Method for bleaching heat-treated wood and method for treating wood

Abstract

To provide a method for bleaching heat-treated wood which suppresses the deterioration of dimensional stability and can adjust the color to the same level as that of wood before heat treatment even when the heat-treated wood which has become dark brown by heat treatment for a long time is bleached.SOLUTION: The method for bleaching heat-treated wood according to the present invention involves bleaching the heat-treated wood at a temperature of 30°C or higher and 90°C or lower by using a treatment solution containing an oxygen-based bleaching agent in an amount of 3 mass% or more and 50 mass% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to methods for bleaching heat-treated wood and methods for treating wood. [Background technology]

[0002] Conventionally, heat-treated wood has been produced by various methods.

[0003] For example, Patent Document 1 describes a method for producing heat-treated wood in which heat-treated wood is immersed in an aqueous solution containing a bleaching agent for a required period of time. The heat-treated wood is produced through a heat treatment process that includes at least the steps of holding the wood in a heated state in a sealed space formed between the heating platens of a press device equipped with upper and lower heating platens, supplying high-pressure steam to the wood held in the sealed space, and releasing the pressure in the sealed space. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-345183 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the bleaching method for heat-treated wood described in Patent Document 1, when bleaching heat-treated wood that has turned dark brown due to long-term heat treatment, there is a risk that the color will not be adjusted to the same level as the wood before heat treatment. Furthermore, when bleaching heat-treated wood, it is desirable to suppress a decrease in dimensional stability.

[0006] Therefore, the inventors have found the problem of providing a method for bleaching heat-treated wood that can suppress the decrease in dimensional stability and can adjust the color of heat-treated wood that has turned dark brown after long-term heat treatment to approximately the same color as the wood before heat treatment, even when bleaching the heat-treated wood. [Means for solving the problem]

[0007] The present disclosure provides a method for bleaching heat-treated wood, in which heat-treated wood is bleached at a temperature of 30°C or higher and 90°C or lower using a treatment solution containing 3% by mass or higher and 50% by mass or lower of an oxygen-based bleaching agent. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments of the present disclosure will be described in detail.

[0009] [Bleaching method for heat-treated wood] In the method for bleaching heat-treated wood of this embodiment, a treatment solution containing 3% by mass to 50% by mass of an oxygen bleaching agent is used to bleach the heat-treated wood at a temperature of 30° C. to 90° C. Therefore, even if heat-treated wood that has turned dark brown after a long heat treatment is bleached, the color of the heat-treated wood can be adjusted to a color similar to that of the wood before heat treatment.

[0010] If the oxygen bleaching agent content in the treatment solution is 3% by mass or more, the color of the heat-treated wood that has turned dark brown after a long heat treatment can be adjusted to a color similar to that of the wood before heat treatment, even when bleaching the heat-treated wood. If the oxygen bleaching agent content is 50% by mass or less, the dimensional stability of the heat-treated wood is prevented from decreasing. The oxygen bleaching agent content in the treatment solution is preferably 40% by mass or less.

[0011] If the bleaching temperature for heat-treated wood is 30°C or higher, the color of the heat-treated wood can be adjusted to approximately the same color as the wood before heat treatment, even if the heat-treated wood has turned dark brown due to long-term heat treatment, and if the bleaching temperature is 90°C or lower, the deterioration of the dimensional stability of the heat-treated wood is suppressed. The temperature for bleaching heat-treated wood is preferably 40°C or higher and 70°C or lower.

[0012] The oxygen bleaching agent is not particularly limited as long as it can adjust the color of the heat-treated wood to approximately the same color as the wood before the heat treatment, but examples thereof include hydrogen peroxide and sodium percarbonate. Of these, hydrogen peroxide is preferred.

[0013] The time for bleaching heat-treated wood is preferably 0.5 to 5 hours, and more preferably 1 to 3 hours. If the bleaching time is 0.5 hours or more, the color of the heat-treated wood will be adjusted to approximately the same color as the wood before heat treatment, even if heat-treated wood that has turned dark brown after a long heat treatment is bleached, and if the bleaching time is 5 hours or less, the deterioration of the dimensional stability of the heat-treated wood will be suppressed.

[0014] The difference in brightness ΔL between heat-treated wood before and after bleaching * It is preferable to bleach the heat-treated wood so that the color is at least 21. This allows the color of the heat-treated wood to be adjusted to approximately the same color as the wood before heat treatment, even if heat-treated wood that has turned dark brown after a long period of heat treatment is bleached.

[0015] The method for bleaching heat-treated wood is not particularly limited, but examples include a method of immersing the heat-treated wood in a treatment solution and a method of spraying the treatment solution onto the heat-treated wood. Among these, the method of immersing the heat-treated wood in a treatment solution is preferred because it bleaches the heat-treated wood uniformly and prevents color unevenness.

[0016] When heat-treated wood is immersed in a treatment solution, the mass ratio of the treatment solution to the heat-treated wood is preferably at least 10. When the mass ratio of the treatment solution to the heat-treated wood is at least 10, the heat-treated wood is sufficiently bleached.

[0017] The treatment solution is preferably an aqueous solution with a pH of 9 to 10. This promotes decomposition of the oxygen bleaching agent, making it easier to bleach the heat-treated wood. The base contained in the treatment solution is not particularly limited, but examples include sodium hydroxide.

[0018] The treatment liquid may further contain a surfactant, a stabilizer, and the like.

[0019] In heat-treated wood with a thickness of 2 mm or more, the treatment solution generally penetrates only to the surface, so the center is less susceptible to bleaching. In this case, it is easy to adjust the color of the surface layer of heat-treated wood while maintaining the dimensional stability that is a characteristic of heat-treated wood, so it is more effective to apply the heat-treated wood bleaching method of this embodiment to heat-treated wood with a thickness of 2 mm or more.

[0020] Heat-treated wood that has been heat-treated for a long time and turned dark brown has a lightness of, for example, L * is 60 or less.

[0021] Heat-treated wood bleached by the method for bleaching heat-treated wood of this embodiment can be used for, but is not limited to, building materials such as door materials, toilet wall materials, bathroom wall materials, washroom wall materials, sash materials, window frames, window grilles, ceiling materials, floor materials, and fence materials.

[0022] [Wood processing method] The wood treatment method of this embodiment includes a step of heat-treating wood at a temperature of 160°C or higher and 250°C or lower to obtain heat-treated wood, and a step of bleaching the heat-treated wood using the heat-treated wood bleaching method of this embodiment.

[0023] The wood is not particularly limited, but examples include natural woods such as cedar, cypress, Douglas fir, Japanese cypress, Japanese hemlock, pine, poplar, eucalyptus, sawara, ash, oak, Japanese cypress, larch, black pine, oak, chestnut, cherry, oak, walnut, Japanese linden, beech, white ash, red oak, birch, sapele, hard maple, black cherry, mahogany, teak, bubinga, and zebra wood, and processed woods such as plywood.

[0024] When the temperature for heat treating wood is 160°C or higher and 250°C or lower, the dimensional stability of the heat-treated wood is improved. The temperature for heat treating wood is preferably 200°C or higher and 240°C or lower. The time for heat treating wood is preferably 4 hours or higher and 12 hours or lower, and more preferably 6 hours or higher and 10 hours or lower. When the time for heat treating wood is 4 hours or higher and 12 hours or lower, the dimensional stability of the heat-treated wood is improved.

[0025] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments, and the above embodiments may be modified as appropriate within the scope of the spirit of the present disclosure. [Example]

[0026] Examples of the present disclosure will be described below, but the present disclosure is not limited to these examples.

[0027] [Example 1] A 6mm thick piece of cypress wood was heat-treated at 210°C for 6 hours to obtain a 6mm thick piece of heat-treated cypress wood. The heat-treated cypress wood was then immersed in a treatment solution at 70°C for 2 hours to obtain bleached cypress wood. The treatment solution used was an aqueous solution containing hydrogen peroxide (20% by mass) and sodium hydroxide (2.5% by mass) with a pH of 10. The mass ratio of the treatment solution to the heat-treated cypress wood was 15.

[0028] [Example 2] Bleached cypress wood was obtained in the same manner as in Example 1, except that the heat-treated cypress wood was immersed in a treatment solution at 70°C for 1 hour and an aqueous solution of pH 10 containing hydrogen peroxide (40% by mass) and sodium hydroxide (5% by mass) was used as the treatment solution.

[0029] [Comparative Example 1] Bleached cypress wood was obtained in the same manner as in Example 1, except that the heat-treated cypress wood was immersed in the treatment solution at 25°C for 5 hours.

[0030] Comparative Example 2 Bleached cypress lumber was obtained in the same manner as in Example 1, except that the heat-treated cypress lumber was immersed in a treatment solution at 25°C for 64 hours and that an aqueous solution containing sodium chlorite (20% by mass) with a pH of 11 was used as the treatment solution. Sodium chlorite is a chlorine-based bleaching agent.

[0031] Comparative Example 3 Heat-treated cypress wood was obtained in the same manner as in Example 1, except that the heat-treated cypress wood was not bleached.

[0032] Comparative Example 4 Hinoki wood before heat treatment was used.

[0033] Color Value Using a colorimeter, the color values ​​(L * , a * and b * ) was measured.

[0034] [The difference in brightness ΔL between heat-treated cypress wood before and after bleaching] * ] formula (Bleached cypress wood lightness L * )-(Lightness L of heat-treated cypress wood (Comparative Example 3) * ) Therefore, ΔL * asked for.

[0035] [Dimensional change rate] Bleached cypress wood (Examples 1 and 2, Comparative Examples 1 and 2), heat-treated cypress wood (Comparative Example 3), and cypress wood (Comparative Example 4) were left in an environment of 70°C for 24 hours, and the dimensional change rate in the width direction (the direction perpendicular to the grain) was measured.

[0036] Table 1 shows the measurement results of the color values ​​and dimensional change rates of bleached cypress wood (Examples 1 and 2, Comparative Examples 1 and 2), heat-treated cypress wood (Comparative Example 3), and cypress wood (Comparative Example 4).

[0037] [Table 1]

[0038] From Table 1, it can be seen that the heat-treated cypress wood of Comparative Example 3 is dark brown in color due to a long-term heat treatment of the cypress wood of Comparative Example 4. On the other hand, the bleached cypress wood of Examples 1 and 2, which was obtained by bleaching the heat-treated cypress wood of Comparative Example 3, had a small dimensional change rate and was adjusted to a color similar to that of the cypress wood of Comparative Example 4. In contrast, the bleached cypress wood of Comparative Examples 1 and 2 was not adjusted to a color similar to that of the cypress wood of Comparative Example 4 because the temperature for bleaching the heat-treated cypress wood of Comparative Example 3 was 25°C.

Claims

1. A method for bleaching heat-treated wood, comprising bleaching the heat-treated wood at a temperature of 30°C to 90°C using a treatment solution containing 3% by mass to 50% by mass of an oxygen bleaching agent.

2. 2. The method for bleaching heat-treated wood according to claim 1, wherein the time for bleaching the heat-treated wood is from 0.5 hours to 5 hours.

3. The difference in brightness ΔL between the heat-treated wood before and after bleaching ＊ 3. The method for bleaching heat-treated wood according to claim 1, wherein the heat-treated wood is bleached so that the .gamma.-to-.gamma.

4. 3. The method for bleaching heat-treated wood according to claim 1, wherein the heat-treated wood is immersed in the treatment solution.

5. 3. The method for bleaching heat-treated wood according to claim 1, wherein the mass ratio of the treatment solution to the heat-treated wood is 10 or more.

6. 3. The method for bleaching heat-treated wood according to claim 1, wherein the treatment solution is an aqueous solution having a pH of 9 or more and 10 or less.

7. 3. The method for bleaching heat-treated wood according to claim 1, wherein the heat-treated wood has a thickness of 2 mm or more.

8. A step of heat-treating wood at a temperature of 160°C or higher and 250°C or lower to obtain the heat-treated wood; A method for treating wood, comprising the step of bleaching the heat-treated wood by the method for bleaching heat-treated wood according to claim 1 or 2.

9. 9. The method for treating wood according to claim 8, wherein the time for heat treating the wood is from 4 hours to 12 hours.

10. The heat-treated wood has a lightness of L ＊ 3. The method for bleaching heat-treated wood according to claim 1, wherein the saturation is 60 or less.

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