With the continuous expansion of international textile trade and the improvement of people’s living standards, people’s awareness of environmental protection is also increasing, and the requirements for textile comfort, cleanliness and safety are increasing. After China’s entry into WTO, the textile printing and dyeing industry is facing unprecedented opportunities and severe challenges. By increasing the intensity and difficulty of inspection, foreign businessmen try to restrict the export of China’s textiles, of which the important requirement is the color fastness of textiles.
As one of the four natural environment-friendly fibers, cotton fabric plays an important role in the textile arena because of its good moisture absorption, warmth retention and soft hand feel. Reactive dyes [3] have become the main dyes for cotton fabric dyeing because of their complete chromatography, bright color, low cost, economy and environmental protection. But at the same time, there are some problems. While reactive dyes form covalent bond reaction with fibers, because the dyes that are not involved in the reaction and partially hydrolyzed cannot be completely cleaned, floating color will be formed on the surface of the fabric. Even if covalent bonds have been formed on the dyed fabric, the stability of covalent bonds also has a certain limit, which may break, resulting in poor wet treatment fastness of the dyed fabric. Therefore, reactive dye dyeing, Especially when dyeing deep and strong colors, it usually needs to be treated with color fixing agent.Early color fixing agents, such as color fixing agent y, are the products obtained by the reaction of dicyandiamide and formaldehyde. Although they can improve the color fastness of dyes, they have the problem of releasing free formaldehyde, which is harmful to human health. Therefore, scientists have carried out a lot of research work on formaldehyde free color fixing agents. From the perspective of textile processing process, formaldehyde on textiles mainly comes from color fixing treatment after printing and dyeing and resin finishing in finishing. At present, some developed countries in the world, such as Germany, Japan and the United States, have successively adopted and implemented relevant regulations to limit the content of formaldehyde on textiles. It is stipulated that the content of formaldehyde on underwear must be controlled within 75mg / kg and that on coat should be controlled within 300mg / kg . Therefore, some scientific researchers try to remove formaldehyde by high-temperature baking after color fixation, but the effect is not ideal. The impact of printing and dyeing auxiliaries on the ecological environment is far more than the textile itself. Therefore, the development of a color fixing agent with good fastness improvement effect, small color change and no formaldehyde has become an urgent requirement of the current printing and dyeing auxiliary industry.
From 1960s to 1980s, it was a golden period of color fixing agent research. With the increasingly strict requirements for color fastness and formaldehyde content in the international textile market, our country has strengthened the development of formaldehyde free color fixing agent from the middle and late 1980s to replace the traditional aldehyde containing color fixing agent. From the current situation, the research on color fixing agents mainly has the following directions. Most of the aldehyde free color fixing agents used are cationic color fixing agents synthesized by amines and epichlorohydrin, and on this basis, they can be further improved or compounded to improve the comprehensive color fixing ability. Although great achievements have been made in the formaldehyde free and color fixing effects of color fixing agents, some indicators, such as wet rubbing fastness, color fastness, light fastness and chlorine fastness, need to be further improved. This topic also aims to study formaldehyde free polyamine reactive color fixing agents with high wet treatment fastness.
Development of color fixing agents
Since the 1930s, major chemical companies at home and abroad have studied color fixing agents successively. At that time, there were no reactive dyes. Therefore, the focus was on direct and acid dyes. Among them, dicyandiamide formaldehyde resin and copper containing dicyandiamide formaldehyde resin had ideal color fixing effect, and gradually formed color fixing agent commodities, namely color fix y and coprantex B (the corresponding domestic color fixing agents are color fixing agent y and color fixing agent M). In the early 1950s, reactive dyes came out. Aiming at the problem of poor water washing fastness of reactive dyes, bonamen chemical company [20] treated them with cationic fixing agent and weak acid substances to improve their wet treatment fastness. Since then, there have been more and more kinds of color fixing agents, but the chemical structure of color fixing agents has been relatively single for half a century. In the 1980s, with the enhancement of environmental protection awareness, the shortcomings of aldehyde containing color fixing agent [15-18] were gradually exposed. For example, it is easy to cause color change and rough hand feel of dyed fabrics, especially the high content of formaldehyde, which is irritating and toxic to the skin, so its use is limited. Japan, Germany and the European Community [19] stipulate that the formaldehyde emission of textiles in direct contact with skin and infant textiles should be less than 75% respectively × 10-6 and 20 × 10-6 (Japan stipulates that the formaldehyde emission of infant clothing should not be detected); China also imposes mandatory restrictions on the formaldehyde content of textiles, and the requirements for formaldehyde emission are the same as those in Japan and Germany. Therefore, the development and application of formaldehyde free color fixing agent has become the mainstream of the development of color fixing agent.
In recent years, the world textile market has put forward new requirements for the color fastness of dyed fabrics. For example, eco tex and Oeko tex standards [21] require the washing color fastness of dyed fabrics to reach grade 3 ~ 4. The dyed fabric after color fixing treatment should not only have certain color fastness to water washing, friction, sweat, sunlight and chlorine, but also be free of formaldehyde, non-toxic and do not affect the feel and color of the fabric. The performance requirements of the color fixing agent are more strict. Therefore, the development and application of green high-performance color fixing agents that meet the environmental protection indicators [22] and requirements has become the current development trend. At present, there are several kinds of color fixing agents studied more: waterborne polyurethane, cationic color fixing agents and polyamine color fixing agents [23]. The research of this kind of color fixing agent will turn to the research of color fixing agent with low cost, which will provide an opportunity for the development of this kind of color fixing agent with high color fixing performance [24]; In recent years, there are more and more studies on cationic color fixing agents. These color fixing agents have excellent performance and have little impact on fabric color [25], so they have great development prospects; Polyamine color fixing agents not only contain cationic groups, but also can combine with fiber reactivity. They have the advantages of high performance, no formaldehyde and little influence on color light and hand feeling. Therefore, the research on polyamine color fixing agents is also more and more.
Fixation mechanism
Since the 1930s, scientists have begun to study the color fixing mechanism of various color fixing agents on textile fibers in the process of studying the synthesis and application properties of color fixing agents for textile industry. From the perspective of the development of aldehyde free color fixing agents, the dependent mechanisms are mainly the following:
(1) Insoluble lakes are formed by using fixing agents and dyes
The cationic groups such as quaternary ammonium salt in the color fixing agent molecule can be combined with the anionic groups in the dye molecule in the form of ionic bond to form a polymer Lake slightly soluble or insoluble in water, and close the water-soluble groups in the dye to deposit inside and outside the fiber. At the same time, in the alkali bath, the anionic fiber combines a large number of cationic groups to promote the surface cation of the internal and external pores of the fiber, so as to change the interface potential of the fiber in the dyeing bath, reduce the potential barrier during dyeing, and promote the adsorption of anionic dye molecules. Therefore, the stronger the cationic property of the color fixing agent, the better the color fixing effect.
(2) The reactive group in the fixing agent molecule is used to crosslink the dye
The reactive group in the color fixing agent molecule can be crosslinked with the reactive group on the dye molecule and the hydroxyl group of cellulose molecule. The color fixing agent acts as a bridge to reduce the water solubility of the dye, improve the soaping and white cloth color fastness of the dyed fabric, and improve the wet treatment fastness of the dye.
(3) Film forming ability of color fixing agent on fiber surface
The film-forming property of the color fixing agent on the fiber surface is used to improve its color fastness. The test results show that the color fixing effect of the color fixing agent with good film-forming property is better. The high polymer polymerized by olefins can improve the color fastness even if it does not contain reactive groups or cationic groups. This is because the high polymer forms a film on the fiber surface. During the baking process of the treated dyed fabric, the reactive groups of the color fixing agent are self crosslinked into macromolecules, forming a protective mold with a certain strength on the fabric surface. Therefore, the color fixing agent with good film-forming property reduces the dye dissolution and has a good color fixing effect. If the reactive group or cationic group is introduced into the film-forming material, the color fastness can be improved. At present, new color fixing agents mostly use this way to improve their color fastness.
(4) Using the molecular gravity between the color fixing agent and the fiber
The molecular attraction between the color fixing agent and the fiber is used to increase the fixation strength of the color fixing agent, so as to improve the color fastness. Here, the intermolecular attraction is mainly hydrogen bond attraction. For example, the color fixing agent made of polyethylenepolyamine and epichlorohydrin has better color fastness than the color fixing agent made of dimethylamine and epichlorohydrin. Another example is the condensate of diethylenetriamine and dicyandiamide. Its color fixing effect is mainly due to its strong hydrogen bond attraction and weak cationic property. In addition, N1 (diethylenetriamine) ∶ N2 (epichlorohydrin) is mostly a 1:1 condensate. If the amount of epichlorohydrin is increased on this basis, a three-dimensional condensate can be formed. The reactive groups in the molecules increase, and the color fixing effect should be improved. However, the fact is the opposite. The reason is that the color fixing agent is a three-dimensional structure rather than a plane structure, which weakens the hydrogen bond attraction between the color fixing agent and the fiber, resulting in the reduction of the color fixing effect. (5) The buffering ability of color fixing agent is used to improve the sweat fastness of dyes.
Reactive dyes are not acid resistant. Under acidic conditions, the covalent bond between reactive dyes and fibers will be weakened due to hydrolysis, which is easy to reduce the fastness to perspiration. Because sweat contains acidic substances, it is necessary to improve the fastness of sweat stains
The molecular structure of the color fixing agent should have a certain acid absorption capacity, that is, it should have a good pH buffer capacity, so it is best to contain nitrogen atoms in the color fixing agent molecule. For example, polyol amine condensate as a color fixing agent can improve the unique sweat fastness of dyed fabrics.
(6) The smoothing agent in the color fixing agent is used to make the fiber surface smooth and soft to improve the friction fastness of the color fixing agent. After the fabric fiber is dyed with dye and fixed with aldehyde free color fixing agent, the surface smoothness is not greatly improved, which affects the wet friction fastness of the color fixing agent to a great extent. For this reason, the fixative additives used to improve wet rubbing fastness have been developed at home and abroad recently, and some products are sold. These special additives are actually softening agents, such as polyethylene emulsion, filtered amino silicone oil and so on. However, these softeners are effective only when the dosage is large (more than 50g / L), and the use of such additives can only be mixed with color fixing agents. Therefore, a soft substance that can be grafted with color fixing agent is being developed, so as to achieve the purpose of both softness and improving wet rubbing fastness.
(7) The UV absorber was grafted into the fixing agent molecule
The ultraviolet absorption group is used to absorb the ultraviolet in the sunlight to prevent the damage of ultraviolet to the dye structure and improve the color fastness to sunlight. According to patent [31], salicylhydroxamic acid is first added to water, then dissolved in NaOH, saturated CuSO4 · 5H2O solution is added, stirred for 10 minutes, and filtered to obtain green gray powder, that is, sun resistant color fixing agent, which has good application effect when pH = 6 ~ 8. Direct use of copper phosphate and salicylaldehyde oxime also has good light resistance.
In fact, the fixation process of most color fixing agents uses a variety of fixation mechanisms to improve the color fastness of dyed fabrics to water washing, sunlight, friction, acid and alkali and chlorine, so as to achieve satisfactory fixation effect.
