WO1991017217A1

WO1991017217A1 - Passivated aqueous metal pigment compositions and process for making same

Info

Publication number: WO1991017217A1
Application number: PCT/US1991/002508
Authority: WO
Inventors: Russell L. Ferguson, Jr.; William G. Jenkins
Original assignee: Silberline Manufacturing Co., Inc.
Priority date: 1990-05-08
Filing date: 1991-04-16
Publication date: 1991-11-14
Also published as: AU7687191A

Abstract

A process for producing aesthetically acceptable metal pigment-containing composition useful for forming aqueous coating compositions, includes the steps of passivating milled metal pigment particles with an inorganic chromium or vanadium compounds, washing the passivated particles with water, further washing the particles with a mixture of a lubricant dissolved in a cosolvent, and adjusting the non-volatile content of the resulting product to form a moist paste. The particles are maintained in at least a moist condition during the process. The particles produced are substantially free from agglomeration.

Description

PASSIVATED AQUEOUS METAL PIGMENT COMPOSITIONS AND PROCESS FOR MAKING SAME BACKGROUND OF THE INVENTION The present invention is related to paste compositions containing metal pigments suitable for forming coating compositions, particularly aqueous coating systems. Increasingly stringent environmental regulations have required that coating systems dramatically reduce volatile organic solvent levels. One way to comply with such regulations is to use water in place of the volatile organic solvents previously used.

However, in the area of coating systems utilizing metal pigment particles, aqueous systems can present rather formidable difficulties. This is particularly true with respect to aluminum and zinc pigments. Thus, the metal pigment can readily react with water to generate hydrogen gas. The amount of gas generated can produce a safety hazard, creating high pressures within the composition containers. Also, the water reaction substantially diminishes the aesthetic value of the metal pigments. The reaction of aluminum pigments with water can be depicted as follows:

2A1 + 6H₂0 -> 2A1(0H)₃ + 3H₂ Due to the increasing demand for aqueous systems, a number of techniques have been proposed for inhibiting the attack on the pigment particles by water. Unfortunately, most of these techniques have not provided sufficient protection.

One technique which has provided good inhibiting properties is the passivation of the metal pigment particles with an inorganic vanadium or chromium compound, as disclosed in

Kondis U.S. Patent No. 4,693,754, the disclosure of which is incorporated herein by reference. However, this technique suffers from certain disadvantages in that the aesthetic properties of the pigment particles are damaged. The present invention is provided to overcome these disadvantages. SUMMARY OF THE INVENTION The present invention is directed to a process for producing a metal pigment-containing paste, especially aluminum, which is useful for forming an aqueous coating composition. The process comprises passivating milled metal pigment particles with an inorganic chromium or vanadium compound, washing the passivated particles with water, then washing with a mixture of lubricant dissolved in a cosolvent to displace water from the particles, and then adjusting the non-volatile content of the resulting product to form a paste. The pigment particles are maintained in at least a moist condition during the process. The resulting paste can be used successfully in aqueous coating systems without significant water attack on the metal pigment particles, while maintaining acceptable aesthetic values.

BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1-3 represent particle size distribution data for certain metal pigment compositions discussed in the Examples below. DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to the production of a metal pigment paste composition, particularly an aluminum pigment, which can be used in aqueous coating systems without suffering the disadvantages of unacceptable hydrogen gas generation or loss of aesthetic qualities. The process for producing such a paste involves the steps of passivating milled metal pigment particles with an inorganic chromium or vanadium compound, washing the passivated particles with water, again washing the previously washed particles with a mixture including a lubricant dissolved in a cosolvent to displace water from the particles, and then adjusting the non-volatile content of the resulting product to form a moist paste, with the particles having been maintained in at least a moist condition during the process. The paste obtained is well suited for use in aqueous coating compositions and does not suffer from loss of aesthetics. There is little if any agglomeration of the metal particles and the particle size distribution remains substantially unchanged from that of the untreated product. The average particle size thus is increased by no more than 10%, preferably less than 5%, over that of the untreated product.

The milled metal pigment particles ordinarily are supplied by the manufacturer in the form of a paste system. Thus, the paste would include metal pigment particles of the desired size, a suitable lubricant, such as oleic acid, and solvent. Commercially available metal pigment pastes can be used, such as Silberline non-leafing pigment available from the Silberline Mfg. Co. Other such pastes include Sparkle Silver^R 5245 AR aluminum paste, Sparkle Silver^R 3622 aluminum paste, Sparkle Silver" 5242 AR aluminum paste, Sparkle Silver" 3141 ST aluminum paste, Sparkle Silver" 5000 AR aluminum paste and Sparkle Silver" 6246 AR aluminum paste, all available from Silberline Mfg. Co.

The pigment paste obtained can be used in a variety of known coating systems, as a direct replacement for currently used pastes. Examples include maintenance, general industrial, roof coating and automotive coating systems. Thus, the paste may be used, for example, with acrylic polymer emulsions, water reducible alkyd resin systems, water reducible alkyd/ elamine cross-linked systems, waterborne epoxy coatings, polyester emulsions and water reducible polyester melamine coatings. The passivation step is carried out by first dispersing the metal pigment paste in a coupling agent. An example of a suitable coupling agent is the acetate ester of diethylene glycol monoethyl ether, which can be represented by the formula CH₃COO(CH₂)₂0(CH₂)₂OCH₂CH₃, sold by Union Carbide Corp. under the name Carbitol acetate. Other coupling agents include dimethyl forma ide, isopropyl alcohol, ethylene glycol monobutyl ether (sold under the name Butyl Cellosolve) , diethylene glycol monobutyl ether acetate (sold under the name Glycol Ether DB Acetate) and ethylene glycol monobutyl ether acetate (sold under the name Glycol Ether EB Acetate) .

The passivating agent, which can be an inorganic chromium or vanadium compound, is then added to the dispersion. This passivating agent is a strong oxidizing agent, and seems to passivate the particles by oxidizing the surface of the particles. Examples of suitable compounds include chromium trioxide, ammonium dichromate, ammonium vanadate, vanadium pentoxide and metavanadic acid. The passivating agent may be used, for example, as a one molar aqueous solution. The amount of the solution of the passivating agent should be such that the passivating agent is present in an amount of about 5% by weight based on the amount of metal particles. Larger amounts of the passivating agents can be used, but increasing the amount of the passivating agent tends to disadvantageously decrease the opacity provided by the product. It is believed that the strong oxidizing agents used for passivation may actually consume small pigment particles. The passivation is carried out under vigorous stirring for a period of about 15 minutes up to 48 hours, with a period within the range about 30 to 60 minutes being preferred, and at a temperature of not more than about 80°C. At the end of the passivation, the metal pigment particles are filtered from the dispersion. Filtering is not carried out to the point of dryness and the particles are continually in at least a moist condition. That is, the filtered particles have a non-volatile content of about 40 to 90% by weight, with 50 to 60% being preferred.

The passivated particles then are washed with water, preferably deionized water. The washing step removes excess passivating agent from the moist pigment particles. The water washing can be carried out in several stages, and the washing can be conducted by slurrying or a continuous filtration with the water or both. However, the metal particles again are maintained at least in a moist condition at all times.

Following the water wash, the still-moist particles are treated with a mixture comprising a lubricant dissolved in a cosolvent. This mixture permits the displacement of water from the particles and replacement of the water with the lubricant. One example of a suitable lubricant is a fatty acid. Others include fatty amines, fatty alcohols and fatty esters. Specifically, stearic acid, oleic acid, isostearic acid, lauric acid, palmitic acid, stearyl alcohol and stearyl amine may be used as lubricants. In essence, the lubricant replaces the oleic acid which is oxidized by the passivating agent in the treatment of non-leafing pigments or the stearic acid which is removed by washing from leafing pigments. The lubricant helps to prevent agglomeration of the particles. The cosolvent must be at least partially miscible with water and displaces water from the metal pigment particles and carries the water away while delivering lubricant to the particles. Such cosolvents are well known and commonly used in aqueous coating technology. Examples include propylene glycol onomethyl ether (sold under the name Dowanol PM, a product of Dow Chemical Co.) , ethylene glycol monobutyl ether

(sold under the name Butyl Cellosolve, a product of Union Carbide Corp.), diethylene glycol monobutyl ether acetate (sold under the name Glycol Ether DB Acetate) , ethylene glycol monobutyl ether acetate (sold under the name Glycol Ether EB Acetate) , diethylene glycol monoethyl ether acetate (sold under the name Glycol Ether EB Acetate) , isopropyl alcohol, diethylene glycol monoethyl ether (sold under the name Glycol Ether DE) , propylene glycol monomethyl ether acetate (sold under the name Glycol Ether PM Acetate) and other ethers, alcohols and acetates. The lubricant is present in the mixture with the cosolvent in an amount of about 1 to 30% by weight. The amount of the mixture used with a given amount of metal particles is such that the cosolvent is present in an amount of about 10 to 60% by weight, the metal particles in an amount of about 40 to 90% by weight and the lubricant in an amount of about 1 to 5% by weight. Again, this washing step can be carried out in several stages. The washes may be continual, or as a dispersion, or a combination of the two in a multi-stage wash. Again, the particles are maintained at least in a moist condition at all times. The water is substantially completely displaced from the metal pigment particles, i.e. no more than about 1.5% by weight of water with respect to the metal particles remains.

The thus-treated particles can be conveniently collected in an amount of about 60% metal particles to about 40% cosolvent-lubricant mixture. Additional cosolvent can be added to bring the solvent level to 50% by weight or more, without separation. In commercially available pastes, the maximum solvent level is about 30 or 40%. Higher solvent levels assist in preventing agglomeration of the particles. By maintaining the metal pigment particles at least in a moist condition during the processing, undesirable agglomeration of the particles is avoided, and the aesthetic values of the product are maintained. EXAMPLES Example 1 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml carbitol acetate, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80 " C for 30 min. The slurry is then filtered to a non-volatile content of about 50%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 50%. The filter cake is then washed with a mixture of Butyl Cellosolve and 5% by weight stearic acid, and maintained at a non-volatile content of about 50%. The filter cake is slurried with a mixture of Butyl Cellosolve containing 5% by weight stearic acid and filtered to a final non-volatile content of about 50%. The particle size distribution of the final paste is shown in Fig. 1, and is similar to that of the starting metal pigments, shown in Fig. 2. The average particle size of the final paste is 22.1 μ. An automotive topcoat formulation is prepared by mixing 22.3 kg of the treated paste obtained in 14.5 kg of N-Butyl Cellosolve and 20.8 kg of rheology, flow and leveling agents. 311.0 kg of polyester emulsion is added and mixed for one hour. 12.3 kg of a 5% DMEA/DI water soluble is added slowly with an additional hour of mixing. The viscosity is adjusted to 28 seconds on Ford 4 with DI water. 381 kg of an automotive topcoat formula are obtained. This formula provides a coating for which the following properties are observed: total reflectance-68.1; Datacolor-25°-117.22, 45°- 61.19, 70°-36.92; Heg an grind gauge-0.5; distinctiveness of image-70. Example 2

40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml dimethyl formamide, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80"C for 30 min. The slurry is then filtered to a non-volatile content of about

45%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 56%. The filter cake is then washed with a mixture of Butyl Cellosolve and 5% by weight lauric acid, and maintained at a non-volatile content of about 50%. The filter cake is slurried with a mixture of Butyl Cellosolve containing 5% by weight lauric acid and filtered to a final non-volatile content of about 50%.

A general industrial coating formulation is prepared by mixing 209.3 kg of water, 5.0 kg of ammonium hydroxide, 93.3 kg of water reducible alkyd resin, 2.4 kg of cobalt drier, 0.9 kg of drier accelerator/stabilizer, 5.6 1 of Butyl Cellosolve, 1.2 kg of manganese drier, 12.0 kg of Butyl

Cellosolve and 52.5 kg of the aluminum paste obtained. 381 kg of a general industrial coating formulation are obtained.

Example 3 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml dimethyl formamide, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH ₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80°C for 30 min. The slurry is then filtered to a non-volatile content of about 57%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 53%. The filter cake is then washed with a mixture of Dowanol PM and 5% by weight stearic acid, and maintained at a non-volatile content of about 48%. The filter cake is slurried with a mixture of Dowanol PM containing 5% by weight stearic acid and filtered to a final non-volatile content of about 50%. 15.5 kg of water, 12.4 kg of A sco Solve PM, 3.1 kg of Amsco Solve DPM, 25.8 kg of the paste obtained and 2.3 kg of Surfynol 104BC are pre ixed in a low shear mixer until well dispersed. Then, 15.5 kg of water and 312.8 kg of Unocal 76 RES 1018 are added and mixed. 387 kg of a general industrial coating formulation are obtained.

Example 4 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml carbitol acetate, to which is added 7.5 ml deionized water and 40 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80"C for 30 min. The slurry is then filtered to a non-volatile content of about 42%. The filter cake is washed with deionized water to remove excess (NH )₂Cr₂0₇, and maintained at a non-volatile content of about 45%. The filter cake is then washed with a mixture of Butyl

Cellosolve and 5% by weight stearic acid, and maintained at a non-volatile content of about 51%. The filter cake is slurried with a mixture of Butyl Cellosolve containing 5% by weight stearic acid and filtered to a final non-volatile content of about 50%. The paste obtained is useful in the formulations of Examples 1-3.

Example 5 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml isopropyl alcohol, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80°C for 20 min. The slurry is then filtered to a non-volatile content of about 53%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 50%. The filter cake is then washed with a mixture of isopropyl alcohol and 1% by weight stearic acid, and maintained at a non-volatile content of about 48%. The filter cake is slurried with a mixture of isopropyl alcohol containing 1% by weight stearic acid and filtered to a final non-volatile content of about 50%. The paste obtained is useful in the formulations of Examples 1-3. Example 6

40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml carbitol acetate, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 25°C for 48 hrs. The slurry is then filtered to a non-volatile content of about 41%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 44%. The filter cake is then washed with a mixture of Butyl Cellosolve and 5% by weight stearic acid, and maintained at a non-volatile content of about 46%. The filter cake is slurried with a mixture of butyl cellosolve containing 5% by weight stearic acid and filtered to a final non-volatile content of about 50%. The paste obtained is useful in the formulations of Examples 1-3.

Example 7 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml carbitol acetate, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80"C for 30 min. The slurry is then filtered to a non-volatile content of about 54%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 58%. The filter cake is then washed with a mixture of glycol ether EB acetate and 3% by weight stearyl amine acid, and maintained at a non-volatile content of about 52%. The filter cake is slurried with a mixture of glycol ether EB acetate containing 3% by weight stearyl amine and filtered to a final non-volatile content of about 50%. The paste obtained is useful in the formulations of Examples 1-3.

Example 8 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml dimethyl formamide, to which is added 7.5 ml deionized water and 40 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80°C for 30 min. The slurry is then filtered to a non-volatile content of about 50%. The filter cake is washed with deionized water to remove excess (NH₄)₂Cr₂0₇, and maintained at a non-volatile content of about 55%. The filter cake is then washed with a mixture of Butyl Cellosolve and 5% by weight stearic acid, and maintained at a non-volatile content of about 50%. The filter cake is slurried with a mixture of Butyl Cellosolve containing 5% by weight stearic acid and filtered to a final non-volatile content of about 50%. The paste obtained is useful in the formulations of Examples 1-3. Example 9

40 gm of aluminum metal particles, having an average particle size of 21.2 microns, is slurried in 150 ml. carbitol acetate. To this slurry is added 41.5 grams of an NH₄V0₃/deionized water slurry (10.0 grams NH₄V0₃, 31.5 grams distilled water) . The slurry is then stirred vigorously at a temperature of 80°C for 30 minutes and then filtered to a non-volatile content of about 50%. The filter cake is washed with deionized water to remove excess NH₄V0₃, and maintained at a non-volatile content of about 50%. The filter cake is then washed with a mixture of Butyl Cellosolve and 5% by weight stearic acid, and maintained at a non-volatile content of about 50%. The filter cake is slurried with a mixture of Butyl Cellosolve containing 5% by weight stearic acid, and filtered to a final non-volatile content of about 50%. The paste obtained is useful in the formulations of Examples 1- 3.

Comparative Example 1 Following the teachings of U.S. Patent No. 4,693,754, 40 gm of aluminum metal particles, having an average particle size of 21.2μ is slurried in 150 ml of a mixture of 80% by weight isopropanol/20% by weight water, to which is added 31.5 ml deionized water and 8 gm of a 1M solution of (NH₄)₂Cr₂0₇. The slurry is then stirred vigorously at a temperature of 80°C for 30 min. The slurry is then filtered and washed with water to remove excess (NH₄)₂CF₂0₇. The product is then rinsed with acetone and air-dried. The resulting product has the particle size distribution shown in Fig. 3, which differs significantly from that of the original particles, shown in Fig. 2. The final product has an average particle size of 36.9μ.

When formulated into an automotive coating system as in Example 1, the following properties are observed: total reflectance-58.5; Datacolor-25"-110.83, 45°-73.43, 70°-

47.71; Heg an grind gauge-4.5; distinctiveness of image-20.

Although a detailed description has been provided above, the present invention is not limited thereto, but rather is defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A process for producing a metal pigment-containing composition useful for forming aqueous coating compositions, the process comprising: passivating milled metal pigment particles with a passivating agent selected from the group consisting of inorganic chromium and vanadium compounds; a first washing step of washing the passivated particles with water; a second washing step of washing the previously washed particles with a mixture comprising a lubricant dissolved in a cosolvent to displace water from the particles; and adjusting the non-volatile content of the resulting product to form a composition suitable for forming a coating composition, the pigment particles being maintained in at least a moist condition during the process.

2. The process of claim 1, wherein the metal pigment particles are initially present as a paste and the passivating step comprises dispersing the metal pigment particles in a solution comprising a coupling agent and combining the dispersion with a solution of the passivating agent.

3. The process of claim 2, wherein the passivating agent is present in the dispersion in the amount of at least about 5% by weight based on the amount of metal.

4. The process of claim 2, wherein passivation is carried out for about 15 minutes at a reaction temperature of not more than about 80°C with vigorous stirring.

5. The process of claim 1, wherein following passivation, the material is filtered to dampness before the step of washing with water.

6. The process of claim 5, wherein the first washing step includes multiple water washes.

7. The process of claim 1, wherein the second washing includes multiple washes with the lubricant-cosolvent.

8. The process of claim 1, wherein the passivating agent is selected from the group consisting of chromium trioxide, ammonium dichromate ammonium vanadate, vanadium pentoxide and meta vanadic acid.

9. The process of claim 1, wherein the lubricant is a fatty acid, fatty alcohol, fatty amine or fatty ester.

10. The process of claim 1, wherein the cosolvent is selected from the group consisting of ethers, alcohols and acetates.

11. The process of claim 10, wherein the cosolvent is selected from the group consisting of propylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, ethylene glycol monobutyl ether acetate, diethylene glycol monoethyl ether acetate, isopropyl alcohol, diethylene glycol monoethyl ether and propylene glycolmonomethyl ether acetate.

12. The process of claim 2, wherein the coupling agent is selected from the group consisting of diethylene glycol monoethyl ether acetate, dimethyl formamide, isopropyl alcohol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether acetate, and ethylene glycol monobutyl ether acetate.

13. The process of claim 9, wherein the lubricant is selected from the group consisting of stearic acid, oleic acid, isostearic acid, lauric acid, palmitic acid, stearyl alcohol and stearyl amine.

14. The process of claim 1, wherein the metal is aluminum.

15. A composition useful for forming aqueous coating compositions, comprising: metal pigment particles which have been passivated with a passivating agent selected from inorganic chromium or vanadium compounds; a lubricating agent on the particles; and a cosolvent for the lubricant; the metal pigment particles having an average particle size substantially the same as that of the metal particles before passivation with the inorganic chromium or vanadium compounds.

16. The composition of claim 15, wherein the cosolvent and lubricant are present in an amount of about 10 to 60% by weight based on the metal particles.

17. The composition of claim 15, wherein the metal is aluminum.