VOC-free bismuth-vanadate pigment preparation for improving universal dispersing properties and color strength in aqueous and solvent-based media.

Abstract

Pigment preparation of bismuth vanadate consisting of at least one pigment and at least one high molecular weight dispersing additive soluble in water and solvents.

Description

[0001] Post-treatment of pigments and fillers in various forms has been state of the art for years. This includes, for example, the subsequent coating of inorganic pigments with silicates or silanes, or even sol-gel layers, to improve both the chemical resistance of the pigments and the wetting properties in paints and plastics.

[0002] Pigments are typically synthesized in an aqueous phase and then dried or produced through a calcination process. They are supplied in micronized form for further processing. In the next step, the pigments are incorporated into polymers, where they must be re-encoded and finely dispersed to develop their decorative or functional properties. Ideally, after this incorporation process, they should exhibit the same particle size distribution they had at the time of their original formation.

[0003] Due to the intermediate steps before processing at the end customer, such as drying for pigments synthesized in aqueous phase or mechanical stress during transport as powder in paper bags, big bags or silos, the pigment particles tend to re-aggregate into larger agglomerates and, due to van der Vals forces between the crystal lattices, form larger particles that permanently shift the particle size distribution.

[0004] The end user of the pigments employs dispersing equipment such as dissolvers, stirred mills, or rotor-stator systems to convert the pigments into a liquid phase in the next step and process them into aqueous or solvent-based paints or pigment pastes. To aid pigment wetting, wetting and dispersing agents are typically added to the paint or pigment paste. These agents contain a pigment-affine and a binder-affine group, thus exhibiting a surfactant structure. This accelerates incorporation and draws the pigment onto its surface. As a result, pigment particles are stabilized, leading to improved properties in the paint system, such as color strength and storage stability.

[0005] For both aqueous and solvent-based paint or pigment paste systems, additive manufacturers offer a wide variety of different additives compatible with solvents or water, with different polymer structures and functional pigment-affine groups, resulting in different molecular weights, which can be used universally or selectively for the respective binder system or pigment class.

[0006] However, recent developments in the field of high molecular weight selective block copolymer wetting and dispersing additives enable a new technical approach to this.

[0007] These polymers possess a very high molecular weight polymer structure, allowing for the combination of various copolymers and potentially containing double bonds. Side chains can then be generated within this polymer chain via controlled radical polymerization. Due to its characteristic shape, this type of polymer is also referred to as a comb polymer. Pigment-affine groups can then be incorporated into these side chains, either uniformly or alternately arranged in groups.

[0008] Current technologies enable the production of 100% VOC-free, room-temperature liquid wetting and dispersing additives based on mallein-styrene anhydride (MSA) with pigment-affine side chains. A specific group of these polymers are both highly soluble in water and readily soluble in polar solvents, exhibiting broad compatibility with commercially available aqueous and solvent-based binders, as well as excellent pigment affinity. By appropriately selecting the type of pigment-affine side chain, solubility and compatibility in aqueous and solvent-based systems can be further improved, thus enabling the application of this utility model in both media.

[0009] In the present application, it has been shown that the MSA copolymer wetting agent is preferably absorbed onto the pigment surface during pigment synthesis in the aqueous phase before re-drying. For pigments from non-aqueous synthesis processes, these must first be processed into an aqueous slurry to be subjected to the wetting process.

[0010] To wet the pigment surface, the additive is added to the slurry while stirring and drawn up under pH and temperature control. It is then filtered and fixed to the surface by drying. A sudden drop in viscosity is noticeable as soon as the additive is added to the slurry; this is caused by the polymer being drawn up onto the pigment surface.

[0011] It has been shown that the dewatering properties in the filtration process, as well as press cake and drying times, can be improved. This can lead to further savings in process costs.

[0012] With appropriate dosage of the MSA copolymer additive, dust-free granules can also be produced, eliminating the need for micronization after drying prior to delivery. In granule or pigment form, the material exhibits good storage stability and flow properties.

[0013] For pigments that are unstable in the aqueous phase, such as aluminum pigments, wetting and stabilization can alternatively also take place in solvents.

[0014] Due to its very high wetting properties, the additive can also be applied by mechanical mixing with the pigment as an alternative to the wet application method. For this purpose, it is sufficient to add the additive as an admixture to standard micronization processes or to incorporate it into an additional high-speed mixer or knife blender, such as the Axiom SpherHelics Type SH or the Lödigen Type L5 pilot plant plowshare mixer.

[0015] Another application of this technology, at lower dosages, is the improvement of the flow properties and storage stability of pigments. This is particularly relevant for the titanium dioxide-type white pigments and the bismuth vanadate group. For decades, the addition of 0.1–0.5% trimethylolpropane (TMP) has proven effective in this regard, and it is added after synthesis and drying in the micronization process. However, due to the hazard classification of trimethylolpropane, a replacement is necessary.

[0016] Due to the coating of the pigment particles produced at the earliest possible point in the supply chain during the manufacturing process at the pigment manufacturer, the dispersion properties can be improved to such an extent that further processing steps in the subsequent processing process are simplified and energy costs, logistics costs and cleaning costs are eliminated.

[0017] By applying pressure to the pigment surface, significantly higher concentrations and more storage-stable slurries can be produced in the pigment synthesis manufacturing process, as well as higher pigment paste concentrations when incorporated into water and solvents, and in the finished coating systems.

[0018] Coating the pigment surface improves the color depth, hue, gloss level, color strength, and opacity of the treated pigments. These treated pigments can be incorporated into both aqueous and solvent-based binder systems using ball or bead mills and three-roll mills, without the need for high-energy wet milling technologies.

[0019] This also makes it possible to implement color mixing systems and tinting systems by adding VOC-free dry pigments or granules to aqueous and solvent-based paint systems. Example formulation: 1) Pigment preparation example (Bismuth Vanadate AL2300 Bruchsaler Farben) Pigment preparation dry method Pigment AL2300 97,00% Addition of additive to pigment dry Disperogen PLF 100 ' 3,00% Ploughshare knife mixer with single or continuous dosing of the additive e.g. - laboratory mixer Kinematica MB950G - Lödigen type L5 technical college plowshare mixer Incorporation and homogenization of the additive into the pigment mixture: 5-15 minutes at 20-60°C 100.00% pigment preparation Example of the resulting improved pigment properties:

[0020] Dispersion using Skandex SK-550 shaker 30 minutes each of 60g test lacquer + 40g glass beads 1mm

[0021] Colour tone and colour strength 1:10 in an aqueous and a solvent-based white lacquer with titanium dioxide TIPURE R706: Reference sample AL2300 standard (100% pigment) Improved sample AL2300 with 3% additive (97% pigment + 3% additive) Measurement data from CIELab d8, elevators at 40µm on LENETA contrast cards: Test varnish 1) Acrylic dispersion paint, aqueous 1:10 BiVa to TiO2

[0022] Color hue and color intensity change measured

[0023] Ref. AL2300 100% pigment to AL2300ED (97% pigment+3% additive)

[0024] DL* = -0.31 Da* = -0.53 Db* = 1.03 Color strength 110% at 97% pigment content. Therefore, calculated color strength 113% at 100% pigment content. Test varnish 1) Short-oil alkyd varnish with 5% proportion of polar solvent, aqueous 1:10 BiVa to TiO2

[0025] Color hue and color intensity change measured

[0026] Ref. AL2300 100% pigment to AL2300ED (97% pigment+3% additive)

[0027] DL* = -0.11 Da* = -0.23 Db* = 0.33 Color strength 108% at 97% pigment content. Resulting color strength 111% (calculated at 100% pigment content).

[0028] This results in improved pigment efficiency per unit of used. The pigment can therefore be sold at higher market prices or, as is common practice in the pigment industry, blended with fillers such as barium sulfate to reduce its color intensity. This saves on raw material costs and allows for higher margins at the same selling price.

[0029] The technology described here only slightly alters the pigment's color. However, the increase in color intensity with the same amount of product is considerable.

Claims

[1] Pigment preparation of bismuth vanadate consisting of at least one pigment and at least one high molecular weight dispersing additive soluble in water and solvents. [2] The bismuth vanadate pigment preparation may also contain a filler. [3] The bismuth vanadate pigment preparation may also contain other colored pigments. [4] The dispersing additive consists of a comb polymer based on a maleic-styrene anhydride copolymer (MSA) or polystyrene-polyacrylic acid (PS-PAA) with pigment-affine side chains that are regularly arranged. [5] At least one side chain of the dispersing additive contains an amino-functional pigment-affine group. [6] At least one pigment-affine side group of the dispersing additive contains a pigment-affine amino-functional group in the form of a quaternary amine. [7] The dispersing additive is VOC-free. [8] The dispersing additive forms a fluid polymer above room temperature. [9] The dispersing additive is soluble in water at a mixing ratio of 1:99 to 99:

1. [10] The dispersing additive is soluble in a mixing ratio of 1:99 to 99:1 in a solvent mixture of 1:1 methoxypropyl acetate (MPA) and Solvesso 150. [11] The concentration of the dispersing additive to the bismuth vanadate is 0.1% to 200%, preferably 0.3% to 10%. [12] The dispersing additive is added to the dry pigment in an intensive mixer or knife mixer and applied mechanically. [13] The temperature when mixing in the dispersing additive is 1°C to 100°C, preferably 10°C to 60°C. [14] The time for mixing in the dispersing additive is 1 minute to 24 hours, preferably 5 minutes to minutes. [15] Alternatively, the dispersing additive can be added to the dry pigment and mechanically applied in the micronization or dry milling process in air jet mills, annular gap mills, pin mills or ball mills. [16] With a correspondingly higher dosage of the dispersing additive, flakes or free-flowing granules can be produced by crushing or tumbling, which enable low-dust or dust-free delivery forms. [17] The resulting increase in the colour strength of the additive-treated pigment allows higher amounts of barium sulfate filler to be used to achieve the same colour strength.