Ashvin Patel Google 'comminution limit' and read this article available for free on RG:

Article Comminution limit (CL) of particles and possible implication...

Note that the CL for alumina (the major constituent of kaolin) is greater than 2 microns. Your best bets are wet milling with appropriate additives (surfactant and perhaps the optimum amount of phosphate stabilizer) or air jet milling. Good luck. Take a look at (registration needed):

Dispersion and nanotechnology

https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat

Also:

https://www.linkedin.com/pulse/what-limits-particle-size-grinding-process-philip-howie/

Note that clays like kaolin form bookleaf structures so you'll need to define what you mean by "< 2 microns" in such a system. A single layer may only be 20 nm or less in thickness...

Micronization (air jet)

Wet bead milling

Thanks Mr.Rawel & Mr. Miller

By Micronization process and repeat milling in miled jares