FI63251B - SAETT ATT SPRUTAPPLICERA HAERDANDE LIM - Google Patents

Description

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National Board of Patents and Registration (44) Nlhtlvlltllpeflon „kuugulkAllun ''

Patent · och registerstyrelaan 'Antöktn utlagd och utUkrtfkM ptiMicerad 01 · 0> (32) (33) (31) Requested scuolkeut — feflrd prteritt * (71) AB Casco, Box 11010, 100 6l Stockholm 11, Sweden-Sverige (SE) ( 72) Emil Johan Lehnert, Saltsjö-Βοο, John Olov Österberg, Bandhagen, Sweden-Sverige (SE) (7M Oy Borenius & Co Ab (5 ^) Method of spraying to apply a curable adhesive

The invention relates to a method of spray-applying a curable adhesive to wood surfaces by separately applying a liquid formaldehyde resin and a liquid hardener.

Curing adhesives have achieved widespread use in gluing wood together to make a variety of wood structures. The most common procedure is to mix the partially condensed formaldehyde resin with a powdered hardener and to apply the mixture to one or both surfaces to be glued together, after which the joint is pressed until the curing is complete. However, this method is limited by the limited shelf life of the mixture of resin and hardener, which means that the application and compression of the adhesive must take place within a short time after the mixing has been carried out. Examples of such curable adhesives are the condensation products of urea, melamine, phenol, resorcinol and phenol resorcinol with formaldehyde.

In recent years, the so-called finger joining started to be used for longitudinal joining of wood 2 63251 goods. The adhesive is then applied to the surfaces to be joined by spraying the two components under high pressure, i.e. separately by spraying the resin and the liquid hardener, instead of using a mixture of powder hardener and liquid resin as is heretofore. In order for the hardener component to be sprayed, it must be in a liquid state. In this case, some disadvantages have occurred due to the fact that the liquid hardener is more or less rapidly absorbed into the porous substrate, so that the strength of the obtained joint is not satisfactory. If the surfaces are uneven and there are gaps between them, there is also a risk of poor adhesive contact. Another disadvantage is that the liquid hardener can run off unless the surface is completely horizontal, as a result of which the amount of hardener is insufficient to achieve a good gluing result.

Various methods for improving two-component sizing are already known. Accordingly, DE-A-2030955 discloses paraformaldehyde-containing hardener compositions to which a thickener can be added. According to the third paragraph of page 5 of the publication, the purpose of this addition is to stabilize the dispersion. According to the publication, the hardener is not intended to be applied to the object to be glued separately from the resin component, and the consistency of the hardener is not intended to be adapted to the consistency of the resin. According to the method, the resin and the hardener are applied only after they have been mixed together in the usual way. Thus, the method does not have the disadvantages inherent in a method in which the components are applied separately. The resin component is also not intended to be applied by spraying, so that the method does not have the special disadvantages which occur when spraying the components separately. This known method thus does not help the person skilled in the art to eliminate these disadvantages.

U.S. Patent No. 3,634,276 also discloses an improvement over the conventional method of applying a finished adhesive composition by mixing a filler and hydroxyethylcellulose into a hardener composition. However, it is not a question of applying the adhesive components separately or by spraying. The filler is added to the hardener 3 63251 in a conventional manner to improve the joint filling properties of the finished adhesive mixture, and the purpose of the addition of hydroxyethylcellulose is to stabilize the dispersion according to column 3, lines 64-71. Nothing is mentioned in the publication which would give the expert a solution to the special problems that occur when resin and hardener are sprayed separately on a wooden surface.

The invention, which is intended to eliminate the above-mentioned disadvantages, is characterized in that a thickener is added to the liquid hardener. This slows down the absorption of the hardener into the substrate, in addition to which the amount of effluent is smaller in the case where the substrate is not horizontal. This is especially important when the surface to be coated with the liquid hardener cannot be kept horizontal for technical reasons. Due to the method according to the invention, the formed seam becomes stronger than a similar seam in the absence of a thickened hardener. This is probably because the thickened hardener fills the seam better.

As the thickener, carboxymethylcellulose, polyvinyl alcohol, alginates, acrylates or water-soluble starch products can be used. An aqueous solution of aldehyde can be used as the hardener.

The following example illustrates the invention.

The injectable phenolic resorcinol-formaldehyde resin was applied to a surface parallel to the direction of the wood fibers. Two pieces of beech wood measuring 4.5 x 1 x 1/8 inch (11.4 cm x 2.54 cm x 0.32 cm) were used in the experiment, applying the standard "British Standard 1204: part 2, 1965". Liquid injectable non-thickened hardener on the one hand and thickened liquid injectable hardener on the other hand were applied separately to two similar pieces. The viscosity of the unpackaged hardener was approximately the same as that of water, while the viscosity of the thickened hardener was such that when measured with a Ford Cup 6 at 20 ° C, 50 g of the 100 g poured had drained off after 41.6 seconds.

4 63251

After various long open times (the time between the application of the glue and the joining of the pieces of wood), the pieces were added together so that the gluing surface became square, and immediately afterwards the pieces were subjected to a compression pressure of 7.7 kp / cm 2. The pressing took place at 20 ° C for 24 hours, after which the adhesive joint was kept for 48 hours in a proportioned room with a temperature of 20 ° C and a relative humidity of 65%. A shear stress test was then performed to obtain the following strength values (averages of 5 tests each):

Open Thin hardener Thickened hardener residence time Strength Wood fiber Strength Wood fiber min. kp / cm2 outages% kp / cm2 outages% 0 256 97 222 75 15 227 69 245 83 30 166 36 238 92 60 88 0 164 21

Research shows that when a thin hardener is used, the strength of the joint decreases significantly as the open time increases. When using a thickened hardener, the strength remains relatively constant with short open times, but with longer open times, the strength begins to decrease. This phenomenon is likely to depend on the thickened hardener penetrating more slowly into the porous wood material. In addition, the thickened hardener tends to give somewhat worse values in the case where the open times are very short compared to the case where they are slightly longer. This is probably due to reduced penetration, which results in water remaining in the adhesive after curing.

In addition, e.g. the moisture content of the wood and the compression pressure affect the penetration rate, so the most suitable degree of thickening of the liquid hardener must be determined experimentally in each case. As a minimum, the viscosity should be at least as high that, when tested with a "Ford Cup 6" at 20 oct, 50 g will drain away within 6 seconds.

Claims (2)

5 63251 Not only in connection with finger joints, the same can be applied to the gluing of flat surfaces, eg lamella gluing in the manufacture of laminated wood products. 1. Sätt vid sputapplicering av härdande lim pä tryttor genom separat applicering av flytande formaldehydharts och flytande härdare, kännetecknat därav, att den flytande härdaren är försedd med förtjockningsmedel. 1. A method of spray-applying a curable adhesive to wood surfaces by separately applying a liquid formaldehyde resin and a liquid hardener, characterized in that a thickener is added to the liquid hardener. Process according to Claim 1, characterized in that the resin is a solution of formaldehyde and phenol resorcinol, resorcinol or phenol precondensate. Process according to Claim 1, characterized in that the hardener is an aqueous solution containing an aldehyde and a thickener. A method according to claim 1, characterized in that the liquid resin is sprayed on one surface of the joint and the thickened hardener on the other surface of the joint, which surfaces are then joined together. 2. A patent according to claim 1, which comprises the use of resins with formaldehyde and phenol resorcinol, resorcinol or phenol.