Printing is actually a local dyeing, so the fixation principle of the dyes used in printing is similar to that of dyeing. However, printing emphasizes pattern effects, and in large-scale production, the printing process has the following characteristics:
(1) Printing takes the original paste as the medium. In order to stabilize the pattern and prevent pattern infiltration during the printing process, nearly half of the original paste should be added to the printing paste; The medium of dyeing is usually water.
(2) It is often necessary to add a cosolvent to the printing paste. Due to the requirement of thick printing paste and the small amount of water used, it is difficult to dissolve the dye. It is often necessary to add cosolvents such as urea and dissolved salt B.
(3) Short fixation time and high temperature. The process of dyeing fibers with printing dyes at high temperatures is called steaming. The dyeing process of printing dyes requires several processes: "size film moisture absorption and expansion → dye re dissolution → dye transfer → dye dyeing", and the entire steaming process should not take too long, otherwise the clarity of the pattern outline will be affected. Therefore, high-temperature means such as steam and baking are often used in production to accelerate the diffusion rate of dyes, help dyes dye fibers, and shorten steaming time. Generally, the dyeing time of the dye cannot exceed 40min, and the temperature is not lower than 100 ℃.
(4) Dyes need to be screened. Printing is local dyeing. When using the same type of dyes on the same fabric, printing and dyeing principles are the same, reflecting consistent color fastness, but not all dyes can be used for printing. Due to the stability requirements of printing patterns, color pastes, and the particularity of steaming and washing environments. Printing requires different dyeing requirements than dyeing. Generally speaking, printing dyes should have good solubility, stability, color fastness, and less direct impact on fibers; When anti discharge printing, it is also required that the dye have anti discharge property or anti discharge property; Dyes used for co printing or paste printing should have good compatibility.
(5) High requirements for pretreatment of semi-finished products. This is mainly reflected in three indicators: whiteness, instantaneous wool effect, and weft skew. For direct printing processes, in order to make the white ground clean and highlight the bright colors of flowers, it is often required that semi-finished products have a good whiteness, especially in the discharge resistant printing process; Secondly, the printing process takes a short time, requiring uniform color, clear outline, smooth lines, and no broken stems. Therefore, semi-finished products should have a good capillary effect, especially a good instantaneous capillary effect, and the capillary effect should be uniform, so that the fabric can quickly absorb color paste and reduce defects such as paste generation; Due to the existence of patterns, the printing effect has the characteristics of irreparable, so it is required that the weft slope of semi-finished products must be low to ensure that the printing pattern is regular.
(6) High washing requirements after printing. Unlike water washing after dyeing, after printing, the original paste should be removed through water washing to restore the feel of the fabric and remove floating colors to improve the color fastness of the product. Dyed products require uniform color, while printed products require clear ground flowers, bright colors, and clear outlines. During the post press washing process, the floating colors of different colors of dyes are washed off and enter the washing liquid together, which can easily cause white stains on the fabric and impure designs, namely, staining. Therefore, the key points of quality control in water washing are to strengthen water washing, remove the original paste and floating color, prevent water washing from staining, and protect the strength of the fabric.
(7) The printing process is long. The general process flow for fabric printing is:
Pattern Design → Color Separation and Drafting → Plate Making
Fabric pretreatment → printing → drying → steaming → washing → finishing → finished product
Imitation color proofing → Preparation of color paste
Therefore, engaging in printing work has characteristics such as wide range of knowledge, high technical content, great difficulty in quality control, and strong challenges. Printing workers must have strong quality awareness, rigorous work attitude, high overall perspective, and excellent professional theory and professional skills.