There are important steps to follow to ensure a quality image when digitally printing on textiles. One of the most important is pre-treating fabric with chemistry designed to offer desired end-use performance that cannot be achieved by the ink and fabric alone. Of the different types of colorant used in digital textile printing ink, pigment has been the slowest to be adopted in the industry partly because it’s the only colorant that requires a physical bond with the fabric using a polymer (binder) to act as a sort of ‘glue’. The other methods are based on dye technology which chemically binds to the fabric. The downside of this is that it makes dye-based inks fabric specific and, in addition, these dye-based technologies don’t have as good a light-fastness as pigment based inks. As an example, outdoor furniture can significantly benefit from a pigment ink because it has the most resistance to UV light. Digital pigment printing on textiles enables bespoke experiences at an attractive price, which is made possible by the right pretreatment technology for the end-use product. As more traditional textile printing companies consider the benefits of digital printing, this market segment has experienced significant growth over the last several years.
To achieve desired results, pretreatment is necessary to ensure fabric is truly prepared for digital printing. Why? Digital printing is about printing dots. If a pretreatment can be used that’s less expensive than ink, then more ink can be kept on the surface of the textile. Without a pretreatment, more ink dives into the fabric, leading to the need to use even more ink to increase color vibrancy and achieve the sought-after look. A pretreatment also improves dry and wet crock. Fabric that is properly prepared has no oils or contaminants from previous processing and is perfectly wound on the appropriate core to avoid head strikes or waste. Through proper chemistry, it is pretreated to enable desired end-use performance in a variety of textiles, from apparel and quilting to signage and home décor.
Achieving this desired performance is all about balance: durability for UV stability and dry/wet crock; fabric integrity for softness and no change to fabric/weave appearance; print quality for optimal dot gain and density, and no metamorism; and the manufacturing process. There are some key performance requirements that any pre-treatment must meet in order enable the most benefits from pigment-based ink systems:
- First, the fabric must maintain its 'hand', which is essentially the feel of the original fabric. Printing can make a textile feel rough, stiff or “boardy.” So, the pre-treatment must have minimal effect on the hand
- Secondly, the pre-treat process holds the colorant at the surface and in this way optimizes color strength and print quality. However, holding the ink on the surface of the surface of fabrics can make rub fastness a challenge. Rub resistance, or ‘crock resistance,’ is measured by assessing the color transfer onto white fabric when rubbed back and forth against a printed surface for a set number of times under a given weight. Crock is measured in a range of grades from 1-5 and should be high. Manufacturers target a minimum of grade 3, but usually aim for 4+. If pre-treating doesn’t do all the work necessary, some suppliers implement a post treatment, but this adds cost and lead time, which defeats one of the big advantages of digital printing and its shorter lead times.
- Thirdly, to achieve desired performance, pre-treating fabrics requires matching the substrate and ink, and that requires different chemical approaches. At Lubrizol, we create textile pre-treatment solutions for each of the four fabric types—cotton, polyester, cotton/polyester, and other synthetics.
- Finally, ink is another consideration. All inks aren’t designed the same. Some are more robust for durability; some for color. The pretreatment needs to be able to accommodate all types of ink.
Application methods are also important to get the right result. Padding (dip and squeeze) is the most common application method. Other new methods are being developed, such as spray, foam and jetting. These methods are designed to use less pretreat and only where needed. So, when considering pre-treating fabric for digital pigment based printing, it’s important to work with a partner who can help you make the right choices and that is adept in understanding global regulations that affect the textile print industry.
https://www.lubrizol.com/Coatings/About-Performance-CoatingsIn digital pigment printing, fabrics have to be pre-coated to increase the colour gamut and durability of the print. Pigment printing provides a simple process involving printing and thermo-fixation by either a heat press or a fabric baker. However, with pigment printing, pre-coating is also an essential in terms of enhancing the colour gamut and fastness of the fabric. So faced with the inevitability of pre-coating, volume digital textile printers are faced with two important choices, first the choice of chemicals and second the choice of machinery to pre-coat their fabrics. As far as chemicals are concerned the printer has a wide array of product available. In many cases coating formulations are supplied by Ink manufacturers to pair up with use of their inks. In this field, major manufacturers include, Epson Genesta Inks Pre-Gen, Neo Coat from Swiss Performance Chemicals and the P601 Pre-Coat from Pigmentinc. However, many chemical companies independently supply excellent pre-coating chemicals, these companies include Lubrizol of the USA, Tanatex of the Netherlands, Rudolf Chemicals of Germany and Sarex of India. In general terms, these pre-coating formulations, which often use thickeners and cross linking agents, improve the mark and colour intensity of the print, as well as the wash, and rub fastness of the fabric.
