CA1218785A - Protective coating composition and method of use therefor - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Metal parts, such as bolts, fasteners, and the like having improved corrosion resistance are obtained by (a) phosphating the metal part and, thereafter (b) coating the metal with an aqueous coating composition consisting essentially of: (1) a phosphating oil, (2) a siloxane which is either a polyalkyl-siloxane or an alkylpolysiloxane, and (3) water.

Description

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PNYr~CTIV~ OOATINa CoMPOSlTlON
AND M~,THO~ OY U~E THER~OR

~AcKarlouND 0~ Tll~ INVl~NTION

~ eld of the lnventlon The present inventlon concerns contlng com-posltlons and methods o~ u8e therefor. More partlcul~rly, the present Inventton concerns coating com-poaltlon~ for renderlng met~ pnrt3 corroslon reslstant end methods o~ use there~or. Even more partlcul~rly, the ~ present Inventlon concerns coating composltlons useful In renderlng metalllc p~rts resistant to ~alt spray corro-810n nnd methods ot u~e thare(or.
Il. Prlor Art The oxid~tlon or rustlng o~ met~lllc pQrts upon prolonged exposure to the elements is well documented.
As an industrial problem, oxidation problerns sre mnny-fold. A partlculHrly signlfic~nt Industrial problem occurs In the ~utomotive industry when oxld~tion of m~t~lllc parts of a vehlcle, such ~s bolts, nuts, ctc.
occur. First, there 15 the replscement problem.
Oxidation or rustlng, when coupled with g~lv~nlc welding, may make It vlrtuQlly imposslble to remove and replace 8 rusted bolt or nut, thereby necessltatlng the need to burn it off with ~ torch or slmilss tool. Likewise, a bolt or nut may become so ox~dized as to break. This, ~n turn, csn rupture or weaken a signl~lcant structural com-ponent thereby l~nding to potentiHl in~ury and/or ~cci-dent with the vehicle.

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To ~llovl~to th~ problem ~f ru~tl ng ~ ~ ~ t en ~ r H
nnd ~ther componcnts ot a vehlole, tha automotlvc manu-t~cturera hnva estnbl lshcd c~rt~ln mlnlmum corroolon stRndards. Unle~ a f~3tener cnn meet the~e stand~rd~, It 1~ unsultubl~ for u~. The most common Industry test ~9 a salt sprny corrosion test wherein ~ ~astener i8 exposed to a salt spray atmosphere, for a pre-determlned tlme. The extent ot corroslon ot the part arter the pre-determlned tJme perlod determlnes If the part Is accep-t~ble or not.
Therefore, fasteners expected to meet automotive Industry corroslon resl3tance standards have conven-tlonally been tre~ted wlth a phosphate solutlon, such a~
zlnc phosph~te or the like, In accordance with well-known technlques. There~rter, the part is coated wlth a "phosphating oil" or other salt-resistant coating. Yet, such so-treated parts have great difficulty in passing corroslon resistance tests. The present inventlon, thus, seeks to overcome this problem in the prlor art by pro-o v~d~ng a coatin~ composltlon for Imp~lrlng corroslon resistance to metal fasteners and other parts which can successfully pass an automotive industry test. As will be evident from the ensuing disclosure, the composition hereof is distinct from prior art compositions. For ~5 example, United States Letters Patent No. 4,2l6,032 teaches an improved "phosphating oil" whereln ~n effec-tive Qmount of polyvinylpyrrolidone and zinc powder is added to the oil.

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~UM~ARY OF TH~ INVENTION

In ~c~ord~nce wlth the present Inventlon, there i9 provlded a coat~ng composltIon, partlcul~rly ~dapted for enhRnclng corroslon-re~l~t~nce ot mct~l ~asteners ~nd consIsting essentlally of:
(a) ~ phosphatlng oll, and (b) a siloxane compound whlch ts elther an alkylpolysiloxnnc or ~ poly~lkyl~lloxane.
The compositlon hereor, whlch ~ an aqueous solution, generally, comprises from about 5% to 35%, by volwme, of the phosph~ting o~l and from about 0.1% to 25%, by volume, of the siloxane and the balance being substan-tially water based. Preferably, the composition comprl-se8 from ~bout 5 to 25%, by volume, of the oII nnd 0.1 to 10%, by volume, of the sIloxane.
Th~ coating composition, which i 5 deployed as an aqueous solution thereof, 19 applied to a t~stener or other metHllic part, after being sub~ect to ~ phosphate treatment. The coating composltion is applied at ambient conditions and by any suitable method, such as by spraying, brushing, immersion or the like.
Parts treated in accordance herewith have evi-denced cap~bility of surpassing a four hundred hour salt spr~y exposure test.
For a more complete understQnding of the present invention, reference is made to the followlng detailed description and accompanying illustrative examples of the present invention.

~ ~L21~ ; v DETAILED DRSCRIPTION 0~ T~IE PREPEl~R~D EMBODIM~NTS
A8 hcreinnbov~ noted, the present invontlon pro-vldes ~ coatin~ composltlon for render1ng metul fa~tener~
or other p~rts aorroslon reslstant and whloh, generally~
oomprlsas ~n ~qu~ou~ ~slutlon ot a mlxturc ot (a) a "phosphating" oil, and (b) a slloxane, More spcclflc~lly, the cont1n~ composltlon hereof comprl~es an aqueous solutlon havlng from about 5%
to about 35%, by volurne, of the oil and from about 0.1% to 25%, by volume, o~ the siloxane OEnd the balance being substantially water. Preferably, the coating com-posltion comprlses from about 5% to about 25~, by volume, of the oil and from about 0.1% to nbout 10%, by volume, of the siloxane, with the balance being substantially water.
Phosphatln¢ oils as is understood lo those skillcd in the art, defines u long chain allphatic or cycloal1phat1c oll, su~h ~s, for ~xal1lple, castor oll, tung oll, linsacd oil, naphthenic oils, etc. As noted, these are commonly referred to QS "phosphating oil~". Typically, phosphatin~ oils ~re commercl~lly Rv~ ble products comprising aqueous emuls~ons of the oils whlch contain ~tabillzers, emulsirying ~gents~ and oth~r ~ddltlves.
The phosphat1ng oils are 8va ilable under a variety of tradenames and trademarks such as Permoil WS from Detrex Chemical; NAPREX which ~s available from Mobil Oil Corp.; Tectyl R which is ava11~ble from Ashland Petroleum Company~ and others.
Any of the commercially available phosphating oils work with substantially equal efficacy herein.

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The ~lloxane~ nB 15 known to tho~ sklll~d In the ~rt to which the present invention pertains, are gen~rally prep~red by the conden~tlon of sllox~ne~ to torm th~
characterlstics Sl - O - ~l bond. The~e nllox~nes whlch ~ arc u~eful h~reln nrc th~ poly~lkylslloxnne~ ~nd the akylpolys~lox~nes, as well a9 mlxture~ thereof.
Preferably, th~ slloxane~ employ0d hereln are poly~lkyl~lloxanes whereln the alkyl rndlcal h~s trom about one to four carbon atom~, and mlxtures thcr~ot.
It has been found that tn the practlce of the present invention ~minofunctional polyalkylsiloxanes are ~emlnently useful. The ~nlnofunctlonal polyalkyl~lloxane~
ar~ commerclally avallable products, ~uch R8 those sold by Dow Cornlng under the names DOW oORNING 531 and DOW
OORNING 536. These products are described ~ ~minofunc-tion~l polydimethylsiloxane copolymers with the followlng phy~lcal propertiess D~W OORNING DOW CO~NIN~
_______ _ ______________________ Active Ingredlents, % 50 100 Solvents Alphatic Solvents none ~ i~opropyl alcohol Yisco~lty at 77 F, cs 159 35 Refractlve Index at 77-F 1.410 1.408 Specific Gravity at 77-F 0.860 0.985 Flash Point, closed cup, Pensky-M~rtin Method, F 56 60 Aminofunction~l ~lloxAnes? per se, ~re de~crlbed in the literature such as in United States Letters Patent Nos. 3,508,933; 3,836,371, and 3,890,271, as well a8 Canadian Patent 1,031,485~

' ~ ~IL2~7~5 ~, In ordor to onhanoo tho corroslon reslstance ot the amlnofunctlonal polyslloxane3 thoy can be ~urther reActed wlth ~ ~mplc ~ well qs ~tty ~cid, such a8~ ror example~ ~oetlc aold~ st~ar~c acld, l~ostearl¢ ~cld, S l~urlo acld, eta., ls~ners &nd derlvAtlves thereo~ ag well as mlxture~ thereo~. Pref~rably, where the ~cld reactlon ls used, the slloxane ls rencted wlth a fatty acid The reactlon o~ aminor1Jnctlonal polyslluxanes w~th ~atty acids are well knowrl in the art.
In prep~ring a c~ating composltion hereof, generally, an aqueous solution thereof is employed. The aqueous solution ~s prepared by admlxing the silicone component with the phosphating o!l which ~s ordlnarlly~
an aqueou~ emulsion thereof. Gen~rally~ the resultlng ; coatlng compo~ition comprlses fr~n about S to about 25~, by volume, of phosphating oil, from about 0.1 to about 25%, by volume, of siloxane and the balance being water. In prepnring the ~queous solution, the oil and slloxAne are ordin~rlly present In a respectivo volumetrlc ratio ) ranging fr~m ~bout ~Osl to about 1;1.
It should be noted w~th respect hereto that ~dditional ingredients may be incorporated hereinto, such as, emulsifier~, surfactants, solventsg etc. to promote storage storablity, solubility, etc.
S It should, also, be noted with respect hereto that the results were unexpected in that the literature advises against mixing a phosphating oil and R
polysiloxane.

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The coating composltion her~ot Is applied to a mot~l produat, suQh ~8 ~ m~tul f~stoner or the llke, atter the metal product hQ~ been "phosphat~d", Ag~ln, ~8 1~ known to thosc Dkllled In th~ art to which the pre~ent Inventlon perta~ns, th0 "phosphatlng" of a met~l part, whlch is usunlly a ferrou~ part, comprlses exposln~ the part to ~ hot or heated phosphate solutlon, such ns ~ hot 2inc phosphate, hot phosphoric ucid, or R simllar hot solution, and, thereafter, coollng it to, thus, pas~lvate the met~l fastener.
- ln applying the coatlng composltlon hereof, any useful technlque can be employed, such as, Immerslon, spr~yln~, brushln~ or the llke. Also, tho composltlon during use Is employed at a temperature ranglng from about 60-Y to about 175-F, and, preferably, from about 70 P to about 150'~. The elevated temperatures, where used, are employed to promote the solubllity of the composltion.
For a more eomplete understanding o~ the present invention reference is made to the following illustratiYe examples. Tl~e examples are to be construed as illustratlve, not limitative, of the present invention.
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F.XAMPLE I
This example illustrates the effic~cy of the present inventi~n in its ability to pass an automotlve manufacturing specification which requlres palnted metal parts to surpass a 240 hour salt spray test after washing with a solution of Dupont's RALLYE car wash at 0.5 concentratlon.

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A s~rles o~ Iron bolts are phosphated by irnner-~lon In ~ ~lo~Vy ~lno phosptlato nolutlon. Therc~ttor, tl~o bolts ar~ rlnsed ~nd ~eal~d In n ~onventlonul mnnner.
Th~n, the bolt~ are drled snd next pnlnted wlth ~ blnck pnlnt ~S5 s~cond vlscoslty). After palnt~ng, the bolt~
are ov~n cur~d Rt 350 ~ untll dry. Th~ bolt8, Qtter curlng, ~r~ Inm~r~ed In ~n ~qu~ou9 co~tlng 901utlon O~
(a) 20% by volume of a phosphatlng oll 301d by S~:
Detrex Chemlcal under the name PERMOIL W~;
(b) 20% by volume, of an amlnofunctional poly-dimethyl311Oxane 801ut~0n cont~lning Qbout 7% by ~olume of the slloxane, Rnd ;
tc) 60%, by volume, of water After lmmersion, the bolts ~r~ alr drled ror 24 hours at room temperatur~
Next, the bolts are washed in a 1/2% con-centratlon aqueous RALLYE car w~sh solution. The bolts are, then, rlnsed in tap water nnd alr blown dry.
Thereafter, the bolts ~r~ placed In ~ 22"
Harshaw S~lt Spr~y Cablnet. A~t~r 312 hour~ in the cQbl-net the bolts show no slgns of rust.
In conducting this example, the aminofunctional polydimeth~lsiloxnne employed ls a commercially avRllable product sold under the nam~ POI.Y~I~IT~ whlch hns substantinIly the following composition:
INGREDIENT AMT, ~bw __________ ___ _ __ Dow Corning DC 538 6.0 Dow Corning DC 531 2.0 isosteari~ Ac~d 0.6 EmuIsifiçr (1) 1.0 Solvent (2) 46.4 Water 64.0 tl) an alkanolamide emuls~fler sold under the nane WITCAMIDE 511.

(2) a mixture of kerosene and mineral spirits.

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Examplc I 1~ repe~ted using th~ Pcrmoil WS ~nd ~n ~mlnotunatlon~l dlmethyl9110xan~ aqueous solutlon whlch ls prepQred trom thc tollowlng~

INGREDlENT AMTL_~bv Dow Cornln~ DC 53~ a.o I~o~aarlo ~old 1.0 Ernul~lrler ~IJ 1~0 Stoddard ~olvent 34.0 10 W~tor a2~0 (1) Wltcoamlde 511.

In preparing this composition, the acld is ndded to the ~lloxane and mlxed therewlth for About flfteen mlnutcs. Durlng thl 3 t~me perlod, ~n exothermlc reac~
tion occurs and ls ~omp1eted. Thereaft~r, the emulsifler 18 added to the slloxane And Acld mlxture. Next, the sol~ent and, then, the w~ter ls added thereto. The resultlng aqueous system is then, added to the PERMOIL
WS to form a 20%: 20~: 60%, by volume, solution.
~0 Bolts treated in accord~nce herewith showed no rust ~ft~r 240 hours In the salt spray cablnet F.XAMPLE III
____ _ ___ _ Example I is repeated, except that the palnt step ls elimln~ted. Using twelve bo1ts as the mct~l parts, after 240 hours In the cablnet, only two bolts show light rust. The rema~ning ten bolts show no rust aiter 336 hours in the cabinet.

_g _ ~ ~Z~87~S ~9 EXAMI' I.E_ 1 V
~ xampl~ 1 lo repe~tcd but ustng an aqueou~
solutlon ot 10% by vol~le o~ Permoll WS, 10~ by volumo or the siloxane solutlon and 80~ by volume of w~ter. The ~o-troat~d bolt3 bogln ovldcncln¢ ruAt ~t 144 hour3.
When repeated wlth dl~erent molecular welght aminoiunctiona1 dimethylslloxflne, the bolts showed rusting nft~r 188 hoUrs In th~ cublnet.

EXAMPLE V
Example V is repeated, but using a coating com-posltlon of 10% PERMOIL W~ phosphating oll, 20% by volume of the aminofunctional dimethylsiloxane solution iden-tIfied in ~xnmple I and 70~ by volume of water. ~olts ~o te~ted show llght rustlng ntter 168 hours in the salt spray cabinet.
EXAMPLE VI
__________ Example I i5 repeated, but in lieu of the slloxane, an equal amount of an acryllc wax sold un~er the name FUTURE is substituted therefor. After 48 hours in the cabinet the bolts are rusted.
It is to be appreclflted that by the practlce o~
the present Invention ~ignificant improvements ~n corro-slon resistAnce ~re ~chleved.
HavinK thus, descrlbed the invention, what is clalmed Is:

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Claims (21)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An aqueous coating composition for improving corrosion resistance of metal parts, consisting essen-tially of:
(a) a phosphating oil, (b) an alkylpolysiloxane or polyalkylsiloxane, and (c) water.

2. The composition of Claim 1 wherein the siloxane is an aminofunctional polyalkylsiloxane.

3. The composition of Claim 2 wherein the siloxane is an aminofunctional dimethylsiloxane.

4. The composition of Claim 2 wherein the siloxane is the reaction product of an aminofunc-tional polyalkylsiloxane and a fatty acid.

5. The composition of Claim 4 wherein the siloxane is an aminofunctional dimethylsiloxane and the acid is isostearic acid.

6. The composition of Claim 1 which comprises:
(a) from about 5% to about 35%, by volume, of the phosphating oil, (b) from about 0.1% to about 25%, by volume, of the siloxane, and (c) from about 90% to about 50%, by volume, of water.

7. The composition of Claim 6 wherein the oil and the siloxane are present in a respective volumetric ratio ranging from about 40:1 to about 1:1.

8. The composition of Claim 7 wherein:
(a) the phosphating oil is a naphthenic oil, and (b) the siloxane is the reaction product of aminofunctional dimethylsiloxane and isostearic acid.

9. The composition of Claim 1 which further includes:
(a) an emulsifier for promoting oil-in-water solutions and (b) organic solvents.

10. A method for improving the corrosion resistance of a metal, comprising:
(a) passivating the metal with a phosphate solution and (b) coating the phosphated metal with an aqueous coating composition consisting essentially of:
(a) a phosphating oil, (b) an alkylpolysiloxane or polyalkylsiloxane, and (c) water.

11. The method of Claim 10 wherein the siloxane is an aminofunctional polyalkylsiloxane.

12. The method of Claim 11 wherein the siloxane is an aminofunctional dimethylsiloxane.

13. The method of Claim 10 wherein the siloxane is the reaction product of an aminofunctional polyalkylsiloxane and a fatty acid.

14. The method of Claim 13 wherein the siloxane is the reaction product of an aminofunctional dimethylsi-loxane and isostearic acid.

15. The method of Claim 10 wherein the coating composition comprises:
(a) from about 5% to about 35% by volume of the phosphating oil, (b) from about 0.1% to about 25% by volume of the siloxane, and (c) from about 90% to about 50% by volume of water.

16. The method of Claim 15 wherein the phosphating oil and the siloxane are present in a respec-tive volumetric ratio ranging from about 40:1 to about 1:1.

17. The method of Claim 16 wherein:
(a) the phosphating oil is a naphthenic oil, and (b) the siloxane is the reaction product of an aminofunctional dimethylsiloxane and isostearic acid.

18. The method of Claim 17 wherein the aqueous coating composition is maintained at a temperature ranging from about 60°F to about 175°F.

19. The method of Claim 10 wherein the aqueous coating composition is maintained at a temperature ranging from about 60°F to about 175°F.

20. A metal part treated in accordance with the method of Claim 10.

21. A metal part treated in accordance with the method of Claim 19.