[Abstract] Since the mid-1980s, the proportion of synthetic fibers in textile fibers has been continuously increasing worldwide. From 1995 to the present, the proportion of synthetic fibers has surpassed that of natural fibers, becoming the main source of fibers used in textiles and clothing. In terms of production tonnage, although raw cotton increased from 17.99 million tons in 1992 to 19.198 million tons in 2002, the production of raw wool decreased from 1.719 million tons to 1.271 million tons during the same period. The proportion of both in textile fibers has decreased by 11% in 2002 compared to 1992. In the same 10 years, the significant growth in the production of synthetic fiber filament yarn and staple fiber increased by 1.41 times and 0.56 times, respectively. Especially, the development of synthetic fiber filament yarn has provided textile designers and manufacturers with more opportunities to develop new fabrics with innovative aesthetic visuals and performance, leading to a production increase that exceeds 1.5 times that of synthetic fiber staple fibers.
　　
　　Since the mid-1980s, the proportion of synthetic fibers in textile fibers has been continuously increasing worldwide. From 1995 to the present, the proportion of synthetic fibers has surpassed that of natural fibers, becoming the main source of fibers used in textiles and clothing. In terms of production tonnage, although raw cotton increased from 17.99 million tons in 1992 to 19.198 million tons in 2002, the production of raw wool decreased from 1.719 million tons to 1.271 million tons during the same period. The proportion of both in textile fibers has decreased by 11% in 2002 compared to 1992. In the same 10 years, the significant growth in the production of synthetic fiber filament yarn and staple fiber increased by 1.41 times and 0.56 times, respectively. Especially, the development of synthetic fiber filament yarn has provided textile designers and manufacturers with more opportunities to develop new fabrics with innovative aesthetic visuals and performance, leading to a production increase that exceeds 1.5 times that of synthetic fiber staple fibers. Among the synthetic fibers used in textiles and clothing, polyester fiber made from polyethylene terephthalate has grown the fastest, with production increasing by 14.292 million tons from 1992 to 2002, making its proportion in synthetic fibers reach 76% in 2002, an increase of 14% compared to 1992. During the same period, although the production of polyamide fibers and polyacrylonitrile fibers also increased by 741,000 tons and 763,000 tons, their proportions in synthetic fibers in 2002 decreased by 9% and 5%, respectively, compared to 1992, with polyamide fibers accounting for 14% and polyacrylonitrile fibers only 10%. The rapid growth of polyester fiber production capacity and output has led dye manufacturers to focus their development efforts on disperse dyes for polyester fibers, similar to how they concentrate on reactive dyes for cotton and other cellulose fibers. At the same time, the development of blended fabrics composed of elastic fibers (i.e., block polyurethane fibers) with polyester fibers, polyamide fibers, cotton, and other cellulose fibers has prompted dye manufacturers and dyers to address the dyeing performance and color fastness requirements posed by these new blended fabrics. Additionally, the existing disperse dyes' dyeing performance and color fastness do not meet the requirements of new polyester fibers such as polylactic acid fibers (PLA) and polyethylene terephthalate glycol (PIT). All of these have promoted the research and development of new textile chemicals to improve the color fastness of synthetic fibers.
　　
　　1. New disperse dyes for improving the color fastness of polyester fibers.
　　
　　First, the development of ultra-fine polyester fibers, especially those made using composite spinning methods to create island-type ultra-fine polyester fibers, has greatly improved the wear performance of fabrics made from polyester fibers. The suede-like fabrics made from them are very similar to natural suede, leading to an annual increase in the production of ultra-fine polyester fibers. However, the supramolecular and morphological structures of these fibers have changed significantly, resulting in a large specific surface area, which has introduced new issues in the dyeing speed, dye uptake, dye visibility, uniformity, and fastness of traditional disperse dyes and early disperse dyes for ultra-fine polyester fibers. Therefore, it has become urgent to improve and enhance the uplift and fastness of disperse dyes for ultra-fine polyester fibers. The Lumacron MFB dye developed by M. Dohmen Company is a new generation of disperse dyes designed to meet the high fastness standards required by ultra-fine polyester fibers. They not only cover the entire color spectrum, including yellow, orange, bright red, red, ruby, turquoise, blue, navy blue, and black, but also possess excellent uplift, compatibility, and wet fastness. The excellent performance of Lumacron MFB dyes makes them widely adaptable to ultra-fine polyester fibers. By using suitable dyeing auxiliaries such as 1-2g/L Dispertan MF and 2g/L Doregal WMB, and matching dyeing processes, they can be used for dyeing various ultra-fine polyester fibers, including island-type and differentiated composite types. To avoid the double-sided color difference effect, the company recommends using the three primary colors of Lumacron MFB dyes, which have excellent coverage for the differences in fiber dyeability, namely Lumacron Orange MFB, Lumacron Rubine MFB, and Lumacron Blue MFB or Lumacron Navy MFB. For light dyeing requiring high light fastness, M. Dohmen Company recommends using Dorospers K-type dyes. Additionally, Kayalon Microester dyes from Japan's chemical company are also a new type of disperse dye that improves the color fastness of previous disperse dyes used for ultra-fine polyester fibers. It has four series: A, B, C, and D, suitable for different application requirements, with good coverage, excellent light fastness, wet fastness, sublimation fastness, and ease of dyeing into deep colors. It is also applicable for dyeing island-type ultra-fine polyester fibers and differentiated composite ultra-fine polyester fibers. Dystar's Dianix SF-type dyes, Dianix SPH, and UPH dyes are also suitable, with Dianix SPH dyes particularly suitable for situations requiring fast diffusion rates.
　　
　　In recent years, polyester fiber fabrics such as sportswear, casual wear, and automotive interior fabrics need to undergo heat setting treatment after being dyed with disperse dyes to ensure consistent and stable finished product dimensions. Due to the high heat setting temperature, which exceeds 140°C, the disperse dyes inside the fibers will undergo reverse thermal migration compared to the dyeing process, with some dyes migrating back to the fiber surface, leading to a decrease in color fastness of the heat-set fabrics, primarily in wash fastness and sweat fastness, and may stain adjacent linings or pollute the environment. In the past, the wash fastness data provided by disperse dye manufacturers were based on polyester fabrics dyed with disperse dyes and then reductively cleaned without heat setting treatment, thus failing to reflect the thermal migration resistance of disperse dyes. Additionally, polyester fabrics, especially blended fabrics composed of polyester fibers and cellulose fibers, often require finishing treatments such as softening and waterproofing. Many softeners and waterproofing agents available in the market, such as amino silicone softeners, are emulsified using non-ionic surfactants, which act as carriers that can dissolve and disperse the dyes, causing the already dyed disperse dyes to not only undergo thermal migration due to heat but also migrate to the fiber surface due to dissolution in the carrier, thereby reducing wash fastness. This migration can occur even during storage and transportation, contaminating adjacent white fabrics. Practice has shown that a considerable portion of older disperse dyes has poor thermal migration resistance, which can lead to a decline in wash fastness after heat setting or finishing treatments such as softening and waterproofing. For example, C.I. Disperse Red 54, C.I. Disperse Red 60, C.I. Disperse Red 73, C.I. Disperse Red 152, C.I. Disperse Red 153, C.I. Disperse Red 167, C.I. Disperse Blue 183, as well as disperse blue EX-SF300% and disperse black EX-SF300% made from C.I. Disperse Purple 93:1, C.I. Disperse Blue 291:1, and C.I. Disperse Orange 76, are all such disperse dyes. It should be noted that the impact of softening and waterproofing treatments on the wash fastness of dyed polyester fabrics is related to the properties of the softeners and waterproofing agents used, as well as the structure of the disperse dyes used for dyeing. For instance, polyester fabrics dyed with 40 g/L disperse deep blue H-GL will have reduced wash fastness when treated with methyl organic silicone softeners, failing to meet requirements, while using fatty amide softeners for finishing improves wash fastness and meets requirements. Similarly, using fluorinated acrylate waterproofing agents for waterproofing dyed polyester fabrics will reduce wash fastness and fail to meet requirements, while using fluorosilicone waterproofing agents improves wash fastness and meets requirements. To enhance the thermal migration resistance of disperse dyes, Ciba Specialty Chemicals has developed Terasil W type disperse dyes and Terasil WW type disperse dyes, especially the latter, which are a class of third-generation wash-resistant disperse dyes with phthalimide azo structures, covering the entire color range. Fabrics dyed with these dyes exhibit excellent wash fastness after heat setting or finishing treatments such as softening, even under strict washing conditions (such as 60°C washing), still meeting high wash requirements. They have significantly improved and advanced compared to the first and second generation wash-resistant disperse dyes. For example, the first generation wash-resistant disperse dyes C.I. Disperse Red 111 and C.I. Disperse Blue 284 have improved wash fastness compared to C.I. Disperse Red 167, but they perform poorly in strict wash tests, washing of blended fabrics made of polyester fibers and other fibers, and washing of dark fabrics. The second generation wash-resistant disperse dyes developed later, such as C.I. Disperse Red 356, have excellent wash fastness (even under very harsh conditions), but their dyeing performance is not satisfactory, especially in terms of reproducibility and sensitivity to dyeing conditions such as dyeing temperature, making it difficult to achieve deep colors. The third generation wash-resistant disperse dyes not only improve the wash fastness of the aforementioned second generation dyes but also enhance other dyeing properties, as shown in Table 1.
　　
　　Lumacron MFB dyes also exhibit excellent thermal migration resistance. For example, comparative tests stored at 60°C for 5 weeks show minimal staining on white polyester fibers, even when using Lumacron Black MFB for dyeing, and this remains true after softening treatments. Dystar's Dianix XF type dyes and Dianix SF type dyes are also new dyes with excellent wash fastness, such as Dianix Bfill Scarlet XF, as well as Dianix Red SE-3B, Dianix Royal Blue SE-R, and Dianix Yellow SE-GBN. They form a tri-primary disperse dye with high thermal migration resistance, high wash fastness, high strength, and high brightness. Fabrics dyed with these dyes exhibit not only excellent wash fastness after heat setting or finishing treatments such as softening but can also replace low-energy to medium-energy tri-primary disperse dyes made from Disperse Red 3B, Disperse Blue 2BLN, and Disperse Yellow RGFL (Disperse Yellow RGFL is a banned dye).
　　
　　With the increasing requirements for the color fastness of automotive interior decorative fabrics, Dystar has developed a series of new high light fastness disperse dyes to replace older disperse dyes, such as the Dianix HLA series dyes, which not only have higher light fastness than Dianix KIS-U dyes (for light colors) and Dianix KIS-M dyes (for medium colors) but also solve the issue of color consistency in fabrics dyed with Disperse Black SPC. Dianix AM Specialities dyes have higher light fastness than Dianix AM Classics dyes and are suitable for dyeing from light to dark colors, while Dianix AM-SLR dyes are a class of disperse dyes with ultra light fastness, also suitable for a wide range of dyeing from light to dark colors. The Dianix AM Formula One dyes developed based on them not only have ultra light fastness at high temperatures without color change but also fully comply with the new sunlight test requirements set by General Motors and the light fastness requirements specified by the International Automotive Manufacturers Association and other tests. They have four main varieties and five auxiliary varieties, covering over 90% of commonly used colors.
　　
　　2 New dyes and new auxiliaries to improve the color fastness of polyamide fiber dyeing.
　　
　　In recent years, the application of polyamide (nylon) filament yarn in sportswear and blended fabrics made with elastic fibers has grown rapidly. To improve the color fastness of dyed polyamide fibers, Dystar has developed Isolan NHF-type dyes, which are 1:2 metal complex dyes for dyeing polyamide fibers with comprehensive fastness. They not only have excellent light fastness and high wet fastness but also exhibit great compatibility and good color matching with polyurethane elastic fibers, significantly improving the color fastness of previous dyes. They can be mixed with Telon M-type dyes (acid dyes) and Isolan S-type dyes (metal complex dyes) in any combination. The Dorasyn XL dye launched by M. Dohmen is also a modified acid dye that improves the color fastness of polyamide fiber dyes, featuring excellent wet fastness and good dyeing uniformity. This characteristic distinguishes this type of dye from others, as other dyes for polyamide fibers often require a choice between color fastness and dyeing uniformity. Additionally, this type of dye is free of metals (except for turquoise dyes), offering greater ecological safety. To effectively use this type of dye and ensure good dyeing performance and high color fastness and reproducibility, M. Dohmen recommends using Doregal XL as a suitable leveling agent instead of the ordinary leveling agents available on the market. If the polyamide fabric shows obvious weft stripes, an additional 2.5%-5.0% of Doregal BRC should be added. If necessary, Domapal B conc. (a non-volatile acid) can be used to achieve better dyeing performance and fixation rate. When dyeing dark colors, the initial pH of the dye bath should be adjusted to 3.5 using Donapal B conc., and the final pH can also be adjusted to 3.5 as needed. For polyamide fabrics with higher color fastness requirements, such as high standards for alkaline sweat stain fastness, washing fastness, and chlorine water fastness, a treatment bath containing 3%-4% Domafix ACL can be used after dyeing, treated at pH 4.5 and 75°C for 10-20 minutes.
　　
　　Additionally, white synthetic fiber fabrics such as polyamide fabrics face a yellowing problem during storage or transportation. This phenomenon often occurs where the fabric or clothing comes into contact with packaging materials, due to the presence of a colorless additive in the packaging material, namely butylated hydroxytoluene (BHT), which is an antioxidant. When in contact with textiles, it can transfer to the textiles and react with nitrogen oxides (NOX) from exhaust gases to form a yellow nitro dye. The rate of formation increases with higher humidity and temperature during transportation or storage. To address this issue, BASF has successfully developed a new additive, TX1567, which can reliably prevent the binding of nitrogen oxides with butylated hydroxytoluene molecules, even under high ambient temperatures in tropical climates. This is particularly important for developing countries with high nitrogen oxide levels or high traffic density. TX1567 can be used for all white or light-colored textiles, and it can be applied alone or in combination with fluorescent whitening agents or dyes in exhaustion processing or pad-dry-cure (thermofix) processing. For example, using 5%-15% TX1567 and 0.5%-1% Ultraphbr TC Liquid (fluorescent whitening agent) for the impregnation of polyamide fabrics, with a bath ratio of 5:1-20:1, starting at a temperature of 30°C-60°C, then raising the temperature to 100°C within half an hour and maintaining it for 30 minutes can yield excellent results.
　　
　　To improve the chlorine fastness, ozone fastness, and wet fastness of polyamide fibers and their blended fabrics with elastic fibers, Ciba Specialty Chemicals has also developed a new additive, Cibafix CL-01. It is a purified natural product that is 100% biodegradable and can be used with acid dyes, metal complex dyes, or reactive dyes in all dyeing and printing processes. It operates effectively across a wide pH range (pH 3-6), providing high dye uptake, excellent leveling, and dyeing uniformity, significantly improving the chlorine resistance of dyed fabrics. It is especially suitable for producing high-quality, durable swimwear and can remove stains with detergents. Furthermore, this additive does not affect the hand feel and light fastness of the fabric. Practical experience has shown that certain dyed fabrics treated with Cibafix CL-01 actually improved their light fastness.
　　
　　Due to the characteristics of blended fabrics made from polyamide and polyester fibers, such as anti-white striping effects, differential dyeing, and uniform color depth effects, woven fabrics with polyamide fibers as weft and polyester fibers as warp have become popular in the market in recent years. Additionally, the widely used blended fabrics made from polyamide and polyester bi-component ultra-fine fibers in artificial wool fabrics, silk-like fabrics, sportswear, ultra-high-density fabrics, and high-tech clean clothing make it important to develop suitable dyes for dyeing. Generally, disperse dyes for such fabrics require consistent light color enhancement, low staining of polyamide fibers during single dyeing, easy wash-off of disperse dyes during secondary dyeing processes with acid reduction cleaning, and reliable exhaustion of dye baths to prevent uneven dyeing. The acid dyes and acid metal complex dyes used must have low staining of polyester fibers, adaptability to different types of polyamide fibers, and good fastness properties. Based on these requirements, when the dyeing fastness requirements for polyester/nylon blended fabrics are not high and only one disperse dye is used for light color dyeing, azo-type disperse dyes are typically sufficient, such as Dianix Yellow AC-Enew, Dianix Pink AM-REL, and Dianix Blue AC-Enew. When the dyeing fastness requirements for polyester/nylon blended fabrics are high, or when flash colors or two-color dyeing is needed, or when dyeing medium to dark colors, the two-bath method or one-bath method using disperse/acid or metal complex dyes should be selected. Ciba Specialty Chemicals recommends disperse dyes with low staining on nylon, such as Terasil Yellow 4G, Terasil Red 3BL-01, Terasil Blue P-2BR, and Terasil Blue BGE-01. Acid dyes used for one-bath dyeing have characteristics of migration, leveling, and good color fastness, such as Tectilon Yellow 3R, Tectilon Red 2B, and Tectilon Blue 4R-01. Dystar recommends disperse dyes for medium to dark colors, such as Dianix Yellow S-6G, Dianix Red S-2B, Dianix Dark Blue K-R, and Telon Yellow A2R, Telon Rubine A5B, Telon Navy AMF, which can be used in one-bath dyeing processes or in two-bath dyeing with the aforementioned disperse dyes and Isolan metal complex dyes to achieve high washing fastness.
　　
　　Nylon/cotton textiles are also one of the new blended interwoven fabrics with a large production volume in recent years, generally dyed using a two-bath method with reactive/acidic or metal complex dyes. Recently, Japan's Daiichi Kasei Co., Ltd. successfully developed specialized Multifix NH reactive dyes (for nylon) and Multifix NC reactive dyes (for cotton), which can be dyed using a one-bath dyeing process. This involves adding acetic acid (5mg/L) to the dye bath composed of Multifix NH and Multifix NC dyes during the deep dyeing of the dark color at 70°C, allowing the Multifix NH dye to quickly adhere to the nylon. Then, Glauber's salt (40-60g/L) is added, followed by soda ash (8-14g/L), allowing the Multifix NC dye to adhere to the cotton at the same temperature. Finally, the temperature is lowered to 50°C, followed by draining, water washing, soap washing, and water washing again. Due to the non-polar bonding between the dye and the fibers, both types of fibers exhibit excellent color matching. This new type of dye has characteristics such as time-saving, water-saving, energy-saving, steam-saving, low processing costs, good dyeing color matching, and excellent color fastness, improving the previous issues of poor color matching and color fastness during dyeing, and developing dyes and dyeing techniques for nylon/cotton textiles.