Section 7 Textile Printing - 2

(3) Discharging and printing is also called "carving and printing", which refers to the use of a discharge agent to print on colored fabrics to destroy some of the pigments that have been dyed, and thus obtain a variety of printing methods on patterns and patterns. Dispensing agent is a chemical that decolorizes the stained background. Such as: hanging white block, stannous chloride and so on. This method can be divided into white (pull white) and pattern is colored (pull) two. The latter dyeing method makes the fabric pattern fine, but the process is complicated and the cost is high.
Because of the different fabrics. The chemical reducing agent (pulling agent) used is different. In general, rayon fabrics are usually used for hanging white blocks (carved white blocks), white blocks or crystalline powders. The scientific name "formaldehyde sodium bisulfite" (NaHSO2 · CH2O · 2H2O). Silk fabrics usually use tin chloride (SnCl2), while polyester fabrics use "Decolin" as discharge agent. This requires the screening of dyes, such as the use of Acid Red G, which is not resistant to stannous chloride and therefore produces achromatic effects. While Chai Linyan 6B is resistant to stannous chloride, the adhesive is usually an acrylate.
Discharge printing can be used for horse cloth, but also for finished clothing. Discharge printing for finished garments, also called printing, ie color discharge.
The printing of garments generally uses screen printing methods to print a water-based printing paste containing a special discharge agent onto clothing. The truth of this printing is the same as other water-based printing pastes printed on colored clothing. The next step is drying at a certain temperature. The discharge agent is activated by heat to selectively remove the dye from the garment and neutralize it so that it can express the color of the printed water-based printing paste. However, it is still a water-based system and must be completely dry (ie, the water content must be thoroughly evaporated), and the effect of discharge printing should be checked by cleaning. If the pattern fades, the drying time needs to be increased. The color rendering principle is that the discharge agent discolors the original dye on the fabric, and the color of the printing paste penetrates into the fabric fibers, giving it a new color. Color discharge has the advantages of high production efficiency, good product feel, water-based color paste safety, and easy handling.
In general, the drying temperature for drawing the dyed paste is 300-350°F (147-175°C), 2-3 miin and sufficient airflow to remove moisture during drying of the paste. When the colorant reaches 250°F (about 120°C), the discharge process starts. The discharge process must be carried out while the paste is still wet. For best results, print your clothing immediately after printing. If the color paste is allowed to dry before heating, the discharge process does not fully work. Once the discharge process is complete, the water must be completely removed to solidify the water-based paste.
One of the best features for printing with draw-dyed pulp is the ability to print multicolor patterns on dark fabrics without the need for background color or flash drying. This saves preparation time and gives printers a cooler environment, saves on screens, returns and energy costs.
Some common problems and solutions in the production of discharge dyeing process are listed in 4-23.
Table 4-23 Discharge Printing Failures and Troubleshooting
Dye is not fully discharged. Increases drying time. Too much temperature. Too much dye. Correct amount of dyeing agent. Reconstituted colorant. Dyeing and dyeing. Pigment colorant is incompatible with the dye. Use recommended colorant. Dyeing and dyeing fabrics can be tested whether the fabric can be discharged to increase the urea in the color paste, reduce the drying time, the temperature paste is not properly deposited, or infiltrate into the fabric to reduce the color paste viscosity; increase the speed of the printing operation; before printing Immersion; returning and silk screen water in the color paste too quickly reduce drying time, temperature; increase urea content Over-dyeing of clothing fabrics (according to manufacturer) Moisture-free evaporation increases drying time and temperature Insufficient drying of colorants in pastes. Increases drying time and temperature. Reconstitute colorants. Add colorants. Infiltration of water into the fabric reduces the viscosity of the paste; increases the squeegee speed; increases the hardness of the squeegee Improper emulsifier in poor color paste; poor screen-proven double-dried emulsion; review screening production techniques; proper ink removal; proper application; dry emulsion before exposure; avoid underexposure; screen/template to match correct Full or partial blockage of screen printing paste Improper cleaning of screen plate; Immersion before printing; Thorough mixing of color paste, mixing with drill, mixing knife or homogenizer Inadequate mixing techniques using mixing knives or homogenizers;
In the addition of dye discharge agent to the base material plus color material (4) screen printing material Flower Burnt series uses two kinds of fiber-blend fabrics with different acid resistance, after the acid burn-in pulp printing and chemical processing, will not be acid-resistant natural Part of the fiber is rotten, exposing part of chemical fiber that is acid-resistant, forming a transparent and crystal pattern. Its special style makes burnt-out products have a high-grade and splendid feel. Burnt-out products are not only beautiful in appearance, but also have excellent internal quality. They are wear-resistant, high-strength, good-cleaning, quick-drying, and non-ironing. They are welcomed by domestic and foreign markets. The research and application of burnt-out technology has prevailed in the textile printing and dyeing industry in recent years.
1. Burnt-out applications Burnt-out fabrics are used primarily in polyester/cotton-cored fabrics, that is, polyester filaments are used as the center, and the outer surface is processed by the reclaimed cotton fiber to form the core-spun yarn, and then the textile is processed into the core. cloth. Polyester filaments have good acid resistance, high transparency, and burnt-out parts are crystal clear and transparent. They are beautifully decorated as interior decorations and are high-grade products in burnt-out products. In order to reduce the cost, polyester/cotton blended fabrics were later developed for burn-in. Because the polyester fibers are short fibers and the fibers are blended at the burn-out site, the burn-in sites are poorly translucent and translucent, making them suitable for clothing. . In recent years, trials have been made on sofa backrests and handrails, tea towels, quilts, bedspreads, curtains, and tablecloths. These products have the advantages of high strength, good resistance to major causes, excellent color fastness, no ironing, no wrinkle, good washing, quick drying and so on. Therefore, not only the appearance can be comparable to that of polyester/cotton core fabrics. Physical indicators also reflect the inherent quality. Great prospects for development.
In terms of production methods, the use of screen printing is more suitable for multi-pattern changes. In addition to specialized equipment in individual areas in the production equipment, most small and medium-sized enterprises use manual platens to help brush.
2. The quality of burned flowers requires the quality of burnt-out products, which is reflected in the transparency of the burned-out parts, the clear smoothness of the outline of the flower pattern, no seepage, no more flowers, a lot of flowers, uninterrupted lines, and beautiful flower patterns. The edition is accurate and white, color and various physical properties and other aspects. To improve product quality, you need to pay attention to the following issues:
1 to avoid too small points, lines, surface design, in order to prevent burnt flowers lost, pattern contours and other defects.
2 For the design of rotten and printed patterns, appropriate gaps should be left in the connection of burnt and printed parts to prevent the embossing of the embossed and printing pastes during rotting, and to destroy the rotten printing effect.
3 color should not be too much to avoid the complexity of the version of the version of the difficulties.
4 The combination of rotten and printed patterns can be designed to meet the requirements of the one-step rotting process and reduce the complexity of the production process.
3. Painted version of the draft to make a good version of burnt-out, improve the quality of burn-out, design drawing script, should pay attention to the following questions:
1 Burnt painting should take into account the good effect of rotting, and there must be appropriate gaps at the rotting lines to prevent chemical changes caused by the contact of different slurries and destroy the integrity of the pattern;
2 fine lines, horizontal and vertical, and precise flowers;
3 Films are kept clean to avoid dirt;
4 It is accurate and does not spend much;
5 depicts a smooth, well-proportioned line with no lines, so that after spent burnt flowers, the silhouette is smooth and beautiful.
4. Types of Burnt Grey Fabrics There are mainly three types of burnt grey fabrics currently available on the market:
1 polyester/cotton core cloth: The burnt part has good transparency and is suitable for producing high-grade burnt-out products;
2 Polyester/cotton blended fabric: The burnt-out part has poor transparency and is suitable for producing ordinary burnt-out products;
3 C/cotton core cloth: The burnt-out site has good transparency, but the polypropylene has poor dyeability and poor hand feel, and is suitable for producing general products.
5. The selection and amount of burnt-out agent Burnt-out agent is an important component in the chemical pulp and is used to rot the part of the natural fiber. Hydrochloric acid has the ability to absorb moisture in the air, which easily causes osmotic phenomena in burnt-out sites, affecting the clarity of the outline of the flower pattern. Although it can hydrolyze cotton fibers, it should not be used. Sulfuric acid is generally used to form burn-in paste, which is beneficial to the improvement of burn-out quality.
The amount of acid is one of the main factors that determine the quality of burn-out. With insufficient acid, cotton fiber cannot be rotted. Excessive acidity results in increased waste and corrosion. It is unfavorable for the maintenance of equipment and screens. When burnt-out, in particular, the acid resistance of the equipment should be taken into consideration to avoid the corrosion damage of the scraper metal parts, conveyor belts and drying drums. However, the amount of acid used in burnt fabrics is different from that of the gray fabric yarns and tissues, the ratio of cotton fibers to chemical fibers, and the density of warp and weft. In the different production methods of fingerprint and machine printing, different factors such as the pressure of the squeegee, the number of times of squeegee printing and the penetration time are different, which also determine the difference in the amount of acid used. After tests, under the above-mentioned different factors, when the concentration of sulfuric acid is 98%, the acid amount per litre of burnout slurry is in the range of about 20-60 mL.
6. Paste dosage and selection The purpose of adding the paste in the burn-out paste is to hold the sphagnum relatively fixed on the flower-patterned part to prevent the paste from osmotic and lead to the destruction of the flower-pattern, ensuring the clear and smooth outline of the flower pattern. degree. The slurry is too thin to achieve the purpose of fixing the slurry in the flower position; the slurry is too thick and the permeation effect is poor, affecting the integrity of the pattern, and the operation of the squeegee is difficult; the operation is laborious and the cost is high, so the amount of paste is Choice is also one of the important conditions.
Different pastes have different amounts in the burnout paste. White dextrin with pulp burnout flower pattern outline clear, burnt part of the high whiteness, bright color, but the viscosity is high, the operation is relatively inconvenient, lack of supply. Long Jiao paste is simple, can be used immediately, easy to produce osmotic phenomena after burnout, but the pattern contour is not as good as white paste d