In recent years, digital printing has developed rapidly and has a great potential to replace screen printing. What are the differences between these two printing processes, and how to understand and choose? The following is a detailed analysis and interpretation of the technical characteristics and development prospects of digital printing and screen printing.
Printing refers to the use of dyes or paints to form pictures and texts on the surface of the fabric. Since the development of printing technology, it has formed a pattern in which multiple printing processes such as screen printing, rotary screen printing, roller printing, and digital printing coexist. The scope of application of various printing processes is different, the process characteristics are different, and the printing equipment and consumables used are also different. As a traditional classic printing process, screen printing has a wide range of applications, and it accounts for a relatively high proportion in the printing industry. In recent years, digital printing has developed rapidly, and many people think that there will be a trend to replace screen printing. What are the differences between these two printing processes? The difference between digital printing and screen printing is analyzed here.
There is little difference in the types of printing materials
Digital printing is divided into five categories: acid digital printing, reactive digital printing, paint digital printing, decentralized thermal transfer printing and decentralized direct-injection digital printing. Digital printing acid ink is suitable for wool, silk and other protein fibers and nylon fibers and other fabrics. Digital printing reactive dye inks are mainly suitable for digital printing on cotton, linen, viscose fiber and silk fabrics, and can be used for digital printing on cotton fabrics, silk fabrics, wool fabrics and other natural fiber fabrics. Digital printing pigment ink is suitable for digital inkjet pigment printing of cotton fabrics, silk fabrics, chemical fiber and blended fabrics, knitted fabrics, sweaters, towels, and blankets. The digital printing thermal transfer ink is suitable for the transfer printing of polyester, non-woven fabric, ceramics and other materials. Digital printing direct-injection dispersion ink is suitable for digital printing of polyester fabrics, such as decorative fabrics, flag fabrics, banners, etc.
Traditional screen printing does not have much advantage over digital printing in the types of printing materials. First, the printing format of traditional printing is limited. The inkjet width of large industrial digital inkjet printers can reach up to 3~4 meters, and can print continuously without limitation in length. They can even form a whole production line; 2. It is on some materials that traditional water-based ink printing cannot achieve better performance. For this reason, only solvent-based inks can be used for printing, while digital printing can use water-based ink for inkjet printing on any material, which avoids a large amount of use Flammable and explosive non-environmentally friendly solvents.
Digital printing colors are more vivid
The biggest advantage of digital printing mainly focuses on the fineness of colors and patterns. First of all, in terms of color, digital printing inks are divided into dye-based inks and pigment-based inks. The colors of dyes are brighter than pigments. Acid digital printing, reactive digital printing, dispersive thermal transfer printing and dispersive direct-injection digital printing all use dye-based inks. Although paint digital printing uses pigments as colorants, they all use nano-scale pigment pastes. For a specific ink, as long as the matching special ICC curve is made, the color display can reach the extreme. The color of traditional screen printing is based on the four-color dots collision, and the other is controlled by the pre-printing ink toning, and the color display is not as good as digital printing. In addition, in digital printing, the pigment ink uses nano-scale pigment paste, and the dye in the dye ink is water-soluble. Even if it is a dispersion type sublimation transfer ink, the pigment is also nano-scale.
The fineness of the digital printing pattern is related to the characteristics of the inkjet print head and the printing speed. The smaller the ink droplets of the inkjet print head, the higher the printing accuracy. The ink droplets of the Epson micro piezoelectric print head are the smallest. Although the ink droplets of the industrial head are larger, it can also print images with a precision of 1440 dpi. In addition, for the same printer, the faster the printing speed, the smaller the printing accuracy. Screen printing first needs to make a negative plate, the error in the plate making process and the mesh number of the screen have an impact on the fineness of the pattern. Theoretically speaking, the smaller the screen aperture, the better, but for ordinary printing, 100-150 mesh screens are often used, and the four-color dots are 200 meshes. The higher the mesh, the greater the probability of water-based ink blocking the network, which is a common problem. In addition, the accuracy of the plate during scraping has a great influence on the fineness of the printed pattern. Machine printing is relatively better, but manual printing is more difficult to control.
Obviously, color and fine graphics are not the advantages of screen printing. Its advantage lies in special printing pastes, such as gold, silver, pearlescent color, cracking effect, bronzing flocking effect, suede foaming effect and so on. In addition, screen printing can print 3D three-dimensional effects, which are difficult to achieve with current digital printing. In addition, it is more difficult to make white ink for digital printing. Currently, white ink mainly relies on imported ink to maintain, but printing on dark fabrics does not work without white. This is the difficulty that needs to be broken through to popularize digital printing in China.
Digital printing is soft to the touch, screen printing has high color fastness
The main properties of printed products include surface properties, that is, feel (softness), stickiness, resistance, color fastness to rubbing, and color fastness to soaping; environmental protection, that is, whether it contains formaldehyde, azo, pH, carcinogenicity Aromatic amines, phthalates, etc. GB/T 18401-2003 “National Basic Safety Technical Specifications for Textile Products” clearly stipulates some of the items listed above.
Traditional screen printing, in addition to water slurry and discharge dyeing, other types of printing have a stronger coating feel. This is because the resin content of the printing ink formulation as a binder is relatively high, and the amount of ink is relatively large. However, digital printing basically has no coating feeling, and the printing is light, thin, soft and has good adhesiveness. Even for paint digital printing, since the resin content in the formula is very small, it will not affect the hand feel. Acid digital printing, reactive digital printing, dispersive thermal transfer printing and dispersive direct-injection digital printing, these are uncoated and do not affect the feel of the original fabric.
Whether it is in traditional water-based printing inks or pigment printing inks, resin is used as a binder, on the one hand, it is used to increase the adhesion fastness of the coating to the fabric, making it difficult to crack and fall off after washing; on the other hand, the resin can wrap the pigment Particles make it difficult to decolorize by friction. The resin content in traditional water-based printing inks and pastes is 20% to 90%, usually 70% to 80%, while the resin content in pigment printing inks in digital printing inks is only 10%. Obviously, theoretically, the color fastness to rubbing and soaping of digital printing will be worse than traditional printing. In fact, the color fastness to rubbing of digital printing without certain post-processing is indeed very poor, especially the color fastness to wet rubbing. Although the color fastness to soaping of digital printing can sometimes pass the test according to GB/T 3921-2008 “Textile color fastness test to soaping color fastness”, it is still a long way from the washing fastness of traditional printing. . At present, digital printing needs further exploration and breakthroughs in terms of color fastness to rubbing and color fastness to soaping.
High cost of digital printing equipment
There are three main types of printers used in digital printing. One is the tablet PC modified by Epson desktop, such as the EPSON T50 modified tablet. This type of model is mainly used for small-format paint and ink digital printing. The purchase cost of these models is much cheaper than other models. The second is printers equipped with Epson DX4/DX5/DX6/DX7 series inkjet print heads, among which DX5 and DX7 are the most common, such as MIMAKI JV3-160, MUTOH 1604, MUTOH 1624, EPSONF 7080, EPSON S30680, etc. Each of these models The purchase cost of each printer is about 100,000 yuan. Currently, DX4 print heads are quoted at RMB 4,000 each, DX5 print heads are quoted at RMB 7,000 each, and DX7 print heads are quoted at RMB 12,000. The third is the industrial inkjet digital printing machine. The representative machines include Kyocera industrial nozzle digital printing machine, Seiko SPT nozzle digital printing machine, Konica industrial nozzle digital printing machine, SPECTRA industrial nozzle digital printing machine, etc. The purchase cost of printers is generally higher. high. The individual market price of each brand of print head is more than 10,000 yuan, and one print head can only print one color. In other words, if you want to print four colors, one machine has to install four print heads, so the cost is extremely high.
Therefore, the cost of digital printing equipment is extremely high, and inkjet print heads, as the main consumables of digital inkjet printers, are extremely expensive. The market price of digital printing ink is indeed much higher than that of traditional printing materials, but the printing area of 1 kg of ink output is incomparable with the printing area of 1 kg of ink. Therefore, the cost comparison in this respect depends on factors such as the type of ink used, the specific printing requirements, and the printing process.
In traditional screen printing, the screen and squeegee are consumables during manual printing, and the labor cost is more significant at this time. Among the traditional printing machinery, the imported octopus printing machine and elliptical machine are more expensive than the domestic ones, but the domestic models have become more and more mature and can also meet the requirements of production and use. If you compare it with an inkjet printing machine, its purchase cost and maintenance cost are much lower.
Screen printing needs to improve environmental protection
In terms of environmental protection, the environmental pollution caused by traditional screen printing is mainly reflected in the following aspects: the amount of waste water and waste ink generated in the production process is quite large; in the printing production process, more or less need to use some bad Solvents, and even plasticizers (thermosetting inks may add not environmentally friendly plasticizers), such as printing water, decontamination oil, white electric oil, etc.; printing workers will inevitably come into contact with chemical solvents in actual work. Glue, toxic cross-linking agent (catalyst), chemical dust, etc., have an impact on the health of workers.
In the digital printing production process, only a certain amount of waste liquid will be produced during the pre-treatment sizing and post-treatment washing process, and very little waste ink will be produced during the entire inkjet printing process. The overall source of pollution is less than that of traditional printing, and it has less impact on the environment and the health of the contacts.
In short, digital printing has a wide range of printing materials, colorful printing products, fine patterns, good hand feeling, and strong environmental protection, which are its typical characteristics. However, inkjet printers are expensive, consumables and maintenance costs are high, which are its shortcomings. It is difficult to improve the washing fastness and rubbing fastness of digital printing products; it is difficult to develop stable white ink, resulting in the inability to print better on black and dark fabrics; due to the constraints of inkjet print heads, it is difficult to develop Printing inks with special effects; printing sometimes requires pre-processing and post-processing, which is more complicated than traditional printing. These are the disadvantages of current digital printing.
If traditional screen printing wants to develop steadily in the printing industry today, it must grasp the following points: improve the environmental protection of printing inks, control environmental pollution in printing production; improve existing special printing effect printing, and develop new printing special effects , Leading the printing trend; keeping up with the 3D craze, developing a variety of 3D printing effects; while maintaining the washing and rubbing color fastness of printed products, the development of imitating digital touchless, lightweight printing effects in conventional printing; developing wide-format printing It is best to develop a printing assembly line platform; simplify printing equipment, reduce the cost of consumables, increase the input-output ratio of printing, and enhance the competitive advantage with digital printing.
Post time: May-11-2021