Development and Application of Environment-friendly Discharge Printing Paste

Discharge printing is one of the three types of fabric printing methods (direct printing, discharge printing, and anti-ink printing). Traditional discharge printing is mainly aimed at woven fabrics, a large area of ​​color, and a bright color, a unique style of fine patterns, it is difficult to achieve results with direct printing methods, and come with discharge printing.

The earliest dyeing and printing (1950s of the last century) was the printing of dragons and phoenixes on the large red, red jujube, and deep indigo colors on the basis of twill weave fabrics. It was the favorite quilt for the people in North China, Northwest China, and Northeast China. Flower cloth. The use of vat dyes (printing paste) to pull insoluble azo dyes (ground color), whitening paste is mainly used for white powder, caustic soda and printing glue starch mixed paste.

Early silk fabrics were dyed and printed, ground dyes were made of simple azo acid dyes, direct dyes that were not resistant to reducing agents, and the printing dyes were triarylethanes with antireducing agents, acid dyes with lanthanum structures, and whitening. The slurry is mainly stannous chloride, acetic acid, urea and white dextrin wheat starch paste.

In the 1970s, rayon fabrics were dyed and printed, ground dyes used direct dyes with azo structures, large reds used insoluble azo dyes or reactive dyes, printing dyes used vat dyes, and white pulps were mainly glaucous white and modified starch pastes. material.

Polyester fabrics (including polyester silk fabrics of artificial silk), ground dyes using disperse dyes (fixed without heating), printing dyes also use disperse dyes (resistant to stannous chloride reductant), and whitening paste is mainly used for chlorination. Stannous or added tin, oxalic acid, urea, and chemically modified vegetable gums or starch mix pastes.

These are the traditional discharge printing on the cloth, printing steam fixed after all need to be washed, soaping, in order to obtain bright color, complex process. With the continuous development of paint printing adhesives, the performance of adhesives is getting better and better, and more and more varieties are being used. At the same time, the electrolyte resistance and stability of paint pastes are getting more and more perfect. Color pastes are basically paint pastes. For example: Cotton fabrics are dyed with reactive dyes, and then the paint is used to discharge printing paste. Silk fabrics are dyed with acid dyes or reactive dyes, and they are also discharged with paint. The indigo dyeing and printing of denim is also used to discharge the printing paste with a coating. The whitening paste uses an oxidizing discharge agent, ie, sodium chlorate, citric acid, urea and an acid-resistant paste.

The printing on these cloths, however, uses a paint discharge printing paste, but most of its discharge agents use a white powder containing formaldehyde or Dekolin, or an environmentally friendly additive. Therefore, after discharge printing, it is generally required to be washed to remove the free formaldehyde and the environmentally unfriendly discharging agent from the fabric.

The printing process on garments (garment) is generally: garment (garment) printing - pressing (160-170°C10-20′′) or drying (165°C1′) is completed without washing and Soaping process: Previously printed (dark), dark-colored, and red-colored pieces of clothes (clothes) are printed with light-colored (or white) fine patterns, all of which are printed with glue, and the glue printing process is simple and covered. The force is good and it is suitable for the printing of clothes pieces, but the feel and style of the printed fabric are completely different from the effect of the discharge printing.

If the printing paste is applied to the clothing (garment) with a coating, it can also achieve the same effect as cloth discharge printing. The problem is that the clothing is not washed and soaped after printing. Otherwise, it is necessary to use a discharging agent (reducing agent) that does not contain free formaldehyde, and does not contain environmentally friendly additives. It is also necessary to choose a binder that can quickly form film and not easily block the web, which is suitable for the fast pressing process conditions of the garment, namely, an environmentally friendly discharge printing paste. Both at home and abroad are under research and development and production, but the collected samples have been tested and the discharge results are not satisfactory.

First, the choice of discharge agent

Knitted round-neck t-shirts are generally pure cotton fabrics and are dyed with reactive dyes. There are currently three methods for dyeing and printing of reactive dyes: reducing agent method, sodium sulfite anti-discharge method and special discharge agent DK-TN discharge dyeing Method (Oxidant method can currently only print on the indigo dye denim). Among them, sodium sulfite anti-discharge method and special discharge agent DK-TN discharge method are reactive dye printing pulp to extract reactive dyes to color, which is suitable for cloth discharge printing. The paint discharge printing paste on Yuyi (clothing) can only be a reducing agent method.

The mechanism of discharge printing and dyeing of reducing agent is as follows: after dyeing and fixation of vinylsulfone reactive dye, it chemically bonds with the fiber to form ether bond. The ether bond is very sensitive to alkali, and the ether bond breaks under the action of alkali reducing agent. . The ground color decomposition products that have been broken and destroyed are easily dissolved in an alkaline solution.

Therefore, the reducing agent is the main additive for the discharge printing. The reducing agent that can be used in the discharging printing paste is the inorganic reducing agent and the organic reducing agent:

(I) Inorganic Reducing Agents

1, insurance powder, scientific name: sodium hyposulfite, white fine grain crystals, there is a strong irritating sour, there is a strong ability to restore.

2, sodium sulfite, white powder, reducing.

3, stannous chloride, also known as tin dichloride, colorless crystals.

4, sodium bisulfite, scientific name of sodium bisulfite, sulfur dioxide odor of white crystals.

5, sodium thiosulfate (commonly known as soda), colorless crystals.

6, bleaching hair powder (60% insurance powder and 40% sodium pyrophosphate mixture) white powder.

(B) Organic Reducing Agents

1, Rong white powder (C · I · reducing agent 2), chemical name sodium formaldehyde sulfoxylate (NaHSO2 · CH2O · 2H2O). The white powder has a strong reducing effect under high temperature and is easily deteriorated by moisture, resulting in bad odor.

2, formaldehyde zinc sulfoxylate salt (commonly known as De Kelin), there are two kinds of primary salt and secondary salt:

Primary salt (C·I·Reductant 6), water-soluble zinc salt white powder

Secondary Salt (C·I·Reductant 4), insoluble zinc salt white powder

3, Insoluble white powder calcium salt (C · I · reducing agent 12)

4, thiourea dioxide (C · I · reducing agent 11), trade name: Manofast (Mamofast) its different confinement is formazan sulfinic acid,

5. Biting agent W, scientific name: Dimethyl phenyl benzyl ammonium chloride disulfonic acid calcium salt

6, bite white agent O, scientific name: dimethyl phenyl benzyl ammonium chloride

7. Dissolved salt B, scientific name: Sodium benzylaminobenzenesulfonate, which acts as a hydrogen-inducing agent during discharge printing.

8. Barium, light yellow needle crystals, insoluble in water, large hydrogen-inducing effect during discharge printing.

9, glucose, white crystal, soluble in water, the molecule has an aldehyde group, it is reductive.

The basic composition of the paint discharge printing paste is discharge agent (reducing agent), adhesive and hygroscopic agent. Therefore, the choice of reducing agents, adhesives and hygroscopic agents and other additives must have good compatibility. Inorganic reducing agents are generally strong electrolytes and have strong reduction properties. They can be used as discharge agents for discharge printing pastes (reducing dyes). However, if you want to use as a coating to discharge printing paste, it must be carefully screened, the reducing agent is good compatibility with the adhesive, the current general polyacrylic adhesive emulsion, in case of strong electrolyte can easily cause chaos, condensation.