Abstract: A process of preparing and a method of storing porous poly (vinyl acetal) resin body. A method of storing the porous body involves keeping the porous body wet and free of contamination with organic substances, dissolved ions, and other fine particles. The storing method also involves keeping the body free of mold and avoiding pre-cleaning after a prolonged period of storage.

Abstract: A process of preparing and a method of storing porous poly (vinyl acetal) resin body. A method of storing the porous body involves keeping the porous body wet and free of contamination with organic substances, dissolved ions, and other fine particles. The storing method also involves keeping the body free of mold and avoiding pre-cleaning after a prolonged period of storage.

Abstract: A polyvinyl acetal sponge sheet of a porous structure having fine continuous pores and a film on the surface thereof. This sponge sheet can be used for a wiping material for car washing which does not leave unwiped portions during wiping after car washing and has a small frictional resistance and a high working factor.

Abstract: A surface grinding apparatus in which a work piece having a plate-like, disc-like, circular or annular shape and having a flat surface and a uniform thickness, which is held by carrier plates between upper and lower horizontal surface tables confronting one another, is pressed against the upper and lower surface tables and the upper and lower surface table and carrier plates are slidably moved by different rotary actions to grind the work piece by sliding friction.

Abstract: A surface grinding apparatus including a plurality of grinding wheel segments which are attached to a lapping platen directly or through an attachment plate so that the working surfaces of the segments form one plane, wherein the surface of a material to be ground is brought into sliding contact with the grinding wheel segments to grind the surface of the material. The grinding wheel segments are arranged so that a plurality of grooves are formed extending in a direction opposite to the advancing direction of the platen from the inner side of the platen toward the outer side thereof and communicate with the outer side of the platen.