Pretreatment of polyester cotton blended fabric
The physical chemical properties of polyester fiber cotton fiber are different. In dyeing finishing, both should be taken into account, the corresponding process should be adopted when the fiber blending ratio is different. At present, the polyester cotton blended fabric is based on the cotton fabric dyeing finishing process, the process flow equipment installation route are generally similar, so some inconveniences are brought, which are described below.
1. Preparation of raw cloth
2. singeing
The pretreatment process of cotton fabric is first singeing, then back sizing scouring. Although the burnt wool is also listed before the desizing of polyester / cotton fabrics, it may bring disadvantages. For example, the polyester fiber has been burnt out in time, forming small solution beads scattered on the surface of the fabric due to high heat, which will cause color spots when dyeing with some disperse dyes; polyester / cotton fabrics are usually sized with PVA size, PVA is used when desizing after the high temperature effect of singeing It is difficult to get rid of, the oil stain on the fabric will also be fixed, which will affect the whiteness of the fabric. However, due to the smooth process of grey cloth singeing, convenient management low cleaning requirements of singeing machine, except for singeing after scouring bleaching of some bleached polyester / cotton varieties singeing after dyeing of some deep color cards, grey cloth singeing is still feasible. When singeing, the temperature of the cloth body is required to be lower than 180 ℃, if the temperature is too high, the cloth will shrink too much, the hand feel will be hard rough, the strength will drop even be brittle. Attention should be paid to thin, mesh jacquard fabrics.
The gas singeing machine is still the best equipment for singeing. There is a cold water roller above the fire mouth of the singeing machine used for polyester / cotton fabric. When singeing, the fabric is wrapped on the roller, which can absorb the heat of the cloth body reduce the temperature of the cloth body. The burner can also rotate. Different burner angles are adopted for different fabrics, such as tangential singeing, through burning, direct burning, etc. The temperature of the cloth should be below 50 degrees after the singeing. It can be cooled by cool air cooled by a large cold water roller spray cooling. Static eliminator shall be installed for dry cloth falling to avoid the cloth falling on the whole the fabric being wound on the cloth falling frame.
3. alkali shrinkage
The similar difference between polyester cotton alkali shrinking process pure cotton is that the treatment conditions are mild. As the alkali resistance of polyester is worse than that of cotton, especially at high temperature alkaline conditions, polyester is prone to hydrolysis. Therefore, the concentration of sodium hydroxide in polyester cotton knitting is generally 90-160g / L, which should be strictly controlled at 60-70 ℃, because high temperature is prone to hydrolysis. ? 90-160g / L NaOH? Room temperature soaking for 5-20min.
4. Desizing
PVA its mixed size are often used for sizing of polyester cotton blended fabrics, alkali desizing can be used for desizing. Alkali desizing process uses caustic soda 5-1og / L, appropriate amount of wetting agent, 0.5-1h after alkali rolling at 80 ℃, wash with hot water (80-85 ℃), wash with cold water. When washing, the water should be sufficient to prevent the desized size re adsorbing on the fabric affecting the dyeing. The desizing rate should reach 80%. The oxidant can be used for desizing with 1-2g / L sodium bromate, ph9.5-10.5, 15-2omin after room temperature rolling, 3-5g / L caustic soda at 85-90 ℃, then washed with hot water cold water. Caustic soda hydrogen peroxide solution can also be used for desizing.
5. scouring
When PVA is the main sizing material, it can be decoiled once. If starch is the main sizing material, it should still be decoiled by enzyme before scouring. Due to the poor alkali resistance of polyester fiber, the scouring process should be milder than that of cotton fabric. At present, there are two scouring methods for polyester cotton blended fabric, one is low concentration alkali, high temperature steam scouring process, the other is high concentration alkali, hot stacking process. The scouring equipment is mainly flat steaming equipment. Rope scouring is easy to cause wrinkles, which is generally used. However, a few factories use rope scouring to process medium thin grey cloth for printing. At present, hydrogen peroxide sodium chlorite is used for one bath fast boiling bleaching, which has achieved initial success.
6. bleach
Bleaching of polyester cotton blended fabric is mainly to remove the natural pigment cotton fiber. Chlorine bleaching is only used for bleaching of dark polyester / cotton khaki. Chlorine oxygen double bleaching process can also be used for pretreatment of medium light color varieties. The ability of sub bleaching to remove cottonseed shell is strong, the requirement of scouring is high, but it is limited by equipment. Oxygen bleaching is widely used at present because of its good bleaching degree, no pollution to the environment little corrosion to the equipment. Oxygen bleaching usually uses alkali oxygen double bleaching process, that is, hydrogen peroxide (100%) 5-7g / L, water glass (specific gravity 1.4) 7-10g / L, penetrant caustic soda, pH value 10.5-11, steam at 100-102 ℃ for 40-90min, then re bleaching once, the two processes are identical. The bleached fabric should be bleached once before after heat setting, combined with the whitening process of polyester fiber cotton fiber. The cotton bleaching should be carried out in the same bath when the second bleaching.
7. mercerizing
Mercerizing is to improve the dyeing performance of cotton fiber. Considering that polyester fiber is resistant to high temperature strong alkali, the temperature of washing alkali solution alkali removal tank shall be higher than 80 ℃. After mercerizing washing, the alkali content on the cloth shall be reduced as much as possible, the pH value shall be controlled at about 7 when the cloth is discharged. The mercerizing equipment can be clip mercerizing machine straight roller mercerizing machine.
