RU2156691C1 - Wood bleaching process - Google Patents

Abstract

FIELD: woodworking. SUBSTANCE: wood colored by fungal pigments or darkened from atmospheric or solar effects is bleached in two steps. Wood is first treated with aqueous solution containing 25-55% sodium hypochlorite, 1-5% sodium or potassium hydroxide, and water. In the second step, treatment is carried out with 15- 50% aqueous solution of hydrogen peroxide. EFFECT: achieved complete restoration of damaged wood surface regions. 3 cl, 5 ex

Description

 The invention relates to the field of the woodworking industry, in particular to a method for bleaching wood affected by pigment fungi or darkened from atmospheric and solar exposure.

A known method of bleaching wood by impregnating wood with a 30-50% urea solution, while the wood is heated before impregnation in water at 90-100 ^o C [SU 709358 A, publ. 01/15/80].

 A known method of bleaching wood using peroxide compounds.

 Thus, the known method of bleaching wood (bleaching accessories) involves treating wood with hydrogen peroxide and ammonia [US 3708889 A, publ. 01/09/73]. According to another known method, the bleaching of wood is carried out with hydrogen peroxide in the presence of formamide in a mass ratio of 1:10 - 10: 1 in a neutral or alkaline environment [DE 1792211 A, publ. 09/07/72].

 A method for whitening wood based on the combined action of sodium peroxide and oxalic acid is described; to speed up the bleaching process, the method involves the addition of sulfuric acid (Wood processing .- M: Geleos, 1998, S. 90-91].

 Wood bleaching methods based on the use of sodium hypochlorite solution are also known. So, there is a method of bleaching wood by treating it with an acidic solution of sodium hypochlorite [CH 512976 A, publ. 11/15/71]. According to the known method [FR 2641730 A1, publ. 07.20.90] whitening and bleaching of any wood of exotic species, regardless of color, is carried out by treating it with an aqueous solution of sodium hypochlorite with a concentration of 1-55%.

 The closest known solution to a similar problem is a method of bleaching wood by treating the wood surface with an aqueous solution containing sodium hypochlorite, and involving simultaneous or sequential treatment of the wood surface with an aqueous solution of sodium silicate [DE 3608688 A1, publ. 12/18/86]. The disadvantages of this method include the inability to completely eliminate the darkening of the surface of the wood and restore the affected areas ("blue" or "black") on the surface of the wood, especially hardwood, to its natural state.

 The objective of this decision is to eliminate the above disadvantages.

To solve this problem, the present method of bleaching wood is proposed, which includes treating the wood surface in two stages in succession: at the first stage, the treatment is carried out with an aqueous solution containing sodium hypochlorite and sodium or potassium hydroxide in the following ratio, wt.%: Sodium hypochlorite 25-55, sodium or potassium hydroxide 1-5, water - the rest,
at the second stage, the treatment is carried out with an aqueous solution of hydrogen peroxide containing, wt.%: hydrogen peroxide 15-50, water - the rest.

 The method according to the invention provides for the treatment of a wood surface using, in a first step, preferably a solution additionally containing a water-soluble polymer selected from the group consisting of polyacrylamide, poly-N-vinylpyrrolidone, sodium carboxymethyl cellulose, sodium or potassium polyacrylate or polymethacrylate, 0.1% polyethylene glycol -1.0 wt.%.

 Preferably, the solution used to treat the surface of the wood in the second step further comprises urea in an amount of 0.1-5.0 wt.%.

The method is as follows. The solution used to treat the surface of the wood in the first step is designated solution (I), and in the second step, solution (II). Solution (I) is applied to the wood surface with a brush or other method at a temperature of 0-70 ^o C (in this case, mainly pigmented areas of the wood surface are treated) and incubated from 5 minutes to 24 hours depending on the degree of wood damage and the processing temperature. As a result of treatment with solution (I), the pigmentation (wood "black" and "blue" and atmospheric and solar darkening, etc.) disappears or changes color and intensity sharply, and the general background of the surface becomes yellowish or golden yellow. Then, solution (II) is applied to the same surface. Under the action of solution (II) at a temperature of 0-70 ^o C for 1-10 minutes, the pigmentation residues disappear and the wood acquires a natural color. The wood is dried, after which it can be finished in the usual way (varnishing, tinting, waxing, etc.).

 The consistent use of solutions (I) and (II) is based on a chemical reaction that allows you to enhance the action of the components of each solution and determines their synergistic effect, leading to the rapid obtaining of natural color and its long-term preservation, as well as to the simultaneous mutual neutralization of solutions, making final washing unnecessary bleached wood.

 The additional content of water-soluble polymer in solution (I) increases its capacity in time after its application (inhibits evaporation, retains moisture in the treated layer). The introduction of additional urea in the composition (II) accelerates the processing of wood to achieve the desired result.

 The following examples illustrate the present invention.

 Example No. 1.

 Wall paneling, spruce, affected by fungal "mob".

 First, a solution containing in wt.% Is applied to the wood surface with a brush at room temperature. NaOCl - 50, NaOH - 2, water - the rest.

 Black spots turn brown in 15 minutes and almost disappear, the general background of the wood surface becomes yellowish.

 After that, a 20 wt.% Aqueous solution of hydrogen peroxide is applied.

 Within 3 minutes, the remains of the stains are completely discolored, and the wood takes on a natural color.

 Example No. 2.

 Fence, aspen, dark gray from sun and weather.

Initially, the surface of the wood is treated at a temperature of 60 ^o C with a solution containing in wt. % NaOCl - 30, KOH - 4, potassium polymethacrylate (M. m. = 7 • 10 ⁵ ) - 0.5, water - the rest.

 Stand for 1 hour. The darkening disappears, the color of the wood is golden yellow.

 Then apply a solution containing hydrogen peroxide - 15 wt.%, Water - the rest.

 Within 1 min, the wood becomes a natural white color.

 Example No. 3.

 The rounded bar, a pine, is struck by a fungal "blue".

The surface of the wood is treated in the field at a temperature of 24 ^o C initially with a solution containing in wt.% NaOCl - 40, NaOH - 1, water - the rest and incubated for 2 hours.

 Affected areas are practically discolored, acquire a greenish-brown tint, unaffected wood acquires a yellowish tint.

 Then they act with a solution containing in wt.% Hydrogen peroxide - 20, urea - 2, water - the rest.

 After 5 minutes, the pigmentation residues completely disappear, the wood does not differ in color from the natural color of pine.

 Example No. 4.

Parquet board, birch, affected by fungal blackness and redness. First, it is treated at a temperature of 0 ^o C with a solution containing in wt.% NaOCl-55, KOH - 4, polyacrylamide (M. m. = 2 • 10 ⁶ ) - 0.5, water - the rest. Stand for 3 hours.

 Black and red spots disappear, the general background becomes golden yellow. Then treated with a solution containing in wt.% Hydrogen peroxide - 18, urea - 2, water - the rest.

 After 2 minutes, the wood acquires a natural color.

 Example No. 5 (comparative).

 Wall paneling, spruce, affected by fungal "mob".

 First, the surface of the wood at room temperature is treated with a solution containing in wt.% Hydrogen peroxide - 50, urea - 5, water - the rest.

 When holding for 2 hours, black spots remain unchanged, unaffected areas are bright.

 Then act with a solution containing in wt.%. NaOCl - 50, NaOH - 2, water - the rest.

 Affected areas change color to brown, partially lighten, the general background becomes yellowish. Further action with this solution for 4 hours allows you to almost remove the spots of pigmentation, however, traces of spots remain, and the overall background remains yellow, which indicates the need for a treatment sequence according to the claims.

Claims (3)

1. The method of bleaching wood, including surface treatment of wood with an aqueous solution containing sodium hypochlorite, characterized in that the surface treatment of wood is carried out in two stages: in the first stage, the treatment is carried out with an aqueous solution containing sodium hypochlorite and additionally sodium or potassium hydroxide in the following ratio of components , wt.%:
Sodium Hypochlorite - 25 - 55
Sodium or potassium hydroxide - 1 - 5
Water - Else
at the second stage, the treatment is carried out with an aqueous solution of hydrogen peroxide containing 15 to 50 wt.% hydrogen peroxide, water - the rest.  2. The method according to claim 1, characterized in that for processing the wood surface in the first step, a solution is used, additionally containing a water-soluble polymer selected from the group consisting of polyacrylamide, poly-N-vinylpyrrolidone, sodium carboxymethyl cellulose, sodium or potassium polyacrylate or polymethacrylate and polyethylene glycol , in an amount of 0.1 - 1.0 wt.%.  3. The method according to claim 1 or 2, characterized in that for the treatment of the wood surface in the second stage, a solution is used, additionally containing urea in an amount of 0.1 - 5.0 wt.%.