Method of producing spherical thermoplastic particles

Claim 2

A PROCESS FOR THE MANUFACTURE OF A POROUS THERMOPLASTIC PRODUCT COMPRISING: A. MIXING THERMOPLASTIC POLYMER PARTICLES IN A LIQUID MEDIUM AT A FIRST TEMPERATURE TO FORM A STABLE SUSPENSION B. BREAKING SAID SUSPENSION INTO DROPLETS: C. PASSING SAID DROPLETS THROUGH A HEATING ZONE WHEREIN SAID DROPLETS ARE HEATED TO A SECOND TEMPERATURE SUFFICIENT TO AT LEAST PARTIALLY SOLUBILIZE SAID THERMOPLASTIC AND TO EVAPORATE SAID LIQUID MEDIUM FROM SAID DROPLETS, SAID DROPLETS BEING CONVERTED INTO SPHERES BY SURFACE TENSION, AND WHEREIN SAID SPHERES ARE SUBSEQUENTLY SOLIDIFIED: D. COLLECTING SAID SOLIDIFIED SPHERES: AND E. MOLDING SAID COLLECTED SOLID SPHERES AT A TEMPERATURE SUFFICIENT TO SINTER SAID SPHEREDS THERBY FORMING SAID SPHERES INTO A UNITARY POROUS STRUCTURE, SAID POROUS STRUCTURE BEING DEFINED BY THE INTERSTICES BETWEEN SAID SINTERED SPHERES.

Claim 3

The process of claim 1 wherein said thermoplastic polymer particles are polyvinylidene fluoride of a particle size of less than about 10 microns.

Claim 4

The process of claim 2 wherein said liquid medium is selected from the group consisting of methyl isobutyl ketone, methyl ethyl ketone, dimethyl sulfoxide, and dimethyl foramide.

Claim 5

The process of claim 3 wherein said liquid medium is methyl isobutyl ketone.

Claim 6

A process for forming a porous product comprising: a. mixing polyvinylidene fluoride particles of a size less than about 10 microns in a liquid medium at a first temperature at which said particles form a stable suspension therein; b. breaking said suspension into droplets; c. passing said droplets through a heating zone wherein said droplets are heated to a second temperature within the range of from 200*F to 600*F to at least partially solubilize said polyvinylidene fluoride and to evaporate said liquid medium from said droplets, said droplets having been formed into spheres by surface tension, and wherein said spheres are solidified; d. collecting said solidified spheres; and e. molding said collected solidified spheres at a temperature sufficient to sinter said spheres thereby forming said spheres into a unitary porous structure, said porous structure being defined by the interstices between said sintered spheres.

Claim 7

A process for forming a porous product comprising: a. mixing polyvinylidene fluoride particles of a size less than about 10 microns in a liquid medium at a first temperature at which said particles form a stable suspension therein; b. breaking said suspension into droplets; c. passing said droplets through a heating zone wherein said droplets are heated to a second temperature within the range of from 200*F to 600*F to at least partially solubilize said polyvinylidene fluoride and to evaporate said liquid medium from said droplets, said droplets having been formed into spheres by surface tension, and wherein said spheres are solidified; d. collecting said solidified spheres; and e. molding said collected solidified spheres at a temperature sufficient to sinter said spheres thereby forming said spheres into a unitary porous structure, said porous structure being defined by the interstices between said sintered spheres.

Claim 8

The process of claim 5 wherein said second temperature is within the range of 340*F to 390*F.

Claim 9

The process of claim 5 wherein said liquid medium is methyl isobutyl ketone.