Artificial thin wood is a new type of wooden surface decoration material. It is usually made of common tree seed-cut veneer. It is bleached, dyed, wet-bonded and laminated, cold pressed into wood, and then cut into small pieces. One of the more important aspects of manufacturing is the bleaching and bleaching of the veneers. Through this treatment, the deviation of the color of the material can be eliminated, the discoloration caused by various causes can be removed, the color of the material can be made shallow, and the dyeing liquid can be more easily penetrated. Therefore, bleaching is an important process before veneer dyeing.
1 The cause of wood color
There are many different colors of wood, and the factors affecting the generation and change of wood color are very complicated. The main factors include the following aspects: First, the influence of chemical composition, mainly refers to the quality of wood, wood extract and some special machines. The effect of salt on the color of wood; one is the influence of heart materialization, that is, with the conversion of sapwood to heartwood and the enhancement of heartwood, the pigment materials and phenolic compounds in the heartwood directly or indirectly show the heartwood Kinds of shades. In addition, the environment around the trees has a certain influence on the color of the wood, such as the role of microorganisms in the surrounding environment, the light radiation of sunlight and the oxidation of certain chemical components in the wood in the air. Wood produces a degree of discoloration. Among them, the chemical composition of wood is the most fundamental reason that affects the color and production of wood.
The reason why wood presents various colors is due to its reflection of visible light with a wavelength of 380-780 nm (nanometer). In the visible spectrum, radiation of different wavelengths can cause different color perceptions of humans: 700 nm is red, 580 nm is yellow, 510 nm is green, 470 nm is blue, and the like. If the light of various wavelengths in the visible spectrum can be completely and uniformly reflected, the color tone of the substance is white like paper; on the contrary, the substance that can completely absorb light of various wavelengths is the color of the paper. Printed black on the lead. The selective absorption of the visible spectrum of a substance is determined by the properties of the outermost electrons that make up the atom of the substance, and the electrons of the various atoms of the organic compound that make up the wood just have the potential to produce selective absorption in the visible spectrum, because It contains a substance that is closely related to color. Electron C=C, C=O, benzene nucleus and other chromophores and an OR, NR2, a Cl and other isolated electron pairs. When the molecules of the lignin and the extract in the wood contain a conjugated double bond structure, the electron mobility is large, the energy required for the electron transition is small, and the wavelength of the light is absorbed, thereby shifting the absorption spectrum from the ultraviolet region to the ultraviolet region. In the visible region, the wood produces various colors.
Lignin is one of the main components of wood. It accounts for about 20% to 30% of dry wood. Its basic chemical structure is phenylpropane derivative. There are many chromophoric groups in the lignin macromolecule, such as benzene ring, carbon group, vinyl group and cypress aldehyde group, wherein the cypress aldehyde group consists of three basic chromophore groups (benzene ring, carbon group and vinyl group). It is a large chromophoric group containing C=O and C=C conjugated structures, so many scholars believe that lignin is the main source of wood color.
2. Determination of bleaching agent and bleaching mechanism
2.1 Determination of bleach
Since wood bleaching is achieved by oxidation and reduction reactions, compounds having oxidizing or reducing properties have bleaching action. Reducing bleaches mainly include nitrogen-containing compounds, inorganic sulfur-containing compounds, organic sulfur-containing compounds and acids, and such bleaching agents are less used for bleaching wood. Therefore, the most common method of wood bleaching is oxidative decolorization using oxidizing agents. The most commonly used oxidizing agents for wood bleaching are hydrogen peroxide, sodium hypochlorite, sodium imidate and bleaching powder. Bleached with bleach, with insoluble material calcium bicarbonate. Adhered to the surface of the veneer, the wood loses its original color; although the sodium imidate has a strong bleaching ability, it is mainly expensive to import and is difficult to buy because it is mainly imported. It is very inconvenient to use; Sodium hypochlorite bleaching ability is poor, so the most common chemical agent for wood veneer bleaching is hydrogen peroxide. Hydrogen peroxide not only has strong bleaching power, no pollution, but also moderate price and easy purchase.
2.2 Bleaching mechanism
The hydrogen peroxide ion produced by the hydrogen peroxide dissociation has a strong oxidizing ability, which can make some colored genes in lignin, such as broth and neighboring oxidative cleavage, become leuco genes, thereby improving wood whiteness. .
3, veneer bleaching process
The bleaching process is as follows: to be bleached veneer -> alkali treatment -> water wash dry -> main bleach (plus bleach, additives) -> post treatment
3.1 Alkali treatment
Pretreatment with lye is the first stage of the veneer bleaching process. It mainly plays the following roles: First, it can purify the veneer and eliminate the stains and stains on the surface of the wood. Second, A considerable part of the resin and soluble colored matter in the wood can be leached in the alkali solution, which is beneficial to reduce the consumption of bleach in the main bleaching process. Third, the unipolar penetration is enhanced by swelling the cellulose and hemicellulose. Sex. The concentration of lye can be determined by the degree of soiling on the surface of the veneer and the level of wood inclusions. Alkali treatment generally uses caustic soda, the concentration of 0.5% to 1.0%, time 10-20min, room temperature conditions.
3.2 Washing and drying
Resin dissolved in the alkali solution during the alkali treatment and other impurities such as organic acids should be washed and removed with a large amount of water, which can save the bleaching agent and prevent the peroxide from being caused by some impurities on the surface of the veneer. Inefficient decomposition of hydrogen. After washing, the veneer can be filtered to enter the main bleaching process.
3.3 Main drift
The main bleaching is the most important stage in the bleaching process of the veneer. At this stage, the conjugated double bond on the lignin side chain is broken by the oxidation of hydrogen peroxide, the chromophore group is broken, and the absorption spectrum is ultraviolet light. The movement of the area causes the color of the veneer to become white or light, so as to achieve the purpose of veneer bleaching. In this process, alkali addition is beneficial to the reaction, but in a strong alkaline solution, hydrogen peroxide will also decompose and release oxygen. This unnecessary reaction will greatly increase the consumption of hydrogen peroxide; and the pH is less than 9 At the time, hydrogen peroxide ionization is very slow, so it is important to scientifically control the pH of the bleach. Experiments have shown that the bleaching solution with hydrogen peroxide as the main agent has a pH of 9.5-11, which is disadvantageously high or too low. The pH value is usually controlled by adding sodium hydroxide or sodium silicate.
1 The cause of wood color
There are many different colors of wood, and the factors affecting the generation and change of wood color are very complicated. The main factors include the following aspects: First, the influence of chemical composition, mainly refers to the quality of wood, wood extract and some special machines. The effect of salt on the color of wood; one is the influence of heart materialization, that is, with the conversion of sapwood to heartwood and the enhancement of heartwood, the pigment materials and phenolic compounds in the heartwood directly or indirectly show the heartwood Kinds of shades. In addition, the environment around the trees has a certain influence on the color of the wood, such as the role of microorganisms in the surrounding environment, the light radiation of sunlight and the oxidation of certain chemical components in the wood in the air. Wood produces a degree of discoloration. Among them, the chemical composition of wood is the most fundamental reason that affects the color and production of wood.
The reason why wood presents various colors is due to its reflection of visible light with a wavelength of 380-780 nm (nanometer). In the visible spectrum, radiation of different wavelengths can cause different color perceptions of humans: 700 nm is red, 580 nm is yellow, 510 nm is green, 470 nm is blue, and the like. If the light of various wavelengths in the visible spectrum can be completely and uniformly reflected, the color tone of the substance is white like paper; on the contrary, the substance that can completely absorb light of various wavelengths is the color of the paper. Printed black on the lead. The selective absorption of the visible spectrum of a substance is determined by the properties of the outermost electrons that make up the atom of the substance, and the electrons of the various atoms of the organic compound that make up the wood just have the potential to produce selective absorption in the visible spectrum, because It contains a substance that is closely related to color. Electron C=C, C=O, benzene nucleus and other chromophores and an OR, NR2, a Cl and other isolated electron pairs. When the molecules of the lignin and the extract in the wood contain a conjugated double bond structure, the electron mobility is large, the energy required for the electron transition is small, and the wavelength of the light is absorbed, thereby shifting the absorption spectrum from the ultraviolet region to the ultraviolet region. In the visible region, the wood produces various colors.
Lignin is one of the main components of wood. It accounts for about 20% to 30% of dry wood. Its basic chemical structure is phenylpropane derivative. There are many chromophoric groups in the lignin macromolecule, such as benzene ring, carbon group, vinyl group and cypress aldehyde group, wherein the cypress aldehyde group consists of three basic chromophore groups (benzene ring, carbon group and vinyl group). It is a large chromophoric group containing C=O and C=C conjugated structures, so many scholars believe that lignin is the main source of wood color.
2. Determination of bleaching agent and bleaching mechanism
2.1 Determination of bleach
Since wood bleaching is achieved by oxidation and reduction reactions, compounds having oxidizing or reducing properties have bleaching action. Reducing bleaches mainly include nitrogen-containing compounds, inorganic sulfur-containing compounds, organic sulfur-containing compounds and acids, and such bleaching agents are less used for bleaching wood. Therefore, the most common method of wood bleaching is oxidative decolorization using oxidizing agents. The most commonly used oxidizing agents for wood bleaching are hydrogen peroxide, sodium hypochlorite, sodium imidate and bleaching powder. Bleached with bleach, with insoluble material calcium bicarbonate. Adhered to the surface of the veneer, the wood loses its original color; although the sodium imidate has a strong bleaching ability, it is mainly expensive to import and is difficult to buy because it is mainly imported. It is very inconvenient to use; Sodium hypochlorite bleaching ability is poor, so the most common chemical agent for wood veneer bleaching is hydrogen peroxide. Hydrogen peroxide not only has strong bleaching power, no pollution, but also moderate price and easy purchase.
2.2 Bleaching mechanism
The hydrogen peroxide ion produced by the hydrogen peroxide dissociation has a strong oxidizing ability, which can make some colored genes in lignin, such as broth and neighboring oxidative cleavage, become leuco genes, thereby improving wood whiteness. .
3, veneer bleaching process
The bleaching process is as follows: to be bleached veneer -> alkali treatment -> water wash dry -> main bleach (plus bleach, additives) -> post treatment
3.1 Alkali treatment
Pretreatment with lye is the first stage of the veneer bleaching process. It mainly plays the following roles: First, it can purify the veneer and eliminate the stains and stains on the surface of the wood. Second, A considerable part of the resin and soluble colored matter in the wood can be leached in the alkali solution, which is beneficial to reduce the consumption of bleach in the main bleaching process. Third, the unipolar penetration is enhanced by swelling the cellulose and hemicellulose. Sex. The concentration of lye can be determined by the degree of soiling on the surface of the veneer and the level of wood inclusions. Alkali treatment generally uses caustic soda, the concentration of 0.5% to 1.0%, time 10-20min, room temperature conditions.
3.2 Washing and drying
Resin dissolved in the alkali solution during the alkali treatment and other impurities such as organic acids should be washed and removed with a large amount of water, which can save the bleaching agent and prevent the peroxide from being caused by some impurities on the surface of the veneer. Inefficient decomposition of hydrogen. After washing, the veneer can be filtered to enter the main bleaching process.
3.3 Main drift
The main bleaching is the most important stage in the bleaching process of the veneer. At this stage, the conjugated double bond on the lignin side chain is broken by the oxidation of hydrogen peroxide, the chromophore group is broken, and the absorption spectrum is ultraviolet light. The movement of the area causes the color of the veneer to become white or light, so as to achieve the purpose of veneer bleaching. In this process, alkali addition is beneficial to the reaction, but in a strong alkaline solution, hydrogen peroxide will also decompose and release oxygen. This unnecessary reaction will greatly increase the consumption of hydrogen peroxide; and the pH is less than 9 At the time, hydrogen peroxide ionization is very slow, so it is important to scientifically control the pH of the bleach. Experiments have shown that the bleaching solution with hydrogen peroxide as the main agent has a pH of 9.5-11, which is disadvantageously high or too low. The pH value is usually controlled by adding sodium hydroxide or sodium silicate.
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