FLUOROPOLYMER FINISHES HAVING IMPROVED SCRATCH RESISTANCE

LAQUES A BASE DE FLUOROPOLYMERES RESISTANT MIEUX AUX EGRATIGNURES

English Abstract

ABSTRACT OF THE DISCLOSURE
Compositions containing
(a) fluoropolymer,
(b) mica particles, mica particles coated
with pigment, or metal flake,
(c) a polymer of ethylencially unsaturated
monomers and
(d) a liquid carrier
are useful for coating metal, especially cookware, to give
lubricious surfaces.
- 1 -

Claims

The embodiments of the invention in which an exclusive
property or privilege is claimed are defined as follows:
1. A coating composition consisting essentially of
(a) about 80-99.8% by weight of the total of (a)
and (b), of a particulate polymer of one or
more monoethylenically unsaturated hydrocarbon
monomers completely substituted with fluorine
atoms or a combination of fluorine atoms and
chlorine atoms;
(b) about 0.2-20%, by weight of the total of (a)
and (b), of mica particles, mica particles
coated with pigment or metal flake;
the total of (a) and (b) equaling 100%;
(c) about 2-300%, by weight of (a), of one or more
polymers of monoethylenically unsaturated monomers
which depolymerize and whose depolymerization
products vaporize in the temperature range of
about 150°C below the fusion temperature of (a)
to about the decomposition temperature of (a);
and
(d) a liquid carrier,
said coating composition being suitable for forming finishes
having improved scratch resistance.
2. The composition of claim 1 in which (b) is
present at a concentration of about 2-15%, by weight of the
total of (a) and (b).
3. The composition of claim 1 in which (b) is
present at a concentration of about 8-12%, by weight of the
total of (a) and (b).
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4. The composition of claim 1 wherein the polymer
in (a) is PTFE.
5. The composition of claim 1 wherein the mica
particles in (b) are coated with an oxide of titanium, zirconium,
aluminum, zinc, antimony, tin, iron, copper, nickel, cobalt,
chromium or vanadium.
6. The composition of claim 1 wherein the polymer
in (c) contains one or more monoethylenically unsaturated
carboxylic acid units.
7. The composition of claim 6 wherein the polymer
in (c) is of one or more of an alkyl acrylate or methacrylate
having 1-8 carbon atoms in the alkyl group, styrene, alpha-
methylstyrene, vinyl toluene and the acid unit is of acrylic
acid, methacrylic acid, fumaric acid, itaconic acid, or maleic
acid, optionally esterified with a glycidyl ester of 4-14 carbon
atoms (total).
8. The composition of claim 1 wherein the polymer
in (c) is
(1) a methyl methacrylate/2-ethylhexl acrylate/
methacrylic acid terpolymer,
(2) a butyl acrylate/methyl methacrylate/acrylic
acid terpolymer esterified with a mixed ester
having the structure
<IMG>
where
R1 is CH3
and
R2 and R3 are lower alkyl groups,
R1, R2 and R3 containing a total
of 7-9 carbon atoms.
14

(3) a styrene/methyl methacrylate/acrylic acid
terpolymer esterified with a mixed ester having
the structure
<IMG>
where
R1 is CH3
and
R2 and R3 are lower alkyl groups,
R1, R2 and R3 containing a total
of 7-9 carbon atoms.
or
(4) a methyl methacrylate/ethyl acrylate/methacrylic
acid terpolymer.
9. The composition of claim 1 wherein the carrier
in (d) is water.
10. The composition of claim 1 wherein the polymer
in (a) is PTFE, the mica particles in (b) are coated with
titanium dioxide, the polymer in (c) is a methyl methacrylate/
ethyl acrylate/methacrylic acid terpolymer and the carrier in
(d) is water.

Description

Cookware coated wit~ :~luoropolg~ae~3~ esp~cially
pol~tra~luoxoethylene (PTFE) ~ has csme in~o w~despxead us~
~ re~ent year~ cook~ prefer to u8e~ ~3uch cOOk:~a~8 be-
ca.~e o~ lts non~t~ck propertie~ and becau~e i~ o ~a~y
to cle~.
Nhi:Le cookware o~ thi~ type 13 quit~ d~lrable,, the
fluoropol~mor coal;in~3: t~nas to become ~cratch~d ag~ter ~e~de~
u~e becau~e i~ ~ 80m8Wh~Lt ~o~t~r than the utell~ils u~ed to
10 stir and tur~ the ~o~d in the ware.
~U~ Opl ~E I~ TION
I~ has now been ~ound that th~ scratch res~sta~ce o~
. ~ ~luo~opoly~er coa~ can be ~r~v~. i~ th~ CoD~?~si~ion ~ro~
which t~e ~s:~at~g ~5 der~ed compr~ses
luoxopol~mer~
(~) m~cai p~cle i m:Lca p~icleg coated with
plgme~tg. or metal ~Iak~,
~c) a po~me~ o~ ~onoeth~le~ca~ atuxate~
~on~er~ ~i;ch depo~er~ze~ and ~aporizes
~0 a~ ~out th~ ~luoropolymer~ fusion
temperatlare5,
a~d
(d~ a liquid ca~ri.e~,
Such ~ coating ~:Lso hs~ ~xcelle~ crack re~ista~ce ~d
bl~3~r resi3ta~c~,~ and ha~ a~the~icaIly plea~ing a~pear~n~e..
:~ :
- . . . ..
.
.

P$~
~*3~
~ e ~luoropoly~er~ used; in the compo3itions o~ t~e
in~re~tion are homspolymers a~d copolymea~ (meaning the polymer
conta~ two or more d:~fere~ monomer ~t~) o~ monoet~
le~ical:L~ unsatuxate~ h~drocar~o~ mon~mers compl~ y 3ubst~-
tut~ ~th ~luorin~ atom~ or co~pletely ~ubstitu~ed ~ith a
combirlation of ~luorine a~om~ and chlor~n~ atom~. In~_luded in
thi~ group are per:eluorolerin pol~7mers ~uch ~ polytetra:eluoro-
ethyl~n~ a~ copoly~era o~ t~tra~luoroethyle~e ~n~ hexa~laoro-
propylene in all monomer unit we~ght ratio~ ~luorochloxocarbonpolymers uch as polymonochlorotri~luoroethyle~e,. and the
norfflally solid copol~mers of tetr ~luoroethylene and perfluoro-
~lkyl vinyl e~hers (wherein the alkyl ~roup is o~ 1-5 carbon
atom~). M~ture~ of the~e can also be u~e~.. P~FE is pre~erred
~or its thermal stab~l~ty.
~ The ~luoropolymar~u~ed 1~ partlc~late. The p~rtlcle~
ar~ pr~ferabl~ ~ ~ enough to pas~ through the no2æle o~
spr~y g~ wlthou~- clog~ng i~ 2n~ ~re ~l~o ~m~ll e~ough to
g~a the re~ultin~ ~ilm ~te~rit~.
2Q The-Pluoropolym~r p~e~s~a~ly ~a~ ~ ~umher ar~r~ge
molecul~r ~eigh~ o~ ~t l~a~t sbou~ 20~0~ eYe~ more pre~rab~y
~~~lea~ about 2~0~00 ~ b~cau~e su~h ~luoropo1y~ers~~~hax~er
~ini~h~s.. Nu~e~ aYer~e ~olecular ~elg~t o~ P~F~ easurod
: b~ ~h~ethod aesc:~lbe~ by Su~, Tskehl~a &~d Machi ~n Journal
olu~e 179 pp~. 325~-3257 ~lg73)~
The ~u~b~r a~erage~mol uIar weigh~ o~ ~ te~ra~luoroeth~len~
; hexa~luoroprop~lene copoly~er iæ~me~sured by ~rst determinlng
.
i~* mèlt ~lo~r rate (~) accord~ng tQ AST~ D21l6, u~i~ the MFR ~:~
to dete~ni2l~ ;melt ~i~Go3ity (MV) accordl~g to the equation
,

~ 1?~ ;~ pr~3~ur~ u~ed. (mm) ac or~i.c~ radi~
an~ then d~te~l~g moleculaE ~eight (MW) accord~g ~v the
e~uation
\ 3~4/ 3~V
6 ~ lQ ~
~lmiber average mol~cul~ ~reight o~ a ~luo:roch:loroc~r~on poly
m~r 1~ measured by ASTM D1~30..
Although a po~de~ o~ ~luoropslymer can be u~ed ~d
a c~r~er provided Se!!paratel9`3 a polymer in th~ ~O~D o~ an
aqueous dlsp~rsiorl i~ pr~erred ~or i~s s~abllity and b~cau~e
10 it is most eas~r ob~ained ~ that ~rm.
~ he ~luoropolymer is ordillar~ly pr~nt ~ the compo~$-
ti.o~ a~- a concentrat~on G:~ abou~ 80 9~ , pre~rabl5~ about
85-982~ by Me~ o~ ~he total ol~ ~luoropol~mer ~ iC~L parti-
Cl~r mic~ ~ert~cl ~-co~l~c~ ~el- p~gmen~g or ~o~al ~ke.
e 3~ic~ p~lcles.~ 60~edL mica par~icle~- ~d metal
~ke us~ i~ the com~os~tlons o~ the t~entio~ ean b~ an~ Or
. tho~e ~ilable~ comm~rci~ly. The~ partic~s~ e~ ~a
an averag~ 10~Jt di~en~lors o~ lO to l~0 ~rons; pro~erab3~r
15-~0 m~crons~. ~lth no p~ticles or ~ e~ h~ ~ longe~t
20 dinension o~e ~or~ t~ about 200 ~crons~ Partlcle and ~lake
~iz~ ~ m~a~ured o~p~cally ga~ ~ 3tandard..
T`he :m~c~ part~c~e~ coatedt ~rith pi~e~t pre~erred ~or
use are ~hose d~scr~b~d ~ U,S. Pat~t ~,087,827~ to KIenke and
Sbratton~ and U~ Paterlt~ 33087,828 asld~ 3,087,829~ to Iinton~
T~e d~closure~ o~ the~ pat~t~ are lncorporated i~to this
~ ` , ' .
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3p~C :Eication to d~scr~b~ th~ ~rar~ou~ coalte~ ~ic~ ho~
~hey are prepared~ ~
The mlca~ described in thes~ patents are coated
~h o~ des .or hydrou~ oxides of tita~itIm, zir~o~i~, aluminum~
:~inc, ant~ony~ tirl, iron~ copper, ~cl~el, cobalt~ chrom7~m
or Y~rladium. Tltanium dioxide coated mica ls pre~erred
beca~e o~ ~t~ &vai:Lab1lity.. MiX~ !8 oi~ coa~ed mica~ c~
also be u~ed~
Repres~ntati~r~ OI the metal fla~e whi.ch can b2 u3ed
10 are alumlnum ~lake, ~tainl~s ste~ ke,~ nickel fïake and
bronze flake~ cture~ of flake can ~lso be u~ed.
The mica9 coated mi a or metal ~laks i~ ordinar~ly
pre~ent i~ a compo~ition o~ the invention at a concentration
o~ about 0,,2-2~, by weight o~ the t~tal OI ~luoropolymer and
mica~ coated m~c~ or metal ~la~se, pre~erabl~ about 2 15~6, e~en
more pre~era,bly about 8~
T~ polymer o~ morloeth~lenicall~ un~lLrated mono-
mers usea in the compo~ltlon~ o~ th~ e~ltio~ c~ be any
~olymer or copolymer (in th~ ~en~e of bei2lg compo~ed o~ two or
20 more type~s of monomer~) o~ ~thyl~n~cally- uIlsat~r~ed motlomer~
whic~ à~oly~eriæ~ ~d who$~ depol~n~r~zation products Y~por-
~:Z:~3 in the temperatux ~ r~ge o~ ~rom abou~ 150 0C . belo~ the
~ion temper~eure o~ the ~luoropolgmer used to about the
~luoropolymer ' s decompo~ tion t~erature . The closer th~
depo~rmeriæat~on a~d vapQr~za.t~on t~mperature~ are to th~
fluoropolymert~ f~on te~per~ure, the bette~.
'rDepoly~.erization'r m~s d~gradation of th~ polymer
to the polnt at ~hich the degradatio~ products are volat~l~
at ~he t;emp~ratures ~ncountered ~n curing the Ilnal ~llm;
3 T~e~e d~;radatio~ product~ can be mollom~r~9 dim~rs or ollgomer~.
~ 5 --

~5~5
'1Vaporize" means volatilization o~ the degrada~ion
product~ and their evaporation ~rom the film. Ideally, all
o~ the degradation products pass ~rom the film, but as a
practical matter, a small but ins:Lgn~ficant amount generally
remains.
Illustrative o~ the.pol~mers which can be used are
polymers o~ monoethylenically unsatura~ed monomers which con-
tain one or more mono~th~lenically unsaturat~d acid ~lit~.
Representati~ o~ these monoethylenically unsaturated
monomers are alkyl acrylates and methacrylates hav~ng 1-8
carbon atoms ~n the alkyl group, styrene, a-methyl styr~ne,
vinyl toluene and glycldyl esters o~ 4-14 carbon atoms. Re-
presentative of the monoethylenically unsakurated ~cid~ are
acrylic acid, methacrylic acid~ fumaric acid, itaconic acid
and maleic acid (or anhydride), Mixtures of these polymers can
also be used~
Pre~erred ~or the denslt~ a~d g10SB 0~ the ~inishes
obtain~d when ~hey are used are the polymers of alXyl acrylates~
alkyl methacr~lates~ acrylic acid, methacrylic acid and a
glycidyl ester sold by Shell Chemical Company as "Cardura E'
ester, which i~ a mixed ester o~ the general ~ormula
: :
: ~ ~ \ / R~
H2C - CH - C~2 - 0 - C - C - R2
R9
where
Rl i~ CH3
and
- 6
:,
:
~ . . . . - . - .
' ~, ,

JJ~
and ~3 are lo~er alkyl groups 3
Rl, ~ and R3 containing a total o~
7-9 carbon atoms.
The polymers ~pec~ally pre~erred for the ~ame
rea~on~ ar~
1. methyl methacrylate/2-ethylhexyl acryl~te/
methacryllc acid ~erpolymer~, pre~0rably ~h~
40 50/48-52/1-4 (wei~hk ratio) terpolym~r~;
2~ butyl acrylat~/meth~l m~thacrylat~/CARDURA E*/
acryllc acid qu~dripolymers3 pre~rably the
23-27/33-37/21-25/15-19 quadr~polymers;
ætyrene/methyl ~ethacrylate/CA~DURA E/
acr~lic aci~ ~uadrlp~lymers, p~Per~bly the
28-32/~-32/21-25/15-19 quadrlp~lymer~;
4. methyl methacrylate/ethyl acryl~te/methacrylic
;~ acid terpolymers~ pre~erably the 37-41~55-59/1-6
terpol~mer~.
; Such a polymer ~s ordlnarily prese~t in a comp~s~-
- tion ~ the l~vention at a conce~tr~ti~n o~ a~ouk 2-3Q0~ by
weight o~ the ~luoropQlymer, preferabl~ about 5-20%, I~
can be made by any ~ the conventional free-radical techni-
que3 famlllar to any polym~r chemist~ :
~ The carrier used in the co~position o~ the ln~e~tlo~
; ca~ be any o~ ~ho~e normally used 1~ e~mp~sitio~ of this ty~O
It is a~ lnert, n~t a reac~lve or functlon~ the sense of
* denotes trade olark
~ .
~ '
.:~
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.~
.

contributing to the w~rking c~ the inve~tt on ) component and
it~ nature i~ the~e~ore o~ secondary importance. The carrier
ser~e~ only to keep th~ composition homogerleou~ and a~ts as a
mecha~ or convey~ the ~olid cos~ponent~ to the sub~tr~te.
er a coat~g ha~ been deposited, the carrier e~aporate~.
It i~ nece~ary., there:eore~ only 1;hat lt be compatlble wikh
the other component~ o~ the compo~l;tivn and that it ~ re no
ad~rerse e~ect~ on the coat~g it~eli~
Co~only, the ~luorocar~on pol~mer u~ed in the
10 composit;ion i~ provid~d i21 the ~oxm of` a~ aqu~ous di3persion,
and the wster introduced into th~ compo~ltion wi.th the polymer
also ser~e~ ~s ~11. or as part of the carrler for khe composi-
tion ~ Organic l:iquid~ such as alcohols ~ ketone~, aliphatic
and a~omatic h;ydrocarbons, or mix~ures o~ theseJ ca2l also be
used .,
The composl~ion~ o~ the i~vention c~n ~lso con~ain
such convent~orlal additiv~s a~3~ flow control agen~3. sur-
~cta~t~a~d p:La~tic~zer~ as are nece~sar~r or 3eem de~able~. .
rhese add~t~v~ are added for the usual re~oIl~, in the usu~l
20 ~ ~d in the usu~ aou~s.
The ~mou~t oi~ ~otal solld~ in the coat~g compost-
tions will be gover2~ed by the substPate to wh~ch the compos~;
tlon~ to be applied,, the method o~ appllcation" the curlng
procedura~, a~d like ~actor~ the usual ca e, the composi-
tio~ 1 contain ~bout lO-80%~ by welght, o~ solids,
- The compos~tio~s can be made b~ ~lmply mixing together
appropriate amounts o~ th~ proper compone2~ts. Pigmerlts ean be
added, 1:1~ th;~ ~s desired, by ~irst conventlonally preparing
- 8 -
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a suitable pigment dispersion and then adding this dispersi.on
to the compo 8 ition.
The composltions can be applied in any o~ the usual
ways. Spraying, roller-coating, dippingg doctor-blading --
all are suitable, although spraying is generally the method
of choice. The article to be coated is preferably pretreated
by grit~blasting, by the flame-spraying of metals or by frit-
coating. The article is then primed with a compositlon of`
the type disclosed in U S. Patent 3,655~604 or 3,694,392.
In a preferred embodiment the priming procedure is as ~ollows:
1. The ~ollowing were mixed together:
PTFE dispersion 478.76 parts
aqueous, 60~ solids
Deionized water 130.23 parts
Colloidal silica sol,327.18 par~s
30~ solids in water
(LUDQX AM* colloidal
silica~ E.I. du Pont
de Nemours and Company)
2. The following were separately mixed:
TRITON X-100* 17.52 parts
(Non-ionic sufactant
sold by Rohm & Haas Co.)
Toluene 31~ ~6 parts
Butyl carbitol 13.36 parts
Silicone 34.56 parts
(Dow Corni~g DC-8O1J
60% solids in x~lene)
85.52 part~ o~ (2) were added to (1) in a small
stream, with stirring, over a 2-3 minute period. To this
were then added, with stirring,
* denotes trade mark
, .

TiO2 (45% sollds disperslon35.46 parts
in water3
Channel black (22~ solicls0.85 parts
dispersion in
water)
Stirring was continued ~or 10-20 minutes. The resultlng
composition was then sprayed to a frit coated alumlnum
fry pan to a thickness o~ 0.2-0,6 mil (dry) and dried in
air.
The coating compositions of the invention are
ordin~rily applied to a thickness of about 20-30 microns
(dry) and the coated article is then baked at a tempera-
ture and for a time sufficient to fuse the fluoropolymer
used.
The compositions o~ the invention are most
useful for coating met~l cookware, especiall~ frypans,
but the compositions can also be used to coat other
articles requiring scratch resistant fluoropolymer coatings.
These other articles can be made of glass or any other mater-
lal capable of withstanding the baking temperatures used.
For example, the compositions can be used to coat bearings~
valves, wire, metal foil, boilers9 pipesJ ship bottoms,
oven liners, irorl soleplates~ waffle irons, ice cube trays,
snow shovels a~d plows~ chutes, conveyors, dies, tools such ~-
as saws, files and drills 9 hoppers and other industrial
containers and mcilds. ~ ~-
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,

3~
~ followlng example~ lllu~;tr~te the in7Jellt:Lon.
In these e~amples, all part~ and percent~ge~ ~re by weight
unless indicated otherwise.
The followlng were mixed~, in the order listed:
( 1 ) PTFE dispers ivn 64 . 9 pa~ts
(60% q~lid~ ln water~
TEFLON* Tp~ uorocQrbo~
~sin, Aqueou~ DlspersionJ
T 30, sold by E. I. du Pont
de Nemour~ and Compa~
(2) Deionized wa~er 10.5 parts
( 3 ) T102 coated mica 4 . 00 parts
(.AFFI AIR* NF- 140-D,
sold by :1:. I. du PoIlt de
Ne~ours and Compa~y)
t4) Red mill base 0.2 part
(made by b~ll milling a
rQlxture of
Red iron o~ide44.9 parts
Deionized w~tel~ 33.7 parts
Ole~ c acid30 3 part~
Trietha~olamir~e 6 . 7 part~
But~l c~rbitol2 . 9 p~Lrts
Toluene 8.5 parts)
(5~ A mixture o~
Triethanolamine . 92 part
Ol~ic acid ~ 75 part
To:Luene 3.48 paxts
Bul;yl carbitol 1.3 parts
* denotes trade ~Irk
-- 10 -
.. ~ ,.
' , - ' '

(6~ Methyl methacrylate/ethyl 14 parts
acrylate/methacrylic acid
39/57/4 terpolymer disper-
sion (40% in water)
The resulting compositioll was applied to an
aluminum frypan3 which had been fi:rst fritcoated and primed
according to the ~referred embodiment of a priming procedure
described hereinbefore.
The composition was applied by spraying ts a thick-
ness of 25 microns (dry). The coated pan was khen baked for5 minutes at 425C. to give a scratch-resiskant gold fini~h.
Example 2
The procedure of Example 1 was repeated, except that
the following were substituted for (3) and (4):
(3) TiO coated mica 4 parts
(~FFL~IR NF-154-D
sold by E,I. du Pont
de Nemours and Company)
(4) Mill base
(made by ball milling a
~ mixture Or
: Deionized water ~5 par~s
C~balt oxide blue 45 parts)
The resulting composition was applied to a frit
coated, primed aluminum frypan, as in Example 1, to give a
scratch resistant silver finish.
- 11
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~e~
The following were mix~d, in the srdel listed:
(1) PT~E di~per~l~n ~ Example 1 69.7 parts
(2) D~ionized water 8.7 par~s
( 3 ) T~02 coated mica 1. 0 pQrts
(AFPLAIR NF-140~I), 301dl by
E. I. du Po~t de Nemours and
Compa~y)
( 4 ) Red mlll bas ~ o:E Example 1 0 . 2 part
(5) The mi~sture in (5) o~ Example 1 6,45 p~r~s
(6) ~he disperslon of (6) in Example 1 14.0 part~
The r~sultirlg c~p~sition was applied to a ~:rit-
coated, primed alumi~um ~ryp~n3 as i~ :E5xample 1, t~ give a
~cratch resistant copper ~ini~h..
~ ~ .
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