| 摘要 |
513,742. Moulding synthetic resins. RENFREW, A., DAVISON, J. W., and IMPERIAL CHEMICAL INDUSTRIES, Ltd. April 19, 1838, No. 11738. Drawings to Specification. [Class 87 (ii)] Polymerized ethylene is compression moulded at a temperature not less than the melting point of the polymer. The melting point is defined and determined by placing a disc of polymerized ethylene on a flat steel plate and subjecting it to a uniform load of 1 kg. from a steel cylinder placed thereon. The temperature is raised and the relative movement of the cylinder and plate is plotted against temperature. Near the melting-point the movement increases sharply to form a substantially vertically straight portion of the plotted curve and the melting point is defined as the intersection with the temperature ordinate of the extrapolation of that straight portion. The melting point is normally 100-120‹C. and the moulding temperature is preferably about 10‹ higher, for example, 125‹ or 130‹C. Pressure is maintained on cooling and may be increased gradually. In an example, a sample whose melting point was determined at 116‹C. was moulded at 130‹C. and a pressure of 200 lb. per sq. in., the pressure being finally raised to 1,100 1b. as the temperature dropped to 90‹C.
|
