u00b1 0 5 pa u00b7 s when the lubricant prepared above was centrifuged for 60 minutes at 3 800 rpm from 0 to 0 5 vol of oil supernatant formed when a lubricant prepared in the same way as described above aside from not using an organic bentonite was centrifuged under the same conditions from 4 to 5 vol of oil supernatant formed when a lubricant prepared in the same way as describe above aside from not using a nonionic surfactant was centrifuged under the same conditions from 2 to 3 vol of oil supernatant formed the lubricant prepared above was examined under an electron microscope and the graphite dispersion state was compared with that in a conventional oil based graphite lubricant prepared without using bentonite electron micrographs of each are shown in fig2 in the electron micrographs areas that appear white are oil ingredients and areas that appear black are graphite the conventional oil based graphite lubricant appeared whitish overall with the graphite being present in an agglomerated insufficiently dispersed state on the other hand the lubricant of the working example appeared blackish overall with the graphite being present in a very finely dispersed state the effect of the lubricant on the plunger injection force was evaluated by measuring the axial force of the plunger rod at the time of injection axial injection force foil strain gauges were attached to the outer periphery of the plunger at four points top bottom left and right the amount of.