How to allocate anilox roller to flexo printing machine
Most printed products have solid ground, lines, and continuous tone images. In order to meet the needs of various printed products, users must not adopt the method of installing several anilox rollers with several printing units on the flexo printing machine. Take the narrow-width unit type flexo printing machine as an example. At present, most of the domestic introductions are 6 + 1 type, that is, 6 color groups are designed for multi-color printing. The last unit can be used for printing and UV coating.
We recommend that for prints up to 150 lines, this 6 + 1 flexo printing machine should be equipped with 9 anilox rollers. Among them, four 700 lines, an ink layer thickness of 2.3BCM (1 billion cubic micrometers / inch), an anilox roller of 60 ° is used for gradation printing? 3 360 ~ 400 lines, BCM6.0, 60 ° anilox The roller is used for solid plate printing? 2 200 lines, around BCM15, 60 ° anilox roller is used for gold printing and glazing. If you use water-based gloss oil, you should choose 360 ​​line anilox roller, so that the oil layer is slightly thinner, and will not affect the printing speed due to the problem of drying of the gloss oil. Water-based gloss oil does not have the special smell of UV gloss oil. The position of the anilox roller during printing can be determined after testing and comparison. The thickness of the ink layer that the operator can observe during the test mainly depends on the number of lines and the BCM value of the anilox roller.
What problems should be paid attention to during the use of anilox roller
The anilox roller we mentioned here refers to the laser engraved ceramic anilox roller. It is a high temperature and wear resistant coating material in aviation and aerospace. It is used according to a certain density, depth and a certain angle and shape. Laser engraved. This anilox roller is characterized by high cost and wear resistance. If used properly, its life can be up to several years. If not used properly, not only will the life be shortened, but also the anilox roller will be scrapped.
In the use process, the position of a certain anilox roller on the printing machine depends on the specific print. Different prints have different positions of the anilox roller, so the anilox roller is often replaced during printing. At present, most of the narrow-width machines are solid steel anilox rollers, which are very heavy. When installing the anilox roller, care should be taken to avoid touching the surface cover of the anilox roller with other metal objects. Because the ceramic coating is very thin, it is easy to cause permanent damage after collision. In the process of printing and cleaning the machine, the ink should be prevented from drying on the anilox roller. The special detergent recommended by the water-based ink manufacturer should be used. The brush should be cleaned with a stainless steel brush to ensure clean and thorough cleaning. And develop the habit of frequently using high magnifying glass to observe the anilox roller net hole. Once the ink is found to deposit on the bottom of the net hole and there is a trend of increasing gradually, it should be cleaned in time. If the above method does not work, it can be treated by ultrasonic or sandblasting, but it must be carried out under the guidance of the anilox roll manufacturer.
Under normal conditions of use and maintenance, there is no need to worry about the wear of the anilox roller. The parts that are easy to wear in the ink transfer system are mainly squeegee blades. In contrast, the wear of the anilox roller ceramic coating can be said to be minimal. After the anilox roller is slightly worn, the ink layer will become thinner.
What's going on
As everyone knows, flexographic printing has a phenomenon of unidirectional elongation along the direction of printing paper. The proportion of elongation is related to two factors, one is the diameter of the plate cylinder (including double-sided tape), and the other is The thickness of the version itself. The larger the diameter of the plate cylinder, the smaller the plate thickness and the smaller the elongation. One concept that needs to be clarified here is that the elongation phenomenon is not caused by pressure during printing. In fact, the elongation deformation has occurred when the flexible printing plate is adhered to the plate cylinder through double-sided adhesive. Therefore, when designing the ink drawing, it is necessary to reduce the size, and the ratio is obtained by looking up the table according to the actual thickness of the plate and the actual printing length. If computer-based plate making is used, it is only necessary to give a one-way reduced version instruction before designing the ink image color separation. If you use hand-made film, you need to use a deformation machine, you can also get a scaled film.
What is the relationship between the number of printing screen lines and the number of screen lines of the anilox roller
In many articles introducing flexo printing technology? X, the ratio of the number of printing screen lines to the number of screen lines of the anilox roller is set to 1: 3.5 or 1: 4. Based on practical experience and analysis of the award-winning products evaluated by the American Flexo Printing Technology? X Association (FTA) in recent years, the author believes that this value should be higher, about 1: 4.5 or 1: 5, for individual fine For printed products, this ratio may be even higher. The reason is that the most difficult problem to solve when printing a gradation plate with a flexographic printing machine is dot expansion. Selecting an anilox roller with a higher number of screen lines, the ink layer is thinner, and the dot expansion deformation is easier to control. If the ink color is not strong enough during printing, a water-based ink with higher color density can be selected to ensure the quality of the printed product.
How to design a flexographic ink map for easy overprinting
In the printing process, one of the key indicators that people often pay attention to is overprinting, because waste products caused by inaccurate overprinting often account for a large proportion of all waste products. Although the flexographic printing machine manufacturers have provided a good basis for accurate overprinting in the design and processing process, and the automatic monitoring system has also provided a guarantee for accurate overprinting, but the operator's skills? X level and proficiency are also very important for the accuracy of overprinting Big impact. If you can make some adjustments for the convenience of overprinting when designing ink drawings, you can greatly reduce the difficulty of printing and reduce the rate of waste. The easiest way is to use reverse white characters when designing the original ink manuscript, or hollow out between the two colors to form a reverse white outline, or you can cover the third slightly thicker at the edges of the two colors overprint Dark contour lines, for the printing of finer prints, can use trapping (Trapping) technology? X, the amount of trapping depends on the accuracy of the printing press, the quality of the paper used for printing and the level of the operator. Trap processing is easy to implement on a calculator. If there is no calculator, only the ready-made dichroic film, you can use a special trapping processor (TrappingModifier), enter the amount of trapping amount, the machine will automatically generate a trap Printed film. If there is no trapping processor, you can put a transparent spacer between the color separation film and the copy film and expose it with a single point light source copy machine, and you can also get a film with a similar effect.
What are the requirements for the type of film to produce flexo
When placing the flexographic plate on the front of the plate-making machine for exposure, in order to ensure the quality of the film and the flexographic printing surface, the plate-making machine is equipped with a vacuum pump to evacuate, and the side of the film near the flexo must be rough (matte), This can prevent air bubbles remaining between the film and the flexo plate and affect the quality of the flexographic printing surface. The pressure bar used to press the edge of the film and the flexo plate should also be one with indentation and lateral air conduction. In addition, there are specific requirements for the blackness and transparency of the film.
How to make high-quality online version and field version on one printing plate at the same time
Generally speaking, when the printing unit of the flexo printing machine is sufficient, the screen version and the solid version of the same color should be divided into two productions, because the screen version requires a thinner layer of ink, while the field and line version need to be thicker Ink layer. However, in some special cases, it is necessary to print the same color of the network cable and the solid image on the same plate. In this case, on the one hand, when printing, the selection of the anilox roller has to be compromised. Usually, the printing requirements of the stencil are first met, at the expense of the thickness of the solid ink layer. On the other hand, when making a plate, Master different exposure times to ensure the quality of the Internet and field parts of the same printing plate. The difference between the screen image part and the field part is mainly the depth of corrosion. If the screen part is to "stand" during the process of scrubbing the printing plate, it needs to have a strong foundation, so the corrosion depth is shallower. Different etching depths can be obtained with different back exposure time by covering the local method. The front exposure time should also be done in a similar way, but it is said that the current flexographic plate manufacturer has introduced a new type of flexographic plate. Regardless of whether the printed part is a screen or a field, this plate requires only a uniform front exposure Time, avoiding the trouble of multiple exposures, making flexo plate making more convenient.
Why the rubber roller is easy to wear
The rubber inking roller is driven by the gear of the anilox roller, which has two functions. One is to move the ink from the ink tray to the ink transfer system. The second is to "rub" the excess ink and leave it on the anilox roller. A relatively uniform layer of ink, but its effect is far less than that of a reverse doctor blade. Regardless of whether the machine is printing or not, once ink is filled in the ink tray, the rubber ink roller and anilox roller should start to rotate continuously. However, once there is no ink or water between the two rollers, that is, in the case of complete drying, it should be absolutely avoided that the two rollers rotate when the surfaces are in contact. Although the surface of the two rollers are in contact, the linear speed of the surface is different. The linear speed of the surface of the rubber roller is slightly lower than that of the anilox roller, so the excess ink will be "rubbed" and the ink acts as Lubricant between the two rollers. In the absence of water or ink between the two rollers, if the two rollers contact and rotate, the hard skin of the rubber roller will be worn out in a very short period of time, and then the degree of damage will increase, making the entire rubber ink roller scrapped. Therefore, it should be remembered that rubber rollers and ceramic anilox rollers cannot be "dried".
What you should pay attention to when using a doctor blade
Whether to use the doctor blade in the ink transfer system is optional. For rough field printing or UV coating, there is no need to use the doctor blade, just adjust the pressure between the rubber ink roller and the anilox roller. You can get a substantially uniform ink layer. For the printing of general printing products, the doctor blade should be used. At this time, the pressure between the rubber roller and the anilox roller should be smaller, to ensure that enough ink hits the blade edge uniformly, so that behind the doctor blade In order to get a uniform ink layer. In addition, the screws on the doctor blade holder should be carefully adjusted. The screws can change the contact pressure between the doctor blade and the surface of the anilox roller. If the above method does not work, that is, a smooth and uniform ink layer is still not available, you can check the blade of the doctor blade to see if it is physically damaged or unhealthy. It may also be that the screw fixing the doctor blade holder is loose, causing the blade and the net The axis of the pattern roller is not parallel. Don't scrap scrapers with small defects easily, you can run them in other spare printing units, and use them after the defects are removed. An squeegee can continue to be used even if it wears off a few millimeters in its lifetime.
How to understand the flexographic plate making in general
At present, the flexographic plates introduced in China are basically solid photosensitive resin plates, and the thickness of the plates is selected according to the requirements of flexographic printing machines. The common plate thickness is 1.70 mm and 2.29 mm. The flexographic plate making is the process of transferring pictures and texts to the printing plate through negative film, which mainly includes the following procedures:
(1) Expose the plate with ultraviolet light. Its function is to determine the height of the relief on the plate, that is, the depth of corrosion, and to solidify the substrate.
(2) Expose the printing plate together with the film under ultraviolet light to form the image printed part on the printing plate and cure it.
(3) The printing plate is placed in a solvent and brushed, the purpose is to brush away the unexposed part of the plate, so that the graphic part forms a relief.
(4) Place the printing plate in a dryer to dry, so as to prompt the solvent absorbed in the plate material to evaporate as soon as possible, and restore the thickness of the printing plate to the original standard value.
(5) Post-exposure and debonding treatment of the dried plate material can further solidify the shoulder and base, and improve the printing performance of the flexible plate. The high-quality flexographic printing plate should have a print resistance rate greater than 500,000 prints, or even as high as 1 million prints.
How to calculate the shrinkage of flexo film
The amount of shrinkage is only related to the diameter of the plate cylinder (including double-sided tape and plate material) and the thickness of the plate material itself. Here is a formula for calculating the amount of film shrinkage (percentage) when making a flexographic plate by plane exposure: Shrinkage (percentage) = K / Rx100%. In the formula, the coefficient K depends on the thickness of the plate used. When the thickness is 1.70 mm, K = 9.89 mm? And when the thickness is 2.29 mm, K = 13.56 mm. R is the printing length of the plate cylinder in mm. If the printing length of a product is R = 235 mm, the thickness of the plate is 1.70 mm, and K = 9.89 mm, the amount of shrinkage = 9.89 / 235x100% = 4.21%. When the design ink draft is out of the film, it should be longitudinally reduced according to the above ratio, and then made by plate exposure, so that the printed product will meet the size requirements. It needs to be further explained that when analyzing and estimating in actual production, the printing length The determination of R needs to consider various factors, such as when the plate cylinder gear module is 1/8 inch, the printing length can only be increased or decreased in 3.175 mm steps? Other factors include reducing the paper consumption and leaving the sticky version The margin, and the limitations of processing indentation die-cutting tools, etc.
How to do a back exposure test
We can first determine the back exposure time suitable for different corrosion depths by doing a back exposure test on the plate-making machine. In order to facilitate comparison, we adopt the method of performing multiple exposures on the same plate with different exposure times. Take a plate with a size of about 320 mm long and 100 mm wide. When performing back exposure on the plate-making machine, we use a red masking strip to perform partial partial masking. The plate-making machine is exposed multiple times, resulting in five different back exposure times Plate of the area. In addition, a blank of about 20 mm should be left at one end of the plate for the plate washer to hold. Suppose we chose the AV-500 combined plate-making machine made in the Netherlands and GRACE company's flexible plate with a thickness of 1.70 mm. After partial covering and multiple exposures, on the same printing plate we get exposure times of 0, The five parts of 15, 20, 25, 30 seconds, after exposure, put on the drum of the printing plate to wash the plate, about 7 minutes. Then dry in a drying oven at a temperature of 50. c, the time is 1.5 hours. Finally, take out the printing plate and use calipers to measure the four different thickness values ​​of the printing plate, while the unexposed part of the printing plate is left with a hard polyester plate.
Through the above test, you can quickly become familiar with the plate-making machine, and its test results are also of guiding significance for adjusting the corrosion depth of the printing plate. From the above experiments, it can be seen that the length of the back exposure time will affect the thickness of the plate base. Therefore, for different printed graphics, different back exposure times should also be used when making a plate. Still taking the 1.70 mm thick flexible plate as an example, the highlights and large solid parts on the printing plate have a deeper corrosion depth (that is, the plate is thinner), which can reach about 1.0 mm, and the back exposure time is the shortest? The corrosion depth of the ordinary graphics is about 0.85 mm, and the back exposure time is moderate. As for the small lines and dots, the corrosion depth should be the shallowest, about 0.63 mm, so the back exposure time needs the longest. .
In addition, there are two points worth noting: when the printer switches to another thickness of flexographic version or another brand of flexographic version, the back exposure test must be repeated. As the use time of the ultraviolet lamp is extended, the light intensity will be reduced, and the back exposure time should be adjusted accordingly.
How to do a positive exposure test
Front exposure is also called main exposure, which forms the graphic printing part of the flexographic version. Appropriate positive exposure and back exposure work together to obtain high-quality printing plates that meet the requirements of various graphic types. Generally speaking, underexposure will cause the bottom of the shoulders around the image to be washed away, affecting the service life of the printing plate. Excessive positive exposure will cause insufficient corrosion, which can easily cause paste and cause waste products during printing.
Before conducting the front exposure test, we recommend that the operator prepare a test "sample" specifically for the production of flexographic plates. The "sample" should contain small highlights, ordinary highlights and solids, ordinary graphics, and small The basic types of printed graphics such as lines, characters, and dots, and reflect a certain number of screen lines (such as 150lpi) from 10% high to 100% on the ground are reflected on the "sample".
The positive exposure test can be carried out by using "samples" on the plate-making machine through partial masking and multiple exposures. In the early stage, you can start with a less difficult business, from easy to difficult, accumulate experience, and fully master the technology of flexible version X. Theoretically, the finer the picture and text, the longer the positive exposure time, but keep in mind the common effect of it and the back exposure. For example, inverse characters require less back exposure and front exposure, while the small dots require a shorter depth of corrosion, so it takes longer time for back exposure and front exposure.
After a long time of exploration and practice, the plate-making operator should understand the limits of his plate-making, such as the thinnest lines, the smallest characters, the densest dots, and whether 3% of the dots can "stop", and whether 50% of the dots are highlighted "Open up" and so on.
What should be paid attention to after washing and drying
As the number of solvents used increases, the time for scrubbing the plates should be properly extended. The position between the fine brush and the plate drum should be adjusted according to different plates, so as to adjust the pressure of the fine brush and the plate surface. The dots should be based on the standard thickness position to further reduce the pressure of the fine brush to prevent the dots from being washed away.
The drying temperature is about 50. c. The time is about 1.5 ~ 2 hours? It should be taken out several times during the drying process. Check the surface of the plate for solvent spots or other defects. You can use a clean cloth that does not lose fibers. Soak some fresh solvent and wipe gently. The surface of the plate is then put back in the drying oven to continue drying.
Plates after post-exposure and debonding can greatly improve printability. The prepared flexographic plate is best placed for 12 hours before sticky printing, the purpose is to make all the residual solvent absorbed into the printing plate evaporate during plate making.
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