US2296742A - Method for production of glue for veneers and plywood - Google Patents

Description

Patented Sept. 22, 1942 METHOD FOR PRODUCTION OF GLUE FOR VENEER-S AND PLYWOOD Curt Schiilein, 'Bopfingen, Wurttemberg, Germany, assignor to Taccalin Chemical Corporation, Long Island City, N. Y., a corporation of New York No Drawing. Application November 24, 1937, Serial No. 176,388. In Germany July 6, 1935 4 Claims.

This invention relates to a method for the preparation of a glue employable for the production of veneers, plywood by hot pressing. According to this method layers of wood are placed the one on the other and glue is introduced between the individual layers. This superposed mass is then pressed in a heated press with application of higher pressure.

In the commonly used method for the production of veneers by hot pressing the pile of wood layers must be left in the press for a longer time and Whilst the pile is under pressure the press itself has to be cooled to room temperature. In the continuous operation the press is therefore alternately highly heated and then strongly cooled again.

This method is very complicated and requires time, not to mention that by the strong continual temperature fluctuations to which the press is submitted the apparatus is greatly stressed and does not work accurately any longer after a comparatively short time of service.

It has been found that it is possible to produce veneers and plywood as well as other articles made by gluing together layers of wood and by hot pressing without the necessity to cool the press or the body under pressure. The new method therefore considerablysimplifies the usual working method, means a considerable saving of the press and permits to better utilize the apparatus than has been possible up to the present.

The problem is solved thereby that to the glueroth to be used special properties are imparted special additions and by a certain preparation. According to the invention the individual wood layers to be united are soaked in a hot glue-broth as poor in water as possible and which has been produced by dissolving animal-glue, with addition of small quantities of substances exerting a liquefying effect, considerable quantities of finely distributed, insoluble organic or inorganic substances and little quantities of substances exerting a hardening efiect upon the glue. By the addition of the substances exerting a liquefying effect-as such naphthalene-sulfoacid alkali salts, urea, sodiumand potassiurnor ammonium-thiocyanate may be mentioned-4t becomes possible to produce glue-broths which are very poor in water, that is highly concentrated. By the liquefying agents it is, however, secured at the same time that already during a pressing pressure of short duration the gluebroth penetrates well into the pores of the wood to be glued together, what can for instance not be attained without the presence of the liquefying agent.

The problem can, however, not be solved by the liquefying agent alone, as the liquefactionv at the same time retards the drying or hardening of the glue, and it is evident that such retardation of the drying cannot result in an acceleration but rather in a prolongation of the pressing period.

It is therefore further necessary, that the gluesolution contains considerable quantities of finely distributed, insoluble inorganic or organic sub--, stances which serve to absorb the liquefying substance in order that such liquefying substances do not retard the hardening of the glue, Such substances are for instance dolomite, chalk, plaster of Paris or gypsum, anhydrite, wood powder, cork powder, paper fibres. Finally it is necessary to still add small quantities of substances exerting a hardening effect onto the glue, such as for instance formaldehyde, aluminium-sulfate, chromates, alums and the like. The quantities of the finely distributed insolublesubstances to be added must be considerable, that is amount to at least 50% of the weight of the glue, however, preferably 100 to 200% of these substances have to be employed. The quantities of the hardening means are, however, to be small. These means have to be adapted to the quantity of the liquefying agents which are used and to be selected so that they just do not yet disturb the liquefying effect of the addition substances in the initial glue-broth.

By using a glue-broth prepared in the manner described, the problem can be solved Without difficulty.

The proceeding is for instance as follows: To 100 kgs. of animal glue powder prepared from skins 60 kgs. of a mixture, consisting of 90% dolomite and 10% wood powder, are added and further 4 kgs. of ammonium thiocyanate. The mass obtained by treatment in a mixing drum is dissolved in a quantity of water of 60 C. equal asregards weight, and to this solution 1 kg. of paraformaldehyde is then added. With the gluebroth prepared in this manner wooden plates are painted, the glue coating having to be as thin as possible. The wooden plates to be united are placed the one on the other and left for drying during a certain time, for instance 30 minutes.

The superposed wooden plates are then brought into the press which is maintained at a temperature from to C. The pile of wood plates is held in this press at first during several minutes under lower pressure, then in slowly increasing'the pressure during 5 to 8 minutes at a pressure or 4 to 6 kg./cm.=. The veneers or the ply-- wood can be removed then at once from the press and conveyed to the storing place.

Instead, or besides the above mentioned ammonium thiocyanate for instance 8 kg. of urea (to 100 kg. animal glue) or several of the said substances might be added. The paraformaldehyde may be replaced by double the quantity of aluminium-sulfate or alum, or alkali chromate. Instead of the mixture dolomite-wood powder a mixture 0! for instance gypsumcork powder or of anhydrite-paper fibres may be used. Different additional substances may be employed at the same time. In any case the presence oi.

finely-powdrous or finely-fibrous substances of organic character is advisable.

I claim:

1. A method for producing a glue broth for gluing veneers and plywoods by hot pressing comprising mixing pulverulent animal glue with a comparatively small quantity or liqueiying agents and a considerable quantity of finely distributed insoluble substances, adding water and heating up to 60 C. to prepare a concentrated glue-broth and adding a very small quantity of substances exerting a hardening effect upon the glue.

2. A method for producing a glue-broth ior gluing veneers and cross-ply sheets of wood by hot pressing comprising mixing 100 parts or pulverulent animal glue with 4 to 8 quarts of liqueiying agents and to 200 parts of finely distributed insoluble substances, adding water and heating up to C. to prepare a concentrated glue-broth and adding 1 part of a substance exerting a hardening effect upon the glue.

3. A method for producing a glue-broth for gluing veneers and cross-ply sheets of wood by hot pressing comprising mixing pulverulent animal glue with a small quantity or an alkali salt 01 naphthalene-sulio-acid and a considerable quantity 0i? finely distributed insoluble substances and then adding a very small quantity or paratomialdehyde.

4. A method for producing a glue-broth tor gluing veneers and cross-ply sheets or wood by hot pressing comprising mixing parts of pulverulent animal glue with 72 parts of dolomite powder, 8 parts or wood powder, 4 parts or ammonium thiocyanate, dissolving the mixture in an equal quantity by weight or water at 60 C., and adding 1 part of paraiormaldehyde to the solution.

CURT scHiJLEIN.