Discharge printing is also called engraving. It uses the reducing agent and oxidizer to destroy the background color of the colored fabric (that is, to print on the colored fabric with a discharge agent to destroy part of the pigment that has been dyed) to obtain partial decolorization or color. Printing methods of various patterns and patterns. Because the patterns of discharge printing are more detailed and lifelike, the patterns are rich in layers, plump and gorgeous, the color contrast is strong, the contours are clear and detailed, and the background color is full. China Xuchang Wig Co., Ltd , https://www.hairxuchang.com
The discharge printing process can be roughly divided into two steps, namely dyeing the fabric into a single color first, and then printing the pattern on the fabric. In pattern printing, the printing paste contains chemicals that can destroy the background dye (such as strong bleach, also known as discharge agent), which will destroy the background color during the post-steaming process, so it can be produced by this method. The white dot pattern on the blue background is called white printing. When the bleach and the dye that does not react with it are mixed in the same color paste (the vat dyes belong to this type), the color printing can be carried out. That is, while pulling out the white and destroying the background color, adding a dye that is stable to the dye discharge agent in the anti-dye paste, and the dye is dyed on the pattern of the printing at the same time, you can obtain a colored pattern different from the ground color, namely the color effect. Therefore, when a suitable yellow dye (such as a vat dye) is mixed with a colored bleach, a yellow dot pattern can be printed on the blue base fabric. White printing and color printing can be applied to a pattern at the same time, collectively called discharge printing.
Because the background color of discharge printing is mostly dyed by horse dyeing, if the same background color is printed on the floor, the color of the background color is richer and deeper. This is the main purpose of discharge printing. Discharge printing fabrics can be printed by roller printing and screen printing, but not by thermal transfer printing. Compared with direct printing, the production cost of pull-out fabrics is very high, and it is necessary to be very careful and accurately control the use of the reducing agent required. Fabrics printed in this way have better sales and higher prices. Sometimes, the reducing agent used in this process will cause damage or destruction of the fabric at the printed pattern. If the background color of the front and back sides of the fabric is the same (because it is dyed), and the pattern is white or different from the background color, it can be confirmed as a discharge printing fabric; carefully check the reverse side of the pattern, it will The trace of the original background color is revealed (the reason for this phenomenon is that the chemical agent that destroys the dye cannot fully penetrate the reverse side of the fabric).
Discharge agent is the main solvent used in discharge printing. Discharge agent is a chemical reducing agent, which has the effect of decolorizing the dyeing base. Such as: hanging white block, stannous chloride, etc. This method can be divided into two patterns: white (pulling white) and colored (pulling). The latter dyeing method makes the fabric pattern fine, but the process is complicated and the cost is high. Due to the different conditions, regions and types of printing in various printing and dyeing factories, the additives and processes used in discharge printing are also very different. For example, caustic soda, soda ash, potassium carbonate and other alkaline agents commonly used in discharge dyeing aids have different processes and objects due to different characteristics. Caustic soda is generally suitable for indigo and vat dye printing with slow reduction speed and coarse particles. For example, when vanillin blue is used as caustic soda, its discharge effect is better. The amount of caustic soda is about 10% of the weight of the color paste. Because caustic soda will reduce the stability of the white powder in the color paste, the color paste should not be stored for a long time. Soda ash is suitable for most vat dyes. But its solubility is small, up to 6%. When using soda ash as the alkali agent, the humidity during steaming should be large to ensure the full decomposition of the white powder, which is conducive to dyeing and fixing on the vat dye. The basicity of potassium carbonate is the same as that of soda ash, but the solubility and hygroscopicity are better, especially when it is steamed, it can maintain the wet state, which is conducive to fiber swelling and dye penetration, can make the color bright and full, and can increase the amount of color. The general dosage is 9% -10%, and the dosage ratio of soda ash to anhydrous potassium carbonate is 78: 100. In addition, the alkaline agents used are mixed alkalis, namely sodium hydroxide and potassium carbonate. The amount of alkali agent for vat dyes with anthraquinone structure is higher, and the amount of alkali agent for vat dyes with easy reduction is less, and only 4% to 6% of potassium carbonate is needed.
In discharge printing, for different fabrics, the selected discharge agent is also different. For example, under normal circumstances, rayon fabrics and reactive dyes generally use carved white blocks (hanging white blocks) or Degulin as the discharge agent. The carved white blocks are white blocks or crystalline powder. The scientific name is "formaldehyde hyposulfite. "(NaHSO2 · CH2O · 2H2O). Silk fabrics usually use stannous chloride, while polyester fabrics use "Decolin" as the discharge agent. In addition, sodium hypochlorite can be used as discharge agent for those with low whiteness requirements; acid dyes, disperse dyes and cationic dyes can use stannous chloride as discharge agent; sulfurized and indigo dyes can use oxidant-potassium permanganate or sodium hypochlorite Discharge agent, but there is a need to choose the dye used. Generally, those easy-to-extract azo dyes are used as the base color. Therefore, we must pay attention to the combination of discharge agent and dye, such as the use of acid scarlet C, this dye is not resistant to stannous chloride, so it produces a decolorizing effect. While Chai Linyan Blue 6B is resistant to stannous chloride, the adhesive is usually acrylic.
In discharge printing, the most widely used reactive dyes are white and color. Woven fabrics are generally more white-pulled, while knitted fabric manual plates are more white-pulled and color-pulled. The whitening agent selected is generally carved white powder and Degussa (carved white zinc), and the whiteness is not high, and the only ones that are shallow can also be printed with sodium hypochlorite. After determining the discharge agent, it is the key to choose what kind of paste to meet the requirements of discharge printing. The printing paste must have good water holding capacity and strong resistance to reducing agent. At the same time, it must not react with the reducing agent. Only in this way can the definition and fullness of the outline of the printed product be guaranteed. The main components of the drawing paste DP-1 and the drawing white paste DP-2 are copolymers of polyurethane and acrylate. It has good water holding capacity, the whitening agent does not dilute, the white drawing effect is excellent, and it is easy to use. It can be used for white drawing and printing. It is suitable for rotary screen printing and manual plate printing. After printing, it can be processed by steaming, pressing, high temperature baking, etc., which can achieve the ideal Discharge effect. If it is white, you can add an appropriate amount of whitening agent in DP-2 and mix it to print. If it is white, you can use DP-1 to add an appropriate amount of whitening agent and paint color paste. The process of reactive dye discharge printing is that before discharge, reactive dye dyeing cloth should be selected for easy discharge; after printing, it is best to steam or press on the same day to avoid long-term exposure of the printed surface to the air. Discharge dyeing fails; before steaming and pressing, do not stack the fabrics after discharge printing to avoid sticking of the discharge paste. Even after steaming and pressing, the printed fabric should be cooled and fully It can only be stacked on top of each other after drying; sometimes the main color fades after washing with water. The main reason is that the selected dye and color paste are not suitable. If you use paint color paste, you need to increase the amount of color paste and increase the drying time.
Among the factors that affect the discharge effect, different fabrics have different effects, which should also be paid attention to in the discharge printing. For example, naphthol, color base structure and directness to cotton fibers have a great influence on discharge dyeing. When the color of lake decomposition products is darker and has a greater affinity for cotton fibers, it is difficult to obtain a good whitening effect. The whitening effect is generally determined by naphthol, and the relative stability of the azo component to the reducing agent is different. Although it also affects the whitening effect, it is subordinate to the former. Floating color during dyeing will affect the discharge effect. When there are many floating colors, the discharge effect will be poor. In order to reduce the floating color, it is very important to control the proper coupling ratio of chromanol, color base and appropriate color development conditions, such as controlling the appropriate pH value and adding appropriate penetrants. In addition, the post-treatment should be fully washed with water, but should not be vigorously soaped. Eating oxidant is to dry the fabric padding oxidant after dyeing and before printing. During discharge printing, due to the influence of the reducing agent, the ground color may be damaged to a certain extent during the printing and steaming process. This phenomenon is called relief. Especially the old flower tube, the surface finish is reduced, the color is easy to scratch, and even the ground color will be severely dull or white hair. This relief phenomenon can be prevented by eating oxidants.
In addition, pay attention to the following points in discharge printing:
(1) The paste used for discharge printing must have certain acid resistance, adjuvant resistance, good storage stability and easy paste removal. Moreover, it is required to have good permeability, uniform printing, and clear outline; after printing the discharge dye, the fabric should be fully dried to prevent color matching.
(2) After printing, the fabric should not be stored for a long time, and should be steamed in time. If the steaming is insufficient at one time, it can be re-steamed once to effectively improve the discharge effect.
(3) Dyeing printing should use dyes with better whitening effect as much as possible. If necessary, some dyes with medium whitening effect can be used to adjust the color light. Dyes with poor whitening effect should not be used.
(4) After the discharge printing fabric is steamed, it should be fully washed and soaped to improve the printing effect of the discharge printing. This is an important factor affecting the whiteness of discharge.
(5) The design of the manuscript should consider the characteristics of discharge printing and design the pattern. Generally speaking, the patterns suitable for discharge printing include large-area deep color printing, fine white flowers and some complex patterns.