Copolymer coating

A copolymer for a protective coating is formed from a mixture of .alpha., .beta.-ethylenically unsaturated monomer, .alpha., .beta.-ethylenically unsaturated carboxylic acid monomer, and amphiphilic monomer. The protective coating has an average molecular weight of 7000 to 25000 to provide the desired properties of rapid drying, substantial film strength, and easy removal with an alkaline aqueous solution.

BACKGROUND OF THE INVENTION 
The present invention relates generally to a protective copolymer coating, 
and, more particularly, to a protective copolymer coating which can be 
removed by an alkaline aqueous solution. 
It is customary to use a protective coating on new products when 
transporting them or otherwise exposing them to the elements. An ideal 
protective coating must dry rapidly, have the strength to protect the 
surface of the product from the elements, and be easily removed. 
Prior coatings have not had all of the foregoing properties. Rapid drying 
has been achieved by using a coating with a low acidity. However, the 
lower the acidity, the more difficult it is to remove the coating with an 
alkaline aqueous solution. The strength of the coatings is improved when 
it has a high glass transition point, but this also limits the ease of 
removing the coating with an alkaline aqueous solution. A coating with a 
high acidity and a low glass transition point is more readily removable 
with an alkaline aqueous solution, but it does not dry rapidly and is not 
very strong. This is the problem with the coating in Japanese Laid-open 
Patent Publication No. 62-253673. This patent discloses a protective 
coating of alkyl acrylate, alkyl methacrylate, .alpha., 
.beta.-ethylenically unsaturated carboxylic acid, and .alpha., 
.beta.-ethylenically unsaturated monomer that can be removed by an 
alkaline aqueous solution. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the invention to provide a protective 
coating which overcomes the drawbacks of the prior art. 
It is a further object of this invention to provide a protective coating 
which dries rapidly, is strong enough to protect the coated surface from 
the elements, and can be removed with an aqueous alkaline solution. 
Briefly stated, the present invention provides a copolymer for a protective 
coating which is formed from a mixture of .alpha., .beta.-ethylenically 
unsaturated monomer, .alpha., .beta.-ethylenically unsaturated carboxylic 
acid monomer, and amphiphilic monomer. The protective coating has an 
average molecular weight of 7000 to 25000 to provide the desired 
properties of rapid drying, substantial film strength, and easy removal 
with an alkaline aqueous solution. 
According to an embodiment of the invention, there is provided a copolymer 
comprising: an .alpha., .beta.-ethylenically unsaturated monomer, an 
.alpha., .beta.-ethylenically unsaturated carboxylic acid monomer, and an 
amphiphilic monomer. 
According to a feature of the invention, there is provided a copolymer for 
a protective coating which is removable by an alkaline aqueous solution 
comprising: an .alpha., .beta.-ethylenically unsaturated monomer, an 
.alpha., .beta.-ethylenically unsaturated carboxylic acid monomer, and an 
amphiphilic monomer. 
According to a further feature of the invention, there is provided a 
protective coating composition comprising: an .alpha., .beta.-unsaturated 
monomer, an .alpha., .beta.-ethylenically unsaturated carboxylic acid 
monomer, an amphiphilic monomer, and an additive. 
According to a still further feature of the invention, there is provided a 
protective coating composition comprising: an .alpha., .beta.-unsaturated 
monomer, an .alpha., .beta.-ethylenically unsaturated carboxylic acid 
monomer, an amphiphilic monomer, and a solvent. 
According to a feature of the invention, there is provided a protective 
coating composition comprising: an .alpha., .beta.-unsaturated monomer, an 
.alpha., .beta.-ethylenically unsaturated carboxylic acid monomer, an 
amphiphilic monomer, an additive, and a solvent. 
According to a further feature of the invention, there is provided a method 
of preparing a protective coating which comprises: neutralizing a 
copolymer, and adjusting the copolymer to a pH of 6 or greater with a 
volatile and water soluble amine. 
According to a still further feature of the invention, there is provided a 
method of removing a protective coating comprising a copolymer which 
comprises applying an alkaline aqueous solution to a substrate. 
According to an embodiment of the invention, the copolymer has an average 
molecular weight of 7000 to 25000, as measured by Gel Permeation 
Chromatography (GPC). The .alpha., .beta.-ethylenically unsaturated 
monomer is 65 to 93% of the copolymer's weight, the .alpha., 
.beta.-ethylenically unsaturated carboxylic acid monomer is 7 to 20% of 
that weight, and the amphiphilic monomer is 0.2 to 15% of that weight. 
According to a feature of the invention, the protective coating formed from 
the copolymer may contain additives such as surfactants, ultra-violet (UV) 
absorbers, corrosion inhibitors, anti-oxidation agents, or anti-foaming 
agents. 
The above and other objects and advantages of the present invention will 
become apparent from the following description read in conjunction with 
the accompanying tables, in which like reference numerals designate the 
same element.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A copolymer for forming a protective coating, used to protect products in 
transport and from the elements, according to this invention has an 
average molecular weight of 7000 to 25000. The protective coating made 
from the copolymer is not strong enough when the weight of the copolymer 
is less than 7000 and it is too difficult to remove when the copolymer 
weighs more than 25000. 
The preferred percentages of the copolymer components are 73 to 88% 
.alpha., .beta.-ethylenically unsaturated monomer; 10 to 18% .alpha., 
.beta.-ethylenically unsaturated carboxylic acid monomer; and 1 to 10% 
amphiphilic monomer. 
The coating is not as easily removed with an alkaline aqueous solution when 
the .alpha., .beta.-ethylenically unsaturated monomer exceeds 93% and when 
the .alpha., .beta.-ethylenically unsaturated carboxylic acid is less than 
7%. The coating is less waterproof when there is less than 65% .alpha., 
.beta.-ethylenically unsaturated monomer and more than 20% .alpha., 
.beta.-ethylenically unsaturated carboxylic acid monomer. When there is 
more than 15% amphiphilic monomer the coating does not dry as rapidly and 
is less resistant to acid rain. When there is less than 0.2% amphiphilic 
monomer the coating does not polymerize effectively. 
The .alpha., .beta.-ethylenically unsaturated monomer may be one or more of 
the following: alkyl acrylate, alkyl methacrylate, aromatic vinyl 
compound, heterocyclic vinyl compound, vinyl ester compound, halogenated 
vinyl compound, .alpha.-olefin compound, or a monomer having a polar 
functional group. It is preferable to use n-butyl acrylate and methyl 
methacrylate. 
The alkyl acrylate of the .alpha., .beta.-ethylenically unsaturated monomer 
may be methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl 
acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, or lauryl acrylate. 
The alkyl methacrylate of the .alpha., .beta.-ethylenically unsaturated 
monomer may be methyl methacrylate, n-propyl methacrylate, i-propyl 
methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, or lauryl 
methacrylate. 
The aromatic vinyl compound of the .alpha., .beta.-ethylenically 
unsaturated monomer may be styrene or .alpha.-methylstyrene. The 
heterocyclic vinyl compound may be vinylpyrrolidone. The vinyl ester 
compound may be vinyl acetate, or vinyl propionate. The halogenated vinyl 
compound may be vinyl chloride, vinylidene chloride, or vinylidene 
fluoride. The .alpha.-olefin compound may be ethylene, propylene or 
butylene. The monomer having a polar functional group may be acrylamide, 
methacrylamide, acrylonitrile, methacrylonitrile, .beta.-hydroxyethyl 
acrylate, or .beta.-hydroxyethyl methacrylate. 
The .alpha., .beta.-ethylenically unsaturated carboxylic acid monomer may 
be a monobasic acid such as acrylic acid, methacrylic acid, or crotonic 
acid. It may be a monobasic acid as described above and one or more 
dibasic acids such as itaconic acid, fumaric acid, or maleic acid. It is 
preferred to use acrylic acid or methacrylic acid. 
An amphiphilic monomer should be soluble in a hydrophilic or a hydrophobic 
medium. It is preferred to use a moderately hydrophilic amphiphilic 
monomer. The amphiphilic monomer may be selected from one or more of the 
following: diacetone acrylamide, N,N-dimethylacrylamide, or 
N-acryloylmorpholine. 
The copolymer according to this invention can be produced by polymerizing a 
mixture of the aforementioned monomers by emulsion or solution 
polymerization. 
When the copolymer is produced by emulsion polymerization, a normal anionic 
emulsifier is used. The polymerizing initiator can be a water soluble 
peroxide including persulfate or a water soluble azo compound including 
azoamide compound. 
When the copolymer is produced by solution polymerization the polymerizing 
initiator can be an oil soluble peroxide including alkyl percarboxylate or 
an oil soluble azo compound including azobisisobutyronitrile. The medium 
used is an alcohol, ester, ketone, or aromatic hydrocarbon solvent. 
To use the copolymer it must first be neutralized and then its pH adjusted 
to 6 or more using a volatile and water soluble amine including ammonia or 
triethylamine. 
It is preferable to add an additive to the copolymer. The additives that 
may be used include surfactants, ultra-violet (UV) absorbers, corrosion 
inhibitors, anti-oxidation agents, and anti-foaming agents. When a 
surfactant is added the wetting property of the coating is improved, 
resulting in a uniform film. A preferred surfactant is an organic 
fluorochemical compound. When a UV absorber is added its absorption of the 
UV rays from the sun prevents the deterioration of the coating and 
enhances its removability. Several UV absorbers are preferred including 
2-hydroxybenzophenone, benzotriazole, and salicylic ester. 
The drying property of the polymer solution obtained from the 
polymerization process and the solubility of the additives is enhanced in 
the presence of 1 to 50% solvent relative to the polymer solution. The 
solvent may be an alcohol including isopropyl alcohol, methoxypropanol, 
ethoxypropanol or 2-butoxyethanol, or an ester including glycol ether, or 
a ketone including methyl isobutyl ketone, or an aromatic hydrocarbon 
including xylene. 
The protective coating is readily removable by an alkaline aqueous 
solution. 
Table 1 illustrates the varying performances and properties of the coating 
formed according to this invention depending on the percentage and type of 
monomer used to form the copolymer. Table 2 illustrates the comparative 
embodiments used to test the performances and properties of the coating 
formed according to this invention. Referring to Tables 1 and 2, the 
embodiments labeled 1, 2, 4, and 6 in Table 1 and the comparative 
embodiments labeled 1, 2, 3, and 5 were prepared by using a flask equipped 
with an agitator, two funnels, a thermometer, a nitrogen inlet, and a 
reflux condenser. A solution of 134.8 parts of deionized water and 0.4 
parts of anionic emulsifier were admixed in the flask. The anionic 
emulsifier used was ELEMINOL MON-2 produced by Sanyo Chemical Co., Ltd., 
Japan. 
First the air in the flask was replaced with nitrogen gas through the 
nitrogen inlet and the flask was heated to 80.degree. C. A polymerization 
initiating solution comprising 40 parts of deionized water and 0.3 parts 
of ammonium persulfate was added dropwise for 140 minutes from a dropping 
funnel into the flask, while a pre-emulsion prepared from the particular 
monomer compositions listed in Tables 1 and 2, 1 part lauryl mercaptan, 80 
parts of deionized water, and 0.6 parts of ELEMINOL MON-2 was added 
dropwise for 120 minutes from the other dropping funnel. The flask was 
then maintained at a temperature of 80.degree. C. for one hour to complete 
the polymerization. 
The polymer was then cooled while being neutralized by dilute ammonia 
water. A resinous solution of 20% concentration was obtained. Tables 1 and 
2 show the molecular weight, pH, acid value (theoretical value), and glass 
transition temperature (theoretical value) of the resinous solution. 
Next, 48 parts of butoxyethanol, 3 parts of UV absorber, and 0.5 parts of 
fluorochemical surfactant were added to the resinous solution. Deionized 
water was added to the resinous solution, and its viscosity was adjusted 
for 20 seconds using a Ford cup No. 4. 
The embodiments labeled 3 and 5 in Table 1 and the comparative embodiments 
labeled 4 and 6 in Table 2 were prepared by using a flask equipped with an 
agitator, two dropping funnels, a thermometer, a nitrogen inlet tube, and 
a reflux condenser. 
First the air in the flask was replaced with nitrogen gas through the 
nitrogen inlet and the flask was heated to 115.degree. C. Then a solution 
of 30 parts of butoxyethanol was poured into the flask. A polymerization 
initiating solution of 8 parts of butoxyethanol and 1.5 parts of 
tert-butyl peroxy-2-ethylhexanoate was added to the flask through one 
funnel dropwise for 180 minutes. The appropriate monomer compositions 
listed in Tables 1 and 2 were added through the other funnel dropwise for 
180 minutes. 
After the flask was maintained for 30 minutes at 115.degree. C., a solution 
comprising 4 parts of butoxyethanol and 0.3 parts of tert-butyl 
peroxy-2-ethylhexanoate was added dropwise for 30 minutes. Then the flask 
was maintained at 115.degree. C. for an additional 90 minutes to complete 
the polymerization. 
Next, the flask was cooled to 80.degree. C. and a solution of 3 parts of UV 
absorber and 0.5 parts of a fluorochemical surfactant were added to the 
flask. Additionally, dilute ammonia water was added to the flask to 
neutralize the copolymer while the flask was cooled to room temperature. A 
resinous solution of 20% concentration was obtained. 
Tables 1 and 2 show the molecular weight, pH, acid value (theoretical 
value), and glass transition temperature (theoretical value) of the 
resinous solution. 
Deionized water was added to the resinous solution, and its viscosity was 
adjusted for 20 seconds using a Ford cup No. 4. 
The coating compositions obtained according to the procedures detailed 
above were tested for their drying property, their resistance to acid 
rain, their resistance to rust from metallic powders, and their 
removability by an alkaline aqueous solution. 
The tests were carried out by spraying each coating on a plate of cold 
rolled steel treated with zinc phosphate (SURFDINE SD 2500, produced by 
Nippon Paint Co., Ltd.). A base coating (POWER TOP U-53, produced by 
Nippon Paint Co., Ltd.) was put on each test plate by electro-deposition. 
Subsequently, an intermediate coating (ORGA TO-4820, produced by Nippon 
Paint Co., Ltd.) and a final coating (ORGA TO-640 BLACK, produced by 
Nippon Paint Co., Ltd.) were added to each test plate by spraying. A 
plurality of test plates were prepared. 
The coating compositions obtained according to the procedures outlined 
above were sprayed on the test plates with a resulting dried film 
thickness of 10.+-.3 .mu.m. 
The drying time of each plate was tested by placing each plate in a 
wind-free environment to dry at a temperature of 60.degree. C. When the 
plates dried each was spotted with 2 ml of pure water. Then the drying 
time of each plate was determined and listed in Tables 1 and 2. The 
evaluation criteria were as follows: 
.circleincircle.: Within 20 minutes 
.circle.: Within 30 minutes 
.DELTA.: Within 40 minutes 
X: More than 40 minutes 
The test of resistance to acid rain was conducted as follows. After being 
sprayed with the respective coating compositions, each test plate was 
dried for 10 minutes at a wind velocity of 1 meter per second. Each test 
plate was then spotted with 0.1 ml of diluted sulfuric acid having a pH of 
2 and heated to 80.degree. C. and dried. Subsequently, the protective 
coating was removed with 1% monoethanolamine solution and the condition of 
each test plate was observed and listed in Tables 1 and 2. The evaluation 
criteria were as follows: 
.circleincircle.: No change 
.circle.: Slight contamination around the spot 
.DELTA.: Spot trace remained clearly 
X: Spot trace remained clearly over the entire area of the spot 
The coatings were tested for rust resistance by passing iron powder through 
a 200-mesh sieve over the surface of each plate. The plates were 
maintained horizontally for 1 hour at 80.degree. C. The iron powder was 
then removed by a brush. The plate was then subjected to salt spraying for 
48 hours. The protective coating was then removed using 1% 
monoethanolamine solution and the degree of rust spreading was measured. 
The results are listed in Tables 1 and 2. The evaluation criteria were as 
follows: 
.circleincircle.: No occurrence of rust 
.circle.: Spreading area of rust was no more than 1% 
.DELTA.: Spreading area of rust was no more than 10% 
X: Spreading area of rust was no less than 10% 
The removability of the protective coating by an alkaline aqueous solution 
was tested by exposing each plate in the open air for three months during 
the summer on Okinawa island. The protective coating was removed with 1% 
monoethanolamine solution and each plate was washed with water. The 
quantity of protective coating remaining was examined and is listed in 
Tables 1 and 2. The evaluation criteria were as follows: 
.circleincircle.: Nothing remained 
.circle.: Some remained in dotted form, but dissolved in 1% 
monoethanolamine solution 
.DELTA.: Remained in spot form and did not dissolve in 1% monoethanolamine 
solution 
X: Remained and did not dissolve 
Having described preferred embodiments of the invention with reference to 
the accompanying drawings,it is to be understood that the invention is not 
limited to the precise embodiments and that various changes and 
modifications may be affected therein by one skilled in the art without 
departing from the scope or spirit of the invention which is limited only 
by the appended claims. 
TABLE 1 
__________________________________________________________________________ 
Embodiments 
1 2 3 4 5 6 
__________________________________________________________________________ 
Monomer Composition %* 
Methyl methacrylate 
45.7 42.6 48.8 40.1 45.1 43.5 
n-Butyl acrylate 
36.4 37.0 32.0 34.6 31.3 34.6 
Methacrylic acid 
16.9 15.4 -- 15.3 -- 16.9 
Acrylic acid -- -- 12.2 -- 11.6 -- 
Diacetone acrylamide 
1.0 5.0 5.0 10.0 12.0 5.0 
Acrylamide -- -- -- -- -- -- 
.beta.-Hydroxyethyl methacrylate 
-- -- 2.0 -- -- -- 
Emulsion 
Emulsion 
Solution 
Emulsion 
Solution 
Emulsion 
Polymerization method 
polymerization 
polymerization 
polymerization 
polymerization 
polymerization 
polymerization 
Resin Properties 
Number-average molecular 
12 12 12 12 12 12 
weight (.times. 10.sup.3) 
pH 7.5 7.5 7.5 7.5 7.5 7.5 
Acid value (Calculated value) 
110 100 95 100 90 110 
Glass transition temp. .degree.C. 
33 30 30 33 30 35 
Performance of coating 
Drying property 
.largecircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.largecircle. 
Resistance to acidic rain 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.circleincircle. 
Resistance to iron powder 
.circleincircle. 
.largecircle. 
.largecircle. 
.circleincircle. 
.largecircle. 
.circleincircle. 
Removability by alkaline 
.circleincircle. 
.circleincircle. 
.circleincircle. 
.largecircle. 
.largecircle. 
.circleincircle. 
solution 
__________________________________________________________________________ 
*Weight % 
TABLE 2 
__________________________________________________________________________ 
Comparative Embodiments 
1 2 3 4 5 6 
__________________________________________________________________________ 
Monomer Composition %* 
Methyl methacrylate 
46.3 31.7 41.0 40.6 53.5 40.6 
n-Butyl acrylate 
37.9 32.9 33.6 34.1 31.9 28.7 
Methacrylic acid 
15.3 15.4 15.4 15.3 4.6 -- 
Acrylic acid -- -- -- -- -- 25.7 
Diacetone acrylamide 
-- 20.0 -- -- 10.0 5.0 
Acrylamide -- -- 5.0 -- -- -- 
.beta.-Hydroxyethyl methacrylate 
-- -- -- 10.0 -- -- 
Emulsion 
Emulsion 
Emulsion 
Solution 
Emulsion 
Solution 
Polymerization method 
polymerization 
polymerization 
polymerization 
polymerization 
polymerization 
polymerization 
Resin Properties 
Number-average molecular 
12 12 12 12 12 12 
weight (.times. 10.sup.3) 
pH 7.5 7.5 7.5 7.5 7.5 7.5 
Acid value (Calculated value) 
100 100 100 100 30 200 
Glass transition temp. .degree.C. 
30 33 30 33 33 35 
Performance of coating 
Drying property 
.largecircle. 
.DELTA. .DELTA. .DELTA. .circleincircle. 
X 
Resistance to acidic rain 
.largecircle. 
.DELTA. .DELTA. .DELTA. .largecircle. 
.largecircle. 
Resistance to iron powder 
.DELTA. .largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
.largecircle. 
Removability by alkaline 
.largecircle. 
.largecircle. 
X .largecircle. 
X rough surface 
.circleincircle. 
__________________________________________________________________________ 
*Weight %