 |
Description  |
|
|
BACKGROUND OF THE INVENTION
This invention pertains to corrosion inhibiting coating compositions and
more particularly to metal complexed phenolic compositions having low
volatiles content for high solids coatings.
BACKGROUND ART
Recent trends to high build maintenance coatings have resulted in a need
for modifiers to improve the drying properties of high solids alkyds and
increase their corrosion resistance. Alkyds have poor hydrolytic stability
in adverse environments and generally require the addition of corrosion
inhibitive pigments, such as lead or chromium compounds, to minimize their
breakdown. The newer alkyd coatings are being accepted as single
application systems particularly for the refinishing of railroad cars.
The formulation of coatings for steel requires a balance of pigment type
and concentration in order to obtain the desired corrosion resistance,
weathering properties, flexibility, and blister resistance. As the pigment
concentration is increased, the porosity of the coating increases until
the critical pigment volume concentration is reached, at which point
porosity is high and corrosion or salt spray resistance is poor. The
relationship is non-linear and depends on the pigment shape, size and
dispersion. In general, however, low pigment volume concentrations give
good corrosion resistance.
Blister resistance is improved as the pigment concentration is increased.
The increased porosity of the coating allows moisture and hydrogen
generated at the interface to escape. At low pigment concentrations,
hydrogen is trapped and results in blister generation. The presence of a
corrosion inhibitive ingredient which passivates the steel surface
minimizes the gas generation and reduces blistering. Therefore, coating
formulation is a compromise which is guided by the type of environment to
which the coating will be exposed. Most primers are formulated in the
range of 35 to 40% Pigment Volume Concentration (PVC) range. These do not
make good high solids coatings because of excessive viscosity.
It is an object of this invention to provide high solids primer coating
compositions having good corrosion resistance.
It is a further object of this invention to obtain necessary salt spray
performance without employing toxic chromates.
Other objects will become apparent to those skilled in the art on a further
reading of the specification.
SUMMARY OF THE INVENTION
Coating compositions expressed on a solvent free basis, meeting the above
objects have been found comprising:
(A) an organic binder consisting essentially of:
(1) about 4 to about 40 volume percent of a divalent metal complex of a
para-substituted novolac phenol-aldehyde condensation products, and
(2) about 60 to about 96 volume percent of an organic coating material
selected from the group consisting of alkyd resins, epoxy ester resins,
drying oils, epoxy resins and thermoplastic polyhydroxyethers; and
(B) based on the total coating composition, a pigment selected from the
group consisting of about 7 to about 15 volume percent of aluminum-bronze
lamellar pigments, about 20 to about 40 volume percent of a non-lamellar
pigment selected from the groups consisting of talc, zinc phosphate,
calcium carbonate, titanium dioxide, manganese oxide, and iron oxides or
about 50 to about 65 volume percent of particulate zinc metal.
Solvents are preferably incorporated into the above composition to reduce
viscosity for ease of application. Solvent levels used depend upon the
organic binder. Suitable solvents include aromatics, such as xylenes,
toluene, trimethyl benzene, diethyl benzene and the like; ketones, such as
methyl isobutyl ketone, methyl ethyl ketone, and the like; glycol ethers,
such as ethylene glycol monoethyl ether, and the like; esters, such as
butyl acetate and the like. These solvents may be blended with each other
or alcohols such as butyl alcohol, isopropyl alcohol and the like.
The preferred divalent metals used in (1) to prepare the divalent metal
complexes of this invention are nickel, zinc and manganese.
Alkyd resins are described in the Encyclopedia of Polymer Science and
Technology, Vol. 1 pages 663-730 Interscience Publishers NYC (1964)
incorporated herein by reference. The term "alkyd" tends to specify
polyester products composed of polyhydric alcohols, polybasic acids, and
monobasic fatty acids.
The preferred alkyd resins used in this invention are those designated in
the industry as high solids alkyd resins. These have total solids of 80%
by weight or more.
Exemplary high solids alkyd resins include: Aroplaz 6440-A4-85, Cargill
5707, 5713 and 5811, medium to short oil alkyds dissolved in aromatic
solvents, such as Cargill 5262 and Beckosol 12-038, Reichold 11-070 medium
oil alkyd, and the like.
Exemplary drying oils include tung oil, linseed oil, oiticica oil,
dehydrated castor oil, soybean oil, tall oil, fish oils, mixtures thereof
and the like.
Epoxy ester resins useful in this invention are prepared by the
esterification of a diglycidyl ether of bisphenol A with drying oil fatty
acids. These preferably are made from oligomeric diglycidyl ethers of
bisphenol A having an epoxy equivalent weight of about 450 to about 1000
grams per gram equivalent of epoxide. Examples available commercially are
Cargill 7851 and Reichold Epotuf 38-411 or 38-403.
The term "thermoplastic polyhydroxyether" herein refers to substantially
linear polymers having the general formula:
--D--O--E--O].sub.n
wherein D is the radical residuum of a dihydric phenol, E is a hydroxyl
containing radical residuum of an epoxide and n represents the degree of
polymerization and is at least 30 and is preferably 80 or more. The term
"thermoplastic polyhydroxyether" is intended to include mixtures of at
least two thermoplastic polyhydroxyethers.
The thermoplastic poly(hydroxyethers) can be prepared by admixing from
about 0.985 to about 1.015 moles of an epihalohydrin with one mole of a
dihydric phenol together with from about 0.6 to 1.5 moles of an alkali
metal hydroxide, such as, sodium hydroxide or potassium hydroxide
generally in an aqueous medium at a temperature of about 10.degree. to
about 50.degree. C. until at least about 60 mole percent of the
epihalohydrin has been consumed. The thermoplastic poly(hydroxyethers)
thus produced have reduced viscosities of at least 0.43. Reduced viscosity
values were computed by use of the equation:
##EQU1##
wherein t.sub.o is the efflux time of the solvent (tetrahydrofuran,
t.sub.s is the efflux time of the poly(hydroxyether) solution, c is the
concentration of the poly(hydroxyether) solution in terms of grams of
poly(hydroxyether) per 100 ml. of tetrahydrofuran.
The dihydric phenol contributing the phenol radical residuum, D, can be
either a dihydric mononuclear phenol such as those having the general
formula:
##STR1##
wherein Ar is an aromatic divalent hydrocarbon such as naphthylene and,
preferably, phenylene, Y and Y.sub.1 which can be the same or different
are alkyl radicals, preferably having from 1 to 4 carbon atoms, i.e.,
fluorine, chlorine, bromine and iodine, or alkoxy radicals, preferably
having from 1 to 4 carbon atoms, r and z are integers having a value from
0 to a maximum value corresponding to the number of hydrogen atoms on the
aromatic radical (Ar) which can be replaced by substituents and R.sup.1 is
a bond between adjacent carbon atoms as in dihydroxydiphenyl or is a
divalent radical including, for example
##STR2##
--O--, --S--, --SO--, --SO.sub.2 --, and --S--S--, and divalent
hydrocarbon radicals such as alkylene, alkylidene, cycloaliphatic, e.g.,
cycloalkylidene, halogenated alkoxy or aryloxy substituted alkylene,
alkylidene and cycloaliphatic radicals as well as alkarylene and aromatic
radicals including halogenated, alkyl, alkoxy or aryloxy substituted
aromatic radicals and a ring fused to an Ar group; or R.sup.1 can be
polyalkoxy, or polysiloxy, or two or more alkylidene radicals separated by
an aromatic ring, a tertiary amino group, an ether linkage, a carbonyl
group of a sulfur containing group such as sulfoxide, and the like.
Examples of specific dihydric polynuclear phenols include among others:
The bis(hydroxyphenyl)alkenes such as 2,2-bis(4-hydroxyphenol)propane,
2,4'-dihydroxydiphenylmethane, bis(2-hydroxyphenyl)methane,
bis(4-hydroxyphenyl)methane,
bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane,
1,1-bis(4-hydroxyphenyl ethane, 1,2,bis(4-hydroxyphenyl)ethane,
1,1-bis(4-hydroxy-2-chlorophenyl)ethane,
1,1-bis(3-methyl-4-hydroxyphenyl)ethane,
1,3-bis(3-methyl-4-hydroxyphenyl)propane,
2,2-bis(3-phenyl-4-hydroxyphenyl)propane,
2,2-bis(3-isopropyl-4-hydroxyphenyl)propane,
2,2-bis(2-isopropyl-4-hydroxyphenyl)propane,
2,2-bis(4-hydroxylnaphthyl)propane, 2,2-bis(4-hydroxyphenyl)pentane,
3,3-bis(4-hydroxyphenyl)pentane, 2,2-bis(4-hydroxyphenyl)heptane,
bis(4-hydroxyphenyl)phenylmethane,
1,2-bis(4-hydroxyphenyl-1,2-bis(phenyl)propane,
2,2-bis(4-hydroxyphenyl)1-phenyl-propane and the like;
(Di(hydroxyphenyl)sulfones such as bis(4-hydroxyphenyl)sulfone,
2,4'-dihydroxydiphenyl sulfone, 5'-chloro-2,4'-dihydroxydiphenyl sulfone,
5'-chloro-4,4'-dihydroxydiphenyl sulfone and the like;
Di(hydroxyphenyl)ethers such as bis(4-hydroxyphenyl)ether, the 4,3'-,
4,2'-, 2,2'-, 2,3'-, dihydroxydiphenyl ethers,
4,4'-dihydroxy-2,6-dimethyldiphenyl ether,
bis(4-hydroxy-3-isobutylphenyl)ether,
bis(4-hydroxy-3-isopropylphenyl)ether, bis(4-hydroxy-3-chlorophenyl)ether,
bis(4-hydroxy-3-fluorophenyl)ether, bis(4-hydroxy-bromophenyl)ether,
bis(4-hydroxynaphthyl)ether, bis(4-hydroxy-3-chloronaphthylether,
bis(2-hydroxydiphenyl)ether, 4,4'-dihydroxy-2,6-dimethoxydiphenyl ether,
4,4'-dihydroxy-2,5-diethoxydiphenyl ether, and the like.
Also suitable are the bisphenol reaction products of 4-vinylcyclohexene and
phenols, e.g., 1,3-bis(p-hydroxyphenyl)-1-ethylcyclohexane and the
bisphenol reaction products of dipentene or its isomers and phenols such
as 1,2-bis(p-hydroxyphenyl)-1-methyl-4-isopropylcyclohexane as well as
bisphenols such as 1,3,3-trimethyl-1-(4-hydroxyphenyl)-6-hydroxyindane,
and 2,4-bis(4-hydroxyphenyl)-4-methylpentane, and the like.
Particularly desirable dihydric polynuclear phenols have the formula
##STR3##
wherein Y and Y.sub.1 are are previously defined, r and z have values from
0 to 4 inclusive and R.sup.1 is a divalent saturated aliphatic hydrocarbon
radical, particularly alkylene and alkylidene radicals having from 1 to 3
carbon atoms, and cycloalkylene radicals having up to and including 10
carbon atoms.
Mixtures of dihydric phenols can also be employed and whenever the term
"dihydric phenol" or "dihydric polynuclear phenol" is used herein,
mixtures of these compounds are intended to be included.
The epoxide contributing the hydroxyl containing radical residuum, E, can
be monoepoxide of diepoxide. By "epoxide" is meant a compound containing
an oxirane group, i.e., oxygen bonded to two vicinal aliphatic carbon
atoms, thus,
##STR4##
A monoepoxide contains one such oxirante group and provides a radical
residuum E containing two hydroxy groups. Saturated epoxides, by which
term is means diepoxides free of ethylenic unsaturation, i.e. >C.dbd.C<
and acetylenic unsaturation, i.e. --C.tbd.C--, are preferred. Particularly
preferred are halogen substituted saturated monoepoxides, i.e., the
epihalohydrins and saturated diepoxides, which contain solely carbon,
hydrogen and oxygen, especially those wherein the vicinal or adjacent
carbon atoms form a part of an aliphatic hydrocarbon chain. Oxygen in such
diepoxides can be, in addition to oxirane oxygen, ether oxygen --O--,
oxacarbony oxygen
##STR5##
carbonyl oxygen
##STR6##
and the like.
Specific examples of monoepoxides include epichlorohydrins such as
epichlorohydrin, epibromohydrin, 1,2-epoxy-1-methyl-3-chloropropane,
2,2-epoxy-1-butyl-3-chloropropane, 1,2-epoxy-2-methyl-3-fluoropropane, and
the like.
Illustrative diepoxides include diethylene glycol
bis(3,4-epoxycyclohexane-carboxylate),
bis(3,4-epoxycyclohexyl-methyl)adipate,
bis(3,4-epoxycyclohexylmethyl)phthalate,
6-methyl-3,4-epoxyclohexylmethyl-6-methyl-3,4-epoxycyclohexane
carboxylate, 2-chloro-3,4-epoxycyclohexylmethyl-2-chloro-3,4-epoxycyclohex
ane-carboxylate, diglycidyl ether, bis(2,3-epoxycyclopentyl)ether,
1,5-pentanediol bis(4-methyl-3,4-epoxycyclohexylmethyl)ether,
bis(2,3-epoxy-2-ethylhexyl)adipate, diglycidyl maleate, diglycidyl
phthalate, 3-oxatetracyclo[4.4.0.1.sup.7,10.0.sup.2,4 ]-undec-8-yl
2,3-epoxypropyl ether, bis(2,3-epoxycyclopentyl)sulfone,
bis(3,4-epoxyhexoxypropyl)sulfone, 2,2'-sulfonyldiethyl,
bis(2,3-epoxycyclopentanecarboxylate),
3-oxatetracyclo[4.4.0.1.sup.7,10.0.sup.2.4 ]-undec-8-61 2,3-epoxybutyrate,
4-pentenal-di-(6-methyl-3,4-epoxycyclohexylmethyl)acetal, ethylene glycol
bis(9,10-epoxystearate), diglycidyl carbonate,
bis(2,3-epoxybutylpenyl)-2-ethylhexyl phosphate, diepoxydioxane, butadiene
dioxide, and 2,3-dimethyl butadiene dioxide. The preferred diepoxides are
those wherein each of the oxirane groups is connected to an electron
donating substituent which is not immediately connected to the carbon
atoms of that oxirane group. Such diepoxides having the grouping
##STR7##
wherein A is an electron donating substituent such as --O--,
##STR8##
--S--, --SO--, --SO.sub.2 --,
##STR9##
and Q is a saturated hydrocarbon radical such as an alkyl, cycloalkyl,
aryl or aralkyl radical.
The preferred polyhydroxyether is available commercially as Bakelite
Phenoxy PKHH, a trade designation of Union Carbide Corporation for
condensation polymer derived from Bisphenol-A
(2,2-bis(p-hydroxyphenyl)propane and epichlorohydrin having the structural
formula:
##STR10##
The phenoxy resin is available as a solution in glycol esters such as
Cellosolve acetate (the acetate of a monoalkyl glycol ether sold under the
Trademark Cellosolve by Union Carbide Corporation) or in pellet form which
is readily soluble in a variety of solvents and solvent blends. The solid
phenoxy resin sold under the designation PKHH by Union Carbide Corporation
is soluble in the following solvents: butyl Carbitol, butyl Carbitol
acetate, butyl Cellosolve, Carbitol solvent, Cellosolve solvent, diacetone
alcohol, diethyl Carbitol, dimethylformamide, dimethyl sulfoxide, dioxane,
ethoxy triglycol, mesityl oxide, methyl Cellosolve acetate, methyl ethyl
ketone, and tetrahydrofuran.
Carbitol is a Trademark of Union Carbide Corporation for the monoalkyl
ether of diethylene glycol.
Epoxy resins are commercially available from Shell Oil Company. Their
preparation from bisphenol A and epoxychlorohydrin is described in U.S.
Pat. No. 3,177,090, issued to R. E. Bayes et al.
Novolac resins produced by the reaction of a para substituted phenol with
formaldehyde typically by heating one mole of p-tertiary butyl phenol with
about 0.5-0.9 moles of formaldehyde in an acidic media. When less than 6.5
moles of formaldehyde are used per 7 moles of phenol the products are
permanently fusible and soluble.
In a typical synthesis novolacs are prepared by heating 1 mole of an alkyl
phenol with 0.5-0.9 moles of formaldehyde under acidic conditions. The
temperature at which the reaction is conducted is generally from about
25.degree. to about 175.degree. C.
The preferred novolac resins are those based on p-t-butyl phenol modified
with a dihydric polynuclear phenol, such as bisphenol A (also known as
2,2-bis(p-hydroxyphenyl)propane. Other alkyl phenols which can be used
include: phenol, amyl phenol, octyl phenol, nonylphenol, dodecyl phenol,
and the like.
A preferred resin is one derived from an 80:20 mixture by weight.
Other dihydric polynuclear phenols which can be used as the minor phenolic
component of the novolac resins include:
The bis(hydroxyphenyl)alkanes such as
2,2-bis(4-hydroxyphenol)propane,
2,4'-dihydroxydiphenylmethane,
bis(2-hydroxyphenyl)methane,
bis(4-hydroxy-phenyl)methane,
bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane,
1,1-bis(4-hydroxyphenyl)ethane,
1,2-bis(4-hydroxyphenyl)-ethane,
1,1-bis(4-hydroxy-2-chlorophenyl)ethane,
1,1-bis(3-methyl-4-hydroxyphenyl)ethane,
1,3-bis(3-methyl-4-hydroxyphenyl)propane,
2,2-bis(3-phenyl-4-hydroxyphenyl)propane,
2,2-bis(3-isopropyl-4-hydroxyphenyl)propane,
2,2-bis(2-isopropyl-4-hydroxyphenyl)propane,
2,2-bis(4-hydroxylnaphthyl)propane,
2,2-bis(4-hydroxyphenyl)pentane,
3,3-bis(4-hydroxyphenyl)pentane,
2,2-bis(4-hydroxy-phenyl)heptane,
bis(4-hydroxyphenyl)phenylmethane,
bis(4-hydroxyphenyl)cyclohexylmethane,
1,2-bis(4-hydroxy-phenyl-1,2-bis(phenyl)propane,
2,2-bis(4-hydroxyphenyl)-1-phenyl-propane and the like.
Suitable solvents include aromatic organic compounds such as: benzene,
xylene, toluene, dimethyl benzene, trimethyl benzene which may be blended
with alcohols such as n-butyl alcohol, n-propyl alcohol, isopropyl
alcohol, and the like.
______________________________________
GLOSSARY OF MATERIALS USED
______________________________________
Phenolic Resin A. - 100% phenolic-oil
soluble - non-heat reactive resin derived from
p-t-butyl phenol and Bisphenol A having a softening
point of 195-235.degree. F. (91-113.degree. C.).
Phenolic Resin B - Phenolic Resin A
complexed with zinc oxide - benzoic acid mixture
(4% Zn).
______________________________________
Zirco - 6% Interstab Chemicals, Inc.
325 Mesh Water Ground
The English Mica Company
Mica
Cobalt Naphthenate, 6%
Interstab Chemicals, Inc.
Calcium Naphthenate, 5%
Interstab Chemicals, Inc.
Manganese Naphthenate, 6%
Interstab Chemicals, Inc.
Aluminum Powder MD-5100
Alcan Metal Powders
Division of Alcan Aluminum
Corporation.
Methanol Article of Commerce
ASA (Methyl Ethyl Interstab Chemicals, Inc.
Ketoxime)
Antiskinning agent
Interstab Chemicals, Inc.
Aromatic 100 Exxon Chemical
Tung Oil Article of Commerce
Mineral Spirits Article of Commerce
Bentone 27 N. L. Industries
Titanium Dioxide R-960
DuPont
______________________________________
TEST 1
SALT SPRAY (ASTM B-117)
EXPOSURE RATING FOR COATINGS
Corrosion (ASTM D-610)
______________________________________
10 -- No Change
9 -- Very Slight Change
8 -- Slight Change
7 -- Medium +
6 -- Medium
5 -- Medium -
4 -- Slightly Bad
3 -- Bad
2 -- Very Bad
1 -- Partial Failure
0 -- Failure
T-1 = Rusting without blisters
T-2 = Rusting with blisters
______________________________________
Blisters (ASTM D-714)
______________________________________
F = Few
M = Medium
D = Dense
______________________________________
Number refers to size of blisters.
The Mettler method for determining resin softening point is a hot stage
method wherein the temperature at which the resin softens is noted. The
apparatus is made by Mettler Instruments A.G. Switzerland.
The particulate zinc metal used in this invention is preferably finally
divided zinc dust having a particle size of about 2 to about 15 microns.
Such a grade of zinc is commercially available from the Federated Metals
Corporation as L-15. These particles are roughly spherical.
The invention is further described in the examples which follow. All parts
and percentages are by weight unless otherwise specified.
EXAMPLE 1
Preparation of Resin A
To a jacketed 2 liter resin kettle fitted with a stirrer, thermometer,
reflux condenser with water trap and inlet tube, there was charged:
______________________________________
p-tert.Butyl Phenol 1109 g
Bisphenol-A 277 g
Toluene 83 g
Oxalic Acid 8 g
Dow Corning Paint Additive #3*
0.2 g
______________________________________
*All materials were commercial grade. Dow Corning Paint Additive #3 is an
alkyl polysiloxane dissolved in toluene at 10% solids.
The mixture was heated to 120.degree. C. Over a three hour period, there
was added 375 g of 50% aqueous formaldehyde at 120.degree. C.
(.+-.2.degree. C.). Water was continuously removed via the trap by
azeotropic reflux.
The trap was removed and the reaction mix was then stripped of excess
monomer and solvent to 160.degree. C. under 27-28" Hg vacuum. The water
trap was replaced.
The residue remaining in the resin kettle is resin A. This is used as an
intermediate to make resin B.
EXAMPLE 2
Preparation of Resin B
After cooling to 130.degree. C., there was metered into the resin kettle
containing resin A in Example 1, a premixed solution (shown below) over a
two-hour period with continuous water removal again while maintaining a
temperature of 130.degree. C. (.+-.4.degree. C.).
______________________________________
PREMIX
______________________________________
Zinc Oxide 65.8 g
28% Aqueous Ammonia 257.0 g
Benzoic Acid 258.0 g
______________________________________
After all of the above mixture was added, the water trap was removed and
the reaction mix was again stripped of unreacted material and water to a
temperature of 155.degree. C. under 25" Hg vacuum. The material was
discharged molten, cooled in a sheet form and then broken into flakes. The
product Resin B, contained 0.052% insolubles (10% solution of resin in
toluene) and exhibited a color of 4-5 on the Gardner scale (50% solution
of resin in toluene).
EXAMPLE 3
Evaluation of Resin A and Resin B
Table A compares the corrosion inhibitor efficiency of a p-t-butyl phenolic
Resin A with Resin B. The data is from an accelerated test procedure using
a model compound to simulate a coating under salt spray attack. (cf. G
Salensky "Corrosion Inhibitor Test Method," Corrosion Control by Organic
Coatings, H. Liedheiser, Jr. Editor, NACE, 1981) A value of 1.0 is
complete inhibition, whereas 0.0 indicates no protection. Resin B shows
superior inhibitive properties when 0.5% of it or resin A or the other
compounds in Table A are dissolved in the model compound, diphenyl ether,
and subjected to the test referenced above.
Resin B has a Mettler softening point of 190.degree.-220.degree.
F.-(88.degree.-104.degree. C.) and is soluble in aromatics, alcohols,
ketones, esters or blends of these solvents. It has poor solubility in
aliphatic solvents. Resin B can be incorporated into a paint binder system
by room temperature blending or "cold cutting" with solvents and other
resins, such as, high solids alkyd resins, medium to short oil alkyds,
epoxy esters, epoxy resins and thermoplastic polyhydroxyether resins.
Generally the binder solids are replaced with 5 to 35% of Resin B. A level
of 20% gives good results with high solids alkyds.
An aluminum pigmented high solids alkyd coating was prepared according to
the formulation shown in Table 1. Resin B, alkyd resin, and blend of
methyl isobutyl ketone was mixed until complete solution was obtained.
This was checked by dipping a glass slide into the mixture, air drying to
release the solvent, and making sure that film is free of resin particles.
An alternate, but slower procedure, is to dissolve Resin B in the proper
proportion to produce a 50% solids solution in the solvent blend which is
then added to the high solids alkyd. When solution has been achieved, the
aluminum powder is dispersed using a high speed mixer. The coating is then
cut back with additional alkyd resin, driers, and antiskinning agent.
A control coating not containing Resin B but having the same resin content
was made as a control for comparative testing. The formulation shown in
Table 1 has 20% of its binder solids as Resin B. The viscosity of the
control coating was 22.5 seconds whereas this coating was 21 seconds.
The effect of Resin B on drying properties after eight days is shown in
Table 2. Sward Rocker hardness tests were made on 2 mil dry film thickness
(DFT) on cold rolled steel "Q" panels. Resin B coatings are 75% harder
after an eight day air-drying period.
These same coatings were applied to sandblasted hot-rolled steel to 3.3
mils dried film thickness (DFT), air dried for a minimum of one week and
exposed to salt spray (ASTM B-117).
Corrosion and blistering were rated from 10 to 0 by ASTM D-610 and ASTM
D-714, respectively. Resin B coating had a corrosion rating of 8 versus 4
for the control after 1235 hours (Table 3). Salt spray resistance
decreased when coating thicknesses were reduced to 1.9 mils DFT. Resin B
coating was still superior to the control. Both coatings were stripped
after a salt spray exposure of 760 hours and the steel substrates
examined. Steel under the Resin B coating was a sandblasted metallic gray
color, whereas the control panel was coated with black iron oxide of
corrosion (Table 4). A zinc chromate primer (TTP-645A) was applied to
sandblasted steel and exposed to salt spray for comparison purposes (Table
5). The zinc chromate primer was superior in corrosion and blister
resistance to the control in Table 3 but inferior to the Resin B coating.
It should be noted that the TTP-645A primer specifies a long oil alkyd,
whereas the Aroplaz 6440-A4-85 resin is proprietary. On the basis of the
above information, the Resin B modified aluminum coating should provide a
suitable one-coat system for applications such as railroad cars, etc.
Similar improvements in corrosion resistance were obtained when the high
solids alkyd was replaced with air drying short oil alkyd (Beckosol
12-038) or an epoxy ester (Epotuf 38-403).
Aluminum pigmented tung oil varnishes were also found to have good
corrosion resistance when formulated with Resin B as the hard resin. See
Table 6. Corrosion resistance was superior to a similar coating based on a
phenolic varnish. Formulation is given in Table 7.
Resin B may also be used with corrosion inhibitive pigment to enhance
corrosion resistance. The salt spray resistance of a Resin B modified high
solids alkyd primer containing zinc molybdate (Molywhite 101) inhibitive
pigment is shown in Table 8. Substitution of 20% of the alkyd solids with
Resin B results in a 30% improvement in salt spray resistance after 1500
hours exposure compared to the control. The primer formulation is | | |
