As we all know, the uniformity of ink is an important indicator for evaluating the quality of printed matter. The cause of uneven ink is related to many factors. For example: the original version, printing version, operator skill level, management level, materials, etc.
The original version is divided into two kinds of film and sulfuric acid paper, if their own density is not uniform, the thickness of the line is different, the ink color of the printed product will be mixed. In particular, the user requires the use of sulfuric acid paper for the sake of cost saving. On the sulfate paper, the text lines are composed of dots. The adsorptivity is poor, the obtained density is low, and the printed text lines are of different thicknesses. Each page exists from the top of the sky. To the ground, the phenomenon of gross fineness is different, and there is a difference between each page and each page. It is surely that the prints are different in intensity. Therefore, be sure to check the film carefully before making it. Don't have the above quality problems.
The quality of printing depends mainly on the close cooperation between plate making and printing. Without high-quality printing plates, it is impossible to print high-quality products. Therefore, pay attention to the following points when printing, in order to ensure uniform product ink.
1) Most printing plants now use recycled PS plates. The recycled PS plates are processed by a series of processes such as leveling, cleaning, chemical treatment, electrolytic oxidation, and drying coating. Some PS plates have high sensitivity, rapid development, and easy inking, while some PS plates have poor ink. Therefore, in the selection of the PS version, the defects such as horseshoe print, white spots, severe scratches, uneven thickness, and uneven mesh should all be screened out. The same batch of plates with uniform thickness, the same coating color, high printing rate, and large tolerance should be used for printing.
2) The vacuum pumping of the printing machine must be thorough. If the pumping is poor, due to the scattering of light, the layout graphic deformation may occur.
3) Exposure is an important part of the printing. Iodine lamp is used as the light source. The distance between the light source and the layout should be equal to or slightly larger than the length of the faceplate. The light must be directed to the plate so that the illumination of the plate is even.
4) When developing manually, pay attention to the development time and developer concentration of each plate. The development time is long, the fine dots on the layout are easily deformed or lost; the developer concentration is too high, the stronger the alkalinity, the faster the development, the easier the over-development of the printing plate, resulting in a reduced textural deformation, no light sensitive layer Soluble quickly, so that the performance of fat decreased; the other hand, the developer concentration is too low, too slow development, easy to cause lack of development, dot expansion. Therefore, the developer for fatigue should be replaced in time. Otherwise, the non-image part of the printing plate can not be fully dissolved, and the lipophilicity of each plate is not the same. Usually, replace the developer with more than 40 plates or adjust the pH of the developer in time.
5) Do not take too long to modify the picture, PS version to avoid light preservation, or else it will cause a second exposure, affecting the layout of the oleophilic.
Printing is an important part of ensuring the uniformity of ink color, and it is also a process with strong technical requirements. Not only does the operator have to have a certain level of expertise and adjust the machine's skills, but it also requires extensive experience. To ensure the uniformity of ink should be considered from the following aspects.
1) Printing pressure
Printing is inseparable from pressure. In offset printing, the source of pressure is the elastic blanket, followed by the pressure between the three rollers, between the ink roller and the ink roller, between the ink roller and the printing plate, and between the water roller and the water roller. The pressure between the water roller and the plate. They influence each other and jointly determine the amount of ink transferred from the printing plate to the printed matter and the quality of the printed matter.
1 Between the ink roller and the ink roller, the pressure between the ink roller and the plate is generally adjusted with a thick gauge. Use the ink bar to check whether the ink roller is in contact with the plate. If it is improperly adjusted or the ink picking time of the ink roller is unsuitable, there will be ink bars, dark before or after the front, dark, ghosting, and flower patterns. The rollers are prone to heat aging, causing the surface to harden, crack, and fall off, affecting the transfer of ink to the plate. Therefore, in the printing process should be replaced in time aging, hardening, cracking, shedding, uneven ink roller, so that the ink can be transferred well, the ink uniformity is guaranteed.
2 The pressure between the water roller and the water roller, between the water roller and the plate is not regulated by the thickness gauge, and the pressure regulation between them also directly affects the uniformity of the ink color of the product. If it is improperly adjusted, it will also cause water plume, paste plate, dirty, floral plate, ink emulsification and other phenomena. The well-adjusted water roller should be non-ink-returned to the surface of the water roller to maintain good hydrophilicity, water transfer, and provide uniform and stable water supply to the printing plate.
3 The blanket plays a role in accepting and delivering a certain thickness of the ink film during the process of copying the image, which requires it to be easy to ink and to transfer the ink well. A long time for the blanket may cause stickiness, harden, deterioration of elasticity, deterioration of mechanical properties, and affect its lipophilicity and ink transfer performance. Therefore, in the use of the process, should choose a good performance blanket and use it properly, usually pay attention to the maintenance of the blanket, to extend its life, to ensure its uniformity of the transfer of ink.
4 The pressure between the three rollers is measured with a micrometer after pressing the fuse. Improper adjustment will cause the roller to slip, which will increase the friction of the printing plate, resulting in a flower version. At the same time, it will cause image ghosting, too small imprinting void and so on.
2) Ink balance
Offset can not be separated from water and oil, both too much or too little will bring trouble to production, and only if the two maintain a relative balance, can the ink remain relatively stable in printing. The following factors affect the factors of ink-ink imbalance.
1 printing speed. Printers all know that the speed increases, the water volume increases, the ink transfer rate decreases, the speed decreases, the ink transfer time increases, and the amount of ink increases. It takes a few hundred sheets of paper to reach a new balance. Therefore, the printing speed should be kept stable during the printing process.
2 ink additives. In the printing process, in order to facilitate the smooth force of the printing process, a certain amount of ink additive is added to overcome the problems caused by the excessive viscosity of the ink, and the addition of the ink additive also affects the uniformity of the ink color. The more additives, the thinner the ink, and the insufficient amount of ink transferred to the printing plate and the paper; otherwise, the more ink is transferred. Now most of the projects need to be completed by several machines. The proportion of the additives added to each machine should be the same, so that the amount of ink additives added can be digitized.
3 press idle. Temporary shutdown occurs during the printing process. Usually, the paper feed is stopped, the water roller is still running, the water roller continues to transmit the water bucket solution to the plate, but the water transfer roller stops automatically due to the paper feeding stop. The water on the roller is also reduced accordingly, and the viscosity of the ink is correspondingly increased during idling. At this point, printing, the first few sheets of ink become darker, and after printing more than a dozen sheets of ink, it will be smooth. Therefore, make preparations before printing to minimize downtime.
4 Scrub plates. When the printing plate is scrubbed, the water of the plate is the most, and the viscosity of the ink is affected by the water. After the blanket is washed, the amount of the ink slowly increases, and it is not until the dozens of sheets have reached equilibrium. Therefore, when the printing machine is started, excessive water should not be applied to the printing plate to wet the printing plate, reducing the number of times of washing the blanket.
5 During the printing process, the water rollers will become more and more dirty, and more and more inks will be attached, which will reduce the water received from the water transfer roller and cause the ink and ink to be unbalanced. The temperature is low and the ink is "hard". The ink transfer is difficult. The ink can be balanced after the machine has been running for a certain period of time.
1Before printing, a sample must be taken. It is the key to ensure that the print ink is uniform and other quality indicators meet the requirements. Without proofs, the machines cannot be printed. In the printing process, it is necessary to do three tasks, namely, diligence and proof control, diligent mixing of ink and control of water. Keep batches of product ink uniform and stable.
2 In the printing process, ink is not uniform due to mechanical reasons, such as the uneven rolling force of the back-rolling teeth and the chain teeth, and the ghosting caused by the paper's throwing angle, which is reflected in the printing ink.
3 In the case of this edition of the book, which is side-by-side with pictures and texts, the number of prints is small, and the number of prints is large. It is still more time-tested for operators to keep the ink even between each printed sheet and printed sheets and printed sheets. Due to the different pattern positions, the amount of ink needed for the pattern is different. It is often just the end of the printing process. In order to maintain the stability of the ink, the printing plates should be categorized first and the pattern should be printed in the same position to avoid repeated adjustments of the teeth. Secondly, after the printing plate is placed on the machine, the ink should be adjusted according to the pattern. The amount of ink is adjusted according to the proofs. In this process, the overprinted papers have to be put a little more. When the gauges are played, there is no change in the ink color; when the inks are adjusted, the small teeth are opened and the large gears are opened. .
4 When the semi-finished products are inspected, they will be sampled against the proofs, and the ink sheets that do not meet the requirements and the differences will be removed. The uniformity of the ink in the books and periodicals will be maintained as much as possible.
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