Digital inkjet printing emerges in response to market requirements, is a typical application of high and new technology in printing production, and is a new printing technology developed in recent years at home and abroad. The article focuses on the post-processing process of the cashmere digital printing machine, and puts forward improvements in the post-processing steaming and water washing process, which in turn improves the performance of the cashmere digital printing fabrics in color, permeation and other aspects.
Digital inkjet printing is a new printing technology that appeared internationally in the 1990s. It is another brand-new printing method after gravure printing, flat screen printing, roller printing, rotary screen printing, and transfer printing. A major breakthrough in printing technology. With the continuous development of the economy, China has become the world's largest wool textile production country. Especially with the rapid development of the domestic economy, the boom of the high-end fashion industry has brought great opportunities for cashmere knitted fabric printing.
1 Overview of digital inkjet printing
Due to serious pollution, long production cycle, complicated process and large equipment investment, the traditional printing and dyeing industry is increasingly unable to meet the current consumer requirements for personalization, high-end textile and apparel fabrics, and health, comfort and environmental protection. In this case Digital printing and dyeing technology came into being. It has the characteristics of low energy consumption, no waste, high precision, unlimited colors, fast response, wide application, etc., so it can adapt to the market demand of personalization, small batch and fast response. Its appearance is another textile technology revolution after gravure printing and screen printing. It uses special machines (digital inkjet printing machines) to directly spray dyes on textile fabrics to quickly form high-precision color patterns, and people You can design ideas according to your own wishes, change the combination of direct printing, and are currently developing rapidly in the direction of industrialization.
Digital printing is a high-tech that integrates machinery, electronics, and information processing equipment. It is to input images processed by digital technology (scanners, digital cameras, etc.) to a computer, edited and processed by a computer printing color separation drawing system, and then The inkjet printing system is controlled by special software, that is, the RIP software is used to control the micro piezoelectric inkjet nozzle through the jet printing system to directly spray ink (special dyeing liquids such as active, dispersing, and acidic) onto various fabrics for printing. After processing, textiles with high-precision patterns are obtained. [next]
2 The advantages and problems of digital inkjet printing on cashmere fabrics
After several months of enterprise research, the following analysis of the advantages and problems of digital printing of cashmere fabrics was made.
2.1 Advantages of digital inkjet printing on cashmere fabrics
a) The printing process is simple. Eliminate the complicated pattern making and color matching process of traditional printing.
b) High printing quality. Photos can be used for printing.
c) The computer-controlled proofing process will be automatically memorized. Consistency is guaranteed, which saves time and improves efficiency.
d) Strong production flexibility. The printing samples can be made immediately from the limited basic colors, and continuous, single-frame, positioning printing can be performed.
e) The quantity of spray printing is flexible, which can meet the needs of personalized and quantitative production, small batch and fast response.
f) Conducive to environmental protection. The production process waste water, energy consumption and waste material discharge are very few. And the noise of inkjet printing is low.
2.2 Problems in digital inkjet printing of cashmere fabrics
The advantages of digital inkjet printing are obvious, but at the same time there are high costs, sizing problems, color difference problems of cashmere fabrics after dyeing, ink clogging nozzles, and leakage points. The problem of color difference after dyeing can be improved by post-treatment after dyeing.
2.2.1 Color difference
Before printing cashmere fabrics, because the pictures are photographed, copied, scanned, analyzed, and color-matched by digital cameras, copiers, scanners, computers, and other equipment, there is a problem of color difference caused by mechanical equipment. There is also a problem of color difference in the application of supporting software.
2.2.2 Leakage problem
The dye for the digital printing of cashmere fabric is very important, that is, the ink in the digital printer. If the ejection performance of ink is defective, some problems may occur during inkjet printing. For example, there is usually a phenomenon of missing dots, which refers to spraying the solid components (other colors) on the mouth of the ink nozzle on the fabric where it should not be colored due to clogging of the ink nozzle during printing. The color of the leak point is often black. Because the fabric has been sizing before, it contains a fixing agent, so the general cleaning and other treatment methods cannot be cleaned, which has a serious impact on the appearance of the fabric. At present, when printing small samples in the factory, the white paper is usually placed on the reel and tested on the white paper. After the sample, the colorless areas in the small sample are covered with white paper to prevent the influence of the leakage point on the small sample .
2.2.3 Sizing problem
Sizing is a very important step in the pre-treatment of cashmere digital printing. The selection of sizing has become an extensive research content. The sieving method is usually used for sizing. Pay attention to the fluff on the surface of the cashmere when squeezing the pulp, and ask it to stick to the surface, otherwise there will be problems such as staining and dew point when printing reactive ink.
2.2.4 Cost issues
The cost of each accessory is relatively high. For example, the dye ink used for cashmere products is the following 8 colors: black, cyan, magenta, yellow, gray, light red, light cyan, blue, the price is about 100 yuan / kg; the nozzle is 2000 About RMB / piece, the cost is quite high, and there are problems such as high actual cost when it is used to make a piece of cloth. [next]
3 Process optimization analysis of digital printing of cashmere fabrics
The process of inkjet printing depends on the ink used. The cashmere digital printing machine mostly uses reactive ink. The following is its technological process: fabric pretreatment (sizing) → pre-press drying → inkjet printing → post-press drying → steaming → washing → drying.
3.1 Optimization of pretreatment process
Before digital printing, the fabric should be sizing. The purpose of this is to prevent the penetration of the dyeing liquid during printing and ensure the dyeing and fixing of the dye.
3.1.1 The ratio of printing paste
The quality of the paste in the pre-processing of cashmere digital printing directly affects the effect of printing and dyeing, and the proportion of the components of the paste and their respective functions are also crucial to the paste. At present, the inks of digital printing machines are mostly reactive dyes. Reactive dye inkjet printing fabric pretreatment working fluid is mainly composed of alkali, urea, thickener, anti-reducing agent and defoaming agent. Commonly used alkaline agents include sodium carbonate and sodium bicarbonate. The main function of urea in the pretreatment liquid is to fully expand the fiber during the fixing process, and to create conditions for the dyeing of the reactive dye and the reaction with the fiber. Urea is also a good co-solvent for reactive dyes and an excellent hygroscopic agent, which can improve the fixing rate of reactive dyes. The main function of the thickener is to prevent the ink sprayed on the fabric from seeping during steaming and other processes, which affects the fineness of the printed pattern. Sodium alginate is an excellent thickener for reactive dye inkjet printing. Each glucose residue in the molecule has a carboxyl group. These carboxyl groups ionize to form anions, which are mutually exclusive with the anions in the reactive dye molecule, avoiding The reactive dye reacts with the hydroxyl group in the ring to improve the fixing rate of the reactive dye. The function of the defoaming agent is to eliminate the air bubbles generated during the preparation and padding of the pretreatment working fluid, and to prevent blisters and inkjet printing defects after the pretreatment of the fabric. When preparing the pretreatment working fluid, first dissolve the thickener in deionized water to make the original paste, and other components must also be dissolved in deionized water first, and then make up the solution in proportion. The following is the slurry formula commonly used in cashmere factories:
Sodium alginate 1% ~ 2%
DGT1%
Ammonium sulfate 1.5%
Yuanmingfen 5%
Glycerin 5%
Urea 10%
Water X
100% total
3.1.2 Optimization of sizing method
A simple and easy screen pulping method can be used. 80 mesh screen can be used to scrape the sizing on the manual platform, generally according to the different viscosity of different prescriptions, it is appropriate to scrape 4 to 6 knives, with an opaque bottom as the degree; it can also use a motorized flat screen or a round screen (both 60 ~ 80 mesh, low mesh) Adjust the pressure of the scraper or magnetic rod for sizing, which should be opaque. It is required that the cashmere on the surface of the cashmere be attached to the surface to avoid the problem of dot drift when printing reactive ink. [next]
3.2 Post-treatment process optimization
3.2.1 Significance of post-processing
After the sizing pretreatment, the cashmere fabric is tiled on a digital printing machine, and the cashmere fabric is printed directly according to the computer pattern drawn in advance. The printed fabric should be dried in time to prevent the dye and ink from matching, and on the other hand, it should be steamed and washed in time to prevent the dye from being reduced or oxidized to affect the color after being left for a long time.
3.2.2 Post-processing improvements
a) Improvement of drying
After manual sizing or mechanical equipment sizing, they should be dried in time. Generally, drying in an oven at about 80 ℃ is appropriate. Avoid high temperature drying to avoid damage to wool or cashmere. In order to save costs in the factory, it can also be placed in the summer to allow it to dry naturally. It needs to be placed in a dry place on the shaded surface, but it must not be placed in direct sunlight. After drying, the film is arranged in time to facilitate the process of digital printing in time. Cashmere fabrics should also be dried in time after printing to prevent the fabric from coloring because the dye is not dry. When drying the fabric, different wind and temperature files can be selected according to the different fabrics and door widths. Especially thick fabrics that have not been dried through the use of the largest wind and temperature files should be rolled with a paper pad, and finally placed in a large drying room until the ink is completely dry to ensure the stability of the dye color.
b) Improvement of steaming
Steaming is to promote the diffusion of dye from the surface of the fiber to the inner layer of the fiber under a certain humidity and temperature, so that the dye is fixed to the fabric. The printed fabric must be steamed. The purpose of steaming is to make the dye molecules chemically react with the fiber under certain heat and humidity conditions, so that the dye is fixed on the fiber. After the cashmere fabric is printed, the reactive dyes are only attached to the fabric film, and only after high-temperature steaming can it be truly fixed on the fabric. At present, there are two types of steaming methods: cylinder steamer batch steaming and continuous steamer steaming. At present, the cylinder steamers used by many cashmere digital printing factories have problems such as long air pressure rise time, uneven steam distribution, and inconsistent upper and lower temperatures. This can easily cause uneven hair color. After improving the use of continuous steaming equipment, the steam distribution is uniform, the humidity can be controlled and the up and down is consistent. After continuous steaming treatment, the wool fabric has uniform color development, bright color, and stable quality. Before steaming, the fabric is covered with white paper to prevent water droplets from affecting the color [7]. In addition, in terms of steaming time, due to the use of improved continuous steaming equipment to increase the pressure faster, the steaming time was reduced from the original 40min to about 30min. Thereby reducing the damage of cashmere. After the steaming is completed, the printed cashmere products are placed for a period of time to ensure that the dye fully enters the interior of the cashmere and improve the color yield.
c) Improvement of water washing process
The purpose of water washing is to remove the slurry and floating color on the steamed fabric. The washing process of cashmere digital printing is: steaming-washing 3 times in cold water-soaping at room temperature (neutral white ground antifouling agent or household washing clean 3g / L)-washing in cold water-soft color fixing (acid dye fixing agent 5g / L, room temperature treatment for 10min) —drying (100 ℃), no anti-staining agent is added during the washing process, which will cause the dark and light colors to stick to each other. In addition, attention should be paid to optimizing the washing process and selecting appropriate anti-staining and anti-wrinkle additives to avoid the shedding of dyes on dark patterns, causing stains and wrinkle marks. After leaving the steamed cashmere fabric for a period of time, wash it three times in cold water, add 1.5g / L anti-sticking agent, then soap in water at 60 ℃ for 15min and add 0.5g / L soap boiling agent, 1.5g / L Color-sticking agent) Finally wash twice in cold water. Small batches of fabrics can also be washed on a rope machine. When printing thick wool fabrics, a 1% penetration agent JFC is added. The penetrating agent JFC plays the role of wetting, penetrating, emulsifying, dispersing and penetrating, and also has the ability to wash impurities in the wool, so that the washed wool has a soft feel. Large batches can be washed on the rope machine, but care should be taken to optimize the washing process and select the appropriate anti-staining and anti-wrinkle additives to avoid the shedding of dyes on dark patterns, causing stains and wrinkle marks. disease.
When printing thick wool fabrics, adding penetrant JFC1% is suitable for single-sided sizing. A certain amount of penetrant can reduce the yellowing and strong damage of the fabric. Pay attention to temperature control and time control during drying, washing and re-drying.
4 Conclusion
Digital inkjet printing technology is a new printing method that directly prints on cashmere fabrics, which improves the accuracy of cashmere printing, realizes small batch, multi-variety, and multi-color printing, and solves the large area of ​​traditional cashmere printing. , Serious pollution and other problems, so it has broad development prospects. At present, digital printing technology still has the problems of high production cost and slow speed. In addition, the pre-press technology and post-press processing process have a great influence on the final quality of the product. In view of these factors, the composition of the paste is improved. In addition to the use of advanced equipment in post-processing, the evaporation temperature and time are reasonably controlled , Add targeted additives in water washing, so that the performance of cashmere digital printing and dyeing products can be improved. At the same time, we must combine the actual production to optimize the ink of the digital inkjet printing of cashmere fabrics, the technical requirements during printing and the technological conditions of post-printing processing.
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