Pre-treatment of grey cloth printing and dyeing

Pretreatment: generally refers to the scouring process of grey cloth

Grey cloth needs to be sizing when weaving, and pectin and lignin will be on cotton yarn. In addition, chemical fiber cloth also has oils, which will affect the subsequent bleaching and dyeing effects, so it needs to be removed by scouring. Because it is at the forefront of all printing and dyeing processes, it is referred to as pretreatment.

During the weaving process of woven fabrics, the warp yarns are subject to greater tension and friction, and are prone to breakage. In order to reduce warp breakage, improve weaving efficiency and grey fabric quality, the warp yarn needs to be sizing before weaving to enhance fiber cohesion and form a firm sizing film on the yarn surface to make the yarn tight and smooth, so that the Improves yarn breaking strength and abrasion resistance.

Desizing is to remove the sizing and impurities on the grey fabric and improve the dyeing performance. The sizing rate of woven fabrics is related to fiber quality, yarn count, density, and loom type, generally 4%-8%. The thread fabric can be unsized or the general rate is less than 1%. Tight woven fabrics (such as Poplin) sizing rate can reach 8%-14%. In recent years, the warp sizing rate of high-speed looms has exceeded 14%.

The general rule of sizing rate: the finer the yarn count and the higher the density, the higher the warp sizing rate; the air-jet loom requires a higher sizing rate than the ordinary loom. The pulp used can be divided into natural pulp (starch, sodium alginate), modified pulp (soluble starch, carboxymethyl cellulose), synthetic pulp (polyvinyl alcohol PVA, polyacrylate PA). The existence of the size on the original cloth is not conducive to the subsequent scouring and bleaching processing. The desizing process is the basis for the pretreatment of woven fabrics. This process can remove most of the pulp on the original fabric to facilitate scouring and bleaching, and can also remove some natural impurities.

Desizing method: There are many commonly used desizing methods, such as enzyme, alkali, acid and oxidant desizing, etc. The appropriate desizing method can be selected according to the variety of the original cloth, the composition of the slurry, the desizing requirements and the factory equipment. After desizing, it must be washed with hot water in time, because impurities such as starch decomposition products will re-condensate on the fabric, which will seriously hinder the subsequent processing.

Alkali desizing principle: Under the action of hot caustic soda, starch and chemical pulp undergo strong expansion, and the adhesion to fibers becomes loose, changing from gel state to sol state, and the solubility of chemical pulp in hot alkali increases. , It is easy to wash off the fabric, and the hot caustic soda solution can remove some natural impurities, especially suitable for cotton cloth with more cottonseed husks. Most of the alkali used for desizing is scouring or mercerizing waste alkali, which is low in cost and does not damage fibers, so this process is widely used in printing and dyeing plants. The desizing rate of alkali desizing is about 50~70%, and the remaining pulp can only be further removed during scouring.

Alkali desizing features: low cost, can use waste lye in pretreatment; help cottonseed hull remover to remove part of fiber symbiotically, reduce refining burden, good whiteness and permeability; The disadvantages are: the desizing rate is not high, the stacking time is long, which hinders the continuous production; the alkali has no chemical degradation effect on the PVA slurry, the viscosity of the washing liquid is large, and the washing should be sufficient to prevent the slurry from re-staining the fabric. In the pretreatment of polyester and cotton fabrics, printing and dyeing enterprises mostly use the traditional process of continuous de-scouring and bleaching. The commonly used equipment is de-scouring and bleaching combined machine. The chemicals mainly include caustic soda, surfactants, hydrogen peroxide, etc. The production requires high temperature conditions. There are problems such as long process flow and high processing cost, especially the cost of water, electricity and steam. In view of the shortcomings of the traditional pretreatment process, Huafang Co., Ltd. tested the pretreatment process of polyester-cotton fabrics by low-temperature cold stacking, and applied it to the workshop production, which reduced the cost by more than 35% and achieved ideal results.

The so-called cold heap dyeing means that the fabric passes through the pad dyeing solution and alkali solution at low temperature, and the dyeing solution is adsorbed on the surface of the pure cotton fabric fiber by rolling and padding, and then rolled and stacked, and stacked at room temperature for a certain period of time ( Bonding time) and rotate slowly to complete the dye adsorption, diffusion and color fixing process, and finally wash with water to complete the dyeing method. The process includes three stages: padding working fluid, stacking and color fixing, and water washing.

Finishing after printing and dyeing of grey fabrics

1. Divide the strips into pieces, divide the fading, and roll them according to the fading packaging.

2. When rolling, both ends of the board should be neat, the packaging material should be firm, and pay attention to the number of rolls. Labels, girdle seals, stick to the right place according to customer requirements, and the content is accurate. Rolling at fixed length, rolling in the original natural section, pay attention to cutting off the head part, it is not easy to hit the inside of the roll. When loading the cabinet, the packaging materials should be installed together at multiple spare points, and the damage is convenient for customers to replace.