Making the chemistry work: Choose the right ink for your particular application.
Digital textile printing is fast gaining ground and seeing market acceptance in printing on a variety of fabrics. Diverse markets such as apparel, home furnishings, tradeshow graphics, flag and banner, swimwear, and point of purchase displays are all showing rapid growth.
Compared to analog techniques, the cycle time from design conception to actual production is significantly reduced by using digital printing. Creating the best image quality for digital textile printing is obtained with proper consideration of several key areas:
- Fabric and ink selection
- Preprocessing and postprocessing of textiles
- Color software
- Printing equipment
This article will review the selection of ink types, fabric types, pretreatment/coating of the fabrics, and postprocessing in digital textile printing and how to optimize these elements for the best results.
Generally speaking there are four basic types of inks available to digitally print on textile substrates. Table 1 shows the ink and fabric selection matrix. Table 2 shows an example of a colorant for each ink type and brief description of its mode of attachment to the fabric.
It’s clear from the table that there are specific inks for each specific type of textile fiber/fabric. It is important to select inks that are compatible with the fabric and printer system since not all ink chemistries are available for a given printer system. A system that offers all the different ink chemistries will facilitate the widest selection of fabrics for printing.
Digital textile printing process
Digital printing of textiles with dye based inks require pretreatment and posttreatment of the printed fabric for full color and durability. The chemicals in the fabric coating permit reaction of the dye with the fiber during postprocessing.
After final drying additional treatments can be given to the printed fabric like waterproofing, flame retardant, and so forth.
Note: Pigment ink printing of textiles is an exception to the above flowchart. Pigment printing does not require any coating treatment of the fabric and the fixation treatment usually is a dry heat fusing requiring no washing and drying steps. However, color gamut obtained using pigment inks on textiles is lower than that obtained with dye inks and pigment inks also can make the fabrics feel slightly stiffer to touch.
Textile fabrics can be broken down into three basic types.
Woven fabrics. These have two sets of yarns running parallel and perpendicular to the selvage called warp and weft. These fabrics are dimensionally very stable.
Knitted fabrics. Formed by interlooping of yarns to form loops. Knitted loops are referred to as stitches. Vertical stitches are called wales and horizontal stitches are called courses. Knitted fabrics are dimensionally less stable than the woven fabrics.
Non-woven fabrics. These fabrics have intermingled fibers that are held together by adhesive, thermal bonding, spun bonding, and so forth.
Once the inkset for printing is selected, the selection of fabric needs careful attention to obtain the best image quality.
How is it done?
They use large automated screen presses. The fabric is still in
a large roll. Most likely "Plastisol" inks.(industry standard
for fabrics) Heat treated, and left in roll form; meaning, that
after it has been printed, its rolled up. (that was one color)
As for additional colors, the roll is printed again. Registration
marks or "tick marks", as they say in the business, are used to
align the image. Laser scanners; much like the ones in the grocery
store are used to find these tick marks, and align the screen to
the item thats to be printed