Claims
- 1. In a wallboard selected from the group consisting of hardboard having a density of 800-1100 kg/m.sup.3 and medium density board having a density of 400-800 kg/m.sup.3 made from lignocellulosic fibers, the thickness of the board being 2-25 mm and the board having two surface layers each comprising at least 10% of the board thickness and therebetween a central layer comprising 10-70% of the board thickness and prepared according to the wet process and being reinforced with a set resin, the improvement comprising: the central layer having a mean content of 1-15% by weight of said resin, based on the central layer, distributed evenly throughout said layer and the surface layers having a mean content of said resin of less than 1% by weight, the ratio of the mean resin content of said central layer and that of each of said surface layers being at least 4:1 and the resin content of the central layer steadily decreasing to that of the surface layers and there being no zone of the board having higher resin content than the central layer.
- 2. Wallboard according to claim 1, wherein the central layer comprises between 20 and 50% of the board thickness.
- 3. Wallboard according to claim 2, wherein said resin is a phenol-formaldehyde resin.
- 4. Wallboard according to claim 1, wherein said resin content of said central layer is between 2 and 6%.
- 5. In a process for the preparation of building board selected from the group consisting of hard and medium density board made from lignocellulosic fibers, wherein an aqueous suspension of said lignocellulosic fibers having a consistency in the range of 1.0-4.0% is fed onto a moving wire screen of Fourdrinier type in a board machine for dewatering, whereafter the wet lap dewatered on said moving wire screen is subjected to the normal steps of pressing and baking, the improvement comprising introducing evenly across the width of the suspension an aqueous solution of a thermosetting resin into a central layer of said lignocellulosic fiber suspension having a consistency in said range near the headbox of said board machine such that the resin content of the central layer steadily decreases to that of the surface layers and such that there is no zone of the board having higher resin content than the central layer.
- 6. A process as in claim 5 wherein the aqueous solution of a thermosetting resin is introduced into the suspension where there is a water level on the top of the suspension.
- 7. The process of claim 5, wherein said resin solution is introduced into the aqueous suspension of said lignocellulosic fibers within the headbox of the board machine.
- 8. The process of claim 5, wherein said resin solution is introduced into said aqueous suspension of said lignocellulosic fibers on the wire.
- 9. The process of claim 5, wherein the thermosetting resin content of said solution is 20-50%.
- 10. a process for the preparation of building board selected from the group consisting of hard and medium density board made from lignocellulosic fibers, wherein an aqueous suspension of said lignocellulosic fibers having a consistency in the range of 1.0-4.0% is fed onto a moving wire screen of Fourdrinier type in a board machine for dewatering, whereafter the wet lap dewatered on said moving wire screen is subjected to the normal steps of pressing and heat treatment, the improvement comprising introducing evenly across the width of the suspension a slurry of lignocellulosic fibers having a content of 1-15% by weight of a thermosetting resin into a central layer of said lignocellulosic fiber suspension having a consistency in said range near the headbox of said board machine such that the resin content of the central layer steadily decreases to that of the surface layers and such that there is no zone of the board having higher resin content than the central layer.
- 11. The process of claim 10, wherein said lignocellulosic fiber slurry is introduced into the aqueous suspension of said lignocellulosic fibers within the headbox of the board machine.
- 12. The process of claim 10, wherein the lignocellulosic fiber slurry is introduced into said aqueous suspension of said lignocellulosic fibers on the wire, said suspension having said consistency range of 1.0-4.0%.
- 13. A process as in claim 10 wherein the slurry of fibers containing the resin is introduced into the suspension where there is a water level on top of the suspension.
- 14. In a board making machine wherein a pulp slurry flow of a consistency of less than 4% is fed on to a moving wire screen, the improvement comprising a device for introducing a thermosetting resin solution into the pulp slurry flow in the direction of the slurry flow, said device comprising a straight pipe having the ends closed, the pipe being disposed in the slurry and transversely to the direction of the slurry flow and being provided with an internal partition plate provided with holes for distributing solution admitted to the pipe uniformly along the pipe, nozzles connected to the pipe and directed in the pulp flow direction, inlet means for feeding solution to the portion of the pipe other than that connected to the nozzles, and means for holding the device in position in the pulp flow.
- 15. The device of claim 14, wherein the inlet means comprises at least one pipe connected to the upper part of the horizontal pipe.
- 16. The device of claim 14, wherein the nozzles are combined to form at least one slot.
- 17. In a board making machine wherein a pulp slurry flow of a consistency of less than 4% is fed on to a moving wire screen, the improvement comprising a device for introducing a thermosetting resin solution into the pulp slurry in the direction of the slurry flow, said device comprising hollow, elongated means having circular cross section said elongated means being disposed in the slurry flow and transversely to the direction of slurry flow and being provided with a partition wall which divides the hollow means into two chambers and which is provided with holes to uniformly distribute solution flowing from one chamber to the other, this latter chamber being provided with at least one slot in alignment along the elongated means to admit solution into a central layer of said pulp slurry flow in the same direction as this flow, the elongated means being surrounded by a matching turnable envelope having at least one slot matching said at least one slot in the elongated hollow means so that the flow through both said at least one slot can be controlled and means for feeding said elongated hollow means with solution and means for fastening the device in position in the pulp slurry on the board making machine.
- 18. The device of claim 17, wherein the device is positioned with said at least one slot in a central layer of the pulp flow on the board making machine.
- 19. The device of claim 18, wherein the device is positioned in the headbox of the board making machine.
- 20. The device of claim 18, wherein the device is positioned in the pulp slurry flow on a moving wire screen of the board making machine.
Priority Claims (1)
Number |
Date |
Country |
Kind |
7315156 |
Nov 1973 |
SE |
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Parent Case Info
This application is a continuation-in-part of Ser. No. 519,203, filed Oct. 30, 1974 now abandoned.
US Referenced Citations (6)
Continuation in Parts (1)
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Number |
Date |
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Parent |
519203 |
Oct 1974 |
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