All Cotton Dyeing Technology

1) refining and bleaching: Natural

They all contain impurities, in the process of textile processing, the addition of the various slurry, oil and contaminated dirt, the presence of these impurities, not only hinders the smooth process of dyeing and finishing, but also affects the wear performance of the fabric.

The purpose of scouring and bleaching is to remove impurities from fabric by applying chemical and physical mechanical functions, so that the fabric is white and soft, and has good penetrability to meet the requirements of clothing and prepare for dyeing and printing.

The main processes of scouring and bleaching of pure cotton fabric are: raw cloth preparation, singeing, desizing, scouring, bleaching and mercerizing.

1) raw cloth preparation: original cloth preparation includes cloth inspection, flip cloth (batch, sub box, printing) and sewing head.

The purpose of the original cloth inspection is to check the quality of the grey cloth and find that the problem can be solved in time.

The inspection includes two items: physical indicators and appearance defects.

The former includes the length, amplitude and weight of the original cloth, density and density of warp and weft yarns, and so on, such as spinning defects, weaving defects, various class stains and breakage.

Usually check about 10% of the total.

After the original cloth inspection, the original cloth must be distributed in batches and divided into boxes, and printed on the cloth heads, indicating the varieties, processing technology, batch number, box number, date of issue and the code number of the cloth breaker, so as to facilitate the management.

In order to ensure continuous batch processing, the original cloth must be sewn.

2) singeing: the purpose of singeing is to burn the fuzz on the cloth to make the cloth clean and beautiful, and to prevent dyeing defects and printing defects due to the presence of fuzz in dyeing and printing.

Fabric singeing is the rapid propagation of fabric through a high temperature flame, or the rubbing of a red hot metal surface. At that time, the floss on the cloth quickly rises and burns, and the cloth is relatively tight, and the temperature rises slowly. When it does not reach the ignition point, it has left the surface of the flame or red hot gold, so as to achieve the purpose of burning down the wool and not operating the fabric.

3) desizing: in order to smooth weaving, textile mills often use warp sizing to enhance strength and wear resistance.

The size of the fabric on the grey cloth affects the water absorption of the fabric, and also affects the quality of the dyeing and finishing products, and increases the consumption of dyeing chemicals. Therefore, the slurry should be removed before scouring, which is called desizing.

The slurry on cotton fabric can be removed from the fabric by alkali desizing, enzyme desizing, acid desizing and oxidizing agent desizing.

Alkali desizing increases the size of the pulp, decreases the adhesion to the fiber, and washes away from the fabric by washing.

Enzymes, acids and oxidants degrade starch and increase the solubility in water, which is washed away by water.

Because acid and oxidant are very harmful to cotton fiber, they are seldom used alone. They are often used in combination with enzyme desizing and alkali desizing.

4) cooking:

When growing, there are natural impurities (pectin, waxy substances, nitrogenous substances, etc.) associated with it.

After desizing, most of the pulp and some natural impurities have been removed, but a small amount of slurry and most of the natural impurities remain on the fabric.

The presence of these impurities makes the fabric of the cotton cloth more yellow and poor in permeability.

At the same time, because of the existence of cottonseed hull, the appearance quality of cotton cloth is greatly affected.

Therefore, the fabric needs to be scoured for a long time in high temperature concentrated lye to remove residual impurities.

Scouring is to use caustic soda and other scouring agents to react with pectin, waxy substances, nitrogenous substances and cottonseed husks to produce chemical degradation or emulsification and expansion. After washing, impurities can be removed from the fabric.

5) bleaching: after the cotton fabric is scoured, its appearance is not white enough because of its natural pigments, and its dyeing and printing will affect the brightness of the color.

The purpose of bleaching is to remove pigment, give the fabric the necessary and stable whiteness, and the fiber itself is not significantly damaged.

The usual bleaching methods for cotton fabrics are sodium hyaluronate, double oxygen water and sodium chlorite.

The bleaching liquid of sodium hypochlorite bleaching liquid has a pH value of about 10, which is carried out at room temperature. The equipment is simple, easy to operate and low in cost, but it has great damage to fabric strength and low whiteness.

Hydrogen peroxide bleached with a pH value of 10, bleached at high temperature, bleached fabrics with high whiteness and stability, good handle, and removal of slurry and natural impurities.

The drawback is that the equipment requirements are high and the cost is high.

Under suitable conditions, combined with caustic soda, desizing, scouring and bleaching can be completed at one time.

The bleaching liquid of sodium chlorite bleaching liquid is 4 to 4.5. It has advantages of good whiteness and little damage to fiber at high temperature. However, bleaching is prone to produce toxic gas, pollute the environment, corrode equipment, and the equipment needs special metal materials, so it is limited in application.

Dechlorination should be carried out after bleaching of sodium hypochlorite and sodium chlorite, in order to prevent the fabric from being damaged due to the presence of residual chlorine in the course of existence.

6) mercerization: mercerization refers to the processing of cotton fabrics treated with concentrated caustic soda at room temperature or low temperature under tension in the warp and weft directions, so as to improve the fabric performance.

After the mercerization of the cotton fabric, the natural torsion of the fibers disappeared, and the cross section was elliptical, which led to a more regular reversal of the light and enhanced the luster.

The increase of the invisible zone determines the dye uptake.

The improvement of orientation improves the strength of fabrics, as well as the shaping effect.

After mercerizing, the caustic soda must be used to remove caustic soda, or to remove alkali from the steamer.

2. dyeing and dyeing is based on the combination of dyes and fibers to produce physical or chemical combination or chemical method to produce pigment on the fiber, so that the entire textile has a certain color process.

It is carried out under certain conditions such as temperature, time, pH and auxiliaries.

Dyed products should be uniform in color and need to have good color fastness.

The dyeing methods of fabrics are mainly dip dyeing and pad dyeing.

Impregnation is a method of immersing fabric in dye solution and gradually dyeing dyestuffs.

It is suitable for small batch and multi variety dyeing.

Rope dyeing and rolling dyeing belong to this category.

Pad dyeing is to first immerse the fabric in the dye solution, then pass the fabric through the roll, and evenly dye the dye into the fabric, then steam or melt it.

It is suitable for dyeing large quantities of fabrics.