| 摘要 |
1,144,176. Polyurethane films; sheet casting polyurethane. NAIRN-WILLIAMSON Ltd. 13 April, 1967 [19 April, 1966], No. 17128/66. Addition to 929,442. Headings B5A and B5B. [Also in Divisions B2 and C3] A process for reproducing a fine pattern in relief comprises the steps of feeding a liquid mixture of components which will react to form a solid flexible polyurethane, with pigment, fillers or other additives as desired, on to an endless belt of a silicone elastomer bearing a negative of the fine pattern, running the belt with the mixture on it through a heating chamber to cause the mixture to emerge as a cured layer on the belt, cooling the layer while it is still on the belt, and then stripping it off the belt. The mixture of components which will form a polyurethane on curing normally contains a polyisocyanate together with a polyol or a polyamine or both. The polyisocyanate may be a di- or tri-isocyanate or an isocyanate adduct bearing, e.g., both isocyanate and urethane groups, or a pre-polymer having two or more active isocyanate groups per molecule. Examples of suitable pre-polymers contain urethane and ester groups or urethane and ether groups. The polyisocyanate component must contain at least two isocyanate groups per molecule, and the polyol or polyamine components at least two hydroxyl or amine groups per molecule. The polyol may be a simple diol or triol or a pre-polymer containing urethane groups and ester or ether groups in addition to the active hydroxyl groups. The thermoplasticity of the polyurethane formed may be varied by the choice of the components and their proportions, up to a state of complete non- thermo-plasticity. The curing conditions used to form the polyurethane from the mixture of components depend on the components, and the presence or absence of curing catalysts. Curing may be effected at 120‹ to 180‹ C. for from 3 to 30 mins.; or a two-stage curing process may be used in which the layer is first heated to 120‹ to 180‹ C. for from 2 to 5 mins. to effect partial curing, followed by a second stage curing at 120‹ to 180‹ C. for a further 2 to 30 mins. The endless belt of silicone elastomer is formed as described in the parent Specification. Examples are given. |
