VOC-free pigment and filler preparation for improving universal dispersing properties in aqueous and solvent-based media.

Abstract

Pigment preparation consisting of at least one pigment or filler 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] For medium and high molar masses of the wetting and dispersing additives used, pigment preparations can be carried out exclusively as highly concentrated pastes for the production of universal pigment pastes for use in either aqueous or solvent-based coating systems. In this case, the additive takes over the function of the binder until it is added in the final formulation.

[0007] A form of these pigment preparations that has now become established on the market is pigment pastes that have been dried after the dispersion process. These are formed into storage-stable granules, for example using a spray-drying process, which the user adds to their paint as a dry preparation. Under low shear forces, the agglomerates held together by additive polymers are dissolved.

[0008] In all the systems described here, pigment preparation is produced using dispersion and wet milling technology, which requires considerable energy consumption due to the use of the milling units. In practice, typical dispersion plants require approximately 100 kW per ton of a readily dispersible pigment, and up to 800 kW for a pigment class with unfavorable dispersion properties. It is well known in the paint and printing ink industry that the production of pigment preparations is both energy- and time-intensive. The associated costs, such as the storage of finished products, cleaning, and handling, are complex and expensive. The acquisition, monitoring, and maintenance of a dispersion plant are substantial.

[0009] Current technologies are not yet capable of bringing a universal pigment preparation to market that can be produced with minimal manufacturing effort and possesses all the described properties. A particular challenge is achieving universal compatibility in aqueous and solvent-based systems, being VOC-free in dry form, and possessing the properties to be formulated in both coating systems by stirring under low to medium shear forces.

[0010] However, recent developments in the field of high molecular weight selective block copolymer wetting and dispersing additives enable a new technical approach to this.

[0011] 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] 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.

[0017] For pigments that are unstable in the aqueous phase, such as aluminum pigments, wetting and stabilization can alternatively also take place in solvents.

[0018] 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.

[0019] 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 group of white pigments of the titanium dioxide type. For decades, the addition of 0.1–0.5% trimethylolpropane (TMP) has proven effective in this regard; this is also added after synthesis and drying using a micronization process. However, due to the hazard classification of trimethylolpropane, a replacement is necessary.

[0020] 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.

[0021] By applying the pigment surface, significantly higher concentrations and more storage-stable sturries 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.

[0022] 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.

[0023] 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 recipe: 1) Pigment preparation example (TiO2) Pigment preparation wet method Dry process Water 47,00% - Tioxide R960 50,00% 98,94% Mixer 5 min 5 m / s pH 5.1 Disperogen PLF 100 0,50% PH 6,4 1,06% Ultra Turrax 12,000 RPM 5min Mixing 55 min at 50°C PH 6.9 STOP Filtration Drying at 60°C / 12h Blade Mill 5×1 Min at 40°C max. 10 x 1 min at 60°C max 100,00% 100,00%

Claims

[1] Pigment preparation consisting of at least one pigment or filler and at least one high molecular weight dispersing additive soluble in water and solvents. [2] 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. [3] At least one side chain of the dispersing additive contains an amino-functional pigment-affine group. [4] 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. [5] The dispersing additive is VOC-free. [6] The dispersing additive forms a fluid polymer above room temperature. [7] The dispersing additive is soluble in water at a mixing ratio of 1:99 to 99:

1. [8] 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. [9] The concentration of the dispersing additive to the pigment solid is 0.1% to 200%, preferably 0.3% to 10%. [10] The dispersing additive can be drawn into the wet phase of a pigment slurry while stirring. [11] The pH value of the slurry is pH 2 to pH 11, preferably pH 5 to pH 9. [12] Alternatively, the dispersing additive can be drawn up in a pigment slurry in an organic solvent. [13] The temperature during the application of the dispersing additive is 1°C to 100°C, preferably 10°C to 60°C. [14] The time required to draw up the dispersing additive is from 1 minute to 24 hours, preferably from 10 minutes to 8 hours. [15] Alternatively, the dispersing additive can be added to the dry pigment in the micronization or dry milling process and applied mechanically. [16] Alternatively, the dispersing additive can be added to the dry pigment in an intensive mixer or knife mixer and applied mechanically. [17] With appropriate 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.