At present, in the printing field, flat screen printing and rotary screen printing still occupy a dominant position, and are widely used in printing processes such as reactive dyes, acid dyes, and paints; thermal transfer printing, as an effective auxiliary method, has been maturely applied to polyester fabrics It is known for its four-color, moiré, and gradient colors; at the same time, the rise of cold transfer printing and digital inkjet printing can not be ignored, which makes cotton and other cellulose fiber fabrics show fine moiré and gradient effects become possible.
1 Cold transfer printing inkjet sample production process
First, briefly introduce the principle and process of cold transfer printing. Use reactive dyes with good solubility, fast fixation rate and good hydrolytic stability to print images on paper that has been coated with a release agent, and then dry and roll. Then the cotton fabric (softener, smoothing agent and other water-repellent additives can not be added after refining) dipped in lye, and then aligned with the transfer printing paper, through a pair of even rollers, the lye on the fabric makes the transfer printing paper The color paste dissolves. Under certain pressure, since the affinity of the dye to the fabric is greater than that of the transfer paper, the dye transfers to the fabric and enters the interstices of the fabric. Finally, separate the paper and cloth and roll them separately. When the damp cotton cloth is rolled, use a plastic film as a spacer to cover the image and roll it together to prevent air drying and staining. Finally, during the stacking process, the dye gradually completes the process of adsorption, diffusion, and fixation. After stacking, the fabrics are washed with water to remove trace amounts of slurry and hydrolyzed dyes, and the fabrics are washed to neutrality.
At present, digital inkjet printing has been widely adopted in the proofing production of printing factories, and the proofing speed has been greatly improved. Cold transfer printing also uses digital inkjet printers to produce samples, but in order to be consistent with the mass production of cold transfer printing, the production of cold transfer printing inkjet samples does not use direct injection, and chooses to spray the pattern on the printing paper first And then transfer to the fabric. At the same time, in order to achieve the purpose of rapid sample delivery, the steaming fixation method is adopted. The specific process is as follows:
Inkjet printing paper → transfer fabric → drying → steaming → washing after printing → final product shaping
2 Common problems of cold transfer printing inkjet samples
2.1 Flower type infiltration problem
Pattern bleeding refers to the original clear and smooth lines or patterns on the printing paper, which become blurred after being transferred to the fabric, especially the jagged edges of the lines. The bleeding of the pattern mostly occurs when the pattern of fine lines or the fabric with high liquid rate. For example, in production, we have encountered a group of 60S double-stranded mercerized cotton single jersey fabric. The pattern produced is a square lattice pattern. During the proofing process, there are obvious problems of infiltration. The main reason for the infiltration of lines It is because the liquid rate of the fabric is too high. During transfer, the moisture adsorbed on the fabric is squeezed out of the fabric to dissolve the pattern on the transfer paper. At the moment it leaves the transfer roller, the excess moisture is sucked back into the fabric along the capillary of the fabric. If the liquid-carrying rate of the fabric is too high, too much moisture will be squeezed out when passing through the transfer roller, which will cause the lines to become thicker, and in severe cases, bleeding occurs. Generally speaking, the liquid-carrying rate of light and thin fabrics is relatively high, and the liquid-carrying rate of heavy fabrics is relatively low. Therefore, the thinner the fabric, the more attention should be paid to the problem of pattern bleeding, especially the regular lines or geometric patterns. When this abnormality occurs, we first judge the problem of the fabric's wool effect. Too good wool effect leads to high liquid entrainment and pattern bleeding. However, the wool effect test of the fabric was only 5.3cm/30min, which was far below our normal requirement. Therefore, the fabric was re-pretreated later, and the liquid rate of the left, middle, and right fabric passing through the press roller was checked. Through the test and analysis, we believe that it is indeed the pattern bleeding caused by the fabric with too high liquid rate, so we have made some improvements to this problem.
After the fabric is causticized and before entering the carpet belt, that is, the needle chain part, install an infrared heating device, and add fans on the left and right sides to promote air flow. The purpose is to reduce the liquid rate of the fabric; dry immediately after transfer, preferably Install a supporting dryer after the transfer machine, and add an anti-migration agent to the pretreatment alkali agent to prevent dye migration during the drying process.
Add an appropriate amount of paste (about 10%) to the lye. Because the paste is a polymer material, it has a strong ability to hold water molecules and reduce the amount of free water on the fiber; it can also block some capillary channels , Reduce the capillary effect of the fabric, thereby effectively preventing the phenomenon of bleeding. However, special attention should be paid during use: ①The alkali resistance of the paste, because the alkali agent used in cold transfer is a strong alkali, and the paste generally has alkali resistance problems. If the selected paste is poor in alkali resistance, then The anti-seepage effect is certainly not ideal; ②The alkali resistance stability of the paste, some pastes just add alkali agent, alkali resistance is acceptable, but as time goes by, the viscosity and water holding capacity will decrease rapidly ③The uniformity of the paste in the lye is generally to be stirred evenly through strong stirring. If the mixing is not uniform, flaky or spot-like infiltration may occur.
2.2 The influence of drying moisture content on printing dyes
The two most important factors in the steaming process of printed fabrics are humidity and temperature. For the understanding of humidity, many people are limited to the humidity of the steam during the steaming process, and ignore the humidity problem of the fabric itself after drying, which causes great troubles in production.
Usually the dry fabric enters the steam box, there will be the following four processes, namely, preheating and heating → overheating → cooling → equilibrium with the steam temperature. The first stage of preheating and heating is through the steam heat exchange with the steam, the steam becomes condensed water, which releases heat, so that the surface of the fiber rises rapidly. When the steam temperature (100°C) is reached, the water molecules and cellulose molecules chemically Adsorption (hydrogen bond) exothermic heat will quickly overheat the fabric, which reduces fiber swelling and dye dissolution, and accelerates the hydrolysis of dyes, which is extremely unfavorable for dyeing and fixing of reactive dyes. Therefore, it is best to contain a certain amount of humidity before the fabric enters the steam box, which can effectively shorten the time of the overheating stage. Because the water absorption of rayon is far better than that of cotton fiber, the humidity requirements are higher during the steaming process. The humidity of the steam may not be able to meet the regain of rayon, let alone fix the color? Therefore, during the rayon drying process, do not dry it thoroughly. The humidity should be controlled at 15-25%. It is better to have an on-line measurement of the fabric humidity, which can be precisely controlled to slightly exceed the conventional moisture regain of rayon. Also pay attention to the uniformity of left, middle, right and front, middle and back of the cloth during drying. This will affect the left, middle and right color difference and the color difference between the head and tail.
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