MXPA99005233A - Pasting of inhibited metal pigments containing molybdate pigments and suitable for aqueous coating compositions - Google Patents

Abstract

Metal particles useful for coating compositions, particularly aqueous coating compositions, are produced to date the particles with a molybdate pigment. The molybdate pigment reacts with the surface of the metal particles. The molybdate pigment can be a salt such as molybdate salt, phosphomolybdate or silicomolybdate, and the salt can include a multivalent cation such as calcium, strontium, barium, magnesium, zinc and aluminum. Metal particles show improved resistance to attack by ag

Description

PASTES OF INHIBITED METAL PIGMENTS CONTAINING MOLYBDATE PIGMENTS AND WHICH ARE ADEQUATE FOR AQUEOUS COATING COMPOSITIONS BACKGROUND OF THE INVENTION The present invention is directed to metal particles used to form coating compositions. Said particles are used, for example, to provide metal coatings for automotive use and, in general, maintenance, industrial and roof covering systems. The metal particles are normally flake-shaped and are provided in the form of a paste that is mixed with a suitable vehicle or carrier for a coating. In the paste, vehicles based on organic solvents have been used for coating compositions, with good results. However, the use of such organic-based coating compositions results in the release of significant amounts of volatile organic material into the atmosphere, which has been determined to be harmful to the environment and recently stringent emissions standards have been implemented. organic One way of coating compositions to comply with new rules is to convert them from organic-based vehicles for compositions to water-based vehicles, since in such cases the water is released into the atmosphere instead of the volatile organic material.

In the case of metal coating compositions, the use of aqueous vehicles is problematic, since water can react with the metal particles to generate hydrogen gas. This is particularly true for zinc and aluminum particles. The reaction of aluminum particles with water is described below as an example. 2AI + 6H2O - > 2AI (OH) 3 + 3H2 The amount of gas generated can produce a safety hazard, resulting in high pressures in composition vessels. In addition, the water reaction significantly reduces the aesthetic value of the metal particles. A number of techniques have been proposed to combat the problem of reaction of water with metal particles in aqueous coating systems. An example is the passivation of metal particles with organic phosphate (Patent of US Pat. No. 4,565,716). Another is the use of hexavalent chromium or pentavalent vanadium compounds (U.S. Patent No. 4,693,754). Other techniques include the use of organic phosphites (U.S. Patent No. 4, 808,231) and the use of nitroparaffin solvents and the use of nitroparaffin solvents in combination with organic phosphate, organic phosphite or a vanadium compound. pentavalent (U.S. Patent No. 5,215,579). The use of heteropolyanions and phosphosilicate pigments as treatment agents, alone or in combination, has also been contemplated (U.S. Patent Nos. 5,296, 032, 5, 348,579 and 5,356,469). The descriptions of each of the patents mentioned above are incorporated herein by reference. While some degree of success has been achieved with these treatments, some additional improvements have been desired to provide resistance to the attack of aqueous vehicles for metal particles having desired properties for the coating compositions. SUMMARY OF THE INVENTION In accordance with the present invention, the metal particles useful for coating the compositions are treated with a molybdate pigment that inhibits corrosion. The molybdate pigment has been found to provide highly convenient protection for metal particles against attack by aqueous media, without significant adverse impact on the properties of metal particles as components of the coating system. The treated metal particles are resistant to the evolution of hydrogen gas and maintain useful aesthetic values as well as the adhesion values of intercoated and intracover in a paint film. The molybdate pigment treatment is easily adapted to the shape of the paste in which the metal particles are often supplied and therefore the treatment with molybdate pigment is suitable for practical application. It is thought that the molybdate pigment is subjected to chemical reaction with the surface of the pigment. In a preferred aspect of the invention, the molybdate pigment has the form of a salt, with molybdate salts, phosphomolybdate or silicomolybdate the multivalent cations being preferred examples. Other objects, advantages and aspects of the present invention will be more readily appreciated and understood when considered together with the following detailed description. Detailed Description The present invention is directed to the treatment of metal particles that are useful for forming metal coating compositions. Said metal particles are generally provided in the form of leaflets, although in some cases spherical (and other) shapes can be used. The metal particles will generally have a particle size of about 1 -500 microns, preferably 6-100 microns. The metal particles are used in a wide variety of coating compositions, including automotive coating systems (to provide the metallic finish on cars and trucks and in general maintenance, industrial and roof coating systems.) The present invention can be used, for example, with aluminum particles of aluminum, zinc or bronze, aluminum is perhaps the most widely used.According to the present invention, the metal particles were treated with a molybdate pigment to increase the strength of the metal particle for the attack of an aqueous medium, for example the vehicle or carrier of an aqueous coating composition.Therefore, the metal particles treated according to the present invention are suitable for use in aqueous coating compositions, enjoying levels significantly reduced evolution of hydrogen gas, without losing the adhesion of the intercubierta or intracubierta or degradation of optical properties. The molybdate pigment can be considered to inhibit corrosion and such pigments have generally been considered for use in primers and maintenance coatings, when they protect an underlying substrate from corrosion. The molybdate pigment will generally take the form of an inorganic salt. In one example, the salt includes a multivalent cation such as calcium, strontium, barium, magnesium, zinc and aluminum. A plurality of cations may be included. The molybdate salt may be in the form of molybdate salt, phosphomolybdate or silicomolybdate, for example. Specific non-limiting examples include zinc phosphomolybdate, calcium-zinc molybdate, magnesium-zinc silicomolybdate, calcium-zinc phosphomolybdate and zinc molybdate. It is thought that the molybdate pigment chemically reacts with the surface of the metal particles to provide increased resistance to aqueous attack. The metal particles can be treated with the molybdate pigment in a liquid medium. In order to use metal particles to form coating compositions, the metal particles will often be supplied in the form of a paste containing the metal particles in an amount of about 40-90% by weight. The treatment with the molybdate pigment is suitable for the formation of metal particles containing paste. In one example, the molybdate pigments that inhibit corrosion can be dispersed in a liquid in order to reduce the particle size of the molybdate pigments to a level sufficient to prevent the formation of seeds in a dry paint film. It is useful if the particle size of the molybdate pigments is not greater than 10 microns, preferably not more than 5 microns. The liquid can be any liquid that is compatible with the molybdate pigment and the intended coating composition. Examples, which may be selected depending on the particular coating system in question, include nitroparaffins, mineral spirits, high-ignition naphtha, glycol ethers, glycol ether acetates, water, esters, ketones and combinations thereof. Additional ingredients such as surfactants, anti-foaming agents and dispersants can be used as desired. Among the microparaffins, the lower members of the series, v.gr. , nitromethane, nitroethane and 1-nitropropane, are convenient on the basis of advantageous toxocological properties and availability. Polar solvents such as glycol ethers generally provide the best dispersibility of the pigment. The molybdate pigment can be dispersed in the solvent using high shear equipment, such as high speed dispersers, ball mills, medium mills, grinders, rotor-stator homogenizers and the like. Usually the ratio of solvent: pigment will be on a scale of 4: 1 to 1: 4 by weight, preferably 2: 1 to 1: 2. The ratio can vary as necessary to provide the best balance of grinding time, ie efficiency and pouring capacity. The dispersion of the molybdate pigment can be used in a pulp reduction process. This dispersion of the molybdate pigment in the liquid is used to dilute (i.e., "reduce") a paste of metal particles. Said pastes, for example, can be metallic particles of for example 60-95% by weight (preferably 65-82%) in mineral spirits. The paste is loaded into a mixer and the molybdate pigment dispersion is added thereto. The amount of molybdate pigment dispersion can be in a sufficient amount that provides 1-50% by weight, preferably 5-30%, of molybdate pigment with respect to the metal particles. If necessary, other organic solvents can also be added. The total amount of liquid added to the paste will generally give a final non-volatile content of about 60-72% by weight of the mixture. The mixture is then meically combined for a time, usually from 5 minutes to 8 hours, at a suitable temperature, for example at room temperature to 100 ° C. The mixing conditions should be sufficient to ensure the uniform distribution of molybdate pigment dispersion and metal particles, but not enough to result in adverse effects on the properties of the metal particles, especially the optical acteristics. As another example of a method for treating metal particles with the molybdate pigment that inhibit corrosion, metal particles can be mixed with a solvent to form a slurry having about 1-50% by weight, preferably about 10% by weight. -30%, of metal particles. The dispersion of the molybdate pigment which inhibits corrosion is added in an amount sufficient to provide the amount of pigment with respect to the metal particles treated above. The mixture is then stirred, again to ensure uniform distribution without adversely affecting the metal particles and in this case the stirring takes place, for example at room temperature of 100 ° C for a time of 5 minutes to 24 hours, preferably 30 minutes. minutes to 2 hours. The liquid is then removed from the mixture, for example by filtration, to obtain the desired paste, which will normally have a metal particle content of 40-90% by weight. The molybdate pigment remains with the filter cake. Metal particles will often be formed by a grinding process. It is also possible to carry out the treatment with the molybdate pigments in situ as the particles die. For example, the molybdate pigment can be included in the liquid in a ball mill in which the metal particles are milled. Molybdate pigments will generally be suitable for use with known milling lubrication systems and the surface of the metal particles will be stabilized as the particles are produced. In any of the methods for treating metal particles treated before, suitable materials such as surfactants, dispersants, anti-foaming agents, rheology control agents and the like can be used as needed. The metal particles of the present invention and the pastes containing them, can be used as direct replacements for current products in a variety of known coating systems. Examples include maintenance, coating systems, general industry, roof cladding and automotive cladding. These include, as non-limiting examples, acrylic polymer emulsions, water-reducible alkali metal resin systems, reducible alkali metal / melamine interlacing systems, waterborne epoxy systems, polyester emulsions, and water reducible polyester melamine coating. . It is also possible to treat metal particles after they have been combined with an aqueous coating vehicle. Therefore, the molybdate pigment, either alone or in combination with other treatment methods, e.g. , nitroparaffin, organic phosphate, organic phosphite, heteropolyanion, phosphosilicate, chromium and vanadium treatments, can be added to an aqueous vehicle, by itself either before or after metal particles of the coating composition have been added. If molybdate pigment is added after the metal particles have been added to the coating composition, the delay can not last very long, generally not more than 30 minutes, since a long delay would allow the aqueous vehicle to attack the particles metallic In the case where the addition is made to the coating composition, the amount of molybdate pigment can be the same as that discussed to produce particles treated in the form of paste. Simple mixing techniques can be employed. The treatment with molybdate pigment that inhibits corrosion according to the present invention can be combined with the other treatment methods discussed above, e.g. , nitroparaffin, organic phosphate, organic phosphite, heteropolyanion, phosphosilicate, chromium and vanadium. Combination treatments can give results that are improved against the results of individual treatments. The present invention will be further described through the following examples, which by nature are illustrative and not limiting. Example 1 Heucophos ZMP, a corrosion inhibiting pigment containing zinc cation and molybdate and phosphate anions available from Heubach, is dispersed under high shear stress in propylene glycol monomethyl ether. The dispersion is added to a mixer containing Silberline aluminum paste SPARKLE SI LVER® 5745 in a way that provides 10% pigment with respect to the weight of the aluminum. The mixture is stirred for approximately 80 minutes to produce a uniform paste. Comparative Example 1 Example 1 was repeated, except that no ZMP pigment was added. Example 2 Example 1 was repeated, except that as the pigment that inhibits corrosion, MolyWhite212, a corrosion inhibiting pigment containing calcium and zinc cations and molybdate anion available from Sherwin Williams, and Silberline TU FFLAKE (TM) was used. 3645 was used as the aluminum paste. Example 3 Example 1 was repeated, except that it was used as the corrosion inhibiting pigment MolyWhite92, a corrosion inhibiting pigment containing magnesium and zinc cations and molybdate and silicate anions available from Sherwin Williams, and Silberline TU was used FFLAKE (TM) 3645 as the aluminum paste. Example 4 Example 1 was repeated, except that it was used as the pigment that inhibits corrosion MolyWhiteMZAP, a pigment that inhibits the corrosion containing calcium and zinc cations and molybdate and phosphate anions available from Sherwin Williams, and Silberline TU was used FFLAKE (TM) 3645 as the aluminum paste. Comparative Example 2 Example 2 was repeated, except that MolyWhite212 pigment was not added. Example 5 Example 1 was repeated, except that it was used as the corrosion inhibiting pigment MolyWhite151, a corrosion inhibiting pigment containing zinc cation and molybdate anion available from Sherwin Williams, and Silberline SSP554 was used as the aluminum paste . EXAMPLE 6 Example 1 was repeated, except that it was used as the corrosion inhibiting pigment MolyWhiteZN P, a corrosion inhibiting pigment containing zinc cation and molybdate anion available from Sherwin Williams, and Silberline SSP554 was used as the paste. aluminum. Comparative Example 3 Example 5 was repeated, except that MolyWhite151 pigment was not added. Each of the pastes obtained from the above examples was incorporated into a normal general aqueous industrial coating formulation according to the following procedure. Enough paste to give 20.5 grams of aluminum to be weighed. The paste, 41.2 grams of glycol ether EB, 5.1 grams of "TEXANOL (from Eastman), 1.03 grams of Pateote 51 9 (from Pateote), 0.62 grams from Dow Corning 14 (from Dow Corning), 73.5 grams of deionized water and 3.7 grams of resin Joncril 537 (an acrylic emulsion of Johnson Wax) were mixed to form a uniform composition.The aliquots in duplicate of 200 grams of each composition were placed in a constant temperature bath at 52 ° C. The gas that evolved was recovered in a reversed water bath for 168 hours.The data is summarized in Table 1. Table 1 Example 7 Example 1 was repeated, except that half the solvent content of the pulp was nitroethane. Comparative Example 5 Example 7 was repeated, except that no ZMP pigment was added. The pastes of Example 7 and Comparative Example 5 were evaluated for gas evolution in the same manner as Examples 1-6 and Comparative Examples 1-4. The results were reported in Table 2. Example 8 Example 2 was repeated, except that the aluminum paste was also treated with iso-octyl phosphate according to the Patent of E. U.A. No. 4,565,716. Comparative Example 2 Example 8 was repeated, except that MolyWhite212 pigment was not added. The pastes of Example 8 and Comparative Example 6 were evaluated for gas evolution in the same manner as Example 7 and Comparative Example 5, except that a coating formulation of the manufacturer of the original automotive type was used. The results are reported in Table 2.

Table 2 It can be seen that the treatment with molybdate pigment provided a marked reduction in the reduction of hydrogen gas. While co-treatment with the secondary inhibition systems were able to achieve further improvements, it can be seen that the secondary inhibition only failed to provide the same level of protection as was observed with the molybdate pigment alone. While a detailed description of the invention has been provided, the invention can be modalized in. other specific forms without departing from the spirit or essential characteristics thereof. The modalities described in the application should be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims. All the changes that fall within the meaning and scale of equivalence of the claims are intended to be encompassed therein.

Claims (20)

1. REVIVAL DICTION IS 1. A paste of metal particles to form a coating composition, comprising: metal particles treated with a molybdate pigment that inhibits corrosion; and a solvent.
2. 2. The paste of claim 1, wherein the metal particles comprise aluminum.
3. 3. The paste of claim 1, wherein the metal particles comprise zinc.
4. 4. The paste of claim 1, wherein the metal particles comprise bronze.
5. 5. The dough of claim 1, wherein the metal particles are present in the dough in an amount of about 40-90% by weight of the dough.
6. The paste of claim 1, wherein the molybdate pigment is present in an amount of about 1-50% by weight of the metal particles.
7. 7. The paste of claim 6, wherein the amount of the molybdate pigment is 5-30% by weight of the metal particles.
8. 8. The paste of claim 1, wherein the molybdate pigment is chemically reacted with the surface of the metal particles.
9. 9. The paste of claim 1, wherein the molybdate pigment is an inorganic salt.
10. 10. The paste of claim 9, wherein the salt is at least one selected from the group consisting of a molybdate salt, a phospholibate salt and a silicomolybdate salt. eleven .
11. The paste of claim 9, wherein the salt includes a multivalent cation.
12. The paste of claim 1, wherein the cation is at least one selected from the group consisting of calcium, strontium, barium, magnesium, zinc and aluminum.
13. The paste of claim 1, wherein the solvent is suitable for forming an aqueous coating composition.
14. 14. An aqueous coating composition comprising: a paste containing metal particles according to claim 1; and a watery vehicle.
15. 15. A method for forming a paste according to claim, comprising: contacting metal particles with a molybdate pigment in a liquid medium.
16. 16. The method of claim 15, wherein the paste of the metal particles is mixed with a liquid dispersion of the molybdate pigment to provide a final paste having a desired content of metal particles.
17. The method of claim 15, wherein the metal particles are supplied in a paste, the paste is diluted with a solvent, the diluted paste is mixed with a dispersion of the molybdate pigment in a liquid, and the liquid is removed from it. the mixture to provide a final paste having a desired content of metallic particles.
18. The method of claim 15, wherein the metal particles are produced in a ball mill and the metal particles are contacted with the molybdate pigment present in the ball mill as the metal particles are produced.
19. 19. In a painted article, the improvement in which the article is painted with a coating composition, comprises a metal particle treated with a molybdate pigment.
20. 20. The painted article of claim 19, wherein the article is a car. twenty-one . A metal particle suitable for use in a coating composition, having a surface that is chemically reacted with a molybdate pigment.