Surface-Treated Mineral Filler

The present invention relates to surface-treated mineral fillers and method for the preparation thereof. The fillers are particularly suitable for making emulsion paints.

It is known to admix fillers, which are considered relatively cheap substances, to working materials such as paints, paper, plastic material and the like in order to increase their volume and/or weight. Also, fillers are often added to improve the usefulness of such materials.

The behavior of fillers in plastic materials, paints, and the like is decisively influenced by the nature of the filler surface. Attempts have therefore already been made to improve the properties of fillers by treating their surfaces with chemical substances.

For instance, German Pat. No. 958,830 suggests a method for treating natural calcium carbonate with surface-active materials wherein the calcium carbonate, in the presence of synthetic and natural fatty acids, amino-fatty acids, acid amides, fatty alcohols, waxes, and resins is ground up in quantities of between 0.1 and 40% at a temperature of at least 80.degree. C. The problems to which said German patent are directed are to prevent the conglomeration of chalk particles and to facilitate the process of blending with plastic polymers and the like.

Surface-treated fillers suggested in the art possess more favorable properties when compared to untreated fillers. However, they still require considerable improvement particularly in terms of their practical technical properties.

An object of the present invention is to improve the properties of fillers and particularly the mechanical properties of relatively coarse fillers. One special purpose of the present invention is to provide a filler through surface treatment which can be used advantageously to make emulsion paints, and particularly to improve the wash and scrub resistance of the paints.

Over many years of comprehensive series of experiments, applicant investigated many groups of chemical substances and individual substances for their effectiveness as surface-treatment agents.

The following groups of substances, respectively, were tested for their effectiveness: silicones, cyclic esters, paraffin oil, polyethylene waxes, monocarboxylic acids (i.e., saturated or unsaturated fatty acids), saturated or unsaturated dicarboxylic acids, dicarboxylic acid esters, aromatic monocarboxylic acids, aromatic hydroxymonocarboxylic acids, polycyclic dicarboxylic acids, higher alcohols, amines, emulsifiable polymers, inorganic silicates, inorganic fluorosilicates, and wetting agents. None of the substances tested yielded an improvement in the wash and scrub resistance of emulsion paints that could be used in practice.

Surprisingly enough, however, it was discovered according to the invention that the problem can be solved by surface-treating the mineral filler with a mixture of saturated and unsaturated aliphatic acids.

It is particularly surprising that the use of the mixtures consisting of saturated and unsaturated aliphatic acids provided the advantages achieved according to the present invention since the use of saturated or unsaturated acids alone did not provide any noteworthy improvements.

The present invention is concerned with mineral fillers surface treated with a mixture of saturated and unsaturated aliphatic carboxylic acids.

The present invention is also concerned with a method for preparing the filler which includes grinding the filler in a mill with microgrinding bodies in the presence of the above mixture of acids and in the presence of a dispersing agent. The present invention is also concerned with another method for preparing the filler which includes grinding the filler and subsequently treating it by adding the above mixture of acids.

The present invention is also concerned with the use of the surface-treated fillers to prepare watery paint systems.

It has been found according to the present invention that mixtures of saturated and unsaturated aliphatic carboxylic acids in the surface treatment of mineral fillers provide improved fillers. The carboxylic acids can be straight chained or branched chained and are preferably straight chained. Also, the acids employed are preferably monocarboxylic. The acids employed according to the present invention generally have from about 6 to about 22 carbon atoms, preferably from about 12 to about 20 carbon atoms, and most preferably from 16 to 18 carbon atoms. The acids employed should be free of substituents other than carbon, hydrogen, and the carboxylic acid grouping.

Examples of some saturated acids include lauric acid, myristic acid, stearic acid, and palmitic acid. Mixtures of individual saturated acids can be employed if desired as the saturated acid component. The unsaturated aliphatic acid can be monoethylenically unsaturated and/or polyunsaturated. Mixtures of individual unsaturated acids can be employed as the unsaturated acid component if desired. Examples of some suitable unsaturated aliphatic acids include oleic acid, linoleic acid, and linolenic acid.

One advantageous aspect of the present invention is that the filler can be surface-treated with naturally occurring mixtures of saturated and unsaturated fatty acids. For instance, the fatty acids obtained for instance by hydrolysis from such oils as safflower oil, soybean oil, poppyseed oil, and sunflower oil can be used in the present invention.

Soybean fatty acids are particularly advantageous as a surface-treating agent. Soybean fatty acids consist essentially of linoleic acid, oleic acid, palmitic acid, stearic acid, and linolenic acid.

The mixture of acids employed generally contains from about 10 to 35% by weight of the saturated aliphatic acid component and from about 65 to about 90% by weight of the unsaturated aliphatic acid component. The preferred acid mixtures contain palmitic acid, stearic acid, oleic acid, linoleic and optionally linolenic acid, and preferably in the following amounts by weight:

palmitic acid--about 5 to about 20%,

stearic acid--about 5 to about 15%

oleic acid--about 20 to about 50%

linoleic acid--about 30 to about 70%

linolenic acid--0 to about 10%

According to the present invention, the best results were obtained with a soybean fatty acid made up of 53.0% by weight of linoleic acid, 24.0% by weight of oleic acid, 12.0% by weight of palmitic acid, 6.0% by weight of stearic acid, and 5.0% by weight of linolenic acid.

The materials treated according to the present invention include the mineral or inorganic fillers and include natural, precipitated and/or pyrolytic produced fillers. Examples of some suitable fillers include natural and precipitated carbonates including natural and precipitated calcium carbonate and dolomite, natural and precipitated barium sulfate, and natural, precipitated and/or pyrolytic produced silica such as quartz dust and compounds of silica such as the silicates and including kaolin, mica, and talcum. Particularly favorable results were obtained with marble dust as filler.

The fillers employed generally have a particle size range of about 0.1 to about 100 .mu.m and preferably a particle size range between about 0.5 and about 25 .mu.m.

The relative amounts of filler and surface treatment agent (i.e., mixture of acids) is generally about 90.0 to 99.9% by weight of filler and correspondingly 0.1 to about 10.0% by weight of surface treatment agent, is preferably about 97 to 99.9% by weight of filler and correspondingly 0.1 to about 3% by weight of surface treatment agent, and most preferably is 99.0% to about 99.8% by weight of filler and correspondingly 0.2 to 1% by weight of surface treatment agent. A weight ratio of 99.4% by weight of filler and 0.6% by weight surface treatment agent proved to be particularly advantageous.

According to the present invention, the surface-treated minerals are either made by grinding up the filler in the presence of an organic or inorganic dispersion agent in a mill with micro grinding bodies in the presence of the surface treatment agent or the filler is obtained by grinding and is then surface treated.

The surface treatment agent can be added by heating it, if needed, to temperatures within the range of about 20.degree. to about 80.degree. C., and by spraying and/or using fluid mixers (e.g., mixing or kneading mechanisms).

It was found that mineral fillers, surface treated according to the present invention, are particularly suitable for making watery paint systems and particularly for the production of emulsion paints. Outstanding results were achieved in the production of emulsion paints based on styrene-acrylate copolymer dispersions as binders. Examples of some polymers to which the treated fillers can be added include polymers from monoethylenically unsaturated compounds such as polyvinylacetate, acrylate polymers including ethyl acrylate and methyl acrylate, copolymers of vinyl acetate and esters of acrylic acid, copolymers of vinyl acetate and vinyl ester of versatic acid, copolymers of vinyl propionate and esters of acrylic acid, copolymers of styrene and esters of acrylic acid, copolymers of styrene and butadiene, and terpolymers of vinyl acetate, vinyl ester of versatic acid, and esters of acrylic acid.

In wash-resistant interior emulsion paints, an untreated calcium carbonate (particle size range between 0.5 and 25 .mu.m) demonstrated a washing resistance of 1,100-1,400 cycles, measured according to DIN [German Industrial Standard] 53778. For a discussion of the minimum requirements of synthetic emulsion paints for interior use, see DIN 53778, Part 1, September 1976, disclosure of which is incorporated herein by reference. The same interior emulsion paint, containing the same calcium carbonate as filler except that it was surface-treated according to the present invention, on the other hand, quite surprisingly, gave a washing resistance of 20,000-22,000 cycles. For the surface treatment, 0.6% soybean fatty acid was used. In a scrub-resistant interior emulsion paint, it was possible to increase the number of scrub cycles, by means of the surface treatment of calcium carbonate according to the present invention, from the original 5,000 to more than 65,000.

The increase in wash and scrub resistance as a result of this invention in practice particularly facilitates a qualitative improvement in the dispersion paints with constant binder content or an increase in the economy through binder reduction with practically unchanged wash or scrub resistance. Thus, for example, the binder quantity can be reduced in washproof interior paints from 10.0% to 8.0%, in other words, a 20% reduction. In scrub-proof interior paints, the binder can be reduced from 12.0% down to 9.5%, that is to say, by about 21%. This binder reduction, coupled with the same final product quality, signifies a considerable cost reduction.

Furthermore, the present invention provides the following advantages. It is more waterproof and thus more weather-proof; reduced swellability. Improved sprayability and free flow properties of the powder for easier bulk handling and thus easier silo storage and pneumatic conveyance. Smaller bulk volume. Smaller space requirement during storage. Less dust generation. Less dust pollution. Simple dispersion in watery media due to lesser inclination toward agglomerate formation. Greater surface smoothness of paint film and less scratch and dirt sensitivity. Film surface can be easily cleaned due to slight hydrophobia.

The following examples are presented to further illustrate the present invention wherein marble dust surface-treated in accordance with the present invention is compared to untreated marble dust in emulsion paints with regard to wash and scrub resistance.

In a fluid mixer, 994 parts by weight of a marble dust having particle size range between 0.5 and 25 .mu.m were preheated to a temperature of 40.degree. C. Thereafter, 6 parts by weight of soybean fatty acids, preheated to 40.degree. C. where slowly sprayed onto the marble dust. The temperature rose to 80.degree. C.

The above surface-treated marble dust was tested for wash resistance according to DIN 43778 and was compared to an untreated marble dust having the same particle size range in a wash-proof emulsion paint of the composition given below. The surface-treated marble dust, made according to the present invention, was examined for wash resistance both with the use of 10% by weight and 8% by weight emulsion containing as binder a styrene-acrylate copolymer.

Marble dust, with a particle size range of 0.5-25 .mu.m, is surface treated in accordance with Example 1. Comparative tests were carried out with an untreated marble dust having the same grain size range in a scrub-resistant emulsion paint, of the following composition.

The surface-treated marble dust, prepared according to the present invention, was tested for scrub resistance both with the use of 12% and 9.5% by weight styrene-acrylate copolymer emulsion.

The surface-treated fillers of the present invention were also employed in emulsion paints with the following polymers resulting in the following improvement in scrub resistance when compared to the same filler except being untreated.