The hottest flexographic printing answers 14 quest

Flexographic printing answers 14 questions (12

12 how to do the back exposure test

we can first determine the back exposure time suitable for different corrosion depths by doing the back exposure test on the plate making machine. In order to facilitate comparison, we use the method of multiple exposures for the same plate with different exposure times. Take a plate with a size of about 320 mm long and 100 mm wide. When doing the back exposure on the plate making machine, we use the red covering strip to make the division The plate making machine is exposed for many times to obtain a printing plate with five different back exposure time areas. In addition, leave about 20mm blank at one end of the plate for the plate washer to hold. Suppose we choose a Dutch av-500 combined plate making machine and a 1.70mm thick flexible plate made by grace company. After local covering and multiple exposures, we get five parts with exposure times of 0, 15, 20, 25 and 30 seconds on the same plate. After exposure, we put them on the drum of the printing plate for plate washing, about 7 minutes. Then it is dried in a drying oven at a temperature of 50. c. The time is 1.5 hours. Finally, take out the printing plate, and use a caliper to measure four different base thickness values on the printing plate, while only the hard polyester base is left in the unexposed part of the printing plate

through the above tests, you can quickly get familiar with the plate making machine, and the test results also have guiding significance for adjusting the corrosion depth of the printing plate. It can be seen from the above experiments that the length of back exposure time will affect the thickness of the plate base. Therefore, for different printed graphics and texts, different back exposure time should also be used in plate making. Still take the 1.70mm thick flexible plate as an example. The anti white and large field parts on the printing plate should have a deeper corrosion depth (i.e. the plate base is thin), up to about 1.0mm, and the back exposure time is the shortest; while the ordinary graphic parts have a medium corrosion depth of about 0.85mm, and the back exposure time is moderate; as for the small lines and points, the corrosion depth should be the shallowest, about 0.63mm, so the back exposure time needs to be the longest

in addition, there are two points worth noting: when the printer changes to another thickness of flexo or another brand of flexo, the back exposure test must be carried out again. With the extension of the service time of the UV lamp, its light intensity will decrease. At this time, the back exposure time should also be adjusted accordingly

13 how to do the positive exposure test

the positive exposure is also called the main exposure, which forms the graphic printing part of the flexo. Proper positive exposure and back exposure work together to get a high-quality printing plate that meets the requirements of various graphic types. Generally speaking, insufficient positive exposure will cause the bottom of the shoulder around the text to be brushed off, affecting the service life of the printing plate; while excessive positive exposure will cause insufficient corrosion, which is easy to cause paste, resulting in waste products when the material quality is shrinking

before the front exposure test, we recommend that the operator prepare a test "sample" specially for making flexographs. The "sample" should contain basic types of printed graphics and texts, such as small anti white, ordinary anti white and field, ordinary cross-linking reaction of graphics and texts, small lines and characters, dots, etc, From this, we can also predict that a certain line number (such as 150lpi) is reflected in the "sample" from 10% to 100% of the field

the positive exposure test can be carried out by using "samples" on the plate making machine through local covering and multiple exposures. At the initial stage, you can also start with less difficult businesses, from easy to difficult, accumulate experience, and comprehensively master the technology of making flexo. Theoretically, the finer the picture and text, the longer the positive exposure time is required, but remember that it works together with the back exposure. For example, anti white words require less back exposure and positive exposure, while small points require a shallow corrosion depth, so their back exposure and positive exposure time are longer

after general time of exploration and practice, the plate making operator should understand the limits of his plate making, such as whether the thinnest lines, the smallest characters, the densest points and 3% points can "stop", 5 Tripod: Polyurethane sports universal wheels are installed at the bottom of the fuselage. Whether the four 50% points are "open" and so on

14 what should be paid attention to when processing and debonding after plate washing and drying

with the increase of solvent use times, the time of brushing the plate should be appropriately extended; the position between the fine brush and the plate drum should be adjusted according to different plates, so as to adjust the pressure between the fine brush and the plate surface; if special fine points are made, the pressure of the fine brush should be further reduced on the basis of the standard thickness position to prevent the points 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 to check whether there are solvent spots or other defects on the surface of the plate. You can use a clean cloth that cannot remove the fiber, soak some fresh solvent, gently wipe the surface of the plate, and then put it back into the drying oven to continue drying

after post exposure and debonding, the printability can be greatly improved. The prepared flexo is best placed for 12 hours and then pasted for printing. The purpose is to let all the residual solvents absorbed into the printing plate volatilize during plate making