GB1489407A - Hard board or medium density board and process for production thereof - Google Patents

Abstract

1489407 Board manufacture SVENSKA TRAFORSKNINGSINSTITUTET 8 Nov 1974 [8 Nov 1973] 48424/74 Headings D2A and D2B A hard or medium density board prepared by a wet method and reinforced with a thermosetting binder has a central layer, which is 10-70% of the thickness of the board and has a set binder content of 1-15% by wt., and two surface layers on either side thereof, the binder content of the central layer being substantially higher than the binder content of the surface layers. The binder may be a phenol-formaldehyde, urea-formaldehyde, melamine, acrylic, or resorcinol resin, or a protein e.g. blood albumen. The binder may be added to the stock just before or after it flows out from the head box on to the wire of a board machine of the Fourdrinier type. The wet slab formed may be dewatered by suction boxes, wet pressed, sawed, pressed at elevated temperature, and heat-treated. Apparatus. A board making device for making such a board may comprise a headbox. Fourdrinier wire, and a distributor positioned transversely across the wire at the wet end of the device and adapted to distribute in use an aqueous form of the binder in a central layer of the pulp slurry which flows from within the headbox onto the wire, the outlet(s) from the distributor being immersed in the pulp slurry flow onto the wire and directed substantially in the flow direction of the pulp slurry. The distributor may be a pipe having one or more nozzles: or it may comprise an inner pipe having a slot surrounded by an outer pipe having a slot, the latter pipe being rotatable so as to bring the slots into or out of registration, (Fig. 4 not shown). The distributor may supply the binder to an additional headbox, which is immersed in the stock flow. (Figs. 5-8, not shown). A headbox provided with several vertically-separated discharge gates may also be used in the manufacture of the board.