Method of making permeable diaphragm material

Claim 1

A PROCESS OF PRODUCING A DIAPHRAGM HAVING A SMALL AND REGULAR PORE SIZE, COMPRISING THE STEPS OF FORMING A SHEET BASE DIAPHRAGM MATERIAL HAVING AN IRREGULAR PORE SIZE, ADVANCING THE SHEET BASE DIAPHRAGM MATERIAL AS A CONTINUOUS WEB UNDER AND PAST A FALLING CURTAIN OF FINELY DIVIDED THERMOPLASTIC PARTICLES, BRUSHING WITH A BRISTLED IMPLEMENT THE THERMOPLASTIC PARTICLES OVER THE FACE OF THE BASE SHEET DIAPHRAGM MATERIAL TO FORCE SOME OF THE PARTICLES INTO THE POROUS SHEET BASE DIAPHRAGM MATERIAL AND TO REMOVE SURPLUS PARTICLES SO AS TO LEAVE ONLY A THIN, SELF ADHERENT COATING OF THE THERMOPLASTIC PARTICLES, AND HEATING THE SHEET BASE DIAPHRAGM MATERIAL WITH ITS SELF ADHERENT COATING OF THERMOPLASTIC PARTICLES TO SINTER TOGETHER THE ABUTTING THERMOPLASTIC PARTICLES AT THEIR POINTS OF CONTACT SO AS TO FORM OVER THE FACE OF THE SHEET BASE DIAPHRAPM MATERIAL A THIN, FINE LATTICE WORK OF THERMOPLASTIC IN A CONTINUOUS NETWORK KEYED TO THE SHEET BASE DIAPHRAGM MATERIAL BY FEET PENETRATING INTO THE PORES OF THE SAID MATERIAL, THE FINE LATTICE WORK HAVING INTERSTICES WHICH CONSTITUTE THE PORES OF REGULAR SIZE.