GB1401900A - Production of press boards - Google Patents

Abstract

1401900 Pressed panels R JETZER 11 July 1973 [14 July 1972 11 Jan 1973] 33058/73 Heading C3N [Also in Division B5] Pressed panels are produced from organic fibrous material by mixing the fibres with a curable synthetic resin binder, vibrating the mix to form a loose press cake, precompressing and simultaneously or subsequently heating the cake at 40-100‹ C. at least over 30 seconds and subsequently pressing the cake at temperatures over 100‹ C. until the synthetic resin binder has cured. The fibrous material may be composed of 33% by weight of wood shavings and 67 % by weight of other organic fibrous material. This starting material contained 5% by weight water and was sprayed with 10À5% of its total weight with a synthetic resin binder, e.g. urea formaldehyde or phenolic resin, which contains 5% by weight water based on the total weight of the synthetic binder. During the precompression the height "h" of the press cake is preferably reduced by 30-80%, e.g. 40%, of the difference "h-c" between the press cake height "h" and the finished thickness "c" of the panel. The press cake may be heated at 85‹ C. over 45 seconds simultaneously with or following the precompression. In a process using a single stage press the fibrous material is sprayed with synthetic resin binder and vibrated on a base plate to form the press cake. The press cake is introduced between the pressing rams of a preliminary press which are fitted with high frequency electrodes for heating the press cake. After precompression the cake is introduced between the rams of the main press which are also heated and have a temperature of 130-200‹ C. Fig. 4 illustrates a continuously working apparatus for carrying out the process in which fibres 13 mixed with resin are supplied from a conveyer 12 to a spreading wheel 14 which spreads them on to a continuously moving steel belt, thus forming a press cake 16 (50 mms. in height). This passes to a preliminary press 17 which precompresses the cake to a thickness of 20 mm. after which it is conveyed through two high frequency electrodes 19 at such a speed that the press cake is heated over at least 45 seconds at 85‹ C. The press cake 16<SP>1</SP> is then pressed in a heatable continuous throughput press 20 consisting of two oppositely rotating pressing plates at a temperature of 160- 200‹ C. to form a plate 16" with a thickness of 10 mm.