METHOD AND KIT FOR TREATING WOOD WITH RED UNDERTONES

Abstract

In a method for treating wood with red and/or pink undertones to bring it to the desired colour, the wood is provided with one or more finishing layers with the desired colour, and before the finishing layer is applied the wood is provided with a neutralization layer to neutralize the red and/or pink undertones of the wood to be treated. A kit of two different aqueous solutions, which are applied as a single composition for treating wood with red and/or pink undertones, is suitable for neutralizing the red and/or pink undertones of the wood to be treated. The composition is a mixture of a first and a second component, wherein the first component is a solution of a reactive dye in water and the second component is an aqueous alkaline solution, which is suitable for forming covalent bonds with the fibres of the wood to be treated.

Claims

1. A method for treating wood with red and/or pink undertones to bring it to a desired colour, wherein the wood is provided with one or more finishing layers with the desired colour, comprising: providing the wood with a neutralization layer before the one or more finishing layers are applied, in order to neutralize the red and/or pink undertones of the wood to be treated; wherein the neutralization layer is a mixture of a first and a second component, which is applied as a single composition; wherein the first component is a solution of a reactive dye in water and the second component is an aqueous alkaline solution suitable for forming covalent bonds with the fibres of the wood to be treated.

2. The method according to claim 1, wherein the first component has a pH value between 3 and 5, preferably 4.

3. The method according to claim 1, wherein the second component comprises at least 97% water.

4. The method according to claim 1, wherein the second component has a pH value between 8.5 and 12.5.

5. The method according to claim 1, wherein the alkaline solution comprises urea.

6. The method according to claim 1, wherein the alkaline solution comprises at least 75% water.

7. The method according to claim 1, wherein the ratio of the first to the second component in the neutralization layer is 50/50.

8. The method according to claim 1, wherein the first finishing layer that is applied on the neutralization layer comprises a water-based colouring stain or an ageing stain.

9. A kit of two different aqueous solutions, which are applied as a single composition for treating wood with red and/or pink undertones, which is suitable for neutralizing the red and/or pink undertones of the wood to be treated, comprising: a mixture of a first and a second component; wherein the first component is a solution of a reactive dye in water and the second component is an aqueous alkaline solution suitable for forming covalent bonds with the fibres of the wood to be treated.

10. The kit according to claim 9, wherein the first component has a pH value between 3 and 5.

11. The kit according to claim 9, wherein the second component has a pH value between 8.5 and 12.5.

12. The kit according to claim 9, wherein the ratio of the first to the second component is 50/50.

13. The method according to claim 5, wherein the alkaline solution comprises 8% to 15% urea.

14. The kit according to claim 10, wherein the first component has a pH value of 4.

Description

DETAILED DESCRIPTION

[0020] For further explanation of the properties of the disclosed methods and kits and to present additional advantages and features thereof, there now follows a more detailed description of the methods used and the compositions disclosed. It should be clear that nothing in the description given hereunder is to be interpreted as a limitation of the protection claimed in the claims for the present invention.

[0021] The present disclosure relates on the one hand to a method for treating wood with red and/or pink undertones to bring it to the desired colour. On the other hand the disclosure relates to a composition (kit) for treating wood with red and/or pink undertones, which is suitable for neutralizing the red and/or pink undertones of the wood to be treated.

[0022] The method (and composition) according to the disclosure is in particular suitable for being applied on American red oak, beech, birch, maple, Tasmanian oak, white oak (when for example it has anomalous colours), etc. In principle, this method (and composition) is applicable to nearly all wood species that are of light hue and anomalous red.

[0023] The development according to the present disclosure has the innovative feature that the surface of wood with ‘pink hue’ as a typical feature can as it were be reset by a specially developed staining treatment, which is universally applicable, both industrially and on-site with the existing techniques, so that it can then be further finished with the known techniques and/or products. The wood substrate acquires a definite added value thereby.

[0024] Stains based on pigments are, owing to the covering nature of the colouring elements, very suitable agents for modifying—covering up—the colour of a substrate, preferably a well-defined wood species, but have the disadvantage that the wood structure and the natural effect are largely lost, so that they will not come into consideration for the aim of this innovation. Nevertheless, this technology is used to a certain degree for upgrading inferior wood species but the degrees of freedom in finishing are limited. Another approach is that by making use of colour theory by means of a subtractive mixture of transparent dye stain and substrate, the colour of the wood is reset: neutralized. However, it becomes innovative when by applying a first stain (neutralization layer or neutralization mixture), a bond is produced which is embedded stably and insolubly in the fibres and is free from binder and is sufficiently transparent so that application of a second water-based layer (second stain) becomes possible without dissolving the previously applied layer (first stain) again and all degrees of freedom of finishing are maintained, and in addition on wood species which to date have not come into consideration for such applications.

[0025] An important component of this innovation is the composition of the neutralization layer. Reactive dyes, for which it is known that, in contrast to the other types that are available for colouring wood, they undergo covalent bonding with the cellulose fibre, form an essential component of the neutralization layer. Knowing that in the wood-processing industry it is usual to supply ready-to-use wood stains, yet we wish to employ a colouring mechanism based on reactive dyes, then in order to be able to guarantee a product with a long enough shelf life, an answer must be found for the problem of hydrolysis that is associated inherently with the colours of reactive dyes. A technical solution was found in splitting the neutralization mixture (stain) into two compatible components, namely a first component (A) that contains the required colour combination and a second component (B) that constitutes the reactive portion, the latter in the alkaline pH region.

[0026] Ageing stains, the mechanism of which is based on reaction between stain and constituents (including tannin) of the wood, now make up an important part of the market in the high-end flooring segment. The demand for finishes of this type is at present greater than the availability of suitable substrate; being able to employ alternative wood species, which currently do not come into consideration on account of their individual character and the state of finishing techniques, would constitute a technological innovation. Since the activity of the neutralization layer is based on affinity with respect to cellulose, there is no competition between the two types of stains, and combining said neutralization layer and ageing stain is an ideal scenario for obtaining aged finishes on wood substrates which at first sight, in particular on account of their pink coloration, are less suitable. This was confirmed in practice, and such finishes are described further in the examples accompanying the description.

[0027] For preparing the first component (A), preferably reactive dyes that are commercially available are used, preferably reactive dyes from the vinyl sulphone group. The dyes are selected on the basis of light-fastness, moderate reactivity (basically less sensitive to hydrolysis) and suitability for the so-called KKV process. The KKV process (German term: Klotz Kurzverweil Verfahren/English term CPB—cold pad batch) is a widely used technique for reactive dyeing a textile and in its most original form, the textile is pulled through a bath in which dye solution and an amount of alkali required for fixation are added together, after impregnation the textile is wound up again and usually wrapped in film to prevent drying-out of the edges and the top layers of the roll during the resting/reaction time, depending on the dye composition it is stored for a period from 4 to 12 hours until the reaction of the reactive dyes is completed and is then unwound again, to be washed (non-fixed dyes, alkali, etc.) and finally dried and wound up.

[0028] More particularly, the dye solution that forms the first component (A) and whose pH is set between 3 and 5 (ideally pH 4) will be a mixture that comprises one or more reactive dyes from the vinyl sulphone group and a buffer pair NaAc/HAc.

[0029] Because the colour combination requires great precision and the percentages of dye required for the purpose are low, it is preferable to work with master solutions of the aforementioned dyes, adjusted to 10% standard dye strength. Results of application tests carried out on 3 typical laboratory compositions after 4 weeks of storage at 5° C. and at 50° C. were comparable to the reference, so that we can assume that long-term stability is achieved. Furthermore, it is not excluded that for specific applications, a small amount of an aqueous TiO.sub.2 preparation may be added to the recipe.

[0030] A typical composition of the first component contains for example: 95 to 97% water, 0.2 to 0.45% sodium acetate, 0.5-1.5% reactive dye, 0.01-0.08% preservative and 1-2% acetic acid (40%) to pH 4.

[0031] The second component (B), also called the reactive component, comprises chemicals that are important for application, diffusion, adsorption and fixation. Additives that work effectively in low-viscosity systems free from strong polar binders and display pseudo-plasticity and/or thixotropy are preferred for adjusting the rheology. Bentonites and Ca-bentonite in particular, fumed silicas, mixtures of fumed silica and dispersed aluminium oxide and co-fumed products thereof may be used for this purpose. Urea acts as a moistener, it prevents the wood fibre drying out during the reaction period (open air), urea increases the swelling of the fibre and is able to break hydrogen bridges, thus improving the penetration and mobility of the dye. Moreover, it is known that urea increases the limits of solubility of dyes, which may be useful when a strong solution is necessary. Urea is the preferred moistener, but other moisteners, such as e.g. propylene glycol, are not excluded. The fixation, covalent bonding, between dye and cellulose fibre takes place in a buffered alkaline medium. Fixation alkalies such as NaOH, KOH, Na.sub.2CO.sub.3, NaHCO.sub.3, Na.sub.2B.sub.4O.sub.7, Na.sub.2SiO.sub.3 and combinations thereof are usable for this. Fixation is an important aspect, and is controlled by maintaining the correct pH. The type of alkali that is used provides a correct pH and optimum fixation. Depending on the ratio of dye to water, electrolytes may be necessary to help the dye to leave the aqueous solution and enter the fibre, where it can react.

[0032] Reactivity of the dye, pH range and temperature are determining for the rate of reaction and hydrolysis. It is known that alkaline substances and chemicals such as ammonia can react with wood with a high content of polyphenolic tannins, and cause a brown discoloration, setting a lower pH of the second component is advantageous here, and in addition this has a positive effect on the degree of hydrolysis, but it results in a slower reaction rate with cellulose fibres. As established experimentally, this need not necessarily lead to poorer fixation. Wood species with lower content of constituents and which are thus less sensitive to the undesirable brown discoloration can have a higher pH.

[0033] A typical composition of the second component contains for example: 75 to 90% water, 0.2 to 1.2% fumed silica, 0.3-0.7% Ca-bentonite, 10 to 12% urea, 0-1% propylene glycol, 2 to 10% fixation alkalies, wherein the pH setting is between 9.5 and 11.2.

[0034] The first and the second component are stored separately, it is only at the time of application that the two components are mixed together, so as to form a composition for treating wood with red and/or pink undertones, which is suitable for neutralizing the red and/or pink undertones of the wood to be treated, a so-called neutralization solution. For each component individually, a shelf life can be guaranteed, which makes it possible to market the system as a ready-to-use two-component neutralization solution (stain). A solution is thus offered for the problem of hydrolysis of the reactive dye as a function of time. At the time of application, the first component (A) and the second component (B) are mixed in a 50/50 ratio. To date, it has not been found that the neutralization solution loses its activity within a realistic operating time.

[0035] With regard to the type of wood on which this neutralization solution may be applied, there is no fundamental limitation, any type of wood that naturally has a red hue may be considered. Certain wood species are easier to colour than others, and certain species (e.g. red oak) may preferably be considered from the economic standpoint.

[0036] For optimum dye take-up, the wood must be prepared correctly. Pretreatment (conditioning) of the wood substrate consists as a rule of several sanding operations, and in the last sanding operation the grain number is selected to be suitable for the particular wood species and as a function of the desired end result. For extra accentuation of the wood structure, additionally a brushing treatment (wire brush and/or Tinex) may be applied, and exceptionally, planed substrates may be used.

[0037] In practice, for application of the neutralization solution consisting of a 50/50 mix of the two components, it is understood that the neutralization solution is sprayed, applied with a roller and possibly by a vacuum-coating system. All existing techniques and production installations may be considered for this. On site, the stain is applied with a brush. The amount to be applied may vary, as a function of substrate and technique, between 40 and 80 g/m.sup.2, ideally 60 g/m.sup.2 is applied and is levelled afterwards.

[0038] To make the time for adsorption, diffusion and reaction between the neutralization solution and cellulose fibres of the wood as long as possible, it is preferably air-dried. A high relative humidity is advantageous. A so-called “reaction time” of at least 6 to 8 hours is anticipated; forced drying may give rise to poorer fixation.

[0039] Following this, a (first) finishing layer (second staining operation, wherein application of the neutralization layer is regarded as the first staining operation) may be applied. Because application of an ageing stain, for example from the range known under the brand name Ciranova, offers the greatest added value, this type of stain is used ideally, without being limiting. Tests with water-based pigment stains as the second staining operation have, rather surprisingly, made finishes possible on certain wood species that could not be produced without applying a neutralization layer. Transparent finishing, i.e. without application of a finishing layer, offers possibilities, by means of an appropriate formulation of the colouring component, for producing modern, natural-looking finishes.

[0040] “Finishing” generally means the application of a functional protection, which for industrial applications is as a rule of photochemical nature (UV Oil or UV Varnish) and for on-site applications it is either an oxidatively drying oil or a water-based varnish, which may or may not be preceded by extra colouring by applying a second water-based stain. Ideally but not absolutely necessarily, a sealer with a typical composition is applied between the colouring operations and the functional finishing, for extra fixing of the underlying colour combination. A particular feature of this is that the natural appearance of the wood is preserved, we see, as the main application, enabling typical finishes on wood species that are less suitable for this by nature.

[0041] Some examples are described below, wherein a number of wood species were provided with a composition (neutralization solution) according to the disclosure. In the tables, PB2C is used as the abbreviation for the neutralization solution, wherein the numbers 1239, 1240, 1241, 1242 are the patent holder's internal reference numbers for the first component and the numbers 7953, 8501, 7953, 8417 are the patent holder's internal reference numbers for the second component.

Example 1

[0042] Because of non-availability of the standard European white oak substrate, a relatively simple aged finishing was applied on white oak derived from Northern Europe (with some older slow-growing trees, the wood may have a pink colour) with the result that the finish had a pink undertone. Because the rest of the production process can be maintained, application of the method according to the disclosure is an ideal solution for this.

TABLE-US-00001 TABLE 1 Details Step Prod. No. EU White No. EU White substrate Type application EU White oak oak oak Step X PB2C 60 g/m.sup.2 Mix Step 1 Ageing stain 50 g/m.sup.2 230-002061 230-002061 1239/7953 Step 2 10-15 g/m.sup.2 175-005232 175-005232 230-002061 Step 3 UV Oil natural 6-8 g/m.sup.2 680-005149 680-005149 175-005232 white 680-005149 UV Oil clear matt Reference Pinkish =Reference

Example 2

[0043] American Red oak, a possible alternative for the expensive European white oak, which is of limited availability, has a typical pink/red hue and is therefore unsuitable in its present form. Application of the method according to the disclosure makes it possible to produce attractive finishes on American red oak which bear comparison with European white oak. Application of a water-based sealer between stain and finish accentuates the natural effect.

TABLE-US-00002 TABLE 2 Step Details substrate Prod. Type application US Red Oak US Red Oak US Red Oak US Red Oak Step X PB2C 60 g/m.sup.2 Mix Mix Mix Step 1 Ageing stain 50 g/m.sup.2 1239/8501 1239/7953 1239/7953 Step 2 WB Sealer Oculto 50 g/m.sup.2 230-001972 230-007942 Step 3 UV Oil base clear 10-15 g/m.sup.2 680-007413 163-007285 163-007285 163-007285 Step 4 UV Oil clear matt 6-8 g/m.sup.2 680-005149 680-007413 680-007413 680-007413 680-005149 680-005149 680-005149 Pinkish Natural =EU Quality =EU Quality

Example 3

[0044] Maple is a wood species that is often used in North America, but a disadvantage is that white finishes have a pink sheen. Use of the composition and application of the method according to the disclosure is ideal for this. It can be seen from a comparative test (8 h reaction/open air/½ sample washed out) with fixation alkalies such as Na.sub.2CO.sub.3, Na.sub.2SiO.sub.3 and Na.sub.2B.sub.4O.sub.7/Na.sub.2CO.sub.3 mix that this is usable for the method according to the disclosure.

TABLE-US-00003 TABLE 3 Step Details substrate Prod. Type application Hard Maple Hard Maple Hard Maple Hard Maple Step X PB2C 60 g/m.sup.2 Mix Mix Mix Reaction 1240/8417 1241/8417 1242/8417 time UV Oil X-tra 10-15 g/m.sup.2 680-005510 8 Hr 8 Hr 8 Hr Step 1 White 6-8 g/m.sup.2 680-005149 680-005510 680-005510 680-005510 Step 2 UV Oil clear matt 680-005149 680-005149 680-005149 Pinkish Neutral Neutral Neutral

Example 4

[0045] Beech is used in Europe for interior applications, such as staircases, plank floors and furniture and is sometimes steam-treated, which makes the wood pink. Tests on steamed beech have shown that the pink hue can be suppressed considerably when the composition and application of the method according to the disclosure are used.

TABLE-US-00004 TABLE 4 Details Step Prod. Steamed Steamed substrate Type application Beech Beech Step X PB2C 60 g/m.sup.2 Mix 1239/8417 Step 1 Aquapad 50 g/m.sup.2 240-006363 240-006363 White Step 2 UV Oil 10-15 g/m.sup.2 175-006508 175-006508 white Step 3 UV Oil 6-8 g/m.sup.2 680-005149 680-005149 clear matt Pinkish ±Neutral

Example 5

[0046] The reactive component based on propylene glycol as moistener was tested on a standard commercial finishing, with American red oak as substrate. It proved effective, with colour combination comparable to the recipe based on urea.

TABLE-US-00005 TABLE 5 Step Prod. Details substrate Type application US Red Oak US Red Oak US Red Oak Step X PB2C 60 g/m.sup.2 Mix 1239/7953 Mix 7993/7953 Reaction overnight overnight time Ageing stain 50 g/m.sup.2 230-002061 230-002061 230-002061 Step 1 UV Oil natural 10-15 g/m.sup.2 175-005232 175-005232 175-005232 Step 2 white 6-8 g/m.sup.2 680-005149 680-005149 680-005149 Step 3 UV Oil clear matt Pinkish =EU Quality =EU Quality