AU472995B2 - Coating composition, coated metal, and coating including electrocoated top-coatings - Google Patents

Description

621 n2 Background of the Invention

Chromic acid and pulverulent metal in a liquid medium

have heretofore been applied to metal substrates followed

by baking to attain a corrosion-resistant coating, such as disclosed in U.S. Patent Application, Serial No. 96,967.

Such compositions are typically dispersions of pulverulent

metal powder or metal flake in water or t-butanol and

resulting coatings offer corrosion resistance and electrocon-

ductivity to coated substrates.

Working with such systems depending primarily upon t-butar

can present a fire hazard whereas working in such systems

that are essentially aqueous media, and especially where

the pulverulent metal is supplied in flake form, can provide

problems in achieving a resulting coated substrate wherein

the coating displays excellent uniformity and adhesion. It is difficult to upgrade such characteristics without deleteriot

effect on other coating characteristics plus coating bath

stability.

472.99

621 n2 Compositions of typically aluminum flake, a polymeric

glycol plus a wetting agent have been taught in U.S. Patent

No. 3,318,716 as useful anti-foaming compositions in paste

or liquid form. They may be used to supply pigmentation to

coating compositions but do not ostensibly lend particular

advantages to resulting coatings except as attributed to the

metal flake component.

The compositions containing aluminum flake provide a

barrier coating or film on the underlying substrate. This

barrier coating provides an essentially inert metallic flake

that resists attack, such as from mild alkali, and thus

protects the underlying substrate metal, through the mechanism

of its generally inert nature. On the other hand, compositions

containing zinc flake, and which compositions are of particular

interest herein, provide a coating that under attack sacrifices

the coating in place of, and thereby protects the underlying

metal. Such action typically provides protection through

galvanic action.

Summary of the Invention

A coating composition for metals has now been found

that offers excellent coating uniformity on the coated substrate.

Resulting coatings exhibit augmented adhesion and desirable

color and non-staining characteristics. The coating uniformity

extends to non-tearing, a particular problem of prior aqueous

medium compositions that is exhibited by variations in coating

uniformity resulting when parts removed from a coating bath

drained unevenly leaving excessive coating composition build-

up where the drainage was greatest.

Such coating characteristics have been obtained without

sacrifice to coating bath stability, including retention of

472,995 n 621 72 pulverulent metal flake inertness in the bath as well as excellent dispersion in the coating bath. In addition to providing coatings of excellent protective value, and includii augmented resistance to mild alkali, such coatings exhibit electroconductivity, for subsequent weldability or application of electrocoat paint. Resulting electrocoated substrates exhibit highly desirable corrosion resistance and overall coating adhesion, of primer to the metal substri and of electrocoat paint to primer.

Broadly, the present invention is directed to an aqueous

coating composition for appliction to, and curing on, a metal

Ssubstrate, thereby preparing an adherent, water insoluble,

alkali and corrosion resistant coating on said substrate,

which composition before curing comprises an intimate mixture

in aqueous liquid medium of: a hexavalent-chromium- providing substance, supplied by at least about- 80 weight

percent chromic acid and providing not in excess of aboue 100 grams per liter of chromium, expressed as CrO 3 not substantially above about 500 grams per liter of liquid mediun

of pulverulent metal selected from the group consisting of

zinc, aluminum, mixtures thereof and alloys of same, said

composition having a weight ratio of chromium, expressed as

Cr0 3 to pulverulent metal of between abeut 1:1 and 1:15;

between about 5--9 volume percent, based on the volume

of the total liquid of the aqueous composition, of water-

dispersible organic liquid that is a high boiling organic

compound of carbon, oxygen, and hydrogen having one or more

oxygen-containing constituents selected from the group

consisiting of hydroxyl, oxo, low molecular weight ether,

and mixtures thereof, such compound having a boiling point above 100° C. at atmospheric pressure; and, above about-

A 472.995

621 n2 0.0005 volume percent, basis total volume of such coating

composition, of surface active agent.

In addition, the present invention relates to a coated

metal substrate, and the preparation of such a substrate,

exhibiting the above described adherent, alkali and corrosion

resistant coating. It is further directed to the preparation

of weldable substrates, to welded articles, to electrocoat

painted substrates, and to electrocoat painted, welded metal

assemblies.

The metal substrates contemplated by the present invention

are exemplified by the metal substrates to which a chromic

acid plus pulverulent metal in a liquid coating may or can

be applied for enhancing corrosion resistance of such

substrate metals. For example, such metal substrates may be

aluminum and its alloys, zinc and its alloys, copper and

cupriferous, brass and bronze. Additionally, exemplary

metal substrates include cadmium, titanium, nickel, and its

alloys, tin, lead, chromium, magnesium and alloys thereof, and

for weldability, preferably a ferrous metal substrate such as

iron, stainless steel, or steel such as cold rolled steel or

hot rolled and pickled steel. All of these for convenience

are usually referred to herein simply as the "substrate".

For convenience, the hexavalent-chromium-containing aqueous

coating composition is often referred to herein as the "treating

composition" or "primer" or "base coating" and the "residue"

on a metal surface is such resulting surface condition obtained

after application of such composition to, and heating resulting

applied composition on, a metal substrate. Also for convenience,

the high boiling organic compound is often termed herein as

the "high boiling hydrocarbon" or just the "hydrocarbon".

472,995

621n72 Description of the Preferred Embodiments

The corrosion-resistant, hexavalent-chromium-containing

primer composition contains chromic acid as the hexavalent-

chromium-providing substance or its equivalent in aqueous med- ium, for example, chromium trioxide or chromic trioxide or

chromic acid anhydride. But a minor amount, 20 percent or less, of such chromium can be supplied by a salt such as

ammonium dichromate, or by sodium or potassium salts, or by substances such as calcium, barium, magnesium, zinc, cadmium, and strontium dichromate. Additionally, a minor amount such as 20 percent or less of the hexavalent-chromium-providing

substance might be a mixed chromium compound, include trivalent chromium compounds. Although the aqueous composit- ion might contain only.a small amount, 5 grams per liter of hexavalent chromium, expressed as CrO and may contain as 3

much as about 100 grams per liter of. composition of hexavalent

e 472.995

621/12 of such total liquid and advantageously for best economy, as

will as enhanced coating characteristics, supplies preferably

above about 10 volume percent, and typically between about

to about 35 volume percent of such total liquid. It is most

important that this high boiling organic compound have a boil-

ing point at atmospheric pressure above 100°C.

Since for economy and efficiency water supplies such a

large amount of the aqueous composition liquid medium, and

since the high boiling hydroarbon)is a critical ingredient in

the formation of the resulting coating, it is necessary for

such hydrocarbon)to boil higher than the water boiling point.

The .docarbon should also be easily dispersible in water and

preferably soluble in water. Yet, it must not be highly toxic

to avoid uneconomical expense in handling and use. Such),hdrocarbns as' are serviceable -in he present in- vention are also those that are retained during baking on the metal substrate in sufficient amount and duration to permit participation of the hydrooarbenin the formation of a coating. This participation is best exemplified by such characteristics as reduction of chromium in the coating from hexavalent to the

trivalent state, most desirable leafing into a layered, sub-

stantially uniform coating of the metallic flake as well as characteristics of the resultant coating, for example as exhib-

ited from mild alkali resistance testing. The organic com-

pounds contain carbon, oxygen and hydrogen and have at least

one oxygen-containing constituent that may be hydroxyl, or oxo,.

or a low molecular weight ether group, a C 1 -C6 ether

group. Since water dispersibility and preferably water sol-

ubility is sought, polymeric hydroea-rbens,)?are not particularly

suitable and advantageously serviceable) hydrocarbons-contain

472.995

621n2 less than about 15 carbon atoms. Particularhydrooarbens which can or have been used include di- and tripropylene gly-

col, the monomethyl, dimethy, and ethyl ethers of these gly-

cols, as well as diacetone alcohol, the low molecular weight

ether of diethylene glycol, and mixtures of the foregoing.

472.995

621/72 The pulverulent metal flake, zinc flake or aluminum

flake, or mixtures of such flakes, but preferably/for galvanic

protection and coatability, are most typically such pulverulent

metals having a thickness on the order of 0.1-0.3 micron and

most typically a size in the longest dimension of not substan-

tially above about 15 microns. Aluminum flake, also sometimes

termed leafing aluminum pigment has been discussed, for example,

in U.S. Patent 2,312,088. Flake may be blended with pulverulent

metal powder, but typically in only minor amounts of the powder,

and such powder should have particle size so that all particles

pass 100 mesh and a major amount pass 325 mesh ("Mesh" is used

herein as U.S. Standard Sieve Series). The powders are generally

spherical as opposed to the leafing characteristic of the flake.

The coating composition, should be made up with an amount

of pulverulent metal sufficient to supply not substantially

above about 500 grams of metal per liter of coating composition

liquid medium. The presence of greater than about 500 grams

per liter of pulverulent metal flake is undesirable, for example,

can add expense without a significant increase in protection for

the coated substrate. Preferably, for economy and desirably

coating characteristic, the composition contains between

about 50-350 grams of metal per liter.

Also, for such primer coating compositions, the chromium,

expressed as Cr0 3 should not exceed more than about 100 grams

per liter of composition medium. Greater than about 100 grams

per liter of chromium is uneconomical and can deleteriously

detract from the characteristics of the coated metal surface,

for example, the most desirable corrosion resistance for the

coated metal substrate. Further, such composition should

have a weight ratio of chromium expressed as CrO 3 to metal

flake of at least about 1:15. 47 9 47,9

62 1 2 A ratio of less than about 1:15 may not provide sufficient

chromium in the coating to achieve augmented bonding of the

pulverulent metal to the metal substrate. A ratio of as

great as about 1:1 may be achieved, but should preferably be

at metal concentrations of less than about 100 grams per liter.

As the metal content approaches about 500 grams per liter and

thus the chromium content can approach about 100 grams per

liter the upper weight ratio of chromium, expressed as Cr0 3 to pulverulent metal approaches 1:5. These coating composition

are virtually always made as very concentrated coating compo-

sitions and have particular utility in the coating of small

parts as opposed to application to large substrate areas such

as metal coils.

The coating ingredients may be combined into separate

packages, a two package system with one containing the

hexavalent-chromium-providing substance in aqeuous medium,

and the other package being a water-free dispersion in high boiling hdroerbo ofpulverulent metal; each package may additionally contain some surface active agent, or it may all b

in the package with the metal. Such separate packages are then

mixed before application to the metal substrate.

Such coating.compositions may be applied to the metal

substrate by any conventional method for coating a substrate

with a liquid, for example, dip coating, roller coating or

reverse roller coating, or combinations of techniques as, for

example, spray and brush techniques. Typically the composition

is applied by simply dipping the article into the composition.

The metal surface can be a preheated metal surface to assist

in the curing of the composition, or the coating composition

may be applied from a heated bath, for example, one heated up

to 2000 F. The coating composition should contain some, and

472.99

621 72

generally contains up to, for example, about 0.05 volume

percent, basis total composition liquid, of a surface active

agent. Such agent may be present in as little as 0.0005 volume

percent, also on a total liquid basis. The preferred agents

for effecting pulverulent metal dispersibility are polyethoxy

adducts, exemplified by the alkylphenoxypolyethoxyalkanols,

and derivatives thereof, some of which are described in U.S.

Patent 3,281,475. Such agents are nonionic and have between

about 7 and 50 oxyethylene units in the molecule. Advantageously,

for best dispersibility the agent is present in the coating

composition in an amount between about 0.001-0.02 volume percent,

on a total liquid basis. The resulting primer coating weights

on the metal substrate may vary to a considerable degree but,

exclusive of the metal flake the residue will most typically

always be present in an amount supplying above about 5 milli-

grams per square foot of chromium, expressed as chromium and

not CrO 3 Furthermore, residues containing below about

milligrams per square foot of chromium, expressed as chromium

and not CrO 3 should be topcoated to impart significant enhance-

ment in corrosion resistance of the coated substrate. Also if

the coated metal substrate is to be subsequently formed, the

residue should contain not substantially above about 150

milligrams per square foot of chromium as the coating may be

subjected to cracking or crazing during forming operation,

although for typically finished products when subsequent

forming is not contemplated, and extended corrosion resistance

without topcoating may be desirable, such residue may contain up

to about 500 milligrams per square foot of chromium.

A subsequent paint topcoating is also a consideration

for the amount of pulverulent metal that should be present

on the surface of the substrate in the coating residue. Such

11 472.995

621 n2 residues containing about 10-20 milligrams per square foot of

pulverulent metal are virtually always topcoated. However,

subsequently topcoated residues can contain substantially

more pulverulent metal, 600-700 milligrams per square

foot of such metal, and the substrate may contain up to about

5,000 milligrams per square foot of pulverulent metal, whereas

an excess of that amount is usually uneconomical.

It can be appreciated that the primers are compositions

providing coatings wherein there is an excess of pulverulent

metal to chromium, even at the lesser concentrations of the

metal. Generally, the coating should have a weight ratio of

chromium, expressed as chromium and not Cr0 3 to pulverulent

metal of less than about 0.5:1, and, such ratio is most usually

for the less heavy coating weights, since as the coating weights

approach, for example, 5,000 milligrams per square foot of

pulverulent metal, the weight ratio of chromium to pulverulent

metal will be less than about 0.2:1. It has also been found

that for coating small parts, parts adapted for individual

dipping in a coating bath, which can be final products that

will not be normally subjected to subsequent forming, and where

coating weights may approach 5,000 milligrams per square foot

of pulverulent metal, the weight ratio of chromium to pulveruler

metal in the coating may be as low as about 0.02:1.

Other compounds may be present in the hexavalent-chromium-

containing liquid compositions but, even in combination, are

present in very minor amounts so as not to deleteriously affect

the coating integrity, with respect to electroconductivity

and galvanic protection. Thus, such compositions should be

substantially resin-free and can be substantially pigment free,

i.e. contain little, if any, pigment or resin such as 10 grams

per liter total of both or less and should preferably be

12 472.995

621n2 resin free. Also, since the adherence for the particulate metal

to the metal substrate is achieved by the chromiu-providing-

substance ostensible through the interaction of such substance

with the high boiling hydreaT-B&during baking, such coating

compositions need not contain resin, and such coatings that

will be subsequently topcoated are virtually always pigment-

free.

These other compounds further include inorganic salts

and acids as well as organic substances, often typically

employed in the metal coating art for imparting some corrosion

resistance or enhancement in corrosion resistance for metal

surfaces. Such materials include zinc chloride, magnesium

chloride, various chromates, e.g. strontium chromate, molybdates,.

glutamic acid, succinic acid, zinc nitrate, and succinimide

and these are all preferably avoided, but if present, are

most usually employed in the liquid composition in a total

maximum amount of less than 5 grams per liter.

For theeta- substrates containing applied liquid compo-

sition and pulverulent metal, the preferred temperature for

the subsequent heating, which is also often referred to as

curing and which may be preceded by drying such as air drying,

is within the range from about 400* F. but more typically

from about 4500 F. at a pressure of 760 mm. Hg up to not

essentially above about 1,0000 F. Such an elevated substrate

temperature may be attained by preheating the metal prior to

application of the liquid composition. However, such curing

temperatures do not often exceed a temperature within the 0 range of about 4500 F-700 F. At the elevated curing tempera-

tures the heating can be carried out in as rapidly as about

0.2 second or less but is often conducted for several minutes

at a reduced temperature.

472,995

621 n2 The electrodeposition of film-forming materials, i.e., electrocoating, of the applied primers on the metal substrate

can include electrocoating of simply a film-forming material

in a bath or such a bath which may contain one or more pigments

metallic particles, drying oils, dyes, extenders, and the like,

and the bath may be a dispersion or ostensible solution and

the like. Some of the well known resinous materials useful as

film-forming materials include the polyester resins, alkyd

resins, acrylate resins, hydrocarbon resins, and epoxy resins,

and such materials can be reacted with other organic monomers

and/or polymers including hydrocarbons such as ethylene glycol,

monohydric alcohols, ethers, and ketones.

Of particular interest are polycarboxylic acid resins

which can be solubilized with polyfunctional amino compounds

and include the siccative oil-modified polybasic acids, esters or anhydrides which can be further reacted with divinyl benzene

for example or acrylic acid and esters as well as polymerizable

vinyl monomers. Such mention of suitable baths for electro- deposition is made herein by way of example and should not be

construed as limiting. More exhaustive discussions of such film-forming systems have been set forth, for example, in U.S. Patents 3,304,250 and 3,455,805.

Also, substances of particular interest, for example in the automotive industry, are the anodically deposited film- forming materials which have gained considerable acceptance in

this field and are exemplified by U.S. Patent 3,230,162. However, the broad scope to which the electrodeposition of

film-fonring materials relates, includes the deposition of

such materials on anodic or cathodic substrates, and by means

of various techniques for passage of current through a bath,

including even intermittent pulsed current. After electro- deposition -and removal of the coated substrate from the bath, 14 472.995

62 1 n curing of the film-forming materials is performed. The time

and temperature of curing will be dependent upon the film-

forming materials present, but is typically an air cure at

room temperature or a forced cure at a temperature up to 500F.

and for times up to 60-minutes, at more reduced temperatures.

Before starting the treatment of the present invention it

is, in most cases advisable to remove foreign matter from the

metal surface by thoroughly cleaning and de-greasing. De-

greasing may be accomplished with known agents, for instance,

with agents containing sodium metasilicate, caustic soda, car-

bon tetrachloride, trichlorethylene, and the like. Commercial

alkaline cleaning compositions which combine washing and mild

abrasive treatments can be employed for cleaning, an

aqueous trisodium phosphate-sodium hydroxide cleaning solution.

In addition to cleaning, the substrate may undergo cleaning

plus etching.

After heating, the resulting primer coated substrate, or

primer plus electrocoated substrate, of the present invention

can be further topcoated with any suitable paint, i.e. a paint,

primer, including weldable primers such as the zincrich prim-

ers that can be applied before, typically, electrical resis-

tance welding, and paints such as enamel, varnish or lacquer.

Since the coated metal surfaces of the present invention can

exhibit a desirable upgrading in topcoat adhesion when com-

pared, for example, to the uncoated substrate metal, paints

are often applied over such coated substrates. Such paints

may contain pigment in a binder or can be unpigmented, e.g.,

generally cellulose lacquers, rosin varnishes, and oleoresin-

ous varnishes, as for example tung oil varnish. The paints

can be solvent reduced or they may be water reduced, e.g.,

1o 472.,995

621n72 latex or water-soluble resins, including modified or soluble alkyds, or the paints can have reactive solvents such as in the polyesters or polyurethanes. Additional suitable paints which can be used include oil paints, including phenolic

16 472,995

621n2 resin paints, solvent-reduced alkyds, epoxys, acrylics, vinyl,

including polyvinyl butyral and oil-wax-type coatings such as

linseed oil--paraffin wax paints. The paints may be applied

as mill finishes.

The weldability of coated substrates if of particular

interest in regard to electrical resistance welding that can

be exemplified by electrical resistance spot welding wherein

opposing electrodes are closed against weldable substrates

maintained for welding within the gap between the electrodes.

For this spot welding the opposing electrodes are closed onto

the substrate to be welded under pressure, for example of 500

-600 pounds, and for a weld heat that is measured in amp-seconds.

Also of particular interest is the application of the coating

composition to weldable metal studs that are typically solid,

cylindrical metallic articles having a length of a few inches

or less and are used in a welding gun for electrically resis-

tance welding to a metal substrate. The coatings of the present

invention on the surface of these steels, in addition to

providing the other coating characteristics, offer reduced

sputtering during welding that can be a problem at the weld

when studs are used that have a galvanized protective surface

coating.

The following examples show ways in which the invention

has been practiced but should not be construed as limiting

the invention. In the examples the following procedures have

been employed:

Preparation of Test Parts

Test parts are typically prepared for subsequent treatment

by immersing in water which has incorporated therein

ounces of cleaning solution per gallon of water. The cleaning

solution is typically 75% by weight of potassium hydroxide and

17 472.995

621 n2 weight percent tripotassium phosphate. The bath is maintain< at a temperature of about 150°-180° F. After the cleaning treatment the panels are rinsed with warm water and dried.

Application of Coating to Test Parts and Coating Weight.

Clean parts are typically coated by placing in a wire

basket and dipping the basket into coating composition, removinc the basket and draining excess composition therefrom with a

mild shaking action and then immediately baking or air drying

at room temperature until the coating is dry to the touch

and then baking, .the parts being usually placed on a sheet for

baking. Baking proceeds under infrared lamps at a substrate

temperature of about 450 0 F unless otherwise specified, for a

time up to one minute, also unless othenrwise specified.

Coating weights for parts, generally expressed as a

weight per unit of surface area, are determined by selecting

a random sampling of parts of a known surface area and weighing

the sample before coating. After the sample has been coated, it is reweighed and the coating weight per selected unit of

surface area, most always presented as milligrams per square

foot (mgms./sq.ft.), is arrived at by straightforward calculatio

Corrosion Resistance Test (ASTM B-117-64) and Rating

Corrosion resistance of coated parts is measured by means

of the standard salt spray (fog) test for paints and varnishes

ASTM B-117-64. In this test, the parts are placed in a chamber

kept at constant temperature where they are exposed to a fine

spray (fog) of a 5% salt solution for specified periods of

time, rinsed in water and dried. The extent of corrosion on the test parts are then compared one with the other by visual

inspection.

472.995

621 n2 In the following examples the efficacy of the corrosion

resistance obtained on coated parts is, in part, quantatively

evaluated on a numerical scale from 0 to 10. The parts are

visually inspected and compared with one another and the system

is used for convenience in the reviewing of results. In the

rating system the following numbers are used to cover the following results: retention of film integrity, no red rust; initial coating degradation, pinpoints of red rust; less than 3% red rust basis total surface area of the part; 3 to 10% red rust, a significant amount of rust; 10 to 25 percent surface area red rust; greater than 25 percent red rust.

EXAMPLE 1

Sufficient zinc flake having particle thickness of about

0.1-0.2 micron and a longest dimension of discrete particles

of about 15 microns is dispersed in diethylene glycol monoethyl

ether (DGME) together with 3 milliliters (mls.) of wetter

which is a nonionic, modified polyethoxy adduct having a

viscosity in centipoises at 25°C. of 180 and a density at

of 8.7 pounds per gallon, to provide in a final mixed dispersion

300 grams per liter of the zinc flake plus 250 milliliters

per liter of the D.G.M.E. Separately there is

added to deionized water sufficient chromic acid to provide

of Cr0 3 in the final mixture.

The chromic acid solution is slowly added to the metal

flake dispersion to form the final mixture. During the

addition, a slight evolution of heat is observed and some

surface foam is formed which is removed by skimming. An

additional blend is prepared in the same manner but the blend

contains 250 mls./l. of tripropylene glycol monomethyl ether

(TGME) in place of the DGME and only 2 mls. of wetter.

19 472.995

621 n2 Each bath is used to coat ten grade 8 bolts which are 1-1/16 inches long by about 1/4 inch in diameter at the threadc

end and have 7/8 inch of threading on the shaft topped by a

5/8 inch smooth shaft section that terminates in the bolt head. Also, each bath is used to coat ten No. 10-A clips,

sometimes referred to as "speed clips", that are formed by doubling over an about 0.5 inch by 1.75 inch strip of thin sheet metal to provide a clip type configuration when viewed on edge, followed by punching a hole through the doubled config ration and leaving opposing, outwardly extending flanges around one outer clip section of the hole. These parts are coated as described above and the coating cured for 6-12 minutes at 0 475 F. On analysis, as described above, the bolts are cal-

culated to average 1,135 rgms./sq.ft. of coating from the DGME bath and 1,370 mgms./ sq.ft. from the TGME bath.

Five Grade 8 bolts and five speed clips are then coated with a black-pigment electrocoat primer containing at first of non-volatiles which before use is reduced with deionized water in the proportion of one part by volume paint to three parts by volume water. Parts are immersed in the electrocoat

paint bath as anodes and paint is applied for 30 seconds at volts. Following removal from the electrocoating bath, all parts are baked for 20 minutes at 425 0 F. On analysis, as described above, the bolts are calculated to average 1,025 mgms. sq.ft. of coating for the bolts having the DGME primer and

1,240 mgms./sq.ft. for bolts with the TGME primer.

The parts are subjected to the above described corrosion

resistance salt spray test and results of such testing are shown in the table below. In the table below the test results

are reported on the scale hereinabove described.

20 472,995

621 R2

%D 0

N- 14 0 w 'U 0

CD 0l $4 ~1 CD

0 '4 41 4

o 54 0 0

V) eU 0l0 0 4

472.9

621 R2 The above results demonstrate the excellent corrosion

resistance that can be obtained on small parts where the coati

composition employs either the diethylene glycol monoethyl ett

or the tripropylene glycol imonomethyl ether. Such showing is made for those parts coated with the primer alone as well as

for those subsequently electrocoated. As is evident from thes

results, the clips present a challenging problem in coating,

but baths of the present invention can nevertheless achieve

excellent results, as shown by the TGINE bath, and for a greatl

extended duration of testing.

EXAMPLE 2

Various coating compositions are prepared in the nanner o

Example 1 and using 300 grams per liter in each composition of

the zinc flake described in Example 1. Each composition also

contains 5 milliliters of the Example 1 wetter and contains a

concentration of chronic acid as shown in Table 2 below. Also as shown in the Table below, the compositions contain various

amounts of organic compound. The first four compositions

containing diethylene glycol monoethyl ether (MEE) and composi

5-8 contain diethylene glycol rmonomethyl ether (MME).

The baths identified in the Table below as Nos. 3,4,7 and

8 are aged one day prior to use. Bath No. 8 is very viscous

prior to use but is readily mixed to a smooth consistency. Bal No. 7 is smooth and viscous without noticeable viscosity chang(

during the one day ageing. Bath No. 3 has a lower viscosity

than 4 and both stir up very readily.

Each bath is used to coat both Grade 8 bolts and No.

clips, as have been described in Example 1 and the coated partc

are cured as described in Example 1 for curing times up to 14

minutes at a temperature of 475*F. With reference again to

22 472.9

621ln2 baths 3, 4, 7 and 8, the adhesion for the cured coating on the

parts is rated as good except for the adhesion on the parts

coated in bath No. 8 where it does not exhibit the good coating

adhesion of the other baths. Such adhesion is determined simply

by holding the part firmly in the hand and scratching with a

thumbnail and comparing many parts under such scratch test.

The coating appearance for all such parts from the baths is

metallic.

Coating weights per bolt for coatings obtained from each

bath are determined, in the manner described hereinbefore,

based upon a five bolt sample from each bath and the results

are reported in Table 2 below. Also shown in the Table below

are the results of salt spray testing for all coated parts, both

the bolts and the clips.

Representative primer coated test parts are then electro-

coated with the electrocoat primer described in Example 1,

except such primer has a gray, rather than black appearance

and the paint is applied at 80 volts for 30 seconds. Coated

parts are cured as described in Example 1, and electrocoating

paint weights for the bolts are then determined, in the manner

hereinbefore discussed, for each coating and the results are

reported in Table 2 below.

4.72.995

4-LU H~0 0 0 0> 0 a 0> to

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CL'

.d 0 0. 0b L 0, 0 0, 0 4J ri4 1-4 H- q H H- H H

0.

0 rcd'l 0 0 0~ 0 b 0 H H I H H

4 4

4 4. 1.41) 4 4J. 0 0 0 r4

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0 N n I 0 0Ln C 0 CD 0 H 4J oo r- H 0 I A m 0 0 rzz wAQ. (4N O 1 H 1 H H- 44 f-4 4.4 0

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o

472 995

62 1 2 The above results show excellent, virtually consistent

corrosion resistance, at a lengthy test duration of 96 hours

for electropainted parts and 168 hours for primer coated

parts, with all small parts having a considerable range in the

weight of bath coatings on the parts. The corrosion resistance

under the salt spray testing has been rated in accordance

with the manner hereinbefore discussed, and both types of

parts, including the hard to coat clips, can consistently

achieve the highest possible rating.

47 2995

621 R2 THE CLAIMS DEFINING THE INVENTION ARE AAS FOLLOWS:

1. aqueous coating composition for application to,

and curing on, a metal substrate, thereby preparing an adherent,

water insoluble, alkali and corrosion resistant coating on

said substrate, which composition before curing comprises an

intimate mixture in aqueous liquid medium of:

a hexavalent-chromium-providing substance, supplied

by at least about 80 weight percent chromic acid and providing

not in excess of abe*-t 100 grams per liter of chromium, expresse

as Cr0 3 not substantially above abeut 500 grams per liter

of liquid medium of pulverulent metal selected from the group

consisting of zinc, aluminum, mixtures thereof and alloys of

same, said composition having a weight ratio of chromium,

expressed as Cr0 3 to pulverulent metal of between a4Gut 1:1

and 1:15;

between about &-50/volume percent, based on the

volume of the total liquid of the aqueous compositon, of

water-dispersible organic liquid that is a high boiling organic

compound-of carbon, oxygen and hydrogen having one or more

oxygen-containing constituents selected from the group

consisting of hydroxyl, oxo, low molecular weight ether, and

mixtures thereof, said compound having a boiling point above

100*C. at atmospheric pressure; and,

above about 0.0005 volume percent, basis total

volume of said coating composition, of surface active agent.

26 472.995

621 n 2 2. The coating composition of Claim 1 wherein the

ingredients are combined into two separate liquid mediums, one.

of which contains said component and the other contains

all of said pulverulent metal and at least the major amount of

said component.

3. The coating composition of claim 1 wherein said

organic compound is water soluble and is selected from the

group consisting of di-, and tripropylene glycol, the low

molecular weight ethers thereof, diacetone alcohol, the

low molecular weight ethers of diethylene glycol, and mixtures

of the foregoing.

4. The coating composition of Claim 1 wherein said

chromium-providing substance supplies not substantially above

abeot 60 grams per liter of chromium, expressed as CrO 3 said

pulverulent metal is present in an amount below-about 500 grams

per liter, and said composition has a weight ratio of chromium,

expressed as Cr0 3 to pulverulent metal of between betit

and 1:9.

The coating composition of Claim 1 wherein said

pulverulent metal is zinc flake and said surface active agent

is a nonionic organic liquid.

6. A coated metal substrate having on the surface thereof

an adherent alkali and corrosion resistant water-insoluble

coating, which coating comprises not substantially above abete-

5,000 milligrams per square foot of coated substrate of

pulverulent metal selected from the group consisting of zinc,

aluminum, mixtures thereof, and alloys of same in intimate

mixture with the residue from a hexavalent-chromium-containing

27 472.995

621 R2 aqueous coating composition containing a hexavalent-chromium- /o providing substance, between about ~ovol)e percent; basis total composition liquid, of water-dispersible, high boiling

organic compound in said aqueous liquid medium, and above

about 0.0005 volume percent, same basis, of surface active

agent, with the organic compound of said liquid being composed

of carbon, oxygen and hydrogen and having one or more oxygen-

containing constituents selected from the group consisting of

hydroxyl, oxo, low molecular weight ether, and mixtures

thereof, said compound having a boiling point above 1000 C. at

atmospheric pressure, and said coating composition providing

said residue with not above about 500 milligrams per square

foot of coated substrate of chromium, wherein said coating

contains a weight ratio of chromium, as chromium, to pulverulen

metal of not substantially above about 0.5:1, and said residue

is obtained by applying to said metal surface said hexavalent-

chromium-containing composition and heating said substrate at

a temperature, and for a period of time, sufficient to vaporize

volatile substituents from said coating composition and deposit

on said surface said residue.

7. The coated metal substrate of Claim 6 wherein said

residue is the residue remaining after heating applied coating

at a temperature above about 400 0 F. and for a time of at

least about 0.2 second.

8. The method of preparing a coated metal substrate

having on the surface thereof an adherent, alkali and corrosion

resistant, water insoluble coating, which method comprises:

applying to said surface a hexavalent-chromium- containing aqueous coating composition of hexavalent-chromiun-

providing substance, supplied by at least about 80 weight

28 47299

6 2 1 n2 percent chromic acid, said composition containing above abo.t-

0.0005 volume percent, basis total composition liquid, of /o SO surface active agent and between aett-t 5- volume percent,

same basis, of water-dispersible organic liquid that is a high

boiling organic compound of carbon, oxygen and hydrogen having

one or more oxygen-containing constitutents selected from the

group consisting of hydroxyl, oxo, low molecular weight ether,

and mixtures thereof, said compound having a boiling point above

100 0 C. at atmospheric pressure, said composition being applied

in an amount sufficient to provide not above aboet 500 milligrams

per square foot of coated substrate of chromium, said composition

also containing pulverulent metal selected from the group

consisting of zinc, aluminum, mixtures thereof, and alloys of

same in sufficient amount to provide not substantially above

about 5,000 milligrams per square foot of coated substrate of

said pulverulent metal and to provide said coating with a

weight ratio of chromium, as chromium to pulverulent metal of

(not substantially above abhet 0.5:1, and

heating said substrate at a temperature, and for a

period of time, sufficient to vaporize volatile substituents

from said aqueous coating composition and deposit on said

surface said coating.

9. The method of Claim 8 wherein said substrate is heated

at a substrate temperature above about 400°F and for a time

of at least aIeut 0.2 second.

29 472.995

621n2 The method of Claim 9 wherein said aqueous coating

composition is applied to said surface in an amount sufficient

to provide from abetI 10 to about 200 milligrams per square

foot of said pulverulent metal, said aqueous coating compositioi

further providing from about 5 to about 15 milligrams per

square foot of chromium, and said coated metal substrate' is

subsequently topcoated.

11. The method of preparing a weldable substrate for

electrical resistance welding and having desirable corrosion

and alkali resistance, which method comprises:

establishing on the surface of said substrate, on

at least a portion thereof where welding will take place, not

substantially above aboue 5,000 milligrams per square foot

of coated substrate of pulverulent metal selected from the

group consisting of zinc, aluminum, mixtures thereof, and

alloys of same in intimate mixture with the residue from a

hexavalent-chromium-containing aqueous coating composition

containing a hexavalent-chromium-providing substance between S-6_o abeout 5 volume percent, basis total composition liquid,

of water-dispersible, high boiling organic compound in said

a4eus 4 liquid medium, and above about 0.0005 volume percent, same basis, of surface active agent with the organic compound

of said liquid being composed of carbon, oxygen, and hydrogen,

and having one or more oxygen-containing constituents selected

from the group consisting of hydroxyl, oxo, low molecular

weight ether, and mixtures thereof, said compound having a

boiling point above 100 0 C. at atmospheric pressure, and said

coating composition providing said residue with not above

about 500 milligrams per square foot of coated substrate of

chromium, wherein said coating contains a weight ratio of

chromium, as chromium to pulverulent metal of between about

1:1 and 1:15 30 47 29

621n72 heating said substrate at a temperature, and for

a period of time, sufficient to vaporize volatile substituents

from said coating composition and deposit on said surface a

composition residue and pulverulent metal, thereby preparing

said substrate for welding with a coating providing corrosion

resistance and weldable electroconductivity.

12. The method of Claim 11 wherein said substrate is

heated at a temperature in excess of about 400°F. and for a

time of at least about 0.2 second.

13. A weldable metal substrate prepared for electrical

resistance welding according to the method of Claim 11.

14. The weldable metal substrate of Claim 13 wherein

said substrate prepared for electrical resistant welding is

the substrate of a metallic stud.

The method of electrical resistance welding metallic

articles which comprises:

establishing on the surface of said substrate, on

at least a portion thereof where welding will take place, not

substantially above about 5,000 milligrams per square foot

of coated substrate of pulverulent metal selected from the

group consisting of zinc, aluminum, mixtures thereof, and

alloys of same in intimate mixture with the residue from a

hexavalent-chromium-containing aqueous coating composition

containing/a hexavalent-chronium-providing substance between

about 5-&volume percent, basis total composition liquid,

of water-dispersible, high boiling organic compound in said

aqueous liquid medium, and above abe~t 0.0005 volume percent,

same basis, of surface active agent with the organic compound

472.995

621 2 of said liquid being composed of carbon, oxygen, and hydrogen,

and having one or more oxygen-containing constituents selected

from the group consisting of hydroxyl, oxo, low molecular

weight ether, and mixtures thereof, said compound having a

boiling point above 1000C. at atmospheric pressure, and said

coating composition providing said residue with not above abet

500 milligrams per square foot of coated substrate of chromium,

wherein said coating contains a weight ratio of chromium, as chromium, to pulverulent metal ofnot substantially above

about 0.5:1, and said residue is obtained by applying to said

metal surface said hexavalent-chromium-containing composition

and heating said substrate at a temperature, and for a period

of time, sufficient to vaporize volatile substituents from

said coating composition and deposit on said surface said

residue.

heating said substrate at a temperature and for a

period of time sufficient to vaporize volatile substituents

from said coating composition.and deposit on said surface a

substantially water insoluble and resin-free coating of said

residue and pulverulent metal, said coating providing corrosion

resistance and weldable electroconductivity thereon;

contacting at least a portion of said one article

with another article of metal to be welded;

passing an electrical resistance welding current

through said articles of metal and said coating thereon at

the zone selected for welding; and

fusing said articles together in said zone of said

welding.

472.995

Claims (1)

1. 621jn2 16. The method of Claim 15 wherein said coating is

   deposited on the substrate of a weldable metal stud and there-

   after said stud is electrically resistance welded to another

   article of metal.

   17. A welded metal article prepared according to the

   method of Claim

   18. The method of applying electrocoat paint to a

   substrate treated to receive the deposition of such paint,

   which method comprises:

   applying to said surface a hexavalent-chromium-

   containing aqueous coating composition of hexavalent-chromium-

   providing substance, supplied by at least aei-t 80 weight

   percent chromic acid, said composition containing about -bo"

   0.0005 volume percent of surface active agent, basis total

   composition liquid, and between -5--58-5volume percent,

   same basis, of water-dispersible organic liquid that is a

   high boiling organic compound of carbon, oxygen and hydrogen

   having one or more oxygen-containing constituents selected

   from the group consisting of hydroxyl, oxo, low molecular

   weight ether, and mixtures thereof, said compound having a 0 boiling point above 100 C. at atmospheric pressure, said

   composition being applied in an amount sufficient to provide

   not substantially above v.el- 500 milligrams per square foot

   of coated substrate of chromium, said composition also con-

   taining pulverulent metal selected from the group consisting

   of zinc, aluminum, mixtures thereof, and alloys of same in

   sufficient amount to provide not substantially above aout-

   5,000 milligrams per square foot of coated substrate of said

   pulverulent metal and to provide said coating with a weight

   ratio of chromium, as chromium, to pulverulont mctal of not

   substantially above a6-eA*-t- 0.5:1; 33 472,995

   621 2 heating said substrate at a temperature and for a

   period of time sufficient to vaporize volatile substituents

   from said coating composition and deposit on said surface a

   coating of composition residue and pulverulent metal, said

   coating providing electroconductivity on said substrate and

   thereby establishing a treated surface;

   immersing into a bath of electrocoat paint containing

   an electrode the resulting treated surface and preparing same

   as an electrode; and

   electrolyzing said bath of electrocoat paint.

   19. An electrocoated article prepared by the process of

   Claim 18.

   The method of preparing a corrosion resistant, welded

   metal assembly having an electrocoat painted surface which

   method comprises:

   establishing on the surface of said substrate, on

   at least a portion thereof where welding will take place,

   not substantially above aut 5,000 milligrams per square

   foot of coated substrate of pulverulent metal selected from

   the group consisting of zinc, aluminum, mixtures thereof, and

   alloys of same in intimate mixture with the residue from a

   hexavalent-chromium-containing aqueous coating composition

   containing a hexavalent-chror.ium-providing substance, between

   abee 5-50volume percent, basis total composition liquid of

   water-dispersible, high boiling organic compound in said aqueou

   liquid medium, and above abeout 0.0005 volume percent, same

   basis, of surface active agent, with the organic compound of

   said liquid being composed of carbon, oxygen and hydrogen and

   having one or more oxygen-containing constituents selected

   from the group consisting of hydroxyl, oxo, low molecular

   weight ether, and mixtures thereof, said compound having a 34 472.995

   621/72 boiling point above 1000C. at atmospheric pressure, and said

   coating composition providing said residue with not above.

   ab4et 500 milligrams per square foot of coated substrat& of

   chromium, wherein said coating contains a weight ratio of

   chromium, as metal, to pulverulent metal of/.not substantially

   above abo" 0.5:1;

   heating said substrate at a temperature, and for

   a period of time, sufficient to vaporize volatile substituents

   from said coating composition and deposit on said surface a

   composition residue and pulverulent metal, thereby preparing

   said substrate for welding with a coating providing corrosion

   resistance and weldable electroconductivity,

   contacting at least a portion of the article having

   the prepared substrate with another article of metal to be

   welded;

   passing an electrical resistance welding current

   through said articles of metal and said coating thereon at the

   zone of welding, thereby forming said welded metal assembly;

   immersing into a bath of electrocoat paint containing

   an electrode the resulting assembly and preparing same as an

   electrode; and

   electrolyzing said bath of electrocoat paint.

   21. A welded and electrocoated assembly prepared by the

   process of Claim

   DATED this 15 day of August 1972

   DIAMOND SHAMROCK CORPORATION

   JAMES M.LAWRIE A 00,

   472,995