Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1988-12-14
1991-03-12
Cashion, Jr., Merrell C.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524 13, 524 14, C08J 321, C08L 126, C08L 7504
Patent
active
049993909
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a composite board comprising at least one layer made from organic fibres, particles and/or chips and a binder, and a method and an emulsion for producing the same.
Composite boards, that is, boards comprising at least one layer made from organic fibres, particles and/or chips and a binder, such as particle boards, or fibre boards, are made from finely divided organic materials such as straw, wood, bagasse, waste paper, defibrated wood pulp, and the like by spraying of the organic materials with a binder composition at ambient temperature followed by heat pressing in a discontinuous or continuous plate press with heated panels, whereby the binder typically sets in a few minutes. A more detailed description of this technique is found in Helmuth Lampert, Faserplatten. VEB Fachbuchverlag 1967, Mitlin, Particle Board Manufacture, Press Media Ltd., Kent 1968, and Taschenbuch der Spanplattentechnik, 2. Auflage, DRV-Taschenbuch, Deppe/Ernst.
The preferred types of binder have to a great extent been formaldehyde-containing compounds, as these are satisfactory both with respect to their handling and with respect to the strength of the composite boards prepared therewith.
However, in recent years, a disadvantage associated with this type of binder has to an increasing extent been brought into focus: an evaporation of gaseous formaldehyde takes place, both during the preparation of the boards and by slow hydrolysis for months and years after the preparation of the boards.
Therefore, it has been tried to make alternative binders for composite boards which are as effective formaldehyde-containing binders, but which do not emit undesirable gasses. Among these polyurethanes have been found convenient, especially those formed from aromatic isocyanates such as diphenylmethane-4,4'-diisocyanate (MDI).
There is, however, a number of technical problems associated with the use of isocyanate-based binders.
Among these is the difficulty of distributing the binder evenly over the chips, fibres or particles. To use organic solvents for facilitating the distribution is undesirable, both for toxicological reasons and because of the fire hazard.
It has been suggested to improve the handling and distributive properties of the binder by incorporating the isocyanates in emulsions. However, a number of partly mutually conflicting requirements must be fulfilled by such emulsions to obtain suitable and economic production conditions and, at the same time, obtain satisfactory strength properties of the composite boards. Thus, the emulsion must be stable (that is, the emulsion must remain sprayable and must retain its binding capacity substantially undeteriorated) for a sufficient period after its production to permit realistic production conditions, such as, e.g., a period of at least about 4 hours. The emulsion should have a sufficiently low viscosity to secure effective distribution thereof on the fibres, particles or chips before it releases the highly reactive isocyanate. At the same time, the emulsion must be able to effectively deliver highly reactive isocyanate under the conditions which prevail after it has come in contact with the fibres, particles or chips to secure an high binding efficiency.
The above-mentioned problems and requirements may also be the reason why the prior art methods using isocyanate emulsions for composite board production have used the emulsions in relatively high amounts, typically corresponding to at least 4% by weight of isocyanate applied, calculated on the weight of the chips, particles, and/or fibres.
DE-OS 1 653 177 discloses a method for preparing chip boards wherein a solution of isocyanate is applied on the chips from which the boards are made, in a suggested amount of 2-20% by weight, calculated on the dry weight of the chips. No experimental data on the chips board preparation is given.
The present invention provides an effective method and composition for producing composite boards with good strength properties in an economic and efficient manner using a particular
REFERENCES:
patent: 3428592 (1969-02-01), Youker
patent: 3835081 (1974-09-01), Remley et al.
patent: 4260532 (1981-04-01), Reuther et al.
patent: 4306998 (1981-12-01), Wenzel et al.
patent: 4653177 (1986-09-01), Israel
Azpuru Carlos
Cashion Jr. Merrell C.
Novopan Traeindustri A/S
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