Process for low temperature curable coating composition

A process for preparing improved low temperature curable coating compositions comprising (1) forming a solution of an alkoxymethylmelamine and a styrene-allyl alcohol copolymer in a solvent and (2) adding to the solution a solution of a hydroxy-containing resin.

BACKGROUND OF THE INVENTION 
This invention relates to low temperature curable surface coating 
compositions. More particularly, it relates to a process for preparing 
improved curable coating compositions comprising an aminoplast, a 
hydroxy-copolymer and a hydroxy containing resin. 
It is well known in the coatings art to prepare coating compositions by 
dissolving in organic solvents an alkoxymethyltriazine or alkoxymethylurea 
and a hydroxy functional resin to provide coatings which exhibit 
satisfactory hardness. Efforts are also being made to cure the coatings at 
low temperature to conserve energy and to utilize such coatings on 
substrates such as wood, paper, paper board and plastics that cannot 
survive high temperature cure. However, low temperature cure gives 
coatings that are soft, have poor water and chemical resistance and poor 
durability. 
In solvent coating systems the addition of a styrene-allyl alcohol 
copolymer has been found to improve the properties of coatings cured at 
low temperatures. The styrene-allyl alcohol copolymer is typically added 
to the vehicle separately from the aminoplast crosslinker. Until now, no 
specific procedure has been taught for the addition of the styrene-allyl 
alcohol copolymer to the aminoplast crosslinker or the vehicle. It has 
been found that the surface coating compositions obtained by the procedure 
described below provide improved surface coatings which exhibit superior 
inter coat adhesion particularly in automotive applications, where more 
than one coat of paint may be applied to the automobile to effect a 
two-tone color coating, and superior flexibility and hardness, properties 
which are generally mutually exclusive. 
The method we have discovered consists of adding styrene-allyl alcohol 
copolymer to hydroxy functional resins containing an aminoplast. 
Our method is achieved by 
(1) forming a concentrated solution of an aminoplast and a 
styrene-(meth)allyl alcohol in a solvent and 
(2) adding to the solution a non-aqueous solution of one or more hydroxy 
functional resins and mixing to obtain a uniform solution. 
Another aspect of our invention is directed to the improved coating 
compositions provided by our process and to substrates coated with such 
compositions. 
STYRENE(METH-)ALCOHOL COPOLYMER 
The styrene alcohol copolymers used in the preparation of the new 
compositions of the invention comprise copolymers of styrene and allyl 
alcohol or methallyl alcohol. The molecular weight of the copolymers is in 
the range of about 800 to about 2500 and the hydroxy content is in the 
range of about 4.0 to about 10.0 weight percent and more preferably in the 
range of about 5.0 to about 8.0 weight percent. 
THE AMINOPLAST 
As used in this description the term "aminoplast" refers to any of the 
large number of alkoxylated amino resins which are commonly employed in 
the art of surface coatings. Such amino resins are characterized as being 
soluble in common solvents as distinguished from amino resins of the 
thermosetting type which are employed in molding or casting compositions. 
The aminoplasts which are suitable for the purpose of this invention are 
the alkoxymethyl derivatives of urea and of polyamino triazines selected 
from the group consisting of melamine, methyl-, ethyl- and 
benzo-guanamine. 
The alkoxymethylureas can be prepared in the conventional manner by 
reaction of urea and formaldehyde under alkaline conditions followed by 
etherification with a C.sub.1 to C.sub.4 alcohol under acid conditions to 
provide a condensate with an average degree of condensation of about 3 or 
less and a urea:formaldehyde: alcohol ratio in the range of about 
1:2-3:1-2.5. Preferably the ratio is in the range of about 
1:2.2-2.8:1.3-2.2 and the ratio of formaldehyde: alcohol is at least about 
1.1. 
The alkoxymethylaminotriazines are substantially completely methylolated 
polyaminotriazines substantially fully etherified with alcohol. They can 
be prepared by reaction of the polyaminotriazine with formaldehyde to 
methylolate the amino groups and are then alkylated or etherified by 
reaction with alcohol. The etherified methylolated aminotriazines are 
liquid and are essentially monomeric or at most are oligomeric with an 
average degree of polymerization of no more than about 3, the 
aminotriazine rings being joined by methylene or methylene ether bridges 
formed by condensation of two methylol groups. Thus, the etherified 
aminotriazines within the scope of the invention possess a ratio of 
aminotriazine to combined formaldehyde in the range of about 1:2n-0.5 to 
about 1:2n where n is the number of amino groups per triazine ring and 
possess a ratio of aminotriazine to alkyl ether groups in the range of 
about 1:2n-1 to about 1:2n. The preferred aminotriazine is melamine since 
it has three amino groups per ring and is potentially hexafunctional. 
Thus, the more preferred aminotriazine compounds are the alkoxymethyl 
melamines in which the ratio of melamine to combined formaldehyde is in 
the range of 1:5.5 to 1:6 and the ratio of melamine to alkoxy groups is in 
the range of 1:5 to 1:6. The alcohols suitable for etherification of the 
methylol melamine are branched or straight chain alkyl alcohols. A mixture 
of alcohols such as methanol and butanol can be used for the 
etherification to make a mixed etherified aminoplast. A preferred mixed 
ether is a methoxy/butoxy mixture. The range of the ratio of 
methoxy/butoxy can vary widely. A preferred range is from about 2:1 to 
about 1:2. A single alkyl alcohol can also be used for etherification. For 
such an application, the preferred alcohol is methanol. Among the more 
preferred aminotriazine compounds is monomeric hexamethoxymethyl melamine. 
THE AMINOPLAST/STYRENE-ALLYL ALCOHOL COPOLYMER SOLUTION 
The solvent used for preparing the aminoplast styrene-allyl alcohol 
copolymer solution can be any one or a mixture of solvents. Advantageously 
polar solvents of solubility parameter in the range of about 8.0 to about 
15 and fractional polarity in the range of about 0.07 to about 0.7, such 
as alcohols, ketones, ethers, glycol ethers and acetates are used. Among 
the alcohols are those having from 1 to 5 carbon atoms per molecule 
including methyl, ethyl, propyl, butyl and amyl alcohols. In addition to 
alcohols, ketones, such as acetone, methyl ethyl ketone, methyl isobutyl 
ketone and methyl amyl ketone can be used. Examples of suitable acetates 
are ethyl, butyl and propyl acetate. Examples of suitable glycol ethers 
are methyl cellosolve, cellosolve and butyl cellosolve. A preferred 
solvent is ethanol and mixtures thereof with other alcohols, aldehydes and 
ketones. 
In preparing solutions of the above components, several methods can be 
used. The aminoplast and the styrene-allyl alcohol copolymer can be 
dissolved individually in the solvent and then mixed together. The 
aminoplast can first be dissolved in the solvent and then the 
styrene-allyl alcohol copolymer added to the solution. The styrene-allyl 
alcohol copolymer may be dissolved first in the solvent and then the 
aminoplast added. The styrene-allyl alcohol copolymer and aminoplast can 
both be added at the same time to the solvent. In the preferred method, 
first either the styrene-allyl alcohol copolymer or the aminoplast is 
dissolved in the solvent and then the second component is added to the 
solution and dissolved. The solution is prepared at a temperature in the 
range of about 20.degree. to about 80.degree. C. Temperatures above about 
80.degree. C. should be avoided to minimize interaction of the aminoplast 
and the copolymer. 
Varying amounts of solvent can be used to dissolve the styrene-allyl 
alcohol copolymer and aminoplasts. Generally, at least 3 weight % solvent 
is needed to dissolve the aminoplast and/or styrene-allyl alcohol 
copolymer. Less than 3% will yield a solution that is too viscous. It is 
preferred that the amount of solvent used be in the range of 4 to 20 
weight % of the total solids. Preferably the amount of solvent used is 
sufficient to provide a solution viscosity determined in the selected 
solvent at room temperature of less than about 5000 cps to facilitate the 
dispersion of the solution in the solution of hydroxy functional resin. 
THE HYDROXY-CONTAINING RESIN 
The hydroxy-containing resin can be one of a number of commercially 
available resins. Advantageously the hydroxy containing resin should have 
a hydroxy content of from about 1.3 weight percent to about 10 weight 
percent, preferably about 2.0 to 6.0 weight percent. Hydroxy content is 
defined as the weight ratio of hydroxy groups per 100 parts of solid 
hydroxy containing resin. Thus resin having one equivalent of hydroxy 
groups per 100 parts of resin would have a weight percent hydroxy content 
of 17/100 or 17 percent. Advantageously the hydroxy-containing resin has 
an acid number of at least about 2 and preferably in the range of about 6 
to about 12 and may be stabilized in aqueous dispersion by neutralization 
with ammonia or with a volatile amine or with a hydroxyamine such as 
dimethylethanolamine. 
Examples of suitable hydroxy containing resins are acrylic, and polyester 
resins which include alkyd resins as are described below. 
THE ACRYLIC RESINS 
The acrylic resin which can be used to prepare the coating composition is 
any of a number of commercially available acrylic resins. The acrylic 
resin is a polymer of at least one ester of an alpha-olefinic 
monocarboxylic acid having the general formula: 
##STR1## 
wherein R is either hydrogen or a lower alkyl group of from 1 to 4 carbon 
atoms, and R.sub.1 represents an alkyl, hydroxy alkyl or cycloalkyl group 
of from 1 to 18 carbon atoms, and one or more of the comonomers of the 
formula: 
##STR2## 
wherein 
R.sub.2 is H, CH.sub.3 or CH.sub.2 OH; and R.sub.3 is alkene of 2 or 3 
carbon atoms. 
Examples of esters of alpha-olefinic monocarboxylic acids which may be used 
in the present invention include methyl acrylate, ethyl acrylate, propyl 
acrylate, isopropyl acrylate, butyl acrylate, hexyl acrylate, octyl 
acrylate, 2-ethyl hexyl acrylate, cyclohexyl acrylate, decyl acrylate, 
stearyl acrylate, methyl methacrylate, methyl alpha-ethyl acrylate, ethyl 
methacrylate, butyl methacrylate, butyl alphaethyl acrylate, hydroxy 
propyl acrylate and lauryl methacrylate. 
Examples of the comonomers which may be used in the acrylics of the present 
invention are phenyl allyl alcohol, glycidyl methacrylate, styrene, 
.alpha.-methyl styrene, acrylic acid, methacrylic acid, acrylonitrile, 
maleic anhydride, allyl acrylate, vinyl acrylate, allyl acetate, vinyl 
acetate and ethyl methacrylate. 
THE ALKYD RESINS 
The alkyd resins which can be used in preparing the compositions of this 
invention include those types normally used in baking or air drying 
applications. These resins can contain up to about 45 weight percent of an 
oil or fatty acid. When the fatty acid or oil concentration is increased 
above the 45 weight percent level cure response is diminished and the 
resulting films are soft and subject to mar and solvent attack. However, 
alkyd resins can be prepared which contain no fatty compound and are based 
upon polyols and polyacids only. These alkyd resins or oil-less alkyds are 
especially useful for exterior applications and have a high degree of 
flexibility, adhesion, and possess unique elongation properties. 
Preferably, though, the fatty compound should be present in an amount 
equal to about 20 to about 45 weight percent of the total alkyd resin 
solids with the most preferable range being about 35 to 45 weight percent. 
In addition the particular alkyd resin which is chosen should have a solids 
acid value of at least 2. Lower acid value alkyds exhibit poor cure 
response and film resistance properties. Preferably the acid value of the 
selected alkyd should be in the 6 to 12 acid value range, however, alkyds 
with an acid value as high as 30 can also be employed with only minor 
stability problems. 
When a fatty compound is present in the alkyd resins of this invention, it 
can comprise any of the fatty acids or oils ordinarily used in preparing 
alkyd resins. Included are the following oils and their respectively 
derived fatty acids: tall, safflower, tung, tallow, soya, corn, linseed, 
poppyseed, castor, dehydrated castor, perilla, cocoanut, oiticica, and the 
like. Of special usefulness are those fatty compounds wherein the fatty 
acid portion contains from 12 to 24 carbon atoms per molecule. 
An additional component of the alkyd resins of this invention is a polyol 
or a mixture of polyols. Among the polyols which can be utilized are those 
normally used in producing alkyd resins including pentaerythritol, 
glycerine, trimethyol propane, trimethyol ethane and the various glycols 
such as neopentyl, ethylene and propylene. Preferable among the above 
types of polyols are triols or mixtures containing a major amount of a 
triol and a minor amount of tetra-alcohol. 
Typical of the carboxylic acids in addition to the aforementioned fatty 
acids incorporated into the alkyd resins are phthalic anhydride, 
isophthalic acid, adipic acid, azelaic acid, benzoic acid, etc. These 
acids can readily be replaced by any of the additional acids normally used 
in alkyd resin processing. The preferred system in addition to including 
the aforementioned preferred levels of a fatty compound contains an 
aromatic dibasic acid or a mixture of such aromatic acid with an aliphatic 
dibasic acid. 
The amount of alkyd resin that can be blended with the other components of 
this invention can vary from 45 to 70 solids weight percent based on the 
total composition solids. Preferable results, though, are obtained when 
the alkyd resin is present in the 55 to 65 weight percent range. 
THE POLYESTER RESIN 
The polyester which can be used to prepare the coating composition of this 
invention may be saturated, unsaturated or oil-modified such as those 
polyesters well known in the surface coating art. Polyesters are prepared 
by reacting a polyhydric alcohol (polyol) and a polybasic acid. 
Such polyols include ethylene glycol, propylene glycol, butylene glycol, 
diethylene glycol, dipropylene glycol, triethylene glycol, neopentyl 
glycol, trimethylene glycol, polyethylene glycol, polypropylene glycol, 
1,5-pentanediol, trimethylolethane, trimethylolpropane, glycerol, 
1,2,6-hexanetriol, pentaerythritol, sorbitol, mannitol, methyl glycoside, 
2,2-bis(hydroxyethoxyphenyl) propane, 2,2-bis (beta-hydroxypropoxyphenyl) 
propane and the like. Mono-functional alcohols may also be employed to 
supplement the other polyols and to control the molecular weight. Useful 
alcohols include those having a hydrocarbon chain comprising from about 3 
to about 18 carbon atoms. 
The acid component of such polyesters may include unsaturated acids such as 
maleic acid, fumaric acid, itaconic acid, citraconic acid, glutaconic 
acid, mesaconic acid, and the like, and their corresponding anhydrides 
where such anhydrides exist. Other polycarboxylic acids which may be 
utilized in addition to the above-mentioned acids include saturated 
polycarboxylic acids such as succinic acid, glutaric acid, adipic acid, 
pimelic acid, suberic acid, azelaic acid, sebacic acid, and the like. 
Certain aromatic polycarboxylic acids and derivatives thereof may also be 
useful; for example, phthalic acid, tetrahydroxyphthalic acid, 
hexahydroxyphthalic acid, endomethylenetetrahydroxyphthalic anhydride, 
tetrachlorophthalic anhydride, hexachloroendomethylene tetrahydrophthalic 
acid, and the like. The term acid as used in this specification includes 
the corresponding anhydrides, where such anhydrides exist. 
In many instances it is optional to include a fatty acid. These include 
saturated fatty acids such as decanoic, dodecanoic, tetradecanoic, 
hexadecanoic, octadecanoic, docosanoic, and the like. And in addition, 
unsaturated fatty acids may be used such as 9-octadecenoic, 
9,12-octadecadieoic, 9,12,15-octadecatrienoic, 9,11,13-octadecatrienoic, 
4-keto-9,11,13-octadecatrienoic, 12-hydroxy9-octadecanoic, 13-docosanoic, 
and the like. 
THE COATING COMPOSITIONS 
The components of the coating composition may be combined in various 
amounts. The amount of styrene-allyl alcohol copolymer in the composition 
is selected to provide the desired level of hardness in the cured coating 
and is advantageously in the range of 1 to 10 weight % based on the total 
solids of the composition. The amount of aminoplast is selected to provide 
a sufficient concentration of methoxymethyl groups to provide an adequate 
degree of crosslinking by reaction with the hydroxy groups of the 
styrene-allyl alcohol copolymer and the hydroxy containing resin. 
Advantageously the concentration of methoxymethyl groups is in the range 
of about 0.2 to about 2 per hydroxy group. Within such limits the amount 
of aminoplast is generally selected so that the weight ratio of aminoplast 
to styrene-allyl alcohol copolymer is in the range of about 3:2 to about 
50:1, preferably from about 2:1 to about 20:1 and the weight ratio of 
aminoplast to hydroxy-containing resin is in the range of about 1:1 to 
about 1:10, and preferably from about 1:2 to about 1:9. 
Solutions of adequate viscosity for coating applications, advantageously 
have total solids from 30 to 70 weight %. The preferred range is 40 to 
60%. 
In order to achieve low temperature curing using the compositions of this 
invention an acid catalyst can be used. Included are catalysts such as 
para-toluenesulfonic acid, methanesulfonic acid, butyl acid phosphate, 
hydrochloric acid, and other organic and mineral acids having at least one 
active hydrogen group per molecule. Preferred among these catalysts is 
para-toluenesulfonic acid. Catalyst concentration can range from about 
0.25 to about 6% based on the total weight of the final coating depending 
upon the final end use. Thus when the coating is to be employed as a wood 
sealer as low as 0.25 to 1.0% catalyst can be employed. On the other hand 
when the coating is to be used as a topcoat more complete cure is required 
and therefore from 2 to 6 weight percent catalyst may be used. It should 
be noted that since most of the above acid catalysts are crystalline at 
room temperature, solutions at about 50% solids in methanol or another 
solvent having a boiling point of less than about 162.degree. C. may be 
used to facilitate handling. 
The coating composition of the invention may be colored with a pigment 
usually employed for coloring of such coating compositions such as an 
organic pigment, carbon black, titanium dioxide, and aluminum flake. 
The coating composition of the invention may also have incorporated therein 
other additives such as wetting agents, conditioning agents, flow control 
agents, ultra violet stabilizers, promoters for crosslinking and 
antioxidants. 
The application of the coating composition of the invention may be executed 
by a conventional method. That is, the composition is applied by brushing, 
roller coating, spraying with compressed air or with a petroleum solvent 
of low boiling point or electrostatic spraying. 
The coating composition of the invention may be applied to a variety of 
materials such as wood, paper, paper board, glass, metal, stone, plastics 
and cloth. 
Practical and presently preferred embodiments of the present invention are 
shown for illustration only in the following Examples wherein parts and 
percentages are by weight unless otherwise indicated. 
TEST METHODS 
Knoop Hardness Number (KHN) is determined by ASTM D-1474. The higher the 
value, the harder the coating. 
Gloss is measured at 60.degree./20.degree. according to ASTM-D573. Results 
are given in percent (%). 
Cleveland Condensing Humidity Test is carried out according to ASTM 
D-2247-68 using a Cleveland Condensing Humidity Cabinet at 63.degree. C. 
Pencil hardness is measured according to ASTM D3363-74. Results are given 
in 6B, 5B, 4B, 2B, B, HB, F, H, 2H to 9H going from softest to hardest. 
Impact is measured according to ASTM G14-72. Results are given in joules 
(J).

EXAMPLES 
Aminoplast A 
An aminoplast solution is prepared by dissolving 10 parts of styrene allyl 
alcohol copolymer containing about 70 wt % styrene and 30 weight % allyl 
alcohol, of weight average molecular weight 1700, in 4.3 parts ethanol at 
room temperature with agitation, adding 90 parts of a methoxymethyl 
melamine (MMM), with a melamine to formaldehyde to methanol ratio of about 
1:5.7:5.5, and stirring until dissolved. The resulting aminoplast solution 
contains 96% by weight solids. 
Aminoplast B 
An aminoplast solution is prepared in the same manner as Aminoplast A 
except that 20 parts of styrene allyl alcohol is used with 80 parts of the 
methoxymethylmelamine and 7 parts of ethanol, and the solids content of 
the resulting solution is 92% by weight. 
Aminoplast C 
An aminoplast solution is prepared in the same manner as Aminoplast A, 
except that 20 parts of styrene allyl alcohol is used with 80 parts of 
methoxy butoxy methyl melamine and 8 parts of ethanol. The methoxy butoxy 
methyl melamine is characterized by a methoxy to butoxy ratio of 0.8:1.0 
and a melamine to formaldehyde to alcohol ratio of 1:5.7:5.5. The solids 
content of the resulting solution is 89% by weight. 
Styrene-Allyl Alcohol Copolymer Solution 
A styrene-allyl alcohol solution is prepared by dissolving 70 parts of the 
styrene-allyl alcohol copolymer described above in 30 parts of ethanol. 
Acrylic A 
A thermosetting acrylic resin is used which is a hydroxy functional acrylic 
polymer containing 70% by weight solids in secondary butyl alcohol, with 
an acid value (on solids) of 72. 
Acrylic B 
A hydroxy-containing acrylic vehicle with a hydroxy number in the range of 
120 to 160 mg KOH per g of vehicle solids into which has been dispersed an 
aluminum flake and the solids reduced with butyl acetate to 33% by weight 
acrylic and 10% by weight pigment. 
Acrylic C 
An hydroxy-containing acrylic vehicle with a hydroxy number in the range of 
120 to 160 mg KOH per g of vehicle solids containing 54% by weight of 
acrylic (on solids) in xylene. 
Polyester A 
An oil free polyester resin with an acid number of 10 into which rutile 
titanium dioxide pigment has been dispersed and the solids content reduced 
with methyl amyl ketone to 70% by weight. 
CONTROL C-1 AND EXAMPLES 1 AND 2 
Examples 1 and 2 in comparison with Control C-1 demonstrate improved 
hardness, impact and chemical resistance at low temperature cure 
conditions for coatings prepared by our method. Examples 1 and 2 are 
prepared by combining a single solution of aminoplast and styrene allyl 
alcohol (e.g., Crosslinker A or B) with Acrylic A. Control C-1 is 
identical to Example 2, except that the aminoplast and the styrene allyl 
alcohol copolymer are prepared in separate solutions and added separately 
to Acrylic A. 
Coating compositions shown in Table I are prepared by mixing Acrylic A with 
methylamyl ketone and an aminoplast. The coatings are applied with draw 
down blades at room temperature to cold rolled steel pannels treated with 
zinc phosphate and primed with a pigmented epoxy coating about 1 mil thick 
and baked at 162.degree. C. for 30 min. The films are baked for 10 min. at 
77.degree. C. (designated L for low) or 20 min at 104.degree. C. 
(designated H for high). 
The results of testing the resulting coatings are shown in Table II. In a 
comparison of Examples 1 and 2 to Control C-1, at low temperature cure 
conditions, an improvement in KNH, impact and chemical resistance is 
observed. In the condensing humidity test, Ex-2 for low temperature cure 
condition shows far superior gloss retention after 24 hrs. of exposure to 
that of C-1. Comparing Examples 1 and 2 to Control C-1 at high temperature 
cure conditions, an improvement in KHN, chemical resistance to HCl, and 
gloss retention after 250 hrs. of exposure to condensing humidity is 
observed. 
TABLE I 
______________________________________ 
COATING COMPOSITION 
Ex-1 Ex-2 C-1 
______________________________________ 
Acrylic A 117 117 117 
Aminoplast A 37 
Aminoplast B 38 
MMM.sup.1 32 
Styrene Allyl Alcohol 5.83 
Methyl Amyl Ketone 
83 85 82 
______________________________________ 
.sup.1 Described in Aminoplast A 
TABLE II 
______________________________________ 
COATING TESTING 
Sample Ex-1 Ex-2 C-1 
______________________________________ 
Baking Conditions 
(L/H) (L/H) (L/H) 
Gloss (20.degree.) 
88/97 88/97 88/97 
Pencil Hardness B/2H B/2H 2B/2H 
KHN 1.5/12 2.7/13.6 1/11.5 
Impact 2.26/6.78 2.26/6.78 1.13/6.78 
Chemical Resistance 
5% NaOH.sup.1 9/10 9.5/10 7.5/10 
Appearance.sup.2 
2.5N HCl.sup.1 7.5/9 7.5/10 7/8 
Appearance.sup.2 
Condensing Humidity 
After 24 hrs. 2/10 2/10 1/10 
Appearance.sup.2 
% Original Gloss 
16/88 61/90 2/85 
After 250 hrs. 
% Original Gloss 
--/75 --/86 --/71 
______________________________________ 
.sup.1 30 minutes exposure at 38.degree. C. 
.sup.2 Visual inspection 10 to 0; 10 the best and 0 the poorest 
EXAMPLE 3 
Example 3 demonstrates the inter coat adhesion achieved with our coating 
process. The formulas for base coat and clear coat are shown in Table III. 
The coatings are sprayed at room temperature onto cold rolled steel panels 
treated with zinc phosphate and primed with a pigmented epoxy coating 
about one mil thick and baked at 162.degree. C. for 30 minutes. The base 
coat is sprayed onto the primer coating to a thickness of about 0.7 mil. 
The clear coat is then sprayed on to provide a thickness of about 1.3 mil. 
The panel is baked at 143.degree. C. for 60 minutes. A second coating of 
base coat and clear coat is applied as above to the panel and baked at 
129.degree. C. for 17 minutes. 
The panel is tested for inter coat adhesion by cutting a cross hatch of 
0.32 cm on spacings at right angles and diagonally in one direction. 
Adhesive tape (No. 898, 25 mm wide available from Minnesota Mining and 
Manufacturing Co.) is applied by pressing firmly and removing with an 
upward motion at medium speed. The amount of chipping, flaking or general 
poor adhesion is observed and the per cent adhesion determined. 
The coating of Example 3 is found to have 100% adhesion initially and also 
after three months of aging. 
A second coating identical to that of Example 3 is made, except that 100 
parts of methoxy butoxy methyl melamine (as described in Aminoplast C) in 
8 parts of ethanol is substituted for Aminoplast C. The coating is found 
to have 100% adhesion initially but only 25% adhesion after 3 months of 
aging. 
TABLE III 
______________________________________ 
EXAMPLE 3 
Base Coat 
Clear Coat 
______________________________________ 
Acrylic B 200 
Acrylic C 200 
Aminoplast C 35.5 58 
Catalyst.sup.1 1.25 1.75 
Butyl Acetate 25 
Xylene 30 
______________________________________ 
.sup.1 A blocked sulfonic acid catalyst. 
EXAMPLE 4 AND CONTROL 2 
The coatings of Example 4 and Control 2 demonstrate the improved 
flexibility and hardness of the coatings prepared by our process. 
Coating compositions shown in Table IV are prepared by mixing Polyester A 
with xylol, an aminoplast and p-toluene sulfonic acid. The coatings are 
applied with drawn down blades at room temperature to a primed galvanized 
steel coil stock panel and baked for 42 seconds in an oven at 310.degree. 
C. The panels are tested for flexibility by the T-bend test where the 
coated panel is deformed 180.degree. and inspected for fracturing of the 
coating at the bend. The first deformation is designated T-O. The panel is 
then deformed another 180.degree. around the first fold resulting in a 
flattened roll and designated T-1. The third is designated T-2 and so on. 
As each bend is added, the radius of curvature increases with the 
thickness of the flattened roll. Therefore, the lowest level of bends 
without fracture indicates the greatest flexibility. 
TABLE IV 
______________________________________ 
COIL COATINGS 
Ex-4 C-2 
______________________________________ 
Polyester A 85 85 
Aminoplast B 5.1 
MMM.sup.1 3.6 
Styrene Allyl Alcohol 1.5 
Xylol 8.0 8.0 
p-toluene sulfonic acid 
0.7 0.7 
KHN 13.5 13.2 
T-Bends T-2 T-3 
______________________________________ 
.sup.1 Described in Aminoplast A