Application of Photoelectric Technology in Packaging and Printing

With the introduction of a series of new technologies such as optical and electronic technologies, packaging and printing technology and equipment have become increasingly advanced. Optoelectronic technology occupies an important position in modern printing and packaging technologies, including automatic packaging machines, electronic plate separation and so on. To discuss the application of electro-optical technology in the field of printing and packaging, this article will discuss the photoelectric detection technology in the packaging control process and the laser technology of printing plate making.

First, the photoelectric detection technology of the packaging process

Photoelectric detection is mainly measured by photoelectric sensors. The working principle of the photoelectric sensor is that the light source generates luminous flux, and the parameters of the luminous flux (such as the cross-sectional area of ​​the radiant energy flow, the spectral composition, and the luminous intensity, etc.) are controlled by the measured object, and then converted by the photoelectric device to be converted into electric parameter changes. measuring. Different light sources such as incandescent lamps, lasers, light emitting diodes, etc. can be used in different working environments. Sometimes the controlled object itself is the signal source, such as the MARK line on the packaging bag.

Because the direct detection signal is generally weak and lacks stability, it is often added to the control circuit to enhance the actual operation ability of the system. The measuring institutions include indicating instruments, alarms, digital displays and product sorting devices. They display product-related measurement values ​​or automatically classify products. Usually, in order to realize automatic adjustment of the production process, the controlled quantity will remain unchanged or be changed according to certain rules (such as automatically adjusting the position of the bag cutting), and a feedback circuit needs to be added in the circuit.
Photoelectric detection system has the advantages of simple structure, long detection distance, high precision, fast response and long service life. There are unique advantages in pattern recognition. It can achieve non-contact detection, no force and moment acting on the measured object, even if the measured object has a larger impact, no damage to the detection instrument. In the same way, some products with higher requirements for packaging processes, such as food and medicines, can be measured using the non-contact feature.

Photoelectric detection circuit consists of electronic components or integrated circuits, low cost, high sensitivity, can achieve rapid measurement, the objectivity of the indicated value, easy to automate. With the development of computer technology and machinery industry, it is possible to achieve a combination of light and machine power, calculation and processing of data, verification, logic judgment, storage, etc., thereby realizing the accuracy of the packaging process and the synchronous supply.

To illustrate the problem, here is an example of the position detection and positioning of the packaging automatic control process:

Due to the shrinking of the radius of the reel and the change of the tension of the wrapping paper during the packaging operation, the friction coefficient between the paper feeding roller and the wrapping paper fluctuates due to the influence of the ambient temperature and humidity, as well as the trademark printing error, and the paper feeding and vertical feeding. Differences such as sealing and cutting cause the actual tangent of the knife roll to deviate from the specified position. Although each time the error is small, due to the long-term accumulation of high-speed operation of the machine, the tangential line must be seriously deviated, the quality of the package must be reduced, and even waste products must be produced. For this reason, it is necessary to add an automatic photoelectric position detection control device in the system.

The photoelectric detection and positioning system uses photoelectric tracking to detect the positioning color mark on the packaging paper. By comparing the error of the feeding speed and the horizontal sealing cutting speed, the corresponding control signal is output, and the actuator is automatically positioned or the error is compensated. For reliable detection, there is a clear difference between the positioning color label and the background color of the wrapper. The greater the contrast, the more sensitive the detection. The color standard requires a clear color, printing ink should be uniform, to occupy a certain area, the general color label is rectangular, length and width should have a suitable proportion. According to the different packaging materials, photoelectric detection can be divided into two types: transmissive and reflective. The transmissive type is used for the detection of transparent materials. The packaging material passes between the emitting head and the reflecting head. Even if the packaging material is pulsing during the feeding process, it will not affect the detection sensitivity and is not easily disturbed by the ambient light. . The reflective type has its emitter head and reflector head in the same direction and requires the converging beam to form a focus on the packaging material or the reflector, so no large runout of the packaging material is allowed when passing through the detection site. According to different packaging forms and packaging requirements, there are different photoelectric detection and positioning devices used in the feeding, bagging and sealing packaging machines.

Second, laser technology in printing plate making

Laser is a new discipline and high technology. Since its birth in the early 60s of the 20th century, lasers have attracted the attention of all countries in the world and developed rapidly. The application scope of lasers has been continuously expanded, and profound changes have taken place in many fields corresponding to them. The printing industry all over the world is actively adopting this new technology as well as other industries. Lasers have applications in electronic plate separation, laser illumination, holographic printing, and so on, and have greatly optimized the printing system. Due to space limitations, this article only discusses the application of laser in plate making. The printing plate is an indispensable part of the printing process. It is the medium that transfers the ink to the substrate. The quality of the printing plate is directly related to the quality of the printing product. The printing industry has been working hard to improve the plate making process in order to achieve the best Produce printing plates at the best possible speed while reducing labor intensity and plate-making costs. Previously, the production of gravure, embossed, and offset printing plates relied mainly on manual, mechanical, chemical etching, and electrical energy photographic techniques. However, these methods had shortcomings such as lack of operational stability and long plate-making time. These problems were resolved after the birth of lasers. With the use of laser's high intensity, high coherence and monochromaticity, plates can be produced quickly and reliably.

The laser engraving plate is to shoot the focused laser beam to the plate, melt the specified range of the plate, and then remove unnecessary parts to make convex and concave images. The shape, size and size of the image can be modulated by the electrons. control. In general, plate-making materials (including ceramics) are melted or vaporized when the power density of the laser reaches 10-lOw/cm, and the power density value obtained at the focal point is much larger when the medium-intensity laser beam is focused by the lens. At the above values, the laser is more suitable for engraving plates. Due to its characteristics of monochromaticity, high energy, and good coherence, lasers have shown strong advantages in engraving and platemaking. The development and application of modern violet laser technology have made the printing plate more perfect. The high intensity of the laser not only melt etched non-metallic materials (such as imaging film, photosensitive resin plates, plastic plates, etc.), but also melted metallic materials (nickel, lead, steel, chromium, etc.). Even ceramic rolls with high refractoriness can be etched, and the etching range is much broader than with other methods. Laser plate speed and good quality. Generally, the engraved time is about 3 minutes. If the violet laser technology with shorter wavelength is used, the time will be shorter, and the resolution can be improved to ensure the quality of the outlets. Due to its good coherence and energy concentration, the laser has high engraving efficiency and low total energy consumption. Laser plate making is not perfect, and the problem is that the effect of direct laser engraving of metal is not good. The laser etching of the ink hole is not smooth and burr, while the metal surface of the laser reflection effect, only the use of high-power laser engraving. The general solution to this problem is to put a resin or plastic sleeve over the metal drum. The laser is not directly engraved on the metal plate. The laser technology in the modern plate making industry is mainly reflected in the CTP technology and the violet laser technology.

Third, the conclusion

Photoelectric detection technology and laser technology can all be attributed to the photoelectric technology category. The emergence and development of modern new technologies and new equipment are no longer the development of a single discipline, but rather the result of mutual penetration and complementarity between multiple disciplines. Optoelectronics technology in printing and packaging is an integrated technology developed based on theories of optics, electronics, atomic physics, quantum mechanics, etc., based on the theory of information, control and systems, and their development will certainly give printing and packaging industry. Bring good economic and social benefits.