Topic outline

  • Module: FINISHING, PRINTING and FUNCTIONALIZATION

    The course is developed under Erasmus+ Program Key Action 2: 

    Cooperation for innovation and the exchange of good practices Knowledge Alliance

    Project: ICT IN TEXTILE AND CLOTHING HIGHER EDUCATION AND BUSINESS, Nr. 612248-EPP-1-2019-1-BG-EPPKA2-KA




  • COURSE: FINISHING in the function of DIGITAL PRINTING

    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) 


  • Materials for STUDENTS

    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:

    INTRODUCTION

    BASICS of DIGITAL Printing TECHNOLOGIES

    BASICS of DIGITAL PRINTING Technology on TEXTILES


    COMPUTER Support in DIGITAL TEXTILE Printing


    ADVANTAGES and DISADVANTAGES of Digital Printing on TEXTILE

    SPECIFICS and OPSTACLES in TEXTILE Digital Printing

    • TEXTILE/INK DROPLET Relationship

    FUNCTIONALIZATION and PRE-TREATMENS of Textiles in Digital Printing


    • INTRODUCTION

      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.

    • BASICS of DIGITAL Printing TECHNOLOGIES

      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.

    • BASICS of DIGITAL PRINTING Technology on TEXTILES

      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. 

    • COMPUTER Support in DIGITAL TEXTILE Printing

      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.


    • ADVANTAGES and DISADVANTAGES of Digital Printing on TEXTILE

      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).

      • SPECIFICS and OPSTACLES in TEXTILE Digital Printing

        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. 

      • FUNCTIONALIZATION and PRE-TREATMENS of Textiles in Digital Printing

        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.


      • Material for TEACHERS/RESEARCHERS

        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.


        • Materials for STAFF

          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/