CA1184445A - Metallic pigment particle coated with an epoxy containing copolymer - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Polymer-coated metallic pigments for paints are proposed which comprise metallic pigment particles coated with a polymer.
They are particularly suitable for use with paints for electro-static painting, water-based paints, and paints for plastics, They may comprise a silicone compound.

Description

1 The presen-t .inventi.on relates to polymer-coated metallic pigments used particularly to produce pain-ts for electrostatic painting, water-based pain-ts, and paints for plastic products, and to a process for producing the same.
Metallic pigments have been widely used to prepare paints for construction materials, light electrical appliances, machinery, ships, vehicles, automobiles, etc. and to prepare inks for painting on paper and plastic materials, n the other hand, electrostatic painting, painting using water-based paints, and painting on plastic materials are highligh-ted in recent years for ~etter painting efficiency and pollution-free cleanlines.
However, the use of the conventional metallic pigments for such new types of painting is attended with various problems.
In the electrostatic painting, because of poor withstand voltage of the conventional metallic pigments, the application of high voltage required for this type of pain-ting causes a heavy current leakage. Also, when used for water-based paintsr the conventional metallic pigments react with water during storage to produce hydrogen gas because of poor water resistance so that the paint would lose its metallic luster and blacken. In the plastic painting, baking finish cannot be used because of lo~ heat resis-tance of the plastic to be pain-ted and the paint containing the conventional metallic pigment canno-t but be dried at lo~ temper-ature, usually at 50-60C. This results in poor cohesion o the paint filrn and particularly in poor affinity between the metallic pigment and the binder in the paint fiLm in comparison with the baked film, even if the most suitable combination of binder and organic solvent is selected. The metallic pigments usually used for plas-tic painting are in the form of flakes and they are norm-3~ ally coated with fatty acids, I~ the conventional metallic p.ig-ments are used for plastic painting, they exhibit poor orientation 1 uniformity and poor cohesion in -the paint film because of their poor affinity with the binder. The property for preventing such problems is hereinafter referred to as the peelproofness.
Another problem is that shock due to static electrici.ty is sometimes felt when one touches a metallic coat on an apparatus containing a high voltage generator, such as a TV set. The property of preventing such a phenomenon is hereinafter referred to as the shockproofness.
Another requirement for the plastic painting i5 touch-proofness. This is related to the fact that the paint film isdried not by baking but at low temperatures~ A fingerprint re-mains on the paint film and the touched portion becomes white.
The cause for this phenomenon has not been fully clarified, but a microscopic examination shows that the metallic piqment at the touched porti.on corrodes and minute cracks appear on the ~inder.
On a pain-t fi.Lm having a good touchproofness, no fingerprint is left.
It is an object of the present invent.ion to provide metallic pigments which o~viate such. ~hortcomings and to provide a process for producing the same, The present invention consists in pol~mer-coated metall~
ic pigments for paints comprising metallic pigment particles coated with a polymer in the amount of 0.1 to 3a parts by ~eight in relation to 100 parts by weight of the metallic component in the metallic pigment particles.
The polymer is obtained by polymerizing a monomer Chere-inafter referred to as "monomer A") having a polymerizable double hond and at least one epoxy radical, singly or ~ith at least one comonomer (hereinafter referred to as "comonomer B"~ having a polymeriza~le douhle ~ond, ~2--S

1 The me-tallic partieles used in -the present inven-tion may be alum.inum, copper, zinc, iron, nickel or their alloys.
They are usually flaky in shape, but i.t is not our intention to limit to that shape.
The monomer "A" may be selected from among epoxidated polybutadiene, glycidyl methacrylate, glycidyl acrylate, cyclo-hexenevinyl monoxide~ divinylbenzene monoxide, etc.
The polymerizable comonomer "B" may be styrene, ~methyl-styrene, vinyltoluene, acrylonitrile, methacrylonitrile, vinyl-aeetate, vinylpropionate, aerylic aeid, acrylic ester, methacxylieacid, methacrylic ester, crotonie acid, itaconic acid, eitraeonie acid, oleic acid, maleic acid, maleic anhydride, divinylbenzene, ete, ~ mong acrylie esters ~hich can ~e used, there are methyl aerylate, ethyl aerylate, n-~utyl acrylate, 2-ethylhexyl aerylate, lauric aeryla-te, stearyl aerylate, hydroxyeth~l acrylate, hydroxy-propyl aerylate, methoxyethyl aerylate, ~utoxyethyl acrylate, eyelohexyl aerylate, 1,6~hexanedioldiacrylate, and 1,4-butane~
dioldiaerylate Among methaeylie esters whieh can be used, there are methyl methaerylate, ethyl metahaerylate, n-butyl methaerylate,

2-eth~lhexyl methacrylate, laurie methaerylate, stearyl meth-aerylate~ hydroxyethyl methaerylate, hydroxypropyl methaerylate, methoxyethyl methaerylate, butoxyethyl methaerylate, and eyclo-hexyl methaerylate.
In aeeordanee with. the present invention r the eoating o the metallie pigment partieles with a polymer is performed by dissolving a monomer A or a mixture of a monomer A and a eomo.nome.r B in an organie solvent, dispersing the metallie partieles in the

3~ solution~ heating the reaetion system to a predetermined tempera-ture~ and adding a polymeriza-tion initia-tor to start polymeriza-tion~

1 By this proces~, a polymer is deposited on -the metallic particles.
After reaction, the metallic pigment thus coated is filtered, concentrated and separated from the xeaction system, As the organic solvent, mineral spiri~ is preferable.
However, the following may be used: aliphatic hydrocar~ons such as hexan, heptane, octane and cyclohexane; aromatic hydrocarbons such as benzene, toluene and xylene; halides such as chlorobenzener trichlorobenzene, trichloroethylene and tetrachloroethylene;
alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, n-~utyl alcohol; ketones such as 2-propanone and 2~hutanone;
esters such as ethylacetate and propylacetate; and tetrahydrofuran, diethyl ester, and ethylpropyl ester.
As a polymerization initiator, organic peroxides such as di-t-~utyl peroxide, acetyl peroxide, benzoyl peroxide, lauroyl peroxide, cumyl ~ydroperoxide, and t-~utyl hydroperoxide;
and azo compounds such a a,~'-azo-bisisobutyronitrile may be used.
But~ the last-mentioned is the most preferable because it is pyrolyzed at relatively low temperatures.
The reaction temperature for polymerization should be 60-2Q0C. If ~,~'-azo ~isisobutyronitrile is used, it should be 7Q-~C, For lower or higher temperatures be~ond that range, the reaction speed or the polymerization efficiency would decrease.
The polymerization should preEerably ~e performed under a~mosphere of an inert gas such as nitrogen, helium and argon for higher polymerization efficiency.
The amount of the polymer coated on the metallic pigment particles should be Oel~30 parts by weight, prefera~ly Q.5-15 parts ~y weight, in relation to 100 parts by weight of the metallic component in the metallic pigment particles. For less than 0.1 part, the aimed ad~-~ntages could not be obtained. For more than 1 30 parts, merely the manufacturing C05-t increases without any substantial increase in the performance or function.
The ratio ~y weight of the monomer A to the comonomer B should preferably be 3:10 to 10:10 because such a ratio gives the polymer obtained a higher cross-linking density, thus giving the final product better performanc~s required for use as metallic pigment for paints.
In order to make the polymer-coated metallic pigment dispersi~le in water, a suitable amount ~about 10-16 weight % to the non-volatile component in the pigment~ of a kno~m surface active agent should be added thereto. The surface active agent may be either an anionic one such a~ fa-tty acid soaps, long chained alcohol sulfate~ polyoxyethylene alkylether sulEate, polyoxy-ethylene isooctylphenylether sulfonate, and alkyl~enzene sulfate, or a nonionic one such as polyoxyethylene alkylether, polyoxy-ethylene alkylphenolether, polyoxyethylene alkylamide, polyoxy-ethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, and sorbitan fatty acid ester.
If it is desired to give a good tollchproofness to the paint film on a plastic material, a silicone compound should be added to the polymer-coated metallic pigment thus obtained.
Further~ its addition gives a good wettability to the surface to the paint film~ thus allowing the use for printing~ The addition of silicone compound should be done by dissolving a silicone compound in a medium such as mineral spirit and diluting the solution and adding it to the polymer-coated pigment in an ordin-ary mixing step for adjusting the volatile to non-volatile ratio.
The amount o~ addition should be 0.5-5.4 parts by weight in relation to 100 par-ts by weight of the non-volatile component in the polymer-coated metallic pigment. For less than 0.5 part,

4~5 l the touchproofness would ~e insufficient. For more than 5.4 parts, it would be sufficien-t but ~he cost would be higher and the paint film obtai.ned would not ~e suitable for printing, If a metallic tone of color i5 required for the paint film used for plastic painting, the amount of the polymer coated on -the metallic pigment should be 0.5-3 parts ~y weight~
The silicone compound used in the present invention may be either a silicone oil or a silicone resin, The usa~le silicone oil include dimethyl polysiloxane, epoxy-modified silicone oil and carboxy-modified silicone oil. The silicone re~in may be any known one.
The polymer~coated metallic pigment in accordance with the present invention shows different advantages for different amounts of coating of the polymer as follows~
IE the amount of coating on the metallic pigmPnt is 1.5 p~rts ~y weight or more, preferably 3 part~ or more~ to 103 parts of the rnetallic component in the metalli.c pigmen~, the paint o~tained exh~bits a good withstand voltage and can be used for the electrostatic painting.

If the amount of coating is 0.5 part or more~ preferably .
1 part or more, the paint obtained exhibits a good water stability when used as a water-medium paint~ This property is checked by testing for the amount of gas generated and the change in tone of color, If it is 0,1 part or more, preferably ~.5 part or more, the paint obtained exhibits a good peel-proofness, If it is 3 parts or more, preferably 7 parts or more, a good shockproofness can be expected. If a silicone compound is added to the polymer-coated metallic pigment, a good touch-proofness is ohtained.

To further illustrate this invention, and not by ~ay of l~mitation f the following examples are given~ Unless otherwise stated, quantities are expressed as parts by weight.

_ _ _ _ One thousand grams of mineral spirit was put in a 2-liter four-neck flask, The monomer A or a combination oE monomer A and comonomer B as shown in Table 1 were added thereto and agitated in the flask, ~In the table, EPPB, GMA, GA, 1,6-, and AA are abbreviations for epoxidated polybutadiene, glycidyl methacrylate, glycidyl acrylate, 1,6-hexanedioldiacrylate, and acrylic acid, respectively,) Aluminum flakes were added to the solution and agitated to disperse them uniformly. The aluminum flake~ used were HS~2~ 120QM and MG-lQQ~ all manufactured ~y Toyo Aluminium Co., Ltd. ~In the Table, NV deno-tes the weight ~
of the non-volatile component contained therein.~. The reaction system ~as heated to a predetermined temperature under nitrogen gas atmosphere, One gram of ~ azo bisisobutyronitxile was then added and the system wa~ allowed to polymerize. The re-action temperature and reaction time are shown in the Tahle, After reaction, by filtering and concentrating the mixture, a polymer-coated aluminum pigment was obtained. The weight % of the non-volatile component (NV2 in the pigment obtained i5 shown in the Ta~le.
To determine the amount of polymer-coated on the pig~
ment, part of the pigment obtained was washed with n-hexane, filtered and powdered~ and the metallic component in the pigment powder wa~ dissolved off with a solution consi~ting of hydrochloric acid, nitric acid and water in the ratio by weight of 1:1:2.
The polymer residue was filtered, dried and wei~hed. The amount of polymer coated is shown in the Table in parts by weight in relation to lQ~ parts of the non-volatile component in the polymer-coated pigment.
The pigment o~tained was subjected to mixing by use of a mixer to adjust the percentage of -the non-volatile component.

$

1 In Example 8, epoxy-modified silicone oil(SF-~411, manu~c-tured by 'l'oray Silicone Co.) was added as a silicone compound to the pigment and the mixture underwent rnixing~ In the Table, ~
the amount of SE`-8411 is shown in part by weight to 100 part by weight to 100 parts of non-volatile component in the pigment.
The precentage of the non-volatile component ~NV) af-ter the mix-ing is shown in the Table.
CONTROLS 1 and 2 The control 1 was aluminum pigment ~S-2, Toyo Aluminum Co., Ltd.1, not coat~d ~ith a polymer. The control 2 is the control 1 to which a silicone compound SF~8411 ~as added as in Example 8.
The polymer-coated pigments after mixing and the pigments not coated as the controls ~ere tested for the following six tests. The results of tests are shown in the Ta~le.
TEST
~Electrostatic painting test2 From the pigments obtained the sample paints ~ere pre-pared as follows: 80 par-ts of acryl varnish ~Acrydic*47-712, manufactured by Japan Reichhold Chemicals Inc. NV 50%) and 20 parts of melamine CSuPer Beckamine*J-820 of the same maker, NV
60%L, ~oth ~eing binders, were mixed so that the metallic compon-ent in the pigment would be 15 parts by weight in relation to 100 parts of the solid component in the bincler. The mixture was dil-uted with a solvent consisting of xylene, methyl isobutyl ketone and diacetone alcohol in the ratio by ~eight of 60:25:15 50 tha-t the viscosity measured with the Ford cup No. 4 would be 12 seconds.
The paint thus made was painted on a tinplate by use of a Grooved-Mini~ell electrostatic painting device (manuEactured by Ransburg Japan Ltd.~ at a voltage of gn KV and at a paint supply rate of 200 cc per minute~

* Trade Mark ~8 ~L~8~

~Gas Evolutions Test) 3 grams of each sample metallic pigmen-t ~in terms of its metallic component~ was dispered in 100 grams oE an aqueous medium consisting of wa~er and butyl Cellosolve*in the ratio by weight of 1:4~ The dispersion was kept at 50C for 24 hours and the amount of gas e~oluted from the dispersion was measured. It is shown in the Table in milliliter in rela-tion to one gram of the metallic component in the pigment, ~ .
~Color Difference Test) One hundred parts of each polymer-coated aluminum pig~
ment was kneaded with 3 parts of polyoxyethylene alkylphenolether ~Emalgen*~06 of KaO Sekken Co.~ and 6 parts of polyoxyethylene alk~lether. ~Emalgen 408 of KaO Sekken Co~l To 48 g of the ~ater-dispersi~le aluminum pigment thus ob-tained, ~n g of distilled water, S60 g of water-soluble acryl varnish ~Arolon 557N of Nisshoku Arrow Chemical Co., NV 50%~, 150 g of water-soluble melamine ~arnish ~Sumimal*M-5aW of Sumitomo Chem. Co., Ltd,, NV 7~%1, and 32 g of ph-thalocyanine ~lue (N~ ~lue of Dainippon Ink Co,~ were added and mixed~ The water~dispersible metallic pa~nt thus obtained was kept at 50C for one month. The paints ~efore and after the storage were painted ~ith a doctor blade on a test paper sheet and the difference ~E i~ color ~as measured by use of a differential colorimeter.

~Peelproofness Test) To 10~ g of acryl lacquer (Acrydic A-165 of Japan Reichhold Chemical Inc, NV 50~1 was added 5 g ~in terms of metallic component~ of each aluminum pigment ob-tained, The mixture was * Trade Marks _~_ ., ~

1 diluted with a solvent consisting oE toluene and n-butyl alcohol in the ratio of 9:1 so that the viscosity measured with the Ford cup No. 4 would be 16 seconds. The paint thus prepaxed ~as sprayed onto a polystyrene plate and dried at 5QC for ten min-utes to obtain a paint film about 10 microns thick. It was checked for peel-proofness by use of a cellophane adhesive tape 15 mm wide by seeing if the pigment was not transferred to the tape when the latter was removed. This test is to check for the affinity between the binder and the metallic pigment.

(5hockproofne~5 Testl The paint film obtained in Test 4 was tested for shock~
proofnes~ with a withstand voltage tester. Voltage ~as applied to the paint film through the electrodes spaced by lcm. It was increased from 1 kV to 6 kV step ~y ~tep to check at what voltage an insulation breakdown occurred. In the Table is shown the maximum voltage applied without causing any breakdown.

(Touchproofness Test~
A part of the aluminum pigment obtained in Example 8 was mixed with 35 parts of acryl lacquer CAcrydic A-165 of Japan Reichhold Chemicals Inc, NV:45~) and 62 parts of a solvent con~
sisting o~ ethyl acetate, ethyl cellosolve and cyclohexane in the ratio of 40:30:30. The metallic paint obtained was sprayed onto a polystyrene plate and dried at 50C for 20 minutes to prepare a metallic paint film a~out 10 microns thick. A finger ~as pressed on the surface of the paint film and it was let to stand for ten days at 40C and a relative humidity of ~0%. Thereafter, the paint surface was examined for change.

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Claims (15)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A metallic pigment for paints comprising metallic pigment particles coated with a polymer obtained by copolymerizing a mixture of a monomer having a polymerizable double bond and at least one epoxy radical, and a comonomer having a polymeriz-able double bond in the amount of 0.1 to 30 parts by weight in relation to 100 parts by weight of the metallic component in the metallic pigment particles wherein the ratio by weight of said monomer to said comonomer is 3:10 to 10:10,

2. The metallic pigment as claimed in claim 1 wherein said metallic pigment particles are aluminum flakes,

3. The metallic pigment as claimed in claim 1 or 2 wherein the amount of said polymer coated is 0.5 to 15 parts by weight in relation to 100 parts by weight of the metallic component in the metallic pigment,

4. The metallic pigment for paints as claimed in claim 1, further comprising 0.5-5.4 parts by weight of a silicone compound in relation to 100 parts by weight of non-volatile component in the polymer-coated metallic pigment,

5. The metallic pigment as claimed in claim 4 wherein said metallic pigment particles are aluminum flakes.

6. The metallic pigment as claimed in claim 4 or 5 wherein the amount of said polymer coated is 0.5 to 3 parts by weight in relation to 100 parts by weight of the metallic component in the metallic pigment.

7. A process for producing a metallic pigment for paints comprising the steps of:
dissolving in an organic solvent a monomer having a polymerizable double bond and at least one epoxy radical or a mix-ture of said monomer and a comonomer having a polymerizable double bond, dispersing metallic pigment particles in said solution, and polymerizing said monomer or said mixture at a temperature of 60-200°C in the presence of a polymerization initiator so that the polymer produced will be directly deposited on said metallic pig-ment particles.

8. The process as claimed in claim 7 wherein the ratio by weight of said monomer to said comonomer is 3:10 to 10:10.

9. The process as claimed in claim 7 or 8 wherein said mon-omer is epoxidated polybutadiene and said comonomers are 1,6-hexanedioldiacrylate and acrylic acid.

10. The process as claimed in claim 7 wherein said metallic pigment particles are aluminum flakes.

11. The process as claimed in claim 7 further comprising the step of adding to the polymer-coated metallic pigment 0.5 to 5.4 parts by weight of a silicone compound in relation to 100 parts by weight of non-olatile components in the polymer-coated metallic pigment.

12. The process as claimed in claim 11 wherein said silicone compound is silicone oil.

13. The process as claimed in claim 11 wherein said silicone compound is silicone resin.

14. The metallic pigment for paints as claimed in claim 4, wherein said silicone compound is silicone oil.

15. The metallic pigment as claimed in claim 4, wherein said silicone compound is silicone resin.