Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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. ~ -
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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.
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"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.
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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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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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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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(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.
EXAMPLE 2
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.
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