Prospects for Paste Technology in Textile Printing

Among the colorful textiles, printed fabrics no doubt occupy the most important position. According to estimates by Ciba, the daily production of printed fabrics amounts to more than 40 million meters, of which half are produced in Asia, and only 11% are produced in North America. More than 70% of the printed fabrics are cotton or polyester-cotton fabrics.

In the printed fabric, 65% of the paint, 15% of reactive dyes, 10% of disperse dyes, and 10% of acid and other dyes. Women's outerwear accounts for 40% of the printed fabrics, bedding accounts for 25%, and shirts, furniture and other products account for 35%. Most of these prints currently use the traditional screen printing process, including flat screen and rotary screen printing. Screen printing pastes generally consist of dyes (or pigments), auxiliaries and raw pastes. The function of the original printing paste is to make the color paste have a certain viscosity and fluidity, and it is made of a hydrophilic polymer paste. Paste plays a key role in the formulation of screen printing pastes, which controls the rheology of the printing paste and the penetration and migration of the print colors. In addition to dye properties, paste is the most important factor in determining the quality of printing. Currently the most used natural pastes include sodium alginate (usually used for reactive dyes and disperse dye printing), guar gum or other plant seed gums (usually used for disperse dye printing) and starch (for vat dye printing).

The advantage of the natural paste is that it is easy to clean after the printing is fixed, and a solid protective film is formed to prevent the printing color from sticking. The disadvantage is that the complete hydration takes a long time (8-24h), may react with the dye, and give a lower color amount. Synthetic pastes represented by acrylic acid (PAA) have pseudoplastic rheology, that is, shear thinning characteristics. Under the action of stress, the viscosity changes greatly, and after the stress is relieved, it can immediately return to the original viscosity. Therefore, the synthesis paste needs only 1% to 3% concentration to be effective, and the natural paste concentration needs to be 10% to reach the required viscosity of the color paste, and the synthesis paste has a high hydration speed, a clear print pattern, and a good permeability. Larger color, better color uniformity. However, the traditional PAA paste is sensitive to the electrolyte. The high color concentration of the coating will greatly reduce the viscosity of the color paste, and it is sometimes difficult to fix the color paste. Newly developed printing pastes, including a new generation of PAA pastes, synthetic and natural compound pastes, use invert emulsion technology to produce finer, more uniform pastes. These new pastes can improve the color, smoothness and permeability of printed fabrics.

In textile printing, the paste controls the fluidity of the paste and prevents the pigment from diffusing. The quality of printing such as sharpness, vividness, dye permeability and bleeding mainly depends on the paste properties. At present, in addition to paint printing, the main use of natural paste or modified natural paste, and the paint is usually printed with a kerosene emulsion. However, natural paste has some limitations, such as raw materials are not rich, poor performance stability, poor fluidity, and high cost (such as alginate). In addition, depending on the type of dyestuff used and the type of printing machine, different types of natural pastes should be selected for preliminary printing and adjustment, unlike synthetic pastes or compound pastes, matching paste products introduced by various dyeing and dyeing materials manufacturers can be selected. Due to the high color yield, low solid content, long storage time, easy handling, and pseudoplasticity of synthetic pastes, the global trend is to use synthetic pastes instead of natural pastes, especially for synthetic pastes for coating printing. Kerosene water emulsion pollution problem. Practical applications show that replacing synthetic alginates in reactive dye printing can reduce costs; in synthetic dye printing, the use of synthetic pastes, due to the low solids content helps the dye transfer from the paste to the fabric, so The amount of color increases. Synthetic paste raw materials are mainly ethylene maleic anhydride, acrylamide, acrylate and acrylic monomers. The monomer composition and its properties have a decisive influence on the paste properties, especially the viscosity and dry film-forming properties of the printing paste. Acrylic acid is used to bring the color paste to the desired viscosity. The addition of bases and acrylates gives the polymer some flexibility. Therefore, according to different uses, choose the monomer and its composition. The paste synthesis also requires the selection of an appropriate cross-linking agent and the addition of suitable surfactants. From an environmental point of view, although the natural paste is more easily degraded, the amount of natural paste is much larger than that of the synthetic paste. It will produce a certain amount of pollution. The main raw material of synthetic paste acrylic is a low-pollution chemical, and the polymerization degree of synthetic paste is not high, the amount is much smaller than the natural paste, therefore, the application of synthetic paste in printing does not increase the amount of pollution The paste has an inherent shear flow and can be used for printing to make the hair more brilliant.

The lines are finer, clearer, and the color patches are more uniform. However, general synthetic pastes cannot be used for the preparation of reactive dye pastes because they are extremely sensitive to ions in dyes and form white precipitates on fabrics after washing in printing. This affects the feel and appearance of the printed fabric. United States B. F. Goodrich's researchers used modified polyacrylic acids to make new synthetic pastes that are sensitive to ions and can be completely cleaned.

In addition, it can reduce the amount of urea in printing by half, which is beneficial to reduce the BOD in the wastewater and can quickly adjust the slurry without affecting the dye-fiber bond formation. Three new pastes were used in the test: Carbopol 249I (sodium-neutralized liquid), Carbopol 2491WC (dust-free powder) and Carbopol 2491 WCS (self-neutralizing and dust-free powder), and compared with sodium alginate, using 7 different activities. Dye printing. The results show that Carbopol pastes can achieve better color, brighter lines and softer print quality. BASF's new LutexalGPECO thickeners are used in paint printing to improve contour definition and printing reliability while reducing costs and reducing environmental pollution. Factory trial results show. This printing paste not only makes the printed lines clear, but also has good running performance and brighter and brighter colors. Good color fastness on natural fibres or on synthetic fibres reduces print penetration and thus saves colour paste. The paste has high electrolyte stability, small fluctuation in viscosity, improved print reproducibility, and increased lot color ratio. The paste is powder and can provide particulate products. These products emit smoke lower than liquid products. Therefore, the powdery and granular thickener is the future development direction. This new thickener printing product meets the European ecological standards such as Oko-Tex standard. 100 and so on.

The traditional printing process faces the challenge of the new requirements of high quality and low cost, which has led to the continuous improvement of screen printing technology. Although digital inkjet printing has made major breakthroughs in recent years. However, experts predict that it will take quite a long time to replace the traditional printing process with direct dyeing (such as disperse dyes on reactive dyes or terylene on cellulose fibers). Color concentration strong wet fastness CibaCRONP dye series introduced by Ciba can meet the user's new requirements for reactive dye cotton or viscose fiber printing.

CIBACRON BLACK P-SG and CIBACRON ORANGE P-4R improve the reproducibility of color as a basic color matching dye for brown, beige and olive. To improve the printing quality of fabrics, it is not sufficient to rely solely on dyes. For this purpose, Ciba developed a new generation of paste, ALCOPR1NTRT-BC, which can improve the fineness and color uniformity of prints, and has a good color tone and improved dyeing and dyeing. Sex. The same color depth can save 10%-15% of the dye. Ciba ALCOPRINTDT-CS paste and Ciba TERASIL disperse dyes into a printing paste can obtain high color printing.

The combination of ALCOPRINTP paste and Ciba UNISPERSE coating series makes the printing operation of paints easier and more flexible. ALCOPRINTPT. RV paste can provide extremely clear pattern outlines on all kinds of difficult-printing fabrics without having to use anti-penetrants because the original paste has low electrolyte sensitivity, so it can replace natural pastes for reactive dyes. The direction of future development of textile printing pastes is to gradually increase the amount of synthetic pastes, and each major dyeing and dyeing material manufacturer will develop synthetic pastes with various formulations and dosage forms that are used in conjunction with different dye series. Blending applications of synthetic pastes and natural pastes will also be gradually promoted. It can not only improve the quality of fabric printing, but also can significantly reduce the cost of printing.