

parts parts

The resulting composition was applied to an aluminum frying pan, which had first been enamelled and primed with a primer described in U.S. Pat. Nos. 3,655,604 and 3,694,392.

The composition was applied by spraying to a thickness of 25 gin (dry). The coated pan was then cured for 5 minutes at 425 ° 0 to give a scratch-resistant gold-colored surface. Example 2

The procedure of Example 1 was repeated except that the following ingredients were exchanged for (3) and (4):

(3) Ti0_O-coated glitter 4 parts' - (Afflair 1UM54-D, from EI du Font de

Nemours and Company) (4) Pigment base (made by painting in ball mill a mixture of

Deionized water 55 parts

Cobalt oxide blue 45)

The resulting composition was applied to an uncoated, grounded aluminum frying pan, as in Example 1, to give a scratch-resistant silver-colored surface.

Example 3

The following ingredients were mixed in the order indicated:

<td>(1) FTFE dispersion according to Example 1 (2) A 2 - ionized water</td><td>69.7 dc lar OR; t '-Ί l</td>

j

7608257-7

<td colspan="2">(3) TiO2-coated mica (Afflair NF-140-D, from EI du Pont</td><td colspan="2" rowspan="2">1, 0 parts</td>

<td></td><td>de Nemours and Company)</td>

<td> (4)</td><td>Meat pigment base of Example 1</td><td> 0,2</td><td>u</td>

<td> (5)</td><td>Mixture according to (5) of Example 1</td><td> 8,45</td><td>tt</td>

<td> (6)</td><td>Dispersion according to (6) in Example 1</td><td> 14,0</td><td>it</td>

The resulting composition was applied to an enamel-coated, grounded aluminum frying pan, as in Example 1, to obtain a scratch-resistant copper-colored surface.

7608257-7