Basic requirements for the development of wood-based panel colorants

Wood-based panel coloring can give the product a variety of special functional logos, and help to improve the appearance of the product color, making it more beautiful and bright, uniform color and harmony, and play an effective decorative role. In recent years, various wood-based board colorants have appeared on the market, and the quality and performance are very different, and the coloring effects are also different. In the process of developing wood-based board colorants, the following aspects should be solved.

1. Dyeing (yan) material selection

After determining that the product uses a certain color, it is first necessary to select an appropriate dye or pigment, which can be formulated with a single dyeing material or by two or more different types and colors of dyeing. The correct choice of dyeing materials requires a deep understanding of their basic properties and the coloring properties of wood and its fibers.

Factors such as environmental protection, process adaptability and price should be considered when selecting dyeing materials. Dyeing (pigment) materials that have been banned from use in the textile industry at home and abroad must not be used. From the point of view of environmental protection, the dyeing materials allowed in the textile industry should be universal in the wood-based panel industry. We do not have to put forward more stringent requirements. Of course, except for special circumstances, for example, wood-based panels for food packaging should impose more stringent requirements.

The issues to be considered in terms of process adaptability are more complicated. First of all, it is necessary to consider the coloring ability of the selected dyeing materials for wood or wood fibers. Those dyeing materials which cannot or are difficult to color cellulose fibers are impossible or difficult to obtain a firm color. Secondly, the selected dyeing material must be able to be adjusted to a higher concentration solution. Because they are used in small amounts, generally 0.1 to 0.3% of dry fiber, if they are directly used, they cannot be uniformly dispersed throughout the coloring matter. Furthermore, the coloring conditions must be in accordance with the process conditions for the production of wood based panels. The conditions for coloration during the production of wood-based panels (especially fiberboard and particleboard) are significantly different from those for textile dyeing. The colorant in the production of wood-based panels is incorporated into the glue or applied directly to the wet fibers, and it is not possible to be immersed in a bath with a large color liquid like textile dyeing. The compatibility of colorants with adhesives is a key technical issue. The color of the dyeing material is related to the pH value of the medium, and the dyeing must also be in a certain pH range. This range must be consistent with the value required for the production of wood-based panels, otherwise it will affect the performance of the rubber, especially Applicable period and curing time. This is the pre-requisite for selecting wood-based board colorants. For example, acid dyes and cationic dyes generally require dyeing under acidic conditions. Although this is consistent with the curing conditions of urea-formaldehyde resin adhesives, the adaptation period of the urea-formaldehyde resin adhesive after coloring must meet the production requirements, otherwise To bring trouble to production. The price of the product is one of the decisive factors of sales. It must be considered when selecting the dyeing material. Those dyeing materials with high dosage and high price cannot be included.

2. Preparation of solution

After selecting a good dyeing material, it needs to be formulated into a solution, which is convenient to use. The better the pigment dispersion, the higher the dyeing efficiency and the better the uniformity. To prepare a solution, first consider the solvent. Of course, water is the best solvent, but many dyes are poorly water-soluble. Even those dyes that are well-soluble in water are far from satisfactory in water. If it is adjusted into a very dilute solution, it will cause great troubles for transportation and use, especially when it is used in the rubber, it is necessary to reduce the viscosity of the glue. Therefore, it is necessary to choose a good solvent or a mixed solvent. The requirements are as follows: the dosage is as small as possible, environmentally friendly, safe, and the price is acceptable.

If many cationic dyes and basic dyes are dissolved in glacial acetic acid, it will have a series of negative effects. First, it is incompatible with urea-formaldehyde glue. For example, after the green color dissolved in glacial acetic acid is mixed into the urea-formaldehyde glue for the fiberboard, the adaptation period is only 1 hour in summer, which is unacceptable.

3. Performance improvement

Any dye (paint) material may not fully meet the above requirements, but can be adjusted and improved by various additives. Textile auxiliaries have long been a specialized industry, and of course the textile industry has to be used in the development of artificial colorants. However, as noted above, the production of wood-based panels has its own particularities, and some special conditions are rare in the textile industry. In addition to the ones mentioned above, there are other special restrictions. The hot pressing temperature in the production of wood-based panels is a key process parameter, generally above 170-180 ° C, but the highest hot pressing temperature of modern fast continuous presses can reach above 240 ° C. Due to the limitations of hot pressing and high temperature conditions, many dyes that are considered excellent in the printing and dyeing industry cannot be used in the production of wood-based panels (including decorative paper). Of course, during the hot pressing process, the temperature inside the board, especially the core layer, may exceed 100 ° C for a short time, but it is a serious consideration for the surface layer, because the high temperature resistance of many dyes does not meet the requirements, causing surface fading. This increases the difficulty of sanding and the loss of sanding, and also affects the beauty of the surface color. However, it is regrettable that the textile industry has limited experience in improving the thermal stability of dyes.

4. Basic direction of development

There are few things that are perfect, and they often say: There is no best, only better. Only in the process of development research and actual use, continuous improvement, continuous improvement, in order to be better.

The effect is better, the process is more simplified, and the cost is lower, which is the development direction of the artificial board coloring agent.

Source: "Wood-based Panel Communication" Author: Tim Liu, Lei was given

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