Is there a future for textile pigment inks?
Since the mid-1990s, research on textile digital printing has become increasingly important. This application area offers the possibility to print high quality images with fast design time. Especially for the fashion industry, a huge advantage is the ability to print on demand from small batches to large batches. According to the analysis of WTiN Intelligence:Digital Textiles in the UK, the global textile digital printing output is growing at a rate of about 20% per year. Despite the rapid growth, so far, the proportion of textiles using digital printing is only about 3 to 5%.
A difficult factor in effective industrial digital printing on textiles is that textile substrates range from natural (such as cotton, wool or silk) to synthetic materials (such as polyester and blended fabrics). All of these fabric types require different types of inks, and there are additional requirements for pre- and post-treatment and processing. The types of inks that are primarily used in industry are reactive inks for natural fibers and sublimation/dispersion inks for polyester digital printing.
However, it is desirable to have an ink suitable for use in a variety of textile substrates. This requirement will be achieved through the use of pigmented inks.
In this article, Zschimmer & Schwarz will describe the role of pigment inks in textile digital printing – do they really have opportunities in the future, or are they just castles in the air?
1. Pigment Ink: Characteristics, Applications and Markets
Water-based pigment inks are not soluble dyes, but use insoluble pigments to color textiles. These pigments do not have a true affinity for special fibers compared to dyes, which makes them suitable for both the top layer coloration of various fibers and for blended fabrics.
However, the global textile printing market (Figure 1) shows that pigment inks account for only about 3% of textile digital printing inks. The most commonly used inks are still reactive dyes, disperse dyes and acid dyes. At present, pigment inks have a low share in the textile digital printing market for a number of reasons.
As mentioned earlier, most pigment inks have been subjected to repeated washing and rubbing fastness due to the use of adhesives to improve the adhesion of pigment inks to substrates when printing on fabric surfaces. limit. In addition, the feel of fabrics tends to be harder than reactive prints, which is one of the main problems, especially when used in fashion or bedding.
On the other hand, the use of pigment inks showed some significant advantages (Table 1). Because it is suitable for printing on a variety of textile substrates, pigment inks can be used in a wide range of applications, including home textiles, soft signs, banners, fashion (mainly t-shirts) or specialty products, all of which can be printed using pigment inks. It is also particularly useful where high light fastness is required. Moreover, the entire process of pigment printing is very fast and simple compared to reactive printing.
2. Comparison of pigment printing and reactive printing
One of the benefits of using pigmented inks in textile digital printing is that the process is simple. Figure 2 shows a comparison of the printing process of pigment inks and reactive inks. Due to the chemical nature of the reactive dyes, it must be bonded to the textile fibers after printing. Therefore, it needs to be steamed at 102 ° C (saturated steam) for 8 to 12 minutes. Subsequently, the unbound dye must be removed (compressed) in a complex washing process at different temperature ranges of about 50 ° C to 98 ° C, with soaping agent to 60 ° C, and finally 30 ° C (slightly acidic). Then dry the printed fabric.
In contrast, the pigment printing process does not require complicated steaming and washing processes. Since the pigment is printed only on the top layer of the fabric without any chemical bonding, the fabric must be condensed at 150-170 ° C for a few minutes to cure the pigment. As a result, the amount of water required for the pigment printing process is greatly reduced because there is no cleaning step. This may be the key factor in determining whether or not to use digital pigment printing in the future.
However, there is one more point to note about the printing process of pigment inks. Due to the insolubility of the pigment particles, their settling may cause clogging of the fine nozzles of the ink jet printer. Therefore, to overcome this problem, there are two points to note: First, all ink must be fully stirred before use; second, the necessity of a printhead with a circulation system becomes more and more important. The circulatory system provides a continuous flow that avoids clogging the nozzle due to precipitation. In particular, white pigment inks based primarily on inorganic compound titanium dioxide require those circulatory systems.
Pigmented inks have broad application prospects in the field of textile digital printing, especially in improving the environment and simplifying the process.
In addition to the usual textile materials such as cotton, polyester and nylon, pigment inks can be used to easily print on mixed fabrics, such as cotton-polyester blends that typically require two different types of ink for printing.
In addition, some ink manufacturers are working hard to open up the possibility of printing on pigmented inks on special materials, testing some textile substrates that are often difficult or impossible to digitally print, and these tests have already made people Satisfying result.
Finally, textile digital printing pigment inks have a great opportunity to occupy a place in the market for special materials applications. When energy and water consumption are needed, they can also be used in common textile fibers.