Common Treatment Methods of Cotton Fabric in Printing and Dyeing

Finishing of cotton fabric

1、 Tentering

The stretching is to adjust the state of warp and weft yarn in the fabric under slow drying according to the plasticity of cotton fiber in the wet state, and stretch the fabric door to the given size to achieve uniform and stable shape.

The cotton fabric is usually stretched with clip tenting machine, while the wool fabric, silk fabric and chemical fiber fabric are usually stretched with needle clip tenting machine.

The front end of the stenter is often equipped with a dip mill and a drum dryer, so stenting finishing is often combined with some additive finishing (such as softening, whitening, etc.).

2、 Jamming finishing

The calender finish, calender finish and electrooptic finish can increase the luster of the fabric, and the calender finish can make the surface of the fabric rolled and pressed with three-dimensional concave and convex patterns.

These finishing are accomplished by varying degrees of roller rolling, using the plasticity of cotton fibers in the hot and humid state.

3、 Hard finishing

Stiffening finishing, commonly known as sizing finishing, is to use the size made of macromolecular substances (wet starch or chemical size) with a certain viscosity to form a film on the fabric, so that the fabric can obtain a smooth, stiff, thick and full feel, and improve the fabric strength and wear resistance, and extend the service life.

4、 Softening

Cotton fabric can be softened by adding softener besides obtaining soft handle through calendering and mechanical preshrinking.

There are many kinds of softeners, among which paraffin lotion, "mercerizing paste" and "red oil" are the ones whose effects are not durable; The varieties with durable effect are mostly reactive softeners, such as softener Vs, waterproof agent Pf, rc and reactive organosiloxane lotion.

Softening finishing is usually carried out by hot air stretching finishing combined with dip rolling finishing solution followed by heat treatment.

5、 Whitening

Fluorescent whitening agent can absorb the invisible ultraviolet light in the sunlight and turn it into bright blue purple visible light to radiate, and mix it with the original yellow light on the fabric to form white light, thus greatly improving the whiteness of the fabric. Fluorescent brighteners have affinity for fibers and can be dyed like dyes. Therefore, they can be bleached by dip dyeing or hot air stretching drying after dip rolling.

There are several kinds of fluorescent brighteners commonly used in cotton cloth, such as VBl and VBu; Bsl, Ws, Wg, etc. are commonly used for silk fiber, and VBl can also be used; Polyester whitening agent dt is often used.

6、 Shrink proof and wrinkle proof finishing

When the dry fabric after dyeing and finishing is moistened again in a relaxed state, it will shrink significantly in the warp and weft direction, which is called shrinkage. In dyeing and finishing, mechanical preshrinking and chemical finishing are often used to solve the problem of high shrinkage.

A. Mechanical preshrinking finishing

Mechanical pre shrinking finishing can be carried out with a variety of equipment, such as overspeed feed clip stenter, blanket or blanket pre shrinking finishing machine, etc. In case of overspeed feeding, the linear speed of the fabric fed into the clip chain is slightly higher than the running speed of the clip chain, so that during the stretching process, the warp direction of the fabric is in a tension free state, which can cause free retraction, increase the warp direction shrinkage, and improve the shrinkage rate. During the preshrinking finishing of blankets or rubber blankets, the shrinkage effect of the blankets or rubber blankets when they are stretched and relaxed is used to make the warp direction of the fabric that fits them shrink synchronously, so as to eliminate the potential weaving shrinkage.

B. Chemical shrinkproof and wrinkle proof finishing

Some fibers, such as viscose, have low molecular degree of polymerization and are easier to swell and extend than cotton fiber shrinkage. The dimensional stability of the fabric is poor, which not only has high shrinkage, but also is very easy to wrinkle. For this kind of fabric, if the mechanical preshrinking method is used for finishing, the antishrinking effect is not good, so the chemical finishing method must be used. In production, chemical finishing is rarely used solely for shrink proof purposes, but is often combined with wrinkle proof, because the fabric has also achieved shrink proof effect during wrinkle proof finishing, and the two are inseparable.

At present, the commonly used anti wrinkle and anti shrink finishing method is the chemical finishing process that uses the compound with crosslinking polymerization ability to treat the fabric, make it cross-linked with the fiber, and polymerize and deposit in the fiber. It is commonly known as resin finishing.

There are many kinds of resins used for anti wrinkle finishing, such as urea formaldehyde resin (uf), cyano formaldehyde resin (tMM), dihydroxymethyl dihydroxyethylene urea resin (2d), etc. Although these resins have good finishing effect, their application is limited because they are mostly aldehyde containing compounds, which will release free formaldehyde harmful to human body and environment. In recent years, low formaldehyde and formaldehyde free varieties have been gradually developed, such as polycarboxylic acid (Btca), glyoxal derivatives, tetraoxane, epoxy compounds and thermoplastic resins.

The basic methods of resin finishing are:

Fabric is dipped and rolled with finishing solution containing resin monomer or initial shrinkage, followed by dry heat treatment.

On the basis of the above finishing processes, the non ironing finishing technology which can improve the crease resistance of the fabric in the wet state and the durable pressing finishing technology for clothing with higher requirements have been developed.