1 Preface
UV curing methods have been adopted for inkjet (IT) printers. UV curing ink has three major characteristics, namely, energy-saving drying, a wide range of printability of the substrate, due to high-speed curing can shorten the time passed to the process. For the UV curing on the ink jet printer, in addition to the above features, the characteristics of the digital processing, the manufacturing technology of the inkjet print head, the progress of the control technology, and the combination of the printing technology are expecting new progress. The main application is now:
(1) Printing of variable data such as logos;
(2) Printing of wide-format images with a small number of copies;
(3) Printing of substrates for non-ink-absorbing packaging.
In general, ink jet printing is performed by printing ink on the printing substrate, but UV ink jet printers rely on high speed polymerization and curing of the photopolymer ink to complete the printing. According to such features, UV ink jet printers can adapt to a variety of needs and meet the production with digital processing. This manuscript presents several aspects of the key features, materials and hardware, and imaging technology features of UV inkjet technology, and looks forward to its future.
2 UV curing technology in inkjet printing applications
In general, an ink jet method using a low-viscosity liquid ink causes the liquid on the print head to always maintain a certain state and quickly homogenize after being applied to the substrate to form ink dots. Bringing in large changes in the state of the ink to meet the requirements of image quality and speed, this is greatly constrained compared to other methods using toner and high viscosity inks.
The ink jet method is a true non-contact printing. It has the effect of applying ink to any substrate. However, in order to complete the printing, there are many difficulties, and the UV-curable ink can improve the ink-jet method.
1) Marking inkjet printer
UV inks that cure at high speed without penetrating and evaporating have long been used in the printing of markings due to their non-contact characteristics.
The following materials can be printed with the inkjet printer:
(1) Non-ink absorbing equipment;
(2) Equipment without printing pressure:
(3) Surface equipment:
(4) Equipment not suitable for heating and drying, such as plastic molded products, metal or ceramic products, signs, cans, wires, corrugated cardboard, etc.
The print content includes variable data such as product name, lot number, production date, bar code, and address, as well as resist patterns and decorative graphics.
For the printers used for the above purposes, continuous and on-demand piezoelectric methods are used. The continuous type has expanded the printing object by multi-nozzle and multi-colorization. As a type of UV ink, it is not four-color printing but centered on spot colors, using black, white, yellow, red, and the like. PVB (printed circuit board) resist ink is also introduced in this field.
2) Graphics Printing Machine
The UV ink jet printer for graphics uses four-color overprinting to achieve high image quality by using pigment inks with excellent adhesiveness, and is thus widely used in all existing fields.
(1) Wide UV Inkjet Printer
UV inkjet printers for graphic printing were introduced in 2000. For this type of application, owing to its large area, screen printing or electrostatic printing has been the main method in the past, and POP applications such as large-area billboards, wallpapers, shop signs, hanging screens, interior decorations, etc. Due to the small number of printing parts, the restrictions on the ink and the substrate are small, so the advantages of UV ink jet can be exerted. Oil-based pigment ink jet printers for this area are on the market. Oily inks cause environmental pollution due to volatilization of solvents, coupled with the constraints of a variety of plastic printing materials, and UV is the way to overcome the above two points, only looking forward to change as soon as possible. The biggest contradiction is to deal with large-scale printing materials, such as soft or hard plastic, non-woven fabrics, polyethylene, fabrics, synthetic paper and so on. Take UV ink, in order to obtain the best picture quality, different materials should use the corresponding ink, wide application is the characteristics of UV ink.
(2) High Speed ​​UV Inkjet Printer
The print head is fixed, and a high-speed graphic printer is now available by means of high-speed transfer of the printed substrate. According to the assembly of the print head and the lamp, the arbitrariness of the printing web is high. The use of package printing for sample and test marketing, or the application of similar screen printing, and the combination printing with offset printing are being promoted.
(3) UV inkjet printers for narrow pattern printing
The use of multi-color narrow-web printers has been popularized in the printing of non-ink-absorbing materials such as CDs, card products, and trademarks. Since the type of substrate is limited, the ink technology suitable for the application is very important.
3 Hardware Composition and Printing Methods
The composition of the hardware is based on the configuration of the print head and the lamp, and the printing method is different depending on the consideration of the movable part and the fixed part.
The common topics are:
1 Because of the large printing substrate, the position accuracy when the movement distance is long;
2 Simultaneous application of UV and UV radiation;
3 sequence and image quality of each ink application;
4 distance adjustment of printing substrate and printing head;
5 printing speed.
Most printers set a variety of substrates in advance to improve arbitrariness and extension.
1) Configuration of print heads and lamps
Figure 1 shows an example of the configuration of printheads and lamps on a flatbed UV inkjet printer. As for wide-width printing, the irradiation device adopts a structure that works in conjunction with the printing head in view of the curing time. The drawing head and the lamp configuration are different for the drawing-type operation and the printing-type operation. For the roller feeding method, as shown in FIG. 2 , a variety of arrangements can be made on the printing substrate to be moved on the drum.
From the point of view of the printing process, there are a method of printing a single-color after-curing and a method of sequentially irradiating with the printed full-color ink, and a method of performing a curing treatment after printing a full color, etc., and the selection of it depends on the printing activity. Depends on the item.
2) Print head
The print heads used in UV ink jet printers have until now been effective continuous types and piezoelectric types capable of widely designing the allowable range of the ink. The design elements required for installing UV inks are:
1 print head life needed for commercial printing;
2 Chemical resistance to raw materials such as acrylic monomers that make up UV inks;
3 The basic characteristics suitable for printing quality requirements such as droplet size, splash speed, response frequency, and dot size modulation
4 Conforms to the fluid conditions of the ink fluid.
In particular, the basic properties of the ink are completely different from ordinary inks, so the above 1 to 4 are very important. Because of the high viscosity range of the UV ink, the particle formation performance must be noted that the drive frequency used, the droplet volume of the target, the ejection speed, etc. must be adjusted at any time. The stability and quality of the main drop, follow-up suppression are important. This kind of control does not need much to say about the printing of the picture, have very high value to the circuit. In order to increase the printing speed, a large number of print heads are often mounted, so the drive mode of the accumulation mode is very important.
(to be continued)