At present, the proportion of printed products in the entire printing and dyeing products is about 25%, and new printing techniques and new equipment continue to emerge. Special printing is a bit of plastic (drop), heat transfer (thermal transfer), hot stamping, hot silver, gold and silver powder, luminous, three-dimensional printing, sticky beads, etc., printing equipment used are screen printing machine, transfer printing machine , electrostatic flocking printing machine, digital jet printing machine, pressing machine and so on. Pressing machines are developed with the transfer printing process and the development of the T-shirt industry.
With people-oriented, sustainable development concept deeply rooted in people's minds, consumer demand for ecological textiles is also increasing, requiring printing and dyeing enterprises to adopt environmentally friendly reactive dye printing in the production process. The active dye has a bright color, is easy to use, has a complete chromatogram, excellent fastness, soft hand feeling, and is mostly steam-fixed when it is used for color fixing. This will limit the application of this technology to companies that lack steaming equipment. Therefore, it is of great significance to study and improve the reactive dye printing method and printing process. Taking T-shirt printing as an example, a new fixing process for reactive dyes is practiced using the hot press method.
Process flow
Pattern Design → Photographic Platemaking / Modulation Pulp → Printing → Drying → Pressure Fixing → Cold Wash → Soaping → Hot Wash → Cold Wash → Drying → Finishing After Ironing.
Equipment requirements
Manual presses are currently used for heat transfer printing and heat transfer, and are widely used in T-shirts, bags, handbags, shoes, hats, socks, gloves and other designs. Pressing machine size is 40 × 60cm, the maximum temperature can reach 399 °C, the longest adjustable time to 60s. Since the maximum adjustable time of the device is only 60 seconds, the dye must be quickly fixed in a short time.
Dye selection
Reactive dyes are reactive dyes. Types of dyes are X-type, ME-type, KN-type, and K-type. Currently, they are widely recognized both internationally and domestically. New types of reactive dyes have been continuously developed and applied to production. The color rate is greatly improved. Reactive dyes with complete chromatograms, strong applicability, good soaping fastness, good abrasion resistance, consistent with T-shirts during use, require frequent washing, and require good soaping fastness. As a reactive dye for printing, it should have high solubility, high fixing rate, low directness, good stability, good light fastness and washing fastness, good compatibility and reproducibility. In the experiment, the ME, KN and K reactive dyes with good stability were selected for the process experiment. Due to the high printing process requirements, dyes with high fixing rates should be selected.
Color paste composition
Reactive dye printing paste is usually composed of dye, anti-staining salt S, urea, sodium alginate paste, soda (or soda ash), and water, and is steam-fixed. Due to the use of hot fixing and short time, the use of alkali agents can be considered to increase the alkalinity, shorten the fixing time, and increase the fixation rate. For this purpose, the type of ME-type, KN-type reactive dye paste used in the experiment was selected as the soda ash, the K-type reactive dye paste was selected as soda ash and caustic soda, and the color paste consisted of dye, sodium alginate, soda ash (or caustic soda) and water.
The process recipe uses reactive dyes: 1% to 10%; sodium alginate paste (6%): 60%; soda ash: 2%; or caustic soda (36 Baume degrees): 4ml/100g.
Selection of process recipes and process conditions
Determination of pressing temperature
Using cotton twill weave fabrics, the active black KBR, reactive black KNB and reactive brilliant red M-3BE were selected. The comparison experiments conducted for 60 s respectively showed that with the increase of temperature, the fixing rate increased, and the color increased significantly; When the temperature is 190°C and above, the fabric starts to turn yellow. Therefore, it is recommended that the hot pressure be controlled at a maximum of 180°C.
Determination of pressing time
1) The active black KBR dye was selected, and caustic soda was used as the alkali agent at an experiment temperature of 180°C. It was proved that when the time was less than 40 s, the color was significantly deepened with the increase of the experiment, over 40 s, and the color was increased with time. Obviously lighter.
2) The active black KNB dye was selected, and soda ash was used as an alkali agent. The experiment was conducted at a temperature of 180°C. When the time was less than 40 seconds, the color increased significantly with the growth of the experiment, exceeding 40 seconds, with the increase of time. The shade of light is obviously reddish.
Alkaline agent selection
The active black KBR dye was used, the temperature was 180°C, and the time was 40s. The experiment showed that the alkali enhanced and the color deepened obviously. However, in the application of caustic soda, when the dye concentration is high, the pH of the colorant exceeds 11, making the color paste unstable and forming a gel. It is recommended to choose soda ash as the alkali agent.
experiment analysis
From the above comparison test, it can be seen that the pressing method plays a role in fixing the reactive dyes, and the fixation fastness is good, the white background is not stained, and the pattern is not attached to the surface of the fabric just like the paint, and the dye penetrates into the fabric. In the fiber, the touch feels good, washable, and wear-resistant. However, in the pressing process, attention should be paid to the control of temperature and time. As the temperature increases, the fixing rate increases, and the color deepens as the temperature increases, but the fabric starts to turn yellow after the temperature exceeds 180° C. This temperature is not suitable. The fixation rate increases with time, and the color also deepens. In the course of our experiments, we found that the dye press method requires fast fixing in a short time, and the maximum time is 40 seconds. This is a much shorter time and energy than steaming. The reactive dye press method has its advantages, of course, there are also deficiencies, reactive dyes on the dark base fabric coverage can not achieve the effect of color saturation. This method is only suitable for light-bottomed fabrics. If the fabric is dark, the color of the fabric is not obvious. The reactive dye press method has been proved to be feasible through experiments. It fills the new process of reactive dyes used in hand-made screens and cut pieces for manual screen printing.
Process effect analysis
The reactive dyestuff fixing method avoids the water stain caused by condensate dripping when the reactive dyestuff is steamed and fixed. The reactive dyestuff pressing and fixing method is simple and does not require large-scale machine equipment and only need to manually press the ironing machine. Its simple operation, high flexibility, short process, high fixation rate, bright color, no need to prevent the addition of salt and urea, reduces the consumption of dyeing agents and auxiliaries, reduces printing costs, and saves energy and water. At the same time, the reactive dyes seldom contain harmful aromatic amine structures in their structure, making them the preferred dyes for the production of eco-textiles for cellulosic fibers. The fabrics have good hand feeling, good wash fastness, good fastness to rubbing, and fabric printing. In the process, the tension is small, and the hot press fixing method is particularly suitable for the reactive dye printing process of small printing enterprises' garments such as T-shirts and cut piece printing products, and can also be applied to cellulose fiber fabrics using reactive dye hand-painted and fixed in color. .
With the improvement of people's consumption level, the booming development of small home textiles and T-shirts industry, the reactive dye fixation method due to the required equipment is simple, easy to operate, suitable for small batch and multi-variety production. Being able to meet the individualized pursuit of people will surely be widely used.
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