| 摘要 |
<PICT:1064326/C3/1> Cellular urea-formaldehyde resins are made by a method which comprises in the first stage agitating a mixture of urea-formaldehyde resin, foaming agent and water in the presence of air, the duration and intensity of agitation being sufficient to produce a fine foam in which there are at least 104 cells per cubic centimetre, the proportions of resin, foaming agent and water being selected to provide in the foam a maximum volume of resin which does not exceed that which obtains when the total volume of the solid resin per unit volume of the cellular resin is 2.2% and the average number of cells per cubic centimetre is 106; in a second stage adding a hardening agent in an amount sufficient to harden all of the foam, and continuing to agitate the foam up to a point before gelation, the intensity and duration of which being sufficient to maintain the size of the cells on gelation. The foamed resin may be dispersed into fragments at the point of gelation to produce pellets. Any conventional foaming agent may be used, but those preferred are sodium salts of higher alkyl sulphates. Suitable hardening agents are suphuric, hydrochloric, phosphoric and formic acids. In Fig. 1, a urea-formaldehyde resin and water are fed from supply tank 1 through conduit 2 to a first stage rotary mixer 3. Water containing foaming agent is also fed to mixer 3 from supply tank 5, and the mixer 3 is pressurized with compressed air from compressed air supply 8. The mixture is then beaten into a fine foam and is then fed on to a second stage rotary mixer 14 where it is further beaten whilst an acid hardening agent is added from supply tank 15. From the mixer 14 the gelling foam enters a pelletizer 18 which is shown in Fig. 3. The gelling foam passes through holes 20 in the supply conduit 19 to a gap between a pair of rotating cones 21 and thence into a drying chamber 22 in the form of pellets which are further broken up by air jets from a conduit ring 23 disposed above the cones 21 and having a plurality of holes 23a in its base. The conduit ring 23 is supplied with compressed air from the supply 8. The temperature of the drying chamber 22 is maintained at about 300 DEG F. by circulating heated air through inlets 27 from a fan 25 through a heater 26. At frequent intervals the valve 30 is opened to allow the pellets to fall into chamber 31 and they are then swept by an air stream into a separator cyclone 34 where they settle to the bottom. The pellets then pass through a rotary sieve 36 and are then swept by an air stream into a second separator cyclone 39 from where they pass into a storage hopper 40. |
