A METHOD AND AN AGENT FOR SURFACE TREATMENT OF WOOD,PARTICULARLY FURNITURE SURFACES OF UNDRESSED PINEWOOD

Abstract: For accentuating the surface play of pinewood, especially pinewood furniture, the wood is subjected to an acid/lye treatment, which additionally affects the colour shade of the fresh wood. Instead of aiming at a light colour shade corresponding to undressed wood, the natural colour shade of which is almost impossible to preserve or reproduce, the invention aims at a darker shading, which is achievable as an exactly true to nature patination of the wood, whereby a real natural colour shade is obtainable, though referring to aged undressed wood. The result is obtained mainly by using a relatively concentrated lye liquid.

Description: A method and an agent for surface treatment of wood, particularly furniture surfaces of undressed pinewood. The present invention relates to a method of che¬ mically treating wooden surfaces, particularly furniture or furniture parts of pinewood, for accentuating the wood structure by affecting the colour of the surface parts, whereby the wooden surface is treated by a tannin ' solution and thereafter subjected to a. lye treatment. It is a very old knowledge that the vein structure or play in a surface of oakwood can be strongly accentuated by a so-called acid-washing treatment and that such a treatment gives rise to a very characteristic and drastic change of the colour of the wood, whereby no "natural" colour is aimed at. In connection with pinewood it is normally desirable that the colour impression should still, despite the surface treatment, be maintained close to the natural colour of the fresh wood, because pinewood is extensive¬ ly used as so-called "undressed wood" . In this connection it is well known that without departing considerably from the fresh natural colour the wood structure may be accentuated when the surface is treated first by a tannin solution and then by a suitable base such as soda lye. It has hereby been specifically endeavoured to maintain the light colour shade of the fresh natural or undressed pinewood generally, as far as this is possible, but it is a common opinion among relevant skilled persons that the associated inevitable deviation from the natural colour shade is nevertheless so pronounced that the treated wood surface is not in any way perceivable as natural or undressed pinewood, and for this reason the treatment has not come in widespread use, despite its veine accentuating advantages. The present invention is based on the cognition that although it is difficult or impossible to adjust the acid/lye treatment so as to achieve a natural co¬ lour shade as referring to the appearance of the fresh wood, it is nevertheless possible to produce a fully natural colour shade, viz. when compared with aged wood of a naturally darkened colour shade. In this connection it will be correct to speak of a "patination" of the wood surface in combination with the accentuation of the veine structure, and the method, according to the invention, has..proved usable for . obtaining, a surprising¬ ly true to nature patination. of fresh wood based main¬ ly on a specially adapted acid/lye treatment, which even sets off the veine structure in a suitably temperate manner. Practice has shown -that in the furniture trade it is of utmost importance that furniture pieces of the undressed wood type show a very high degree of natural appearance as far as their colour shade is concerned, and the fulfilling of this condition seems by far more important than the question whether the appearance re¬ fers to fresh or aged wood. Thus, what is important to the relevant industry or trade is to provide furniture of a natural appearance, and so far this has been accomplished by presenting to the customers furniture of either fresh and substantially untreated or undressed wood or furniture of naturally aged wood, and the pro¬ vision of instantly artificially aged or patinated wood according to the present invention is an extremely im- portant contribution, because it enables the furniture to appear with an accentuated surface "play" and yet with a truly natural colour shade, though limited to that of aged wood. As mentioned, however, the real na¬ tural appearance of the wood, whether fresh or old, seems to be much more important than the real or be¬ lieved aging of the wood, and it is an obvious advantage O PI /ir„ WIPO of the invention, therefore, that pieces of furniture are made readily attractive and sellable because of their natural appearance with increased surface "play", with¬ out the wood really having to be aged at corresponding- 5 ly increased expenses. The invention is in no way li¬ mited to the treatment of furniture parts of pieces of an old-fashioned style, because even modern furniture is made attractive by the combination of an accentuated surface play and a really natural colour shade even 10 when the latter refers to aged wood. It should be emphasized that the ' dark ' shading ' of " *' --. '"* the * " * wood- *' -is ..*not--obt-a-irie"d 'by- *' m ' eans ' o ;t ah ~ y dyfes'tuff,* but ** " -- already by the pure acid/lye treatment, whereby the wood reacts by darkening when the base as finally used 15 is relatively concentrated. It could well be known to the experts that the final colour shade will be darker the stronger the base is, but so far this knowledge has been utilized only to adjust the concentration of the base for the attainment of a desired colour shade of the 20 light end of the colour scale. It has not previously been known that a real natural colour can be obtained by entirely leaving the light shade range and pure cultivating quite another natural colour shade, viz. the patinated colour, which is then experienced to be 25 achievable with a remarkable accuracy. When in this connection reference _is made to a re¬ latively concentrated base, normally sodium hydroxide, this should be understood in a pronounced relative manner, by comparison with the prior art, because the 30 discussed darkening of the wood is in fact achieved by a rather small increase of the concentration of the base solution, which is in advance a rather weak so¬ lution. Thus, with the use of NaOH-solution the light colour shades will be obtained by a concentration of 35 some 0.7-0.8%, while for obtaining the darker shade according to the invention the concentration should be O PI some 0.85-1.0%. It will be noted, however, that an in¬ crease from e.g. 0.75% to 0.95% represents an increase of ca. 25%, and moreover it has been experienced that in order to obtain a really natural patination colour shade it is necessary to adjust the base concentration rather accurately, somewhat depending of how the wood is treated otherwise. The invention, in accordance with the foregoing, is defined in the appended claims. The " acid/lye-treatmeh so far described is ne¬ cessary £or achieving the..desάred true to. nature pa¬ tination of the wood, but in practice the result will be fully satisfactory only when further measures are taken and even are followed by a special final treat- ment. In the following, therefore, a more detailed example of the method of the invention will be given: The example relates to a piece of furniture, e.g. a chair or a cupboard made of fresh pinewood, the visible surfaces of which should be treated for pati- nation and accentuation of the surface play. The treat¬ ing liquids can be applied manually or by dipping the entire piece of furniture into a bath of the particular liquid. At first a tannin solution is applied to the wood, preferably with a concentration of ca. 0.75%, a pre¬ ferred component being "Pyrogallol" {"white chip") dis¬ solved in demineralized water, if desired with a small amount of a relaxation agent and a tracer agent, the latter of course being superfluous when the solution is applied by dipping of the entire piece of furniture in¬ to the solution. After this treatment the workpiece is allowed to dry for 3-24 hours or more. The solution may be prepared from 7.5 g Pyrogallol to one litre of demineralized water. Thereafter the workpiece or the relevant surfaces thereof is or are treated by soda lye of a concentration OMPI Λ. WIPO of 0.92-0.98% (NaOH dissolved in demineralized water), and the workpiece is allowed to dry for at least 3 hours. The soda lye may be prepared from liquid NaOH, 34°BE, 27.65% (technical 33%) mixed in the proportion 1:35 with demineralized water. Thereafter a thin layer of an acid-free plastic lacquer, e.g. No. 1302 LS is applied to the workpiece or the relevant surfaces, and the lacquer -is allowed to dry for at least one hour, whereafter the relevant surfaces are . smoothed by means of grinding paper, e.g. ' grain 320,. with subsequent wiping or. brushing off of the slip. If desired, a further layer of lacquer may thereafter be applied to the relevant surfaces. For obtaining a perfect result it is essential that the treating liquids are based on distilled or demineralized water and that the workpiece is subjected to the said lacquering once or still better twice. An essential parameter is the concentration of the base solution. Normally it should be somewhere between 0.9% and 1.0%, but the exact or optimal concentration will depend on the local character of the pinewood. However, to those skilled in the art it will be easy to select the correct percentage of the base solution for obtaining the desired true to nature colour shading of the particular wood as seen in its patinated condi¬ tion. It should be mentioned that the preferred use of demineralized water as a solvent mainly refers to a de¬ sired lack of iron in the water, because even a relative- ly small amount of iron in the water will affect the co¬ lour shade of the product adversely. On the other hand, there are several geographic regions in which the natu¬ ral water has such a low iron contents that it is di¬ rectly usable in the method according to the invention. OMPI _

Claims: CLAIMS 1. A method of chemically treating wooden surfaces, particularly furniture or furniture parts of pinewood, for accentuating the wood structure by affecting the colour of the surface portions thereof, whereby the wooden surface is treated by a tannin solution and thereafter is subjected to a lye treatment for accen¬ tuating the surface play of the wood, characterized in that the' treatment is ' effected in- such " a ' manner and with the use of a base of such a concentration that the wood surface or surfaces adopt a dark shading corre¬ sponding to a natural patination of the wood. 2. A method according to claim 1, in which is used a tannin solution having a concentration of ca. 0.6- 0.9%, characterized in that the liquid as used for the subsequent lye treatment has a base concentration of 0.9-1.9%. 3. A method ' according to claim 2, characterized in that the base concentration is 0.92-0.98%. 4. A method according to claims 2 or 3, characterized in that the tannin solution as well as the base solution is based on distilled or demineralized water. 5. A method according to any of the preceding claims, characterized in that the treated wood is allowed to dry at least 3 hours between the liquid treatments. 6. A method according to any of the preceding claims, characterized in that the wood 3 hours after the lye treatment or later is lacquered by an acid-free plastic lacquer, which is ground off after drying and preferably coated by another thin lacquer layer. 7. A liquid for lye treatment of wood in connection with the method claimed in claim 2, characterized in that is consists of a base dissolved in substantially OMPI demineralized or distilled water and has a base concen¬ tration of 0.9-1.9%, preferably 0.92-0.98%. OMPI Λ,„ IPO -

Inventors: BAGGER S
Applicants: BAGGER S
Application year: 1981
Main classification: B27K5
IPC codes: B27K5