FI78254C - Preparation process for a fire impregnated veneer - Google Patents

Description

1 78254

Method of making fire impregnated plywood

The application relates to a method for producing fire-impregnated plywood, in which the plywood is only partially treated with a fire retardant.

According to one known method, a fire-retardant plywood is prepared by immersing the finished plywood in its entirety in a solution of the fire retardant and allowing the fire retardant to be absorbed into the plywood. Absorption can be promoted by pressure as in other impregnations. The plywood is then dried. The disadvantage of this impregnation method is that the absorption of the impregnating agent cannot be precisely known due to the variation in the properties of the wood veneers and in particular the effect or variation of the adhesive layers. In this case, the concentrations and distributions of the flame retardant in the two different plywood boards can differ considerably. In addition, this treatment tends to twist plywood for which nothing can be done. Sometimes the plywood may even crack when dry. In addition, in this method, gluing a fire protection film or other, for example a decorative surface layer, if necessary, to the surface of the plywood requires a separate work step.

According to another known method, each veneer entering the plywood is impregnated with a flame retardant and dried, after which the veneer is normally stacked and glued. The disadvantage of this method is that the strength of the plywood decreases because the flame retardant lowers it in each layer, and the result is expensive because the flame retardant is consumed in all veneer layers. In addition, this method generates a considerable amount of hazardous waste because all veneer cutting waste contains a flame retardant. Waste is also generated more than usual due to the tearing of the veneers caused by the many stages of the impregnation process.

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The method according to the invention provides a decisive improvement over the above drawbacks. To achieve this, the method according to the invention is characterized by what is stated in the characterizing part of the claim. The most important advantages of the invention are that twisting and cracking of the plywood during drying can be avoided, that a flame retardant film or other surface layer can be glued to the plywood surface without additional work step and costs, that the flame retardant and thus also costs can be saved. that the fire protection properties of the finished plywood can be precisely controlled for the reasons mentioned above, that no hazardous waste is generated because the flame retardant only treats material of exactly the final length and that the strength of the plywood remains good because some plywood layers are left untreated agent.

In the following, the invention will be explained in detail with reference to the accompanying drawing.

[The figure shows a cross-section of a typical plywood made by the method according to the invention.

In the figure, the finished plywood 16 consists of fifteen veneer layers 1-15, of which the three outermost layers on both surfaces, i.e. veneers 1-5 and veneers 13-15, have been treated with a fire retardant. The middle veneer layers 4-12 have not been treated with a flame retardant.

This plywood is manufactured in the following manner according to the invention. First of all, three-layer plywood 20 and nine-layer plywood 21 are first produced in a manner normally known per se, in which case each plywood is most preferably made of veneers which have not been treated with a flame retardant. The plywood is then cut to its final dimensions, so that the waste veneer and plywood do not contain a flame retardant.

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Next, the three-layer plywood 20 is treated with a flame retardant in a manner known per se. The three-layer plywood still saturates without difficulty despite the adhesive layers and the tendency to tear is substantially lower than with veneer.

Finally, the treated and dried plywoods 20 are glued to both sides of the untreated plywood 21 with adhesive layers 17 and 18. In the same connection, a fire protection film or other surface layer can be glued to one or both of the outer surfaces of the finished plywood 16. Figure 1 shows only the fire protection film 19 glued to the second outer surface. · After this, the plywood is ready for packaging, use, etc. without cutting steps.

In the above-mentioned manner, when supplied to the surface plywood 20, the twists and cracks that may occur in the fire protection treatment are corrected by gluing the two surface plywood 20 and one middle layer plywood 21 together into a finished plywood 16. No waste containing fire protection material is generated. dimensions. The strength of the finished plywood 16 is good because there is only a flame retardant in the surface layers 1-3 and 13-15 · Similarly, the flame retardant is saved because it is only in the above surface layers 1-3 and 13-15 and finally the lamination of the fire protection film 16 does not bring additional work. , because it can, if desired, be glued in the same work step as the plywoods 20 and 21 to each other.

With the method according to the invention, exactly the desired properties can be obtained in the final product, because the number of surface veneers to be impregnated can be precisely determined and the impregnation can be precisely controlled, while the middle layers can be left untreated or treated with other substances to achieve other properties. The surface plywood 20 consists of at least one veneer, but typically 2-4 plywood plywood and most preferably 3-ply 78254 plywood. Plywood with more than 4 layers is no longer completely impregnated with fire retardant without difficulty. If more layers are needed, they can be obtained by gluing several thin surface layer plywoods on both sides of the middle layer plywood 21. For example, a 6-layer surface plywood is obtained from two 3-layer, etc.

According to the invention, the plywood 16 shown in Fig. 1 can also be made by gluing three veneers 1-3 and 13-15 on each side of the middle plywood 21 or by gluing fire-protected veneers 1-3, untreated veneers 4-12 and fire-protected veneers 13-15 together. In this case, the result, i.e. plywood 16, is exactly the same as that obtained with the method variant described above. The only difference is that the use of veneers generates hazardous waste. The other advantages are essentially the same as above.

Claims (4)

5 78254 A method of making a fire-impregnated plywood, wherein the plywood is only partially treated with a fire retardant, characterized in that the predetermined surface veneers of the plywood are treated with a fire retardant and the veneers forming the central part of the plywood are not treated with a fire retardant and the predetermined surface veneers are first glued thin as a surface plywood, which is then treated with a flame retardant and then glued to the middle plywood forming the central part of the finished plywood, the veneers of which have not been treated with a flame retardant. Method according to Claim 1, characterized in that the surface layer plywood treated with the flame retardant has 2 to 4 and most preferably 3 layers of veneer. Method according to Claim 1 or 2, characterized in that the fire-protected surface layer plywood is obtained by gluing together several fire-protected thinner surface layer plywoods. Method according to one of the preceding claims, characterized in that when gluing the surface layer plywood treated with fire retardant to the middle layer plywood forming the central part, a fire protection film or other finished surface is glued to one or both sides of the finished plywood.