Talking about the quality control of lithographic printing plate
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
The dot representing the graphic information on the original plate is transferred to the printing plate by means of sensitization, and at the same time, the portion representing the graphic information on the printing plate has oleophilic hydrophobic property, and the blank portion has hydrophilic property, and the information is transferred. The process we call lithographic printing.
The printing plate is the link between the pre-press process and the proofing and printing process. On the one hand, it should completely and faithfully transfer the original graphic information to the PS plate; on the other hand, it should make the graphic part ink-friendly. The blank portion is hydrophilic and allows the printing plate to withstand tremendous long-term pressure between the rollers without changing the hydrophilic properties of the ink.
When we are making the PS version, we always hope that the outlets will be firm and smooth; because the plates are solid and smooth, the edges of the dots can withstand the long-term erosion of water and ink and are not prone to shrinkage or expansion. Printing can ensure the relative stability of the plate dot size. Otherwise, if the printing plate dot is imaginary and hairy, a small amount of change in the ink-and-wash balance in the printing, the inking of the printing plate dot may be contracted or expanded at any time, thereby affecting the stability of the ink dot transfer data. In addition, we also hope that the blank part of the printing plate is clean and has no dirty spots, and the graphic part is very lipophilic; the sun-made PS version has high printing durability. So, what are the factors that determine the quality of the print? We summarize the following points:
(1) The appropriate original. For the original version, it has an important impact on the quality of the print. First of all, our printing plate usually uses a purple light source or an ultraviolet light source with a wavelength of 400μm, which has strong penetrating power, in order to completely transfer the original negative film net point to the printing plate, and does not make the image portion of the image in the future. The photochemical reaction of the rubber layer requires that the density of the original film on the film should reach 3.3 or higher. Otherwise, it is difficult to achieve the desired effect. Secondly, the fog of the original plate is low, otherwise it will affect the density contrast on the plate; The original version should be clean and free of dirt, otherwise it will bring dirty on the printing plate; finally, the original version is preferably a piece of film without a knife edge and a collage tape, which ensures that the film is tightly combined with the PS plate to avoid scattering due to light. The dot is faint, and even if it is necessary to tile, the tape should be too flat or equal to 7 mm from the dot representing the image information.
(2) The glass of the printing frame is required to be clean. Otherwise the dust on the glass can easily make the PS plate dirty. Because our current working conditions are difficult to achieve absolute dust-free printing shop, so before printing, use alcohol to wipe the glass frame.
(3) Appropriate form of illumination. We should try to reduce the phenomenon of light seepage caused by the form of illumination and the phenomenon of dot reduction caused by the light-viscosing PS version during the printing process.
(4) The resolution of the PS version. The most important factor affecting the virtual point of the printing plate is the resolution of the plate. So how do we test the resolution of the plate?
UGRA1982 test strips have helped us a lot.
UGRA1982 control strip consists of five parts: 1, high light and dark control area, usually when printing on the machine version: to ensure that 98% of the outlets are not pasted, 2% of the outlets to be retained: when drying the sample: to ensure 98% The outlets are not ambiguous, and 3% of the outlets are reserved. 2. Test the ghost area. 3. The dot area used to measure the dot enlargement and print contrast. 4, 12 yin and yang pattern areas with a diameter of 4.5mm, the width of the line is between 4μm and 70μm, this section can be used to determine the correct exposure time and PS version resolution; 5, used to test whether the development is normal ash Step section.
Under the guidance of Mr. Schmitz, a professor of vocational education in the German printing industry, who came to the Hefei Sino-German Printing Training Center, put the UGRA measuring and control strip on the 8th Fuji version used as the GTO printing version, using 2T , 4T, 8T, 16T, 32T, 40T beat grading exposure of the PS plate, and after development under normal development conditions, observe the reproduction of the yin and yang lines of the UGRA control strip yin and yang circle area (at least 50% can be clearly reproduced as quasi).
According to the UGRA1982 test strip, at the same exposure time, the same level of the Yin and Yang lines of the Yin and Yang circle can be clearly observed at the same time, then this level is the resolution of the plate, so the PS version we tested The rate is 6 μm.
(5) Appropriate pumping time; because the contact degree of the original film and the plate glue layer is changed at any time during printing. Such as: the unevenness of the printing glass and the blanket, the dust pad, the tape on the film and the padding of the dirt, and the lack of vacuum of the suction, etc., will cause poor adhesion between the film and the photosensitive layer of the plate. There is a gap, which causes a serious hazard of light penetration, thereby changing the size of the transfer point of the printing plate. Therefore, we can closely match the PS plate to the original plate by finding the right pumping for correct exposure.
(6) Appropriate exposure time. If we only have a high-resolution PS version, good exposure conditions are not enough, there must be sufficient and not excessive exposure time to produce a good PS version.
According to the results of the previous stepwise exposure, the resolution of the plate was 6 μm. It should belong to the PS version with a resolution between sμm and 8μm. The actual exposure time is the range of exposure times required for the minimum reproducible male line width listed in Table 2 between 12 μm and 15 μm.
The following figure is based on the data obtained from the graded exposure. (The horizontal axis is the change in exposure time; the vertical axis is the minimum resolvable male line width of the tested PS plate at this exposure time)
The red line in the figure indicates the minimum reproducible pan line width on the PS plate as a function of exposure time; the blue line in the figure indicates the minimum reproducible pan line width on the PS plate as a function of exposure time. The ordinate corresponding to the intersection of the two fold lines is the resolution of the PS version being tested. It can be seen from Table 2 that we should use the corresponding abscissa range (22-32Takt) between 12μm and 15μm. This time range is the optional exposure time when using this PS version of the net draft, and the exposure time should be slightly extended for the dry line draft.