Abstract Filter materials for filtering aerosols, such as cigarette filters for filtering tobacco smoke, are provided comprising rigid polyurethane particles devoid of any cellular structure. Preferably the particles are granular and of jagged, spiny, cragged nature. The rigid polyurethane is produced from a polyol and a polyisocyanate. The particles are produced by first preparing a rigid polyurethane foam, preferably with the aid of a blowing agent, granulating the foam, treating the granules with hot water or steam to hydrolyze unreacted isocyanate and other free materials to render them inert, and then dried. Preferably, inorganic additives may be present during the preparation of the rigid polyurethane foam, such as the lower alkyl silicates, e.g., ethyl silicate, and water soluble salts of the acids of metals of groups VA and VIA of the Periodic Table, e.g., sodium tungstate. Inorganic additives may be added to the filter particles, such as an alkaline earth metal carbonate, silicate or hydroxide.
A process in accordance with claim 1 wherein the polyisocyanate is tolylene diisocyanate.
Claim 2
Dependent Claim
26 words
A process in accordance with claim 1 wherein between about 40 and 150 parts by weight of polyisocyanate are employed for each 100 parts of polyol.
Claim 3
Dependent Claim
35 words
A process according to claim 1 wherein the polyurethane is prepared in the presence of a water-soluble salt of an acid of a metal of Groups VA and VIA of the Periodic Table of Elements.
Claim 4
Dependent Claim
36 words
A process according to claim 1 wherein the polyurethane is prepared in the presence of a water-soluble alkali salt of an acid of a metal selected from the class consisting of tungsten, vanadium, chromium and molybdenum.
Claim 5
Dependent Claim
19 words
A process according to claim 1 wherein the polyurethane is prepared in the presence of a water-soluble alkali tungstate.
Claim 6
Dependent Claim
29 words
A process according to claim 4 wherein the amount of said water-soluble alkali salt employed is between about 0.2 and 4 parts by weight per 100 parts of polyol.
Claim 7
Dependent Claim
19 words
A process according to claim 1 wherein the polyurethane is prepared in the presence of a lower alkyl silicate.
Claim 8
Dependent Claim
30 words
A process according to claim 1 wherein the polyurethane is prepared in the presence of up to about 5 parts by weight of ethyl silicate per 100 parts of polyol.
Claim 9
Dependent Claim
29 words
A process according to claim 1 wherein there is added to the dried product a member selected from the class consisting of alkaline earth metal carbonates, silicates and hydroxides.
Claim 10
Dependent Claim
24 words
A process according to claim 10, wherein said member is added in an amount not exceeding 25 percent by weight of the dried product.
Claim 11
Dependent Claim
34 words
A process according to claim 1 wherein there is added to the dried product between about 3 and 15 percent by weight of an approximately equal parts mixture of aluminum hydroxide and magnesium trisilicate.