Befestigungsmittel,dafuer geeignete Dichtungsmittel und Herstellungsverfahren

摘要

1,230,854. Microcapsules. MINNESOTA MINING & MFG. CO. 14 May, 1968 [15 May, 1967 (2)], No. 22920/68. Heading B8C. [Also in Divisions C3 and F2] Microcapsules containing a liquid epoxy resin are prepared by: (1) forming an aqueous solution of a urea-formaldehyde precondensate containing predominantly dimethylolurea and 6-10% by wt. (of the urea) of melamine. The solids content is 3-30%, the mole ratio of formaldehyde to urea + melamine is 1À2 : 1 to 2À6 : 1 and the solution contains 0À5-10% Na 2 SO 4 . (2) Liquid epoxy resin is dispersed in the precondensate soln. with agitation. (3) Sulphuric acid is gradually added, whilst maintaining agitation, to bring the pH to 1À5-3À0 to cause the precondensate to polymerize. The polymerization is continued for at least two hours to form a water-insoluble continuous shell round the droplets of epoxy resin. The resultant aqueous slurry of microcapsules is dried at 200-350‹ F. The resultant capsules may be dispersed in a polymeric binder to form an adhesive cement (see Division C3).