What is soft finishing? What problems may arise during the soft finishing process?

During the dyeing and finishing process, textiles are subjected to moist heat treatment with various chemicals and mechanical tension, which not only deforms the tissue structure, but also causes stiffness and roughness in the hand. Softening is a process that compensates for this defect and makes the fabric feel soft. .

Reasons for soft finishing of fabrics

Natural fibers

Cotton fiber is naturally soft because it contains oil and wax. Natural fibers such as wool and silk also have a unique soft feel. However, after bleaching, dyeing, printing processing or functional finishing, due to the removal of wax and oil and damage to the fiber, The fabric becomes rougher, the luster becomes darker, and even the sewing performance is affected, so it needs to be softened.

Synthetic fibers

The feel of synthetic fibers is worse than that of natural fibers such as cotton, wool, silk, and linen. After the synthetic fiber fabric is highly stabilized, the feel becomes very rough and hard. Only through soft finishing can it be given the soft touch of natural fibers. , to ultimately improve its performance.

The purpose of soft finishing

In recent years, soft finishing has become particularly important in textile processing. Almost every textile product coming out of the textile factory has been softened.

The main goal of soft finishing is to obtain a soft feel to facilitate textile processing and improve wearing performance. Usually, a pleasant soft feel is the decisive basis for customers when purchasing a textile. Therefore, soft feel is considered an important factor affecting textile sales.

(1) Obtain the required softness (usually can be described as: slippery, super soft, elastic, dry, lubricated);

(2) Increase technical properties, such as: antistatic, hydrophilic, elastic, sewing, friction fastness, etc.

(3) Give synthetic fibers a certain natural touch and improve wearing comfort by improving the secondary effects of fibers (moisture absorption adjustment, flatness).

(4) Improve processing performance.

Soft finishing methods

01Machinery

Mechanical softening mainly uses mechanical methods to flex the fabric multiple times under tension to reduce the rigidity of the fabric and restore it to the appropriate softness. However, this finishing method is not washable, so softener treatment is generally preferred.

Equipment: calender, fabric shrinking machine, AIRO-1000 type loose mechanical soft finishing machine, sanding machine and fleece machine, etc.

02Chemistry

The chemical method uses softeners to reduce the friction coefficient between fibers to achieve a soft effect. Chemical methods are more commonly used, sometimes supplemented by mechanical methods. Usually, textiles are soaked in softener solution for a certain period of time, then dehydrated and dried. Sometimes softeners can be used together with other finishing agents. Some softeners can produce wash-resistant finishing effects after baking.

Classification of softeners

Non-surface active types: natural oils (stearic acid, coconut oil, white oil), paraffin, amine salts of fatty acids;

Surfactants: yin, non, yang, benign;

Reactive softeners: acid anhydride derivatives, ethyleneimine derivatives, pyridine quaternary ammonium salt derivatives;

High molecular polymer emulsion: polyethylene resin emulsion, silicone type

Requirements for softeners for fabric softening

(1) Easy to operate; liquid, easy to measure, stable, and easy to be pre-diluted;

(2) Good compatibility with other additives;

(3) It has no allergic or irritating effect on the human body, and no bad gas escapes during processing;

(4) There is no yellowing or discoloration, and it does not affect the color fastness of the dye;

(5) Low foam, not sensitive to shear force, non-stick to the roller;

(5) Meet the requirements for high-temperature treatment in dyeing and finishing;

(6) The price is moderate, the process is simple, and the storage is stable.

The mechanism of soft finishing

Reduce the surface tension of the fiber

Textile fibers are materials composed of linear polymers with a large specific surface area. They are very slender in shape and have good flexibility in the molecular chains. When surfactant (or softener) is added to the finishing liquid, since the surfactant is prone to directional adsorption on the interface (textile fiber and finishing liquid), the interfacial tension of the fiber is reduced, and the work required to expand the surface area is reduced. Allowing the fiber to easily expand its surface and extend its length. The result is a voluminous, voluminous fabric that creates a soft hand.

Reduce the friction coefficient of fibers

The surfactant adsorbs a thin layer on the surface of the fiber, and the hydrophobic groups are neatly arranged outwards. In this way, friction occurs between hydrophobic groups that slide against each other. The longer the hydrophobic group, the easier it is to slide.

1. Reduce the friction coefficient of fiber. Reduce the friction resistance between fibers or between fibers and the human body to obtain a soft feel.

2. Properly reducing the friction coefficient can also makeWhen the fabric is subjected to external force, the yarn is easy to slide, thereby dispersing the stress and improving the tear strength. Or the fibers under tension during processing can easily return to a relaxed state and the fabric becomes fluffy.

Soft finishing FAQ
Doesn’t feel as good as it should feel

The soft style of soft finishing varies with customer requirements, such as soft, smooth, fluffy, waxy, oily, dry and slippery, etc. Different softeners are selected according to different styles. Among the soft sheets, there are softener sheets with different structures, which have different softness, fluffiness, slipperiness, yellowing, and influence on the water absorption of the fabric. In silicone oil, the properties of modified silicone oil with different modified genes are also different, such as amino silicone oil, hydroxyl silicone oil, epoxy modified silicone oil, carboxyl modified silicone oil, etc., all have different properties.

Color changes to yellow

Among soft sheets, cationic soft sheets are soft and have good hand feel. They are easily adsorbed on fabrics and are prone to yellowing and discoloration, which affects hydrophilicity. Amino silicone oil is currently the most widely used silicone oil. Amino groups can cause discoloration and yellowing. Cationic surfactants such as 1227, 1831, and 1631 are sometimes used as emulsifiers during emulsion polymerization. These emulsifiers can also cause yellowing. Different emulsifiers are used when emulsifying silicone oil, and their “color stripping effects” are different, which will cause color stripping and light color under different circumstances, which is considered a discoloration.

Decreased hydrophilicity of fabric

Generally, the structural problems of the film used, the lack of water-absorbing genes after the silicone oil film is formed, and the blocking of water-absorbing centers such as the hydroxyl groups of cellulose fibers, carboxyl groups, and amino groups on wool cause the water absorption to decrease.

Treatment method: Anionic, non-ionic film and hydrophilic silicone oil should be used as much as possible.

Dark spots

Cause:

① The oil stains on the fabric were not removed during pre-treatment, and the oil stains were darker in color during dyeing.

② There is too much foam in the dyeing bath, and the mixture of foam, floral sweaters, dyes, etc. stains the fabric.

③The defoaming agent drifts oil and causes dark oil spots.

④The tar-like substance in the dye vat is stained on the fabric.

⑤Dye agglomerates under different circumstances to form dark stains.

⑥Excessive calcium and magnesium ions in the water combine with dyes and stain the fabric.

Processing method:

①Add degreaser for refining during pre-treatment.

②Dyeing auxiliaries use low-foaming and non-foaming auxiliaries.

③Choose defoaming agents that are less prone to oil drifting, add chelating agents to improve water quality, and add dissolving and dispersing agents to prevent dye aggregation. Use tank cleaning agent to clean and wash the tank promptly.

Light spots

Cause:

① The pre-treatment is uneven, and the hair effect in some parts is not good, resulting in a certain dye repellency and containing dye repellent substances. During pre-treatment, the cloth contains calcium soap, magnesium soap, etc. or the mercerization is uneven.

② Semi-finished products are unevenly dried.

③The cloth surface is stained with solids such as undissolved Yuanming powder and soda ash.

④ Add water to the dyed material before drying.

⑤Stains caused by additives during post-finishing such as softening of dyed goods.

Processing method:

Strengthen pre-treatment. When selecting pre-treatment additives, it must be difficult to form calcium magnesium soap, and pre-treatment must be uniform and thorough (this is related to the selection of scouring agent, penetrating agent, chelating dispersant, mercerizing penetrating agent, etc.). Yuanming powder, soda ash, etc. must be melted into the tank and production management must be strengthened.

Alkali spots

Cause:

Alkali removal after pre-treatment (such as bleaching and mercerization) is not clean or uniform, resulting in alkali spots.

Processing method:

It is necessary to strengthen the alkali removal process in the pre-treatment process.

Softener Stains

Cause: The soft flaking material is not good, and there are lumps of softener adhering to the fabric. There is too much foam after the soft sheet material is turned into a soft sheet. When the cloth comes out of the vat, the cloth will be stained with softener foam. The water quality is poor, the hardness is too high, and the impurities in the water combine with the softener and aggregate on the fabric. The cloth surface contains anionic substances, which combine with the cationic softener to form stains during the softening process, or the cloth surface contains alkali, which causes the softener to agglomerate. Softeners have different structures, and some cause the softener to change from an emulsified state to a slag-like substance that adheres to the fabric at higher temperatures. The tar-like softener and other substances originally in the tank fell off and stuck to the fabric.

Silicone oil stains

Cause: The PH value of the cloth surface is not neutral, especially if it contains alkali, causing the silicone oil to break down and float. The water quality of the treatment bath is too poor and the hardness is too high. Silicone oil can easily float in water with a hardness of >150PPM. Silicone oil quality problems include poor emulsification (poor emulsifier selection, poor emulsification process, too large emulsified particles, etc.) and intolerance to shearing. Choose silicone oil that is resistant to shear, electrolytes, and pH changes, but pay attention to how the silicone oil is used and the environment. You can also consider choosing hydrophilic silicone oil.

Poor fluff

Poor raising is closely related to the operation of the raising machine (such as tension control, raising roller speed, etc.). When applying softener (commonly known as waxing), control the dynamic and static friction system of the fabric.�� is the key, so the preparation of fluff softener is the key. If the softener is not used properly, it will directly cause poor fluff.