What is textile printing?
• It is a process of decorating textile fabrics by application of pigments, dyes or other materials in the form of patterns using various techniques.
• The four main methods a printing are block, roller, screen and heat transfer printing.
• In each of these methods the application of the colour which is usually a thickened paste, is followed by fixation done by steaming or heating and then removal of access colour is done by washing.

What is digital textile printing?
• Digital textile printing is a process of printing on textiles and garments using inkjet Technology to print colorants onto fabric.
• It is often referred to as direct to garment (DTG) printing. It is the process of printing on Textiles and garments using specialised or modified inkjet technology.

Evolution and progression of digital textile printing:
• The inkjet printing Technology used in digital printing was first patented in 1968.
• Digital inkjet printing of continuous rolls of textiles fabrics was shown at ITMA [The International Machinery Exhibition] in 1995.
• Again at ITMA in 2003, several industrial inkjet printers were introduced to the market place which made digital printing on textiles the new industry standard.
• The technology has now continued to develop and there are now specialized wide-format printers which can handle a variety of substrates – everything from paper to canvas to vinyl and ofcourse fabric.

Ink-jet Printing Technology:
• This technology enables the delivery of liquid ink to a medium whereby only the ink drops make contact with the medium.
• It is therefore a non-impact printing method.
• The theory behind the ink jet technology was developed at the end of the 19th century by Lord Rayleigh (Rayleigh, 1878) but the development of the technology itself did not start until the late 1950s and 1960s.

Components of Ink-Jet Printer:
Basically Ink jet has three basic components. These are the print head, the ink, and the medium all of which need to work well in order to produce an acceptable output.

A brief explanation of all these components are as follows:

1. The Print Head:
There are two types of print heads-
(A) Continuous Inkjet (CIJ) :
In CIJ, ink is squirted through the nozzle at a constant speed by applying a constant pressure. The jet of ink is unstable and breaks into droplets, as it leaves the nozzle, the drops are left to go to the medium or are deflected to a gutter for recirculation depending on the image being printed. The name ‘continuous’ originates in the fact that drops are ejected at all times.
(B) Drop on demand (DOD) :
In DOD, drops are ejected only when needed to form the image.
The 2 main drop ejector mechanisms used to generate drops are- piezoelectric inkjet (PIJ) and Thermal inkjet (TIJ)
2. The Ink:
There are two major classes of colorants namely dyes and pigments. The choice of dye depends upon the ink used, whether it is aqueous, solvent or hot-melt and on the type of printer.
Solubility: A dye for ink jet should have as high solubility as possible to minimise any tendency for the dye to crystallize and cause problems such as nozzle blockage.
Light Fastness: The final printed product must have reasonable light fastness (that is Resistance to fading by light) if it is to serve any useful purpose.
Water fastness: The final print should have resistance to water so that the dye does not get smudged or fade.
Shade: The shade or hue appears the same irrespective of the substrate on which it is printed. For instance, paper varies in texture, absorption, additives and pH and ideally the dye should be insensitive to this differences.
3. The Medium:
The Third component is the medium which is the fabric or material that is to be printed.

How Digital Printing Works:
The following are the successful digital printing methods:
1. Dye-Sublimation Printing:
It is a digital printing Technology using full colour artwork that works with polyester and polymer coated substrates. The process is commonly used for decorating apparel, signs and banners as well as novelty items such as cell phone covers, coffee mugs and other items with sublimation friendly surfaces.

Application on textiles:
• In this process heat and pressure are applied to a solid, turning it into a gas through an endothermic reaction without passing through the liquid phase.
• Unique sublimation dyes are transferred to sheets of transfer paper via liquid gel ink through a piezoelectric print head.
• The ink is deposited on these papers which are used for the next step of the sublimation printing process
• After the design is printed onto the sublimation transfer sheets, it is placed on a heat press along with the substrate to be sublimated.
• In order to transfer the image from the paper to the substrate, it requires heat press that is a combination of time, temperature and pressure.
• The end result of the sublimation process is permanent, high resolution, full colour print.
Advantages:
The print wont easily fade away and the colours can be extraordinarily brilliant due to the bonding of the dye to the fibres.

2. Direct to fabric and Direct to garment digital printing:
The name itself explains the process for direct to fabric printing that is printing done on the fabric directly whereas direct to garment process uses specialized aqueous ink in order to print directly onto the garment using a printer. The printer inks are jetted or sprayed onto the textile by the print head.

Below video shows how DTG is done:

Pre-Treatment of Fabric:
The methodology is to ‘two-phase’ conventional printing as opposed to the ‘all-in’ approach. In the latter case all the dyes Chemicals and thickeners required are included in the print paste, whereas in the former some of the ingredients, particularly chemicals are applied before or after printing.
Reasons:
Main reasons for separating the dye ink from thickeners and other chemicals and applying them separately to the fabric are as follows:
• All-in inks are less stable and have lower storage stability.
• Chemicals in the ink cause corrosion of jet nozzles. Thickeners in the ink often do not have the desired properties.
• Some chemicals can be utilized in pre-treatment fabric but would cause stability problems in the ink.

Post Treatment:
• When the pre-treated fabric has been dried and then Jet printed there is usually little need to provide a drying station to dry the print as the printing process is so slow.
• In most instances fixation and washing will be necessary. This not only ensures that the full fastness properties of the dyes are realised but also brightens and alters the colours significantly.

Fabrics and Inks:
The table here demonstrates four basic inks and the fabrics that they are able to print on:

Software:
• The software that comes with the printer converts the data generated in the design created on a computer into information the printer can understand.
• It will optimise the colours of the design to get as close a match to what you want as possible.
• It also tells the printer where to place the ink drops and in what size.
• Some software programs I will also let you manipulate an image with steps repeats and drops so that you don’t have to do that in the design software such as Photoshop.

Advantages:
Digital Printing has completely changed the way businesses create their printed materials. It is fast effective and provides an alternative to the more traditional method of textile printing.
• Quality: images are essentially flawless aligned and the colour is vibrant.
• Speed: another perk of using digital printing is its ability to switch over to a new label almost instantly because there is no lost time setting up plates and printing machinery.
• Lower water and power consumption: it eliminates the substantial amount of water and electrical energy one requires for Rotary screen preparation, printing and clean up.
• Less chemical waste: it results in significantly less ink usage and waste relative to screen printing. Taking into account the additional chemistry and chemical waste from screen production.
• Large repeat sizes: one can print large designs for example cartoon characters on sheets and blankets without the usual Rotary screen printing limitation in pattern repeat size.
• Variety of print design choices for printing: it provides the option to print photographic or continuous tone images, sport colour pattern designs or a combination of both. This expands creative printing for fashion and interior designers too.
• Low capital investment: it is relative low capital investment to set up a digital textile shop especially compared to rotary screen printing production. And makes it possible to start small and expand as business grows.

Limitations:
• Metallic colours cannot be printed by these machines due to large particle size.
• Without getting too technical Digital Printing process run at a maximum of about 50 feet per minute. While this speed is sufficient for low volume (10,000-15,000 items) projects, larger volume work will benefit from using traditional presses that can run at speeds between 300 to 500 feet per minute. Although traditional presses are more expensive to configure and operate, they will save you money if your jobs are very large.
• While it handles colour and ink well, digital inks have a tendency to fade quickly sometimes due to various reasons. Also sometimes the opacity of the ink is not quite up to how it is required. If proper finishes are applied then it can be solved.

Conclusion:
• Digital printing provides an opportunity to meet the present day market trends of mass customization.
• It has established as an acceptable technology for sample production.
• Among other technology problems, speed of printing is the main hurdle in commercialization of technology.
• Attempts are being made to achieve commercially acceptable printing speeds.
• Hence this industry is growing at a fast rate and new innovations are carried out which makes printing even more easy and less time consuming.

References:
• Ujiie, H. . Digital printing of textiles. Boca Raton: CRC Press.
•https://en.m.wikipedia.org/wiki/Digital_textile_printing
•https://textilelearner.blogspot.com/03/digital-printing-textiles.html?m=1
• https://www.britannica.com/
• Textilelearner.blogspot.com
• Textileschook.com
• https://study.com/academy/lesson/digital-textile-printing-machine-process.html
•  Direct To Fabric (DTF) Printing versus Direct To Garment (DTG) Printing. Retrieved from https://digitaltextilereview.com/?p=814
• Cie, C. The effect of ink jet printing on design for the textile industry. Ink Jet Textile Printing, 153–164. doi: 10.1016/b978-0-85709-230-4.00012-1
•  Dye-sublimation printer. Retrieved from https://en.m.wikipedia.org/wiki/Dye-sublimation_printer

-Manali Bhanushali