Black Preparations

It is generally known that pigment black powders have to be dispersed very extensively to achieve development of coloristic properties. Degussa is now able to offer a preparation in which the pigment black powder has been incorporated into an aldehyde resin matrix by a newly developed production process. The resulting pigment preparation is in granular form, providing an easy-to-handle, zero-VOC, dust-free preparation having excellent pigment stability. INXEL™ pigment preparations represent the next-generation pigment providing high quality and easy to-handle solutions to paint manufacturers, and they are designed for solvent-based and solvent-free coatings systems.

Technical Fundamentals of INXEL™ Pigment Preparations

Degussa pigment blacks are incorporated into an aldehyde-based binder using a proprietary production process. This resin is soluble in most commonly used solvents and has broad compatibility with many coating raw materials, such as:

• alkyd resins;
• cellulose nitrate;
• cellulose acetobutyrate;
• vinyl chloride copolymers;
• chlorinated rubber;
• hydroxypolyacrylates;
• melamine-formaldehyde resins;
• aromatic and aliphatic epoxy resins;
• hydrocarbon resins; and
• phthalate plasticizers.

The granules, produced by an innovative process, have a diameter of 1-3 mm and contain up to 40% pigment black. The granules can be mixed directly into a solvent or a blend of resin and solvent without using sophisticated dispersion equipment. The dispersion time can be reduced further by prior soaking the granules in solvent or a solvent binder blend for 30 minutes. After mixing for 15 to 30 minutes using just a dissolver, a well-dispersed and stabilized pigment black mill base is obtained. No subsequent milling is required, and the paste can be directly letdown. Figure 1 indicates the required dispersion times of a typical pigment black powder compared to the newly developed INXEL preparation.

In the following section, examples for the use of INXEL pigment preparations in different acrylic coatings systems are given. Relevant coating parameters achieved with these pigment preparations, like fineness of grind, are always similar to values obtained with powder pigments dispersed in the traditional way. Regarding the coloristic properties, INXEL pigment preparations showed significant improvement. In addition, excellent stabilization of the pigments was obtained in the coating systems evaluated.

INXEL Pigment Preparations in Acrylic Systems

In high-performance coatings, acrylic resins are widely used in different coating formulations. In this test series hydroxyl functional acrylates were crosslinked with the aliphatic isocyanate Desmodur® N 75 (Bayer Material Science). To evaluate the properties of INXEL pigment preparations five commonly used acrylate resins were chosen, as shown in Table 1.

The INXEL granules were soaked in the solvent binder blend for 30 minutes and afterwards dispersed with a dissolver at a tip speed of approximately 8 m/s. After a dissolving time of 15 minutes a stable and well-ground millbase was obtained. The let down was done with usual stirring equipment. For all masstone applications the concentration of pigment black was 5% based on binder solids. The coatings were sprayed onto metallic panels, flashed off for 30 minutes and cured for 30 minutes at 80 °C. The jetness (MY) and undertone (dM) results of INXEL Black A902 in five different acrylate resins are shown in Figure 2.

Our tests confirmed that INXEL pigment preparations are highly compatible in the acrylate resins tested. The five acrylates all provided comparable high jetness with a strong blue undertone. The blue undertone confirms the excellent stability of the pigment black preparation in masstone applications across the range of binders tested. A comparison of jetness (MY) and undertone (dM) of a system produced with INXEL Black A903 and a respective pigment black powder is shown in Figure 3. While the jetness is comparable, the undertone is significantly more bluish with the INXEL Black A903 preparation. This confirms the excellent stability of the dispersed black pigment in a two-pack acrylate system. To evaluate the stability of pigment blacks incorporated via INXEL pigment preparations in comparison to powder pigments, grey coatings were prepared with a TiO2/pigment black ratio of 100:4. After applying the coating systems onto a substrate, the liquid coating was rubbed with a finger on a small area. This creates a slight manual dispersion and remixes possible pigment segregation.

A very small difference in color density between the original applied coating and the rubbed area confirms good pigment stability. Differences in rub-out of an INXEL Black A904 and a Low Color Furnace Black are shown in Figure 4. While the system with pigment black powder shows a significant difference in density before and after rub-out, the discrepancy is strongly reduced with INXEL Black A904. This means that the pigment black incorporated via INXEL Black A904 is much better stabilized in the coating system.

Conclusion

INXEL pigment preparations show excellent compatibility in all acrylate resins that were evaluated. The jetness values were always comparable or even higher compared to the corresponding powder pigment. The strong blue undertone in masstone applications and very good rub-out performance in tint demonstrate the excellent stability of the pigment preparations. In addition to the acrylate resins, tests in alkyd and polyester systems were also conducted. Very positive results were obtained for these systems also. Meanwhile, various preparations based on Degussa pigment blacks can be offered in different jetness ranges. Step by step the color range will be widened.

This paper was presented at the Nürnberg Congress held during the European Coatings Show, Nürnberg, Germany, May, 2007 and organized by the Vincentz Network. See events@coatings.de.

Sidebar:
Benefits of the new INXEL Pigment Preparations

The tests in acrylate, alkyd and polyester systems have shown the broad compatibility of INXEL pigment preparations in various coatings systems. Beside the significantly reduced dispersing time, INXEL pigment preparations have shown comparable or even better coloristic values and stability. To sum it up, INXEL pigment preparations provide the following benefits:

• Zero VOC;
• No need to grind pigments;
• Significant reduction in dispersion time;
• Excellent pigment stabilization providing very good color development;
• Absolutely dust-free handling;
• Very precise granule metering;
• Very good solubility in common solvents;
• Compatible with most binders for solvent-based systems.