Application of pH value in textile printing and dyeing

In the production process of home textiles, especially in the printing and dyeing process, the pH value has a wide and important role. The following production processes are divided into refining, bleaching, dyeing, printing and finishing.

Refining

The wax on the cotton fabric is not easy to interact with caustic soda, and it must be removed by emulsifying it with an emulsifier (soap). The emulsification should be carried out in an appropriate pH range.

Removal of silk sericin should be refined by soap alkali, but the alkalinity should not be too high, otherwise it will affect the feel and gloss. The suitable pH for silk refining is 9.5~10.5. The applications of real silk in home textiles include headscarves, handkerchiefs, bedding, silk batik (tie-dye), and decorative accessories (such as tassels and colorful ears).

After being carbonized, wool should undergo alkaline scouring to remove fat, but wool is a protein fiber. In order to prevent damage to amino acid structure and prevent rough hand feeling, the scouring pH value should be controlled. The pH value is generally controlled at 10~10.5. Wool is an important raw material for home textiles such as hand-knitted carpets, blankets, and artistic wall hangings. In recent years, the use of wool can be made into bedding, which has opened up new ways for wool in the field of home textiles.

The alkali reduction of polyester fabric is an important production process of polyester printed silk scarves. The key to the alkali reduction process is the control of the concentration of caustic soda. If the alkali concentration is too low, the effect of imitating silk is not good, and the drape is not obvious; if the alkali concentration is too high, the strength of the fabric will be damaged and cracks will occur.

Bleaching aspect

Hydrogen peroxide is a commonly used bleaching agent for cotton bleaching. The optimum pH value for bleaching is 10.5~11. At this pH value, hydrogen peroxide can slowly decompose, play an oxidative bleaching effect, remove the pigment on cotton fabrics, and will not cause serious cellulose fiber strength. decline.

For sodium hypochlorite bleaching, the pH value should be controlled at 8.5~10, and for sodium chlorite bleaching, the pH value should be controlled at 3.5~4. However, these two bleaching agents can cause adsorbable organic halide (AOX) problems, so they are gradually eliminated .

For dyeing

Vat dye dyeing: Vat dye dyeing is often used in yarn dyeing of yarn-dyed handkerchiefs and yarn-dyed towels. Vat dyes are water-insoluble dyes. The dyes themselves have no affinity for fibers and cannot be dyed directly. They must be dissolved into sodium salt of leuco body with caustic soda and sodium hydroxide. The pH value depends on the depth of the color, according to the change from light color to dark color, the corresponding change in the range of 12 to 13.5.

Dyeing with insoluble azo dyes: When dyeing with insoluble azo dyes, the control of the pH value of the color developing solution is very important. If the pH value is too high, the color will be fast, and the color will not be fast; the pH value is too low, the color will be slow, the color will be light, and the pH value Generally controlled within 3.5~4.5. However, the color development pH of Van Laming Blue should be higher and should be controlled between 6.5 and 7.0. It should be noted that although insoluble azo dyes have played an important role in the history of home textiles production, because their color base contains many carcinogenic aromatic amines, the gas released by the diazotization of the color base is harmful to the health of the operator and has tended to Eliminated.

Cationic dye dyeing: The PH value of cationic dye dyeing should be controlled at 4.5~5, and the pH buffer solution should be composed of acetic acid and sodium acetate. In the production of home textiles, cationic dyes are used in all dyeing involving the use of acrylic fibers, such as the dyeing and printing of acrylic carpet materials, the dyeing and printing of acrylic artificial fur used in pillows, and the acrylic fancy yarns used in curtains and sofas. Dyeing, electrostatic flocking acrylic flock dyeing, etc.

Acid dye dyeing: acid dye dyeing, the change of the pH value of the dye bath has a great influence on the dye uptake rate and dye uptake rate. Generally speaking, the more acidic the dyeing bath is, the faster the dyeing will be, and the more the dye solution will eventually absorb the color. However, if the acidity is too strong, it is easy to cause uneven dyeing and poor hand feeling. For specific dyeing, different pH values are used depending on whether strong acid dyes or weak acid dyes are used. Strong acid dyes have a pH value of 3-4, and weak acid dyes have a pH value of 5-6. For silk, wool, Acid dyes are used for printing and dyeing of home textiles made of nylon, such as real silk bedding, silk headscarves, mulberry silk and tussah silk thread, wool carpet wool, blanket wool, cotton and nylon interwoven imitation peach skin, etc.

After finishing

Fluorescent whitening: Cotton cloth is fluorescently whitened, and the pH value is generally slightly alkaline, and the pH value is generally 8-9; for polyester fluorescent whitening, the pH value is required to be slightly acidic, and the pH value is generally 5-6.

Anti-wrinkle and non-iron finishing: Tartaric acid and magnesium chloride are often added as catalysts in the anti-wrinkle and non-iron finishing liquid. Tartaric acid is an acidic substance, and magnesium chloride is heated to decompose acidic hydrogen chloride with catalytic effect. The presence of these acidic substances not only affects the strength of the cellulose fiber fabric, but also causes the pH of the fabric to drop. After anti-wrinkle and non-iron finishing, it is generally not washed in water.