Recent Advancements in Textile Printing

Pallavi Sunil Gudulkar
Department of Textiles (Textile Chemistry)
DKTE’S Textile & Engineering Institute, Ichalkaranji, India
Intern at Textile Learner
Email: pallavigudulkar@gmail.com

Introduction:
Textile printing is the most versatile and important of the methods used for introducing color and design to textile fabrics. Printing has always been an important tool for improving the aesthetic quality of textile materials. During the last few decades, there have been rapid advancements in textile printing technology, particularly in terms of the machinery used for printing, print manufacturing and post-treatment of printed fabrics, in order to meet the demand for high rates of production and complexity in such printing. This article includes some textile printing methods with their recent advancements.

Recent Developments in Textile Printing:

1. Inkjet Printing
Inkjet printing is a rapidly evolving technique that allows us to deliver small amounts of materials in the form of ink to particular areas of a substrate. Inkjet printing is a non-impact form of printing. Drops of ink are projected onto the surfaces to be printed. The commercial applications of ink jet printing are still limited to computer-aided office outputs, hard copy output of textile design onto paper, and carpet and pile fabric printing. Attempts to print onto textile substrate using the principle of inkjet printing are being made in developed countries with fine resolutions.

Figure 1: Inkjet printing process (Image courtesy: www.hitachi-iesa.com)

1.1 Methodology of inkjet printing:
The pressure is applied to the substrate during the ink transfer in this printing machine and later conventional derivatives such as offset printing and screen printing, which is known as contact-printing. Non-contact printing refers to the transfer of ink to the substrate without physical contact between the ink dispenser and the substrate in modern printing methods. The substrate is only in contact with the ink containing the printing material in non-contact printing, and there is no mechanical pressure on the substrate, eliminating the possibility of harming the pre-patterned substrate or contaminating it. Non-contact printing also enables high-accuracy, high-resolution, and high-speed patterned printing and multi-layered deposition.

For direct patterned deposition of solution-based materials, inkjet printing evolved as a non-contact approach. In this approach, ink is transferred from the ink reservoir to the nozzle-head and expelled in microdroplets. To achieve the printing, the released ink droplets hit the substrate at particular rates. Controlled displacement of the substrate or the print-head can be used to create the printed patterns. The printed ink next goes through a process of evaporation and solidification. To eliminate solvents, increase adhesion and change the material structure, the printed substrate is usually post-processed at high temperatures in the form of thermal annealing, sintering, or calcination.

1.2 Types of inkjet printing:

1.2.1 Drop on demand:
This approach is used by the majority of printers nowadays. Only produces an ink droplet when it’s required and then hits the substrate. Drop charging and deflection hardware are no longer complicated. The droplet ejection rate is 25,000 droplets per second per nozzle. The resolution can be up to 2880 DPI. It can be used for a variety of applications including billboards, banners, draperies and wall hangings. It works on either a thermal or a piezoelectric principle.

1.2.2 Continuous flow:
A narrow nozzle with a diameter of 15 m is used to drive ink through a high-pressure synchronous droplet ejection technique. Up to 2880 DPI resolution can be obtained. Droplet ejection rate of 50,000-1,00,000 drops/sec/nozzle. The needle spacing in the jets is 12 needles per inch. Binary, multilayer, hertz, and microdot are four techniques for obtaining design using this technology.

1.3 Advantages:

With ink jet printing, one can print photographic designs with unlimited colours and large repeats which aren’t limited by screen and roller size.
Its printing technology is environmentally friendly.
There is no need to clean the apparatus between runs.
The printing nozzles need not make contact with the fabric.

1.4 Disadvantages:
There are some drawbacks in various aspects of inkjet printing, such as printing speed, cost–benefit issues, health and environmental concerns, printed film uniformity and material, and fluids’ jet-ability as ink, which must be overcome.

2. Screen Printing
The digital fabric printing method of screen printing has been around for a long time. It is the technique of smearing a coating of ink over a screen to transfer it onto a piece of fabric, as previously stated. This screen is also known as a stencil, and each design requires a unique stencil. In the past, the procedure required a huge number of prints to be cost-effective. However, technological advancements have opened the way for more cost-effective and adaptable screen-printing methods.

2.1 Types of screen printing:

2.1.1 Fully automatic flat screen printing:
It was important to design a method of printing all the colours simultaneously in order to improve the speed of flat screen printing. Unfortunately, flat screens are not adequate coloration units for a completely continuous process and the colour is applied through the screens when the fabric is stationary in all successful machines for fully automatic flat screen printing.

The machine can be divided into following:

Fabric feeding unit
Gumming (adhesive system) unit
Printing unit
Drying unit (Printed fabric)
Blanket washing & drying unit

All of the design screens (one for each colour) are accurate at the top of the blanket, which is a long continuous belt. On average, a machine can hold 16 or more colours. A whole number of lengthwise design repeats must be the size of the gap between regions printed by any two adjacent screens. At the entry end, the fabric is gummed to the blanket and moves in an alternating pattern with the blanket, one screen-repeat distance at a time. While the fabric is stationary, all of the colours in the design are printed simultaneously, then the screens are lifted and the fabric and blanket move on. When the fabric reaches the turning point of the blanket, it is taken off and placed in a drier. The soiled blanket is washed and dried on the machine’s underside on its return trip.

Figure 2: Fully automatic flat screen printing machine

Adhesive system
At the entry end, a water-based glue is applied to the blanket using rollers or a sticky semi-permanent or permanent adhesive coating on the blanket. When heated, these coatings become sticky and heat can be applied directly to the adhesive layer or the fabric.

Squeeze system
It may be either by a pair of parallel rubber-blade squeeze (double blade squeeze) or magnetic rod squeegee.

Drying unit
After printing, the blanket returns to the underside of machine and the printed cloth is moved to the drying unit to dry. Photovoltaic cells regulate the speed of the blanket and the drying unit blanket.

Recent Technological Developments in Flat Screen Printing Machine:
The advancements in flat screen printing machines aim to print large repeat sizes, have a better drier design, a modified feeding unit and a suitable punch card programmer etc. The following are some of the advancements that have developed over time to increase productivity, printing quality and machine reliability.

MECCANOTESSILE’S Hydra Flat Bed Screen Printing Machine
REGGINI’S ‘AVANT’ Model Flat Bed Screen Printing
REGGIANI’S MECCANO FILM HS Flat Bed Screen Printing
Stork’s FMX-I model of Flat Bed Screen Printing
Viero-Italy Represented SIGMA DG-160 Flat Bed Printing
REGGIANI’S ‘PRIMA’ Flat Bed Printing
ZIMMER’S (Austria) MAGNOPRINT Flat Bed Printing
LYOPRINTER LX of Gali Spain Flat Bed Printing
ZIMMER’S Flat Bed Printing for Flag Printing

2.1.2 Rotary screen printing machine
Continuous rotation of a cylindrical screen while in contact with the fabric allows genuinely continuous printing in rotary screen printing. During printing, the print paste is fed into the screen and forced out through the design area with the help of a stationary squeeze.

The majority of machines are designed in the same way as fully automatic flat screen machines, with an endlessly driven blanket, screen positions at the top and blanket washing and drying taking place under during the return trip. The use of a thermoplastic adhesive is popular, with a curved surface heating plate used to warm the cloth before pressing it onto the blanket. Because cylindrical screens can be placed considerably closer together than flat screens, the blanket is shorter (for a give number of colours). To allow the printed fabric to be adequately dried at faster operating speeds, the fabric dryer must be longer and have a higher temperature of 160–180^oC.

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Even in completely automatic machines, the print paste is frequently poured by hand into flat screens, but the continuous movement of circular screens and restricted access require automation of this activity. The print paste is fed into the screen through a flexible pipe from a container on the machine’s side. The paste pipe has a stiff structure inside the screen since it also serves as a support for the squeeze. Because the paste is pumped in from one end, the holes in the pipe must be wider at the end furthest from the pump to provide an even spread across the full width of the screen. When the paste level goes below a pre-set height, a sensor (paste level controller) activates the pump.

Developments:
As rotary screen printing machines are costly, it pays to keep downtime to a minimum. Reggiani has introduced the idea of washing screens between colours on their latest machine. Excess paste is pumped out of the screens after the first color is printed and the screens are then sprayed with water from the inside while still in place on the machine. Microprocessor control and computer control software are now available from most manufacturers. All of the necessary data for a print run is recorded, including machine settings, so that the design may be set up considerably more rapidly the next time it is printed.

Rotascreen of Zimmer, Austria
Rotascreen V, of Zimmer, Austria
Rotascreen G of Zimmer, Austria
Rotamac 5 of Buser
‘Pegasus’ of Stork Brabants, Netherland

3. Transfer Printing
Transfer printing refers to the process of transferring a design onto fabric at high temperatures and pressures in a short period of time without causing image distortion.

3.1. Types of transfer printing:

3.1.1 Sublimation transfer:
The use of a volatile dye in the printed design is required for this procedure. The dye is preferentially adsorbed from the vapour phase by the textile material with which the heated paper is in contact when it is heated. This is the most important transfer printing process in terms of commercial importance.

3.1.2 Melt transfer:
Since the 19th century, this approach has been used to transfer embroidery designs on fabric. The design is printed on paper with waxy ink, and the paper is pressed against the cloth with a hot iron on the reverse side. When the ink comes into touch with the fabric, it melts. The first commercially successful transfer process, known as Star printing, was developed in Italy in the late 1940s on this foundation. It’s found in ‘hot-split’ transfer sheets, which are widely employed in today’s clothing design.

3.1.3. Film release:
This method is similar to melt transfer except that the design is held in an ink layer that is transferred completely to the textile using heat and pressure from a release paper. Between the film and the cloth, adhesion forces emerge that are stronger than those between the film and the paper. Although the process was designed for both continuous web and garment panel printing, it is generally mainly employed for either. It is comparable to sublimation transfer printing in terms of commercial value.

3.1.4 Wet transfer:
A printing ink contains water-soluble dyes that are used to create a design on paper. Using carefully controlled contact pressure, the design is transferred to a wet textile. Diffusion of the dye through the aqueous medium occurs. At the moment, the method isn’t employed in any major way.

3.1.5 Flexographic printing:
The technique involves transferring ink from the surface of a flexible plate on which an image is represented to a substrate, one colour at a time. Additional colours are added, each of which is registered to the same areas as those previously printed. The photographic quality of the halftone printing effect is possible when the plate surface consists of a pattern of dots. Dot patterns can be combined to create colours that aren’t represented by the ink. Flexo process printing is the name given to this method. A doctor blade assembly removes excess ink amounts from the cylinder surface during ink metering, allowing for good control of the volume of ink transferred from each cell.

Advancements in flexographic printing:
Technologies are being developed to (1) reduce the time and expertise required for prepress, platemaking, and plate changeovers; (2) improve the recyclability of printed labels and packages; and (3) minimize the high levels of waste caused by prepress or press set-up errors.

Extended Color Gamut (ECG) Flexo printing:
To match a higher percentage of Pantone color, Extended Color Gamut (ECG) Flexo printing uses orange, green, and violet inks in addition to cyan, magenta, yellow, and black inks. The mixing and supply of these seven process colours of UV-curable inks will be controlled by digital technologies. There have also been developed systems to automatically engage the plate cylinder, set the right impression, and register each colour.

Hybrid Flexo/inkjet printing systems:
Another area of technological advancement is hybrid Flexo/inkjet printing systems. Inkjet printing units have been modified into several flexographic presses, allowing full-color changeable data to be added to Flexo-printed products. This enables Flexo print shops to better service customers that wish to add codes to their packaging for tracking or authenticating, or to connect consumers to online data.

4. Digital Printing
The method of printing digital-based images directly onto a variety of media substrates is known as digital printing. Unlike offset printing, there is no requirement for a printing plate. Printing on paper, picture paper, canvas, fabric, synthetics, cardstock, and other substrates is possible with digital files such as PDFs or desktop publishing files supplied straight to the digital printing machine. Digital production print technology is rapidly growing, and the quality of digital printing output is constantly improving. These developments have resulted in print quality that is comparable to offset. Digital printing inks include cyan, magenta, yellow and black (CMYK) toner and ink, as well as extended color gamut inks such as orange, blue and green as well as specialty dry inks for metallic, white or clear effects.

4.1 Advantages:

Print on demand
Cost effective short runs
Personalized, Variable Data Printing (VDP)
Fast turnarounds

Conclusion
Textile printing methods have advanced recently, resulting in time and cost savings. Textile printing is becoming more easier, environmentally friendly, and cost-effective.

References:

Inkjet Printing, Atasheh Soleimani-Gorgani, in Printing on Polymers, 2016
Recent advances and prospects of inkjet printing in heterogeneous catalysis By Hesam Maleki and Volfango Bertola
Screen Printing Techniques – Present and Future Scenario By Prof. S.K. Chinta,
Flexographic Printing by Thomas Dunn
Textile printing, Revised Second Edition
https://www.xerox.com/en-us/digital-printing/insights/what-is-digital-printing
https://ordant.com/what-is-flexographic-printing/
https://texpedia.org/blog/2012/12/19/transfer-printing-and-its-methods-of-applications/

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.