1 Introduction
In recent years, inkjet printing is advancing toward almost all printing fields and its printing quality is getting better and better. As can be seen from DRUPA 2004, inkjet printing is among the technical highlights and will be the subject of DRUPA 2008.
The so-called "ink-jet printing" is a non-contact, pressureless, non-printing printing and copying technology. It has the common features of digital printing without printing and can realize variable information printing.
The principle of ink-jet printing is to first input the graphic information stored by an electronic computer into an ink-jet printer, and then, under a control of the electronic computer, nozzles spray droplets of ink droplets on the surface of the substrate according to the charge. The effect is directly imaged on the surface of the substrate and becomes the final print.
2 Classification of Inkjet Printing
1 by inkjet system classification
The basic principle of ink-jet printing is to generate small ink droplets and guide them to the set position. According to the different inkjet systems, it can be divided into continuous and on-demand two.
The so-called continuous inkjet printing (CIJ), whether imprinted or non-printed, is the continuous generation of ink droplets in a flowing manner, and then transferred by the electric field deflection to form an image, and finally the non-imprinted droplets are recycled or dispersion.
In so-called drop-on-demand printing (DOD), ink droplets are generated only in the printed portion. Specially used for printing excellent quality images, suitable for packaging color pictures, textiles and large-format billboards, is an ideal choice for full-color, high-precision printing. Print quality is its most important consideration.
2 according to the printing color classification
Inkjet printing can be divided into black and white ink jet printing and color ink jet printing according to its printing color. Single ink for black and white ink jet printing, machine structure and ink system are relatively simple, and color ink jet printing is relatively complicated.
3 Factors that restrict inkjet printing
In the process of development, inkjet printing is inevitably constrained by a number of factors. Currently, the following factors affect the quality of inkjet printing:
1 color conversion
Accurate color conversion technology is the key to influencing the quality of inkjet printing. Specifically, the accurate conversion of the light source color (RGB mode) to the color mode of the inkjet system (CMYK mode) is a complicated problem.
2 Resolution For black-and-white inkjet printers, the higher the resolution, the higher the quality of the printed matter. Therefore, the resolution of a black-and-white machine is the key to print quality, but for a color inkjet printer, the resolution is Refers to how many ink dots can be printed in one inch width, regardless of whether ink dots overlap. Therefore, the color gamut and the resolution are equally important for the color inkjet printer.
The images and images output by the 3 color gradation are composed of many points (called pixels, pixels), and each point has its own color and brightness so as to present a beautiful bright image or image quality. The current ink jet printing technology can precisely control the color gradation of the ink droplets, and control the color ink from the same position to not spray one droplet to sixteen droplets, thereby controlling the color gamut of the output image.
4 The print head controls the ink dots to be sprayed onto the paper via the nozzles, and the nozzles and the print heads are used together. Therefore, the technical and control accuracy of the print heads is very important.
5 Ink ink is also one of the important factors that affect the quality of inkjet printing. The ink used for ink-jet printing is a special-purpose ink with a moderate viscosity, and has non-toxic, stable, non-clogging nozzles, good moisture retention and jetting properties, and no corrosion to the metal components of the head.
At present, ink-jet inks are mostly dye-based. The ink must have sufficient surface tension to prevent sputtering when ejected, and it must have quick-drying properties to prevent haziness on the paper.
6 Substrate Material Inkjet printing paper requires a smooth surface and a certain degree of sizing. After the sprayed ink evaporates and dries, the ink dots are round, and the printed letters are clear and beautiful. Paper for color inkjet printing, the surface is preferably a very thin layer of transparent coating, both rapid absorption of ink, but also to avoid light scattering.
4 Application Fields and Prospects of Inkjet Printing
Since the copying effect of the ink jet printing is very stable and the gamut range that can be expressed is wide, it has quite a wide application prospect and development space in the future digital printing.
After inkjet printers achieved color inkjet, variable specifications, and increased printing speed, digital inkjet printing equipment formed a booming market for digital inkjet printing equipment, digital proofing equipment, and digital inkjet equipment. Its application area can be roughly divided into four aspects.
Application area 1: The output device is connected with a computer, and together with a laser printer, it continues to assume the role of an output device, and its market prospects will be very broad.
Application area 2: output film film uses digital inkjet output film film, splits a small laser image-setter and the traditional camera, film processing equipment market, due to the popularity of laser imagesetter and the rapid rise of digital plate-making machines, this kind of The development of equipment has been hindered, and therefore there is limited room for development.
Application Area 3: High-Resolution Inkjet Printing Equipment With the ever-increasing resolution of inkjet heads, high-resolution inkjet printing equipment forms a branch of three applications:
1 As an output device of a digital camera, digital photos are directly output to form a competitive situation with traditional analog photography and photo processing;
2 As a digital inkjet proofer or exporter, the proofing effect of this equipment is close to the printing effect. Many publishing houses output proofs in this way for proofreading and evaluation, and help to adjust printing equipment and improve printing. quality;
3 Digital inkjet printers have entered the short-run, fast-printing market, becoming the main model of competition with small-sized offset printers, and occupying market share at an unprecedentedly high speed.
Application area 4: The digital inkjet digital inkjet device has entered the large advertising inkjet market and challenges the traditional screen printing field. This printing method has been widely applied in street advertisements, body advertisements, light boxes, plaques, etc. with lower resolution, larger printing width, and continuous printability without length limitation.
Source: "Printing World"
School of Printing and Packaging Engineering, Xi'an University of Technology, Zhao Hongyan Zhang Erhu