Coating compositions of thermoplastic acrylic-urethane copolymers

A coating composition based on a thermoplastic copolymer prepared by polymerizing one or more ethylenically unsaturated monomers in the presence of a fully reacted polyurethane. The resulting copolymer can be coated as a clear film, air dried and has particular utility, when combined with pigments and metallics, in automotive finishes.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to polymeric coating compositions which can be 
applied to a variety of substrates, and in particular, to a coating 
composition that is useful in automotive finishes. 
2. Description of the Prior Art 
A great need exists for a coating composition that can be used to repair 
damaged lacquer coatings, in particular, acrylic lacquer coatings which 
are widely used in the auto industry. A coating composition of this type 
would find wide use in the repair of damaged autos and trucks and in the 
production of autos and trucks where portions of the vehicle often require 
touch-up painting after assembly. Methacrylate coating compositions are 
well known in the art as shown by Crissey and Lowell U.S. Pat. Nos. 
2,934,509 and 2,934,510, both issued on Apr. 26, 1960. Coating 
compositions formed from cellulose acetate butyrate and a methacrylate 
polymer have been successfully used on metal substrates as shown in Evans 
U.S. Pat. No. 2,849,409, issued Aug. 26, 1958. Polymers containing 
oxazoline drying oils have been used as coatings and are disclosed in 
Miranda et al U.S. Pat. No. 2,208,981, issued Sept. 28, 1965, and Purcell 
U.S. Pat. No. 3,248,397, issued Apr. 26, 1966. The coating compositions of 
these prior art patents are excellent for many uses but do not have the 
properties preferred for a repair composition. 
Generally, films of the so-called methyl methacrylate lacquers prepared 
from polymers containing methyl methacrylate as a main monomer have 
excellent characteristics in such properties as colorlessness, 
transparency, gloss retention over a long period and resistance to 
yellowing. 
However, when formed into a film, a methyl methacrylate lacquer obtained by 
polymerizing methyl methacrylate alone or in combination with a small 
amount of an acrylate of C.sub.2 -C.sub.16 alkanol, e.g. ethyl acrylate, 
n-butyl acrylate or 2-ethylhexyl acrylate, or a methacrylate of C.sub.4 
-C.sub.16 alkanol, e.g. 2-ethylhexyl methacrylate or lauryl methacrylate 
(these monomers are so-called internal-plasticizing monomers), tends to 
form cracks in the film by swelling or shrinking action due to temperature 
variation or to moisture, and encounters difficulties in impact resistance 
and in adhesion onto coated substrate surfaces. Further, this kind of 
lacquer is liable to cause shrinking or cracking phenomenon when recoated 
onto its own film or overcoated onto other films. That is, the lacquer is 
inferior in recoating and overcoating. 
In case the amounts of said plasticizable monomers are increased, the above 
drawbacks can be overcome to a considerable extent, but the resulting film 
becomes soft, and it becomes high in temperature susceptibility and 
thermoplastic tendency and also its gasoline resistance and water 
resistance deteriorates. 
Even in the case of a methyl methacrylate lacquer in which an 
internal-plasticizing monomer has been used in such a suitable amount as 
to satisfy, from the standpoint of its composition, the hardness, gasoline 
resistance and crack resistance of the resulting film and such proportion 
as recoating and the like, these properties are not satisfactory, in 
practice, unless the molecular weight of the polymer employed is made 
higher than a definite limit. However, the molecular weight of a copolymer 
obtained by solution polymerization is closely connected with the 
viscosity of the copolymer solution, and therefore such methyl 
methacrylate lacquer cannot be applied, in general, unless it is diluted, 
before application, with a large amount of solvent. This indicates the 
fact that such a methyl methacrylate lacquer as mentioned above is not 
well retained on a substrate to be coated and cannot be applied thickly. 
Polyurethanes constitute a broad class of polymeric materials having a wide 
range of physical characteristics. The polymers are usually produced 
through the interaction of a polyfunctional isocyanate with a 
polyfunctional chemical compound having an active hydrogen in its 
structure. 
In U.S. Pat. Nos. 3,865,898, 3,257,476 and 3,291,859 there are disclosed 
block copolymers and processes for forming them. In U.S. Pat. Nos. 
3,257,476 and 3,291,859 the block copolymers are of an A-B-A structure. 
These patents teach a synthesis route to the preparation of block 
copolymers wherein one block is a vinyl copolymer and the other block can 
generally be referred to as a polyurethane. In the general scheme of 
synthesis as taught by these patents, a prepolymer is formed by reacting 
an aromatic diisocyanate with a polymeric material having functional 
groups with active hydrogen to form an "isocyanate-capped" prepolymer. The 
prepolymer is then usually reacted with tert-butyl hydroperoxide, a cumene 
hydroperoxide, or a dual-functional free radical initiator to form a 
peroxycarbamate which has reactive sites capable of initiating the 
polymerization of ethylenically-unsaturated monomers to form a block 
copolymer. 
SUMMARY OF THE INVENTION 
It has now been found that a superior coating composition can be prepared 
based on a thermoplastic copolymer prepared by polymerizing one or more 
ethylenically unsaturated monomers in the presence of a fully reacted 
polyurethane. The thermoplastic acrylic-urethane copolymer can be coated 
as a clear film, air dried, and has particular utility, when combined with 
pigments and metallics, in automotive finishes.

DETAILED DESCRIPTION OF THE INVENTION 
The present invention is directed to a coating composition comprising a 
copolymer of (a) one or more ethylenically unsaturated monomers and (b) a 
fully reacted polyurethane. 
By ethylenically unsaturated monomer I mean any of the known polymerizable 
ethylenically unsaturated monomers characterized by the presence therein 
of at least one polymerizable ethylenic group. These monomers are well 
known in the art and include the hydrocarbon monomers such as butadiene, 
isoprene, styrene, alpha-methyl styrene and the like; substituted styrene 
such as chlorostyrene, dichlorostyrene, bromostyrene, p-vinylphenyl phenyl 
oxide and the like; the acrylic and substituted acrylic monomers such as 
methyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, methyl, 
ethyl and butyl acrylate, phenyl acrylate, phenyl methacrylate, 
alphachloroacrylonitrile and the like; the vinyl esters and vinyl ethers 
such as vinyl actate, vinyl acrylate, vinyl methacrylate, vinyl propyl 
ethers, vinyl butyl ethers and the like; acrylic acid and methacrylic 
acid; other water soluble monomers such as hydroxy ethyl acrylate or 
methacrylate, hydroxy propyl acrylate or methacrylate and the like. Any of 
the known polymerizable monomers can be used and the compounds listed 
above are illustrative and not restrictive of the monomers suitable for 
use in this invention. 
The ethylenically unsaturated monomers which are preferred in the practice 
of this invention include the acrylic and substituted acrylic monomers as 
well as styrene. 
The fully reacted polyurethane composition, in which the in situ 
polymerization of one or more ethylenically unsaturated monomers is 
effected, is formed by the reaction in a solvent of a diisocyanate 
component with a polyol and a compound containing at least two reactive 
functional groups. Suitable polyurethanes include water soluble or water 
reducible polyurethane compositions. 
The diisocyanate components which are useful according to this invention 
include those conventionally used in preparing polyurethane resins and 
include for instance toluene diisocyanates, such as the 2,4- and 
2,6-isomers and their mixtures, 1,5 naphthylene diisocyanate, p-phenylene 
diisocyanate, 3,3'-dimethyl-4,4'-diphenylmethane diisocyanate and 
4,4'-diphenylmethane diisocyanate. 
Preferred diisocyanates are the aliphatic type since it has been found that 
these provide better color stability in the finished coating. Examples 
include isophorone diisocyanate, 1,6-hexamethylene diisocyanate and 
methylcyclohexylene diisocyanate. Mixtures of diisocyanates can also be 
employed. An especially preferred diisocyanate is a cycloalkyl-substituted 
diisocyanate designated as bis (4-isocyanatocyclohexyl) methane and having 
the structure 
##STR1## 
This diisocyanate is commercially available from E. I. duPont Chemical 
Company and referred to as Hylene W. 
The polyols can be either low or high molecular weight materials and 
preferably include a mixture of the two and in general will have average 
hydroxyl values as determined by ASTM designation E-222-67, Method B, 
between about 1000 and 10, and preferably between about 500 and 50. 
The polyols include low molecular weight diols. The low molecular weight 
diols useful in the instant invention are known in the art. They have 
hydroxy values of 200 or above, usually within the range of 1500 to 200. 
Such materials include aliphatic polyols, particularly alkylene polyols 
containing from 2 to 18 carbon atoms. Examples include ethylene glycol, 
1,4-butanediol, 1,6-hexanediol, cycloaliphatic polyols such as 
1,2-cyclohexanediol and cyclohexane dimethanol. 
Where flexible and elastomeric properties are desired, the polyurethane 
should preferably contain at least a portion of a higher molecular weight 
polymeric polyol. Such a polymeric polyol should be predominantly linear 
(that is, absence of trifunctional or higher functionality ingredients) to 
avoid gelling of the resultant polymeric product and should have a 
hydroxyl value of 200 or less, preferably within the range of about 
150-30. 
The most suitable polymeric polyols include polyalkylene ether polyols 
including thio ethers, polyester polyols including polyhydroxy 
polesteramides and hydroxyl-containing polycaprolactones. 
Any suitable polyalkylene ether polyol may be used including those which 
have the following structural formula: 
##STR2## 
where the substituent R is hydrogen or lower alkyl including mixed 
substituents, and n is typically from 2 to 6 and m is from 2 to 100 or 
even higher. Included are poly (oxytetramethylene) glycols, poly 
(oxyethylene) glycols and polypropylene glycols. 
Polyester polyols can also be used as a polymeric polyol component in the 
practice of the invention. The polyester polyols can be prepared by the 
polyesterification of organic polycarboxylic acids or anhydrides thereof 
with organic polyols. Preferably, the polycarboxylic acids and polyols are 
aliphatic or aromatic dibasic acids and diols. 
Besides polyester polyols formed from polybasic acids and polyols, 
polycaprolactone-type polyesters can also be employed. These products are 
formed from the reaction of a cyclic lactone such as epilson-caprolactone 
with a polyol or a hydroxy acid. 
The higher polymeric polyol component is preferably combined with low 
molecular weight polyol described above. It has been found that by 
blending high and low molecular weight polyols, optimum properties can be 
obtained in the resultant polyurethane. Preferably, the polymeric polyol 
is the major component, being present in an amount of about 25 to 95 
percent by weight based on total weight of the polyol used to prepare the 
polyurethane, the remainder being low molecular weight polyol. 
The polyurethane can be terminated with a compound containing at least one 
reactive functional (capping) group. The functional group can contain an 
active hydrogen atom that is displaced during the reaction with the 
isocyanate. These active hydrogen atoms are characterized by a positive 
Zerewitinoff test. The most common functional groups (capping agents) 
containing these active hydrogen atoms are 
##STR3## 
--SH, --NH.sub.2. Some of the more common examples of capping agents are: 
mono functional alcohols 
methanol, ethanol, isopropanol 
difunctional --OH containing compounds 
1,4-butanediol, ethylene glycol, propylene glycol 
mono functional organic acids 
formic acid, acetic acid 
difunctional organic acids 
succinic acid, glutaric acid 
difunctional amines 
1,2-propylene diamine, ethylene diamine 
The especially preferred compounds are the difunctional hydroxyl containing 
compounds. 
The type and ratio of solvents used in the synthesis of the polyurethane 
and in the conversion of the acrylic monomer to polymer and the solubility 
of the acrylic-urethane copolymers formed is important. 
The solvent(s) must be: 
(a) volatile enough to form an air dry tack free film in 1 hr, 
(b) such that the solvent would not interfere with the polyurethane 
formation. 
Similarly, it is also important that the solvent(s) have an effect on the 
drying characteristics and ultimate gloss of the dry coating. Suitable 
solvents include methyl ethyl ketone, methyl Cellosolve acetate, etc. and 
preferably a mixture of solvents such as a methyl Cellosolve 
acetate/methyl ethyl ketone mixture. 
A ratio of from about 2 to about 7 parts acrylic monomer to 1 part fully 
reacted polyurethane can be used to prepare the copolymers according to 
this invention. An especially preferred ratio is 3 parts acrylic monomer 
to 1 part fully reacted polyurethane. 
Pigments are used in the novel coating composition of this invention in the 
amounts of 0.1-20.0% pigment volume concentration, preferably, a pigment 
volume concentration of about 0.1-14% is used. Examples of the great 
variety of pigments which are used in the novel coating composition of 
this invention are metallic oxides, preferably titanium dioxide, zinc 
oxide, and the like, metal hydroxide, metal flakes, chromates, such as 
lead silica, talc, china clay, organic dyes and lead, iron blues, organic 
reds, maroons, and the like, organic dyes and lakes, etc. 
The novel coating compositions of this invention can be applied to a 
variety of substrates, for example, wood, glass and metal, by any of the 
usual application methods, such as spraying, dipping, flowcoating and 
brushing. These coatings can be air dried or can be baked, for example, 
about 10-50 minutes at 125-175 degrees C. The resulting coatings or films 
can be rubbed or polished in accordance with conventional techniques, if 
desired, to improve smoothness gloss or both. 
The novel coating compositions of this invention are particularly useful in 
repairing lacquer coatings and in particular acrylic lacquer coatings. The 
novel composition of this invention has excellent adhesion and durability 
when dry and can be pigmented to blend with refinished area with the 
adjacent areas of the coating which makes the refinished area 
unnoticeable. 
The dried coatings of the compositons of this invention are characterized 
by increased freedom from water spotting and have excellent craze 
resistance in combination with outstanding durability and gloss retention. 
Coatings of this invention also have good gasoline resistance and improved 
adhesion as compared with conventional methyl methacrylate lacquers. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The following specific examples are given to further illustrate the 
invention. In the examples and elsewhere, the "parts" are by weight unless 
otherwise stated. 
EXAMPLE I 
______________________________________ 
A reaction mixture consisting of 
Parts 
______________________________________ 
Polytetramethylene glycol, M.W. 
630 
of 2000 
1,4 Butanediol 14.16 
bis(4-isocyanatocyclohexyl) methane 
165.1 
(Hylene W) 
2-methoxyethyl acetate 1503.0 
Dibutyl tin dilaurate 0.8 
______________________________________ 
was heated at 75.degree.-80.degree. C. in a nitrogen atmosphere for three 
hours or until a constant NCO assay of &lt;0.1 milliequivalents of NCO per 
gram of 35% solution was obtained. Sufficient 1,4 butanediol was added to 
reduce the NCO assay to about 0.035 milliequivalents of NCO per gram of 
35% solution. At this point, sufficient 1,4 butanediol was added to 
produce a hydroxyl terminated polyurethane. The calculation of the amount 
of 1,4 butanediol was made as follows: Grams of 1,4 butanediol 
required=0.035 milliequivalents of NCO per gram.times.batch weight in 
grams.times.molecular weight of butanediol/1000. 
EXAMPLE II 
The following compounds are substituted for the 1,4 butanediol of Example 
I. 
(A) ethylene glycol 
(B) propylene glycol 
(C) isopropyl alcohol 
(D) ethyl alcohol 
The reaction is followed as in Example I and fully reacted polyurethanes 
are obtained. 
EXAMPLE III 
Preparation of acrylic-urethane copolymer. 
To a reactor was charged 280 parts of the hydroxyl terminated polyurethane 
from Example I, 294 parts of methyl methacrylate, 171 parts of methyl 
Cellosolve acetate, 235.0 parts of methyl ethyl ketone and 5.9 parts of 
t-butyl peroctoate. The reactants were heated to 85.degree. C. for 3-4 
hours in a nitrogen atmosphere for 6-7 hours producing a 40 percent solids 
polymer solution. A free film of this resin cast on glass and allowed to 
air dry was clear and glossy. 
EXAMPLE IV 
An acrylic-urethane copolymer was prepared similar to Example III except a 
portion (approximately 30%) of the methyl methacrylate was replaced by 
styrene. The copolymer produced formed a clear and glossy film when cast 
on glass and air-dried. 
EXAMPLE V 
The following acrylic monomers were substituted for the methyl methacrylate 
of Example III. 
(A) ethyl methacrylate 
(B) cyclohexyl methacrylate 
(C) butyl methacrylate 
(D) n-propyl methacrylate 
The reaction similar to Example III was followed and the copolymers so 
prepared are useful in the preparation of clear films. 
EXAMPLE VI 
Physical blend of polymethylmethacrylate and hydroxyl terminated 
polyurethane. 
(a) Preparation of Polymethylmethacrylate 
A reaction mixture consisting of the following was prepared: 
______________________________________ 
Parts 
______________________________________ 
Methyl methacrylate 550.0 
Methyl ethyl ketone 342.7 
2-methoxyethyl acetate 342.6 
t butyl peroctoate 11.0 
______________________________________ 
One third of the above reaction mixture was charged to a reaction flask and 
heated in a nitrogen atmosphere to 85.degree. C. at which time the 
remaining 2/3 was added dropwise over 11/4 hours, then held 3 hours at 
85.degree. C. At this time an additional 2.5 parts of t butyl peroctoate 
in 5 parts of methyl ethyl ketone was added and the reaction continued an 
additional 2.5 hours at 85.degree. C., then cooled to room temperature. 
The resulting 44 percent solids solution was clear and colorless. 
(b) Preparation of acrylic-urethane blend 
To a reactor was charged the following: 
______________________________________ 
Parts 
______________________________________ 
Polymethylmethacrylate (44% solids) 
from Example (a) 441.5 
Hydroxyl terminated polyurethane 
from Example I 185.0 
Methyl ethyl ketone 45.4 
2-methoxyethyl acetate 9.7 
______________________________________ 
The hazy incompatible mass was stirred one hour at room temperature 
(25.degree. C.) with no improvement in compatibility. The reaction mixture 
was then heated to 100.degree. C., held for 7 hours, then cooled to room 
temperature. The resulting hazy resin, on standing, separated into two 
layers. Thus it can be seen that physical blends of acrylic and urethane 
polymers are not useful according to this invention. 
EXAMPLE VII 
A coating composition was prepared using the copolymer of Example III. 
______________________________________ 
Pigment Dispersion Parts by Weight 
______________________________________ 
Example III polymer 140.7 
Ethylene glycol mono ethyl ether acetate 
33.0 
Butyl acetate 49.9 
Ethylene glycol mono ethyl ether 
30.6 
Toluene 23.2 
Rutile titanium dioxide 
220.0 
497.4 
______________________________________ 
After ball milling the above to a fineness of 10 microns the following 
coating was prepared. 
______________________________________ 
Parts by Weight 
______________________________________ 
Above Dispersion 113.1 
Example III polymer 198.2 
Butyl Benzyl Phthalate 10.0 
Acrylic Lacquer Reducer 
327.5 
648.8 
______________________________________ 
The resulting lacquer had a weight solids of about 23.1% at 14 seconds Ford 
No. 4 spray viscosity and was useful as an automobile paint composition. 
EXAMPLE VIII 
______________________________________ 
Parts by Weight 
______________________________________ 
Example III polymer 358.0 
Premix and Add 
Aluminum Flake 7.0 
Toluene 8.6 
Adjust to spray viscosity with 
Acrylic Lacquer Reducer 
606.4 
980.0 
______________________________________ 
The resulting lacquer had a weight solids of about 14.7% at 13 seconds Ford 
No. 4 spray viscosity and was useful as an automobile paint composition.