MJC212 You wrote, “Resin-fibre composites typically use calcined...

MJC212

You wrote, “Resin-fibre composites typically use calcined kaolin as the hydrous version gives issues with curing and degradation.” I do not know enough to comment on those words.

However, the 1988 patent that I mentioned, spurred me to do more Internet searching on applications that suit coarse hydrous kaolin, and I found https://patents.google.com/patent/US10995200B2/en, a patent application for using hydrous kaolin in thermoplastic resin compositions that can effect high glossiness. On its own, the document informs readers that using coarse hydrous kaolin comes a decrease of impact strength, which can be mitigated by surface treatment (particularly ethyl silicate).

On PSD, the patent application reads, “The average particle diameter is, in terms of the value measured by a wet method using a laser diffraction particle size distribution measurement device, preferably 0.1 to 20 μm, more preferably 0.3 to 15 μm, and still more preferably 0.5 to 10 μm. If the average particle diameter is too small, the glossiness of a thermoplastic resin composition may decrease. If the average particle diameter is too large, high impact strength and glossiness of the thermoplastic resin composition may not be able [to be obtained]”.

On the silicate surface treatment, the patent reads, “The amount of silicate for the treatment is, relative to 100 parts by mass of kaolin clay, 0.2 to 10 parts by mass, preferably 0 to 5 parts by mass, and preferably 1 to 3 parts by mass. If the amount of silicate for the treatment is too small, high impact strength and glossiness of the thermoplastic resin composition may not be able to be obtained. If the amount of silicate for the treatment is too large, this may cause problems, such as decrease in the strength of the thermoplastic resin composition.”

Unfortunately, Shiraishi Kogyo Kaisha's web page states, “September 1967 – Tied up with Thiele Kaolin Company (USA) in the sale of kaolin.” Japanese companies are very sticky when it comes to business relationships. Further information from Shiraishi Kogyo Kaisha states:

“The Group handles the three major white pigments used in the paper and pulp industry: heavy calcium carbonate, light calcium carbonate, and kaolin clay.

“Recently, initiatives to conserve paper have resulted in decreased paper usage in Japan. We have responded to diversifying needs by offering a wide product lineup for the three major white pigments.

“We handle kaolin clay produced by the Thiele Kaolin Company in Georgia, USA. We also act as sales agents for Thiele in Japan, China and Indonesia.

“We also