Characteristics and Research of Electrostatic Printing (2)

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.

This experiment studied the dye-based toner, mainly to study the selection of raw materials and toner preparation methods. The toner was prepared by ball milling, spray drying and jet milling. The binder was selected from natural starch and sodium alginate. These are commonly used pastes for traditional printing. The raw materials are readily available, inexpensive and environmentally friendly. The printed fabric is washed with water without affecting the hand.

Source: China Washing & Dyeing Industry Information Center

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