New Method for Reducing VOC: Innovative Grinding Resin in Liquid Form

A grinding resin without precedent on the market provides paints and coatings formulators with freedom of choice in raw materials for industrial coatings, thanks to its advanced molecular structure. "Emission limits for volatile organic compounds (VOCs) are being lowered worldwide. For several years now, various upper limits for VOCs have been in force in the European Union; for example, in the automotive industry, this limit for repair paints is 420 g/l. This limit was also set by China in recent years for spray paints, and as a result, taxation of paints containing VOCs is now taking place in certain regions of the country. Countries that have not yet set a limit value for VOCs will follow the same legislation, and in the coming years, particularly in important markets such as the EU and USA, VOC regulations will become much stricter. This situation presents a major challenge for formulators. To comply with legal regulations, they must significantly reduce the solvent ratio and be restricted in their choice of raw materials. Until now, raw material manufacturers for paints and coatings products have focused on developing solutions for the VOC ratio in base coatings. Nevertheless, the focus in new product development has been on pigment concentrates, which have high VOC content that determines the final paint's VOC content. Previously, the addition of pigment concentrate to the base paint increased the paint's VOC percentage by weight. This process has been reversed: the addition of pigment concentrate has reduced the VOC content in the paint."

The new liquid grinding resin can reduce the VOC content of the finished paint by approximately 20 percent compared to solvent-containing industrial paints available on the market.

The new grinding resin provides viscosity reduction through two properties: First, the product itself is liquid. Second, it ensures that the pigment concentrate produced has low viscosity. For example, if VOC content is limited to 310 g/l, a standard product on the market (together with a standard additive) must have a viscosity value greater than 15,000 mPas – which makes that product impractical. However, the viscosity of the new liquid grinding resin (when combined with a standard additive) is 600 mPas at the same VOC value. The resin's acceptable affinity for pigments and good stability properties for optimal pigment loading enable high levels of viscosity reduction. For this purpose, the resin was designed by Evonik's development engineers to prevent the flocculation tendency of pigment particles. To prevent Van der Waals forces from undergoing flocculation, there must be sufficient free space between particles, thereby facilitating the movement of particles in succession. Since the liquid grinding resin contains affinity groups for pigments and its chemical structure imparts wetting properties to the resin – even without additives – the stability properties are very good. Reducing the interaction between pigment particles lowers the viscosity of the pigment concentrate and provides excellent stability properties. By wetting pigment particles with an appropriate additive, the liquid grinding resin achieves higher color strength than other grinding resins. On a light grey polyurethane test surface, it visibly delivers better results while having the same amount of pigment according to market standards (when used with an appropriate additive). Low viscosity reduces the amount of solvent required in the pigment concentrate and thus allows for higher pigment loading. In this way, at an equal concentrate amount, the color strength of the paint is improved.

For a target viscosity of 2,000 mPas, when the new grinding resin is combined with an appropriate additive, it allows 50 percent more pigment loading compared to a comparable competing product.

Additionally, paint formulators require less pigment concentrate for the same color intensity as before, thereby obtaining high-solids systems in a more economical manner. In addition to all this, because the grinding resin is liquid as opposed to the granular form used until now, it does not need to be dissolved in solvent prior to processing, and this preliminary preparation step can be entirely omitted. The resin being liquid does not cause any problems related to the hardness of the finished coating. The production process was designed so that the low viscosity of the grinding resin has minimal impact on the paint's hardness. The glass transition temperature was adjusted by modifying the monomer composition to achieve low but significant impact on hardness and high impact on VOC reduction. The molecular structure of the new grinding resin was achieved after approximately two years of intensive work. Furthermore, it meets all standard requirements for a grinding resin. As shown by test results, the new grinding resin has shown minimal effects on coating properties such as gloss (DIN EN ISO 2813), resistance to weathering (DIN EN ISO 9227, DIN EN ISO 6270-2), adhesion (DIN EN ISO 2409), drying time (ASTM D 5895), chemical resistance (DIN EN ISO 2812-4) and flexibility (DIN EN ISO 1520). Paints and coatings made with the new grinding resin show lower rub-out effects under the same conditions with both polar and non-polar solvents compared to market standards.

Resistance to weathering (DIN EN ISO 9227, DIN EN ISO 6270-2)

The liquid grinding resin is a ketone resin and exhibits high compatibility with many binder and resin types, such as alkyd resins, polyethers, epoxy resins and nitrocellulose.

While formulators prefer MPA as a solvent, studies have shown this is not the correct choice in terms of providing viscosity reduction, and butyl acetate should be used. The new grinding resin offers various formulation options in addition to a wide range of raw material choices: for example, the resulting paints and coatings are more suitable for spraying. Due to its elasticity, the liquid resin can also be used as an auxiliary resin to aid adhesion of intermediate coats to steel, galvanized steel or PVC surfaces. The liquid resin can also be used to extend pot-life. The new grinding resin provides advantages even to formulators who currently do not need these properties. With low viscosity and high color strength, a more efficient and economical tinting process can be achieved. Tego Variplus LK can also be used to increase efficiency. Formulators wish to use more economical types of solvents by using less resin per gram of pigment without changing the pigment concentrate and without compromising rub-out values and color strength. Another advantage is: With the new capabilities of the liquid grinding resin, formulators can increase pigment concentration while reducing the concentrate amount needed. Evonik has developed an appropriate additive to best utilize the viscosity advantages of the grinding resin: Tego® Dispers 676 supports viscosity reduction and increases the resin's effectiveness. Development engineers achieved this by keeping the molecular core very compact and integrating many binder groups, thereby achieving very good pigment wetting.

Summary

Tego® VariPlus LK grinding resin, together with Tego® Dispers 676, reduces the VOC content of solvent-containing industrial paints and is therefore a unique product on the market. The new grinding resin gives formulators the opportunity to reconsider binders they could not use previously due to VOC limits. Particularly given the long production cycles of pigment concentrates and strict VOC limit values, the new combination provides planning security for future years. In addition, with this innovative system, formulators have become freer to create different viscosities, pigment concentrates and formulations.