The so-called organic dyes refer to organic compounds that can be dissolved in water or solvents and dye fiber materials or other substances into bright and indelible colors through appropriate methods. Organic dyes are widely used not only in textile industry, but also in rubber products, plastics, grease, ink, ink, photosensitive materials, printing, papermaking, coatings, medicine and other fields. The application of organic dyes in the field of wood processing originated from the application of aniline ester in 19 13 in solid wood dyeing. Since 1960s, Japan has done a lot of research work in the field of wood dyeing. German, Italian and other countries attach great importance to the development of practical industrial technology for wood dyeing, and have formed their own patented technology. The products have been sold in China. In the late 1980s, China began to explore wood dyeing technology. Because dyeing is an important means to increase the decorative effect and added value of wood, wood dyeing is receiving extensive attention and attention in the field of production research.
I. Dyes for Wood Dyeing
Wood dyeing is a process in which dyes react with wood chemically or physico-chemically, so that wood has a certain solid color. It is an important means to improve the surface quality of wood, improve its visual characteristics and increase its added value. There are many kinds of dyes and their structures are complex. Water-soluble organic dyes commonly used in wood industry include direct dyes, acid dyes, basic dyes and reactive dyes. Direct dyes can directly act on wood without special treatment, and their combination with lignocellulose depends on van der Waals force and hydrogen bond force between molecules. Acid dyes, also known as anionic dyes, are dyes that effectively dye fibers in acidic media. These dyes contain a lot of carboxyl, hydroxyl or sulfonic groups. Basic dyes, also known as cationic dyes, are salts formed by organic bases and acids, such as phenylmethane, azo and xanthene. Reactive dyes are organic compounds that contain reactive genes in their molecules and can form valence bonds with hydroxyl groups in wood.
1964, Yong et al. began to dye wood with direct dyes, acid dyes and alkaline dyes. 1978 Song Tian Jian dyed a pair of bleached wood with disperse dyes. 197 1 year, Yoko Kitamura and others studied the dyeability of various dyes to wood. The results show that acid dyes have good permeability and are suitable for wood dyeing. In 1990, Inada Shinshui et al. carried out dyeing experiments on 58 kinds of hardwood and 3 kinds of softwood, using 2/kloc-0 kinds of direct dyes, acid dyes, alkaline dyes and reactive dyes. 1993, Liu Yuan published an article introducing wood colorants and their characteristics.
Two. Dyeing method
There are many ways to dye wood, depending on the purpose of dyed wood. Commonly used are veneer dyeing, solid wood dyeing and standing wood dyeing. The dyeing process of veneer varies greatly with different tree species and dyes. Veneer dyeing is a method of dyeing veneers and veneers uniformly by impregnation. The thickness of veneers is 0.2- 1 mm, and the dyed veneers can be used as veneers of artificial boards, furniture veneers and artificial simulated wood. Yoko Oomura studied the dyeing process of wood veneer in 1975. It was found that the higher the temperature, the shorter the dyeing time. The impregnation thickness of 2h at 90℃ is longer than that of 24h at 50℃. From 65438 to 0989, Chen Yunying and others explored the dyeing methods of Canadian poplar, basswood and eucalyptus. Through the observation and analysis of wood dye uptake and color difference, the dyeing test of 0.5mm thick paulownia bleached veneer was carried out with acid scarlet GR dye. Solid wood dyeing is the dyeing treatment of square wood or log. Dyed wood is mainly used to cut thin wood or make high-grade furniture. Because of the thick and long wood, it is difficult to dye wood evenly and thoroughly by the self-permeability of dyeing solution under conventional conditions, so in 1992, Tian conducted dyeing experiments on solid wood under complex conditions such as high temperature, high pressure and vacuum. Standing wood dyeing is usually to immerse the roots of newly harvested wood with certain activity in dyeing solution, and drive dye molecules to move upward along the trunk through the flow of active juice in wood capillaries. From 65438 to 0990, 58 species of broadleaf trees and 3 species of coniferous trees were tested.
Three. Dyeing process
The different uses and dyeing methods of dyed wood determine the diversity of wood dyeing process. In 1964, Yong et al. used normal temperature impregnation method to dye wood. Because of the large volume of wood, it is difficult to dye it evenly, so he tried boiling dyeing. However, cooking for a long time will change the wood structure, and dyes also have bad hair color, so this method is only suitable for dyeing with specific dyes or chemicals. So he began to study the temperature difference dyeing method, which is to heat the wood first, then soak the hot wood in cold dyeing solution, and the heated air and water in the wood expand and move out. After the cold dye solution is put in, negative pressure is generated inside the wood, so that the dye solution can penetrate into the wood smoothly. 1966, Akio Bucun et al. dyed Hokkaido wood and Nanyang wood by pressure injection with Cedar B Brown A 13 12n (FBY) dye. In 1992, Tian used vacuum pressure method to dye solid wood. Dyeing is completed under complex conditions such as high temperature, vacuum and high pressure, and the thickness of treated wood is 32 mm. The purpose of vacuum decompression treatment is to remove air and excess water from wood. The decompression time at 30℃ is: cork 8- 10h, hardwood12h; ; The decompression pressure is 10mmHG. However, cork was treated at a pressure of 20Kg/cm2 for 6 hours, while hardwood was treated at a pressure of 30Kg/cm2 for 8 hours.
Four. Wood dyeing theory
With the in-depth study of dyeing technology and higher requirements for dyed products, the research of dyeing theory is also developing. In 2000, the author introduced the composition and dyeing process of wood water-soluble dyes, discussed the main factors that had great influence on wood dyeing effect, and put forward some suggestions for the development of wood dyeing industry in China.
1) dye permeability and diffusivity
Because of the large size and deep dyeing depth of wood, the permeability of dyes in wood has become an important factor affecting dyeing. During the period of 1968, Takuro Yokota studied the diffusion mechanism of chemicals in wood, and thought that the transverse channels of dye penetration were the communication systems between conduits, between conduits and wood fibers, between wood fibers and conduits, between wood fibers and parenchyma by means of pits, and local communication channels such as instantaneous gaps between cell cavities and cell walls.
From 65438 to 0975, Yoko Kitamura observed the permeability of more than 60 kinds of acid dyes in wood. It was found that there were great differences in dyeing among tree species. The permeability of dyes in wood is influenced by the microstructure of wood, the molecular size and structure of dyes and the simple interaction between dyes and wood. Dyes with strong adsorption have poor permeability. The longitudinal permeation channel of dye aqueous solution in broad-leaved trees is a capillary system composed of conduits, wood fibers and axial parenchyma in parallel. The process of dye infiltration can be divided into three stages, namely, the diffusion stage of dye to the fiber surface, the adsorption stage of dye on the fiber surface, and the diffusion and infiltration stage of molecules adsorbed on the fiber surface into wood. Dyes that are difficult to diffuse in wood can penetrate into wood well after a period of impregnation under the condition of high moisture content of wood, and solvents such as ethanol are helpful for dye penetration.
198 1 year, Maoshuyata et al. studied the capillary rising and decompression injection of water and dye aqueous solution in hardwood under normal pressure, observed the dyed wood under microscope and measured the permeability. From 65438 to 0989, the relationship between liquid rising height and liquid surface tension in longitudinal capillary of wood was studied.
1993 Zhao Guangjie et al. studied the permeability of dyes in wood, and analyzed the permeability of dye aqueous solution in wood through the relationship between the seepage flow and overflow flow in wood under the action of constant pressure difference. It is found that the inflow rate decreases with time, which is due to the triangular dye adsorption of dye molecules, which makes the effective flow channel smaller and smaller.
2) dyeability
Wood dyeing is done in a certain dyeing process. The so-called dyeing is the process in which the dye is transferred to the fiber and infiltrated into the fiber. With the passage of time, the dye concentration on the fiber gradually increased, while the concentration in the dye solution decreased accordingly. 197 1 year, Yoko kitamura began to study the dye uptake of wood chemical composition and texture. The treated wood flour was dyed with acid dyes, alkaline dyes and direct dyes, and the dyeability of cellulose, hemicellulose and lignin was discussed, and the dyeability of dyed wood was observed by microscope. It is found that acid blue 1 17 has poor dyeability to cellulose and hemicellulose, but good dyeability to lignin and wood flour. Direct blue 1 has good dyeability to wood fibers of hardwood, but poor dyeability to wood rays, conduit walls and perforated plates.
During the period of 1978, a pair of bleached wood was dyed with Song Tian Jane, and the dye uptake of different dyes was analyzed. In 1995, Wu Jingsheng and others used the ratio K/S of light absorption coefficient (k) to scattering coefficient (s) of wood as the main parameter of dye absorption rate agenda, and verified this theory with colorimeter. In 2000, the author systematically studied the main factors affecting the dye uptake of wood dyeing, such as the composition of dyeing solution and dyeing process parameters.
3) light resistance
Dyed wood is easy to change color in use. Therefore, in 1986, Yoko Kitamura studied the light fastness of dyed wood, treated the dyed wood with a light fastness agent and observed their light fastness. The light-resistant agent is 2- hydroxy -4- methoxybenzophenone -5- sodium sulfonate, nitrogen-containing compound, polyethylene glycol malonate and polyethylene glycol # 4000. During the period of 1989, Linping Jingyan used chitosan pretreatment to improve the light fastness of dyed wood, and observed the discoloration of dyed wood under aging conditions such as xenon lamp and natural light. 199 1 year Matsuura also studied the light fastness of dyes. During the period of 1996, Tomoshi Sakuragawa studied the methods from wood bleaching to wood dyeing and the prevention of photochromism of dyed materials. People think that direct dyes can not be dyed in bright areas, but can be dyed in middle and dark areas. Reactive dyes must use auxiliary dyes to improve the dyeability of wood components. In this paper, the methods to prevent the discoloration of dyed materials are put forward, that is, the use of light-fast dyes should be considered first, and then the wood should be acetylated. In addition, we can also use ultraviolet absorbers such as benzotriazole and cerium and light stabilizers such as hindered amine to improve the light resistance of dyed materials.
The development trend of verb (verb's abbreviation) wood dyeing
In the future, we should study wood dyeing technology, technology and equipment from the aspects of dyes and auxiliaries, dye uptake of structure and tissue, and permeability of dye solution, and judge the quality and technology of wood dyeing according to the following standards: (1) Good transparency, good wood grain; (2) Good light resistance; (3) the dyeing effect is uniform; (4) The interior of wood can also be dyed; (5) The dyed veneer has no adverse effect on the subsequent process; (6) Good manufacturability and simple operation; (7) the price is cheap.