US 4,849,480 AGrant

Crosslinked Polymer Microparticle

Issue Date:1989-07-18

•5 Claims

Abstract

Crosslinked polymer microparticles that have a particle size of about 0.1-5 microns of polymerized monomers of styrene, alkyl methacrylate having 1-12 carbons in the alkyl group, alkyl acrylate having 1-12 carbon atoms in the alkyl group and mixtures thereof, about 0.1-5% by weight of a crosslinking monomer of an alkylene glycol dimethacrylate or diacrylate each having 1-8 carbon atoms in the alkyl group and about 0.1-5% by weight of allyl methacrylate or allyl acrylate; said polymer having a weight average molecular weight of about 500,000 to 5,000,000; polymeric chains are grafted onto the polymer microparticles; the microparticles are useful as additives for coating compositions to control rheology and in particular for metallic pigment flake and sag control.

Metadata

Assignee

E. I. Du Pont de Nemours and Company

Inventors

Joseph A. Antonelli
Joseph E. McLaughlin
Clifford H. Strolle

Application Information

Application Number:US 1066609

Filing Date:1987-10-13

Priority Date:1985-10-23

Art Unit:151

Classifications

IPC:

C08F25702C08F26504C08F26506

Field of Search:

525303;304;305;902

Patent Drawings

This patent does not have any drawings.

Description

The following examples illustrate the invention. All parts and percentages are on a weight basis unless otherwise indicated. Molecular weights are determined be gel permeation chromatography.

Example 1

The following constituents were charged into a reaction vessel equipped with a stirrer, heating mantle and a reflux condenser:

Portion 1 was heated to 80.degree. C. and then Portions 3 and 4 with about 25% of Portion 2 which was premixed were added and the remainder of Portion 2 was added at a uniform rate during the next 1.5 hours while maintaining the temperature at 82.degree.-89.degree. C.

The resulting mixture was then held at 80.degree.-85.degree. C. for 2 hours and cooled to room temperature.

The resulting latex had a polymer solids content of about 20% by weight and the latex polymer was 48% methyl methacrylate, 31% butyl methacrylate, 20% styrene, 0.5% 1,4-butane diol diacrylate and 0.5% allyl methacrylate. The polymer had a weight average molecular weight of about 1,500,000 and a number average molecular weight of about 500,000.

Sodium chloride was added to the latex to precipitate the polymer. The precipitated polymer was thoroughly washed with water and then dried at 50.degree. C. for 12 hours to form a polymer powder. The resulting polymer powder then was dispersed in propylene glycol mono ethyl ether acetate to form a dispersion of polymer microparticles.

A base coating composition was prepared by mixing together the following constituents:

Portion 1 was charged into a mixing vessel and thoroughly mixed and then Portion 2 was added and thoroughly mixed with Portion 1. The resulting composition was reduced with glycol monomethyl ether acetate to a 20 sec. viscosity measured with a #2 Fisher cup.

The above base coating composition was sprayed onto primed aluminum panels. The composition did not sag or run but exhibited excellent rheology control. A clear acrylic coating composition of an acrylic polymer and melamine formaldehyde crosslinking agent was then sprayed over the above applied composition and the panels were baked at 120.degree. C. for 30 minutes to form a base coat/clear coat on the panels. The panels had a base coat thickness of about 0.5 mils and a clear coat thickness of about 1.7 mils. The resulting coating had distinctness of image of 89.2, a gloss measured at 20 degrees of 91.4 and L value measured with a colorimeter of 119.8 and a flop index of 9.5.

In general, the panels had an excellent appearance and the coating would be considered commercially useful for the exterior of automobiles and trucks.

A clear coating composition was prepared by blending together the following constituents:

The above constituents are thoroughly blended together and then reduced with naphtha to a 40 second viscosity measured using a #2 Fisher cup.

The above prepared base coating composition was sprayed onto suitably primed aluminum panels and then the above prepared clear coating was applied. The compositions did not run or sag but exhibited excellent rheology control. The panels were baked at 120.degree. C. for 30 minutes. The panels had a base coat thickness of about 0.6 mils and a clear coat thickness of about 1.4 mils. The panels had a distinctness of image of 45.1, a head on brightness measured with a spectrophotometer of 123.24 and a flop index of 10.51. In general, the panels had an excellent appearance and the coating would be considered commercially useful for the exterior of automobiles and trucks.

Example 2

Grafted polymeric microparticles were prepared as follows:

Portion 1 was charged into a polymerization vessel equipped as in Example 1 and the constituents were heated to reflux temperature of about 133.degree. C. Portion 2 was premixed and added over a three hour period while maintaining the reflux temperature and then held at its reflux temperature for an additional 2 hours. The resulting composition was cooled to ambient temperatures and filtered.

The resulting dispersion of polymer microparticles had a solids content of 25%. The core is about 65% of the polymer microparticles and the grafted polymeric chains are about 35% of the microparticles. The core contains 48% methyl methacrylate, 31% butyl methacrylate, 20% styrene, 0.5% 1,4-butane diol dimethacrylate and 0.5% allyl methacrylate and the grafted polymeric side chains grafted via the allyl groups contain 25% styrene, 25% ethyl methacrylate, 20% lauryl methacrylate and 30% hydroxy ethyl acrylate.

A pigmented coating composition was prepared by blending together the following constituents:

Portion 1 was mixed together and then added to Portion 2 to form a coating composition. The resulting composition had a Brookfield Viscosity measured at 2 RPM of 1900 centipoises and at 20 RPM of 780 centipoises and had a ratio of Brookfield Viscosity measured at 0.2 RPM/Brookfield Viscosity measured at 20 RPM of 8.7.

The paint was reduced to a spray viscosity and sprayed onto a primed steel panel and baked at 120.degree. C. for 30 minutes. The resulting coating had a gloss measured at 20.degree. C. of 52.6 and in general had an acceptable appearance.

Example 3

The following constituents were charged into a reaction vessel equipped as in Example 1:

Portion 1 was charged into the reaction vessel and heated to 80.degree. C. About 25% of Portion 2 was then added and then Portion 3 was added and mixed 5 minutes. The remainder of Portion 2 was added over a 90 minute period while maintaining the temperature at 80.degree. C. and then held at this temperature for an additional 2 hours. A latex was prepared.

Water was removed from the latex by using the following azotropic distillation procedure:

The xylene was charged into a reaction vessel equipped as above and heated to about 95.degree. C. Then the latex was slowly added while water was removed and then held at this temperature for 5 hours until all water was removed to form an organic polymeric dispersion.

A grafted polymer microparticle dispersion was prepared by adding the following constituents to the above prepared polymeric dispersion:

Portion 1 was added to the polymer dispersion over a 3 hour period along with Portion 2. The temperature was held at about 139.degree. C. Then the composition was cooled to room temperature. The resulting grafted polymer microparticle dispersion had a solids content of about 13.65%.

The dispersion had a ratio of Brookfield viscosity measured at 0.2 RPM/Brookfield viscosity measured at 20 RPM of 21.6.

The dispersion was added in the same solids amount to the base coating composition described in Example 1 in place of the dispersion used in Example 1. The resulting paint was reduced to a spray viscosity and sprayed onto a primed steel substrate and a clear coating was applied and baked as in Example 1. The resulting finish had acceptable gloss and appearance and is acceptable as an automotive coating composition.

Example 4

By using the same procedures as in Example 3, the following microparticle polymer dispersions were prepared:

Each of the above microparticle polymer dispersions was separately used in the base coating composition described in Example 1. Each of the resulting compositions was sprayed onto primed steel substrate and topcoated with a clear composition as described in Example 1 and baked using the same conditions. In each case the resulting finish had good gloss and appearance and is acceptable as an automotive and truck finish.

Claims

We claim:

1. Crosslinked polymer microparticles useful as a rheology control additive for coating compositions and having a particle size of about 0.1-5 microns consisting essentially of a core of polymerized monomers selected from the group consisting of styrene, alkyl methacrylate having 1-12 carbons in the alkyl group, alkyl acrylate having 1-12 carbon atoms in the alkyl group and mixtures thereof and about 0.1-5% by weight of a crosslinking monomer of an alkylene glycol dimethacrylate or diacrylate each having 1-8 carbon atoms in the alkyl group, and about 0.1-5% by weight of allyl methacrylate or allyl acrylate; said polymer having a weight average molecular weight of about 500,000 to 5,000,000 and having polymeric chains grafted to the core through residual allyl groups; wherein the chains have a weight average molecular weight of less than 20,000 and consist essentially of polymerized monomers selected from the group consisting of styrene, alkyl methacrylate having 1-12 carbons in the alkyl group, alkyl acrylate having 1-12 carbons in the alkyl group and mixtures thereof and hydroxy containing monomers of a hydroxy alkyl acrylate or a hydroxy alkyl methacrylate.

2. The crosslinked microparticles of claim 1 in which the core comprises about 40-80% by weight of the microparticle and the chains comprise about 20-60% by weight of the microparticle and have a weight average molecular weight of about 3,000-18,000.

3. The crosslinked microparticles of claim 2 in which the core consists essentially of polymerized monomers of methyl methacrylate, butyl methacrylate, styrene, 1,4-butane diol dimethacrylate and allyl methacrylate and the chains grafted to the core consist essentially of polymerized monomers of styrene, ethyl methacrylate, lauryl methacrylate and hydroxy ethyl acrylate.

4. The crosslinked microparticles of claim 2 in which the core consists essentially of polymerized monomers styrene, butyl acrylate, butane diol dimethacrylate and allyl methacrylate and the chains grafted to the core consist essentially of polymerized monomers of methyl methacrylate, ethyl methacrylate, lauryl methacrylate and hydroxy ethyl acrylate.

5. The crosslinked microparticles of claim 2 in which the core consists essentially of polymerized monomers of styrene, butyl acrylate, butane diol dimethacrylate and allyl methacrylate and the chains grafted to the core consist essentially of polymerized monomers of styrene, butyl acrylate, butyl methacrylate, hydroxy ethyl acrylate and hydroxy propyl methacrylate.

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