Choosing the right fabric can be a daunting task since there are so many available. Making sure you have the appropriate fabric and ink combination is essential for high print quality. To attain the best print quality, fastidious attention must be paid to the quality of fabric since errors at this stage can lead to bigger problems further along in the production process. Surface defects can not only worsen the print quality but can be detrimental to printhead life. Undesirable fabric attributes include broken fibres or filaments, wrinkles or creases, the presence of lint and non-uniform surface tension throughout the fabric. There are also dimensional issues to consider such as shrinkage. Distortion can occur during post-treatment if the fabric has not been preshrunk at the beginning of the production process. Knitted fabrics are particularly susceptible to stretch distortion during both printing and coating so maximum dexterity is recommended. Many other fabric defects can occur.

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Pretreatment

Before printing can take place, the fabric must be coated in a solution specific to the ink technology being used (except pigment inks which usually do not require pre-treatment). This is an essential process to maximise the substrate’s absorption levels and reactivity to the ink, while also minimising lateral bleeding which may impact colour definition and intensity. While pre-treated fabrics are becoming more readily available, specific chemical formulations are usually patented and confidential. Chemical solutions range from simple to very complex. Simple formulations use soda ash, alginate or urea,  while complex formulations can be made from combinations of polymers, inorganic particulates, cationic agents and softeners. Regardless of the particular formulation, the process for applying the pre-treatment is the same: the fabric is fully submerged in a vat of the pre-treatment solution and subsequently hung out to dry in the open air.

Fixation

Once inkjet printing is complete, dying exhaustion must take place in order to completely fix the ink to the substrate. Each ink technology has different fixation requirements.

1) Reactive ink printed substrates are fixed by steaming in atmospheric steamers for 8-10 minutes at temperatures of 100-101˚C (212-214˚F). In pressurised steamers the duration is usually 20-30 minutes. When printed on a cellulosic fibre (e.g. rayon), the colorant is fixed to the fibre by covalent chemical bonding. The fabric must then undergo a washing procedure which consists of at least two cycles of differing water temperature. Each wash cycle removes an amount of extraneous unfixed dye left over from the printing procedure (loose dye can 'backstain' the fabric if not removed).

2) Acid inks are also fixed by steaming. The temperatures are the same as reactive based inks but the times are longer. In atmospheric steamers the duration is about 20 minutes and in pressurised steamers around 40-60 minutes. Several wash cycles are also necessary for this type of ink.

3) Disperse inks require different fixation methods depending on whether they are transferred from paper or printed directly onto the fabric. For the former, the paper is transferred in a press at 193-210˚C (380-410˚F) for 30-90 seconds. When disperse inks are directly printed on the fabric they must be cured or thermosoled (at the same temperature). Washing is also necessary.

4) Pigment inks are the easiest to fix, needing to be cured in an oven at 162-176˚C (325-350˚F) for 30-90 seconds. In some cases, UV curing rather than thermal curing is used, and the ink can be exposed to UV light during printing, giving a very simple production process.

Summary

With so many inks and textile fabrics to choose from, all with different properties, it is essential to select the right combination dependant on your application. To ensure optimal print quality, all stages of the production process must be carried out stringently. As market demands continue to change, digital technology has become more desirable as a method for printing onto textiles. The pros and cons of analogue vs. digital will depend on the requirements of the job at hand. However, digital printing’s unique advantage is the rapid introduction of new designs produced economically at shorter run lengths. Print houses are already offering digitally printed clothing items (both high and low quality) at an affordable rate. Digital production speed may not be as fast as analogue in most cases, but this gap is expected to close significantly in the future. As chemical, hardware and software technology continue to evolve, it is likely that the current application of inkjet printing in the textile industry is only the tip of the iceberg.

Tim Phillips, Catenary Solutions

Further Reading

Provost Inkjet

Digital textile printing: how to choose the right ink?

For many companies, entering the textile printing field seems to face many challenges. In addition to choosing the right printer, you must also consider choosing the right ink for the printer and fabric. On the contrary, ink and fabric also determine the choice of printer.

In textile printing, there is no “one size fits all” solution. There are many factors to consider when choosing ink. First, ask yourself: “What is the purpose of the product?” For example, the ink required for printing fashion products is very different from that for logo printing. Fashion products require ink to have good color fastness, and printed logos usually pay more attention to light fastness.

To figure this out, it’s time to make a decision. “Do I want to print on natural fabrics (such as cotton, silk, linen)? Or do I print on synthetic fibers (such as polyester)?” This question is often difficult to answer because many people do not like polyester and think they Very cheap. But that is not the case. A large number of existing polyesters on the market can successfully imitate natural fibers such as silk and cotton. Some polyesters can even be synthesized from 100% recyclable materials.

According to your answers to these questions, the choice of ink is usually divided into the following four types:

Acid Dyestuff

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Acid dyes are commonly used to print fashion products. They are combined with the protein fibers in the fabric, such as the protein in silk and wool. Therefore, the applicable printing materials for acid dyes are very limited, but the printing effect is very good, such as printed neckties.

The fabric needs to be pretreated before printing and dyeing with acid dyes, which can allow the fabric to absorb the dye better and prevent lateral bleeding when touching the fabric. When the dye is printed directly on the textile, the color will usually appear dull, but it will change after post-processing.

Acid dyes require “wet” processing, including steaming and washing. During the steaming process, the dye is “fixed” on the fabric. At this stage, the fabric will change color, and the color will usually be brighter and brighter when taken out of the steamer.

Then, the fabric needs to be washed to remove the residue from the pretreatment and the excess dye that was not fixed during the steaming process.

Reactive dyes

Reactive dyes are used in cellulosic fabrics, such as cotton and linen. Compared with acid dyes, reactive dyes can print and dye more fabrics. Reactive dyes can even be used to print protein-based textiles, and are often used to print fashion and furniture.

Like acid dyes, the use of reactive dyes also requires pretreatment of the fabric and then directly printed on the textile. The processing process is also very similar, including cooking and washing, but because reactive dyes cure faster than acid dyes, the processing time will be different.

Pigment Textile ink

Pigment inks are very different from other dyes in that they cannot be completely immersed in the textile, but stay on the surface. In a sense, this is a good thing. Because the composition of the fabric will not be a restriction on the selection of dyes when printing, this means that pigment inks can be printed on a variety of textiles. However, the disadvantage is that the color fastness may not be so good.

Since pigment inks were first used in digital textile printing, there has been considerable development. Along with pre- and post-processing, the development of ink means that pigments have become a viable choice for many production applications and are one of the fastest growing branches of the market. Due to its good light resistance, pigment inks are particularly popular in the home decoration and home textile fields.

Unlike other direct printing solutions, pigment inks do not require pretreatment of textiles before printing. However, in order to obtain the best color fastness and the most vivid effect, pretreatment is still recommended.

Pigment ink adopts “dry” processing technology, which is “fixed” by heating, so it is favored by people. It can be processed with a hot press and a fixed drying device. In this process, the color generally does not change much, and the fabric can be made into a finished product after completion.

Disperse (sublimation) dyes

The sublimation market is another fast-growing field in the textile printing industry. The inks used are called disperse dyes and come in many different forms. Some are dedicated to direct printing (called “true disperse dyes”), some are used to transfer paper, and some are a mixture of the two.

The application of the product will determine which dye meets its own needs. For example, direct disperse dyes have good light resistance and ink permeability, so they are favored by logo printers. The transfer dye has a wide color gamut and clear printing, so it is favored by sportswear printers. Regardless of the dyes, they are mainly used in synthetic fibers such as polyester.

When disperse dyes are used to print fabric and paper, the initial color looks dull and soft. The color will become brighter during post-processing. Sublimation dyes need to be “dried” with heat, but direct disperse dyes can also use steam to fix the color.

Time, pressure and temperature are the three key factors affecting sublimation printing. In the use of flat heat press (for rigid substrates or textile panels), calender (for longer fabrics), curing device (for fabrics with direct disperse dye printing), and autoclaves (for direct printing) The effect is particularly significant when printing on fabrics.

“Sublimation” refers to the process in which a substance changes from a solid to a gas without entering the liquid phase, and then to a solid. Sublimation printing is one of the most diverse printing methods on the market. From exhibition signs to personalized product customization, people from all walks of life are using sublimation for printing production.

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