For inks, paints, sealants, PVC sols, acrylic sols and the like, they are first prepared in the form of a paste sol and the paste sol is then used to implement coating, painting, application, mixing or other operations. If properties, quality or other conditions of a cured product do not allow the incorporation of so much filler into the paste sol, there is used a filler capable of imparting, even in a small amount, a high viscosity to the sol, such as fumed silica.
Fumed silica allows the sol to exhibit high thixotropy, however, simultaneously providing high viscosity. Furthermore, fumed silica also presents a problem in that it extremely changes the sol viscosity with a very small variation in additive amount.
Meanwhile, calcium carbonate is used as a filler for various polymeric materials, such as plastics, rubbers, inks, paints, sealants, PVC sols, and acrylic sols. Therefore, if the addition of calcium carbonate can impart high thixotropy to these materials, calcium carbonate can be used as a relatively inexpensive thixotropy imparting agent.
Patent Literature 1 discloses a surface-treated calcium carbonate that is a calcium carbonate surface-treated with an unsaturated fatty acid and a saturated fatty acid in a predetermined mixture ratio. When this surface-treated calcium carbonate is used and added to inks, paints, sealants, PVC sols, acrylic sols and the like, high thixotropy can be imparted to these materials.
However, from viewpoints of environmental health and other factors, consideration has recently been given to saving the usage of diluent, plasticizer and the like. With the use of the surface-treated calcium carbonate in the above known technique, the materials can achieve high thixotropy but increases the viscosity, which makes it difficult to save the usage of diluent and plasticizer. Therefore, there is demand for a surface-treated calcium carbonate capable of imparting high thixotropy together with low viscosity.
Patent Literature 2 also proposes a surface-treated calcium carbonate for imparting high thixotropy. However, also with the use of the surface-treated calcium carbonate disclosed in this known technique, it is difficult to impart both of low viscosity and high thixotropy.
Patent Literature 3 proposes a calcium carbonate surface-treated with a surface treatment agent containing lauric acid and myristic acid in a total content of 85% or more. However, also with the use of this surface-treated calcium carbonate, it is difficult to impart both of low viscosity and high thixotropy.