What is the pre-processing and bleaching process?

2.1 Preparation of original fabric

The original fabric preparation includes original fabric inspection, fabric turning and seaming head. The purpose of the original fabric inspection is to check the quality of the grey fabric and solve the problems in time. The inspection content includes physical indicators and appearance defects. The former includes the length, width, weight, warp and weft yarn density and density, and strength of the original fabric, and the latter includes spinning defects, weaving defects, various stains and breakages. After the original fabric inspection, the original fabric must be divided into batches, and the type should be printed on the cloth head for easy management. If you produce in your own factory, you can omit the inspection of the original fabric, and the weaving factory will inspect the above items.

In order to ensure continuous batch processing, the original fabric must be stitched together. The pins at the joint should not be too dense or too thin. Too dense will easily cause joint marks when rolling, and too thin will easily break the cloth.

2.2 Bristles, singeing

The purpose of singeing is to burn off the fluff on the cloth surface to make the cloth surface smooth and beautiful, and to prevent uneven dyeing and printing defects due to fluff during dyeing and printing. Fabric singeing is to pass the open width of the fabric quickly through the high temperature flame. The singeing opening usually has two positives and two reverses, which can be selected according to the thickness of the fabric. Generally, one positive and one reverse of a thin cloth can be used. Thick cloth needs two positives and two opposites. anti.

At this time, the fluff existing on the cloth surface quickly heats up and burns, and the cloth itself is tighter and heats up slowly. Before reaching the ignition point, it has already left the flame, so as to burn the fluff without burning the fabric. the goal of.

2.3 Desizing

In order to smoothly weave fabrics, textile mills often sizing warp yarns to improve strength and abrasion resistance. The slurry on the grey fabric not only affects the water absorption performance of the fabric, but also affects the quality of dyeing and finishing products, and will increase the consumption of dyeing chemicals. Therefore, the slurry should be removed before scouring. This process is called desizing.

The size on the fabric is usually PVA starch slurry. Its characteristic is that it is easily soluble in hot water above 80℃, so most of the size can be removed before scouring. PVA size is difficult to degrade and easy to cause. For environmental pollution, the slurry from the hot water can be collected together for recycling. The recycled PVA can continue to be used in the weaving factory. The PVA recycling device can reduce the pressure of sewage treatment and save costs.

2.4 Cooking

When cotton fiber grows, it is accompanied by natural impurities (pectin, waxy substances, nitrogenous substances, etc.). After the cotton fabric is desizing, most of the size and some natural impurities have been removed, but a small amount of size and most of the natural impurities remain on the fabric. The presence of these impurities makes the surface of the cotton fabric yellowish and poor in permeability. At the same time, it greatly affects the appearance quality of the cotton cloth.

Therefore, the fabric needs to be scoured under the action of high-temperature concentrated lye and some auxiliary additives to remove residual impurities. Scouring is the use of caustic soda and other scouring aids to react with pectin, waxy substances, nitrogen-containing substances, cotton seed hulls for chemical degradation, emulsification, puffing, etc. The impurities are removed from the fabric after washing.

2.5 Bleaching

After the fabric is scoured, because there are natural pigments on the fiber, its appearance is not white enough. It is used for dyeing or printing, which will affect the vividness of the color. The purpose of bleaching is to remove pigments and impart necessary and stable whiteness to the fabric, while the fiber itself is not significantly damaged. Commonly used bleaching methods for cotton fabrics are the hydrogen peroxide method and the sodium hypochlorite method.

Usually the factory uses hydrogen peroxide for bleaching. The chemical solution has a PH value of about 10. When bleached at a high temperature, the bleached fabric has high whiteness and stability, good hand feeling, and can also remove pulp and natural impurities. The disadvantage is that it requires high equipment and high cost. Under proper conditions, combined with caustic soda, desizing, scouring and bleaching can be completed at one time. Bleached fabrics give the following processes a uniform whiteness and water absorption performance, and better control the leveling effect of dyeing or whitening fabrics.