University of Ljubljana, Faculty of Natural Sciences and Engineering, Ljubljana, Slovenia
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BSTRACTThe chapter presents the possibilities and a correct procedure for a color management application in the field of digital printing onto textile substrates. The introduction of color management into the field of digital textile printing enables better quality control, faster prepress, reduction in the use of material and better repeatable color prints on textile substrates. Due to the high price of printing colors used in digital textile printing, and the costs connected with the pre- and aftertreatment of printed fabrics, an appropriate preparation of color patterns and simulated prints is of even greater importance.
The aim of this chapter is hence to present how long-term and expensive pre- and aftertreatments of textile substrates can be avoided with the help of an appropriate use of printer color profiles for all print devices included in the workflow, e.g., print simulation on paper printed with a laser or inkjet printer. On the basis of simulated prints on paper, a customer can decide on the color that gives the best results on a selected pattern.
Digital printing on a textile substrate – a banner made for indoor and outdoor applications, using the color profiles is presented as well. This includes experimental data and the methods for testing the lightfastness and weatherability of the substrate with a Xenotest, and for defining the uniformity of prints – mottling. The method for defining the uniformity of prints is included in the draft of the standard ISO 15311 and is also proposed by the German Printing Association FOGRA.
In addition, the importance of the optical brightener used for the improvement of substrate whiteness in digital textile printing is discussed. Furthermore, the calculation of the color inconstancy index CMCCON02 when defining the influence of different illuminants on the color change of substrates is presented.
* Corresponding author: Dejana Javoršek, University of Ljubljana, Faculty of Natural Sciences and Engineering,
Keywords: Color management, ICC profiles, digital textile printing, print simulation, color
inconstancy index CMCCON02
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NTRODUCTIONThe technology of digital printing is more and more established [1] in the field of textile printing [2–5] as it allows unlimited color sampling and good durability of prints, as well as in the field of pharmaceutical research [6,7], electronics and micro-engineering industries for printing electronic materials, such as printed circuit boards (PCB) [8, 9] and a humidity sensor directly printed on a textile using the inkjet printing technology [10], and even food decorating uses the digital printing technique as a major working tool. Recently, the inkjet technology has also been successfully applied in the biomedical field [11], where the DNA molecules have been directly printed onto glass slides using commercially available inkjet printers for the high-density DNA microarray fabrication [12], and inkjet printers were used to print cells and biomaterials for 3D cellular scaffolds [13].
In the case of inkjet technology, printing on various substrates is performed by means of non-impact printing or jetting drops of ink on a substrate. The most important component of inkjet technologies is the printing ink alone, which greatly affects the quality and reliability of the output [14]. Thus, in the digital textile printing, various inks that are designed for different needs and requirements are used, including reactive, acid, disperse and pigment dyes [15]. Despite the advantages and widespread use of pigment dyes [16–18], reactive dyes still occupy an important position in the printing of textiles, especially with thermal (bubble) inkjet printers. Reactive dyes are used for the printing on cotton fabrics and their blends, and on linen and silk fabrics. Reactive dyes for the printing with inkjet printers are now widely accessible to everyone yet relatively expensive. Therefore, a number of studies aimed at the improvement of digital printing on cotton with reactive dyes. Yang and Naarani researched the printing of cotton with reactive dyes using the inkjet printer. They studied the impact of matting conditions on the cotton print and how to improve the lightfastness of printed cotton with reactive dyes [19,20].
Digital textile printing with reactive dyes is different from conventional printing, especially:
in the substrate pretreatment with appropriate chemicals, as ink due to viscosity and stability does not contain chemicals that are necessary for the binding of the dye to fibers, and
in the aftertreatment when a chemical bond between the fibers and the reactive dye is formed, resulting in excellent wet fastness of color prints.
A lot of research has been conducted in this area [21–23]. It is known that these two, pre- and post-processing treatments, are essential as they further influence the change in color tone [24]. Moreover, the dimensional stability of the fabric patterned with the inkjet printer was controlled as well [25]. Weiguo et al. also analyzed the color print on the cationic agent printed cotton with reactive dyes and established that a color print is better on the cotton which was treated with a cationic agent than on the cotton treated with alkali, urea and
thickener [26], while some other researchers preferred modified chitosan pretreatment of polyester fabric for the printing with inkjet ink where the pretreated fabrics produced a much better color quality than the untreated fabrics [27], and preferred the pretreatments of the silk fabric with amino compounds for the inkjet printing where the amino compound pretreatments held and fixed the additional ink on the fabric surfaces resulting in a wider color gamut of the inks [28]. Kaimouz et al. provided a quantitative insight into the effect of pretreatment chemicals on the color strength, dye fixation and ink penetration on the inkjet printed Lyocell and cotton fibers, using a statistical analysis approach [29].
The trend in small print collections and unique products requires greater flexibility of printing companies and a fast production of color patterns and products. By using graphic programs, the expectations of textile and clothing designers and of small businesses are growing. In most cases, they require that a specific color pattern or color sample presented on paper be exactly reproduced on the textile substrate. However, the path from the model presented on paper to the final product printed on a textile substrate is relatively complex. Problems arise when discrepancies between the color patterns on paper, computer screen and the textile substrate occur.
In graphic technology, color management and the use of ICC (International Color Consortium) color profiles ensure a consistent color reproduction throughout the technological process and on all kinds of devices, regardless of the color space, including the original, scanner, digital camera, display screen and color printer. Color management has been used in graphics for a number of years, which is evident from the literature [30–35].
By introducing color management into the field of digital textile printing, the time required for prepress could be shortened and the use of materials could be reduced, which would lower the printing process costs [36]. Due to the high price of printing colors used in the digital textile printing and the costs connected with the pre- and aftertreatment of printed fabrics, an appropriate preparation of color patterns and simulated prints is very important. A print simulation in textile printing can be observed on a screen (i.e., soft proof) or conducted on another printer (i.e., hard proof), which enables – with appropriately built profiles for any device and their correct use – a simulation of particular color patterns on a different output device.
In one typical research [36], the linearization and characterization of three printers for paper and textiles, two inkjet and one electrophotographic (“laser”) printer, were implemented. It was demonstrated that an accurate creation of color profiles ensured the top quality of prints and successful hard proof on both laser and inkjet printers. While digital printing has become a link between the traditional and electronic media, the need for an accurate color reproduction is increasing. The users’ expectations have risen, representing new challenges for both, the color reproduction and manufacturers of a variety of substrates. In the textile industry, more and more optical brightening agents (OBA) are used in order to increase the whiteness of a fabric. With the same purpose, they are integrated in detergents, wherein they optically increase the whiteness of washed goods. Nevertheless, the performance of optical brighteners can be the source of incorrect and inaccurate measurements caused by errors in the measurements. In one study, they assessed the impact of the optical brightener in the fabric, before and after the treatment with washing agents [37]. This means that in addition to the initial treatment of the fabric with an optical brightener, the perception of the fabric color and the printed colors is clearly affected by the amount of optical brighteners in detergents that bond with the fabric during the washing process.
When color profiles for all devices involved in the process of printing (i.e., display screen, printer and printer for hard proof) are generated, it is recommended to test the colors under different illumination, since patterns are usually observed under various light conditions. This can be predicted by calculating the color inconstancy index, which is described below [38, 39]. The quality of prints can be controlled in different ways. One possibility is the calculation of the heterogeneity footprint with the M-Score method [40].
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XPERIMENTAL In our research, three substrates were used: textile cotton fabric which was printed with the inkjet printer Mimaki Textile Jet Tx2-1600 (Mimaki, Japan) using 8 reactive dyes [36], and
two textile synthetic fabrics, i.e., banner and textile banner made for indoor and outdoor applications, which were printed with Canon Image Prograf W8400.
In the first case [36], we focused on hard proofing, where the matching between the original colors and hard copy simulation of the colors was investigated using the color difference equations ∆E00. The purpose of the researches was to establish whether a print on a
textile made with a digital printer produced by Mimaki can be simulated with a print on a paper with an inkjet (Canon Image Prograf W8400, Canon, Japan) and laser (Canon Image Press C1+, Canon, Japan) printer.
In the second case, we focused on defining the print quality of presentational posters substrate – banner, using the color difference equations ∆E00. This included experimental data
and methods for testing the lightfastness and weatherability of the substrate with a Xenotest Alpha (Atlas, USA), and for defining the uniformity of prints – mottling. The method for defining the uniformity of prints is included in the draft of the standard ISO 15311 and is also proposed by the German Printing Association FOGRA.
Materials
The cotton fabric used in the research was provided by Tekstina Plc, Ajdovščina, Slovenia. The basic fabric properties are as follows: raw material: 100% cotton, plain weave, warp thread density: 54 threads/cm, weft thread density: 29 threads/cm, mass per square meter: 130 g/m2, breaking force in warp direction: 38.0 daN, breaking force in weft direction: 26.0 daN, breaking elongation in warp direction: 17.6%, breaking elongation in weft direction: 12.0% and fineness of warp and weft threads: 14 tex.
Two textile synthetic substrates, namely the high-impact, highly durable textile substrates were used, i.e., a vinyl banner (in the text called banner) and a textile (in the text called
textile) produced in China. The basic fabric properties are as follows: material: PES
(polyester), plain weave, Sample 1: mass: 1.1213 g/dm2, thickness: base – 0.180 mm, print – 0.182 mm; Sample 2: material: PES (polyester), mass: 1.9526 g/dm2, thickness: base – 0.321
density: 23 threads/cm, weft thread density: 30 threads/cm for Sample 1 (cf. Figures 1 and 3) was defined.
The analysis performed under a stereomicroscope (Leica EZ 40) and SEM microscope JEOL 6060LV is presented in Figures 1–4.
Figure 1. Sample 1, Print/Base, Leica EZ 40.
Figure 2. Sample 1, SEM microscope JEOL 6060LV.
Figure 4. Sample 2, SEM microscope JEOL 6060LV.