KR102744479B1 - Manufacturing method for carbonized wood using wax impregnation and heat treatment - Google Patents

Abstract

The present invention relates to a method for manufacturing carbonized wood using wax impregnation and heat treatment. Since the manufacturing method of the present invention performs high-heat treatment in a compressed state, the manufacturing time can be shortened, thereby increasing productivity. In addition, since the heat treatment is performed at a lower temperature and in a wax solution than in the conventional heat treatment, the risk of fire can be reduced. Carbonized wood manufactured by the manufacturing method of the present invention has excellent weather resistance (absorbency) and bending strength, dimensional stability, and antiseptic performance. In addition, since the high-heat treatment is performed while immersed in a wax solution, not only is there almost no material deterioration due to oxidation, but also it is possible to control the brightness of the color of the carbonized wood by controlling the temperature and time, thereby producing heat-treated products having various wood colors from the same wood species, thereby expanding the range of choices for consumers.

Description

{Manufacturing method for carbonized wood using wax impregnation and heat treatment}

The present invention relates to a method for manufacturing carbonized wood using wax impregnation and heat treatment.

Wood is a natural organic material that has been used for various purposes in our lives since long ago, and its use is expected to continue to increase in the future. It is a material that is friendly to the human body and the environment, but it is a material that shows 'material deterioration phenomena' such as decomposition, deformation, and deterioration due to various causes such as organisms, moisture, fire, and mechanical wear during use.

Meanwhile, the academic and industrial communities related to wood have developed and are using various practical technologies such as preservation treatment, dimensional stabilization treatment, and fire prevention (flame retardant, flame retardant) treatment to prevent or delay deterioration in order to maximize the usable life of wood.

Material deterioration prevention treatment has mainly been carried out by injecting compounds (preservatives, flame retardants, synthetic resins, etc.) into the wood cell walls and cell cavities to express the desired function. It has been known in Europe for centuries that burning the surface of wood in a bonfire can increase the durability of wood for outdoor use, and the Vikings used this method to treat outdoor structures such as fences. This is the origin of the technology for manufacturing heat-treated wood, and it began to be scientifically studied in Germany in the 1930s and in the United States in the 1940s. The industrial-scale wood heat treatment process (ThermoWood process) was developed by VTT (Valtion Teknillinen Tutkimukeskus, Finnish Technical Research Centre, English) in Finland, and heat-treated wood is currently manufactured under the product name ThermoWood.

The wood heat treatment process is licensed by members of the International Thermowood Association. The wood heat treatment process consists of three stages: the first stage is a high-temperature drying stage using heat and steam (maximum temperature 130℃, time until the wood moisture content becomes completely dry), the second stage is a heat treatment stage (maximum temperature 185~215℃, 2~3 hours), and the third stage is a cooling and humidity control stage (minimum temperature 80~90℃, wood moisture content 4~7%). Since wood heat treatment uses steam, it is environmentally friendly, and the wood color darkens, making it more stable in moisture content changes than untreated wood, improving insulation, and imparting decay resistance, but there is a drawback of reduced bending strength. The International Thermowood Association specifies two standard treatment products, Thermo-S and Thermo-D, distinguishing between softwood and hardwood.

In coniferous wood, Thermo-S is a product group treated at a temperature of 190℃, which slightly improves weather resistance and dimensional stability, has no change in bending strength, and slightly darkens the wood color. In coniferous wood, Thermo-D is a product group treated at a temperature of 212℃, which greatly improves weather resistance and dimensional stability, reduces bending strength, and greatly darkens the wood color.

In hardwood, Thermo-S is a product group treated at 185℃, which does not change weather resistance and bending strength, but slightly improves dimensional stability and slightly darkens the wood color. In hardwood, Thermo-D is a product group treated at 200℃, which slightly improves weather resistance and dimensional stability, reduces bending strength, and greatly darkens the wood color.

Meanwhile, the main target species for heat treatment in Finland are pine, spruce, birch, and aspen (Polleria), and there are also examples of heat treatment for radiata pine, ash, larch, alder, beech, and eucalyptus. In Northern Europe, including Finland, the home of heat treatment wood and the developer of treatment technology, standard temperature conditions are set for each heat treatment product group (Thermo-S and D), quality is explained, and the main target species for heat treatment are determined.

In Korea, there is still no standard process for producing heat-treated wood (wood species, treatment temperature, etc.), and each heat-treated wood manufacturer produces products using its own unique process. The heat treatment process applied by domestic heat-treated wood manufacturers is summarized below.

1) Temperature rise range: Room temperature → 180 ~ 200℃ (maximum temperature varies by company)

- The time is approximately 7 to 8 hours (depending on the machine's performance, capacity (amount of wood to be processed), etc.)

- When the temperature reaches 120℃, heat it by steaming it intermittently (to prevent cracking and fire)

2) Temperature and holding time

- Temperature: 180~200℃

- Time: 2.5~4 hours (depending on the desired color. The longer you leave it, the darker it becomes)

3) Temperature drop time

- Maximum temperature: Up to 100℃ (It takes a long time because it does not easily go down below 100℃. Therefore, it is recovered when it goes down to this level.)

- Steam injection when lowering from the highest temperature to about 120℃

- From 120℃ to 100℃, it is reduced by fog spray.

- The moisture content of the recovered product is approximately 3%.

4) Domestic high-heat treatment wood manufacturing time

- Varies depending on machine performance and capacity

- About 12 hours for small wood, about 48 hours for large wood.

- Manufacturing time depends on cooling time (large capacity machines take a long time to cool down)

The mechanism by which the dimensional stability, weather resistance, or decay resistance of heat-treated wood are improved is the thermal decomposition of hemicellulose, one of the main components of wood cell walls. When wood is heated to 180℃ or higher, hemicellulose, which has the lowest thermal decomposition start temperature among the three (cellulose, hemicellulose, and lignin) main components of wood cell walls, is thermally decomposed to generate furfural and sugars, which polymerize to form a water-insoluble polymer, thereby reducing hygroscopicity and imparting dimensional stability, etc.

Since the dimensional stability improvement effect is realized only when hemicellulose is thermally decomposed to form a water-insoluble polymer, the temperature in the production of heat-treated wood at home and abroad must be raised to 180℃ or higher, which is the temperature at which hemicellulose thermal decomposition begins. Accordingly, since heat treatment is performed at a temperature higher than 180℃, where the dimensional stability improvement effect is realized, it is impossible to control the color of the product, and it is inevitable to produce products with a uniform color for each wood species.

In order to produce a product having a lighter color than that exhibited at a heat treatment temperature of 180℃ or higher, heat treatment must be performed at a lower temperature. However, if heat treatment is performed at a temperature lower than 180℃, hemicellulose thermal decomposition does not occur, so a water-insoluble polymer is not generated, and thus the effect of improving dimensional stability cannot be obtained.

In order to expand the demand for heat-treated wood, it is necessary to produce and supply products with various colors (from light to dark) that suit the tastes of consumers depending on the wood species while maintaining the effect of improving dimensional stability, and the development of technology capable of producing such products is required.

Meanwhile, as a technology related to heat-treated wood, Korean Patent No. 1333574 discloses a method for processing pine wood characterized by removing the carbonized epidermis after heating to a temperature below the combustion temperature, and a technology related to pine wood using the method, and Korean Patent No. 1162893 discloses a technology related to a method for manufacturing carbonized wood and carbonized wood manufactured using the method. However, the method for manufacturing carbonized wood using the wax impregnation and heat treatment of the present invention has not been disclosed.

The present invention was derived from the above-mentioned needs, and the present invention provides a method for manufacturing carbonized wood using wax impregnation and heat treatment, and carbonized wood manufactured according to the manufacturing method of the present invention has excellent weather resistance (absorbency) and bending strength, dimensional stability and antiseptic performance, and since high heat treatment is performed while immersed in a wax solution, there is almost no material deterioration due to oxidation, thereby completing the present invention.

In order to achieve the above purpose, the present invention comprises the steps of: (1) placing a high-melting point wax in a container within a main body, and melting the wax by raising the temperature above the melting point of the wax;

(2) After the step (1), a step of immersing wood in a container containing the molten wax;

(3) After the above step (2), a step of removing moisture present in the cell walls of the wood immersed in the above step (2) and air present in the cell lumen in the form of bubbles by heat treatment under atmospheric pressure;

(4) After the above step (3), a step of heat-treating the wood impregnated with wax by applying a temperature of 140 to 180°C under the conditions of injecting nitrogen gas and having a pressure of 14 to 15 bar; and

(5) A method for manufacturing wax-impregnated and heat-treated carbonized wood is provided, including a step of, after the step (4), lowering the internal pressure of the main pipe to atmospheric pressure and opening the main pipe to recover the heat-treated wood impregnated with wax.

In addition, the present invention provides a wax-impregnated and heat-treated carbonized wood manufactured by the above-mentioned manufacturing method.

The present invention relates to a method for manufacturing carbonized wood using wax impregnation and heat treatment. Since the manufacturing method of the present invention performs high-heat treatment in a compressed state, the manufacturing time is shortened, thereby increasing productivity. In addition, since the heat treatment is performed at a lower temperature than conventional heat treatment and in a wax solution, the method is capable of reducing the risk of fire.

In addition, carbonized wood manufactured by the manufacturing method of the present invention has excellent dimensional stability and antiseptic performance, as well as excellent weather resistance (absorbency) and bending strength, and since it is subjected to high heat treatment while immersed in a wax solution, not only is there almost no material deterioration due to oxidation, but the brightness of the color of the carbonized wood can be adjusted by controlling the temperature and time, so that it can meet the taste of the consumer.

Figure 1 is a photograph showing the change in wood color according to coniferous wood species and heat treatment temperature.
Figure 2 is a photograph showing the change in wood color according to the hardwood species and heat treatment temperature.
Figure 3 is a photograph showing the change in color of coniferous wood species and heat treatment time.
Figure 4 is a photograph showing the change in color of deciduous wood species and heat treatment time.
Figure 5 shows the results of comparing a commercially available high-heat treated product with a wax-impregnated heat treated product according to the present invention. (a) Untreated product, (b) commercially available product subjected to high-heat treatment at 175°C, (c) commercially available product subjected to high-heat treatment at 190°C, (d) product subjected to wax-impregnated heat treatment at 150°C for 11 hours according to the present invention, and (e) product subjected to wax-impregnated heat treatment at 160°C for 6 hours according to the present invention.

The present invention comprises the steps of: (1) placing a high-melting point wax into a container within a main body, and melting the wax by raising the temperature above the melting point of the wax;

(2) After the step (1), a step of immersing wood in a container containing the molten wax;

(3) After the above step (2), a step of removing moisture present in the cell walls of the wood immersed in the above step (2) and air present in the cell lumen in the form of bubbles by heat treatment under atmospheric pressure;

(4) After the above step (3), a step of heat-treating the wood impregnated with wax by applying a temperature of 140 to 180°C under the conditions of injecting nitrogen gas and having a pressure of 14 to 15 bar; and

(5) A method for manufacturing wax-impregnated and heat-treated carbonized wood, comprising the step of, after the step (4), lowering the internal pressure of the main body to atmospheric pressure and opening the main body to recover the heat-treated wood impregnated with wax.

The high melting point wax is a wax that melts at a temperature of 100℃ or higher, and is preferably polyethylene wax or FT wax (Fissher-Tropsch wax), but is not limited thereto. However, in the present invention, low melting point wax, natural oil, or synthetic oil are not included in the wax of the present invention. If low melting point paraffin wax is used, stickiness may occur even at room temperature, and there may be a problem of wax dissolution when the product (carbonized wood) is exposed to direct sunlight in the summer. In addition, if natural oil such as vegetable oil or synthetic oil is used, the carbonized wood becomes slippery or problems such as oil dissolution may occur, which is not preferable in terms of product quality.

The above wood is preferably, but not limited to, a coniferous tree selected from pine, Douglas fir and spruce, or a broadleaf tree selected from birch, beech and ash.

The heat treatment in the above step (3) is performed at a temperature that melts the high-melting point wax, preferably at a temperature of 100 to 140°C, more preferably at a temperature of 110 to 130°C, and even more preferably at a temperature of 120°C, but is not limited thereto.

The heat treatment of the above step (4) can be adjusted according to the desired color depending on the type of wood, the combination of time and temperature. When the heat-treated wood is a broadleaf tree, it is preferable to heat treat at 140 to 160°C for 6 to 11 hours, and when the wood is a conifer, it is preferable to heat treat at 160 to 180°C for 4 to 11 hours, but is not limited thereto.

In addition, the present invention relates to wax-impregnated and heat-treated carbonized wood manufactured by the above-mentioned manufacturing method.

The above carbonized wood has the characteristics of excellent moisture absorption and water absorption (i.e., reduced water absorption) and has the effect of improving bending strength.

The characteristic of the present invention is that the technology of impregnating wood in a high-melting-point wax solution and performing high-heat treatment allows the color of the final heat-treated wood product to be arbitrarily controlled by controlling the wax impregnation temperature and time, thereby manufacturing heat-treated carbonized wood having a desired color. In the manufacture of conventional heat-treated wood, the heat treatment must be performed at a temperature of 180°C or higher, which is the start temperature of hemicellulose thermal decomposition, but the present invention has the characteristic of maintaining dimensional stability even when the heat treatment is performed at a temperature of 180°C or lower to obtain a bright color. The dimensional stability is not achieved by the production of a water-insoluble polymer, but by preventing moisture from approaching and penetrating into the wood cell walls by filling the intracellular cavities and gaps of the heat-treated wood with hydrophobic wax.

Hereinafter, the present invention will be described in more detail using examples. It will be apparent to those skilled in the art that these examples are only intended to explain the present invention more specifically and that the scope of the present invention is not limited by these examples.

1. Heat treatment agent (heat transfer medium during heat treatment process)

- In the conventional method, the heat transfer medium of the wood heat treatment process is air (treatment is performed by heating air), and the heat transfer medium of the present invention is a wax solution.

- It is preferable that the type of wax of the present invention be a wax having a melting point of 100°C or higher, and preferred examples include polyethylene wax or FT (Fisher-Tropsch) wax.

2. Heat treatment process

a) Drying process

① High-melting point wax was placed inside a container with a main contract, and the wax was melted by raising the temperature (approximately 120℃) above its melting point. → ② Afterwards, wood was immersed in the molten wax container (immersion treatment is a process in which moisture present in the wood cell walls escapes to the outside in the form of bubbles together with the air in the cell lumen) → ③ Heat treatment was performed under atmospheric pressure until bubble generation stopped.

a) Heat treatment process

After the drying process of the above wood, ① the temperature inside the main pipe was set within the temperature range of 140 to 180℃ depending on the wood species, for conifers within the temperature range of 140 to 160℃, for deciduous trees within the temperature range of 140 to 160℃, high-pressure nitrogen gas was introduced to increase the pressure to 15 bar, and then heat-treated for 11 hours (in the heat treatment process, the treatment temperature and treatment time were arbitrarily adjusted to obtain the desired color (in order to obtain each carbonized wood disclosed in the examples below, various temperatures and times were performed, but the pressure was fixed constantly in all performances.) → ② After the heat treatment was completed, the pressure inside the main pipe was gradually lowered to atmospheric pressure. → ③ the main pipe was opened and the carbonized wood was recovered.

Example 1. Fix the heat treatment time to 11 hours and check the change in color according to the change in heat treatment temperature.

a) Coniferous wood: Pine, Douglas fir, spruce

- Heat treatment temperature of coniferous wood: 140, 150, 160, 180℃

Variation of dE ^* values by coniferous wood species and heat treatment temperature 140℃ 150℃ 160℃ 180℃ pine tree 9.7 20.1 23.1 56.8 Douglas Furr 14.5 15.9 36.1 55.9 Spruce 8.7 12.2 37.4 55.3

In all coniferous tree species, the wood color tended to darken as the heat treatment temperature increased, and it was confirmed that the wood color darkened rapidly from 160℃.

The change in ash color was measured by treatment temperature using a colorimeter. The dE ^* value, which can evaluate the degree of ash color change (darkening) of treated wood compared to the ash color of untreated wood, was investigated. As the dE ^* value increased, the darkening of the ash color also increased.

In the present invention, the color difference (dE ^* ) disclosed means a value that quantitatively expresses the visual difference between the color of a sample with respect to a reference color (untreated wood), and is a value calculated as the distance between two colors among color solids that are visually the same.

As disclosed in Table 1 above, there was no significant difference in the darkening of the wood color between wood species when heat treated at 180°C for 11 hours.

As disclosed in Fig. 1, by producing a color comparison table by heat treatment temperature for each coniferous tree species and showing it to consumers so that they can make a selection, it is possible to produce heat-treated wood that meets consumers' preferences and expand the demand for heat-treated wood.

b) Broadleaf trees: birch, beech, ash

- Heat treatment temperature for hardwood: 140, 150, 160℃

Changes in dE ^* values by hardwood species and heat treatment temperature 140℃ 150℃ 160℃ Birch 10.7 26.0 42.6 You too, beech tree 19.6 31.0 44.1 Water lily 16.0 26.5 38.7

Broadleaf lumber is relatively darker in color than coniferous lumber even in the untreated stage and changes color easily with heat treatment, so 160℃ was set as the highest heat treatment temperature. It was confirmed that there was no significant difference in the darkness of lumber color due to heat treatment among tree species when heat treated at 160℃ for 11 hours (Fig. 2).

Example 2. Fix the heat treatment temperature and check the change in color according to the change in heat treatment time.

a) Coniferous wood: Pine, Douglas fir, spruce

- Heat treatment temperature of coniferous wood: 180℃

- Heat treatment time for coniferous wood: 4, 6, 11 hours

Changes in dE ^* values by coniferous wood species and heat treatment time 4 hours 6 hours 11 hours pine tree 26.3 29.0 55.7 Douglas Furr 31.3 34.5 57.5 Spruce 35.0 44.2 52.1

The heat treatment temperature was fixed at 180℃, and the heat treatment time was treated differently. When the treatment time was shorter than 4 hours, the change in color (darkening) was not significant compared to the untreated material. Therefore, it was determined that a heat treatment of 4 hours or longer was necessary.

b) Broadleaf trees: birch, beech, ash

- Heat treatment temperature for hardwood: 160℃

- Heat treatment time for hardwood: 6, 8, 11 hours

Changes in dE ^* values by hardwood species and heat treatment time 6 hours 8 hours 11 hours Birch 21.2 31.3 42.6 You too are a beech tree 34.9 36.9 44.1 Water lily 33.4 38.1 38.7

By fixing the heat treatment temperature to 160℃ and varying the heat treatment time, similar treatment results to the aforementioned coniferous wood were confirmed.

Example 3. Color comparison with commercially available high-heat treated wood products

The color of the wax-impregnated heat-treated wood according to the present invention (ash wood, heat-treated at 160°C for 6 hours; ash wood, heat-treated at 150°C for 11 hours) was compared with that of the heat-treated wood produced and sold domestically.

Comparative product: Product produced and sold domestically using existing heat treatment processes

Wood species of the comparison product: Broadleaf wood (ash tree)

Heat treatment temperature of comparative products: 175℃, 190℃ (no data on heat treatment time and process)

Comparison of dE ^* values of commercially available high-temperature treated products and wax-impregnated heat-treated products 175℃ 190℃ 150℃(11 hours) 160℃(6 hours) Commercially available high heat treatment products 26.3 31.1 - - Wax impregnated heat treated products - - 26.6 33.4

As disclosed in Table 5 above, when compared with a commercial product heat-treated at 175°C, the wax-impregnated heat-treated product of the present invention, which was treated at a heat treatment temperature of 150°C for 11 hours, showed a similar dE ^* value, and when compared with a commercial product heat-treated at 190°C, the wax-impregnated heat-treated product of the present invention, which was treated at a heat treatment temperature of 160°C for 6 hours, showed a similar dE ^* value.

Example 4. Comparison of moisture absorption and water absorption of commercially available high-heat treated wood products and wax-impregnated heat treated products of the present invention

The moisture absorption and water absorption, which are closely related to dimensional stability, were measured to compare the commercially available product with the wax-impregnated heat-treated product according to the present invention.

Moisture absorption and water absorption of commercially available high-temperature treated products and wax-impregnated heat-treated products Moisture absorption (kg/㎡) Absorption (kg/㎡) Unprocessed 0.31 1.0 Commercially available high heat treatment products (190℃) 0.07 0.50 Wax-impregnated heat-treated products (160℃, 6 hours) 0.07 0.01

When comparing the wax-impregnated heat-treated product with the commercially available high-heat-treated product, the product shows the same performance in terms of moisture absorption related to moisture penetration, but in terms of water absorption, which is a measure of the degree of direct water penetration, the product shows almost no water penetration at 1/50th of the level, indicating high dimensional stability. As disclosed in Table 6 above, the reason the water absorption is significantly lower than that of the commercial product is because the hydrophobic, nonpolar wax penetrates into the treated wood tissue and fills the cell lumen or gaps.

Example 5. Comparison of bending strength with commercially available heat-treated wood products

The flexural strength of a commercially available high-heat treated product and a wax-impregnated heat treated product of the present invention was confirmed.

The biggest drawback of heat-treated wood is the decrease in bending strength, but it was confirmed that there is an effect that minimizes the decrease in bending strength.

As disclosed in Table 7, commercial products show a decrease in bending strength of about 60% compared to untreated wood, but wax-impregnated heat-treated products show a decrease in bending strength of only about 17%, showing a characteristic of a small decrease in bending strength. It was determined that the small decrease in bending strength of wax-impregnated heat-treated wood is because the heat treatment temperature is low and the time is short, so the degree of thermal decomposition of the wood tissue is small.

Comparison of commercially available high-temperature treated products and wax-impregnated heat-treated products (ash tree) Bending strength (N/㎟) Unprocessed 148 Commercially available high heat treatment products (190℃) 58 Wax-impregnated heat-treated products (160℃, 6 hours) 123

Claims (7)

(1) A step of placing polyethylene wax or FT wax (Fissher-Tropsch wax) into a container within the main contract and melting the wax by raising the temperature above the melting point of the wax;
(2) After the step (1), a step of immersing wood in a container containing the molten wax;
(3) After the above step (2), a step of removing moisture present in the cell walls of the wood immersed in the above step (2) and air present in the cell lumen in the form of bubbles by heat treatment under atmospheric pressure;
(4) After the step (3), a step of heat-treating the wood impregnated with wax by applying a temperature of 140 to 180°C under the conditions of injecting nitrogen gas and having a pressure of 14 to 15 bar, and if the wood is any one of broadleaf trees selected from birch, beech and ash, heat-treating at 140 to 160°C for 6 to 11 hours, and if the wood is any one of coniferous trees selected from pine, Douglas fir and spruce, heat-treating at 160 to 180°C for 4 to 11 hours to induce a color change; and
(5) A method for manufacturing wax-impregnated and heat-treated carbonized wood, characterized in that the water absorption is reduced and the bending strength is increased, comprising the step of lowering the internal pressure of the main pipe to atmospheric pressure and opening the main pipe after the step (4). delete delete A method for manufacturing wax-impregnated and heat-treated carbonized wood, characterized in that in the first paragraph, the heat treatment in step (3) is performed at a temperature of 110 to 130°C. delete A wax-impregnated and heat-treated carbonized wood manufactured using the manufacturing method of claim 1 or 4, characterized in that the absorption amount is reduced and the bending strength is increased. delete