Since the mid-1990s, the research of textile digital printing has become more and more important. This application area provides the possibility of printing high-quality images at fast design time. Especially for the fashion industry, a huge advantage is to be able to print on demand from small batch to large batch. According to the analysis of wtin Intelligence: Digital textiles in the UK, the global textile digital printing production is growing at an annual rate of about 20%. Despite the rapid growth, so far, the proportion of textile production using digital printing is only about 3-5%.
One of the difficult factors for effective industrial digital printing on textiles is the variety of textile substrates, from natural (such as cotton, wool or silk) to synthetic (such as polyester and blended fabrics). All of these fabric types require different types of ink, and there are additional different requirements for their pre-treatment and processing. The ink types mainly used in industry are active ink for natural fiber and sublimation / dispersion ink for polyester digital printing.
Pigment ink: characteristics, application and market
Water based pigment ink is not a soluble dye, but uses insoluble pigment to dye textiles. Compared with dyes, these pigments have no real affinity for special fibers, which makes them suitable for both top coloring of various fibers and blended fabrics.
However, the global textile printing market shows that pigment ink only accounts for about 3% of textile digital printing ink. The most commonly used inks are still reactive dyes, disperse dyes and acid dyes. There are many reasons for the low share of pigment ink in textile digital printing market.
As mentioned earlier, most pigment inks are limited in their fastness to repeated washing and rubbing due to the use of adhesives to improve the adhesion of pigment inks to the substrate when printing on the fabric surface. In addition, the hand feel of fabrics is often harder than that of reactive printing, which is one of the main problems, especially when applied to fashion or bedding.
On the other hand, the use of pigment ink shows some significant advantages. As it is suitable for printing on various textile substrates, pigment ink can provide a wide range of applications, including home textiles, soft labels, banners, fashion (mainly T-shirts) or professional products, etc., which can be printed with pigment ink. It is also particularly useful where high light fastness is required. Moreover, compared with reactive printing, the whole process of pigment printing is very fast and simple.
One of the advantages of using pigment ink in textile digital printing is its simple process. The printing process comparison between pigment ink and reactive ink is shown below. Due to the chemical properties of reactive dyes, they must be bonded to textile fibers after printing. Therefore, it is necessary to steam at 102 ℃ (saturated steam) for 8-12 minutes. Subsequently, the unbound dye must be removed (treated) in a complex washing process of different temperature ranges from about 50 ° C to 98 ° C, soaped to 60 ° C and finally 30 ° C (slightly acidic). Then dry the printed fabric.
In contrast, pigment printing process does not need complex steaming and washing process. Since the pigment is only printed on the top layer of the fabric without any chemical composition, the fabric must be condensed for a few minutes at 150-170 ℃ to cure the pigment. As a result, the amount of water required for the pigment printing process is greatly reduced due to the lack of cleaning steps. This may be the key factor to decide whether to use digital pigment printing in the future.
However, there is still a point to be pointed out about the printing process of pigment ink. Due to the insolubility of pigment particles, their deposition may cause clogging of the fine nozzle of the inkjet printer. Therefore, to overcome this problem, we need to pay attention to two points: first, all ink must be fully stirred before use; second, the necessity of printing head with circulation system becomes more and more important. The circulation system provides a continuous flow to avoid clogging the nozzle due to sedimentation. In particular, white pigment inks based primarily on the inorganic compound titanium dioxide require those recycling systems.
Pigment ink has a broad application prospect in the field of textile digital printing, especially in improving the environment and simplifying the process.
In addition to commonly used textile materials such as cotton, polyester and nylon, pigment ink can also be used to print easily on mixed fabrics, such as cotton polyester blended fabrics which usually need to be printed with two different types of ink.
In addition, some ink manufacturers are trying to open up the possibility of printing on special materials with pigment ink. Some tests have been carried out on textile substrates which are usually difficult or almost impossible to carry out digital printing, and these tests have achieved satisfactory results.
Finally, the textile digital printing pigment ink has a great opportunity to occupy a place in the market of special material applications. When it needs to save energy and water, it can also show its skills in the commonly used textile fiber.