GB1565842A

GB1565842A - Fluoropolymer primer compositions

Info

Publication number: GB1565842A
Application number: GB31863/76A
Authority: GB
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1975-07-31
Filing date: 1976-07-30
Publication date: 1980-04-23
Also published as: DE2634422C2; JPS5218740A; JPS6035380B2; BE844759A; IT1064694B; SE426502B; BR7604973A; NL182001C; SE7608573L; DE2634422A1; CA1105168A; NL7608510A; FR2319695B1; FR2319695A1; LU75497A1; NL182001B

Description

(54) FLUOROPOLYMER PRIMER COMPOSITIONS (71) We, E. I. DU PONT DE NEMOURS AND COMPANY, a Corporation organised and existing under the laws of the State of Delaware, United States of America, located at Wilmington, State of Delaware, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- Background of the Invention Cookware coated with fluoropolymers, especially polytetrafluoroethylene (PTFE), has come into widespread use in recent years. Many cooks prefer to use such cookware because of its non-stick properties and because it is so easy to clean.

It is well known that the adhesion of fluoropolymers to metal is of a rather low order, so in the fabrication of such cookware it is customary to improve adhesion by applying a primer composition to the metal before applying the fluoropolymer topcoat. Such a primer composition is described in U.K. Application No. 25112/76 serial No. 1563814. The composition described there comprises (a) a fluoropolymer, (b) a binder comprising colloidal silica and the amine salt of a polyamide acid, (c) a coalescing agent, and (d) a liquid carrier.

While cookware primed with such a composition is quite durable, its entire fluoropolymer coating tends to become scratched after extended use.

Summary of the Invention It has now been found that the scratch resistance of such a coating is improved if the primer composition contains mica particles, mica particles coated with pigment, or metal flake.

Detailed Description of the Invention The mica particles, coated mica particles and metal flake used in the compositions of the invention can be any of those available commercially. These particles and flakes usually have an average longest dimension of 10 to 200 microns, preferably 15-50 microns, with no more than 50% of the particles of flakes having longest dimensions of more than about 500 microns. Particle and flake size is measured optically against a standard.

The mica particles coated with pigment preferred for use are those described in U.S. Patent 3,087,827 to Klenke and Stratton, and U.S. Patents 3,087,828 and 3,087,829 to Linton. The disclosures of these patents are incorporated into this specification to describe the various coated micas and how they are prepared.

The micas described in these patents are coated with oxides or hydrous oxides of titanium, zirconium, aluminum, zinc, antimony, tin, iron, copper, nickel, cobalt, chromium or vanadium. Titanium dioxide coated mica is preferred because of its availability. Mixtures of coated micas can also be used.

Representative of the metal flake which can be used are aluminum flake, stainless steel flake, nickel flake and bronze flake. Mixtures of flake can also be used.

The mica, coated mica or metal flake is ordinarily present in a composition of the invention at a concentration of 0.2-20%, by weight of the total solids, preferably 215%, even more preferably 512%. "Total solids" means the sum of fluoropolymer, mica, coated mica or metal flake, polyamide acid salt, colloidal silica, solids and any pigment used.

The fluoropolymers used in the compositions of the invention are homopolymers and copolymers (meaning the polymer contains two or more different monomer units) of monoethylenically unsaturated hydrocarbon monomers completely substituted with fluorine atoms or completely substituted with a combination of fluorine atoms and chlorine atoms, or copolymers of at least one such completely substituted hydrocarbon monomer and a perfluorinated (ether-substituted hydrocarbon) monomer.Included in this group are peifluorolefin polymers such as polytetrafluoroethylene and copolymers of tetratluoroethylene and hexafluoropropylene in all monomer unit weight ratios, fluorochlorocarbon polymers such as polymonochlorotrifluoroethylene, and the solid copolymers of tetraflnoroethylene and perfluoro(alkyl vinyl)ethers (wherein the alkyl group is of 1--5 carbon atoms). Mixtures of these can also be used. PTFE is preferred for its thermal stability.

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

The fluoropolymer preferably has a number average molecular weight of at least about 20,000, even more preferably at least about 200,000, because such fluoropolymers give harder finishes. 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, pp. 3253-3257 (1973).The number average molecular weight of a tetrafluoroethylene/hexafluoropropylene copolymer is measured by first determining its melt flow rate (MFR) according to ASTM D2l 16, using the MFR to determine melt viscosity (MV) according to the equation pixpressure used (mm)xorifice radius (mm) MV= 8xMFRxorifice length (mm) and then determining molecular weight (MW) according to the equation

Number average molecular weight of a fluorochlorocarbon polymer is measured by ASTM D1430.

Although a powder of fluoropolymer can be used and a carrier provided separately, a polymer in the form of an aqueous dispersion is preferred for its stability and because it is most easily obtained in that form.

The fluoropolymer is ordinarily present in the composition at a concentration of 1090%, preferably 680%, by weight of the total of fluoropolymer and binder (as will be defined later).

The binder in the compositions of the invention comprises a colloidal silica and the amine salt of a polyamide acid. this binder is ordinarily present in the composition at a concentration of 10-90%, preferably 20--400/,, by weight of the total of fluoropolymer and binder.

The colloidal silica component of the binder can be any of those which airdries to form a continuous film when laid down by itself. Such silicas are generally provided in the form of aqueous sols containing 3(50%, by weight, of colloidal silica. The preferred colloidal silica is a sodium stabilized colloidal silica.

Illustrative of the colloidal silica sols which can be used are those sold by E. I.

du Pont de Nemours and Company as "Ludox HS-40"e "Ludox HS"e "Ludox LS"g "Ludox AS"o "Ludox SM-30" "Ludox TM"e and "Ludox AM".

The most preferred colloidal silica sol is "Ludox AM".. This product is a sodium stabilized colloidal silica having a pH of about 9 at 250C., and a silica content (calculated as SiO2) of 30%, whose particles are surface-modified with aluminum and have a particle diameter of 13-14 millimicrons and a specific surface area of 210230 square meters per gram.

Mixtures of colloidal silicas can also be used.

The colloidal silica is ordinarily present in the binder at a concentration of 595%, preferably 1080 n by weight of the binder.

The polyamide acid salt component of the binder can be any of those described in U.S. Patent No. 4,014,843. The portions of that application which describe these polyamide acid salts and how they are made are incorporated into this application by reference.

The polyamide acid salts used in the compositions of the invention are those of polyamide acids with tertiary amines or morpholine.

The polyamide acids can be represented by the structure

where G is hydrogen or a carboxyl group; denotes that the groups so indicated may be interchanged to provide different isomers; R is a tetravalent organic radical containing at least two carbon atoms, no more than two carbonyl groups of each polyamide acid unit being attached to any one carbon atom of said tetravalent radical; R, is a divalent radical containing at least two carbon atoms, the amide groups of adjacent polyamide acid units each being attached to separate atoms of said divalent radical; and n is a number large enough to give the polyamide acid an inherent viscosity of at least 0.1, measured as a 0.50/, by weight solution in N,N-dimethyl acetamide at 30"C.

These polyamide acids are neutralized with stoichiometric amounts of tertiary amines or morpholine to give the amine salts.

The amine salts of polyamide acids preferred for use in the binder component are those prepared from at least one amine represented by the structure 112N-R1-NH2 and at least one aromatic acid anhydride represented by the structure

where, R and R, are as previously defined, (with the proviso that R is aromatic) neutralized with a stoichiometric amount of a tertiary amine or morpholine.

The amine salts of polyamide acids especially preferred for use in the binder component are those prepared from (1) meta- or para-phenylenediamine, bis(4-amino-phenyl)ether, benzidine, 2,2bis(4'-aminophenyl)propane, bis(4-aminophenyl)methane, bis(4aminophenyl)sulfone, bis(4-aminophenyl)sulfide or 1 ,6-hexamethylenediamine; and (2) pyromellitic dianhydride, trimellitic anhydride, 2,2-bis(3',4'dicarboxyphenyl)propane dianhydride, or bis(3,4-dicarboxyphenyl)ether dianhydride, neutralized with a stoichiometric amount of trimethylamine, triethylamine, dimethylethanolamine, diethyl 2-hydroxyethylamine, tributylamine, tris(2-hydroxyethyl)amine, ethyl bis(2-hydroxyethyl)amine, N,N-dimethylaniline, morpholine, pyridine, N-methylpyrrole, or mixtures of these. Attention is drawn to the provisions of the carinogenic substances Regulations 1967 in respect of the use of benzidine.

The polyamide acid salt most preferred for use in the binder component is one prepared from bis(4-aminophenyl)methane and trimellitic anhydride, neutralized with a stoichiometric amount of a 2/1 weight ratio mixture of triethylamine and diethyl 2-hydroxyethylamine.

The amine salt is ordinarily present in the binder at a concentration of 5-95%, preferably 290% by weight of the binder.

The coalescing agent used in the composition of the invention is, generally speaking, an organic liquid which can dissolve the polyamide acid amine salt used.

Organic liquids of this type are highly polar and have boiling points above 100"C.

The coalescing agents are selected from N-methylpyrrolidone dimethylformamide dimethylacetamide dimethylsulfoxide cresylic acid sulfolane and formamide.

The coalescing agent preferred for use because of its availability and low toxicity is N-methylpyrrolidone.

The coalescing agent is ordinarily present in the compositions of the invention at a concentration of 10--900/, by weight of the polyamide acid amine salt used.

Dreferably 20-50%.

The compositions of the invention will have more workable viscosities at higher solids content if they contain 15-200%, preferably 80-150%, by weight of the polyamide acid amine salt used, of a viscosity reducing agent which is an organic liquid whose solubility parameter, 6,, falls within the range of 10-21.6 and which is miscible with water.A definition of solubility parameter appears in Kirk Othmer, "Encyclopedia of Chemical Technology", second edition 1971, Supplement Volume pages 889-896. Tctal solubility parameter, T, has the following component parameters: Dispersion component, S, 7.10.0 Polar component, ap 2.011.0 Hydrogen bonding component, aH 7.0--14.0 where the equation aT2=8D2 ap2 H2 describes the relationship of the components to the total solubility parameter.

Illustrative of such viscosity reducing agents are furfuryl alcohol, l-butanol, 2propanol, ethylene glycol monoethyl ether, triethylene glycol, formic acid, and mixtures of two or more thereof. Furfuryl alcohol is preferred for its effectiveness.

The compositions of the invention can also contain such conventional additives as pigments, flow control agents, surfactants and plasticizers as are necessary or seem desirable. These additives are added for the usual treasons, in the usual ways and in the usual amounts.

The carrier used in the compositions of the invention can be any of those normally used in compositions of this type. It is an inert, not a reactive or functional (in the sense of contributing to the working of the invention) component and its nature is therefore of secondary importance. The carrier serves only to keep the composition homogeneous and acts as a mechanism for conveying the solid components to the substrate. After a coating has been deposited, the carrier evaporates. It is necessary, therefore, only that it be compatible with the other components of the composition and that it have no adverse effects on the coating itself.

Commonly, the fluoropolymer used in the composition is provided in the form of an aqueous dispersion, and the water introduced into the composition with the polymer also serves as all or as part of the carrier for the composition. Organic liquids such as alcohols, ketones, aliphatic and aromatic hydrocarbons, or mixtures of these, can also be used.

The amount of total solids in the coating compositions will be governed by the substrate to which the compositions are to be applied, the method of application, the curing procedures, and like factors. In the usual case, the composition will contain 10--800/,, by weight, of solids.

The compositions can be made by simply mixing together appropriate amounts of the proper components. Pigments can be added, if this is desired, by first conventionally preparing a suitable pigment dispersion and then adding this dispersion to the composition.

The resulting compositions can be applied by spraying, brushing, rollercoating, dipping, or by electrodeposition. The substrate is preferably pretreated by grit blasting, by the flame spraying of metals or metal oxides, or by frit-coating, although the compositions can also be applied to phosphated and chromated metals.

A composition of the invention is ordinarily applied to a thickness of about 2 15 microns (dry) and is then air-dried. This primer coat is then topcoated with a conventional clear or pigmented fluoropolymer enamel and baked in the usual way to give an adherent fluoropolymer coating.

Although the best coating is obtained with the two-coat system just described, a strongly adherent fluoropolymer coating can be obtained with a one-coat operation. To do this, a coat of a composition of the invention is applied to a thickness of 5-50 microns (dry). This coat is then air-dried and baked at a temperature high enough to fuse the fluoropolymer used.

The compositions of the invention are most useful for priming metal cookware, especially frypans, before coating them with PTFE, but the compositions can also be used to prime other articles requiring tightly bonded fluoropolymer coatings. These other articles can be made of glass or any other material capable of withstanding the baking temperatures used. For example, the compositions can be used to prime or coat bearings, valves, wire metal foil, boilers, pipes, ship bottoms, oven liners, iron soleplates, waffle irons, ice cube trays, snow shovels and plows, chutes, conveyors, dies, tools such as saws, files and drills, hoppers and other industrial containers and molds.

The following example illustrates the invention. In this example, all parts and percentages are by weight unless indicated otherwise.

EXAMPLE The following were added to a vessel in the order given and mixed: parts (A) (1) The polyamide acid amine salt solution of Example I of U. S. Patent No. 4,014,843 (containing 18% of furfuryl alcohol and 10% of N-methyl pyrrolidone) 31.98 (2) Furfuryl alcohol 3.21 (3) Deionized water 109.47 (4) Pigment dispersion 27.39 Made by ball-milling a mixture of parts Cobalt oxide 45 Water 55 (5) TiO2 coated mica 7.6 ("Afflair"e NF-152-D, sold by E.I. du Pont de Nemours and Company) Component (5) was added with vigorous mixing. After the addition was complete, the product was stirred for 10 minutes.To it were then added, with mixing parts (6) PTFE dispersion . 91.17 (60% solids in water, "Teflon" TFE-Fluorocarbon, Resin, Aqueous Dispersion, T-30, sold by E.I. du Pont de Nemours and Company--"Teflon" is a registered Trade Mark) (7) "Ludox". AM 36.78 The resulting primer composition was sprayed on a degreased aluminum panel to a thickness of about 8 microns (dry) and air-dried.

A topcoat composition was prepared by adding the following to a vessel in the order stated, with mixing: parts (B) (8) The PTFE dispersion of (6) above 179.7 (9) Deionized water 2.7 (10) TiO2 coated mica of (5) above 9.5 (11) Pigment dispersion of (4) above 3.5 (12) Mixture of parts Toluene 11.24 Triethanolamine 14.78 Butyl Carbitol ("Carbitol" is a regist ered Trade Mark) 4.27 Oleic acid 4.72 Cerium octoate solution (12% in 2 ethyihexanoic acid) 2.88 "Triton X-100" (non ionic surfactant sofd by Rohm & Haas Co.

"Triton' is a registered Trade Mark) 1.61 (13) Methyl methacrylate/ethyl acrylate/methacrylic acid 39/57/4 terpolymer dispersion (40% in water) 33.4 The resulting topcoat composition was sprayed to a thickness of about 20 microns (dry) on the panel primed in (A). The panel was then baked for five minutes at 425"C.

The resulting finish showed significantly better scratch resistance than a similar one lacking the coated mica component.

WHAT WE CLAIM IS: 1. A coating composition comprising (a) lO%-90%, by weight of the total of (a) and (b) solids, of a homo or copolymer of one or more monoethylenically unsaturated hydrocarbon monomers completely substituted with fluorine atoms or a combination of fluorine atoms and chlorine atoms or a copolymer of at least one such completely substituted hydrocarbon monomer and a perfluorinated (ether-substituted hydrocarbon) monomer; ; (b) 100/,--90%, by weight of the total of (a) and (b) solids, of a binder which comprises (1)5-95%, by weight of the total of(1) and (2) solids of a colloidal silica which air-dries to form a continuous film when laid down by itself, and (2) 5-95%, by weight of the total of(1) and (2) solids, of a salt ofapolyamide acid represented by the structure

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Component (5) was added with vigorous mixing. After the addition was complete, the product was stirred for 10 minutes. To it were then added, with mixing parts (6) PTFE dispersion . 91.17 (60% solids in water, "Teflon" TFE-Fluorocarbon, Resin, Aqueous Dispersion, T-30, sold by E.I. du Pont de Nemours and Company--"Teflon" is a registered Trade Mark) (7) "Ludox". AM 36.78 The resulting primer composition was sprayed on a degreased aluminum panel to a thickness of about 8 microns (dry) and air-dried. A topcoat composition was prepared by adding the following to a vessel in the order stated, with mixing: parts (B) (8) The PTFE dispersion of (6) above 179.7 (9) Deionized water 2.7 (10) TiO2 coated mica of (5) above 9.5 (11) Pigment dispersion of (4) above 3.5 (12) Mixture of parts Toluene 11.24 Triethanolamine 14.78 Butyl Carbitol ("Carbitol" is a regist ered Trade Mark) 4.27 Oleic acid 4.72 Cerium octoate solution (12% in 2 ethyihexanoic acid) 2.88 "Triton X-100" (non ionic surfactant sofd by Rohm & Haas Co. "Triton' is a registered Trade Mark) 1.61 (13) Methyl methacrylate/ethyl acrylate/methacrylic acid 39/57/4 terpolymer dispersion (40% in water) 33.4 The resulting topcoat composition was sprayed to a thickness of about 20 microns (dry) on the panel primed in (A). The panel was then baked for five minutes at 425"C. The resulting finish showed significantly better scratch resistance than a similar one lacking the coated mica component. WHAT WE CLAIM IS:

1. A coating composition comprising (a) lO%-90%, by weight of the total of (a) and (b) solids, of a homo or copolymer of one or more monoethylenically unsaturated hydrocarbon monomers completely substituted with fluorine atoms or a combination of fluorine atoms and chlorine atoms or a copolymer of at least one such completely substituted hydrocarbon monomer and a perfluorinated (ether-substituted hydrocarbon) monomer;; (b) 100/,--90%, by weight of the total of (a) and (b) solids, of a binder which comprises (1)5-95%, by weight of the total of(1) and (2) solids of a colloidal silica which air-dries to form a continuous film when laid down by itself, and (2) 5-95%, by weight of the total of(1) and (2) solids, of a salt ofapolyamide acid represented by the structure

G is hydrogen or a carboxyl group; denotes that the groups so indicated may be interchanged to provide different isomers; R is a tetravalent organic radical containing at least two carbon atoms, no more than two carbonyl groups of each polyamide acid unit being attached to any one carbon atom of said tetravalent radical; R, is a divalent radical containing at least two carbon atoms, the amide groups of adjacent polyamide acid units each being attached to separate atoms of said divalent radical; and n is a number large enough to give the polyamide acid an inherent viscosity of at least 0.1, measured as a 0.5% by weight solution in N,N dimethylacetamide at 300 C., neutralized with a stoichiometric amount of a tertiary amine or morpholine; (c) 10-90%, by weight of the polyamide acid amine salt, of N-methyl pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, cresylic acid, sulfolane or formamide; (d) 0.2-20%, by weight of the total solids (as herein defined) of mica particles, mica particles coated with pigment, or metal flake; and (e) a liquid carrier.

2. The composition of Claim 1 containing by weight of the polyamide acid amine salt 15-200% of an organic liquid which may also serve as a carrier, miscible with water and having a solubility parameter of 1021.6, the parameter having a dispersion component of 7--10, a polar component of 211 and a hydrogen bonding component of 7-14.

3. The composition of Claim 2 wherein the organic liquid is furfuryl alcohol, 1butanol, 2-propanol, ethylene glycol monoethyl ether, triethylene glycol, formic acid, or a mixture of two or more thereof.

4. The composition of Claim 1, 2 or 3 wherein the colloidal silica is a sodium stabilized colloidal silica.

5. The composition of any one of the preceding claims wherein the salt of the polyamide acid is one prepared from at least one amine represented by the structure H2N-R1-NH2 and at least one aromatic acid anhydride represented by the structure

where, R and R1 are as defined in Claim 1 (with the proviso that R is aromatic) neutralized with a stoichiometric amount of a tertiary amine or morpholine.

6. The composition of Claim 5 wherein the salt of a polyamide acid is one prepared from (a) meta- or para-phenylene diamine, bis(4-aminophenyl)ether, benzidine, 2,2bis(4'-aminophenyl)propane, bis(4-aminophenyl)methane, bis(4-aminophenyl)sulfone, bis(4-ariiinophenyl)sulfide or 1 ,6-hexamethylene-diamine, and (b) pyromellitic dianhydride, trimellitic anhydride, 2,2-bis(3',4'dicarboxylphenyl)propane dianhydride or bis(3,4-dicarboxyphenyl) ether dianhydride, neutralized with a stoichiometric amount of a tertiary amine or morpholine.

7. The composition of any one of the preceding claims wherein the fluorocarbon polymer is PTFE.

8. The composition of any one of the preceding claims wherein the carrier is water.

9. The composition of any one of the preceding claims wherein the (d) component is mica particles coated with TiO

10. The composition of any one of the preceding claims comprising (a) PTFE; (b) a sodium stabilized colloidal silica; (c) the salt of a polyamide acid prepared from trimellitic anhyride and bis(4aminophenyl)methane, neutralized with a 2/1 weight ratio combination of triethylamine and diethyl 2-hydroxy ethylamine; (d) mica coated with TiO2; and (e) water as a carrier.

11. The composition of any one of the preceding claims additionally containing 15200 ,' by weight of the polyamide acid salt, of furfuryl alcohol.

12. The composition of any one of the preceding claims wherein component (d) is present in an amount of 2 to 15% by weight of the total solids.

13. The composition of Claim 12 wherein component (d) is present in an amount of 5 to 12% by weight of the total solids.

14. An article bearing a primer coat of the composition of any one of the preceding claims, topcoated with a fused fluoropolymer enamel.

15. A method for improving the adhesion of a fluoropolymer coating to its substrate, comprising priming the substrate, before the fluoropolymer coating is applied, with a composition according to any one of Claims 1 to 13.

16. A coating composition according to Claim 1 substantially as described herein with reference to the Example.

17. An article bearing a primer coat and a topcoat substantially as described herein with reference to the Example.

18. An article coated with a coating composition according to any one of Claims I to 13 or 16.

19. A method of improving the adhesion of a fluoropolymer coating to its substrate according to Claim 15 substantially as described herein and exemplified.

20. A substrate having an adhered fluoropolymer coating obtained by the method of Claim 15 or 19.