Alex Mighall, operations manager at R A Smart, explains how to choose the right type of ink for your digital textile prints
For many businesses, getting into textile printing can seem a daunting prospect. As well as choosing the right printer, you also have to consider which ink chemistry is going to suit your application and fabric type best. This, in turn, will determine the ancillary equipment you will require. When it comes to textile printing there is no ‘one size fits all’ solution. The ink required will depend on a variety of factors.
The first thing you have to ask yourself is, “What is my end application?” For example, someone who is printing for fashion is likely to require a different solution than someone who is printing flags.
People printing fashion often require a solution that will offer good colourfastness, whereas flag printers are generally more concerned with lightfastness. Once you have that figured out, it’s time to decide, “Do I want to print onto natural fabrics – ie cotton, silk, linen – or do I want to print onto synthetic fabrics – ie polyester?” This can often be a difficult question to answer, as many still consider polyester to be somewhat cheap and nasty which, nowadays, is simply not the case. There is a plethora of polyesters out there that successfully mimic natural fabrics such as silk and cotton, and some even have the benefit of using 100% recycled materials. Depending on your answers to these questions your best ink match will normally fall into one of four dierent chemistries…
Acid dyes are generally adopted by businesses that are printing for fashion. They were developed to work with protein fibres in fabrics – for example, those found in silk and wool. As such, they are useful for printing onto only a limited range of materials. They provide an especially good solution for users that provide a very specialised service – eg printing silk ties.
The fabric used must first be pretreated to allow proper absorption of the dye and also limit any lateral bleeding when it touches the fabric. The dye is printed directly onto the textile but often appears dull and subdued until the post-treatment process has been applied. Acid dyes require a ‘wet’ finishing process, which involves steaming and washing. During the steaming process the dye is ‘fixed’ onto the textile. It will change colour during this phase and colours are often much more vivid and bright once the fabric comes out of the steamer. Afterwards, the prints need to go through a washing process – this removes any excess dye that hasn’t been fixed and also the pretreatment that was initially put onto the textile.
Your end application will determine which is the best type of disperse dye for your needs
These dyes were developed to work with cellulose fibres in fabrics – for example, those found in cotton and linen. Reactive dyes can be printed onto a much wider fabric range than acid dyes and can even be used to print protein-based textiles as well. They are often used by people printing for fashion or home furnishings. Similar to acid dyes, reactive dyes require the textile to be pretreated beforehand and they are printed directly onto it. The finishing process is also very similar and involves steaming and washing – however, the timings change as reactive dyes cure more quickly than acid dyes.
Pigment inks differ significantly from other solutions as they don’t fully impregnate themselves into the textile, rather they offer more of a surface print. In one way, this is a good thing as the composition of the fabric doesn’t necessarily dictate the successful use of pigment inks, meaning they can print onto a large range of textiles. The compromise is their colourfastness may not be as good as one of the dyes.
Acid dyes provide an especially good solution for specialised services such as printing silk ties
Having said that, pigment inks have come a long way since they were first used in digital textile printing. Developments with the ink, along with pre- and post-treatment options mean that pigments are now a viable option for many applications and one of the fastest growing segments of the market. They are particularly favoured by those in the home furnishing and household textile sectors as they offer good lightfastness results.
Unlike other direct-to-textile solutions, pigments don’t require the textile to be pretreated before printing. However, for the best colourfastness and most vibrant results, it is recommended.
Disperse (sublimation) dyes
Another massively growing sector for textile printing is the sublimation market. The inks used here are known as disperse dyes and can come in many different forms. Some are manufactured specifically to print directly onto the substrate (sometimes referred to as ‘true disperse dyes’), others are for paper transfer and some are a hybrid of the two.
Your end application will determine which type of dye will best suit your needs. For example, direct disperse dyes can offer better lightfastness and ink penetration, so are favoured by flag printers. Transfer dyes offer crisper prints and a larger colour gamut, so are favoured by sportswear printers. Regardless of the dye type, they are all manufactured to work predominantly with synthetic fibres, in particular polyester. When the fabric or paper is printed with disperse dyes the colours initially look dull and subdued. It is only during the post-processing that they will come alive. For sublimation this is normally a ‘dry’ process using heat, however direct disperse dyes can also be fixed using steam.
With sublimation printing there are normally three key factors that come into play: time, pressure and heat. This usually takes place in either a flatbed heat press (good for rigid substrates or textile panels), a calender heat press (good for lengths of textile), a fixation unit (for fabric printed directly with disperse dyes), or a high- pressure steamer (which is also used for fabric printed directly).
The term ‘sublimation’ refers to the process whereby a material transitions from being a solid to a gas then a solid again without entering the liquid phase. Sublimation printing is one of the most diverse methods of printing on the market and people from all sectors utilise it to create everything from personalised products through to exhibition signage.