High solids coatings with reactive diluent

A high solids, thermosetting coating composition for painting substrates comprises low molecular weight acrylic polymer, low molecular weight polyester polymer, and low molecular weight urethane diluent, where the acrylic and polyester and urethane components each contain hydroxyl functionality and are coreactive with an amine derivative crosslinking resin to render the coating thermosetting.

BACKGROUND OF THE INVENTION 
This invention relates to high solids thermosetting protective coatings and 
particularly to a blend of polyester and acrylic copolymer for use in high 
solids coatings further containing a hydroxyl functional urethane diluent. 
High solids coatings are non-aqueous coatings containing minor amounts of 
organic solvents and are particularly useful as coatings on appliances, 
aluminum extrusions, general metal surfaces, and wood substrates. 
Acrylic polymers are known to generally provide useful coatings exhibiting 
good film properties. These polymers can contain reactive functional 
groups which are coreactive with other polymers or resins to provide 
thermosetting binder systems. Such acrylic binders can be produced by 
solution or bulk polymerization of ethylenically unsaturated monomers 
including acrylic monomers. Solvent can be added in minor amounts to 
render the acrylic polymer fluent. Various acrylic polymers have been 
suggested to provide high solids polymeric compositions such as disclosed 
in U.S. Pat. No. 4,374,164, or combined other polymers such as suggested 
in U.S. Pat. No. 4,397,989 or U.S. Pat. No. 4,369,283. Commonly assigned 
U.S. Pat. No. 4,716,200 issued Dec. 29, 1987 discloses low molecular 
weight acrylic copolymers combined with low molecular weight polyester 
polymer to provide high solids coatings whereas U.S. Pat. No. 4,397,989 
discloses a high molecular weight acrylic copolymer in conjunction with a 
polyester polymer to provide acrylic high solids coatings. 
Reactive diluents are described in U.S. Pat. No. 4,022,726 and U.S. Pat. 
No. 4,417,022, which described hydroxy functional urethane containing 
diluents. These diluents are characterized as having one primary or 
secondary hydroxyl group and have a retained solids value of greater than 
80 percent by weight. The reaction of mono- and di-amines with 
monocyclocarbonates has been described by M. F. El-Giamal and R. C. 
Shultz, Makromol. Chem., 177(8), 2259 (1976), which discloses hydroxyl 
urethanes being furter reacted with isocyanates or acid functional 
materials to form alternating polyester-urethanes or copolyurethanes. 
It now has been found that polyester acrylic polymeric blends useful in 
high solids coatings can be formulated with urethane containing diluents 
having hydroxyl functionality and provide good retention of the diluent in 
the coating film. These diluents have the added advantage that they have a 
large effect on the reduction of viscosity of a fluid coating and do not 
have an adverse effect on the final coating appearance or coating physical 
properties. These and other advantages of this invention will become more 
apparent by referring to the detailed description of the invention along 
with the illustrative examples. 
SUMMARY OF THE INVENTION 
Briefly, the invention comprises a coating composition based on an acrylic 
copolymer and a polyester polymer as the binder combined with a hydroxyl 
functional urethane diluent. On a weight basis, the polymeric coating can 
contain between 5% and 60% hydroxyl functional urethane diluent additive 
based on the binder system of acrylic copolymer, polyester polymer, and 
hydroxyl funtional urethane diluent. 
DETAILED DESCRIPTION OF THE INVENTION 
This composition comprises a high solids coating comprising a reactive 
acrylic copolymer, a reactive polyester polymer, and a hydroxyl functional 
diluent. 
Referring first to the acrylic binder, the acrylic polymer comprises an 
organic solvent solution or bulk copolymerized ethylenically unsaturated 
monomers, including acrylic monomers, to produce a non-aqueous acrylic 
polymer containing reactive primary hydroxyl groups and having a number 
average molecular weight between 500 and 2500, and preferably between 900 
and 1200. Number average molecular weights are measured by gel permeation 
chromatography (GPC) according to ASTM methods such as D3016-72; D3536-76; 
D3593-80; or D3016-78. The acrylic polymers are liquid at room temperature 
and generally have a Tg between -20.degree. C. and +20.degree. C. as 
calculated by the Fox equation based on the ratio of specific monomers. 
The hydroxyl number of the acrylic polymer is broadly between 50 and 200 
and preferably between 100 and 150. The acrylic polymer can be produced by 
bulk polymerization of ethylenically unsaturated monomers including 
acrylic monomers, activated by peroxide or azo or other free radical 
inhibitor at polymerization temperatures typically between 70.degree. C. 
to 170.degree. C. and preferably between 120.degree. C. to 150.degree. C. 
Typically 0.5 to 2% peroxide initiator is utilized based on the weight of 
the monomers. Typical polymerization initiators can include for instance 
benzoyl peroxide, t-butyl hydroperoxide, tertiary butyl perbenzoate, 
cumene peroxide and similar peroxide polymerization catalysts which are 
preferred. Other initiators include azo initiators such as azo bis 
isobutyronitrile and persulfate or ammonium persulfates. 
Copolymerizable ethylenically unsaturated monomers useful in producing the 
acrylic copolymer are monomers containing carbon-to-carbon unsaturation 
and include vinyl monomers, acrylic monomers, allylic monomers, acrylamide 
monomers, and mono- and dicarboxylic unsaturated acids. Vinyl esters 
include vinyl acetate, vinyl propionate, vinyl butyrates, vinyl benzoates, 
vinyl isopropyl acetates and similar vinyl esters. Vinyl halides include 
vinyl chloride, vinyl fluoride, and vinylidene chloride. Vinyl aromatic 
hydrocarbons include styrene, methyl styrenes and similar lower alkyl 
styrenes, chlorostyrene, vinyl toluene, vinyl naphthalene, divinyl 
benzoate, and cyclohexene. Vinyl aliphatic hydrocarbon monomers include 
alpha olefins such as ethylene, propylene, isobutylene, and cyclohexene as 
well as conjugated dienes such as 1,3 butadiene, methyl-2-butadiene, 
1,3-piperylene, 2,3 dimethyl butadiene, isoprene, cyclopentadiene, and 
dicyclopentadiene. Vinyl alkyl ethers include methyl vinyl ether, 
isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether. 
Acrylic monomers include monomers such as lower alkyl esters of acrylic or 
methacrylic acid having an alkyl ester portion containing between 1 to 12 
carbon atoms as well as aromatic derivatives of acrylic and methacrylic 
acid. Useful acrylic monomers include, for example, methyl acrylate and 
methacrylate, ethyl acrylate and methacrylate, butyl acrylate and 
methacrylate, propyl acrylate and methacrylate, 2-ethyl hexyl acrylate and 
methacrylate, cyclohexyl acrylate and methacrylate, decyl acrylate and 
methacrylate, isodecylacrylate and methacrylate, benzyl acrylate and 
methacrylate, and various reaction products such as butyl, phenyl and 
cresyl glycidyl ethers reacted with acrylic and methacrylic acids, 
hydroxyl alkyl acrylates and methacrylates such as hydroxyethyl and 
hydroxypropyl acrylates and methacrylates, as well as amino acrylates and 
methacrylates. Acrylic acids include acrylic and methacrylic acid, 
ethacrylic acid, alpha-chloracrylic acid, alpha-cyanoacrylic acid, 
crotonic acid, beta-acryloxy propionic acid, and beta-stryl acrylic acid. 
Olefinic unsaturated acids include fumaric acid, maleic acid or anhydride, 
haconic acid, citraconic acid, mesaconic acid, muconic acid, glutaconic 
acid, aconitic acid, hydrosorbic acid, sorbic acid, alpha-chlorosorbic 
acid, cinnamic acid, and hydromuconic acid as well as esters of such 
acids. Ethylenically unsaturated carboxylic acid amides and derivatives 
can be added in very minor amounts up to 5% and can include acrylamides or 
methacrylamides such as N-methylol acrylamide, N-ethanol acrylamide, 
N-propanol acrylamide, N-methylol methacrylamide, N-ethanol 
methacrylamide, and similar alkyl acrylamide or methacrylamide monomers 
containing methyl, ethyl, propyl, n-butyl or iso-butyl alkyl groups. 
Hydroxyl containing monomers are hydroxy containing ethylenically 
unsaturated monomers including hydroxyl alkyl acrylates such as 2-hydroxy 
ethyl acrylate and methacrylate, 2-hydroxypropyl acrylate and 
methacrylate, and similar hydroxy alkyl acrylates. On a weight basis, the 
monomers comprise at least 5% and preferably between 5% and 95% acrylic 
monomer, between 5% and 30% hydroxyl monomer, and the remainder being 
acrylic and/or other ethylenic monomers to provide an acrylic copolymer 
having an Acid No. between 1 and 30 and a Hydroxyl No. between 50 and 200. 
Typical solvents useful in preparing the acrylic copolymer, if desired, can 
include for instance, toluene, ethyl acetate, acetone, methylisobutyl 
ketone, methyl n-amyl ketone, methylisoamyl ketone, ethylamyl ketone, amyl 
acetone, methylethyl ketone, ethyl alcohol, mineral spirits, ethylene 
glycol monoethyl ether acetate, and other aliphatic, cycloaliphatic and 
aromatic hydrocarbon, esters, ethers, ketones and alcohols. After the 
polymerization is completed, solvents can be stripped off to increase the 
polymer solids content of the resulting polymer solution. 
Preferred acrylic high solids compositions comprise an acrylic copolymer in 
conjunction with a linear polyester polymer to form the high solids 
acrylic binder component of the coating. 
Referring next to the polyester component of the polymeric mixture, the 
polyester polymer is a low molecular weight linear polymer having a number 
average molecular weight measured by GPC between about 250 and 2,000 and 
preferably between 400 and 1,000 based on number average. Linear 
aliphatic, non-ether type glycols are esterified with considerably lesser 
molar amounts of aromatic dicarboxylic acid and a linear saturated 
dicarboxylic acid having between 2 and 10 linear carbon atoms such as 
adipic, azelaic, succinic, glutaric, pimelic, suberic or sebacic acid to 
produce low molecular weight polyesters. Preferred and commercially 
available linear saturated dicarboxylic acids are adipic or azelaic acid. 
Aromatic dicarboxylic acids (anhydrides) include phthalic, isophthalic, 
terephthalic, and tetrahydrophthalic. Isophthalic is preferred for 
superior films exhibiting detergent, salt spray and corrosion resistance. 
Suitable glycols include non-ether linear alipatic glycols having 2 to 8 
carbon atoms such as 1,3 or 1,4 butylene glycol, 1,6 hexane diol, 
neopentyl glycol, propylene glycol and similar linear glycols. Preferred 
glycol is neopentyl glycol. The molar excess of the glycol over the lesser 
molar amounts of aromatic and linear saturated dicarboxylic acid is 
between about 10% and 80% and preferably between about 20% and 60%. On a 
molar basis, the preferred low molecular weight polyester polymer 
comprises between 0.1 and 0.5 moles of aromatic dicarboxylic acid and 0.5 
and 0.1 moles of linear saturated dicarboxylic acid per 1 mole of glycol. 
Hence, the polyester contains considerable excess unreacted hydroxyl 
groups to provide a hydroxy polyester having a hydroxyl number between 115 
and 285 and preferably between 175 and 240. The polyester contains free 
carboxyl groups imparting an acid number that is preferably below 15 and 
typically between 5 and 10 mg KOH per gram of polyester. Glycol can be 
esterified with minor amounts of up to about 5% by weight of unsaturated 
dicarboxylic acids (anhydrides) including maleic, fumaric or itaconic 
acids; or monocarboxylic acids such as acetic, propyl-, and higher chain 
aliphatic acids up to about 8 carbon atoms. The polyester component can be 
produced by solvent or bulk polymerization although bulk polymerization is 
preferred. The raw materials can be charged in bulk and esterification 
polymerized at temperatures typically between 190.degree. C. to 
240.degree. C. although moderately higher or lower temperatures can be 
utilized satisfactorily. An esterification catalyst can be used, typically 
at less than 1% levels based on charge, such as an organo tin compound. 
Referring next to the hydroxyl urethane diluent, the urethane is a 
reactive, hydroxyl functional, very low molecular weight diluent 
preferably formed by reacting a primary or secondary amine with a cyclic 
carbonate. Amino functional materials can optionally contain a hydroxyl 
group. Examples of suitable diamines are Isophorone diamine, piperazine, 
hexane diamine, N,N'-dimethyl 1,6 hexanediamine, dodecanediamine, 
1,4-diaminocyclohexane or 2-methyl pentamethylene diamine. Suitable 
hydroxyl amines are ethanolamine, diethanolamine, neopentanolamine and the 
like. Preferred cyclic carbonates are ethylene carbonate and propylene 
carbonate. The reaction of mono- and di-amine with monocyclocarbonates has 
been described by M. F. El-Giamal and R. C. Shultz, Makromol. Chem., 177 
(8), 2259 (1976), and the same is incorporated herein by reference. The 
resulting hydroxyl functional urethane diluent can comprise on an 
equivalent basis one equivalent of amine coreacted with between 0.8 and 
1.5 equivalents of cyclic carbonate where the idealized structure 
comprises two cyclic carbonate molecules coreacted with a diamine 
molecule. The hydroxyl number can be between 100 and 750 and the number 
average molecular weight as measured by GPC of the hydroxyl urethane 
diluent can be between 150 and 1000. The hydroxyl urethane diluent can 
comprise between 5 and 60 by weight of the high solids polymeric mixture 
of polyester, acrylic and crosslinking amine resins. 
The foregoing hydroxyl functional, urethane diluent, acrylic, and polyester 
polymers can be combined with a coreative amine derivative crosslinking 
resin such as aminoplast including glycolurils. Examples of useful 
aminoplast resins are the reaction products of ureas and melamines with 
aldehydes further etherified with an alcohol. Examples of aminoplast resin 
components are urea, ethylene urea, thiourea, melamine, benzoguanamine. 
Aldehydes useful in this invention are formaldehyde, acetaldehyde and 
propionaldehyde, although formaldehyde is clearly preferred. The 
aminoplast resins can be used in the alkylol form but, most preferably, 
are utilized in the ether form by etherifying with a monohydric alcohol 
containing from 1 to about 8 carbon atoms. In a melamine molecule, for 
instance, up to 3 of the 6 active hydrogens on the amine group can be 
advantageously substituted with an alkanol group having 1-8 carbon atoms. 
Higher levels such as 6 substitution can be used in Cymel 300 
(1,3,5-triazine-2,4,6-triamine polymer) which contains 6 substituted 
methylol groups. The alkanol groups stabilize the melamine or other amine 
derivative under ordinary temperature, but enable reaction at higher 
temperatures. Preferred substitutions are between 2 and 4 substitutions to 
avoid popping or solvent entrapment with a fast curing film. Examples of 
aminoplast resins are methylol urea, dimethoxymethylol urea, butylated 
polymeric urea-formaldehyde resins, hexamethoxymethyl melamine, methylated 
polymeric melamine formaldehyde resin and butylated polymeric melamine 
formaldehyde resin. Glycoluril derivatives are disclosed in U.S. Pat. No. 
4,064,191 and are also known as acetylendiureas. Glycolurils are derived 
by reacting two moles of urea with one mole of glyoxal to provide a 
complex ring structure where substitute constituents can be a hydrogen, or 
a lower alkyl radical, or can be methylolated partially or fully by 
reacting with 1 to 4 moles of formaldehyde to provide a methylol 
glycoluril. The preparation of various glycolurils is illustrated in U.S. 
Pat. No. 4,064,191 such as tetramethylol glycoluril, tetrabutoxymethyl 
glycoluril, partially methyolated glycoluril, tetramethoxymethyl 
glycoluril, and dimethoxydiethoxy glycoluril. Useful glycoluril 
derivatives include for example, mono- and dimethylether of dimethylol 
glycoluril, the trimethylether of tetramethylol glycoluril, the 
tetramethylether of tetramethylol glycoluril, tetrakisethoxymethyl 
glycoluril, tetrakispropoxymethyl glycoluril, tetrakisbutoxymethyl 
glycoluril, tetrakisamyloxymethyl glycoluril, tetrakishexoxymethyl 
glycoluril and the like. Glycoluril derivatives can further include 
dimethylol dihydroxy ethylene urea which is disclosed in U.S. Pat. No. 
4,540,735 and incorporated herein by reference. 
On a polymer solids weight basis, the blend of polymers comprises broadly 
between 5% and 50% acrylic copolymer, between 10% and 60% polyester 
polymer, between 5% and 60% hydroxyl urethane diluent and between 20% and 
40% amine derivative cross-linking resin. Preferred polymeric blend 
compositions comprise 15% to 25% acrylic polymer, 20% to 50% polyester 
polymer, between 10% and 30% hydroxyl urethane diluent and 25% and 35% 
cross-linker such as aminoplast resin. 
In use, the acrylic copolymer containing amounts of primary hydroxyl groups 
can be used as a grind vehicle for preparing a pigmented vehicle base. 
Suitable pigments include titanium dioxides, carbon black, cadmiums, 
yellow, brown, and tan iron oxides as well as other oxide pigments and 
further include inert fillers such as talcs, clays, and fumed silicas. The 
acrylic polymer physically wets the titanium dioxide pigment surface for 
instance and further maintains the pigment in stable dispersion. Up to 
about six weight parts and typically between about 3.5 and 4 weight parts 
of pigment can be combined with one weight part of acrylic polymer 
depending on the adsorbtion properties of the pigment particles. Pigmented 
coatings typically comprise a pigment to binder ratio of about 1 to 1 for 
white or light colored paints. Black or dark colored paints may have a 
pigment to binder ratios as low as 0.5 to 1.0. The preformed acrylic 
polymer pigment grind can be combined with the polyester polymer, the 
hydroxyl urethane additive, and the amine derivative cross-linking resin.

The merits of this invention are further illustrated by the following 
examples wherein parts indicated are by weight and temperatures are in 
centigrade unless otherwise indicated. 
EXAMPLE 1 
Synthesis of a hydroxy functional urethane reactive diluent: 320 grams of 
Kemamine DP-3680 is charged to a 1 liter flask equipped with a stirrer, 
thermometer, reflux condenser and an addition funnel. 112.3 grams of 
propylene carbonate is then added over a 50 minute time period. Following 
this the reaction mixture is heated to 85 C., and held for 3 hours. The 
final product has an ASTM non-volatile content of 97.9, a base number of 
8.5 and a Gardner-Holt viscosity of Z6+3/4. Optionally, the free amine can 
be removed via neutralization with aqueous lactic acid followed by passing 
the material through an ion exchange column filled with Amberlite 200CH 
packing material. Kemamine DP-3680 is a diprimary amine with an 
approximate chain length of 42 carbons and is a product of Witco Chemical 
Corporation. 
EXAMPLE 2 
200.4 grams of N-methylethanol amine is charged to a 1 liter flask fitted 
as above. 299.6 grams of propylene carbonate is added over a 50 minute 
time period. The reaction mixture is heated to 100 C. and held for 4 
hours. The final product has an ASTM non-volatile content by weight of 
71.6 and a base number of 5.6. 
EXAMPLE 3 
213 grams of ethanol amine is added to a 1 liter flask as above. 391.5 
grams of propylene carbonate is added over a 45 minute time period. The 
reaction mixture is then heated to 100 C. and held for 2 hours. The final 
product has an ASTM non volatile content of 89.7, a base number of 1.9 and 
a Gardner-Holt viscosity of X. 
EXAMPLE 4 
176.7 grams of isophorone diamine is added to a 1 liter flask. 233.4 grams 
of propylene carbonate is added over a 15 minute period. The flask is 
heated slowly to 120 C. and held for 2 hours. 100 grams of methyl amyl 
ketone is added and the mixture cooled. The final product has a ASTM 
non-volatile by weight of 72.7, a base number of 15.9 and a Gardner-Holt 
viscosity of Z5+2/3. 
In an analogous manner to the previous examples 287 grams of 
neopentanolamine is reacted with 313 grams of propylene carbonate. The 
resulting product has a base number of 4.7 and a Gardner-Holt viscosity of 
Z5+1/4. 
EXAMPLE 6 
As a further example, 73.2 grams of anhydrous piperazine is reacted with 
191 grams of propylene carbonate. The product in this case has an ASTM 
nonvolatile content of 88.2 and a base number of 10.5. The product slowly 
crystallized on standing. 
EXAMPLE 7 
Preparation of a modified high solids coating 
______________________________________ 
Weight 
(grams) 
______________________________________ 
Dispersion Phase 
.sup.1 High Solids acrylic resin 
31.65 
Butyl Acetate 14.04 
Titanium Dioxide 100.00 
Reduction Phase 
.sup.2 High Solids polyester resin 
30.23 
Hydroxy urethanes from examples #1-6 
15.12 
.sup.6 Cymel 303 31.68.sup.5 
.sup.3 Silica Gel 6.07 
Butanol 7.50 
Dinonyl Napthalene Sulfonic Acid 
0.35 
.sup.4 Surfactant solution 
1.10 
Butyl Acetate 14.90 
______________________________________ 
.sup.1 A high solids acrylic resin based on the reaction product of 
styrene, butyl acrylate and 2hydroxyethyl acrylate. 
.sup.2 A high solids polyester resin based on the reaction product of 
Isophthalic acid, Neopentyl Glycol and Adipic acid. 
.sup.3 A dispersion of 7% of synthetic amorphous silica (Aerosil R974) 
available from DeGussa in high solids polyester. 
.sup.4 A 50% solution of a nonionic surfactant (Dislon L1980) from King 
Industries in Butyl Cellosolve Acetate. 
.sup.5 The level of melamine crosslinker was varied for each paint in 
keeping with maintaining the stochiometric level. 
.sup.6 Cymel 303 is a melamineformaldehyde condensation product from 
American Cyanamid Co. 
(COMATIVE) EXAMPLE 8 
Preparation of a Standard High Solids Paint 
A standard high solids paint is made according to the following formula. 
______________________________________ 
Weight 
(grams) 
______________________________________ 
Dispersion Phase 
High Solids acrylic resin 
31.65 
Butyl Acetate 14.04 
Titanium Dioxide 100.00 
Reduction Phase 
High Solids polyester resin 
45.89 
Cymel 303 34.00 
Silica Gel 6.07 
Butanol 7.50 
Dinonyl Napthalene Sulfonic Acid 
0.35 
Surfactant solution 1.10 
Butyl Acetate 10.85 
______________________________________ 
The resulting paint made from this formula has a calculated weight solids 
content of 80%, a measured ASTM voc of 2.45, but a viscosity of 50 seconds 
as measured by a Zahn #2 cup at 80 F. 
EXAMPLE 9 
The paints made from the examples cited are shown in the following table. 
______________________________________ 
Diluent Viscosity (Z2 @ 80F) 
ASTM NV 
______________________________________ 
None (comparative Ex. 8) 
50 seconds 79.1 
Example 1 37 seconds 80.3 
Example 6 39 seconds 80.1 
______________________________________ 
This invention provides for the use of hydroxyl functional urethane 
reactive diluents for use in high solids coatings where the diluents 
impart the desirable property that low levels of volatile organic solvents 
are required to reduce the viscosity of the paint for application, and is 
illustrated by the foregoing description and examples, but is not intended 
to be limiting, except by the appended claims.