Textile flat element having a denim structure and method for the production thereof

Abstract

The invention relates to a textile flat element having a denim structure. The denim structure comprises a coloring and appearance of denim goods, which is formed in the form of a digital pigment print.

Description

[0001] German Institutes for Textile and Fiber Research Denkendorf

[0002] 73770 Denkendorf

[0003] Textile surface element with a denim structure and methods for its production

[0004] The invention relates to a textile surface element with a denim structure and a method for its production.

[0005] The production of denim textures in textiles is known to be achieved by weaving dyed warp threads and undyed weft threads. Denim textures are defined color variations and appearances, especially in jeans fabrics.

[0006] Dyeing warp threads for denim production consumes extremely large amounts of water and energy and causes significant wastewater pollution from chemicals and unfixed dyes. For example, conventionally dyeing 1 kg of denim with indigo requires up to 40,000 liters of water, and the process takes place at temperatures above 50°C, resulting in an energy consumption of up to 140 kWh / kg of denim. Significant emissions also result from subsequent fashion effects such as laser treatment and stonewashing.

[0007] In authentic denim, the warp threads of the fabric are dyed blue, while the weft threads remain undyed, as described, for example, in https: / / fashionuni-ted.de / nachrichten / hintergrund / alles-was-man-ueber-jeans-und-denim-wissen-sollte / 2022120549360#herstellt. Indigo is used for dyeing, which is readily absorbed by the cotton fibers. Indigo itself is a water-insoluble vat dye and must be converted to the water-soluble leuco-indigo by reduction in an alkaline solution with sodium dithionite before dyeing. Typical application concentrations in the dye bath are approximately 1 g / l for sodium hydroxide and indigo dye, and 2 g / l for sodium dithionite, with the fixed amount of dye being less than 70%. For dyeing, the cotton fabric, or rather the warp threads of the jeans, are placed in the alkaline aqueous vat solution.The soluble dye component is absorbed by the fiber, and during air drying, insoluble indigo is formed again through oxidation. Unbound indigo must then be laboriously washed out. With a global indigo consumption of 66,000 tons, almost 20,000 tons of the dye, along with alkali and sodium dithionite, end up in the wastewater. Currently, approximately 2.5 billion pairs of jeans are produced worldwide, representing a total fabric volume of approximately 4 billion meters. 2 / a at a fabric weight of approximately 400 g / m² 2 This corresponds to the energy consumed in this process, approximately 210 TWh, and the volume of wastewater is 6 billion m³. 3 .

[0008] The invention is based on the objective of providing an environmentally friendly and sustainable manufacturing process for producing high-quality denim looks in textiles.

[0009] The features of the independent claims are provided to solve this problem. Advantageous embodiments and expedient further developments of the invention are described in the dependent claims.

[0010] The invention relates to a textile surface element with a denim structure. The denim structure comprises a coloring and appearance of denim fabric, which is formed in the form of a digital pigment print.

[0011] The invention also relates to a corresponding method.

[0012] A key advantage of the invention is that a denim look is digitally printed onto the textile surface element; that is, the image is based on a digital image or scan of jeans, which is printed directly onto the textile surface element as a color design. Effects such as stonewashed or laser bleached therefore do not need to be created in a separate step; instead, the visual impression is simply printed onto the fabric as an image. Since pigment inks are used and the color pigment bonds to the fibers of the textile surface element during the pigment printing process, all subsequent washing processes are also eliminated. This eliminates the very complex and water-intensive indigo dyeing of warp threads and the subsequent fabric production using undyed weft threads.Since pigment printing does not require rinsing, no wastewater is produced and water consumption can be reduced to virtually zero. Furthermore, fixing the pigment prints requires only less than 1 kWh / kg of fabric (>99% energy savings). Similar processes to those described in WO 2024 / 088872 Al utilize reactive printing, which requires rinsing and, due to residual dyes and alkalis washed out, also leads to wastewater pollution. This coloring process can be applied to all types of textile substrates, especially woven fabrics, including blends. The result is a wastewater-free and resource-conserving coloring process through direct printing of denim designs onto a textile substrate, applicable to all textile materials, particularly cellulosic materials.

[0013] In the textile surface elements according to the invention, the rub and wash fastness of the pigment print depends crucially on the amount of binder mixed into the pigment ink. High binder content leads to high fastness, while printing with pure color pigments can lead to more or less complete abrasion of the printed patterns.

[0014] Both low-viscosity inks (inkjet printing) and high-viscosity inks (chromojet printing) can be used for digital printing.

[0015] Many pigment inks for digital printing on textiles were originally formulated without binders, as many binders led to nozzle clogging and also increased ink viscosity. However, binder dispersions with a particle size of < µm are now available that no longer exhibit these disadvantages, or only to a limited extent. These are advantageously used for pigment printing according to the invention. For coloring pigment printing, dispersions of organic and inorganic color pigments can be used, such as Pigment Blue 15:3 (cyan), Pigment Red 122 (magenta), Pigment Yellow 83 (yellow), and Pigment Black 07 (black, K) in application concentrations of up to 6%. In the case of thermally fixable pigment inks, the ink contains the water-dilutable binder in application concentrations of up to 15% (dry substance).The binder adheres the color pigment to the surface of the fiber of the textile element. Aqueous polymer dispersions based on PUR acrylate, acrylates, N-methylol acrylate, styrene acrylate, styrene butadiene, acrylonitrile butadiene, and butadiene acrylate copolymers, as well as silicone-based binders, can be used as binders. Another class of compounds consists of radiation-curable binders based on urethane acrylate with free, uncrosslinked acrylate groups, which undergo radical polymerization by UV light in conjunction with photoinitiators such as benzophenone, BAPO, and α-hydroxy ketones. Manufacturers of textile pigment inks include DuPont and MS, as well as BASF, Fuji, Sensient, Farbenpunkt, Kodak, Brother, ITACA, and ink formulators from Asia.As an application method for printing on textiles, digital printing, such as inkjet printing for low-viscosity inks or Chromojet printing for high-viscosity inks, is advantageous compared to screen printing because customer requests can be addressed very quickly and individually, and higher printing speeds (up to 100 ifm / min) can be achieved than with screen printing, as described in: J. Provost, Digit. Text., 4(2016) 20 and L. Chapman, ITMA Technology: Digital Printing (online: http: / / www.textileworld.com / textile-world / features / 2016 / 05 / itma-techno-logy-digital-printing / ; last accessed May 2016).

[0016] Digital printing offers universal applicability on various substrates with maximum flexibility, enables personalization, and provides rapid responses to fashion changes. It allows for small print runs, just-in-time deliveries, and quick design sharing. Furthermore, it has no negative environmental impact due to low energy costs, as described in: S. Gupta, Indian J. Fibre Text. Res., 26 (1-2) (2001) 156 and B. Goel, R. Singh and GB Pant, Man-Made Text. India, 40 (8) (2021) 265.

[0017] When working with low-viscosity pigment inks, there is a fundamental risk that the printed samples will bleed significantly without appropriate pretreatment, resulting in poor color depth and blurred contours. In the case of inkjet printing with color pigments, the inks often cannot be mixed with the required amount of binder necessary to achieve the desired color fastness. Therefore, it is necessary to integrate binders and color fastness-enhancing compounds (e.g., crosslinkers, adhesion promoters) into the pretreatment formulations and to perform a pretreatment. A rapidly water-absorbing polymer can be applied to improve contours.These are primarily thickening agents, which are used as natural (alginate) or synthetic (modified sodium polyacrylate) polyelectrolytes or as modified natural polymers (carboxymethylcellulose, carboxymethyl guar, barboxymethyl starch, cellulose ethers) and polyvinyl alcohol. Furthermore, cationic compounds can also be used for interaction with the mostly anionically formulated color pigment dispersions. These are usually quaternary nitrogen compounds (quaternary ammonium and amino groups) that inhibit dye migration. The addition of the aforementioned binders and crosslinkers (e.g., blocked polyisocyanate) during the pretreatment of the textile surface element can also improve the rub fastness of the pigment print.Furthermore, adhesion promoters based on modified polyol olefins, silane adhesion promoters, and metal-organic adhesion promoters based on zirconates and titanates can be used. These increase the wettability of the substrate and form chemical bonds between the substrate surface and the ink binder. Corona pretreatment, through the introduction of functional groups, can also lead to improved wetting and adhesion of the binder. Hydrophobing can also improve the print quality under surface printing. To improve rub fastness, post-printing treatment with binders, acting as a protective topcoat, is also conceivable. Key criteria for pre- and post-treatment in pigment printing on denim are good print adhesion, good contour quality, and a soft feel.

[0018] Cellulosic denim fabrics, especially those printed with selected binder-containing pigment inks, have a soft feel and good fastness properties, particularly good lightfastness, rub fastness and wash fastness.

[0019] For fixing or curing pigment prints on textile surfaces, thermal fixing units such as tension frames and calenders, as well as IR (infrared) radiation, can be advantageously used. However, the particularly efficient drying and fixing with NIR (near-infrared) radiation can also be employed, promoting sustainability and saving energy. When using radical-curable inks, fixing with electron beams and, alternatively or additionally, extremely fast and energy-saving curing of the inks using UV radiation in the presence of a photoinitiator are also possible. Conventional inorganic and / or organic color pigments are advantageously used for coloring.

[0020] Should the selected pigment inks nevertheless exhibit insufficient rub and wash fastness and low color depth, the adhesion of the ink can be improved by pretreating the textile with, for example, binders and adhesion promoters and / or by post-treating the printed goods with binders in the sense of a protective topcoat.

[0021] A further significant advantage of the inventive method is that it can, in principle, be applied to all fiber materials and is also suitable for blended fabrics. As a result, even non-cellulosic fiber materials can be made accessible for the denim look. The concept of sustainability is underscored by the use of eco-certified inks and materials from sustainable cultivation. As a special feature and hallmark of sustainable denim production, the reverse side of the denim look remains unprinted.

[0022] The invention is explained below with reference to examples and figures. These show:

[0023] Figure 1: First example of the inkjet printing according to the invention on a textile surface element.

[0024] Figure 2: Second example of the inkjet printing according to the invention on a textile surface element.

[0025] The following examples show the spectrum of achievable dry and wet rub fastness of the various pigment inks on two selected and representative denim fabrics with 98% cotton and 2% elastane (Denim 1: basis weight approx. 290 g / m²). 2 Denim2: Basis weight approx. 205 g / m² 2 ) again.

[0026] Example 1

[0027] Suitable and preferred pigment inks were selected using inkjet printing on a representative denim fabric (Denim 1) under defined printing conditions. For this purpose, commercially available binder-based CMYK printing inks (T1...T5) were applied to the entire surface using a dGen inkjet printer (dGenArtrix) at a print resolution of 720 dpi x 720 dpi and subsequently fixed in a tension frame (Matthis) according to the manufacturer's instructions (approx. 160°C for 3 minutes). The amount of ink applied for full-surface printing is approximately 20 g / m². 2 . The generated print samples were characterized with regard to dry and wet rub fastness as well as the achieved color depths and were favored for denim printing if a wet rub fastness rating of >3 was achieved.

[0028]

[0029]

[0030] When evaluating color depth, the main focus is on the achievable color depth of the cyan ink, as this constitutes the majority of a denim color. Therefore, inks 3-5 are initially favored from a color perspective. However, considering the dry and wet rub fastness ratings, inks 3 and 4 emerge as the overall favorites. These inks deliver good color depth and very good richness ratings and can be used to create the denim look.

[0031] Example 2

[0032] The textile printer was loaded with ink 4 (CMYK) and the color reproduction was calibrated using the "Texprint" software program (Ergosoft) to ensure accurate color reproduction for the specific printing environment (print resolution, substrate, pretreatment, ink, fixing). It was then used to create the denim look. The color calibration performed ensures accurate color reproduction of the print template for the specified printing parameters and environment. Color-calibrated jeans designs (i.e., jeans designs captured with a color-calibrated camera or scanner) and designs provided by jeans manufacturers were used as the print motif. These could then be transferred to the textile with high color fidelity and true-to-life photographic reproduction. Printing was performed on the dGen Artrix at a resolution of 720 dpi x 720 dpi, followed by fixing at 160°C for 3 minutes.Figures 1 and 2 clearly show that the denim look is reproduced very well. Visually, there is no difference to real denim fabric. The printed samples achieved dry and wet rub fastness ratings of better than 4-5 and show no hardening of the touch, meaning the printed samples have a soft feel.

[0033] Example 3

[0034] If inks (T5) with a low fastness rating or those with weak color depth are used in the printing process, the color reproduction and fastness rating can be improved by pretreating the fabric to be printed. Pretreatment formulations based on cationic polymers, binders, thickeners, adhesion promoters, and crosslinkers can be used. Various pretreatments are listed below, along with an illustration of the fastness ratings that can be achieved through fabric pretreatment. For this purpose, the fabric to be printed is treated with an impregnating solution at a fabric speed of 2 m / min. The fabric (Denim2, basis weight 205 g / m²) is then treated with an impregnating solution. 2 The excess impregnating solution was removed at a squeeze-off pressure of 1 bar (70% degree of squeeze-off). The impregnated goods were then dried at 100°C for 2 minutes in a Benz dryer.

[0035] The following aqueous impregnation solutions or pretreatment solutions were used:

[0036] VB1: 50 g / l of a cationic polymer based on modified cyanoguanidine as a pretreatment chemical

[0037] VB2: 25 g / l of a cationic polymer based on modified cyanoguanidine as pretreatment chemical; 65 g / l of a mixture of emulsifiers and emulsifying components as pretreatment chemical

[0038] 5 g / l of a crosslinker based on bis(trimethylsiloxy)methyl(propylhydroxy)silane as a pretreatment chemical

[0039] VB3: 50 g / l of a polyolefinic adhesion promoter as a pretreatment chemical

[0040] VB4: 100 g / l of a polyacrylate binder as a pretreatment chemical

[0041] VB5: 100 g / l of a cationic migration inhibitor as a pretreatment chemical

[0042]

[0043]

[0044] The measurement data clearly demonstrate the improvement in the rub resistance of the resulting printed material. Furthermore, pretreatment can lead to a considerable increase in color depth (saving ink when producing a specific shade and color depth). As this example shows, even pigment inks with low rub fastness can be raised to a level of fastness required for printing on denim through appropriate pretreatment. All inks and pretreatments presented are suitable for creating a denim look.

[0045] Example 4

[0046] The combination of pretreatment and preferred printing ink is demonstrated using the example of printing on denim fabric 2. The textile fabric is impregnated with the pretreatment described in Example 3 on the scarf, and after intermediate drying, printed with the preferred ink T4 and then thermally fixed.

[0047] The combination of pretreatment followed by printing with the particularly favored T4 ink also results in an increase in the level of color fastness. Furthermore, a significant increase in color depth is also noticeable with this ink. The presented combination of pretreatment and ink enables the production of a printed denim look with rub fastness ratings of 4-5 and better.

[0048]

[0049]

[0050] Example 5

[0051] As a further method for improving fastness, the post-treatment of the printed material with an acrylate binder on denim fabric 2 is presented. In this case, the acrylate binder is applied as an ink with a 7.5% solids content via an inkjet printer. The printing conditions were chosen to achieve an ink application of 20 g / m². 2This was achieved. Other application methods, such as spraying with a binder or application using a foulard, are also possible. After fixing at 160°C for 3 minutes, excellent rub fastness is obtained. The color and visual appearance of the prints are not affected by the post-treatment.

[0052]

[0053] Example 6

[0054] To improve the rub resistance of pigment prints, the inks can, of course, also be combined with pre- and post-treatment. For example, the prints pre-treated according to Example 3 were then post-treated and fixed with an acrylate binder, as described in Example 5. As the results show, the combination of pre- and post-treatment can achieve a considerable improvement in rub fastness compared to prints without pre- / post-treatment.

[0055]

[0056] The results show that inkjet printing on denim using selected pigment inks containing binders can already achieve a very high level of colorfastness. With appropriate pre- or post-treatment, the rub fastness can be increased considerably. This is especially true for the combination of pre- and post-treatment. Using a color-calibrated inkjet printer, true-to-life color prints with a denim look can be achieved.

Claims

German Institutes for Textile and Fiber Research Denkendorf 73770 Denkendorf Patent claims 1. Textile surface element with a denim structure, characterized in that the denim structure comprehensively forms a color scheme and appearance of denim fabric in the form of a digital pigment print.

2. Textile surface element according to claim 1, characterized in that the pigment print has a color-calibrated digital coloring.

3. Textile surface element according to one of claims 1 or 2, characterized in that the pigment print consists of eco-certified inks and contains raw materials from sustainable cultivation.

4. Textile surface element according to one of claims 1 to 3, characterized in that the denim structure has stonewashed effects and laser bleaching effects.

5. Textile surface element according to one of claims 1 to 4, characterized in that it is a woven fabric, in particular a mixed fabric or a cellulose-based fabric.

6. Textile surface element according to one of claims 1 to 5, characterized in that only its front side has a pigment print, and that its back side is unprinted as a marking means, and / or that the pigment print contains a digital image or a scan of jeans.

7. Method for producing a denim structure on a textile surface element, characterized in that the denim structure, comprising the coloring and appearance of a denim product, is produced by a digital pigment printing process.

8. Method according to claim 7, characterized in that the digital pigment printing is produced with an eco-certified ink, and / or that the denim structure is produced by a color-calibrated coloring on the textile surface element.

9. Method according to one of claims 7 or 8, characterized in that binder-containing color pigment inks are used which lead to high rub and wash fastness without re-washing of the textile surface element.

10. Method according to one of claims 7 to 9, characterized in that the ink of the pigment printing is fixed by means of hot air, infrared or near-infrared radiation or a calender by contact heat transfer or by means of UV light or electron beams.

11. Method according to one of claims 7 to 10, characterized in that an ink with organic or inorganic color pigments is used for the pigment printing process.

12. Method according to one of claims 10 or 11, characterized in that the printed and fixed textile surface elements are not washed afterwards.

13. A method according to any one of claims 7 to 12, characterized in that the textile surface element is provided with a pretreatment which contributes to improving the contour quality and the fastness of the pigment print.

14. A method according to claim 13, characterized in that the textile surface element is pretreated by means of a corona treatment, or that a pretreatment chemistry consisting of binders or adhesion promoters and / or cationic polymers and polyelectrolytes or crosslinking chemicals and / or mixtures thereof in application concentrations of up to 10% as well as softening agents is used.

15. Method according to one of claims 13 or 14, characterized in that the textile surface element is provided with a post-treatment consisting of binders or polymers and / or crosslinking chemicals which contribute to improving the fastness of the textile surface elements, wherein in particular the post-treatment is applied together with the pre-treatment to further improve the fastness of the textile surface element.

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