Composite resinous material particles and process for producing same

A production method of a composite resin material particle, comprising:

• filling at least a resin material particle, a conductive nano-material, a solvent for propagating ultrasonic waves, and liquid carbon dioxide, into a pressure vessel;
• holding the inside of the pressure vessel at a temperature and a pressure which can keep the liquid carbon dioxide in a subcritical or supercritical state;
• dispersedly mixing the conductive nano-material from a surface of the resin material particle to an inside of the resin material particle by using ultrasonic waves;
• thereafter evaporating the liquid carbon dioxide by reducing the pressure;
• and
• further volatilizing the solvent either concurrently or with time lag, to obtain the composite resin material particle comprising:
• a resin-only region that is solely composed of a resin material of the resin material particle;
• and a dispersion mixing layer which is obtained by dispersedly mixing the conductive nano-material from the surface of the resin material particle to the inside of the resin material particle, wherein
• the resin-only region is present in the inside of the composite resin material particle and 60% or higher of a surface of the resin-only region is enclosed by the dispersion mixing layer,
• the mixed thickness of the dispersion mixing layer is from 0.1 μm to 1 μm,
• the conductive nano-material within the dispersion mixing layer has a shape with an outer diameter of 150 nm or smaller and a length of 500 nm or longer,
• the dispersion mixing layer includes a conductive net that is composed of the conductive nano-materials,
• the resin material is polytetrafluoroethylene, and
• the conductive nano-material is one or more selected from the group consisting of a carbon nanotube, a carbon nanofiber, a carbon nanocoil, a carbon nanotwist, a carbon nanohorn, a metal nanoplate, a metal nanorod, and a metal nanowire.