Application of photochromic materials in textile

Photochromic materials with novel visual impact, decoration and functionality are playing an increasingly important role in functional textiles, clothing, decorative materials, anti-counterfeiting materials and security fields. At the same time, photochromic materials play an important role in the field of information storage materials technology because of their properties of reversible color-changing reaction in light response. With the increasing awareness of novelty and functionalization of textiles, the demand for color has changed from practical type to the pursuit of fashion forward type with special functions, and the demand for photochromic textiles is also increasing. Photochromic materials are increasingly active in the field of civil textiles, and gradually attracted attention, which can be used in the production of T-shirts, pants, swimsuits, casual wear, sportswear, work clothes, children's wear, hats, backpacks, curtains, anti-counterfeiting trademarks, shoes and toys.
Photochromic materials are sensitive to the effects of solvents and auxiliaries in finishing process and external factors in the process of use. There are some problems such as oxidation caused by solvent polarity color development, pH value, oxidation, light and temperature, fatigue resistance and poor light stability. In addition, these interference factors will also cause the irreversible color-changing reaction of photochromic materials, so as to lose the ability of reversible color-changing. Some photochromic materials need to be coated in microcapsules with organic solvents or photoinitiators at the same time in order to maintain the condition of color-changing reaction and produce color-changing effect.
Some water-based photochromic materials lack affinity and binding force for fibers and cannot be dyed by conventional dyeing. Other oily photochromic materials cannot be processed with water as a medium, and are only applied to fabrics using adhesives and traditional printing finishing methods. Therefore, in terms of the application of photochromic materials on fabrics, it is an effective method to cover the fabric with microcapsules and then fix it with adhesives. Some researchers at home and abroad have made some attempts to improve the resistance to fatigue by using microencapsulation. By microencapsulation and adding photostabilizers and antioxidants containing blocked amine, the performance and resistance to fatigue of photochromic microcapsules have been effectively improved. However, hindered amine photostabilizer is a kind of alkaline free radical trapping agent, which has antagonism with acidic substrates or additives. Its performance will be affected by acidic environment, and it has some disadvantages such as volatilization, frosting, migration and extraction.
Microcapsules can be applied to fabrics in adhesive dispersions by finishing agent rolling, baking, spraying, dipping and screen printing techniques. However, these technologies have some disadvantages, such as poor air permeability and hindering the release of active substances, which limit their application to a large extent. The lack of strong chemical binding between many functional materials and textiles leads to poor washing fastness. Chemical crosslinking has been used to improve the binding fastness, including polycarboxylic acids, citric acid and glutaraldehyde. Due to the small particle size, high dispersion and large surface area of microcapsules, the chemical crosslinking method in which microcapsules are dispersed in finishing solution can provide a strong binding force with the fabric and generate closer contact with the fabric, which can not only form a uniform and continuous thin coating on the surface of the fabric, but also be fixed in the pores between the fibers.
Application of photochromic materials in textile
The application of photochromic materials in textiles should not only study the existing process, but also develop new coloring ways.
grafting
The photochromic groups or photochromic compound molecules are bonded to the main chain or side chain of the polymer by covalent bonds, so that the polymer polymer has photochromic characteristics and fast light response speed, and the photochromic effect is not affected. The photochromic polymers synthesized by this method are applied to textiles by fiber technology. A novel water-soluble photochromic polymer was prepared by grafting 9 '-allyl indoline spiroxazine-phenoxazine onto carboxymethyl chitosan. SBS thermoplastic elastomer triblock copolymer containing naphthalene pyran polymer as side link dendrimer was prepared by polymerization of naphthalene pyran acrylate monomer with styrene-butadiene-styrene block copolymer (SBS) solution dissolved in tetrahydrofuran. The decay rate of naphthalene pyran elastomer films can be adjusted by adjusting the drawing lubrication film and changing the length of the double bond connection between the acrylate and naphthalene pyran monomer. Acrylate side chains containing photochromic azophenyl groups (disperse red 1,2) are grafted onto different polymer substrates: Polypropylene, low-density polyethylene, polyethylene glycol terephthalate, and polycarbonate CR-39 were prepared by esterification with disperse red 1 in the presence of triethylamine by gamma radiation from polymer films in an acrylyl chloride solution in toluene. The nanoparticles of spiropyranol monomer crosslinked methyl methacrylate were prepared by a simple one-step fine emulsion polymerization. The photoreversible nanoparticle aqueous dispersion has excellent photoreversible properties. The grafting modification method has the disadvantages of low yield and poor fastness, the speed of discoloration and fading is slowed down, and the fatigue resistance is also decreased.
Dyeing method
Printing and dyeing techniques are the earliest and easiest way to apply photochromic materials to fabrics. The dyeing technology of photochromic dyes is basically the same as that of ordinary dyes. Photochromic dyes show colors such as red, yellow, orange, blue, sky blue, peach and purple after excitation. Their specific induction wavelength is different, and the absorption rate of light is also different. In order to achieve obvious photochromic compatibility, it is necessary to look for photochromic dyes with obvious and large degree of color change, and then design with appropriate color matching with common dyes. The main color-changing dye is a dye with photochromic properties, which requires minimum amount control. If the amount of main color dye is too little, the absorbance difference of different bands is small, will not produce obvious color effect; The function of auxiliary photochromic dyes is to increase the difference of absorbance between different bands and enhance the effect of color change. The ratio relationship between primary and secondary photochromic dyes is an important factor affecting the photochromic effect. Generally, the dyeing of photochromic dyes does not need to change the conventional dyeing process and equipment. In order to obtain the dyeing effect and discoloration effect with excellent fastness (uniformity and color depth), the key factor is the selection of photochromic dyes. Fabrics with photochromic properties developed by the above dyeing techniques have the disadvantage of low dyeing fastness. The photochromic dyes are directly exposed to the external environment, and will be affected by auxiliaries and surrounding environmental factors during dyeing and finishing processing and use. Even some oily photochromic pigments can not be dyed directly by dyeing methods.
Printing process
The printing process is the main method for the application of photochromic materials in textiles because of its simple operation, simple process flow, easy quality control, no need for complex and expensive instruments and equipment, and no special requirements for fabrics. The printing process disperses the photochromic compounds in a color paste containing adhesives and thickeners, and then uses the color paste to print the fabric to obtain the photochromic printed fabric. This method has no selectivity for fabric fibers, especially for cotton woven fabrics and knitted fabrics.
Printing process can be conventional screen, roller printing equipment processing, or the use of ink jet and transfer printing, can also be applied dyeing technology, the use of color paste spectrochromic dye paste and photochromic microcapsule color paste two categories. Some photochromic pigments are water-soluble and do not have photochromic properties in water, so they need to be encapsulated into microcapsules before preparing photochromic pigments. The printing process is similar to the conventional pigment and paint printing process. Photochromic microcapsules are printed on the fabric to produce the printed fabric with photochromic properties. 2.4 Spinning method
The application of photochromic compounds by fiber technology has the advantages of good hand feel, washing resistance, and long-lasting color changing effect. Fiber technology is mainly solution spinning and melt spinning. The fibers produced can be made into embroidery thread, knitting yarn, woven yarn, used for decoration, stage clothing, outdoor clothing, children's wear, hats, sports shoes, sweaters and other products.
Photochromic fibers prepared by solution spinning are spun by directly adding color-changing compounds to the spinning solution. Through this method, Matsui Pigment Chemical Industry Co., Ltd. of Japan has applied for a patent. It has also been studied that spinning solution containing spiroxazine and sebacate compounds was spun into water bath by solution spinning method, and photochromic fibers were obtained after washing.
Photochromic fibers prepared by melt spinning can be divided into three types: polymerization, blending and core-skin composite spinning. Polymerization method is to introduce photochromic groups into polymer polymers through the reaction, and then spin the polymer into fiber, such as the synthesis of sulfur-containing derivatives of the polymer into fiber. The method of blending silk is to melt and blend the photochromic compounds with the polymer, or disperse the photochromic compounds in the resin carrier to make color masterbatch, and then mix with the polymer to melt spinning.
Photochromic spinning requires the addition of photochromic dyes in the solid phase, but the effect of discoloration is not ideal, the play of its photochromic properties is affected, but also affected by polymer polymers and microstructure, so it is necessary to select and control the types of polymers and fiber microstructure involved in spinning. In addition, the restriction of spinning conditions is also an important factor. The photochromic compounds used for spinning require high temperature resistance, so their application in this spinning condition is limited.
Finishing method
The finishing technique involves impregnating a fiber, yarn or fabric with a finishing solution containing a photochromic monomer, usually using styrene or vinyl acetate. The photochromic compounds are polymerized within the fiber to give the fiber, yarn or fabric a photochromic property.
The post-finishing method can maintain the photochromic properties of the textile for more than 6 months, and can be used for the special and novel visual effect of umbrellas, clothing and other textiles. Due to the introduction of color-changing compounds after spinning, the treatment method is not limited by temperature, the influence of spinning blends or copolymers, and does not affect the mechanical properties of fibers, yarns and fabrics. In view of the requirements of clothing hygiene for the post-finishing of textiles, the residues of chemical reagents and auxiliaries on the fabrics treated by this post-finishing polymerization technology are difficult to meet the standards of clothing wear, so this method is more suitable for industrial textiles, not for the production and processing of textiles and home textiles.
Chemical crosslinking
The covalent bond formed by chemical crosslinking of bishell urethane-chitosan photochromic microcapsules to cotton fabric with citric acid has good washable fastness and thermal stability, showing a bright color. In addition, the microcapsules have a larger specific surface area when chemically cross-linked by the coating method, which can form a closer contact with the fabric and fibers. In addition, microcapsules can also form a film of surface cross-linked system on the surface of the fabric, which exists in the form of clusters of microcapsules combined with irregular fragments on the surface of the cotton fiber. These microcapsules are not only fixed on the fiber of the cotton fabric, but also constitute an irregular fragment film that can be embedded and fixed in the pores between the fibers to further enhance the bonding fastness.
A novel approach of photochromic microcapsules binding firmly to cotton fabric was discussed. Bivalve urethane-chitosan photochromic microcapsules can be blended with more than 20 colors according to the mass ratio of yellow/red/blue bivalve urethane-chitosan microcapsules to meet the application of multi-chromatographic bivalve microcapsules in textiles and clothing. The outdoor clothing sunscreen indication label designed by bishell urethane-chitosan photochromic microcapsules and their color matching microcapsules covalently combined on cellulose fiber fabric has the function of indicating the ultraviolet radiation intensity in sunlight and health protection early warning. It has the performance characteristics of fast response speed, obvious change of color characteristics and bright color. It meets the combination of health protection function and decoration in outdoor clothing.
conclusion
The photochromic properties of organic photochromic compounds are mainly manifested in that the excitation spectrum range of response discoloration is UV-visible band, the excitation spectrum light source is simple and easy to obtain, and there is no strict and detailed restriction on the excitation spectrum range. After excitation, the response discoloration speed is fast, the color is bright, and the application range is wide. However, there are still some problems in the current research and application status. The first is the poor fatigue resistance under continuous high intensity irradiation and the limited number of reversible discoloration under repeated irradiation in the range of excitation spectrum. In addition, photochromic materials are sensitive to solvents and auxiliaries in the finishing process as well as external factors in the process of use, such as solvent polarization color development, pH value, oxidation, light and temperature factors brought by oxidation, fatigue resistance and light stability, etc. These interference factors will also cause the irreversible color-changing reaction of photochromic materials, so that they lose the ability of reversible color-changing. Second, some photochromic materials need to be coated with organic solvents or photoinitiators in microcapsules at the same time in order to maintain the condition of color-changing reaction and produce color-changing effect. Third, some water-based photochromic materials lack affinity and binding force for fibers, which can not be dyed by conventional dyeing. Other oily photochromic materials cannot be processed with water as a medium and can only be applied to fabrics using adhesives and traditional printing finishing methods. Fourthly, grafting modification method has the disadvantages of low yield and poor fastness, its discoloration speed and fading speed are slowed down, and fatigue resistance is also reduced correspondingly. Fifth, the photochromic compounds used in spinning need to be resistant to high temperature, and their application is limited. Sixth, the residual amount of chemical reagents and auxiliaries on the fabrics treated by post-finishing polymerization technology is difficult to meet the hygienic and safety standards of clothing.
In order to improve the fatigue resistance and photochromic properties of photochromic compounds in the process of use, microencapsulation method is a safe and effective way to reduce or even avoid the oxidation and interference of photochromic materials on solvents and additives in the finishing process and external factors in the process of use. Microencapsulated photochromic compounds can significantly expand the safe and efficient application of photochromic materials in textiles. The wall shell of photochromic microcapsules also has functional groups that can be covalently cross-linked with cotton fabric, so as to achieve the goal of covalently combining microcapsules with cotton fabric. The treated cotton fabric has excellent bonding fastness, washing fastness, thermal stability, acid and alkali resistance and bright color. A novel way for the printing finishing of photochromic microcapsules on cellulose fiber fabric is discussed. It provides a novel reference to endow fabrics with photochromic properties. Through its characteristics of changing color in response to sunlight and changing color depth with sunlight irradiation intensity, it can be applied to the sign pattern that can indicate ultraviolet irradiation intensity in sunlight. It has the characteristics of fast response speed and high color recognition under different sunlight irradiation intensity.