CA1092286A - Levelling agent for aqueous paints - Google Patents

Abstract

Abstract of the Disclosure A levelling agent for use in aqueous paints is composed of a copolymer of monoethylenically, alpha, beta-unsaturated carboxylic acid and an alkyl acrylate or an alkyl methacrylate having in each case from 1 to 18 carbon atoms in the alkyl moiety, the copolymer having an average molecular weight of from about 2,000 to 80,000 and an acid value of from about 30 to 200, the carboxyl groups of the said copolymer being neutralized with a bas . The levelling agent, when used in an aqueous paint, provides improved surface gloss as well as improved surface properties for re-coating.

Description

10~2Z86 The present invention relates to a levelling agent for use in an aqueous paint. More particularlyt the present - invention relates to a levelling agent which can improve or prevent defects on the surface of a coating of aqueous paints, such as craters or detachment. The levelling agents of the present invention are provided with a combined property of improved surface gloss on the coating surface as well as improved surface properties for receiving a further coat of paint.
Aqueous paints have advantages with respect to atmospheric pollution prevention, security against fire or explosion and sanitary application under conditions free from malodor because they contain organic solvents in considerably lower concentrations than conventional organic solvent-type paints. From these advantages, aqueous paints have been used in increasingly amounts in various fields. The aqueous paints, howev~er, have some disadvantages which are associated with the use of water as a medium. The water may present defective results on the surface of the coating because of its high ~ 20 surface tension and may provide the coating with surface ; defects such as craters or detachment. These defects on the ; coating surface impair the appearance of the coating and decrease its coating efficiency to a considerable extent.
Heretofore, however, little development work has been done -- -on improvement of levelling agents for use in aqueous paints.
Water-soluble silicone resins and fluorine-containing sur- ~ -factants have been used for this purpose. However, these -materials are unsatisfactory in that they do not provide a suitable coating surface for the reception of an addition paint coat, i.e. for re-coating. As levelling agents for use in solvent-type paints, it is known that alkyl acrylate - ~0~Z~86 or alkyl methacrylate polymer~ have been used, such a~
described in Japanese Patent Publication No: 9570/1969 It has been found, however~ that these levelling agents do not provide satisfactory results in aqueous paints.
It is therefore an object of the present invention ; to provide an improved levelling agent for use in aqueous paints.
: It has now been found that a highly ~atisfactory levelling agent for aqueous or water-base paints is a copolymer of a monoethylenically alpha, beta-unsaturated carboxylic acid and an alkyl acrylate or an alkyl methacrylate having in each case from 1 to 18 carbon atoms in the alkyl moiety, the copolymer having an average molecular weight of from 2,000 to 80,000 and preferably from about 10,000 to 40,000 and an acid value of from about 30 to 200 and preferably from about 50 to 100, in which the carboxyl groups are wholly or sub-stant~ally wholly neutralized with a base.
The monoethylenically alpha, beta-unsaturated carboxylic acids may include a mono- or poly-, particularly di-, carboxylic acid having a polymerizable double bond in-their alpha and beta position and having from 3 to 12, preferably from 3 to 6, carbon atoms. Examples of the carboxylic acids are, for example, acrylic, crotonic, isocrotonic, methacrylic, angelinic, tiglic, 2-pentenic, alpha-ethylacrylic, :
beta-methylcrotonic, 2-hexenic, alpha-ethylcrotonic, maleic, fumaric, itaconic, citraconic and mesaconic acid and anhydrides thereof. The carboxylic acids may be used alone or in combina- -.
tion. The alkyl moiety of the alkyl acrylate and methacrylate .~ ;
is any alkyl group, unbranched or branched, having from 1 to : 30 18, preferably from 2 to 12, more preferably from 4 to 8, carbon atoms and it may include, for example, methyl, ethyl,

- 2 -.

Z~86 n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, isoamyl, hexyl, 2-ethylhexyl, heptyl, octyl, capryl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cesyl and cetyl. The alkyl acrylate and the alkyl methacrylate may be used alone or in combination.
The copolymers of the monoethylenically alpha, beta-unsaturated carboxylic acids may be prepared by means of conventional solution polymerization in which a hydro-phillic solvent such as an alcohol, e.g., ethanol, isopropyl alcohol or butanol, a cellosolve, e.g., butyl cellosolve or cellosolve acetate, or an ether, e.g., carbitol, may be employed. The monoethylenically, alpha, beta-unsaturated carboxylic acid may be used in an amount of from about 5 to 50 percent by weight with respect of the total weight of the mixture of the two constituents. A polymerization initiator may also be used and it may be a radical initiator customarily us,ed for this purpose, such as benzoyl peroxide, azobisiso-butryronitrile or cumene hydroperoxide. The polymerization initiator may be employed in an amount of from about 0.5 to 2 percent by weight with respect to the total weight of the monomers. The solution polymerization may be generally effected at a temperature of 70 to 110 C. The application of a too low temperature is not appropriate because it may result in excessive copolymerization and require a prolonged reaction time. The application of a too high temperature is not desired because it may present difficulty in adjusting the reaction temperature and result in the formation of a copolymer having a too low copolymerization degree. The polymerization time may range from about 3 to 5 hours. In order to facilitate the adjustment of the reaction temperature, Z2~6 it is preferable to add dropwise to said solvent an appro-priate amount of said polumeri~ation initiator in the form of a solution in said monomers The copolymers to be used according to the present invention possessan average molecular weight of from about 2,000 to 80,000 and an acid value of from about 30 to 200 Copolymers having a lower average molecular weight may not exhibit sufficient viscosity for levelling agents. The vis-cosity of copolymers with an average molecular weight greater than the said upper limit may be too high to defoam and such copolymers may not have a sufficient compatibility with aqueous paints, thereby causing defects on the coating sur-face such as craters or detachment when applied. Where the acid value of a copolymer is lower than said lower limit, its solubility in water may be insufficient when used for the neutralization of the carboxyl groups of the copolymer with a base, as will be in more detail described hereinbelow.
Conversely, a copolymer having an acid value greater than the sàid upper limit may possess such a high compatibility with water that it can no more maintain a surface tension to a level needed for levelling agents.
The levelling agent of the present invention is ~ ~-prepared from the copolymers having said properties by -treatment with a base, thereby wholly or substantially wholly neutralizing the carboxyl groups of the copolymer. -The base may be an inorganic or organic base such as, for example, a primary, secondary or tertiary amine, e.g., monomethylamine, monoethylamine, dimethylamine, triethyl-amine, ethylene diamine, diethylene triamine, triethylene tetramine, monoethanolamine, N-methylethanolamine, dimethyl-l~Z;~
ethanolamine or triethanolamine, an alkali metal hydroxide,e.g., sodium hydroxide or potassium hydroxide, or ammonia.
Of the amines, a tertiary amine is preferred. If an aqueous paint contain a base in an amount sufficient to neutralize the carboxyl groups of the copolymer to a satisfactory extent, no addition of such a base is any longer necessary-and the copolymer may be used as such. The amount of base required for neutralization is usually about 1-25% by weight based on the levelling agent.
The levelling agents of the present invention may be applied to any aqueous paint, for example, either of a type which dries at ambient temperature or of a type which dries at elevated temperatures. The levelling agent may be used in an amount ranging from 0.1 to 4 percent by weight with respect to the total amount of an aqueous paint prepared for application. The surface coating provided with this aqueous paint has no undesirable surface defects such as craters or detachment and has an improved surface gloss.
The coating surface can also possess properties appropriate for re-coating an aqueous paint thereon. The addition of the levelling agent can prevent or decrease the flooding phenomenon to a considerable extent because of increased wettability on the part of the pigments.
The following examples serve to illustrate the present invention without, however, limiting the same -thereto. In the following Examples, part or parts mean part or parts by weight.

50 parts of butyl CELLOSOLVE* were introduced into a four-necked flask equipped with a stirrer, a condenser and a dropping funnel and heated to 90C. A mixture of 44 parts * Trademark for glycol butyl ether of n-butyl acrylate, 6 parts of acrylic aoid and 0.5 part of benzoyl peroxide was added dropwise thereto over a period of 3 hours through the dropping funnel, while ~eing stirred.
The mixture was stirred for another 2 hours at 90C. for the completion of polymerization. To this was added dropwise a mixture of 12.4 parts of triethanolamine and 10 parts of deionized water over a period of 30 minutes while being stirred at 90C., and the mixture was stirred for another 30 minutes at the same temperature, thereby resulting in the completion of neutralization. The resulting copolymer solu-tion was found to contain 51 weight percent solids. It was also found that the copolymer prior to neutralization had an average molecular weight of 17,960 (when measured by the GPC
method) and an acid value of 66.

40 parts of butyl CELLOSOLVE were heated at 80C.
in the same manner as in Example 1. A mixture of 33.5 parts of 2-ethylhexyl acrylate, 14.5 parts of acrylic acid and 0.5 part of benzoyl peroxide was added dropwise thereto over a period of 3 hours while being stirred. The mixture was stir-red for another 2 hours at 80C. The resulting copolymer was ~' found to have an acid value of 158 and an average molecular ~ -weight of 24,999.
The copolymer was then treated by adding dropwise thereto 20 parts of triethylamine over a period of 30 minutes while being stirred and maintained at 80 C. The mixture was stirred for another 30 minutes at the same temperature. The resulting copolymer solution was found to contain 45 weight percent solids.

31.5 parts of 2-ethylhexyl acrylate, 18.5 parts of acrylic acid and 0.5 part of benzoyl peroxide were polymerized 109ZZ~6 in the same manner as in Example 2, thereby resulting in a copolymer having an acid value of 205 and an average molecular weight of 25,600. The copolymer was further treated with 25.7 parts of triethylamine as in Example 2. This gave a copolymeric solution having 43.1 weight percent solids.

47.9 parts of 2-ethylhexyl acrylate, 2.1 parts of acrylic acid and 0.5 part of benzoyl peroxide were polymerized by the procedures employed in Example 2, thereby giving a copolymer with an acid value of 23.2 and an average molecular weight of 22,210. The copolymer was then treated with 2.9 parts of triéthylamine as in Example 2. This resulted in the formation of a copolymeric solution having 53.8 weight percent solids.

42.7 parts of 2-ethylhexyl acrylate, 7.3 parts of acrylic acid and 0.5 parts of benzoyl peroxide were polymerized by the method used in Example 2, thereby resulting in a copolymer having an acid value of 80 and a~ average molecular weight of 23,980. The copolymer was then treated with 10.1 parts of triethylamine in the same manner as in Example 2. This gave a copolymer solution having 50.0 weight percent solids.
EXAMPLE A
An aqueous paint was formulated by adding 1.0 part of the copolymeric solution prepared in Example 1 to a blue enamel having the following composition (parts by weight):
Water-soluble, oil-free polyester resin ("EPOKY XY-616", trade mark Mitsui Toatsu Chemicals, Inc.) ............ 100 - 7 - , ;

~9ZZ~6 ' . . , Water-soluble melamine resin ~ (Mitsui Toatsu Chemicals, Inc.) .,......... 17 Amyl alcohol .............................. 11 Titanium oxide ............................ 75 Phthalocyanine Bl~e ...................... 15 Phthalocyanine Green ...................... 10 COMPARATIVE EXAMPLE A
For the comparative example, an aqueous paint was prepared by formulating the said blue enamel composition used in Example A.
COMPARATIVE EXAMPLE B
An aqueous paint was prepared by formulating the blue enamel composition used in Example A and 0.3 part by weight of a silicone resin ("TORE SILICONE SH 28", trade `
mark of Tore Silicone K. K.).
i EXAMPLE B -An aqucous paint was prepared by adding 1.0 part by weight of the copolymer solution of Example 2 to a while enamel having the following composition and diluting the 20 . product with deionized water so as to amount to a viscosity of 35.

Water-soluble, thermosetting acrylic resin ("Arrolon 557N", trade mark of Nichi-Doku Arrow K. K.) .................................... 100 Water-soluble melamine resin ("Nikalac MW-30", trade maxk of Nippon Carbide K. K.) ..................... 17 Titanium oxide ............................ 46 COMPARATIVE EXAMPLE C

. An aqueous paint was prepared by formulating the ::
.:

~, ~09ZZ~

while enamel composition used in Example B.
COMPARATIVE EXAMPLE D
An aqueous paint was prepared by adding 0.2 part by weight of the silicone resin employed in Comparative Example B to the composition employed in Example B, instead of the levelling agent used therein.
COMPARATIVE EXAMPLE R
An aqueous paint was prepared by adding to the white enamel composition used in Example B 1.0 parts by weight of the levelling agent of Comparative Example 1, instead of the levelling agent used therein.
COMPARATIVE EXAMPLE F
An aqueous paint was prepared in the same manner as in Example B except for the use of the levelling agent of Comparative Example 2 instead of the one used in Example B.
, EX~MPLE C
An aqueous paint was prepared in the same manner as in Example B except for the use of the, levelling agent of Example 3 instead of the one used in Example B.
RUN I
A clean tin plate was sprayed with the aqueous paint of Example A by means of a percorator so as to result in a dry coating thickness of 20 microns. The coating was baked for 1 minutes at 250 C. - ,' The resulting product was observed for the performance,', evaluation. The results are shown in Table I. '-RUN II
:
The aqueous paint of Comparative Example A was g _ , ;,~, , . , ~ .

applied to a clean tin plate in the same manner as in Run I.
The results are shown in Table I.
. RUN III
The aqueous paint of Comparative Example B was applied in the same manner as in Run II. The results are set out in Table I.
RUN IV
, A clean tin plate was sprayed with the aqueous ` paint of Examle B so as to result in a dry coating thickness of 20 microns. The coating was left to stand for 10 minutes at room temperature and baked for 30 minutes at.l40 C. The results are shown in Table II.
RUN V
.
The aqueous paint of Comparative Example C was apjplied to a clean tin plate in the same manner as in Example B. The results are shown in Table II.
RUN VI
_ The aqueous paint of Comparative Example D was applied in the same manner as in Run V. The results are set out in Table II.
RUNS VII THROUGH IX
,,, The agueous paints of Comparative Example E and F
and Example C were applied respectively in the same manner as in Run IV. The results are shown in Table III.

,.
.:

l~9ZZ86 TABLE I

RUN NOS.
Performance -Evaluation I II III
Formation of Craters. None Abundant None Surface GlossExcellent Poor ~airly Good Peeling-off None Much None Flooding None . MuchFairly Much Re-coatingExcellentGood Poor TABLE II

RUN NOS.
: Performance . Evaluation IV V VI
Formation of : Craters None Abundant None - Surface GlossExcellent Poor Fairly Good Peeling-off None Much None ~ -Re-coatingExcellentGood Poor :-- . - .
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TABLE III

RUN NOS.
Performance Evaluation VII VIII IX
Formation of Craters Much MuchNone Surface GlossFairly Good PoorExcellent Peeling-offFairly Good PoorExcellent -It is to be noted from Table III that the levelling agents having an acid value beyond the specified range provide an unsatisfactory coating surface for the reception of a furth~r coat of aqueous paint.

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Claims (14)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A levelling agent for use in an aqueous paint comprising a copolymer of a monoethylenically, alpha, beta-unsaturated carboxylic acid and an alkyl acrylate or an alkyl methacrylate having in each case from 1 to 18 carbon atoms in the alkyl moiety, the copolymer having an average molecular weight of from about 2,000 to 80,000 and an acid value of from about 30 to 200, the carboxyl groups of the said copolymer being neutralized with a base.

2. A levelling agent according to claim 1, wherein the monoethylenically alpha, beta-unsaturated carboxylic acid is a mono- or poly-carboxylic acid having a polymerizable double bond between the alpha and beta posi-tions.

3. A levelling agent according to claim 2, wherein the carboxylic acid is a mono- or poly-carboxylic acid having a polymerizable double bond between their alpha and beta positions and having from 3 to 12 carbon atoms.

4. A levelling agent according to claim 3, wherein the carboxylic acid is acrylic acid, crotonic acid, isocrotonic acid, methacrylic acid, angelinic acid, tiglic acid, 2-pentenic acid, alpha-ethylacrylic acid, beta-methyl-crotonic acid, 2-hexenic acid, alph-ethylcrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid or mesaconic acid or an anhydride thereof.

5. A levelling agent according to claim 1, wherein the alkyl acrylate is an acrylate having in its alkyl moiety from 1 to 18 carbon atoms.

6. A levelling agent according to claim 5, wherein the alkyl moiety is an unbranched or branched alkyl group.

7. A levelling agent according to claim 6, wherein the alkyl group is methyl, ethyl, n-propyl, iso-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, isoamyl, hexyl, 2-ethylhexyl, heptyl, octyl, capryl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cesyl or cetyl.

8. A levelling agent according to claim 1, wherein the alkyl methacrylate is a methacrylate having in its alkyl moiety from 1 to 18 carbon atoms.

9. A levelling agent according to claim 8, wherein the alkyl group is methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-amyl, isoamyl, hexyl, 2-ethylhexyl, heptyl, octyl, capryl, nonyl, decyl, undecyl, lauryl, tridecyl, myristyl, pentadecyl, cesyl or cetyl.

10. A levelling agent according to claim 1, wherein the base is an inorganic or organic base comprising a primary, secondary or tertriary amine, an alkali metal hydroxide, or ammonia.

11. A levelling agent according to claim 10, wherein the base is monomethylamine, monoethylamine, di-methylamine, triethylamine, ethylene diamine, diethylene triamine, triethylene tetramine, monethanolamine, N-methyl-ethanolamine, dimethylethanolamine, triethanolamine, sodium hydroxide, potassium hydroxide or ammonia.

12. A levelling agent according to claim 1, wherein the monoethylenically, alpha, beta-unsaturated carboxylic acid is contained in the copolymer in an amount of from about 5 to 50 percent by weight of the weight of the copolymer.

13. A levelling agent according to claim 1, wherein the base is employed in an amount of about 1 - 25%
by weight based on the levelling agent.

14. A levelling agent according to claim 1, combined with an aqueous paint in an amount of about 0.1 -4% by weight.