GB2182073A - Method of depth treatment of wooden materials by liquids - Google Patents

Abstract

The surface of wooden material containing 2 to 180% water or solvents forming part of a treating liquid is exposed at a temperature from 10 to 140 DEG C for one second to 70 minutes to the action of the treating liquid. The excess liquid is thereafter removed and a penetration and diffusion of the liquid from surface layers to the depth of the wooden material to 0.2 to 3.0mm is accomplished in a closed space saturated with the vapour of the solvent used in the treating liquid at a temperature from 10 to 250 DEG C for at least 2 minutes.

Description

SPECIFICATION Method of depth treatment of wooden materials by liquids The invention relates to a method of depth treatment of wooden materials by liquids, particularly of veneers by solutions of refining materials such as dye stuffs, chemical compounds used for protection of wood, synthetic bitumen, water repellent means and softeners.

Actually known methods for depth treatment of wood are mostly basing on the penetration of refining solutions into the wood due to pressure differences. Methods of depth colouring of wooden veneers in their whole depth are generally performed by heating this material in colouring solutions at temperatures between 80 and 110 C for usually 3 to 6 hours at most veneers used for manufacture of furniture. A prolonged heating in colouring solutions or other refining liquids is performed in case a uniform diffusing penetration of refining agents is required, particularly of organic colouring agents to the whole depth of the wood and also in case parts of wood with difficult penetrance has to be treated such as parenchymatic cells, core parts of hearth wood and the like.A drawback of processes used for diffusion refining of veneers to their depth is the requirement of a prolonged heating in a large volume of a refining solution and a high power consumption. Power is needed not only for heating of colouring solutions but also for liquidation or cleaning of resulting waste waters.

It is an object of this invention to eliminate or at least to reduce said drawbacks. The method for depth treatment of wooden materials by refining liquids according to this invention consists in that the surface of the wooden material is exposed to the influence of some refining liquid at a temperature within 10 to 140"C for one second to 70 minutes, whereafter the excess refining liquid is removed from the neighbourhood of the surface of the wooden material and a penetration and diffusion of the refining agent from the surface layers to the depth of the wooden material of 0,2 to 3,0mm is accomplished in a closed space saturated by vapors of solvents of the used liquid at a temperature between 10 to 250"C, advantageously at 140"C for at least 2 minutes, depending on the required penetration of the refining agent.

Advantages of this method of refining wooden materials by liquids are that the time of storage of wooden materials in refining liquids is substantially reduced. Further advatages of this method of refining are that claims on the capacity of required refining equipments are equally reduced. The refining solution which is used is concentrated and is in contact with the treated wooden material solely for a short time. The time for heating veneers in a colouring solution at a diffusion colouring of veneers at elevated temperatures is reduced from the average 3 to 8 hours to the order of several seconds to minutes, due to which the life time of these colouring solutions is substantially prolonged. In case penetration outside the refining bath in closed spaces at surrounding temperature is used, claims on power consumption are substantially reduced.

In the course of the first stage of this process the refining agent is caused to penetrate solely a certain part of the volume of the wooden material, for instance by submerging into a refining liquid or by surface spreading for instance by application by a cylinder or by spraying or by vacuum-pressure impregnation.

The penetration of the refining agent from the surface to the interior of the wooden material is accomplished in a closed space either at heat supply or without any external heating.

The medium of saturated vapors in said closed space is created either by spontaneous evaporation of solvents of the refining liquid or in case of application of larger spaces by atomizing said solvents at the penetration temperature in the closed space. In case of application of the described process for colouring of veneers a veneer saturated by water with reduced humidity on its surface is advantageously used. A hot concentrated colouring solution is thereafter applied on the surface of veneers either by submerging of veneers in a circulating colouring bath or by some other surface application of the colouring solution, whereafter the veneers are piled one on the other to form stocks and the penetration is accomplished in a closed space advantageously at temperatures from 60 to 980C.

Example 1 Veneers of abachi wood/Triplochiton ocleroxylon k.Schumm/ of a thickness of 0,8mm and a 110% humidity /related to the weight of dry wood/ have been submerged in an aqueous solution of an acid colouring agent composed of 1,8 g.-1 of Acid Yellow 11, 0,3 9.1-1 od Acid Orange 7 and 0,8 g.l-' of Acid Blue 62, the colouring solution containing furthermore 4 9 1-1 of polyethyleneglycol of a molecular weight My=1500 and 1 g.1-1 of nonionogenic emulgator. The veneers have been submerged in the colouring solution at a temperature of 95"C for 5 minutes at pH -4,5.The veneers have been thereafter removed, placed in a container with water heated to 98"C above the surface of the water, the container has been hermetically closed and the veneers have been heated for 150 minutes. After removal from the container, rinsing of the surface of the veneers and drying of veneers at a temperature of 1600C to a humidity of 12% the uniformity of colouring of veneers has been checked. The uniformity of colouring on the surface of ven eers /DIN 5033 and DIN 0174/ has been "us=1,21 and inside of veneers AEs= 1,30 at a measuring at ten circular places of a diameter of 20mm.

Example 2 Veneers of beech wood /Fagus silvatica/ and abachi wood /Triplochiton ocleroxylon/ of a thickness of 0,8mm have been heated in water at a temperature of 95"C for 20 minutes, they have been thereafter left in a vertical position for 10 minutes and the surface of veneers has been predried at a temperature of 160"C so that the surface layers of veneers contained 20 to 40% of the value of the internal humidity. The surface of veneers has been thereafter provided with a layer of aqueous colouring solutions of organic acid colouring agents and of reactive colouring agents and of their mutual mixtures. A cylindrical two-sided applicator has been used for this application.

The molecular weight of used colouring agents has been within 350 to 860. The deposits of colouring solutions have been 15 to 220 g.m-2. The concentrations of tested colouring solutions 0,5 to 4,1%. After application of the colouring solution the veneers have been piled one on another, pressed to a plane by a plate of stainless steel or of plywood. The veneers have been thereafter placed into a pressure vessel heated to 95"C. The diffusion of the colouring solution from the surface of veneers inside and simultaneously the fixing to the lignocellulose substance has been accomplished above the water level within 3 hours at a temperature of 95"C. The veneers have been after drying coloured within their whole depth.

Example 3 The colouring method described in the following can be advantageously applied for depth colouring and for refining of sliced fancy veneers of lower thickness. The veneers are soaked in hot water of a temperature of 95"C, the veneers with a humidity of 90 to 120% and a temperature of 60 to 80"C are provided on both sides with a deposit of hot colouring solution of a temperature of 60 to 90"C containing known colouring agents used for depth colouring of veneers. After the application the evaporation of water or of some other used solvent is prevented by using a foil and by piling the veneers one on another advantageously in a space which can be closed and which is closed after filling.The veneers are left therein at a temperature within 60 to 95"C until the dye stuff is diffused to the whole thickness of veneers. The time of diffusion depends on the kind of used dye stuff, on the kind of wood stuff and on the thickness of veneers. In case a mixture of dye stuffs is used, the time for uniform colouring is determined by the dye stuff which diffuses most slowly. For instance for full depth colouring of common fancy veneers of a thickness of 0,3mm at a temperature of 95"C the time of 5 to 25 minutes is required for dye stuffs Cl Acid Red 73, Cl Acid Red 97, one to 12 minutes for dye stuffs Cl Acid Yellow 11, Cl Acid Yellow 42, Cl Acid Blue 41, Cl Acid Orange 3.At temperature of 95"C the diffusion time for a full colouring of veneers of a thickness of 0,8mm amounts to 0.5 to 3 hours for most monosulpho dye stuffs with a molecular weight within 350 to 550. At the temperature of 50"C the time for diffusion and fixation of the dye stuffs in the veneers is about twice times prolonged. The penetration time of dye stuffs in said fancy veneers of a thickness of 0,8mm in a space saturated by steam is at a temperature of 20"C within 2 to 6 days for most mentioned dye stuffs and kinds of wooden material.

Example 4 To hot veneers of popular wood /Populus marilandica/ of a thickness of 0,9mm and of a humidity of 112% a solution of 50 g.l-l of the dye stuff Cl Acid Orange 7 having the temperature of 95"C has been applied at the amount of 35 g.m-2 by means of rubber cyiinders. The veneers have been thereafter wrapped in a polyethylene foil and subsequently in an aluminium foil and the colouring solution has been allowed to penetrate in case of one batch of veneers at the temperature of 20"C for 3 days, in case of another batch at the temperature of 95"C 65 minutes and in case of a third batch at the temperature of 140"C for 15 minutes. The penetration of the dye stuffs in the veneers has been accomplished in a closed space.All three batches of veneers have been after drying uniformy coloured to their whole depth.

Example 5 Sliced veneers of abachi wood /Triplochiton ocleroxylon k. Schumm/ of a thickness of 0,6mm with an overall humidity /determined by weighing/ of 56% and with a surface humidity about 27% have been submerged in a colouring bath of 15 g.l-' Cl Solvent Yellow 32 and 8 g.l-' Solvent Orange in a mixture of 96% ethylalcohol and ethyleneglycol /7:3/ for 3 seconds. They have been thereafter wrapped in a polyethylene foil and in a closed space heated at 50"C for 30 minutes.

The veneers have been after removal dried at 1200C and have been uniformly coloured within their whole depth.

Example 6 Peeled veneers of abachi wood of a thickness of 0,9 mm and a humidity of 35% have been submerged in a colouring solution of acid dyes mentioned in example 1 with an overall concentration of acid dye stuffs within 0,5 to 3 g.-' in a mixture of solvents : water: ethyleneglycol : isopropylalcohol /6:2:1/ for 10 to 20 seconds at a temperature of 60"C.

The veneers have been after removal wrapped in a PE-foil, placed in a hermetically closed vessel and heated at 60"C for 150 minutes.

The veneers have been after removal uniformly coloured to their whole depth.

Example 7 The described method can be utilized in connection with classical colouring thermostat controlled equipments with a circulating colouring solution. Veneers of a thickness of 0,8mm are placed on veneer carriers so that for 1 mum thickness of wood material a free space within 2,2 to 5mm is provided. The carrier with veneers is submerged in a coloured ing bath for 5 to 20 minutes at a temperature of 90 to 99"C in pressure free colouring arrangements. Or the veneers are vacuum-pressure impregnated for the same time in pressure colouring arrangements, whereby the temperature of the colouring solution amounts to 100 to 1400C. In the course of this time the colouring solution circulates in the colouring arrangement.At pressure free arrangements it is advantageous to use a repeated submerging of veneers in the bath for shorter time intervals. The veneers are thereafter removed and are left standing in a space saturated with vapours of solvents of the colouring bath at a temperature within 60 to 95"C.

The time for diffusion of dyeing stuffs in the medium of vapors of applied solvents of the colouring bath is determined according to the kind of used dyeing stuff and the required depth of penetration. For instance for veneers of a thickness of 0,8mm said time is within 1 to 4 hours.

Example 8 Veneers of beech wood /Fagus silvatica/ of a thickness of 0,3mm and a humidity of 12% have been submeeged in a refining bath of acid dye stuffs as in example 1 at a temperature of 95"C for 2 minutes. After removal from the colouring bath after this first stage of refining the dye stuff has practically penetrated the whole depth of veneers, but the heartwood has not been fully coloured. These veneers have been placed into a closed vessel for 75 minutes at a temperature of 85"C.

After removal the veneers have been uniformly coloured also in the heartwood.

The described method of depth refining of wood can be utilized in the wood and furniture industry for improvement of properties of wood at a homogenous refining or dyeing of veneers to their depth. The thus treated veneers can be ground to a considerable depth without exposing not modified or not fully coloured parts of the wood material.

The described homogenous colouring of veneers can also be used for manufacture of veneers with a reproducible design by glueing together coloured veneers to blocs by planar or shaped pressing and by subsequent cutting at a certain angle similar as in case of classical manufacture of fancy veneers.

Claims (5)

1. Method of depth refining of wooden materials by liquids such as solutions used for protection of wood, colouring solutions, impregnation means for preparation of wooden plastics where the active refining material is solved in water and/or in an organic solvent or in a number of solvents, whereby the refining liquid is capable to be absorbed by the wood at least to 60% of its absorptivity of water, by which method the surface of the wooden material with a content of 2 to 180% of water or of solvents which are part of the refining liquid is exposed to the action of the refining liquid at a temperature within 10 to 140 C for one second to 70 minutes, whereafter the excess refining liquid is removed from the neighbourhood of the surface of the wooden material and a penetration and diffustion of the refining material from the surface layers into the interior of the wooden material to a depth of 0,2 to 3,0mm is accomplished in a closed space saturated by vapors of solvents of the used liquid at temperatures within 10 to 250"C, advantageously at 140"C for at least 2 minutes, depending on the required depth of penetration of the refining liquid.

2. Method of depth refining of wooden materials in liquids as in claim 1 where the penetration of the refining liquid into the interior of the wooden material is accomplished in a closed space saturated by vapors of this liquid at heat supply or without external heat supply.

3. Method of depth refining of wooden materials by liquids as in claim 1 where the medium of saturated vapors in the closed space is obtained by atomizing solvents forming part of the refining liquid in the closed space or by spontaneous evaporation of the refining liquid from the wooden material.

4. Method of depth refining of wooden materials by liquids as in claim 1 where as wooden material to be refined veneers are used with a moisture content of 40 to 180%, which veneers after application of the refining agent are prior to placing in a closed space piled one on another to batches and are pressed to a plane by pressure of 0,1 to 1,3 MPa.

5. A method of depth refining of wooden materials by liquids substantially as described in any one of the examples.