| 摘要 |
1360672 Coating processes CARL FREIDENBERG 20 Aug 1971 [22 Aug 1970] 39218/ 71 Heading B2E [Also in Division C3] A process of preparing a microporous sheet on a support by coagulation comprises forming a solution in a solvent of a polyurethane prepolymer obtained by reacting a first active hydrogen containing component having a molecular weight above 400 with a polyisocyanate and reacting this prepolymer in the solution with second active hydrogen containing component having a molecular weight less than 400 and a polyisocyanate, the total amount of second active hydrogen containing component and polyisocyanate that reacts with the prepolymer being from 20 to 40% by weight of the prepolymer, to form a final polymer which is insoluble or only slightly soluble in the solvent, spreading the solution during reaction as a layer on a support and removing the solvent. Suitable first active hydrogen containing components are polyester polyols, polyether polyols, polycaprolactam polycaprolactones and polycarbonates; examples of polyesters being decarboxylic acids and glycols or glycol mixtures. The isocyanates used to form the prepolmer may include 4,4'-diphenylmethane diisocyanate, 1,5 naphthalene diisocyanate, 1,4- phenylene diisocyanate, tolylene diisocyanate, tolylene diisocyanate, xylylene diisocyanate, isiphorone diisocyanate, hexamethylene diisocyanate, 4,4'-dicyclohexylmethyne diisocyanate, or mixtures thereof. The molar ration of polyol to diisocyanate is 2:1 or from 1:1.2 to 1:2, and the prepolymer is formed at elevated temperatures, for example for 10 minutes at 130‹C. Additional isocyanate added to the prepolymer solution includes those described above and the second active hydrogen containing component is predominantly difunctional but may contain a few percent trifunction compounds. Suitable difunctional compounds are diols and diamines, for example butan-1, 4-diol, propane-1,2-diol, propane-1,3-diol and ethylene glycol. To accelerate reaction of prepolymer with the isocyanate and active hydrogen containing reagents catalysts such as triethylene diamine, dibutyl tin dilaurate and tin dioctoate are uses. Suitable supports include glass sheet or paper from either of which the microporous coating sheet is stripped, or a non-woven fibre structure to which the coating sheet may adhere. The reacting solution of final polymer and precursors may be sandwiched between two films to provide a gas permeable bond therebetween and the solution may contain conventional additions such as mineral fillers, pigments, dyes, silicones and emulsifiers. The amount of second active hydrogen containing component and polyisocyanate is preferably 20 to 40% by wt. of the amount of prepolymer. The amount of solvent is preferably from 15 to 50% by wt. of the reaction constituents. Three specific examples are given. |
