Pad printing features and application analysis

Pad printing can be considered as an alternative type of special printing. Its greatest feature is that it is suitable for the surface printing of shaped surface objects, thus filling the gaps of screen printing and other printing. With the integration of new and high technologies and the development of printing in the direction of diversification, printing will inevitably blossom in splendid colors, and the development prospects will be broad and attractive.

First, the main features of printing

Pad printing The graphics on the steel intaglio plate (or photoengraving pad) can be transferred onto the substrate by a silicone rubber-made pad printing head. It can be used for printing flat or various shapes, such as glass products, plastic products and metal products. , watches, electronic and optical products. Its main feature is the printing of irregular irregularities on the surface. It is difficult or even impossible for these printing methods to use other printing methods, but it can be easily completed by using pad printing, and multi-color printing can be realized. This is an ideal printing method for surface printing of instruments, equipment and some small products.

There are many similarities between pad printing and screen printing. For example, it is widely adaptable to printing materials. There are a wide range of inks. Pad printing inks and screen printing inks can be basically used; different fixtures and printing plates can be easily completed by changing fixtures and printing plates. Product printing and so on. Therefore, in many printing situations, pad printing and screen printing are as close as a pair of twin sisters and play an important role in special printing technologies. Because of this, many printing experts have classified the printing process in the field of screen printing without subdividing specialized printing technology and research institutions. However, there are differences in the characteristics and use of printing and screen printing. First of all, from the point of view of the ink transfer process, there are obvious differences between pad printing and screen printing; the structure of pad printers and screen printers is also different; the types of products that pad printing technology adapts to and screen printing are also quite different. From an objective point of view, the difference between printing and screen printing is much greater than the similarities between them. The reason why we are accustomed to tying them together is that the bigger reason is that printing and screen printing face the same thing. The market, in this common market, screen printing can not be separated from printing. It is not necessary to peel off the printing from the screen printing industry, but it is not necessary to understand it in depth. It is not necessary to examine it only by the screen printing industry.

To sum up, the characteristics of pad printing are: (1) Suitable for curved printing. Flexible silicone printing heads can print on substrates with complex shapes such as secondary and tertiary curved surfaces and irregular surfaces outside the plane; (2) Finer graphic images can be printed, generally fine lines of 0.05 mm can be printed. (3) The printing is stable and continuous. Even if it is printed for a long time, the printing accuracy will not change. (4) The drying process can be omitted and multi-color printing can be performed continuously. (5) The printing range is wide and can be used in plastic, metal, glass. Any concave and convex surface on a variety of materials such as ceramics, leather, bakelite, etc. accurately prints monochrome, two-color, and color images, soft touch prints, and soft items such as fruits, pastries, and eggs. Etc.) and printing on fragile and fragile items (such as ceramics, glassware, etc.); (6) The pad printing process is easy to learn and reliable, and has no special esoteric technology.

Second, the current status of printing and development prospects

Pad printing is a special printing technology that was introduced into China in the 1980s. It has obvious advantages in printing on products with small areas and irregular shapes, filling the gaps in screen printing and other printing processes. It is widely used and developed rapidly. . Especially after the 1990s, with the wave of reform and opening up spreading to all walks of life, a large number of foreign-funded enterprises, mainly electronics, plastics, gifts, toys and other traditional industries, have entered the Chinese market one after another, and their products have increased substantially, and these products have been driven. The decorative printing has promoted the rapid development of printing. According to statistics, currently, pad printing accounts for most of the printing market for these products. However, due to the fact that printing is only good at printing in the non-printing mainstream, the connection with paper is still a blank. Therefore, the overall technical level of the printing process is not high, and the production cost in developed countries remains high. Under the circumstances, it is very difficult to continue to develop. However, there are promising prospects for developing countries with low labor costs such as ours. At present, except for a few foreign companies that also manufacture automated printing lines, most of them have already moved their production bases to China. From the current point of view, the current status and development prospects of pad printing mainly include the following aspects.

1. From the perspective of printer equipment and technology

At present, common pad printers include mechanical pad printers and pneumatic pad printers. The mechanical pad printing machine mainly refers to the mechanism that the squeegee used in the first-generation pad printing machine is a mechanical dropping knife. The overall structure of this type of pad printing machine is relatively complicated and bulky, and the scraper frame is mounted on the two sides of the paddle frame. The guide sleeve moves horizontally along the large guide post to complete the work cycle. The working principle is that the squeegee case is moved horizontally while driving the squeegee frame that hangs below it. The radius of curvature of each point on the outer circle of the brush surface is different, and the position of the fixed point on the surface of the camshaft also constantly changes, so that the swinging movement is performed for the blade holder member and the shaft to move up and down. Through the action of the ejector rod, the doctor blade first drops (press down) and raises, and then the brush holder falls and raises, thus completing the function of adding ink and scraping ink to the pattern steel plate. When the blade holder is raised, the movement is horizontal forward. The brush holder brush can brush the ink in the ink tray onto the pattern steel plate. The blade holder (ie, the doctor blade) is dropped. At this time, the motion is horizontally retracted. The blade is closely attached to the surface of the pattern steel plate, and excess ink on the pattern plate is scraped off to complete one working cycle. In order to facilitate adjustment and control of the degree of drop and elevation of the blade, an adjustment device is provided to change the size of the downward force of the blade, so as to achieve the requirements of the blade to clean the ink and realize the application of printing. Squeegee pressure directly affects the print quality of the pattern. Squeegee pressure is too small. The ink on the platen cannot be completely scraped. Excess ink outside the pattern will be smeared on the silicone head and transferred to the substrate, destroying the integrity of the pattern or causing dirt. Squeegee pressure is too high, the blade will be deformed under pressure, scraper blades will contact the pattern at the concave surface due to the bending deformation of the blade will scrape the ink pattern should not be scraped off, resulting in the pattern of concave ink and steel The surface of the plate is uneven. When the offset head is rapidly printed, the part of the gas-isolated silicone head remaining in the concave surface of the pattern is brought into contact with the ink, resulting in that the printing head is not stained with ink, and the ink is transferred to the substrate. There are white dots (ie, bubbles) on the print pattern, making the printed pattern incomplete. Once the squeegee mechanism has been debugged, the action is relatively reliable and the cost is low, but the debugging is inconvenient and requires a certain level of technology. Because of the mechanical guarantee movement, the error of the component processing directly affects the quality of the squeegee, so the component processing must be improved. Accuracy.

Pneumatic pad printers are widely used at home and abroad. It uses a pneumatic knife setting mechanism and is a second-generation printing machine. The entire mechanism is relatively simple and reliable. Its working principle is that a bracket is mounted on the frame of the squeegee frame, a two-position and five-way valve of a limiting position reversing element is mounted on the bracket, the horizontal movement of the frame of the squeegee frame can be performed along the large guide column, and the small guide column can be along the frame of the squeegee frame. The small guide sleeve on the body does vertical movement. The cylinder link is attached above the beater assembly. When the squeegee case moves horizontally from front to back, the two-position five-way valve moves together, and the beam is equipped with a retractable platen. When the wheel of the two-position five-way valve hits the platen, the direction of the gas line is changed. The cylinder drives the blade holder assembly and the brush holder assembly to move downwards, and the blade scrapes the ink. When the wheel of the two-position five-way valve leaves the pressure plate, the gas path direction changes between the blade holder assembly and the brush holder assembly. The upward moving blade does not scrape ink. The pressure plate can be retracted and adjusted in position to achieve the purpose of adjusting the squeegee position and the squeegee force. There is a spring self-adjusting mechanism on the scraper assembly, which can make the blade contact with the pattern steel plate more ideal. This air-controlled knife-drop mechanism has a simple structure and high reliability. The whole machine is simple and lightweight, and the debugging and maintenance of the machine are very convenient. Due to pneumatic control, the other parts of the machine are connected with the air control, which greatly enhances the unity of the machine.

The scraping process of the scraper in the two scraper mechanisms is completed at the same time during the operation of the scraper frame, that is, the fall of the scraper falls during the horizontal operation, and there is an invalid length in front of the scraper. The pad printer cannot fully utilize the flush cylinder. Stroke; On the other hand, the fall of the blade during operation is relatively rapid in the wear of the blade, and in the case of rapid velocity, the wire drawing phenomenon during the scratching process is prone to occur. If the debugging is improper, the printing quality will be affected. In response to the deficiencies of these two squeegee mechanisms, some manufacturers have improved the drop mechanism to form a front drop mechanism, ie, the squeegee is dropped when the squeegee case is moved to the foremost position, and then the horizontal operation of the squeegee case is performed. . This reduces the invalid length and makes full use of the squeegee stroke, which not only expands the printable range of the substrate, but also eliminates the squeegee that is prone to wear and the print quality. On the machine, besides modifying individual mechanical parts, only a simple modification of the control air path of the scraper mechanism (ie using a double acting cylinder or using a single acting cylinder) is sufficient. This control air circuit is currently used on a pad printer and works well.

In general, the current level of automation and specialization in pad printers is relatively low and cannot be compared with other printing technologies. With the relatively high degree of automation of the rotary transfer printing machine, although the printing process is completely automatic, the placement and removal of the workpiece still rely on manual operation, which seriously affects the degree of automation. In fact, the automation of the printing machine essentially means the automation of product delivery. As for the transfer printing part, the change is very small. In addition, the countermeasures adopted by the vast majority of production companies when quality problems occur in printing are not perfect. It is such a printing machine that faces many challenges in order to complete a truly automated printing. In the future, the development of printing must be oriented toward automation, intelligence, specialization, and multi-functional combination. This is the fundamental way to increase production efficiency, stabilize print quality, and reduce costs. It is also the future of labor-intensive printing. The inevitable requirement for the transformation of technology-intensive industries. Therefore, increasing the automation of printing machines and producing intelligent multi-function printing machines will be the future direction of development. In the printing of new technologies, the infiltration of other printed high technologies has brought new inspiration and new ideas to the printing technology. Although general-purpose, multi-functional automatic pad printers are relatively rare at present, automatic pad printing machines targeting specific products still give people many surprises. For example, full-automatic pad printing machines that print CDs and printing bottle caps. Automatic printing machine. In addition, pad printers with a variety of special functions and applications have been put into production and application. For example, (1) Pad printers. Any printing process faces both sheet-fed and web-fed paper feed methods. Pad printing technology is the only technology that does not integrate with paper printing, let alone printing web. Although the reason why the pad printing process has no advantage in terms of paper is due to the fact that the paper format is too large, there is still an advantage in the use of a pad printing process for a type of printing such as conventional adhesive paper. Because it does not have the technical problems of paper printing, its printing area is very small. Compared with resin-type adhesive printing presses, printing roll paper is less difficult to manufacture, and the operation is more convenient and the machine price is lower. From a technical point of view, since screen printing can be applied to the printing of webs, there should be no problem with pad printing for web printing. At present, some manufacturers are already working on the development of this monochrome web printing machine. It is estimated that products will be available soon. (2) Multi-function pad printer with cleaning device. Japan first installed a plastic head cleaning device on the pad printing machine to improve the printing quality. In the printing process, since the ink on the surface of the plastic head cannot be completely transferred to the printed product, the remaining ink gradually changes the edge of the graphic trace on the surface of the plastic head, causing the sharpness to decrease. The solution to this problem is mainly to improve the deinking ability of the plastic head and install a plastic head cleaning device. To improve the deinking ability of the rubber head, it is necessary to study and improve the performance of the printing head. This should be the content of the material research. The installation of plastic head cleaning device is to add new functions to the printing machine. The pad printing machine equipped with a plastic head cleaning device is more common than the ordinary pad printing machine