Section outline
-
The origins of ink jet printing on textiles can be traced to the late 1960’s. Because of the less demanding requirements in terms of resolution (definition) and printing speed, carpet printing was the first application of ink jet to a textile substrate. The first commercial system for the ink jet printing of textiles was launched by Stork at the 1991 ITMA exhibition in Hanover, with its TruColor printer. The most interesting development was the use of high purity reactive dyes based on Procion P dyes (Zeneca but now DyStar) in the ink jet inks. This allowed the subsequent print to be processed in the same manner (steaming and washing) as a conventional print prepared by screen or roller printing with reactive dyes. This development effectively heralded the beginning of the ink jet printing of textiles.
The essential elements of a textile inkjet printing system are:
- An assembly of one or more inkjet print heads, which generate the streams of microscopic ink droplets and aim them to their target. There are many types of inkjet head technology in the market today and inumerable further sub-variants, each with distinctive economic/technical advantages and limitations for different fabrics and applications.
- A machine or system which feeds and presents the fabric to the traversing inkjet heads and ensures perfect registration and alignment throughout, even for delicate and unstable fabrics, such as knits or fine silks. If required, this machinery may also pre-heat and dry or set the printed fabric before finally rolling-up the output smoothly and even with tenstion.
- Post-treatments associated with the printing operation, e.g. baking, steaming, and/or washing. These processes are similar to those used for conventional textile prints, except taht the process is undertaken with a much smaller batch size, typically a few tens of metre or even individual sample length. Critically, such processing steps must not negate the quick response benefits of digital textile printing which show its economic and market attractiveness.
- Software including printer drivers, raster image processing (RIP) and color management system to convert computer-based design into the electronic signals which control the scanning inkjet head and machine. These system can also ensure faithful and reproducible results with different batches of fabric, and provide a total interface with the other components of the digital design, sampling and production environment.
- Inkjet inks comprising pigments and/or dyestuff, which need to be milled and filtered to much finer tolerances than for conventional screen or roller printing. Inkjet inks must be formulated with precise viscosities, consistent surface tension, specific electrical conductivity and temperature response characteristics, and long shelf life without settling or mildew growth.
- Textile substrates which generally need some pretreatments or special preparation to ensure proper take-up and absorption provide adequateadhesion and/or reactivity and be compatible with any post-treatments or conditions of use.
-
Because of its high demand in custom T-shirt printing and its possibility of providing unlimited design alternatives with the help of Textile Design Software, digital textile printing is being highly adopted in this specific market. It is on the unstoppable popularity of T-shirts that the commercial application of digital printing has developed, enabling fast response, individualization of design and printing on demand.
Print and cut is another feature of the digitalization commercialization. Simultaneous application of the design to the plotted cutting parts saves production time because the printing phase and the rooting phase merge into one. It also allows unlimited freedom and creativity of making and positioning the pattern depending on the requirements of the garment.
In the context of commercialization, well established systems are small series printing, prototyping, partial printing on limited parts of the clothing, T-shirt printing with pigment and water based printing inks. Those established settings and the accelerated development of technology and chemistry opened the gateway for wide formats and industrial applications, that were until a few years ago mostly dependent on traditional rotary screen printing technology. -
In designing digital ink-jet printing systems, one of the difficult tasks to consider is formulation of the ink. Digital ink-jet ink formulation needs compromises between printing quality, nozzle maintenance and dry time. It is always possible to improve ink composition for one criteria, but at the expense of another. For example, short dry time implies a volatile fluid vehicle, which compromises nozzle maintenance. Whatever the technology being used, the ink must satisfy specific physical parameters such as surface tension and viscosity. Surface tension is one of the primary factors. In CIJ, surface tension determines where the drop will form while in DOD, surface tension helps control meniscus at the nozzle. In both cases, a high surface tension is desirable.
Due to the requirement of purity and specific conductivity for digital ink-jet printing, ink formulation used in digital ink-jet printing must meet stringent physical and chemical criteria. For example, physical properties needed in ink formulation for the Inkjet and conventional printing methods are dramatically different and some of their contrasts are shown in Table.
Following table is showin a list of important features of inkjet textile digital printing:
An appropriate ink formulation comprises colourant, vehicle for ink, anticlogging fungicide, surfactant, pH buffer and oxygen absorber. The best vehicle for inks is water because of its viscosity, ionic nature, suitable conductivity requirements, safety, cost, low odour and dye solubility. The ink must possess physical properties not only for drop formation but should also be capable of producing sharp, dense and permanent images. Viscosities of digital ink-jet fluids must be quite low compared to rotary screen printing paste. The viscosities of fluid for several types of digital ink-jet print heads are listed in following Table.
Other rheological parameters (e.g., surface tension, density and conductivity requirements) also differ with different types of print heads. Chemical stability of ink is another equally important factor. The ink must be compatible with the substrate and must satisfy various requirements of a specific digital ink-jet printer. Colorants used for digital ink-jet printing must possess proper affinity for the substrate for producing a wide range of colours and ensure the required fastness properties for desired end-uses.
Some other basic requirements of inkjet printers are:
- a homogeneous droplet which is reproducible in size, speed and direction must be ejected in a steady manner
- ejection should be properly synchronised with the signal given with virtually no clogging at any time
- wetting should be proper and fast
- concentration of printing ink should be high
- ink properties should not vary much with the change in temperature
- the printing ink should be stable for a long period.
-
Colorants for use in digital ink-jet printing must possess essential characteristics such as high purity, high chroma, clear tone of the colour, high solubility in water and acceptable wet and light fastness properties on printed fabrics. Therefore, in developing the colorant system for digital ink-jet printing, the system should fulfill these basic requirements.
For decades the graphics industry used only four colours (CMYK = cyan, magenta, yellow and black). A conventional textile printer needs 8-12 basic colours and uses up to 15 dyes because the colour space and fastness requirements are much wider in textile printing. Figure shows the difference between the CIELab colour spaces used in the graphics industry (CMYK, red area) and DyStar’s Jettex® R range of reactive dyes for digital textile printing.
The main types of ink for digital textile printing are divided according to the type of fiber:
- Dyes for cellulosic fibers: pigments, reactives.
- Dyes for polyester fibers: disperse, pigments, dye sublimation.
- Dyes for wool, silk and animal hair (protein fibers): acids, reactives.
- Dyes for acrylic fibers: disperse.
- Dyes for polyamide fibers: acids, disperse.
There are five types of inks used for digital textile printing and can be summarizeed as follows:
- Reactive: they are used on natural or artificial fabrics of plant origin (cotton and viscose), more rarely also on silk
- Acids: used on natural fabrics of animal origin (silk, wool) or synthetic (nylon) with characteristics similar to animal fibers
- Disperse: used mainly on synthetic fibers
- Pigments: they can be used on natural and artificial fibers
- Dye Sublimation: this type of ink can only be used on synthetic fibers
Digital ink-jet colorants must possess some essential characteristics such as high purity, high chroma, clear tone of the colour, high solubility in water, and acceptable wet and light fastness properties on printed fabrics. Colorants must also not have any influence on the rheology. Colorants with low conductivity (formulated with deionised water) are chosen for drop-on-demand (DOD) ink-jet inks. Common salt is added to adjust the conductivity to meet the specifications of continuous ink-jet (CIJ) printers. Therefore, colorant systems designed especially for digital ink-jet printing should fulfill these basic requirements.
In general reactive and acid dyes tend to yield a wider gamut than disperse and pigment formulations.
-
This article gives an overview of the various ink chemistries being developed to address the color related problems in digital textiles inkjet printing and the various pretreatment technologies available for ensuring excellent K/S and color fastness as well as jetting behavior of Newtonian inkjet inks in DOD drop formation. Also, various issues relating to quality of digital inkjet printer fabrics and ink development have been highlighted.
-
A new inkjet textile printing system, Nassenger-V, was developed. Reliability, productivity, and print quality were highly improved in order to meet the requirements as an actual production machine. A newly designed inkjet print head, an ink drop detection system, and a fabric belt feed system developed specifically for this printer are discussed.
-
Textile fabric generally possesses porous surface structure that introduces more ink spread and penetration leading to less printing and color qualities. With different textile surfaces, printing ink has to be compatible with both physical and chemical parameters. Among so many printing processes for textile printing, inkjet printing is gradually taking places of the conventional screen printing process. Likewise, ink chemistry plays an important role in governing printing qualities. Textile surface pretreatment both physically and chemically can improve better textile printed qualities, color reproduction and product performances. This article describes briefly the types of textile fabrics, their surface chemistry, their surface modification, inkjet ink requirement and ink-textile fabric interaction to produce an acceptable printed quality.
-
The aim of this research is to discover such a strategy so that Ink-jet Printing of polyester and cotton blended fabric. This research focuses to develop inks by the combination of Reactive and disperse dyes and by using eco-friendly co-solvents. This paper covers a brief introduction of Ink jet printing technologies and types of inks. A summarized study of the evaluation amid ink jet printing as well as rotary screen printing is also given. In addition to, requirements and composition of water-based ink-jet inks focusing on methodology is given. Furthermore, shelf lives of inks, image sharpness, surface tension, color fastness to rubbing, analysis of head with some personal experiences are also discussed.
-
Photodegradation of the ink-jet prints is a complex process in which many external and internal factors are involved. Nevertheless, the role of colorants and various accompanying substances in the ink is often overlooked. Our research work aimed to determine the fastness of water-based ink-jet inks in aqueous solutions. A printing ink often contains a complex mixture of colorants to achieve optimal optical properties of color and a suitable fastness of the print. Therefore, we investigated the composition and stability of cyan, magenta, yellow, and black inks under the influence of UVC light in the presence of oxygen as well as in an inert environment based on TLC chromatography and spectrophotometric analysis. The process of photodegradation was evaluated based on ink amount and half-life. According to the results, the majority of inks consist of at least two colorants that differ in color and polarity. The results have shown that the presence of oxygen negatively affects the stability of inks; therefore, the inert atmosphere prolongs the durability of ink in water solution.