Application Of Foam Processing Technology In Textile Printing And Dyeing Industry

Development background of foam dyeing and finishing technology

Foam finishing technology is a kind of dyeing and finishing technology with low liquid supply and high energy consumption which was developed rapidly in foreign countries in the late 1970s, which was affected by energy crisis. In 1980s, China launched a wave of research and development. Its related technological achievements have been applied by many printing and dyeing enterprises in China, producing and processing various fabrics of nearly 100 million meters, and the products have been put into the domestic and foreign markets after quality inspection. However, due to the limitations of equipment and technology at that time, this technology has not been sustained and further promoted.

In recent years, with the increasing energy shortage and environmental problems, people's awareness of environmental protection has gradually increased. Driven by policies such as energy conservation, consumption reduction and emission reduction, the call for cleaner production is rising day by day. Coupled with the sharp rise in raw material costs and the increasingly fierce global competition, people demand to win the market by improving and innovating processing technology to reduce costs, but we must emphasize the reduction of energy consumption and efficiency while effectively reducing the environmental impact. Foam processing technology has proved to be a way to help achieve the above goals, and has been applied to many fields of printing and dyeing industry to achieve the same effect as conventional dyeing and finishing process, and some aspects even surpass the conventional process.

Therefore, foam dyeing and finishing technology will be regarded as a new processing technology of energy saving and water saving.

Two. Principles of foam dyeing and finishing technology

The so-called foam finishing is to use as much air as possible to replace the water needed for preparing the finishing liquid. Through air, the concentrated solution or suspension of the finishing agent in water or other solutions is expanded into foam, and then the foam is diffused onto the surface of the fabric to be penetrated to the inside of the fabric so that the uniform distribution of the chemicals can be guaranteed under the condition of the minimum moisture content. Cloth. The essence of foam processing is to replace some of the water with air. The foam of finishing agent, dyestuff or paint can be made into foam with a certain foaming ratio, so that it can reach the fabric surface steadily in half life. Under the pressure of foam system, fabric capillary effect and foam wetting ability, it quickly ruptures and draining liquid and uniformly applies to fabric.

In the process of foam processing, part of the water in the working fluid is replaced by air. The higher the degree of substitution, the less water consumption and the more energy conservation. Foam processing can save the amount of water and the energy needed for drying the fabric, and to a certain extent, improve the quality of finished products, improve the production efficiency, reduce the discharge of waste water, reduce the migration of dyes and chemicals, make more effective use of chemicals and dyes in the working fluid, reduce the consumption of chemicals and control the dyes and chemicals in fibers or fabrics. Penetration of the Department.

Foam dyeing and finishing is a low liquid yield processing technology.

The biggest difference between the method and the rolling method is that the foam dyeing and finishing system can control the penetration distance of the working fluid in the treated fabric. It can make the working fluid only stay on the surface of the fabric, and also can make the working fluid soak through the fabric. Therefore, the application of foam dyeing and finishing system can make different processing on both sides of the fabric, such as the processing of single suction single suction fabric with one side waterproof and one side hydrophilic, and one side waterproofing and flame retardant processing. It is even possible to do double dipping and single suction processing, that is, both sides are waterproofing, and the fabric can absorb water in the middle. It can also dye the two sides of the fabric with different colors, which is simply impossible to achieve by the rolling method.

But it is completely different from coating finishing. Due to the requirements of processing methods, chemical coatings usually form a certain thickness on the surface of the fabric, which is distributed between fabric structures and rarely penetrates into the inner part of the fabric. Therefore, washability and handle are all worse. When froth dyeing and finishing, the frothing agent and foam stabilizer are usually added to the working fluid. There is no big difference between the frothing agent and the working fluid. Therefore, when applied to the fabric, the foam can quickly penetrate into the fiber, so the washability and handle of the fabric are better.

Three. Application of foam dyeing and finishing technology

Foam dyeing and finishing technology has achieved good results in developed countries in Europe and the United States, and has gained more and more attention in China. If applied to sizing, mercerizing and whitening of textile pretreatment, some people try to use foam process to bleach and scour cotton fabric and polyester cotton blended fabric and get better results. In addition, it has achieved satisfactory results in pigment dyeing, pigment printing and reactive dyestuff dyeing. The dyed fabric has attracted people's attention because of its unique style. Other aspects include anti wrinkle, water repellent, oil repellent, hydrophilic, soft, flame-retardant, shrinkproof, antibacterial, anti UV finishing. In these finishing, foam technology can achieve good results. It can also make foam finishing on one side of textiles, or achieve the needs of different functions of textiles, reduce energy consumption and reduce environmental pollution.

The general process of foam processing is foaming, foaming, foam breaking, fabric drying, drying, baking and post processing.

3.1 foam sizing

Foam sizing is a new process for sizing warp yarns with foam as the medium. The sizing of the warp foam is evenly distributed on the warp yarn by using the slurry that can produce foam. When the foam slurry adhered to the warp is passed through the roller, the foam is broken at the rolling point, the gas spills, and the slurry is attached to the warp yarn, so that the warp can be woven. Foam sizing technology is characterized by low energy consumption and fast speed. It can save a lot of processing water, reduce the discharge of sewage and the pressure of sewage treatment. The new technology of foam sizing is attracting more and more attention due to its advantages such as low liquid absorption rate, good energy saving, high speed, less hairiness, less entanglement and less color. The main difference between foam sizing and ordinary sizing is that when the sizing agent is sizing, the slurry is dissolved or dispersed in water, and the slurry is transferred to the fabric with water as the medium. In the foam sizing process, the foam (air and water) is the transport medium.

3.2 foam dyeing

Foam dyeing as a new technology of energy saving and water saving has attracted more and more attention. Foam is formed by gas surrounded by liquid film. It is a microbubble aggregate formed by a large number of gas dispersed in a small amount of liquid. It is isolated from liquid membrane and has a certain geometric shape. It is a small multiphase, sticky and unstable system. The suspension dyeing of vat dyes by foam dyeing method can make the suspension uniformly distributed and improve the levelling property of suspension dyeing. Foaming agents are generally used as surfactants, not only foaming, but also dispersing. Comparing foam dyeing with conventional dyeing, it is found that the former gives better levelling properties of fabrics. Comparing the suspension dyeing with these two methods, it is found that the rubbing fastness, sweat fastness, washing fastness and fastness of the fabric are basically the same.

Foam dyeing can reduce the amount of water and various auxiliaries, and reduce the amount of dyeing wastewater, which can reduce environmental pollution. At the same time, the processing time can be shortened, the color of the surface of the fabric can be increased and the swimming movement of the dye can be reduced. However, due to the characteristics of the dye itself, the uniformity of the foam applied and the stability of the foam, the poor control of foam dyeing process results in levelling.

3.3 foam printing

Foam printing was first applied to carpet printing, and then extended to the printing of cashmere fabrics and general textiles. Foam printing is made by means of air, so that a small amount of liquid is formed into foam, and the foam is carried with dyes or coatings and various auxiliaries. It is applied enough to cover all the fabric evenly, thereby completing the whole printing process with low moisture content, forming the surface printing effect, and achieving the purpose of saving energy and dyeing materials and improving the fabric handle. In the process of foam printing, due to the pressure exerted on the foam, such as scrapers and rollers, and the action of fibers and capillary, the foam breaks down. The dye stays in the original place without the carrier of "paste", thus forming its fine printing effect. Therefore, once the foam paste touches the fabric, it needs to be broken as soon as possible, which is beneficial to the quality of printing.

The foam required for foam printing paste should be stable before printing onto the fabric. After printing on the fabric, it will require rapid rupture. If the bubble is unstable, it will break before printing, and the viscosity of the paste will decrease. It will not be able to achieve bubble printing. If the foam stability is too high, the printed foam will not be evenly broken on the fabric, which will have an impact on the printing quality. Compared with traditional printing, foam printing has higher quality, clearer design and softer hand feel. If the dye penetration is controlled, the dark color can be overprinted on the light color, and wet wet processing technology can be made possible, such as foam printing without direct drying.

3.4 foam finishing

3.4.1 resin finishing

The most common finishing agent for cotton fabric is resin finishing agent. After finishing with resin, the fabric can achieve satisfactory wrinkle recovery angle, but the satisfactory wrinkle recovery angle is at the expense of strength and wear resistance of the fabric. A large number of experiments found that the uneven application of finishing agent was the main reason, and the main reason for the uneven application was caused by the movement of finishing agent in the process of fabric baking.

When using the method of rolling, pre drying and baking, about 28% of the cotton fabric will swim. It is one of the most serious problems in the traditional finishing process of cotton fabrics. When foam finishing is used, the swimming degree will be greatly reduced due to the decrease of liquid ratio, which can reduce the swimming volume to less than 10%, thus greatly improving the fabric strength. This is because the decrease of liquid volume decreases the evaporation of water during drying, and the finishing liquid in the fabric does not swim to the fabric surface as the liquid difference of the surface liquid decreases, thus reducing the amount of swimming in the drying process. In addition, when the same finishing effect is achieved, the foam finishing method can save about 10% to 30% of the resin and auxiliaries than conventional rolling method, and can also improve the handle of the fabric.

3.4.2 foam waterproof and moisture permeable finishing

At present, shirts and other fabrics are routinely impregnated as a water repellent finishing process. Both sides of the fabric have water repellency, so they can not sweat. They feel uncomfortable when they wear them. In order to make the water repellent agent only penetrate to half the thickness of the fabric, and then apply the hygroscopic agent in the same way on the reverse side, and then infiltrate half of the water repellent agent, a double-sided finishing fabric with both water repellent effect and sweat absorption and sweating function can be produced. The moisture absorption of the fabric is improved and the moisture permeability is better. The key to double sided foam finishing is to control the density and amount of foam when finishing, and not to penetrate the finishing agent.

The foam coating disperses the mixture of polyurethane and polyacrylate in water and then forms foam. The foam is stabilized by adding stabilizer, and then coated with one side of the fabric to form a microporous coating after drying. What is important is that the size of the pores formed can permeate the water vapor, but prevent the infiltration of liquid water. The fabric is finally compressed under low pressure to make the coating well bonded with the fabric. Because the diameter of foam is relatively large, fluorinated compounds are used for finishing to improve its waterproofing performance. The production process of this coating does not use organic solvents, and the mode of production is more environmentally friendly.

Finishing of 3.4.3 foam flame retardant coating

There are many ways to flame retardant fabrics, such as rolling, flame retardant, direct back coating and foaming coating. At present, the first two kinds are usually used in China. The flame-retardant liquid is easy to cause color change, hard feel, chicken paw print, salting out, etc. the direct backing coating will also affect the handle, and the air permeability is poor. Overseas countries such as Britain and the United States adopt advanced foam coating on the flame retardant coating. A flame retardant foam layer is coated on the back of the fabric, and the flame retardant layer is used to make the fabric difficult to catch fire. The advantages of foam coating are good flame retardancy, soft handle, good air permeability and low cost. Therefore, this method has a very broad development prospect.

Zhu Guanglin and others used the new foam technology to conduct flame retardant finishing of heavy fabrics. Ethylene polymers were used as coating adhesives, bromine and nitrogen phosphorus flame retardants were added to stir them up, foaming at a certain foaming ratio, so that the low viscosity liquid thickened and reached the coating state. The coating is extruded by coated knives, and the foam is broken into low viscosity liquid and penetrated into the fabric. The results show that compared with the traditional process, foam flame retardant finishing can simplify the process and reduce the production cost. The finished fabric has good flame retardant effect, and the fabric has soft handle, good air permeability and high safety. The fabric can be widely used in tents, military textiles, home textiles, automobile, aircraft and other interior decoration.

Four. Prospect of foam dyeing and finishing technology

As mentioned above, the sizing, dyeing, printing and finishing of textiles can be done by foam processing. However, there are still some disadvantages in foam processing technology, such as instability of foam, levelling of foam dyeing and limitations of foam processing technology. However, this does not hinder the application and promotion of foam processing technology in future production and processing. Under the current energy crisis and clean production background, foam processing technology has met its requirements of saving energy, improving production efficiency and reducing sewage discharge with its unique advantages. Foam dyeing and finishing has the following advantages:

(1) reduce the energy required to dry the fabric per unit of quality.

(2) processing time is significantly reduced and production efficiency is increased.

(3) the liquid absorption rate of the solution is not affected by the moisture content of the fabric, and can be directly processed without drying.

(4) without the influence of fabric's water absorption, the fabric can be evenly processed and the volume of liquid can be automatically controlled.

(5) because of the low liquid absorption rate of fabric, the drying phenomenon of dyes and other chemicals decreased.

(6) the surface of the fabric will not be deformed during processing, and the softness will be improved.

(7) the conversion process is simple, time-saving, flexible and versatile. Double coating, liquid feeding, printing or combination can be used in one process.

(8) reduce environmental pollution.

Five, conclusion

As an environment-friendly technology, foam finishing has a good effect in reducing energy consumption, improving production efficiency and product quality. With the development of the new generation of foam finishing technology, people will pay more attention to and explore the performance of energy saving and emission reduction of foam finishing technology, the performance of cleaner production of foam finishing equipment, and whether the products produced will meet the special needs of society. Today, with the energy shortage and the heavy task of protecting the environment, many advantages brought by foam finishing technology can provide a more convenient way for the dyeing and finishing process of related enterprises.