On the application of inkjet printing technology

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With the continuous progress and development of the digital process, inkjet printing technology has become an important technical means in the field of digital printing because of its low cost and good environmental protection. Inkjet printing equipment mainly includes: small inkjet printer, large format inkjet printer, inkjet printing system, etc. As a product of digitalization and computer technology, inkjet printing covers part of the printing market that cannot be covered by traditional printing, and gradually expands to many fields, with a very broad market prospect. Today, China paper industry takes you into inkjet printing technology and introduces the relevant contents in detail

I. Basic Principle and method of inkjet printing

inkjet printing is a non-contact, pressure-free and plate free printing method, which is composed of system controller, inkjet controller, nozzle, substrate drive mechanism, etc. under the control of inkjet controller, ink is sprayed on the substrate from the nozzle of the nozzle of the nozzle. Color inkjet printers usually have two ways: high temperature and high pressure printing and normal temperature and pressure printing. The former is represented by Canon's bubble technology and HP's thermal technology, while the latter is represented by Epson's Shanghai Machinery Factory; Cmt1302 electronic universal experimental machine is represented by ultra micro piezoelectric printing technology. Thermal foaming relies on the heat of a small resistance to evaporate the surrounding ink and produce bubbles. The expansion of bubbles forces the ink to eject from the nozzle and reach the substrate. After ejecting, the bubbles disappear, and new ink is sucked from the ink tank to produce a continuous bubble working mode. The micro piezoelectric inkjet technology is to put the piezoelectric chip above the inkjet nozzle, add a little current to the chip, generate vibration, and spray the ink by vibration

1. Continuous ink-jet printing

(1) printing with deviated ink drops

when the ink flows through the pressurized spray, it is best to carry its own material to detect, vibrate and decompose into small ink drops. After passing through an electric field, due to the electrostatic effect, the small ink drops fly forward regardless of whether they are charged or not after flying over this electric field. When passing away from the electromagnetic field, the ink droplets with large charge will be strongly attracted and deflected. On the contrary, the deflection is small. The uncharged ink drops will accumulate in the ink collecting ditch for recycling (as shown in Figure 1)

(2) printing with non deviated ink drops

is very similar to the above class, the only difference is that the deviated charge is recovered, and the non deviated charge instead forms an image straight (as shown in Figure 2)

(3) unnecessary ink drops cause electrostatic splitting

the ink flow is still pressurized and ejected from the nozzle, but the pipe hole is more slender, with a diameter of about 10-15 microns. The pipe hole is so thin that the ejected ink drops will automatically decompose into tiny ink drops. When these small ink drops pass through the charged ring of the same electrode, because the same charges repel each other, these charged ink drops will split into fog ink again. At this time, it will lose its directivity and do not print. On the contrary, the uncharged ink droplets will not split and form images. It can be used for continuous tone printing (as shown in Figure 3)

2. Intermittent inkjet printing

(1) use electrostatic pull

use electrostatic pull to jet ink. The ink at the jet hole will form a protruding half moon shape, and then use an electrode plate in parallel. The surface tension of the protruding ink will be damaged by the high voltage on the parallel electrode plate. Therefore, the ink drops will be pulled out by electrostatic force. These ink drops are charged with static electricity and can be offset vertically or horizontally to the set position or recovered on the shielding plate (as shown in Figure 4)

(2) hot bubble inkjet

the ink is instantly heated in a very short time, which expands the volume of the gas near the resistor, and a small amount of ink will turn into steam, squeezing the ink out of the nozzle, making it fly to the paper to form an image. After the ink drops are ejected, the temperature will immediately decrease, so that the temperature in the ink chamber will soon be low, and then the outstanding ink will be pulled back into the ink cartridge by the capillary principle

second, the application status of inkjet printing technology in China

the starting time of inkjet printing industry in China is not far from that in foreign countries, but there is still a big gap in research and development, production and marketing and application compared with developed countries such as the United States and Japan. In terms of regional distribution, it is mainly concentrated in economically developed Guangzhou, Shenzhen, Shanghai and Beijing. At present, the application of ink-jet printing in China is in a polarized situation. At one end, there is a low-end market. Most of the equipment used is non production ink-jet printing machines, and most of the printing parts are short version black-and-white, with a small amount of color. At the other end is the high-end market. Most of the inkjet printing equipment used by practitioners are production inkjet digital printers. Printing is not only ultra short color prints, but also many personalized and variable data printed color prints. Customers of such digital printing companies pay more attention to quality and service, and have high requirements for color and printing quality

in addition, with the continuous improvement of inkjet printing resolution and speed, several application branches have been formed

1. As the output equipment of digital camera, it directly outputs digital photos, forming a competitive situation with the traditional analog photography and photo development process. Although the current inkjet digital printing price is high, with the reduction of cost, the market will further expand

2. The proofing effect of inkjet digital proofing machine or output machine is close to the printing effect. Many publishing houses output proofs in this way for proofreading and evaluating manuscripts, so as to adjust printing equipment and improve printing quality

3. Inkjet printing machine has entered the short version and fast printing market, and has become the main model competing with small lithographic printing machine, and has seized the market share at an unprecedented high speed. Now many foreign manufacturers have participated in the competition

4. Digital inkjet equipment has entered the large-scale advertising inkjet market, challenging the traditional silk printing field. This printing method has been widely used in street advertisements, body advertisements, light boxes, plaques and other aspects with low resolution, large printing format and continuous printing performance without length restrictions

5. The use of inkjet printing machine has good anti-counterfeiting effect. Generally, manufacturers with small economic strength can spray date and other information on the key parts of the package by skillfully using the inkjet printer, which can play a certain anti-counterfeiting role. The combination of inkjet printing machine makes it possible to get up in the morning, brush teeth, squeeze toothpaste and extrude swelling, and the anti-counterfeiting ink has better anti-counterfeiting effect. The use of inkjet printing machine has the function of designing and investing anti-counterfeiting. The anti-counterfeiting ink has the function of secret anti-counterfeiting. The combination of the two has a triple anti-counterfeiting function

III. advantages and constraints of inkjet printing technology

1 Advantages of inkjet printing technology

(1) inkjet printing is a kind of digital printing, which completely breaks away from the cumbersome procedures of traditional printing process. It has low requirements for color overprint and trapping, does not need to consider registration accuracy, short operation preparation time, rapid response to the market, and short operation production cycle. It can complete the production of digital samples and short editions with very high time efficiency and cost efficiency

(2) realize variable data printing and customized printing, and the image information can be changed at any time to meet the user's short version printing and personalized printing needs, such as personal photo albums, product descriptions, materials, trial products, packaging samples, etc

(3) printing on one sheet can reduce waste, and the printing service is more flexible. It usually has an advantage within 1000 prints

(4) digital features make it easier to introduce digital asset management, automated workflow and color 4) beam movement limitations: ≥ 300mm; Management and other digital integration technologies

(5) it can realize remote printing and provide remote printing services through Internet transmission, especially suitable for fast printing of cross regional chain operation

(6) most inkjet printing technologies are non-contact printing, which can be copied on a variety of substrate materials, such as variable inkjet printing on a variety of commodity production lines

(7) digital web ink-jet printing equipment can be free from the limitation of paper length, and can realize the reproduction of large format and panoramic works

2. Constraints of inkjet printing technology

although in digital printing, inkjet printing has a market share of about 5%. However, the development of inkjet printing is more or less restricted by some factors. At present, the main factors affecting the quality of inkjet printing are the following

(1) color conversion. How to accurately convert the color (R, G, b) of the light source system into the ink-jet or printing system (C, m, y, K) is very complex, but only by accurately converting the color can we obtain real and high-quality effects. Therefore, accurate color conversion technology is an important key to the quality of inkjet printing

(2) resolution. For black-and-white inkjet printers, the higher the resolution, the smaller the color scale points printed, and the better the printing quality. However, for color inkjet printers, resolution refers to how many ink dots can be printed on the width of 1 inch, regardless of whether the ink dots overlap

(3) color scale. The current ink-jet printing technology can accurately control the color level of ink drops, and control the color ink from not spraying to spraying 1 drop to spraying 16 drops at the same position

(4) print head control. Ink dots are sprayed onto the paper through the nozzle. Generally speaking, the nozzle and the letterhead are made together, so the technology of the letterhead itself is very important, and the left and right letterheads are the inkjet technology and the precision of the cantilever gear and transmission belt of the printing machine

(5) ink. Ink for inkjet printing is a special ink with moderate viscosity, which should have the properties of non-toxic, stable, non clogging nozzle, good moisture retention, good spray performance, and no corrosion to the metal components of the nozzle. At present, most inkjet inks are dye inks. The inkjet printer inks must also have sufficient surface tension to prevent the ink from splashing out when ejected. In addition, the ink should be fast drying to prevent blooming on the paper. Therefore, the ink itself is also one of the factors affecting the printing quality

(6) substrate material. Ink jet printing paper requires paper with smooth surface and a certain degree of sizing. The ink sprayed is evaporated and dried, and the ink dots are round. The printed words are clear and the graphics are beautiful. For color inkjet printing paper, it is best to have a very thin transparent coating on the surface, which can not only absorb ink quickly, but also avoid light scattering, so as to obtain ideal prints

IV. prospect of inkjet printing

at present, the color performance and high image quality of inkjet printing have satisfied most consumers. Digital proofing has been mostly achieved by inkjet, and its advantages in large format printing are becoming increasingly obvious, and has begun to march into the field of packaging and printing

however, the printing time of ink-jet printing is still too slow, and the requirements for paper are also very high. Although there are many special paper for ink-jet printing on the market, the price is high, which is difficult to be widely used by ordinary families and students. It often costs dozens of dollars to print a high-quality A4 image, so making ink-jet printing technology widely applicable to all kinds of paper is the most urgent technology to be developed now, It is not easy to make special paper with special materials affordable, so developing new ink components is a direct and effective way. In addition, changing inkjet printing technology can also achieve this goal, for example, HP does not

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