US2042825A - Process of coloring wood veneers and the like - Google Patents

Description

Patented June 2, 1936 UNITED STATES PATENT OFFICE PROCESS OF COLORING WOOD VENEERS AND THE LIKE No Drawing. Application May 31, 1934, Serial No.

728,381. In Canada June 24, 1933 1 Claim.

This invention relates to improvements in the process of coloring, by impregnation, wood veneers and similar thin pieces of wood throughout the thicknesses of the veneers, and has for its ob-' 5 ject to produce a uniformity of coloring of the veneers under low cost conditions not only avoiding deleterious eiiects upon the veneers but also obviating any necessity of drying the colored veneers.

Prior attempts have been made to satisfactorily color veneers throughout the thickness thereof, by boiling the veneers in alkaline solutions, or by steaming, necessitating subsequent drying of the impregnated veneers and rendering them subject to checking or cracking. It has also, been found, in the prior employment of the boiling or steaming processes, that the veneers treated in the usual bundles are not uniformly colored throughout the width thereof, showing light centers and imperfections along the grain margins. In other prior attempts to color wood by impregnation, the woodhas been fumed by ammonia gas under temperature and pressure conditions resulting in an undesirable refrigerating 2 action during the introduction of the ammonia gas into the wood container, and in deleterious effects upon the wood.

According to the present improved procedure,

the wood veneers are first dried and preferably to an extent beyond the fiber-saturation point" of approximately 20% moisture content, i. e., the

veneers are preferably dried to have approximately only 4% moisture content. The dried veneers are piled upon a truck or other support providing for convenient introduction of the veneers into a cylinder or receptacle having a door or doors which may then be closed, the receptacle.

being vented to the outside atmosphere. When piling the veneers upon their support, superposed 40 sheets of the veneers built up to a thickness of approximately one inch or slightly less are separated from the next overlying veneers by suitable spacing strips. By means of suitable steam pipes or coils within the closed receptacle into which the veneers are placed, the temperature within the receptacle is raised by heat radiation and convection at atmospheric pressure to a degree insuring a rapid evaporation of the veneer moisture, a preferred temperature attained being approximately 250 F. It will be understood, of'course, that by raising the temperature in the receptacle as mentioned, the veneers will be correspondingly heated throughout their thickness to a corresponding degree. While somewhat lower or higher temperthe gas in the receptacle atures than the specified temperature may be employed with corresponding variations in the subsequent impregnation time, it has been determined that a temperature of 250 F. is highly efllcient for the coloring operation, and is not harm- 5 ful to the veneers under the improved coloring conditions.

When the receptacle temperature has been raised to the degree mentioned, superheated ammonia gas is introduced into the receptacle, said 10 gas when so introduced having approximately the same temperature as or slightly higher than that within the receptacle, and the quantity of gas introduced being approximately 25 lbs. per 1000 board feet of veneers. By heating the'ammonia l5 gas before introduction into the receptacle to approximately thereceptacle temperature, the reirigerationtendency due to the expansion of is minimized. While other means may be employed for providing the 0 heated ammonia gas, it is preferred to generate the gas from aqua ammonia in an evaporator disposed externally adjacent to the receptacle, the heating of the aqua ammonia to approximately 255 F.developing a generated gas pressure in 25 the evaporator sufiicient to cause a natural flow of the heated gas into the preheated receptacle and without materially raising the pressure in said receptacle above atmospheric pressure. The pressure developed in the receptacle by the gas 30 introduction is preferably controlled by a suitable pop valve to confine it to the nominal amount of 1 to 2 lbs. gauge, and preferably does not exv ceed 5 lbs. gauge as a maximum, it being sufiicient to develop a slight indicated gauge pressure 5 merely to insure that the receptacle is filled with ammonia gas. Because of the pressure developed in the evaporator by the generated ammonia gas only a negligible quantity of water vapor is carried into the receptacle with the ammonia gas, the 40 superheated condition of any water vapor carried into the receptacle maintaining the dry condition within the receptacle.

. While it is preferred to employ the above described preheated ammonia gas supplying means, a substitute therefor comprises injecting, for instance aqua ammonia, into an evaporating pan within the receptacle to generate the ammonia gas directly within the receptacle heated by internal radiation and convection. It is to be un- 0 derstood, however, that the temperature of 250 F. initially attained within the cylinder should preferably be maintained substantially constant during the introduction of, the ammonia gas into the cylinder, and that the receptacle pressure 55 medium providing for ready absorption 01' the ammonia gas by the veneers, the ammonia gas reacting with the wood acids to color the veneers uniformly throughout-their thickness, and the heat conditions above described favoring the chemical reaction resulting in the coloring of the veneers.

After the ammonia gas has been introduced into the receptacle as described, the previously attained temperature of 250 F. and the nominal pressure before mentioned are maintained substantially constant for approximately 12 hours,

- after which the veneers are removed. Any pressure drop due to gas absorption by the veneers may be compensated for by introduction into the receptacle of slightly more ammonia gas. The specified time of 12 hours may be somewhat varied by a corresponding change in the receptacle temperature, as has been previously noted.

It will be apparent that the described veneercoloringprocess is performed under dry conditions such that the moisture content of the previously dried veneers is not increased, whereby the colored veneers are ready for use without any further drying operations. The dry conditions mentioned also materially lessen deterioration oi the receptacle, heretofore incident to the relatively wet methods employed for coloring veneers. The veneers are not only uniformly colored, but no trimming of the veneer edges is requiredv to cut away any softened or discolored margins present in prior practised methods of coloring veneers. A particular advantage residing in the practising of the described coloring process, is

that uniformity of coloring is attained in successive runs of the .veneers, and accordingly the coloring may be practised on a commercial basis. Furthermore, the short time required to eflect the coloring operation is still another factor in the low cost of production.

Having thus set forth the nature of the invention, what I claim herein is:-

The process of coloring wood veneers, consist-p ing in loading into a receptacle veneers having a moisture content below the fiber-saturation point, raising the temperature within the receptacle by dry heat'and at substantially atmospheric pressure to approximately 250 F. to completely vaporize the moisture content of the veneers, introducing into the heated receptacle approximately 25 lbs. of preheated ammonia gas per 1000 board feetof veneers, said ammonia gas having been preheated to approximately the temperature within the receptacle, and maintaining the attained temperature oi substantially 250 F. and the substantially atmospheric pressure constant within 'the receptacle for a definite coloring period.

- FRANK G. BRIGHT.