The Characteristics of Electrostatic Printing and Its Research Progress

The principle of electrostatic printing of textiles is to design and store customer's design requirements; computer-processed graphic images are developed by electrostatic latent images, and the color toners suitable for fabrics are transferred to the printed fabrics; Fix the color to get the desired pattern. Inkjet printing is controlled by a computer according to design requirements. The ink containing the pigment is controlled to be sprayed onto the printed substrate (fabric) through a nozzle under the pressure to form a pattern; according to the performance of the ink system, the fabric is properly treated to make the fabric With a certain degree of fastness and brightness.

1. Common points of electrostatic printing and ink jet printing

(1) Combining digital printing with computer CAD system, theoretical design is not limited by the number of colors or screen overlay error. Its image resolution is generally 360dpi (rotary screen printing routine 100dpi, maximum 255dpi), and some even up to 1 440 dpi, fineness accuracy is less than 0.1 mm, can print 16.7 million colors of 256 color levels Make the pattern have a good level of expression. The design and modification of the pattern is extremely convenient. Customers can see the final pattern effect from the computer through the network, and can be modified to truly achieve "WYSIWYG".

(2) In electrostatic printing and ink jet printing, the printing head does not directly contact the fabric, so there is no limit to the type of fabric.

(3) The printing process is simple, eliminating the need for complicated screen plate making and color mixing. From the client's submission of patterns to proofing production, only 2-3 days, greatly improving the printing and dyeing enterprises' rapid response to changes in market demand.

(4) The size and position of the graphics can be freely adjusted, allowing mass customization, and the unit production cost has little to do with the output. Therefore, it is theoretically possible to process printed products of any size and in batches, which can reduce the cost of small batches.

(5) No need for color paste preparation, screen cleaning and screen replacement, clean working environment. In addition, the pattern data can be stored on discs and disks, and it is not necessary to save venues such as net frames and floral cones. Compared with large machines such as printing machines, inkjet printing and electrostatic printing use small equipment, and the process is shortened, manpower is saved, and operation is simple.

(6) Due to the reduced amount of dye and the absence of dye, the colored wastewater is reduced.

2, the advantages of electrostatic printing

(1) Increase in printing speed The speed of ordinary rotary screen printing is 40m/min or more, and the speed of inkjet printing is generally 0.1 to 0.33m/min. From the current paper copy or laser print speed estimation, fabric static printing speed can reach at least 10-15 m/min.

(2) The process is simple
Inkjet printing inks are liquids. In order to prevent the ink from bleeding during printing, the fabrics must be sizing treatment, and these pastes must be washed out after printing. Electrostatic printing uses solid toner, so there is no osmotic phenomenon, so it can be directly printed on the fabric without pretreatment, and the printed fabric is easy to clean and save water.

(3) Reduce costs

1 Reduced cost of printing materials Some people compared the four-color electrostatic printing machines in Japan with inkjet printers. The speed of electrostatic printing is about 50 times that of ink-jet printing, and the price of printing materials required per square meter is about inkjet. One hundred and one hundred percent of the printing shows that the price of materials for electrostatic printing is much lower than the price of ink-jet printing.

2 Reduce the cost of printing machine accessories The design requirements of inkjet printers are high and the cost is high. In particular, the problem of nozzle life is urgently needed to be solved. At present, the cost of the ink is high, the type is small, and the adaptability is poor. The ink easily clogs the nozzle and affects the product's genuine rate. The electrostatic printing uses the toner with a particle size of 5 to 10 μm to print without the need of a nozzle, thereby reducing the loss of equipment and equipment.

3, electrostatic printing research progress

Electrostatic printing is developed based on the principle of electrostatic copying and laser printing on paper. Ordinary paper copy or laser printing printing ink and paper to maintain a certain interval, without direct contact, under the action of the electrostatic field so that the ink is transferred to the paper, and then fixed to the paper by heating. Paper copying is an intermittent operation that prints a single sheet of paper at a time and the width of the door is very narrow. The requirement of fabric printing is different from that of paper copying. The electrostatic printing system equipment and toner must be improved in order to meet the requirements of width and continuous operation of fabric printing. Therefore, its processing equipment is also different to accommodate high-speed continuous operation. Fabric electrostatic printing toner can be adhesive or dyed, but it must be fixed after fabric printing to meet the fabric's various fastness, such as dry and wet rubbing fastness, washing fastness and sun exposure. Fastness and so on.

In recent years, the Georgia Institute of Technology in the United States has conducted a lot of research on the electrostatic printing system for continuous textile printing. According to reports in the literature, the Georgia Institute of Technology developed the electrostatic printing copier. Once the fabrics pass through three photocopiers one after another, they can print out the colorful charged areas. When the fabric is in contact with the roller, a negative charge is added on the reverse side of the fabric to form a positive image on the fabric surface. Fix it on the fabric. They mainly study adhesive toners. When preparing toners, thermosetting resins are used as carriers. Although thermosetting resins have good rubbing fastness, the fixing time is too long and will cause the fabric to yellow. When used in cotton fabrics, the wet rubbing fastness and feel are not approaching. According to a report published by the Georgia Institute of Technology in the United States, a thermoplastic toner and three thermosetting toners are prepared for cotton, silk, polyester, and nylon printing, respectively, and have a certain printing effect, but the fabric has poor hand feeling and transfer rate. Lower.

Over the years, Japan is also studying this technology. In November 2002, Japanese industry tried a static electronic printing device that was completely different from inkjet printing devices. Currently, there are monochrome to four-color printing devices, which will grow to more than eight colors in the future. In February 2004, foreign countries reported an electronic-electrostatic printing direct printing system. The system is in the experimental stage and is equipped with a liquid dispersion or reactive dye toner, with an image receiving drum of an electrostatic charge transfer system. It can be seen that the printing system adopts the same liquid ink as the ink jet printing, and is similar to the electrostatic transfer technology adopted in electrostatic copying.

In 1987, Beijing Institute of Textile Science Xue Digeng and Zhu Guanfu used photoconductors such as zinc oxide and polyvinylcarbazole-trinitrofluorenone to study their properties as insulators in the dark and after exposure to electrical conductors, and to use patterns or photography. The new process of photo printing directly on the fabric. Since then, no follow-up studies have been reported in China, and relevant literature reports have appeared in China in 2004.

In general, toners used in electrostatic printing consist of magnetic powder, colorants, binders, and charge modifiers.

The toner is generally made into four colors, that is, the CMKY four-color printing method commonly used in the printing industry. Electrostatically-printed toners fall into two major categories, namely pigment (cohesive) and dye-based.

When printed with a pigment (adhesive) type toner, the toner is fused to the fabric. The adhesive is generally a high molecular polymer with high electrical insulation, and has good adhesion with pigments and fabrics, and does not require post-processing after printing. This type of adhesive is similar to the binder in paper copy toner. There are many reports on this type of toner in the world. For example, modified epoxy, polyester, and ethylene vinyl acetate (EVA) copolymers have been used as the electrostatic printing toner binder for textiles by the Georgia Institute of Technology. This kind of toner has a more mature application in the printing of paper, but there are still big problems in fabric printing, such as the color fastness and the poor feeling of fabric printing part, the color is not bright and so on.

Dye-type toner theoretically can make up for the above deficiencies. Since the colorant is a dye, the properties after fabric printing are basically similar to the traditional fabric printing. At present, the colorants used in dye-based toners are mainly disperse dyes. They are dyed on polyester fabrics by the melting and sublimation properties of disperse dyes. At this time, only the dyes are fixed to the fibers, and the rest of the additives need to be removed. The agent only plays a role in the formation of the toner particles and has nothing to do with the feel of the fabric after printing. Since the disperse dye in the toner needs to be transferred from the toner to the fabric during the printing process, it is required that the affinity of the dye and the binder in the toner is lower than the affinity of the dye and the fabric. According to the characteristics of dyes and toners, the general adhesives use more polar polymer materials.

Another important component in the toner is a charge modifier. The quality of photocopying and laser printing is governed by a variety of factors, among which the charge modifier plays an important role. It can be divided into two kinds of colored and colorless, the former for black and white copying; the latter for color copying. According to the charge properties can be divided into positive and negative charge regulators. Since textile electrostatic printing is colored, five-color charge modifiers are used. The colorless negative charge modifier is a 1:2 metal complex such as a salicylic acid chromium complex and a zinc complex. Colorless positive charge modifiers are mainly concentrated in aliphatic and aromatic quaternary ammonium salts.

Source: Global Textile Network

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