CA1080382A

CA1080382A - Fluorocarbon polymer compositions

Info

Publication number: CA1080382A
Application number: CA223,459A
Authority: CA
Inventors: Eustathios Vassiliou; William Van Hoeven (Jr.)
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1974-04-03
Filing date: 1975-04-01
Publication date: 1980-06-24
Also published as: AU7967075A; GB1510022A; DE2514647A1; IE42146B1; FR2266722B1; DK140175A; AU497989B2; JPS50135152A; NL161801B; LU72190A1; GB1510023A; BE827478A; NL161801C; DE2514647C3; SE409211B; IT1048805B; NL7503980A; FR2266722A1; JPS5437905B2; DK157306B

Abstract

ABSTRACT OF THE DISCLOSURE

The appearance of a fluorocarbon polymer coating, which tends to degrade during the application process, can be enhanced by the presence in the composition from which coating is derived of a compound of a metal, especially cobalt, iron, bismuth, cerium or manganese, which decomposes at a temperature in the range 100-500°C to give at least 0.2% by weight of the metal, of an oxide or hydroxide.
The coating compositions are preferably applied to metal articles.

Description

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BACKGROUND OF THE INVENTION

Cookware coated with fluorocarbon polymers o~ various æorts has come into widespread use in recent years. Almost every housewife prefers to use such cookware in her kitchen because food is less likely to stick to it and because it is so easy to clean.
These fluorocarbon polymer coatings are ordinarily provided in various colors. The darker o~
these is generally satisfactory, but the lighter colors especially white, and the unpigmented tend to be discolored or gray because of carbonaceous residues ~rom the various ad~uncts and surfactants originally present in the composition from which the coatings are derlved. ~ -, '' : . ' ' '' SUMMARY OF THE INVENTION

This discloration or graynesx can be signi~lcantly reduced and the purity of the color enhanced by adding to the fluorocarbon polymer coating composition (1) an oxide or hydroxide of copper gallium cobalt iridium iron rhodium nickel platinum -chromium palladium vanadium tin :
tantalum tungsten ~ ~-cerium lithium thorium sodium manganese potassium bismuth lead ytterbium cadmium or molybdenum silver or

(2) a compound of any of the metals llsted :
in (1) which decomposes between 100C.
and 500C. to give at least 0.2%, by weight of the metal in the compound, of an oxide or hydroxide.

: Mixtures of the compounds in (1), mixtures of the compounds in (2) and mlxtures of (1) and (2) compounds can also be used, provided they do not react with each other to form discrete compounds.

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It will be ob~ious that those metal compounds toxic to humans should not be used in products that will come in contact with food. Such compounds should be restricted to other industrlal uses.
Typical of the compounds of (2) are the nitrates, nitrites and the salts and hal~ salts of saturated and unsaturated monobasic or dibasic organic acids, preferably of 1-20 carbon atoms, for example, the acetates and octoates. The (2) compounds can also be in the anionic form, for example, vanadate~ and molybdates.
Cerium compounds are preferred for their effectiveness. The~e can be in the +3 or the +4 valence state. Especially preferred are cerous nitrate, cerous acetate and cerous octoate.
The concentration of metal compound in the composition will be dictated by the nature of the compound, the amount of discoloration expected in the final finish and the degree to which this discoloration i8 to be reduced. In the general case, the compound wlll be present at a concentration high enough to provide an amount of metal equal to 0.01 through 5 parts per hundred of fluorocarbon polymer used, preferably 0.1 through 1 part. When the discoloration i8 slight, one may use as llttle as 0.005-0.01 parts, and lf the dlscoloration is great, one may use more than 5 parts.
Indeed, the amount of metal compound that can be used may be limited by the color the`compound itsel~ gives to the final product and the point at which this color is unacceptable.

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The fluorocarbon polymers used in the composltlon are those of hydrocarbon monomers completely substltuted with fluorine atoms or a combination of fluorlne atoms and chlorlne atoms. Included in this group are perfluorolefln polymers such as polytetrafluoroethylene (PTFE) and copolymers of tetrafluoroethylene and hexafluoropropylene ~-ln all monomer unlt welght ratlos, fluorochlorocarbon polymers such as polymonochlorotrlfluoroethylene, and copolymers of tetrafluoroethylene and perfluoroalkyl vlnyl ethers. Mlxtures of these can also be used. PTFE 18 preferred.
The fluorocarbon polymers used are partlculate.
The partlcles should be small enough to pass through the ~-nozzle of a spray gun without clogglng it and also small -~
enough to give the resultlng film integrlty.
The fluorocarbon polymer preferably has a molecular weight of at least 20,000, for a polymer wlth a ~ -molecular weight less than thls tends to be waxy and unsuited for use.
Although a dry flour or powder of fluorocarbon -polymer can be used and a carrier provided separately, a polymer ln the form of an aqueous surfactant-stabilized dispersion is preferred for its stability and because it i8 most easily obtained in that form. ~ispersions of fluorocarbon polymers in organic liquids ~uch as alcohols, ketones, aliphatic or aromatic hydrocarbons, or mlxture~
of these, can also be used. In elther case, the llquid generally ~erve~ as the carrier for tbe ~o~po~ition.

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The fluorocarbon polymer ls ordinarily present in the composition at a concentration of 25% through 95%, preferably 70~ through 90~, by weight of the total of fluorocarbon polymer, pigment and polymeric ad~unct (as will be defined later). If only fluorocarbon and ~ -pigment, or only fluorocarbon and ad~unct are present, the concentration will be based on the total of those.
If neither pigment or ad~unct are present, the amount of fluorocarbon polymer to be used will be governed, for the most part, by the concentration of solids wanted in the composition, generally 10~ through 80~ by weight of the total composition.
Films having greater density and lower porosity, and showing better coalescence, can be obtained by adding a polymeric ad~unct to the composition.
Broadly speaking,the polymer ad~unct can be any polymer of ethylenically unsaturated monomers which depolymerizes, and whose depolymericatlon products vaporize, in the temperature range of from about 150C.
below the fusion temperature of the fluorocarbon polymer used to about the fluorocarbon polymer's decomposition temperature. Thecloserthe depolymerization and vapori-zation temperatures are to the fluorocarbon's fusion temperature, the better.
"Depolymerization" mean~ degradation of the polymer at the point at which the degradation products --~
are volatile at the temperatures encountered in curing the film. m ese degradation products can be monomers, dimers or oligomers.
: .-, ~ :- , -,, ~,, , . . : . . ~ - .

~08~382 "Vaporize" means volatil~zation of the degradation products and their evaporation from the rilm.
Ideally, all of the degradation products pass fro~ the ~ilm, but as a practical matter, a æmall but insigni~lcant amount generally re~Qins.
Typlcally of the polymeric ad~un~ts which ean be used are polymers Or ethylenically un~aturated mDnomers which contaln one or more m~noethylenically un~aturated acld units.
Repre~entative of these ethyleai¢ally unsatur~ted monomers ~re alkyl acrylates and methacrylates havlng 1-8 carbon atoms in the alkyl group, styrene, ~-methyl styrene, vlnyl toluene and glycidyl esters of 1-14 carbon atoms.
Alkyl acrylate~ ~nd methacrylate~ are preferred, because their decomposltion temperatures are close to the rusion te~perature Or PTFE.
Representative of the monoethylenically unsat-urated acids are acryllc a~id, methacryllc acld, fumaric acld, itaconlc acid and maleic acid (or anhydride). Acrylic acid ~nd methacrylic acid are preferred because of their availability.
The pre~erred glycidyl ester unit is one derived ~rom a product sold by the Shell Chemicsl Company a~
CARDURA E* ester. Thi8 i~ a mixed ester of the general formula * denote~ trade mark ..

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~~ R
H2C - CH - CH2 - 0 - C - C - Rz Rs where R1 ~s CH~
and R2 and R~ are lower alkyl groups, ~ -Rl, R2 and R~ containlng a total o~ 7-9 carbon ato~R.

The polymeric adJuncts pre~erred for use are 1. methyl methacrylate/2-ethylhexyl acrylate/methacrylic acid terpolymers, pre~erably the 35-50/40-60/1-15 (weight ratio) ~ -terpolymers;
2. butyl acrylate/methyl methacrylate/
"Cardura E"/acrylic acid quadripolymers, prererably the 23-27/33-37/21-25/15-19 quadripolymers;

3. styrene/methyl methacrylate/"Cardura E"/
acrylic acld quadripolymerQ, preferably the ~
28-32/28-32/21-25/15-19 quadrlpolymers; ~ -

4. methyl methacrylate/ethyl acrylate/
methacrylic acid terpolymers, pre~erably the 30_45/45-60/1-15 terpolymers.

Mixtures of ad~uncts can al~o be used.

- ~ .
- , ~ -10~3~33~2 The polymeric ad~unct ls ordinarily present ln the composition at a concentration of from about 3%
through 60% by weight of the total of fluorocarbon polymer and ad~unct polymer, preferably 4% through 30~, even more preferably 4% through 15%. If pigment ls present, the concentration will be based on the total weight o~ fluorocarbon polymer, ad~unct and pigment.
The polymeric ad~unct can be made by any of the conventional free-radical techniques familiar to any polymer chemist.
The presence of this ad~unct is not necessary, but is preferred.
The composition of the invention can be pigmented or unpigmented. Any pigment ordinarily used in this sort of composition can be used, although the benefits of the invention are minimized if darker shades are used.
~ White pigments are preferred. Typical of these are ; tltanium dioxide, aluminum oxide and silica. Titanium dioxide is especially preferred for its hiding power.
The pigments are ordinarily present at concen-trations of 2~ through 40%, by weight o~ the total of ~luorocarbon polymer and pigment, preferably 5% through 15~. If a polymeric ad~unct is present, the concentration will be based on the total weight of fluorocarbon polymer, pigment and ad~unct.
The compositlon can also contain such conventional `~ additives as ~low control agents, surfactants, plasti-cizers, coalescing agents, etc., as seem necessary or desirable. These additives are added for the usual reasons, in the uæual ways and in the usual amounts.
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The amount of total solids in the composition will be governed by the substrate to which the composition ls to be applied, the method of application, the curing procedures, and like factors. Ordinarily, the co~positlon will contain 10% through 80% by weight of total solids.
The composition is made by first selecting the fluorocarbon polymer, polymeric ad~unct (if one ls used), metal compound, pigment and such conventional addltives as may be used, and the amounts of these best suited to the purpose. This can be done with no trouble by one skilled in this art, using well-known principles of formulation.
Preparation of the composition is then a slmple - matter of making a mill base with the pigment (using standard techniques well known in the art), mixing the metal compound and this mill base and then mixing the mill base and the other components.
The composition will be most useful for top-coating metal cookware, especlally frypans, but can be used ~ust as well on other metal artlcles requiring lubricious surfaces, such as bearings, valves, wire, metal foil, boilers, pipes, ship bottomsJ oven liners, iron soleplates, waffle irons, ice cube trays, ~now sho~els and plows, chutes, conveyors, dies, tools such as saws, files and drills, hoppers and other industrial containers and ; molds.
The composition can be applied in any of the customary ways. Spraying, roller-coating, dipping, "' - ~

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108~)38Z
doctor-blading -- all are suitable, although spraying is generally the method o~ choice.
The article to be coated is preferably pre-treated by grit-blasting, by the flame-spraying of metals or by frit-coating. It is then primedJ the following being an embodiment of the preferred priming procedure:
1. The following are mixed together:
PTFE dispersion478.76 parts aqueous, 60% solids Deionized water130.23 parts Colloidal silica sol,327.18 parts 30~ solids in water (LUDOX AM* colloidal silica, E.I. du Pont de Nemours and Company .
2. The following are separately mixed:
TRITON X-100* 17.52 parts (Non-ionlc surfactant sold by Rohm ~ Haas Co.) Toluene 34.56 parts Butyl carbitol 13.36 parts Silicone 34.56 parts (Dow Corning DC-801 60~ solids in xylene) 85.52 parts of (2) are added to (1) in a small stream, with stirring, over a 2-3 minute period. To this are then added, with stlrring, TiO2 (45% solids dispersion 35.46 parts in water) Channel black dispersion 0.85 parts (22~ solids in water) Stirrlng is continued for 10-~0 minutes. The resulting primer composition was then sprayed to a frit-coated aluminum fry pan to a thickness of 0.2-0.6 mil (dry) and dried in air.

* denotes trade mark .

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-~ 1080382 The coating composition is applied to a thicknes6 of about 0.5-5 mils (dry) and then baked for a time and at a temperature sufficient to fuse or cure the fluorocarbon polymer being used.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
mose skllled in this art will be able to practice this invention more easily by first referring to the following illustrative Examples.
m ese artisans, will, no doubt, be able to compose numerous variations on the themes disclosed, such as changing the amounts of ingredients slightly but insignificantly ~rom those shown, adding innocuous substances, or substituting equivalent or nearly equivalent components ~or those shown. All these variations are con- -sidered to be part of the inventive concept. -~
In the Examples, all parts are by weight.

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.- :. ' . ' ' . - . ~ . ' . ' 1~ 8~ 3 EXAMPLE l A coating composition representative of the invention is made as follows:

(1) prepare a mill base by mixing in order and then pebble milling water 223.02 parts sodium polynaphthalene sulfonate 2.00 titanium dioxlde 180.86 (2) Dissolve 23.~9 parts of Ce(N03)3.6H20 in (1)-(3) With mixing, slowly add the product of (2) to 2853.9 parts of a dispersion of PTFE in water, 60~ solids, containing 6% (by weight) of isooctylphenoxypolyethoxyethanol.
(4) Mix, in order, Triethanolamine 120.2 parts --Oleic acid 72.8 --Toluene 214.94 Butyl carbitol 72.1

(5) Slowly add the product of (4) to the product of (3) with mixing.

(6) To the product of (5) slowly add, with mixing, 625.8 parts of an aqueous dispersion, 40% solids, of a methyl methacrylate/ethyl acrylate/
methacrylic acid 39/57/4 terpolymer.

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" 108038Z

(7) To the product of (6) slowly add, with mixing, 39.3 parts of water.

Spray the resulting composition, to a thickness of 1 mil (dry), on a frit-coated aluminum pan, primed according to the emobdiment of the preferred priming procedure de-scribed hereinbefore. m en bake the pan for 5 minutes at 430C.
The resulting white finish will show significantly less discoloration than the same finish lacking the cerous nitrate.

Another coatlng composition representative of the invention is made as follows: -(1) To 718 parts of an aqueous dispersion of PTFE containing 6% of isooctylphenoxypoly-ethoxyethanol slowly add 157.5 parts of the terpolymer dispersion of Example 1 (6)~ with mixing.
(2) Prepare a mill base by mixing in order and pebble milling Triethanolamine 30 parts Toluene 53.8 Butyl carbitol 18 Oleic acid 18.2 Ti2 45.5 : .. . .. . . . . .. . . . .
, - : ' ' ' ' ':

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(3) Dissolve 5.7 parts of (NH4)6 Mo7024-4H20 in 70.5 parts of water and slowly add the solution to the productof (2), with mixing.
(4) Slowly add the product of (3) to the product of (1), with mixing.

Apply the resulting composition to an aluminum p~and bake as in Example 1. The resulting finish will show significantly -less discoloration than the same flnish lacking the molybdenum compound.
Equivalent amounts of Pb(NO~)2 and Ni(No3)2.
6H20 can be used in place of the (NH4)6 Mo7 o24.4H2o in (3), with equivalent results when applied to an aluminum panel.

_ 14 -

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising (a) at least one fluorocarbon polymer of monoethylenically unsaturated hydro-carbon or vinyl ether monomers completely substituted with fluorine atoms or a combination of fluorine atoms and chlorine atoms, the polymer having a number average molecular weight of at least 20,000, (b) matter selected from the group consisting of (i) a pigment, and (ii) at least one polymer of ethylenically unsaturated and/or glycidyl monomers which depolymerizes, and whose depolymer-ization products vaporize in the temperature range of from 150°C below the fusion temperature of the fluoro-carbon polymer used to about the fluoro-carbon polymer's decomposition temperature; and mixtures thereof, (c) at least one compound of a metal selected from the group consisting of cobalt, iron, bismuth, cerium and manganese, and mix-tures thereof, said compound decomposing in the temperature range of about 100°-500°C
to give at least 0.2%, by weight of the metal in the compound, of an oxide or hydroxide, and being in an amount sufficient to provide at least 0.005 parts by weight of metal per hundred parts by weight of (a);
and (d) a liquid carrier.

2. The composition of Claim 1 wherein the fluoro-carbon polymer comprises 25-95%, by weight, of the total of (a) and (b).

3. The composition of Claim 2 wherein the com-pound of (c) provides an amount of metal equal to 0.01-5 parts per hundred of (a), the matter of (b) is a mixture of polymer comprising 3-60% by weight of the total of (a), (b)(i) and (b)(ii), and pigment comprising 2-40% by weight of the total of (a), (b)(i) and (b)(ii).

4. The composition of Claim 3 wherein the fluoro-carbon polymer is perfluoroolefin.

5. The composition of Claim 4 wherein the per-fluoroolefin is polytetrafluoroethylene.

6. The composition of Claim 5 wherein the metal of (c) is cerium.

7. The composition of Claim 6 wherein the compound of (c) is selected from the group consisting of cerium nitrate, a cerium ammonium nitrate and a salt of cerium hydroxide with an organic acid.

8. The composition of Claim 7 wherein the liquid carrier is water.

9. The composition of Claim 2 wherein the matter of (b) is pigment.

10. The composition of Claim 9 wherein the pigment is 2-40%, by weight, of the total of (a) and (b), and the compound of (c) provides an amount of metal equal to 0.01-5 parts per hundred of (a).

11. The composition of Claim 10 wherein the fluoro-carbon polymer is perfluoroolefin.

12. The composition of Claim 11 wherein the per-fluoroolefin is polytetrafluoroethylene.

13. The composition of Claim 12 wherein the metal of (c) is cerium.

14. The composition of Claim 13 wherein the com-pound of (c) is selected from the group consisting of cerium nitrate, a cerium ammonium nitrate and a salt of cerium hydroxide with an organic acid.

15. The composition of Claim 14 wherein the liquid carrier is water.

16. The composition of Claim 2 wherein the matter of (b) is polymer of (b)(ii).

17. The composition of Claim 16 wherein the polymer of (b)(ii) is 3-60%, by weight, of the total of (a) and (b), and the compound of (c) provides an amount of metal equal to 0.01-5 parts per hundred of (a).

18. The composition of Claim 17 wherein the fluoro-carbon polymer is perfluoroolefin.

19. The composition of Claim 18 wherein the per-fluoroolefin is polytetrafluoroethylene.

20. The composition of Claim 19 wherein the metal of (c) is cerium.

21. The composition of Claim 20 wherein the com-pound of (c) is selected from the group consisting of cerium nitrate, a cerium ammonium nitrate and a salt of cerium hydroxide with an organic acid.

22. The composition of Claim 21 wherein the liquid carrier is water.

23. The composition of Claim 5 wherein the pigment is titanium dioxide, the compound of the metal is selected from the group consisting of cerium nitrate and cerium octoate, the polymer of (b)(ii) is a polymer of ethylenically unsaturated monomers which contains one or more monoethylen-ically unsaturated acid units, and the liquid carrier is water.

24. An article bearing a cured coating of the composition of any one of Claim 1, Claim 2 and Claim 3.

25. An article bearing a cured coating of the composition of any one of Claim 4, Claim 5 and Claim 6.

26. An article bearing a cured coating of the composition of any one of Claim 7, Claim 8 and Claim 9.

27. An article bearing a cured coating of the composition of any one of Claim 10, Claim 11 and Claim 12.

28. An article bearing a cured coating of the composition of any one of Claim 13, Claim 14 and Claim 15.

29. An article bearing a cured coating of the composition of any one of Claim 16, Claim 17 and Claim 18.

30. An article bearing a cured coating of the composition of any one of Claim 19, Claim 20 and Claim 21.

31. An article bearing a cured coating of the composition of Claim 22 or Claim 23.

32. A method for reducing the amount of carbon-aceous residue in a fused fluorocarbon polymer coating, said method comprising mixing with the composition, before it is applied and fused, at least one compound of a metal selected from the group consisting of cobalt, iron, bismuth, cerium and manganese, and mixtures thereof, said compound decomposing in the temperature range of about 100-500°C to give at least 0.2%, by weight of the metal in the compound, of an oxide or hydroxide and being in an amount sufficient to provide 0.01-5 parts of metal per hundred of fluorocarbon polymer.