CA1314351C - Anticorrosive coating compositions - Google Patents

Abstract

ANTICORROSIVE COATING COMPOSITIONS
Abstract of the Disclosure A primer coating system is disclosed that is resistant to abrasion and corrosion and includes a basecoat or first layer comprising a resinous polyepoxide, an aminoplast, phenoplast or blocked isocyanate curing agent, an epoxy-phosphate, a chromium-containing pigment and a clay that has the capacity to fix phosphate. the system may further include an overcoat or second layer comprising a resinous polyhydric alcohol, a polyisccyanate, a chromium-containing pigment and the foregoing clay, and a third layer of a finish coating preferably based on a fluorine-containing polymer.

Description

1 3 1 ~ 3 5 1 ANTICO~ROSIYE COATIN~ COMPOSITIONS
Description Technical ~ield The present invention relates to coating compositions for use as primer coatings on metal surfaces ~o provide coated surfaces that exhibit improved resistar,ce to abrasion and corrosion. The invention includes coating systems which employ such primer coatings.
Background of the Inven~ion Corrosive agents including salt spray, nitrogen dioxide ~nd sul~ur dioxide reduce the ; long-term performance of painted and unpainted metal surfaces. This has rec~ntly become a more serious 1~ problem in many geographical areas with the increase in acidity of the atmosphere and the resulting acid rain. Primer coatings applied to a metal surface before application of a finish coating can increase the level of protection.
Primer coat~ngs can be applied by a variety of methods including brush, spray and immersion techniques. One pa~ticuIarly use~ul method or coating a large surface area is a coil ~oating process wherein a coiled metal sheet is unrolled to : 25 expose the metal sur:face, the surface is coated by rol~ coating, the coating is cu~ed and the metal sheet is recoiled in a continuous operation.
For example, coil coating techniques may be ; employed to coat sheets o~ galvanized steel that are used in the construction industry for wall and roofing panel~. Strands of galvanized ~teel wire and the like may also be coated by coil coating techniques .
As indicated above, a coat~d me~al surface is more resistant to corrosion than an uncoated metal .

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~ 2- 1 31 ~351 ~urface. A coating, to be considered suitable for application by coil coating techniques, howevert ~ust be able to wi~hstand ~evere de~ormation without disrup~ing the continuity of the coating. This is particularly important in the production of wall and roofing panels ~hich comprise coated nletal sheets : that are bent or formed to a given configuration.
Any fracture or break in the coating 21S the metal surface is bent during ~orming would provide an area susceptible to corrosion.
Primer coating composition~ c:an include ~ single layer and multilayered films. The primer ; coating compositions of the prior art, wh~n applied as tbick films, generally lack the ability ~o satisfactorily withstand deformation as the coated metal substra~e is formed.
For example, ~.S. Patent No. 4,433,014 to Gaske et al. discloses pigmented, corrosion resistant, thermosetting coating compositions that include a resinous polyepoxide, a phenoplast resin crosslinking agent~ a pho~phoric acid ester catalyst, a chromium-containing pig~ent and a clay having the capacity to fix phosphate. The phosphoric acid ester catalysts of these coating compositions do not func~ion particularly well in combination with aminoplast resins, so it w~s necessary to use phenoplast resins as the crosslinking agents.
Moreover, such compositions are not well-suited for use in coil coating applica~ions because ~he coatings did not exhibit sufficient resistance to the stresses : incurred in coil Coating processes. These compositions were therefore typically applied to preformed panels by spra~ing.
Thus, a need;exi~ts ~or primer coating composition~ that are flexible after curing, capable .. . . . . . .
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1 3 1 ~35 1 of withs~anding severe forming conditions without film fracture and can be applled as thlck films to metal surfaces to improve resistance to abrasion and corrosion.
Disclosure of the Invention The present invention relates to pigmented, corrosion and ahrasion resistant, thermosetting organic solvent solution ; coating compositions that are suitable for use as protective primer coatings on metal surfaces.
In accordance with the invantion there is provided a pigmented, corrosion and abrasion resistant, thermosetting organic solvent solution coating composition comprising, (a) from about S0 percent to about 85 percent of total resin solids of a resinous ; polyepoxide; (b) from about 10 percent ~o about 20 percent of total resin solids of an aminoplast, phenoplast or blocked isocyanate crosslinking agent for said polyepoxide; (c) from about 5 percent to about 30 percent of total resin sollds of an epoxy-phosphate that is obtainable by reaeting a reslnous polyepoxide with phosphoric acid in an amount of at least 0.05 mole of phosphoric acid per oxirane equivalent; and (d) a chromium-containing pigment providing resistance to corrosion.
More than one coating may be applied to a metal surface ~for example, a galvanized steel substrate) to provide a multi-layered protective primer coating in the ~orm of a multilayered film which provides the desired thickness by means o~ the several layers.
When a two layered primer coating is employed, the layer formed on the surface of the metal substrate is referred to as a . ,. : . ,~

` 13~351 basecoat or first primer composition. The layer formed on the basecoat is referred to as an overcoat or second primer composition. The primer-coated substrate can be topcoated with a ; finish coating to provide the final product.
The basecoat or ~irst primer composition pre erahly - comprises from about 50 to about 70 percent resin solids, based on the total weight of the composition to enable coil coating and the application of relatively thick coa~ings. ~owever, this invention includes the applicatlon of thinner coatin~s and spray applica-tion, so lower resin solid contents are included in this inven-tion.
The basecoats in this invention are thermosetting solvent solution coating compositions on which the resin solids comprise from about SO percent to about 85 percent of a resinous J 3a _4~ 435 polyepoxide, from abou~ 10 percent ~o about 20 percent of an aminoplast~ phenoplast or blocked isocyana~e curing ~gent for the polyepoxide and from about 5 percent to about 30 percent of an epoxy-phosphate which is preferably provided as an agueous dispersion of at least partially neutralized epoxy-phosphate. This neutralizatiorl is with a volatile amine, including ammonium-containing comp~unds.
~hrougho~t this application, all parts and proportions are by wei~ht, unless otherwise specified, The remaining portion, usually about 30 to 50 psrcent of the ~otal weigh~ of the first primer composition, comprises from about 10 to about 4C
percent, based on the total weight of the composition, of an anticorrosive chromium-containing pigment and may also include a clay that has the caEacity to fix phosphate. The use of chromium-containing ~igments in corrosion resistant coatings is well known, and the use of strontium chromate is described herein as illustrativeO Clays that are often used to fix phosphate include kaolin clays.
The composition can further include an amount of a thickening agent sufficient, preferably less than about 2 percent by weight, to stably disperse the chromium-containing pigment and a polar solvent in an amount sufficientt preferably less than about 2 percent by weight, to allow the thickening agent to exhibit its thickening action.
The first primer composition is preferably applied to the metal surface in an amount sufficient to form a layer have a thickness of from about 0.1 to about 0.6 mils, more preferably from 0.2 to 0.4 mils. The coating composition may, of course, be ' ~ ` 1 31 ~351 applied to form a thicker layer, but a thickness of 0.1 to 0.6 mils is usually sufficient to provide the desired abrasion and corrosion resistance.
The applica~ion of any coating comp~sition of this invention may be accomplished by roll coating, immersion, ~raying or other techniques recognized in the art. As previously indicatedl roll coating is preferred.
The first primer coating may be used alone to form the primer coa~ing, but an overcoat of a second primer ooating is ~referably a~plied.
The overcoat or secGnd primer com~osition - may comprise from about 10 to about 80 percent resin soli~s based on the total weight of the c~mposition.
The resin solids comprise from a~ou~ 20 percent to about 90 percent of a resino~s polyhydric alcohol having groups reactive with isocyanate ~roups and from about 10 percent to about 80 percent of a polyisocyanate. The resinous polyhydric alc.ohols may be any solvent-soluble, bydroxy-functional resin having a hydroxyl value of from 50 to 300, pre~erably from 70 to lS0. The polyisocyanates are also ; conventional. These materials wi}l be more fully discussed hereinafter.
The remaining 40 to 60 percent of the total weight of the second primer composition comprises : from about 10 to about 40 percent, based on the total weight of the composition, of an anticorrosive chromium~containing pigment and may also include a clay that has the capacity to fix phosphate. As with the first primer co~positioni the second primer : composition can also.incl~de an amount of athickening agen~ sufficien~, preferably less than about 2 percent by weight, to stably disperse the :~ 35 anticorrosive pigment and a polar solvent in an 1 31 ~351 amount s~fficient, preferably less than about 2 percent by weight, to allow the thickening agent to exhibi~ its thickening action.
The ~econd primer composi~ion may be applied S over the first primer composi~ion in an amount sufficient ~o form a layer, preferably having a thickness ~rom about 0.6 to ~bout 1.4 mils, more preferably from 0.8 to 1.0 mil, although the layer can have a thickness outside that range depending on intended use of the coated surfa~e.
A ~opcoat or finish coa~ing can also be used in a multilayered coating accDrding to this invention. ~ny conventional finish coating may be used such as a fluorocarbon topcoat containing a polymer of vinylfluoride or vinylidene fluoride, preferably polyvinylidene fluoride, which is commercially available under the trade name FLUR~PON
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from DeSoto, Inc., Des Plaines, IL.
The finish coating is preferably pigmented with pigments capable of resisting a high temperature : bake and applied over the second primer composition in an amount su~fioient to form a layer having ~
~- thickness fro~ about 0.7 to about 1~3 mils, more preferably from 0.8 to 1.0 mil.
Thus, a thick ~ilm coating according ~o this invention can include a plurality ~f layers inc~uding a ~irst layer on a meta} ~urface of the foregoing first primer comFosition having a thickness preferably from about 0.1 to about 0.6 mils, a second layer of the foregoing second primer composi~ion having a thickness preferably from about 0.6 to about 1.4 mils and a third layer of a foregoing topcoat or finish coating having a thickness preferably from about 0.7 to about 1..3 mi~s.

r~cl~- rrla~ k "-"` 1 31 ~351 With reference to the first primer composition, any organic solvent-soluble resinous polyepoxide may be used. By a polyepoxide is meant an epoxide having a 1,2-epoxy equivalency of at least about 1.3. Diepoxides are preferred, especially digly-cidyl ethers of bisphenols having a 1,2-epoxy equivalency in the range of 1.3-2Ø
The term "bisphenol" denotes a pair of phenolic groups linked together through an intervening divalent structure which is usually an alkylene group. ~hen the phenolic OH groups on each of the phenol por-tions of the bisphenol are in -the para position, and using 2,2-propylene as the intervening divalent structure, the product is a commercially available material known as bisphenol A.
The suitable bisphenols are well known, and bisphenol A
is used in commerce. Diglycidyl ethers of bisphenol A are commer-cially available and such materials may be used herein. These may have a molecular weight of from about 350 to about 10,000. It is preferred to employ those polyepoxides having a 1,2-epoxy equiva-lency of from 1.7-2.0 and an average molecular weight (by calcula~
~0 tion) of from about 500 up to about 10,000. A molecular weight of from about 2,000 to about 10,000 is particularly pre-Eerred. The use of Epon* 1009 from Shell Chemical Company, Houston, TX, which has a molecular weight of about 8,000, is described herein. ~pon 1007 (also available ~rom Shell) has a molecular weight o~ about 4,500 and further illustrates suitable polyepoxides.
An organic solvent-soluble, heat-hardening aminoplast resin may be used including melamines, ureas, benzoguanamines, glycourils, water-dispersible aminoplasts and the like. Other typical aminoplast resins include hexamethoxymethyl *Trade-mark ~`

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- ~~ r 1 3 1 l~ 3 5 1 melamine and water dispersible transethers thereof.
Urea-formaldehyde conden~ates are pRrticularly preerred because these provide superior ~abrication properties when the compDsitions are used in coil coating and s~bseq~ently fabricated.
The use of the epoxy-phosphate dispersion : catalysts descri~ed he~ein enables the use of aminoplast resins ~s curing agents, whereas in the compositions of the prior art, phenoplast resins were required to cure the coatings. See "Eor example, U.S~ Patent No~ 4,433,014 to Gaske et al. as described above, It is a capacity to use the aminoplast resins which ~llows ~he use of u~ea-~ormaldehyde condensates which provide a coating that can withstand the stresses encountered in the fabrication of coated surfaces by coil coating techniques.
Phenoplast resins are also well known ana are known curing agents of polyep~xides. If the primer coating composition is to be spray applied ~o preformed panels, and not coil coated~ then phenoplast resins may be used as curing agents.
These are ~olvent-soluble, heat~hardening, reacti`on products of formaldehyde with phenol, xylol or a ;~ 25 deriva~ive thereof, like bisphenol A or t-butyl phenol. Xylolol-fvrmaldehyde condensates are the preferred phenoplast resins since other phenolics do not possess the same excellent color stability, but other phenoplast resins are otherwise fully useful.
Xylolol-formaldehyde condensates are commercially available and one representative class includes the ; Methylon~reSins sold by General Electric.
The relative proportions of aminoplas~ (or phenoplast) ~o resinous p~lyepoxide are known and are not the essence of ~his invention. I~ is convenient ~ t~

-` 1 31 ~351 to use a weight ratio of aminoplast (or phenoplast) to polyepoxide of from about 1:1 to about 1:15, more preferably from 1:2 to 1:8.
In order to provide the desired resistance to corrosion, it is importan-t to include materials in the primer coating compo-sition that provide both anionic and cationic protec-tion.
The desired anionic protection is provided by the pre-sence of the chromium-containing pigment which is used in a pig-ment to binder weight ratio of from about 0.1:1 to about 0.6:1, preferably from 0.~:1 to 0.501. The binder comprises the poly-epoxide and the aminoplast (or phenoplast). Chromium-containing pigments that provide corrosion protection are well known and are illustrated herein by strontium chromate.
The desired cathodic protection is provided by the epoxy-phosphate component. Epoxy-phosphates are provided by re-acting any resinous polyepoxide, such as those noted hereinbefore, with phosphoric acid to cause the reaction of one of the three P-0~ groups with the oxirane group of the polyepoxide. At least 0.05 mole of phosphoric acid is used per oxirane equivalent. The reaction is normally carried out in organic solvent solution. All the oxirane groups can be consumed by reaction with the phosphoric acid, but this is not preferred. The epoxy-phosphate may be used as such, or after neutralization with an amine, and even after - dispersion of the neutralized epoxy-phosphate in ~ater.
For exàmple, an oxirane-free epoxy phosphate may be used herein by reacting a resinous polyepoxide with from 0.05 to 0.9 mole, preferably from 0.1 to 0.7 mole, and most preferably from 0.2 to O.S mole of -~r 1~

-10- 131L1~51 or~hophosphoric acid per equivalent of oxirane in the p~lyepoxide using a process in which a water miscible organic ~olvent in admixture with orthophosphoric acid (which contains a limited amount of water) is heated to reac~ion tempera~ure together with an a~ount of water such that the total amount of water is sufficient to hydrolyze that portion of the oxirane functionality in the polyepoxide which does not react with the phosFhoric acid. The epoxy-phospha~e so-produced can be usled as such, or it can be used with an amine like die~hylamine.
~ndeed, the neutralized epoxy-phosphate can be used after dispersion in water. The small amount of water so-introduced into the solvent solution coatings of ~his invention are not harmful.
The resinous polyepoxide is preferably added slowly (incrementally) to the heated mixture o~
' solventg phosphoric acid and w~ter so that reaction with phosphoric acid and hydrolysis of the oxirane groups will occur simultaneously to consume the added epoxy functionality quickly and thereby minimize the concentration of oxirane functionality in the reaction mixture as the reaction proceeds. This ~inimizes epoxy-epoxy reactions which increase the molecular weight of the prsduct which is not preferred, ; The prop~rtion of water can be increased above the minimum ~pecified abo~e and may exceed the equivalents o$ polyepoxide. The amount of water is preferably~sufficient to consume at least about 50 percent and more preferably at least about 75 percent of the oxirane functionality in the epoxy resi~
reactant, but this merely represents present preferred practice.

`~ -1 3 1 -~ 3 5 1 The temperature of reaction for the production of the hydrolyzed epoxy phosphates can vary from about 80C to about 130C. Under these ; moderate conditions, the reaction is limited to essentially only one of the three OH groups in the orthophosphoric acid. It is preferred to use a relatively high boiling ~olven~, like 2-b~toxy ethanol, and to use reaction temperatures near the boiling point of water, e.g., 90C, to 105DC~
. While any water miscible organic solvent can be used, like ace~one, butanol, isvpropanol, and the like, the ethe~ alcohols illusSrated by the preferred 2-butoxy ethanol, are preferred. ~n the presence of the phosphoric acid, n~ catalyst is needed ana the desired epoxy-consuming reactions proceed without it. In a preferred embodiment, more than 75 percent of the organic solvent is 2-butoxyethanQl.
The presence of the phosphoric acid in the epoxy-phosphate provides acidity which can be mea~ured. The phosphoric acid groups catalyze the cure of the aminoplast resin as well as provide the phosphate needed for acid ra~n resistance.
While orthophosphoric acid is u~ually l~sed, pyrophosphoric ac:id is considered an equivalent 25 because it generates orthop~osphoric acid.
Unlike the proce s described i~ V~S. Patent No. 4,433,014, the primer coatin~ may be baked to thermoset the same since the epoxy-phosphate resists the baking temperature needed to provide a ~hermosetting cure. ~he epoxy-phosphat~ is preferably used in the presence of a clay having an anion-exchange capacity of at least about 10 : milliequivalents pe~ 100 grams, preferably at least about 20 milliequivalents. Many clays are known to have this capacity, but kaolin clays having a strong . .
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` -12- 1 31 ~351 anion exchange capacity are readily available and are described herein as being preferred.
The clay may be used in a similar weight ratio as the chromium-containing pigme~t relative to the binder; in par~icular, from about 0.1:1 to 1:1, preferably from 0.3:1 to 0.8:1.
The propor~ion of epoxy-phosphate should be such as to provide at least 0.1 pærce~nt of orthophosphoric acia based on the solids content of ~he coating composi~ion~ preferably at least 0.3 percent. It is preferred to use from 0.5 percent ~o 1.5 percent on the same basis, and up to about 5 percent of the acid may be present, though the upper limit is not precise.
Table I illustrates a number of compositions that are suitable for use as the basecoat or first ~rimer composition. Composition B is particularly preferred.

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Preparation of Basecoat Primer Compositlon COMPOSITIO~
(parts by weight) A B C D E F
Epon 10091 142 142 143 142 114 143 Urea-formaldehyde resin2 85 85 85 85 85 85 Cellosolve* acetate3130 130 130 130 130 130 ADD THE FOLLOWING PRBMIX:
Bentone* 34 gel4 2 2 3 2 2 3 Diacetone alcohol 20 20 20 20 20 20 MIX AND ADD:
Strontium chromate 52 36 - 52 54 Anti-Cor* 705 52 - - 52 Kaolinite clay6 - 109 - - 110 Wollastonite7 156 - 48 - - 48 zpo8 -- 120 Titanium dioxide, rutile ~ 114 - - 96 60 Zinc oxide - - 30 Sicorin* RZ9 - - - - - 15 Barium sulfate -~ 156 Nalzin* 210 - - - - - 150 , ; SANDMILL TO 6-7 and ADD:
Epon 10091 241 277 240 241 268 240 .~ Epoxy-phosphate dispersionll38 40 38 38 38 38 Solvesso* 100 114 77 84 50 90 84 - 1. Epon 1009 is a diglycidyl ether of bisphenol A having an: average molecular weight of 8000 and is commercially available from Shell Chemical Co., Houston, Texas. Epon 1009 was used at 40 ~ percent by weight in a solution including 30 percent by :
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~` ~ i 1 31 ~351 weight Solvesso 100 and 30 p~rcent by weight diacetone alcohol.
2. An ~min~plast curing agent that i~ commercially available from Reichhold Chemicals, Inc., White Plains, NY, as No.
21-511.

3. An ethylene glycol monoethyl ether acetate solvent that is commerclally available from Union Carbide Corp., Danbury, CT.

- 4. An organoclay gelling agent that is commercially available from NL Chemicals, Hightstown, NJ.

5. A zinc ferrite complex used as a corrosion inhibiting pigment that is commercially available from Mobay Chemical Corp., Pittsburgh, PA.

6. A Kaolin clay that is commercially available.from Georgia Kaolin Co., Inc., Union, NJ, under the trade-mark "HYDRITE R".

7. Calcium metasilicate (CaSiO3).
. A zinc phosphate complex used as a corr~sion inhibiting pigment that is commercially available from Heubach, Newark, NJ.
9. An organozinc complex used as a corrosion inhibiting pigment that is commercially available from ~ASF Corp., Holland, MI.
10. An organozinc complex used as a corrosion inhibiting - ~igment that is commercially available from NL Chemicals, Hights~own, NJ.
11. As described in Example 1 (hereinafter) or and in U.S.
Patent No. 4,425,451.
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1 31 ~351 With reference to the overcoat or second primer composition, s~itable polyhydric alcohol resins are illustrated by a hydroxy-functional polyes~er of glycerin and phthalic anhydride having a hydroxyl value o abo~t 100, or a solven~-soluble copolymer of ethyl acrylate c~ntaininc~ rom 5 to 25 perce~t by weight, preferably about 10 percent, of a copolymerized by~roxyethyl acrylate.
The polyifiocyanate can incluc~e any organic polyisocyanate, although diisocyanates are preferred. Suitable polyisocyanates are illustrated by 2,4-toluene diisocyanate and the biu~et derived from the reaction with water of hexamethylene diisocyanate (which is a triisocyanate). ~sophorone diisocyanate and diphenylmethane diisocyanate illustrate additional useful polyisocyanates.
Table II lists a number of second primer compositions prepared according to this invention.
Of the compositi~ns listed in Table Il, Composition J
is particularly preferred~

. ' " - 16 _ 1 3 1 4 3 5 1 231~8-1577 TABLE II
Preparation o~ Overcoat Primer Composition .
COMPOSITION
(parts by weight) G H I J K L M

Desmophen* 670_902 142 142 142 PM acetate3 166 166 166 Solvesso 150 84 84 84 80 80 80 72 Butyl Cellosolve acetate - - - 120 120 120 108 ADD THE FOLLOWIN& PREMIX:
Bentone 34 gel 4 4 2 2 2 4 2 3 Diacetone alcohol 10 10 10 10 10 10 10 MIX AND ADD:
Strontium chromate - 60 60 60 100 Anti-Cor 705 50 - - - - 50 50 Kaolinite clay6 - 96 100 125 Wollastonite7 150 - - - 125150 125 Titanium dioxide, rutile - 70 100100 60 Mica 50 - - - 50 - -Butrol* 238 100 - - - - 100 150 SANDMILL TO 5 ll2-6 and ADD:
Desmodur* BL-1260-609 334 334 334 Dibutyl tin dila~rate PM Acetate3 34 34 34 60 60 45 45 Solvesso 150 16 16 16 40 40 30 30 1. A polyhydric alcohol resin which contains reactive iso-cyanate groups that is commercially availabe from Dynamit Nobel of America, Inc., Rockleigh, NJ.

* Trade mark ~ ,7' .i`~.

~ 17- 1 31ar351 2. A hydroxy-functional pslyester resin that is commercially available from Mobay Chemical Corp., Pi~tsburgh, PA.
3. A propylene glycol monomethyl ether acetate ~olvent that is commercially available from krco Chemical Co., Philadelphia, PA.
4. An organoclay gelling agent that .is commercially available from NL Chemicals, Bightstown, ~J.
5~ Mobay Chemical Corp.~ Pittsburgh, PA.
5. Commercially a~ailable f~om Georg.ia Kaolin Co., Inc., Union, NJ, under the trade name ~YDRITE R".
7. Calcium metasilicate ~CaSiO3).

8. A modified bariummetaborate that is commercially available from Buckman Laboratories, Inc., Memphis~ ~N.

9. A polyisocyanate tblocke~ isocyanate~ that is commercially aYailable from Mobay Chemical Corp. t Pit~sburgh, PA.
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.. ., ;, 1,31 ~351 -lB 23158-~577 EXAMPLE 1 - Preparation of Epoxy-Phosphate Dispersion The epoxy phosphate dispersion of Table I
~ay be prepared as follows or a5 described in U.S.
Patent No. 4,425,451 ~ 14 part~ of a aiglycidyl ether of bisphenol A having an average molecular weight of about 4500 and a l D ~ epoxy equivalency of about 2.0 ~Shell ; Chemical Company ~oduct Epon 1007 may be used) are charged to flask equipped with an addition funnel thermometer and a reflux condenser. 440 parts of 2-butoxy ethanol are also charged to the flask and heat is applied to heat the charge to 125 degrees C
which is maintained until the polyepoxide is lS dissolved in the solvent.
24 parts of 85 percent orthophosphoric acid (in water) are premixed with lO0 parts of 2-butoxy ethanol and the premixture is added from the addition funnel to the reactor over a 30 ~inute period with rapid agitation while holding the temperature at 125 degrees C. This temperature is then maintained for 2 hours, and the content~ of the flask (a monoester) are allowed to cool to 80 degree~ C.
44 parts of dimethyl ethanol amine are then added to the flask at 80 degrees C temperature over a period of 15 minutes and the 80 degrees C temperature is maintained for a further 30 minutes to lnsure complete reaction. l900 parts of deionized water are then added dropwise with ~igh speed agitation to 30 provide a stable aqueous dispersion having a nonvolatile solids content of 2a. 6 percent, a viscosity of U-V on the Gardner-Holdt scale and which possesses a fine particle size in the moderate viscosity noted.

1 31 ~351 An epoxy-phosphate suitable ~or use in this invention may also be prepared ~s follows.
1320 grams of 2-butoxy ethanol, ~4~4 grams of 85 percent ortho phosphoric acid and 130 grams of additional water are heated to 95 degrees C in a reactor and tben 2100 grams of a diglycidyl ether of bisphenol A having a number average molec~lar weigh~
of 1000 ~Shell Chemic~l Company product Epon 1001 may be used) are added slowly over 30 minutes. The temperature is then held at 95 degrees C for 3 hours to insure completion of all the reactions (wi~h the phosphoric acid present and with the water). Then 480 grams of additional 2-butoxy ethanol are added ~o dilute the product to 55.1 percent solids content.
The solution product has a Gardner-Holdt viscosity of Y-Z and an acid value (based on the nonvolatiles) of 41.5.

Example 2 - ~reparation of Basecoat Primer Composition (Composition B of Table I) As shown in Table I in the column designated Composition B, the indicated amounts of the Epon 1009 solution, the urea-formaldehyde resin and Cellosolve acetate are combined with a premix of the Bentone 34 gel in diacetone alcohol. Thereafter, the indicated amounts of strontium chromate, kaoli~ clay and titanium dioxide are added with stirriny. The mixture is added to a grinding mill and is ground to a 6 7 North Standard ~ineness gaugeO
The indicated amounts ~f the addi~ional Epon 1009 ~olution, the epsxy-phosphate dispersion of Example 1 and the solvent are added to proY~de Composition B~

`- 1 3 1 ~35 1 Example 3 Preparation of Overcoat Primer Composition ~Composition J of Table II) As shown in Table II in the colum~
designated Composition J, the indicated amounts of S the polyhydric alcohol ~LH 790) and the solvents are combined with a premix of the Bentone 34 gel in : diacetone alcohol~ Thereafter~ the indicated amountsof strontium chr~mate, kaolin clay and titanium oxide are added with stirringO The mixture is added to a grinding mill and is gro~d to a S 1/2-6 North 5tandard fineness gauge.
The indicated amounts of LH 790~ dib~tyl tin dilaurate catalyst and solvent are added with stirring to provide Composition J.
A thick film primer composition of this invention was prepared by roll coa~ing ~ galvanized ~teel substrate with a first primer composition ~Example 2 - Composition B of Table I) at a thickness of about C.3 mils. The primer composition was cured 20 by baking as a coil at about 420 to 450 degrees Fahrenheit peak metal temperature for about 30 to 45 seconds (or under e~uivalent conditions). A second primer composition ~Example 3 - ComEosition J of Table II~ was roller applied over the ~irst primer composition at ~ ~hickness of about 0.8 to 0~9 mils.
The resulting primer composition was cured by baking as a ~oil at about 435-465 degrees Fahrenheit peak metal temperature for about 30 to 45 seconds (or under equivalent conditions~.
The primed substrate provided above is finish coated by the roller ap~lication of a pigment FLVROPON topcoat. This topcoat includes 70 percent KYNAR~polyvinylidene fluoride homopolymer in admixture with 30 percen~ of Acryloid~B-44 thermoplastic acrylamide resin available from ~ohm ~ t 1~ c~ e~ rlc o .. ~

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~1- 1 31 ~351 ~aas Co. [Philadelphia, PA) this solvent-based coating is pigmented with ceramic pigments to a pigment to binder weight ratio of 0~45 to 1. This coating is baked at about 480 degrees ]?ahrenheit peak metal temperature for about 30 ~o 40 seconds.
After continuous exposure ~o a 5 percent salt spray a~ 95 degrees F for over 1000 hours (in accordance with ASTM B-117), the fini~h coating did not form ~ace blisters and performed in an acceptable manner when subjected to a ~cribe test, This indicates the ability o~ the primer coating to resist corrosion upon e~posure to salt and high humidity.
. ~olvent resistance was determined using the rub method. The rub method uses a two-pQund ball hammer~ The ball end is covered with several layers of cheese cloth and is secured wi~h a rubber band.
The cheese cloth is then saturated with methyl ethyl ketone and the coated surface is rubbed with the solvent-saturated cheese cloth making ~ure not to apply additional downward pressure. Rubbing ~trokes are repeated at the same location until the metal is exposed to view or 100 rubs are exceeded, whichever occurs fir~t. Over 100 rubs were required to expose a metal surace coated with a composition of this invention.
Testing for abrasion resistance was performed using the falling sand method (ASTM
~-968). Thi6 test determines the number of liters of sand (under controlled conditions) required to abrade through a coating to expose the metal surface. The more sand required to expose the metal sur~ace, the more resistant the coating. Over 130 liter~ of sand were required to abrade through the foregoing primer coating.

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-22- 1 3 1 ~35 1 ~ he coatings of this invention exhibited better abrasion and salt spray resistance than the coatings of the prior art. In particular, when subjected to the falling sand test (ASTM 968), the 2 mil coating of this invention required 130 liters of sand before the metal surface was exE~sedO
; Resistance to salt spray was also enhanced.

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Claims (25)

1. A pigmented, corrosion and abrasion resistant, thermo-setting organic solvent solution coating composition comprising:
(a) from about 50 percent to about 85 percent of total resin solids of a resinous polyepoxide; (b) from about 10 percent to about 20 percent of total resin solids of an aminoplast, phenoplast or blocked isocyanate crosslinking agent for said polyepoxide; (c) from about 5 percent to about 30 percent of total resin solids of an epoxy-phosphate that is obtainable by reacting a resinous polyepoxide with phosphoric acid in an amount of at least 0.05 mole of phosphoric acid per oxirane equivalent;
and (d) a chromium-containing pigment providing resistance to corrosion.

2. The coating composition of claim 1 further including a clay having the capacity to fix phosphate.

3. The coating composition of claim 1 wherein said resinous polyepoxide is a diglycidyl ether of a bisphenol having a molecular weight of from about 500 to 10,000 and a 1,2-epoxy equivalency of at least about 1.3.

4. The coating composition of claim 1 wherein said resinous polyepoxide is a diglycidyl ether of a bisphenol having a molecu-lar weight of at least about 2,000 and a 1,2-epoxy equivalency of at least about 1.7.

5. The coating composition of claim 1 wherein said crosslinking agent is a urea-formaldehyde condensate.

6. The coating composition of claim 1 wherein said crosslinking agent is a xylolol-formaldehyde condensate.

7. The coating composition of claim 2 wherein said epoxy-phosphate contains from 0.05 to 0.7 mole of phosphoric acid per oxirane equivalent in said polyepoxide, the balance of the oxirane functionality being consumed by hydrolysis.

8. The coating composition of claim 7 wherein said epoxy-phosphate comprises from about 10 percent to 20 percent of the total weight of the resin solids in the composition.

9. The coating composition of claim 1 wherein said chromium-containing pigment is present in a weight ratio with respect to the total weight of said polyepoxide and aminoplast or phenoplast crosslinking agent of about 0.1:1 to 0.6:1.

10. The coating composition of claim 8 wherein said chromium-containing pigment is present in a weight ratio with respect to the total weight of said polyepoxide and aminoplast, phenoplast or blocked isocyanate crosslinking agent of about 0.2:1 to 0.5:1.

11. The coating composition of claim 10 wherein said chromium-containing pigment is a chromate pigment.

12. The coating composition of claim 2 wherein said clay has an anion-exchange capacity of at least about 10 milliequivalents per 100 grams of clay.

13. The coating composition of claim 2 wherein said clay is present in a weight ratio with respect to the total weight of said polyepoxide and aminoplast, phenoplast or blocked isocyanate crosslinking agent of about 0.1:1 to 1:1.

14. The coating composition of claim 2 wherein said clay is present in a weight ratio with respect to the total weight of said polyepoxide and aminoplast, phenoplast or blocked isocyanate crosslinking agent of about 0.3:1 to 0.8:1.
24a

15. A method of protecting a metal substrate comprising applying thereto the coating composition of claim 1 to form a first layer and then overcoating with a pigmented, corrosion and abrasion resistant, thermosetting organic solvent solution coating composition comprising (a) from about 20 to 90 percent by weight, based on the weight of resin solids, of a resinous polyhydric alcohol; (b) from about 10 to 80 percent of a polyisocyanate; and (c) a chromium-containing pigment providing resistance to corrosion to form a second layer.

16. The method of claim 15 wherein said polyisocyanate is a blocked isocyanate.

17. The method of claim 15 further including a clay having the ability to fix phosphate.

18. The method of claim 15 wherein said chromium-containing pigment is present in a weight ratio with respect to the total weight of said polyhydric alcohol of about 0.1:1 to 0.6:1.

19. The method of claim 15 wherein said chromium-containing pigment is present in a weight ratio with respect to the total weight of said polyhydric alcohol of about 0.2:1 to 0.5:1.

20. The method of claim 15 wherein said chromium containing pigment is a chromate pigment.

21. The method of claim 17 further including a clay having an anion-exchange capacity of at least about 10 milliequivalents per 100 grams of clay.

22. The method of claim 15 in which the total thickness of the first layer and the second layer is least about 0,7 mils.

23. The method of claim 22 wherein the first layer has a thickness of at least about 0.1 mils and the second layer has a thickness of at least about 0.6 mils.

24,. The method of claim 15 further including the steps of baking the coating compositions to thermoset the same, and applying a fluorine polymer-containing coating as a topcoat.

25. A method of claim 24 in which the total thickness of the first layer, the second layer and the topcoat is at least about 1.4 mils.