Topic outline
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When Stork Brabant B.V. 1991, introduced the first InkJet textile printing device, we can say that a new era of textile printing technology has begun. The benefits of digital printing technology have been recognized by designers and technologists. Technology originally developed for graphic applications enters the world of textiles and breaks down the limitations that existed primarily in the creative part of production and impeded the design freedoms, due to the technical requirements of analogue technologies and sample preparation processes. Now, without the expensive and time-consuming preparatory phase that involves preparing samples and templates in analogue printing with a limited number of colors and patterns, digital printing with the ability to reproduce patterns of unlimited shapes and color numbers, provides the ability to respond to market demands extremely quickly, with immediate intervention design, design personalization, uniqueness, individuality with significant savings in water and energy, and pollution reduction, making digital printing a more environmentally friendly technology than analogue.
These advantages justify the considerable research and development work that is continuously invested in finding optimal solutions to the constraints and issues that, despite the great advantages and recognition of digital technology in the world of apparel, still hinder its full commercialization. Due to the complex interaction of the specific surface structural characteristics of textiles as a substrate, the requirements on the composition and rheological properties of printing inks, and the technology of droplet formation, there are still numerous problems that need to be addressed.
This course is part of the MODULE FINISHING, PRINTING and FUNCTIONALIZATION.
THREE TYPES OF LEARNING MATERIALS are available:
- Materials for Students;
- Materials for Staff;
- Materials for Trainers (University Teachers/Researchers)
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In this course, students of creative and engineering specializations will gain knowledge about the application of digital inkjet printing technology on textiles. For students of creative specialties, digital printing technology is a tool of unlimited creative expression, a technology that gives an aesthetic component to textiles without limits in the number of colors, effects or sample sizes.
It will provide students with basic knowledge of the historical development of digital inkjet technology and its gradual application in textiles. An insight into the advantages and justifications of the application of digital textile printing technology is given, but it will also explain the limitations and obstacles that are still encountered in industrial practice in the application of inkjet printing on textiles. The basic mechanisms of bonding dyes and pigments to textiles will be explained, and the structure of dye-based and pigment-based inks will be explained.
Precisely because of the complexity of the interaction of ink and textile, it is necessary to carry out certain types of pre-treatment and post-treatment, which will also be explained. The basic physical, mechanical and optical characteristics of textiles that affect the final appearance and quality of the print and color reproduction will be pointed out.
Ultimately, the goal is to encourage students who have an entrepreneurial spirit and find their interest in the field of printing, to, using the knowledge gained here, further educate themselves, dive deeper into the subject and find themselves in textile printing entrepreneurship.
TOPICS:
INTRODUCTIONBASICS of DIGITAL Printing TECHNOLOGIES
BASICS of DIGITAL PRINTING Technology on TEXTILES
- Features of TEXTILE digital print COMMERCIALIZATION
- INK PROPERTIES for Digital Inkjet Textile Printing
- COLORANTS in digital textile printing
COMPUTER Support in DIGITAL TEXTILE Printing
ADVANTAGES and DISADVANTAGES of Digital Printing on TEXTILESPECIFICS and OPSTACLES in TEXTILE Digital Printing
- TEXTILE/INK DROPLET Relationship
FUNCTIONALIZATION and PRE-TREATMENS of Textiles in Digital Printing -
The introduction of digital technology into industrial processes in general is evolving strongly and dynamically. This fact is visible in the rapid development of printing technology based on the integration of printing machine and computer. Digitization in the development so far has caused numerous changes that are visible in every production of printed textiles in which the application of Ink Jet printing technology (dominant digital printing techniques) creates opportunities for personalized printing and printing on demand. Without the process of digitization and digital printing, it is not possible to imagine today's business activities and their progress. Being able to order a personalized sample of materials, high quality, and in a short time, is really something new. Previously, it depended on a complicated technological process that was unprofitable in a small edition. Now it represents great business opportunities for profit in the market and its profitable conquest. In the world market since 2012, the need for this type of printing is growing rapidly. It is ubiquitous in the fashion industry, and its many practical and creative aspects are increasingly appealing to designers. With the introduction of digital printing, the number of samples that can be printed in small quantities is infinite. For textile printing, it is important to understand how to work with certain textile materials and dyes for the highest quality end product. Printing ink is the most important for a quality print, and in order to achieve product durability, it is necessary to investigate which dyes can withstand external influences, light and washing, and at the same time be suitable for reproducing designs on all types of textile materials.
Many disciplines and competencies contribute to producing digital textile printing. In addition to print head design and manufacture, material handling engineering, and ink chemistry, are textile manufacture and pre-treatment, post-print finishing, design, raster image processing (RIP), and color management software.
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A brief history of the development of Ink Jet technology as key in the transfer of digital printing from graphic technology to textile will be presented. From the first description of the mechanism of breaking the liquid flow into a series of droplets, set by Lord Rayleigh, to the modern technology of piezo, buble-jet and electrostatic system.
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Inkjet printing is a non-contact technology where micro droplets of liquid are ejected through microjects to impact a substrate at a precise location to create an image. Its functional principle is that the pattern is drafted or transferred from any digital model or by scanner from standard photographic models or drawings to the fabric by and inkjet printer.
In the Ink Jet technology, only the ink drops get in contact with the surface. It is generally known as a printing method without any impact.
The basis of the development of digital inkjet technology is the development of writing head technology. To date, a unique printhead printing technology has not been adopted, so it can be said that the development is going in several parallel directions, and they depend on the application of ink flow technology and droplet formation technology.
In this lesson, the basic technologies of flow and droplet formation of printing ink will be described.
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The video shows the working principle of piezo ink flow technology. It features an epson printhead for printers designed for printing on paper, but the same technology applies to textile printing.
This video shows the working principle of thermal inkjet. Also, animation refers to the operation of a paper printer, but the same is applied in inkjet digital textile printing machines.
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In this article you read about the physics involved in the precise manipulation of liquid jets and drops in ink jet printing technology. Over the last 30 years inkjet printing technology has been developed for many applications including: product date codes, mailing shots, desktop printing, large-area graphics and, most recently, the direct writing of materials to form electronic, biological, polymeric and metallic devices. The new non-graphical applications require higher print rates, better resolution and higher reliability while printing more complex, non-Newtonian and heavily solids-loaded liquids. This makes the understanding of the physics involved in the precise manipulation of liquid jets and drops ever more important. The proper understanding and control of jet formation and subsequent motion of the jetted materials requires physical studies into material properties at very high shear rates, acoustic modes in print heads, instabilities of jets, drop formation, drop motion, stretching of fluid ligaments, the role of polymers in jet break up, electrical charging of drops and the aerodynamic and electrostatic interaction of jets and drops in flight. Techniques for observation, measurement and analysis are evolving to assist these studies. This paper presents some examples of the application of physics to understanding and implementing inkjet printing, including recent work at the Cambridge Inkjet Research Centre.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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Digital Textile Printing technology is developed with the continuous improvement of computer technology and gradually formed as one of the high-tech products which combine machinery and computer electronic information technology. The emergence and continuous improvement of Digital Textile Printing technology have brought a new concept to the textile printing and dyeing industry. Its advanced production principles and means lead textile printing and dyeing industry to unprecedented opportunities for development.
Computing power is employed for three distinct stages in the process of printing textiles digitally. First comes the design work, involving a textile print designer; second, processing the image so that it is in a suitable form for printing; and third, controlling the printer so that each pixel is laid down in the right place with the right mix of inks.
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The digital print method is reliant on digital designs to feed the process. Design information must be delivered to the inkjet printer in digital form. The design file is often prepared and supplied in such universal formats as .tif or .jpg files that hold the pattern and color information the printer software requires for image processing and color management. These files are then interpreted for output at the printer by specialized software programs for color management and raster image processing or `RIP'.
The digital design environment provides a flexibility that is a key advantage of inkjet printing.
As long as the design remains digital, it is possible to make quick changes to pattern or coloration. Digital designs are easily stored or archived and retrieved on demand for production purposes. It is possible to harness such design archives, so that customers can review designs from previous lines or seasons and update or reorder as the market dictates. In the digital print environment it is also possible to create highly unique designs that illustrate special tonal or photographic detail and and are almost unlimited in terms of color number and design length.
There is also the applicability for print engineering according to the shape of cut parts and to enhance overall product design.
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The textile and apparel industry comprises a complex network of interrelated sectors that produce fi bers, spin yarns, fabricate cloth, and dye/fi nish/ print and manufacture apparel. Computer technology is one of the most important tools contributing to the signifi cant advancement of this industry. The transition towards digital solutions and computerization is an irreversible trend today and will accelerate in the future.
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Advantages of Inkjet technology and justification for further investment in research and development:
- “Quick response” – sort time answer on market and customer demands.
- Decrease of pre-printing costs (elimination of screen preparation phase as well as screen storage, which enables the capital financial savings. The digital technology does not require additional space for storage since the patterns and all the production dana are saved in computer CAD/CAM data bases).
- Number of colors and pattern size are practically unlimited which allows greater designer freedom and pattern reproduction in large number of repetition with constant colour reproduction quality.
- Production errors are minimized (in compare to analogue printing techniques)
- Optimal consumption of printing pastes (in analogue printing techniques the printing paste consumptions are much higher as well as the amount of waste printing paste)
Limitations and disadvantages of Ink Jet technology in textile printing
- Because of complex interaction of specific surface – structure textile characteristics, demands on composition and rheology properties of printing inks and the technology of ink droplet formation, there are still certain barriers and limitation.
- Problem of textile surface – structure characteristic influence on colour dot formation, dye penetration and capillary diffusion of dye,
- Problem of porosity of textile material,
- Problem of modification and adaptation of dyestuff and printing ink components, for usage in digital printing technology
- Problem of equipment technical requirements which additionally complicate the optimization of textile printing inks for digital production,
- Optimization of textile pretreatment and finishing phase as key phases in application of textile dyestuff based printing inks (example: printing paste based on reactive textile dyestuff).
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All over printing started its journey in our garment industry from the 80’s. Although initially roller printing technique was prevalent, later flatbed and rotary screen printing techniques gained popularity. Peoples tastes, preferences and needs are changing with the change of era. Especially today’s young society is much more aware of their dress and fashion. Therefore, the demand for all over printing is increasing day by day all over the world including Bangladesh. There are many more products including t-shirts, shirts, pants, three-piece, bed-sheets and so on where all over print is being used. However, there are several limitations to the methods of all over screen printing, one of which is all kinds of design can not be printed by using flatbed or rotary screen printing method. All though it is possible to print 1-20 colors by those methods, usually more than 12 colors are not printed, the main reasons are two: 1) Print cost is high & 2) Machine complexity. Also, the photo print and effect of 3D cannot be clearly highlighted through screen printing methods. A new chapter has been added to the printing industry to overcome all these various problems, that is Digital Textile Printing.
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One of the largest problems with digital ink-jet printing on textiles is obtaining the desired colour, as there exists a strong interaction between the relationship between texture of the substrate and the ink. Fundamental research is being conducted to model the relationship between the texture, colour of the textile material, dye and the resulting colour. The relationship between fabric, inks and the resulting colour is complex. The number of textile substrates being used in the industry is very large. It is, therefore, not realistic to suppose that a strictly mathematical model will be found to describe these relationships. Moreover, optical effects have to be taken into account.
Digital InkJet technology is a graphical multicolor image reproduction technology, originally developed for homogeneous, uniform surface structures such as paper. However, textiles as a unique, heterogeneous, three-dimensional form is having its own surface regularities, completely different from homogeneous paper or plastic structures. Previous research on similar topics has confirmed that it is precisely the fundamental mechanisms that define print quality that have not been fully clarified, and the role of the surface structure of textile material has only recently been recognized as one of the fundamental factors for print quality and the achievement of an optimal color gamut. Therefore, any study of the influence of surface structural characteristics of textile materials on the formed shape, degree of deformation and spreading of the droplets on the surface of textile materials and penetration of printing ink droplets into the structure of textiles, contributes to the understanding of these fundamental mechanisms.
- A specific problem is the porosity of the textile material, which causes a certain loss of information in the reproduction, since the penetration of printing ink into the deeper layers of the textile substrate as well as the loss of printing ink on porous parts cannot be prevented.
- Also, the issue of providing an active surface and the specific relationship of chemical constitutions of dyes and functional groups of textiles also defines the platform of the still unresolved issues in digital printing technology.
- Problems of modification and adaptation of inks and components of printing pastes for application in ink jet technology, as well as problems of technical requirements of devices for InkJet printing, additionally complicate the optimization of printing pastes or printing inks.
- Also, a significant problem is the optimization of pre-processing and post-processing methods of textiles as key stages in the application of digital technology.
The picture shows three motifs printed with digital inkjet technology and clearly shows the impact of the background. Motifs and prints were made by the author Ivana Ravlic, a student at the University of Zagreb, Faculty of Textile Technology, graduate study Industrial Design of Textiles and Clothing, generation of graduates in 2016.
The motif, originally created by Ivana Ravlic, was printed using the digital technique of textile InkJet printing on various substrates, with pronounced surface structures (for example, velvet, velvet, jute, linen). The impact of the substrate is immediately visible. Therefore, knowledge of the relationship between the structure and color of the substrate with the printed motif is necessary. It is necessary to be able to predict in which direction and which color parameters will be affected by a certain structure and color of the substrate in order to carry out timely color correction and color matching.-
The spreading of an ink drop on a substrate mainly includes two processes. First one is the drop impacting on the substrate. In this case, according to different impacting conditions, six different phenomena have been observed including deposition, prompt splash, corona splash, receding breakup, partial rebound and complete rebound. The other process is the liquid wetting the substrate. Both the two stages are closely related with the nature of the substrate, such as the surface texture, chemically homogeneous or heterogeneous, hydrophobic or hydrophilic and planar or nonplanar.
When a drop of ink comes out of the nozzle of the print head, during a free fall towards the printing surface, it forms into a regular ball shape. All droplet formation technologies are designed so that when a droplet of the regular shape comes to the printing surface it forms a regular circle. In this way, proper positioning of the droplets and proper mixing of colors is ensured for optimal reproduction of each pixel of the image.
But this is only possible on homogenic surfaces like paper. Such homogenic surface is shown in the right side of the figure, showing a correct circular print of process colors. However, the enlarged photograph of the digitally printed knit (left side of the figure) clearly shows the interaction of the printed image with the structure of the material. Due to the deep penetration of inkjet ink into the structure of the material, the image becomes an integral part of the structure of the material and in addition to the colors defined by the design, it also has a characteristic three-dimensionality consistent with the construction of textile material.
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Cotton fabric has been extensively used as the substrate of inkjet printing to manufacture traditional garments as well as emerging e-textiles due to its comfort, renewability, good dyeability, biodegradability and relatively low cost. In present work, the spreading and coalescence of ink drops on a cotton fabric as well as their effects on the image quality were investigated. A reactive orange 13 dye was selected as the colorant to make it convenient to observe the depositing morphologies of ink drops. The impacting and wetting processes of an ink drop on a cotton fiber were observed through a high-speed camera. Depositing morphologies of an ink drop, coalescing structures of ink drops and patterns printed with different drop spacings were observed through a microscope
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The inkjet printing of functional oxide nanostructures from solutions provides many advantages when compared to conventionally used top-down patterning methods. It does not require masks and—as the material is deposited only where and when needed—any material-removal steps are not needed. This contributes to reduced waste, cost, and time required to fabricate the device. Despite its apparent simplicity, the inkjet printing process offers many challenges, including the ink chemistry, ink-substrate interaction, and drying; these are discussed in the present review. The ink should have suitable values of viscosity, surface tension, density, and vapor pressure to fulfil the requirements for stable drop formation and pattern formation. The substrate properties are discussed from the points of view of wetting and stability of the printed patterns. Drying of wet deposits without build-up of the material at the edges via the coffee-stain effect is a critical step and strategies to overcome it are discussed. Finally, the potential of inkjet printing technology in many different applications is discussed
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When the printing ink touches the surface of the textile material, penetration and spreading occur. The ratio and specific relationship of penetration and spreading will depend on physical characteristic of the substrate surface and on the pre-treatment of substrate. The function of fabric surface pretreatment is to immobilize the ink drop jetted onto the fabric to prevent its bleeding. The role of pre-treatment is to minimize risk of ink bleed in ink-jet printing. Pastes used in pre-treatment contain various agents to improve overall print quality: coloring, color stability and print fastness against washing. Without pre-treatment of target fabrics, ink-jet printing would be unable not only to prevent ink bleed but also to ensure sufficient coloring.
Printing is the absorption and retention of dye, or ink, in definite position. Dyeing involves larger amounts of dye solution (dye bath), while printing involves smaller amounts in a highly controlled manner. However, inks for ink jet printing are not as easy to control as printing pastes in screen printing. Rheology is the study of how matter flows and “viscosity” or “viscous” describes a place on a scale between fluid and solid states of matter. Inks for ink jet printing must be formulated to flow easily through the extremely small orifice of a nozzle, but this lack of viscosity also makes them likely to “wick” along the fibers of the fabric. “Wicking” allows the ink to travel along the fibers of the fabric by capillary action, in defiance of both gravity and the defined area of where the print is supposed to be. Consequently, the print design will appear on the fabric surface to blotch, bleed, or blur. Producing a good print requires:
- “Wettability” - the ink drop must quickly penetrate the surface of the fiber; it must not bounce or diffuse into droplets due to the impact of landing. It must not penetrate too far into the density of the fiber and risk a color losing its brightness. Factors such as these and wicking out along fibers as the ink is absorbed will affect print and color clarity.
- “Settability” - once the ink has been absorbed into the right place on the textile background, it must stay there. The ink must dry quickly, with the print then “set” or “fixed” into the textile for the long term and no discoloration to the main body of the fabric or alteration of color quality within the print.
- “Jettability” - dye is often also concentrated as smaller volumes are generally applied in ink jet printing. This can determine the color and long-term wear qualities of the print. Active ingredients must also not corrode the delicate machinery of the print head and nozzle. Above all, the viscosity of the ink must allow it to pass through the nozzle or jet.
The effectiveness of the pretreatment is dependent on its application as well as its ingredients. Pretreatment solutions can be applied in a number of different ways, ranging from simple spraying to large-scale industrial machinery, such as the padding mangle, that allows cloth to pass fully immersed through the solution, with the excess liquid squeezed out or extracted before the cloth passes through a dryer. Pretreatments can also be applied through screens. Ingredients should be well mixed to avoid settling and uneven distribution of ingredients through the solution. Pretreatments need to be evenly applied, and only enough used to capture the ink/dye molecules during printing. Drying techniques should also be monitored, with even coverage at an even temperature and no overheating or “hot spots.”
The principle and most common ingredients for pretreatments are thickeners, alkalis, and urea:
- Thickeners should be neutral components that will not themselves color the cloth but will hold the dye within a certain area with enough time and some moisture so as to penetrate through the fibers of the fabric. The selection of thickener depends on the chemical composition of the colorant to be used, including its requirements for curing or the fixing of the print so that the ink will not wash out. Common examples include sodium alginate, derived from a type of seaweed, or guar gum, also used as a thickener in foodstuffs.
- Alkali is required for reactive-type dyestuffs to react and form a chemical bond within the fiber. An alkali has a relatively low concentration of hydrogen ions and a pH of more than seven, as opposed to an acid. In conventional dyeing, this can result in significant effluent. Sodium carbonate or “soda ash” is a common example.
- Urea is an organic compound, which aids the dye to dissolve more fully in the liquid carrier, enabling a more concentrated solution and thus enabling a more even, also brighter and/or deeper, coloration. It is “hygroscopic” and acts as a “humectant,” aiding moistening or wetting, and this moisture allows the dye to more completely travel into the fibers in order to stain them. Retaining some moisture can also be significant for fixing, as in some cases drying out through evaporation into the atmosphere will not produce as fixed or set color as through drying by the application of heat. Due to its multiple properties, urea can be difficult to substitute.
More complex ingredients of pretreatments include:
- Cationic agents can increase the fixation rate of a dyestuff, and thus reduce the need for additional pretreatment chemicals, and reduce dye lost as effluent due to wash-off. “Cationic” refers to an ion or group of ions with a positive charge, whereas “anionic” refers to ions carrying a negative charge. Cationically treated, positively charged fiber will strongly attract anionic, negatively charged dye molecules that can then join to form a strong “ionic” or “covalent” bond, that is, joined at the molecular level. Cationic pretreatment may also reduce ink consumption and postprint fixing or setting processes, but as other components in the process may be “anionic,” the cationic component must be selected with care. Not only could the cationic and anionic ingredients be incompatible, they could also be too compatible, leading to staining as the cationic pretreatment attracts the excess anionic reactive dye during the washing-off process.
- Surfactant (surface-active agent), are used extensively in many products and processes as a foaming or wetting agent. By reducing surface tension, it minimizes separation and increases emulsifying and solubility of disparate compounds such as oil and water. These may also be positively (cationic) or negatively (anionic) charged, or not at all (nonionic).
- Softeners such as silicone compounds may improve the handle or feel of the cloth. “Silicone” is a man-made or synthetic compound, typically rubbery and heat-resistant. One of its ingredients is the naturally occurring “silicon”. Silica, or silicon dioxide, can also be used as a fine, particle coating, often ground down into micro and nano-sized particles, and added to help to hold ink in place.
- Binder - dye is soluble, whereas the fine particles of a pigment will not dissolve, instead requiring “suspension” in a fluid carrier. Instead of reacting and chemically bonding with fibers, as “reactive” dyes would do, the particles of pigment-based colorant must be mechanically bonded onto the cloth by a binder. Described generically also as a resin, this is most likely to be a synthetic copy of a resin rather than naturally sourced. Another ingredient may be an acrylic polymer, also known as polyacrylate. Depending on the type of print head, in some cases, some binders can be added in with pigment to an ink formulation. In such an instance, there would be little need for a specific ink jet pretreatment outside of the standard preparation of fabric for print. Compatibility between pigment-based inks or dyes and particular print heads should however be confirmed by the relevant manufacturers, as assumptions could prove costly.
Source and recommended literature:
- Christina Cie: Ink Jet Textile Printing,
- Publisher: ELSEVIER SCIENCE & TECHNOLOGY
- Hardcover ISBN: 9780857092304; e-Book ISBN: 9780857099235
- http://dx.doi.org/10.1016/B978-0-85709-230-4.00001-7
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The application of dyes on textiles, whether by dyeing or printing, requires the addition of various chemicals (alkalis, electrolytes, pH regulators, etc.), which due to specific requirements for purity and conductivity of printing inks in digital printing, may not be contained directly in printing inks. Therefore, extensive research work is dedicated to finding the possibility of applying the required chemicals in the processes of pre-treatment or after treatment of printed material.
This loses some of the primary advantages of digital printing over conventional screen rotary or flat printing, such as, inter alia, shortness and simplicity of the process, purity of the process (minimal external use of chemicals thus increasing the environmental sustainability of textile printing), and economics justification cost reduction - associated with shortening the production process.
- For InkJet textile printing, systems with reactive dyes for cellulose fibers, disperse dyes for PES and synthetic fibers are currently developed, while those with acid dyes for protein fibers are in a slightly lower stage of development, and, unlike systems with reactive dyes, they are not yet in the process of commercialization.
- This chapter will present and explain the currently most used methods of pretreatment of materials that contain cellulose, synthetic and protein fibers, and for the printing process with the specified dyes.
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There are important steps to follow to ensure a quality image when digitally printing on textiles. One of the most important is pre-treating fabric with chemistry designed to offer desired end-use performance that cannot be achieved by the ink and fabric alone. Of the different types of colorant used in digital textile printing ink, pigment has been the slowest to be adopted in the industry partly because it’s the only colorant that requires a physical bond with the fabric using a polymer (binder) to act as a sort of ‘glue’. The other methods are based on dye technology which chemically binds to the fabric. The downside of this is that it makes dye-based inks fabric specific and, in addition, these dye-based technologies don’t have as good a light-fastness as pigment based inks. As an example, outdoor furniture can significantly benefit from a pigment ink because it has the most resistance to UV light. Digital pigment printing on textiles enables bespoke experiences at an attractive price, which is made possible by the right pretreatment technology for the end-use product. As more traditional textile printing companies consider the benefits of digital printing, this market segment has experienced significant growth over the last several years.
To achieve desired results, pretreatment is necessary to ensure fabric is truly prepared for digital printing. Why? Digital printing is about printing dots. If a pretreatment can be used that’s less expensive than ink, then more ink can be kept on the surface of the textile. Without a pretreatment, more ink dives into the fabric, leading to the need to use even more ink to increase color vibrancy and achieve the sought-after look. A pretreatment also improves dry and wet crock. Fabric that is properly prepared has no oils or contaminants from previous processing and is perfectly wound on the appropriate core to avoid head strikes or waste. Through proper chemistry, it is pretreated to enable desired end-use performance in a variety of textiles, from apparel and quilting to signage and home décor.
Achieving this desired performance is all about balance: durability for UV stability and dry/wet crock; fabric integrity for softness and no change to fabric/weave appearance; print quality for optimal dot gain and density, and no metamorism; and the manufacturing process. There are some key performance requirements that any pre-treatment must meet in order enable the most benefits from pigment-based ink systems:
- First, the fabric must maintain its 'hand', which is essentially the feel of the original fabric. Printing can make a textile feel rough, stiff or “boardy.” So, the pre-treatment must have minimal effect on the hand
- Secondly, the pre-treat process holds the colorant at the surface and in this way optimizes color strength and print quality. However, holding the ink on the surface of the surface of fabrics can make rub fastness a challenge. Rub resistance, or ‘crock resistance,’ is measured by assessing the color transfer onto white fabric when rubbed back and forth against a printed surface for a set number of times under a given weight. Crock is measured in a range of grades from 1-5 and should be high. Manufacturers target a minimum of grade 3, but usually aim for 4+. If pre-treating doesn’t do all the work necessary, some suppliers implement a post treatment, but this adds cost and lead time, which defeats one of the big advantages of digital printing and its shorter lead times.
- Thirdly, to achieve desired performance, pre-treating fabrics requires matching the substrate and ink, and that requires different chemical approaches. At Lubrizol, we create textile pre-treatment solutions for each of the four fabric types—cotton, polyester, cotton/polyester, and other synthetics.
- Finally, ink is another consideration. All inks aren’t designed the same. Some are more robust for durability; some for color. The pretreatment needs to be able to accommodate all types of ink.
Application methods are also important to get the right result. Padding (dip and squeeze) is the most common application method. Other new methods are being developed, such as spray, foam and jetting. These methods are designed to use less pretreat and only where needed. So, when considering pre-treating fabric for digital pigment based printing, it’s important to work with a partner who can help you make the right choices and that is adept in understanding global regulations that affect the textile print industry.
https://www.lubrizol.com/Coatings/About-Performance-CoatingsIn digital pigment printing, fabrics have to be pre-coated to increase the colour gamut and durability of the print. Pigment printing provides a simple process involving printing and thermo-fixation by either a heat press or a fabric baker. However, with pigment printing, pre-coating is also an essential in terms of enhancing the colour gamut and fastness of the fabric. So faced with the inevitability of pre-coating, volume digital textile printers are faced with two important choices, first the choice of chemicals and second the choice of machinery to pre-coat their fabrics. As far as chemicals are concerned the printer has a wide array of product available. In many cases coating formulations are supplied by Ink manufacturers to pair up with use of their inks. In this field, major manufacturers include, Epson Genesta Inks Pre-Gen, Neo Coat from Swiss Performance Chemicals and the P601 Pre-Coat from Pigmentinc. However, many chemical companies independently supply excellent pre-coating chemicals, these companies include Lubrizol of the USA, Tanatex of the Netherlands, Rudolf Chemicals of Germany and Sarex of India. In general terms, these pre-coating formulations, which often use thickeners and cross linking agents, improve the mark and colour intensity of the print, as well as the wash, and rub fastness of the fabric.
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- Colour objectification and spectrophotometric analyses, computer data analyses, computer colour and texture visualization
- Characterization of non-treated and treated surface as well as ink droplet behaviour (scanning electron microscopy-SEM, moisture management analyses-MMT, drop shape analysis-DAS, pH measurement, hydrophilicity/ hydrophobicity of textile analyses, fabric touch testing-FTT).
- Data analyses and numerical/graphical presentation, examples of results discussion.
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To improve teaching skills in the field of textile printing, it should be taken into account that textile printing is a technology and industry that intersects several areas, and is basically experiential and multidisciplinary.
To understand and to be able to teach in digital textile printing, one must understand the nature of interaction of following fields: print head design and manufacture, material handling engineering, ink chemistry, textile manufacture and pre-treatment, post-print finishing, design, raster image processing (RIP), and color management with objectification.
It is necessary to distinguish between the methodology of teaching and research in the field of digital printing and the functionalization of textile materials for the needs of digital printing.
- For TEACHERS: materials prepared for the needs of this course are available, with the recommendation of additional literature and guidelines for the organization of the course.
- For RESEARCHERS: In the field of research, numerous areas of application of digital printing on textile materials have been opened, and the directions of research can be defined in the following contexts:
- Previous research has confirmed that it is precisely the fundamental mechanisms that define print quality that have not been fully clarified, and the role of the surface structure of textile material has only recently been recognized as one of the fundamental factors for print quality and the achievement of an optimal color gamut. Therefore, any study of the influence of surface structural characteristics of textile materials on the formed shape, degree of deformation and spreading of the droplets on the surface of textile materials and penetration of printing ink droplets into the structure of textiles, contributes to the understanding of these fundamental mechanisms.
- A specific problem is the porosity of the textile material, which causes a certain loss of information in the reproduction, since the penetration of printing ink into the deeper layers of the textile substrate as well as the loss of printing ink on porous parts cannot be prevented.
- Also, the issue of providing an active surface and the specific relationship of chemical constitutions of dyes and functional groups of textiles also defines the platform of the still unresolved issues in digital printing technology.
- Problems of modification and adaptation of inks and components of printing pastes for application in ink jet technology, as well as problems of technical requirements of devices for InkJet printing, additionally complicate the optimization of printing pastes or printing inks. Also, a significant problem is the optimization of pre-processing and post-processing methods of textiles as key stages in the application of digital technology. Particularly high demands on particle size, surface tension, viscosity, stability, compatibility with printing ink components and ink flow technology are placed on binders as key factors in the application of pigment-based printing inks.
- Therefore, we can now consider which are the most important directions of research and aspects of the application of an innovative approaches in the formulation of printing inks and modifications and pre-treatments of textile materials. We must also take into account that in digital ink jet technology, the development of printing ink formulation takes place in two main streams - one refers to the development of pigment based inks, which includes the development of innovative methods of textile surface pre-treatment and the development of binders. The second refers to the development of dye-based printing inks, which includes research in the field of dye modification, primarily reactive dyes, given the percentage of cellulosic materials being printed on a global market.
- As ink jet is a non-contact technology, the image formation is dependent on the physical-chemical phenomenon of ink spreading and penetration. This is dependent on ink properties (surface tension-viscosity), substrate pretreatment (physical-chemical aspects of dye-fiber interaction) and substrate structure - physical, constructional and chemical. What is indicative and present certain research gap in the field of digital textile printing is that there were no extensive research on ink penetration mechanism, although the significant part of printing ink-textile interaction is defined by the characteristic of absorbency, hydrophilicity and the porosity of textile.
- As much as the modelling of ink penetration and ink spreading, and their effect on print performance of paper have been well studied, these findings are still not verified for textiles where more complex behavior of ink jet inks is anticipated due to the topological nature of woven/knitted textile fabrics, the diversity of colorants (dyes and pigments) and their adsorption behavior on different textile fibers.
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The global textile printing market is expected to be worth a staggering $266.38 billion by 2025. Rapid developments in digital textile printing are expected to trigger accelerated growth for print-on-demand production methods, with total market growth currently set at CAGR 8.9%. Interestingly amongst these statistics - Cotton printed textiles are expected to account for 44.9% by 2025 in terms of global textile volume, as the sustainable agenda gains traction and consumer trends increasingly demand biodegradable and environmentally friendly attributes. (Source: Grand View Research).
With huge growth predicted the textile marketplace offers both a window of commercial opportunity and an opportunity - to not just build new entrepreneurial business models - but to deliver a clean, efficient sustainable textile industry.
- Do You think that you only need to plug in a digital textile printer for it to work?
Using digital inkjet printers for textile printing can be more complex than printing on other materials, like vinyl or paper. However, by understanding a few basics about the chemistry, equipment and process, inkjet fabric printing is achievable with great print results and can become profitable for your business.
If you are a starter with no background in textile printing, it would be advised to combine forces with somebody who knows textiles and textile chemistry. Digital fabric printing requires an understanding of textiles and textile chemistry, but also the machinery and digital technology.
- Is it competible to conventional (analoque) printing?
Digital fabric printing is not competing with conventional rotary or screen printing that may collectively be termed analogue printing systems. Digital fabric printing cannot match the economy of scale that an analogue system affords. Even today most of the digital inkjet fabric printers that get sold in the world have printing speeds of less than 100 sqm/hour. The most important thing for an investor is to understand what digital printing can, analogue printing cannot. Only when an investor sees value in what digital fabric printing can, beyond the boundaries of analogue printing does it make for a successful business. Only those who are ready to invest in marketing and business development for an enhanced product offering will reap the real rewards of fabric printing. It is not just creating value but also understanding the value and conveying the value down the sales channel right up to the person wearing a garment that is digitally printed.
EFI Reggiani Impacts Digital Textile Printing
https://www.efi.com/products/inkjet-printing-and-proofing/reggiani-textile/-
Inkjet printing appears simple, however, inkjet inks ought to meet certain important physicochemical requirements (storage stability, adhesion, surface tension...) which make their chemistry and formulation extraordinary. While formulating digital printing inks, the ink and the substrate pre-treatment are the most important components of the system.
Source: https://coatings.specialchem.com/selection-guide/digital-printing-inks-ingredients-testing