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As everyone knows, the pigments we normally refer to include carbon black, phthalocyanine blue, iron oxide red and medium chrome yellow. Pigments are widely used and are indispensable additives in coatings and paints. With the continuous progress of industrial technology, the compatibility of these inorganic pigments has become a problem, and treating pigments with a titanate coupling agent is a common technical improvement in current processes. The methods and precautions for treating fillers with titanate coupling agents are described below.

1. Pretreatment Method for Pigments and Fillers with Titanate Coupling Agents

The first approach is to pre-coat the surface of the pigment/filler with the titanate coupling agent. Although the process has more steps and is somewhat troublesome, the treatment effect is better. The specific method is to dissolve the titanate coupling agent in a small amount of an aromatic solvent such as toluene or xylene (most titanate coupling agents — GR-101, GR-105, GR-201, GR-401, GR-110, etc. — will hydrolyse on contact with water, so water is not used; if a waterborne coating is involved, the water-soluble coupling agent GR-311 can be used without concern). The pigment/filler is then added, and under high-speed stirring (about 1000 r/min) the temperature is raised to about 70°C; stirring continues for about 10–15 minutes (a somewhat longer time is allowed where conditions permit and gives a better effect) to activate the pigment/filler particles and coat them with a layer of coupling agent. Once coated with the coupling agent, the pigment/filler can be used to formulate paints and coatings in the usual way, achieving good compatibility with the organic resins and improving the levelling and adhesion of the coating.

2. Direct Addition Method for Titanate Coupling Agents

In the manufacture of paints or coatings, the coupling agent can be added directly during the process. Dissolve the titanate coupling agent in a solvent such as mineral spirits or xylene in a solvent-to-coupling-agent ratio of 1:1, add it to the paint or coating together with the pigment/filler, and carry out high-speed dispersion. This method is relatively more convenient in terms of the paint-making process and is the method used by most manufacturers.

3. Approximate Dosage of Titanate Coupling Agents

1. The dosage of the titanate coupling agent should allow its hydrophilic reactive groups to react with the hydroxyl protons supplied by the pigment/filler; a dosage of 0.8%–1.5% is appropriate, and too much should not be used — otherwise the cost rises and the effect is not necessarily better. The optimum dosage can be decided according to the particle size of the pigment/filler and its surface functional groups. The simplest method is to observe the change in viscosity of the coating or paint after adding the titanate coupling agent, and to determine the relationship between viscosity and coupling agent dosage by measurement; the point of maximum viscosity drop corresponds to the optimum titanate dosage. Of course, if the pigment has a very high mesh number — that is, very small particles — a relatively larger amount is needed, because the specific surface area increases with decreasing particle size and the amount of coupling agent must be increased accordingly.