| 摘要 |
1498614 Polyurethane-gypsum foam HOECHST AG 13 Oct 1976 [15 Oct 1975] 42521/76 Heading C3R A process for the manufacture of foamed gypsum and constructional elements composed thereof comprises mixing gypsum with water in the presence of additives for liquefying the gypsum, regulating the foaming time and regulating the setting time of the foam; dispersing in this mixture from 1 to 30% by weight based on the weight of the gypsum of one or more polyurethane prepolymers prepared by reacting excess polyisocyanate with one or more polyesters and/or polyethers containing -OH groups; pouring the dispersion into a mould and allowing it to foam and to set after foaming has terminated to form a constructional member, e.g. a ceiling or wall board. Suitable liquefying additives are melamine resins, e.g. sulphonic acid modified melamine resins which may be used in amounts of from 0À1 to 3% by weight based on the weight of gypsum and a suitable additive for regulating the setting time, i.e. for preventing the gypsum hardening before the completion of foaming, is carboxymethyl cellulose used in an amount of from 0À1 to 2% by weight based on the weight of gypsum. To allow time for mixing and filling the dispersion into a mould the foaming reaction may be delayed, e.g. by 5 minutes, by using an additive consisting of a catalyst, e.g. dibutyl tin laurate absorbed on zeolite powder to diminish the activity of the catalyst. This additive may be used in amounts of from 0À1 to 2% by weight based on the weight of the prepolymer. Additional additives for example silicon surfactants as foam stabilizers and volatile fluorocarbons as blowing agents may be used in the process. Sandwich constructional members may be produced by allowing the prepolymer/gypsum dispersion, which may additionally contain a bonding agent, e.g. a redispersible polyvinyl alcohol, to foam between cover sheets, e.g. of hard board or chip board to which the foamed gypsum adheres. |
