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Three roller milling is a method of dispersing nanofillers by the shearing force between rolls in high viscosity matrix, such as ink, paste material, coating, etc. The machine of three roll milling is composed of three cylindrical rollers with different rotating speeds, and the adjacent rollers rotate in the opposite direction. The particle size distribution and uniformity of the packing can be well controlled as the speeds of the rollers and the gap between them are adjustable. In addition, the shearing force generated between the rollers is higher than that generated by stirring, so the method can be applied to high viscosity materials, and carried out under the condition of little or no solvent. Therefore, this method is often used to disperse some anisotropic nanofillers, such as CNTs [86–89], graphene nanosheets [90–92], nanoclays [93–95], and so on.

However, it should be noted that the distance between adjacent rollers should be at least 1 μm, so the dispersion effect of nanospheres with three-dimensional direction less than 100 nm will not be good. The aggregates of nanospheres can only be turned into smaller units, not broken into individual particle. On the other hand, the rotation of the roller requires the addition of viscous materials, and nanofillers can only be dispersed in the thermosetting matrix but not in the thermoplastic matrix.