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Introduction To Fabric Dyeing And Finishing Process

Apr 29, 2019


The introduction of fabric dyeing and finishing process, the selection of fabric dyeing and finishing process, mainly according to the variety, specifications and finished product requirements of fabrics, can be divided into pre-treatment, dyeing, printing, finishing.

Fabric pretreatment

Natural fibers contain impurities. In the textile processing process, various pastes, oils and contaminated dirt are added. The presence of these impurities not only hinders the smooth progress of dyeing and finishing, but also affects the wearing performance of the fabric.

The purpose of pretreatment is to apply chemical and physical mechanical action to remove impurities on the fabric, make the fabric white and soft, have good penetrating properties, meet the requirements of taking, and provide qualified semi-finished products for dyeing, printing and finishing.

Cotton: original cloth preparation, singeing, desizing, scouring, bleaching, mercerizing.

Polyester: preparation of grey fabric, refining (liquid alkali, etc.), pre-shrinkage, predetermined type, alkali reduction (liquid alkali, etc.).

Singeing of fabric

Usually, after entering the printing and dyeing factory from the textile mill, the grey fabric should first be subjected to inspection, tumbling, batching, printing and sewing, and then singeing.

the reason:

1 Unburned cloth has too many fluffs and varies in length;

2 poor finish, easy to stain;

3 It is easy to lose hair in the subsequent dyeing and finishing process, resulting in printing and dyeing.

Singeing purpose

1 Improve the gloss of the cloth; improve the finish;

2 improve the anti-pilling performance (especially chemical fiber fabric);

3 improve the style, singeing will make the fabric become crisp and bone.

Desizing of fabric

During the weaving process, the warp yarns are subjected to large tension and friction and are prone to breakage. In order to reduce the warp and improve the weaving efficiency and the quality of the fabric, the warp yarn needs to be sizing before weaving, which is the fiber adhesion and cohesion in the yarn, and forms a strong slurry film on the yarn surface to make the yarn tight and Smooth, thereby increasing the breaking strength and wear resistance of the yarn.

Desizing purpose: After sizing, the slurry penetrates into the fiber and is partially attached to the surface of the warp yarn. While improving the yarn performance, the slurry contaminates the dyeing and finishing fluid, hinders the chemical interaction between the fiber and the dyeing material, and dyes the dye. The whole process is difficult to carry out.

First, the introduction of common slurry

Natural pulp: starch, seaweed gum, gum, etc.

Starch properties: 1 acid decomposition, 2 alkali stable, swelling, 3 oxidant can be decomposed, 4 is decomposed by starch decomposing enzymes.

Chemical slurry: cellulose derivatives such as hydroxymethyl cellulose (CMC), polyvinyl alcohol (PVA), polyacrylic acid, polyester, and the like.

PVA properties: 1 is stable to acid and alkali, and viscosity is not lowered. 2 is degraded by oxidants. 3 Wide applicability, good compatibility, no reaction.

Second, the common desizing method

1. Alkali desizing

One of the most widely used methods in domestic dyeing factories, but the desizing rate is not high, and other impurities can be removed in the same fashion as desizing.

Mechanism: treated with dilute sodium hydroxide solution, the starch slurry swells (or puffs) under the action of alkali, and no chemical reaction occurs, which causes the slurry to transform from gel to sol, reducing fiber to slurry. The bonding force is then removed by washing with water and mechanical force. For PVA and polyacrylate-based slurries, it is capable of dissolving a dilute sodium hydroxide solution.

2, (starch) enzyme desizing

Enzymes are also known as enzymes, biocatalysts.

Features: high desizing rate, no damage to fiber, only starch, can not remove impurities.

Features: a. High efficiency. b. Specificity, an enzyme can only catalyze a reaction or even a specific reaction. c. Activity is affected by temperature and pH.

For starch slurry or starch mixed pulp (starch content is dominant), amylase can be used for desizing.

3, acid desizing

There are not many domestic applications, because it is easy to damage the fibers during use, and it is often used in combination with other methods.

A two-step process is used: alkali desizing - acid desizing.

Acid desizing can hydrolyze starch, remove mineral salts and other functions, and make up for each other.

4, oxidative desizing

Oxidizing agent: NaBrO2 (sodium bromate) H2O2, Na2S2O8, (NH4)2S2O8, and the like.

Principle: The oxidant can oxidize and degrade various kinds of slurry, its molecular weight and viscosity are greatly reduced, water solubility is increased, the slurry is prevented from adhering to the fiber, and then the hydrolyzed product is removed by high-efficiency water washing.

Fabric scouring

The purpose of scouring is to remove fiber impurities and improve fabric processing properties, especially wetting properties.

Natural impurities: For cotton fabrics, mainly fiber commensal or companion organisms, including oil wax, pectin, protein, ash, pigment and cottonseed hull.

Artificial impurities: oils, antistatic agents, and impurities such as oil, rust, and residual slurry added in the spinning and weaving process.

These impurities seriously affect the wettability of the fabric and hinder the processing of the dyeing and finishing of the fabric, and must be removed in a scouring system mainly composed of sodium hydroxide and a surfactant.

Fabric bleaching

After scouring, the natural and artificial impurities on the fabric have been largely removed, but for bleached and light-colored fabrics, bleaching is also required. That is, bleaching processing is mainly carried out to remove the pigment and improve the whiteness.

The chemical fiber contains no pigment and is very white after scouring. However, after the cotton fiber is refined, the pigment still exists and the whiteness is poor. Therefore, the bleaching is mainly carried out for the natural impurities on the cotton fiber.

bleach:

Oxidation type: sodium hypochlorite, hydrogen peroxide and sodium chlorite, mainly used for cotton fibers and blended fabrics.

Reduced type: NaHSO3 and insurance powder, etc., mainly used for protein fiber fabrics.

Sodium hypochlorite bleach:

Sodium hypochlorite bleaching is mostly used for the bleaching of cotton fabrics and cotton blended fabrics, and sometimes for the bleaching of polyester-cotton blended fabrics. However, it cannot be used for bleaching of protein fibers such as silk and wool, because sodium hypochlorite has a destructive effect on protein fibers and causes yellowing and damage of fibers. In the bleaching process, in addition to the destruction of natural pigments, the cotton fibers themselves may be damaged. Therefore, the bleaching process conditions must be controlled to achieve acceptable quality and inherent quality.

Sodium hypochlorite is easy to manufacture and low in cost. Sodium hypochlorite bleaching is convenient and the equipment is simple. However, since sodium hypochlorite bleaching is unfavorable to environmental protection, it is gradually replaced by hydrogen peroxide.

Hydrogen peroxide bleaching H2O2:

Hydrogen peroxide is also called hydrogen peroxide, and its molecular formula is H2O2. Hydrogen peroxide bleaching is referred to as oxygen bleaching. Under alkaline conditions, the stability of the hydrogen peroxide solution is poor. Therefore, the commercial hydrogen peroxide is weakly acidic.

The fabric bleached with hydrogen peroxide has good whiteness, pure color and is not easy to yellow when stored, and is widely used for bleaching cotton fabrics. Oxygen bleaching has greater adaptability than chlorine bleaching, but hydrogen peroxide is more expensive than sodium hypochlorite, and oxygen bleaching requires stainless steel equipment, which consumes more energy and costs more than chlorine bleach.

At present, the printing and dyeing plant uses more flat steaming bleaching method. This method has higher degree of continuity, automation and production efficiency, simple process flow and no environmental pollution.

Mercerized fabric (cotton fabric)

The textile is subjected to a certain tension, and by the action of concentrated caustic soda and maintaining the required size, the general luster of the silk can be obtained. This process is called mercerizing.

The purpose of mercerizing: to improve the surface gloss and feel of the fabric, due to the expansion of the fiber, the fiber arrangement is more neat, the reflection of light is more regular, thus enhancing the gloss.

Improve the coloration rate of dyeing: After mercerizing, the crystal area of the fiber is reduced, and the amorphous area is increased, so the dye is more likely to enter the fiber interior, the coloring rate is 20% higher than that of the unsilked fiber cotton cloth, and the vividness is increased, and the pair is increased. The hiding power of the dead face.

Improve dimensional stability: Mercerizing has a shaping effect, which can eliminate rope wrinkles and better meet the quality requirements of dyeing and printing on semi-finished products. The most important thing is that after mercerizing, the stability of the stretch deformation of the fabric is greatly improved, thus greatly reducing the shrinkage rate of the fabric.

Silk fabric

Refined, pre-shrinked (chemical fiber fabric)

The purpose of refining and pre-shrinking is mainly to remove oil, slurry and dirt adsorbed on the fabric (fiber), and also dissolve some of the oligomers in the fiber during high-temperature refining. The grey cloth needs to be pre-shrinked before the alkali amount, and mainly added with additives such as deoiling spirit and caustic soda. The chemical fiber fabric pretreatment is carried out in a high temperature and high pressure dyeing machine.

Fabric shrinkage

Alkali reduction (chemical fiber fabric)

Principle and effect of alkali reduction

Alkali reduction treatment is a process of treating polyester fabric in high temperature and concentrated caustic soda. In the aqueous solution of sodium hydroxide, the ester bond of the polyester molecular chain on the fiber surface is hydrolyzed and broken, and the hydrolysis of different polymerization degrees is continuously formed. The product ultimately forms water soluble sodium terephthalate and ethylene glycol. The equipment for alkali reduction mainly includes overflow dyeing machine, continuous reduction machine and intermittent reduction machine, except for overflow dyeing machine; continuous and intermittent reduction machine can recover the remaining lye. . In order to ensure the stability of the appearance size of the grey cloth, a part of the alkali reduction product needs to be added with a predetermined type of process, and then enters the dyeing process.

Alkali reduction equipment:

Introduction to dyeing and finishing process

Fabric dyeing

Dyeing is the process of obtaining a bright, uniform and strong color of a textile material by a combination of physical or physical chemistry of the dye (or pigment) and the textile material.

The textile material is immersed in the aqueous dye solution at a certain temperature, and the dye moves from the water phase to the fiber. At this time, the dye concentration in the water gradually decreases, and the amount of the dye on the textile material gradually increases. After a period of time, the amount of dye and textile in the water The amount of dye on the material does not change any more, and the total amount of dye does not change, that is, the dye reaches an equilibrium state.

The dye that is reduced in water is the dye that moves onto the fiber. The fiber is taken out at any time, and even if it is twisted, the dye remains in the fiber, and the dye cannot be completely detached from the fiber. The phenomenon in which the dye is incorporated into the fiber is called dyeing.

According to the different dyeing objects, the dyeing methods can be mainly divided into garment dyeing, fabric dyeing (main extension fabric dyeing, knitted fabric dyeing and non-woven dyeing), yarn dyeing (can be divided into skein dyeing, cheese dyeing, warp) Shaft dyeing and continuous warp dyeing) and bulk fiber dyeing in four categories.

Among them, fabric dyeing is the most widely used. Garment dyeing refers to the method of dyeing textile materials into garments, yarn dyeing is mostly used for yarn-dyed woven fabrics and knitted fabrics, and bulk fiber dyeing is mainly used for color textile materials.

Fabric dyeing

Fabric printing

The process of patterning the dye or coating on the fabric is a print. Divided into flat screen printing, rotary screen printing, transfer printing, digital printing and so on. Printing is a partial dyeing that requires a certain degree of color fastness. The dye used is basically the same as the dyeing, mainly adopting the direct printing process, and can also adopt the paint printing, the paint printing process is simple, but the printed large-area pattern feels hard.

Fabric finishing

Textile finishing, also called finishing. Physical, chemical or physical and chemical methods to improve fabric feel and appearance (such as stiffening, soft finishing, calendering or raising), improve fabric quality and impart new functions to fabrics (such as anti-wrinkle, waterproof, anti-fouling) Processing, anti-corrosion, anti-mildew, anti-mite and anti-bacteria.

Generalized: All the improvements and quality improvements that have passed since the lower loom.

Narrow sense: the processing of fabrics during bleaching, dyeing and printing accidents is called fabric finishing.

Purpose of fabric finishing

1. Stabilize fabric size and shape

Through finishing, the door width is stabilized, the shrinkage rate is reduced, the fabric door width is uniform, and the fabric size and shape are in compliance with the prescribed standards.

E.g:

Stretching - the use of cellulose, silk, wool and other fibers in a certain degree of plasticity under wet conditions, the fabric width is gradually widened to the specified size and drying and stable finishing process, also known as the fixed width.

Heat setting - refers to the processing technology of heat treatment of the fiber fabric under certain tension to make its size and shape stable.

2. Improve the appearance of the fabric

Improve the whiteness and drapability of the fabric, improve the gloss of the surface of the fabric and impart a surface pattern effect to the fabric.

E.g:

Calendering - through the mechanical pressure of the calender, the role of damp heat, by means of the plasticity of the fiber, the surface fibers are arranged in parallel to improve the smoothness of the surface, to produce regular reflection of light, and to improve the color of the fabric. .

Rolling finishing - the embossing machine consists of the same heatable hard roll and a soft roll. The surface of the hard roll is engraved with a embossed pattern, and the soft roll is engraved with a smudged pattern. During the finishing, the fabric is embossed by the yin and yang roll by means of the plasticity of the fabric under moist heat conditions, so that the embossed pattern is produced by the fabric.

Grinding - After finishing, the fabric can produce suede, feel improved, comfortable to wear, can be done on the brushing machine, and the fabric is repeatedly rubbed to produce suede.

3. Improve the feel of fabrics

Gives the fabric a soft, full-feeling feel or a stiff hand.

E.g:

Soft finishing - is a process that compensates for the soft feel and rough defects of the fabric to make the fabric soft. Including mechanical soft finishing, chemical soft finishing and stiff finishing.

Mechanical soft finishing is mainly the use of mechanical methods, in the tension state, the fabric is bent over multiple times to reduce the rigidity of the fabric, so that it can return to the appropriate softness.

The chemical method uses a softening agent to reduce the coefficient of friction between the fibers to obtain a softening effect.

Stiffness finishing - is to make the fabric smooth, stiff, thick, full of hand, and to improve the strength and wear resistance, but also to improve the hanging and appearance.

The stiffening finishing process is generally carried out in combination with the fixed length, and a softener is added to the slurry to improve the comprehensive hand feeling. Similarly, a simple soft finishing is to add a stiffening agent to enhance the body bone.

4. Give the fabric special properties

Give the fabric some protective properties or improve the performance of the fabric.

E.g:

Waterproof finishing - coating the fabric to make water and air impenetrable; water repellent finishing makes the hydrophilicity of the fiber surface hydrophobic, and the fabric is both breathable and not easily wetted by water.

Flame-retardant finishing - Finished fabrics have varying degrees of ability to prevent flame spread, and can quickly stop burning after leaving the fire.