Control of the Exposure Process of Flexographic Plates to Printing Plates (Part 2)

How can a printing company differentiate itself from others, satisfy customers, and make profits? With the advent of digital printing, the pioneers of the printing industry have begun to optimize this market and will use this paper as another way to get more profit. Once a new type of product emerges in this industry, the corresponding consumption of copy paper can quickly increase. As long as business is wise, sales and profits can be increased. Some companies have succeeded in providing their customers with various grades of paper. They found that the paper was good and the printing quality was also better. They always try their best to sell more high-quality papers, because more sales will have more profits. For a printing factory, if you have a very friendly relationship with your customers, when customers need to increase sales, they will also solicit your opinions and make you a strategic partner. This very good relationship is based on the quality of printing. Paper, on the other hand, is a very important part of the printing process that affects print quality. Paper is no longer just a commodity Until now, paper has always been seen as a commodity in the copy-related market—prices are the only factor that distinguishes them. Before digital development, black and white copy paper was a very marketable product. Because black-and-white printing requires less than color printing, most paper is suitable, and the cheapest copy paper is very popular. So, for printers, distributors and manufacturers, profits are low. In fact, even those successful device manufacturers have overlooked a potential channel for earning money, that is, using quality paper can help the machine to achieve higher profits. If printers see paper as an unprofitable business, they only focus on obtaining a steady increase in output. In this way, production can produce a large-scale production effect, and it becomes the main source of profit. So, getting profit from paper is less important. The emergence of color reproduction technology is a revolution in the printing industry. Digital or short-run color printing requires the re-evaluation of various factors. The shift of the hue from the film to the printing plate is influenced by many factors. The basic parameters of these significant factors are analyzed in this section. The use of a film plate requires a proprietary, matt film. Film A serves as a direct negative image, and films B and C serve as a contact negative image. From the film, we can see that the shoulders of the outlets are slightly different. Because when the resin plate is exposed, there are more requirements than the other plates. In order to achieve high quality printing results, special parameters must be used to control the exposure process. The surface features of Yin pictures are very important. If there is a bubble between the plate and the film, and cannot be ruled out, it will result in poor contact. In order to minimize this effect, film manufacturers have a deliberate roughness requirement for their products. In the long-term exposure process, in order to prevent UV light penetration, the density in the field should not be less than 4.0. To prevent exposure of the image on the plate, the maximum background haze does not exceed 0.4. The photosensitive resin plate is composed of a peeling layer, a polyester-based layer, a photopolymer layer, and a protective layer. The polyester base is to a certain extent to ensure the stability of the plate size; the photosensitive layer includes a photoinitiator, a stabilizer, and a tackifier. Mixtures, synthetic rubbers and colorants, these factors affect the thickness of the plate, hardness and exposure speed, this layer contains the image from the overcast image; the isolation layer is to prevent pressure and Thermal effect, Yin pictures stick to the plate. During development, this layer dissolves; the non-gloss polyester protective layer is designed to prevent the surface of the plate from being scratched, oxidized, and ash removed before the main exposure process. There are many types of plates, and different plates have different uses. Some plates are designed for use with specific ink systems or provide specific printed images. If they are not used for the printing process, they do not have to be considered for similar tests. The traditional plate thickness is 1.14mm, 1.70mm, 2.54mm, 2.84mm. These plates have good tone transfer stability and strength. For better analysis of these characteristics, 1.14 mm and 2.84 mm plates are used. Of course, the influence of plate thickness in the process of tone shifting should also be considered. In addition, consider printing plates with different surface roughness. Both plates have higher surface roughness. This has the problem of the effect of different surface and plate composition on the tone shift. Exposure time All plates are exposed twice. First, the plate is exposed on the back without a negative picture to obtain a certain degree of convexity. Then, the main exposure is performed by the negative image to form a relief image. The developed and dried plates are post-exposed to enhance the strength of the non-connected parts. Post-production reduces the plate's viscosity. Each plate must be examined after exposure. When the number of developments and exposures had no effect on the dots, the experiment did not need to be further. The plate manufacturer agreed that the test is to test half of the halftone area of ​​the exposure limit in the negative image. In order to control and determine the exposure time, it is recommended that for each printing plate, the halftone edge or no tone zone, and the virtual edge dot drop to zero, should be taken into account. In addition, the bottom ash of the fat sheet must be measured because the higher the bottom ash, the longer the exposure time. During the tone transfer process, the upper and lower limits of the exposure limit can be clearly obtained through comparative measurement. The parameters of the exposure apparatus device also have a very important influence on the hue, and the temperature in different areas of the exposure apparatus is not the same. If the device has no temperature control, the temperature in the external area of ​​the device is lower than the temperature in the central area. Since the polymerization reaction is temperature dependent, it is important to understand the effect of temperature on the hue shift. Due to the different working hours of the exposure device, even with the same fluorescent lamp, different light intensity may occur. How big these differences are and how much they affect the color shift must be clear in the experimental project. Test Measure Evaluation In this experiment, almost 200,000 measurement data were obtained. On the film and plate, ten specified dot values ​​were read each time according to length, width, circumference, smoothness, and surface conditions. The result of the measurement is obtained based on the measured parameter. Film evaluation must be measured with a transmission densitometer before exposure. Two hundred Times the microscope was used to measure the tiny dot values ​​on the film and plate. You can see 4% of the dot on the film, the size and shape will be different. This is due to the fact that the dots on the film are all composed of pixels. In order to avoid the moiré phenomenon caused by the dots at different angles, it is difficult for the dots to look round. In this way, there will be some problems in the process of replication, because non-circular points are difficult to copy 1:1. The microscopic image of the film can see some small, matt, small particles that are transferred to the plate during replication. They are usually 5-10 μm wide and may affect the printing process. Because the particles themselves are transparent, they will be penetrated by enough diffusely reflected light during the exposure process due to the occurrence of glueing. Different films have this phenomenon for each type of plate. Although the results obtained do not indicate its effect on the color shift, it is recommended to use contact exposure. All three photos meet the maximum density requirement of 4.0. However, the fog on the three types of film clearly exceeds 0.04, which means that a longer exposure time is required, affecting the color shift. In the report, all measurements were recorded in detail. As a result, the relevant changes in the outlet areas of the report are very important parts. Measurements of smoothness and equivalent radius are also recorded for reference by interested parties. Plate Evaluation In general, dots A and B have the smallest dot gain, although dot sharpness is large, which is due to the chemical composition of the plate and different surface characteristics. We have not yet been able to confirm that thinner printing plates have better contact characteristics than thick printing plates because both have better printing results, which seems to be due to the internal reflection of the resin layer. The final result is the use of film B and plate A. Both surfaces are the smoothest. Therefore, they can be better contacted with each other during exposure. The surfaces of plates C and D are rough. When there is no uncontrollable reflection on the surface of the plate in contact with the film, the best reproduction effect can be obtained. Exposure time evaluation At a predetermined exposure, only a small amount of hue change occurs. The lower exposure limits of the two versions are based on the stability of the 2% mesh screen dot at 122 lpi. The main exposure time must be long enough to ensure that the relief image thickness provides a stable base for halftone images. At relatively low exposures, the shoulder angles of the two plates are very similar. However, there will be differences in the color shift. After multiple exposures, the hue on one of the plates increases or may be larger or smaller, but the value of the other plate may be higher. Moreover, if the exposure time is longer, the sharpness of the plate will be higher, but some spots will appear at the edge of the dot, and if the tone value is small, the exposure time should be smaller. There may be variations in the mid-tone and shoulder angles, but the criteria for the exposure of the printing plate is such that it does not affect the print quality. Exposure Device Evaluation In order to confirm the influence of the exposure device, we chose film D. Because the plate thickness has no direct influence on the halftone dot, the highlight area of ​​the 1.14 mm thick plate is selected as the evaluation zone. The change in this area is very obvious. Two kinds of exposure devices were used in the experiment: the exposure device X had no temperature control system, and its back was cooled with air; the exposure device Y was equipped with a temperature control system to ensure a continuous stable temperature. The temperature of the Y device usually has a variation of four degrees Celsius up and down, while the X exposure device has a fluctuation of eight degrees Celsius. For each exposure device, exposure was done on a 760 x 1016 mm layout containing 5 test negatives, with the critical highlight area on the edge. Following the general rules of the industry, experiments were conducted using moderate exposure times. Because the effect of exposure temperature is very important, and the result is only related to the amount of light. The test results are listed in detail in this section of the report. The highlight area is the most critical area. If the exposure box temperature is too low, you may not get the smallest printing dot. The amount of light has a greater effect on the polymerization than temperature. Three development devices (P, Q, R) were selected for the development evaluation experiment. Because no water-washed version is used in this project, all developing devices use solvents. In different developing devices, there is no noticeable change in the hue value. Conclusion The purpose of all experiments is to illustrate the problem of the color shift accuracy from film to plate in the printing process, and how the exposure process affects the transfer of tones. The exposure data shows that for all tone values, the change in film using different grades is basically the same. Plates A, B change much less than plates C, D. In the experiment process, we used a very high-precision test method, so it is effective for the transmission accuracy of the highlight region. In the midtones and dark areas, there are larger dot changes. These changes may be caused by the matt layer of the negative film and the surface and processing of each plate. Because of the different surface roughness of the Yin picture and the plate, there are different reflections. At the same time, the surface of the plate is affected by the development. These factors may have caused changes in the midtone region. When comparing the exposure limits, the upper exposure time may cause greater variations depending on the film and plate used. If the mesh of the highlight area is lower than this value, there will be problems. Therefore, we must pay strict attention to the size of the highlights to avoid color changes. Exposure devices also produce different color changes. Irregular temperatures and light levels can cause irregular tone changes. When making a relatively large printing plate, it is necessary to maintain the exposure device at a regular temperature, thereby ensuring effective color tone transfer. In order to keep the temperature and the amount of light standard and stable, it is preferable to perform temperature control of the exposure device during the operation. At the same time, the intensity of the fluorescent light should be checked regularly. <End>

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