PS and CTP Printing Plates

1. PS and CTP Printing Plates Abstract: PS and CTP printing plates are two important kinds of printing plate in commercial printing. What are they and their difference? How to choose aluminum plate substrates? Learn more. The PS And CTP Printing Plates in China The PS and CTP printing plates for offset printing features high printing quality, strong printing resistance, environmental protection, reasonable cost, high resolution, clear writing, fast speed and strong reproducibility. The aluminum plate base is 1050, 1060, 1070 and 1052 alumnum ≥99.50%, ≥99.60%, ≥99.70% and ≥99.52% respectively. Aluminum plate base has the advantages of low density, high strength, moderate wear resistance, easy processing, good shape, good hydrophilicity, high stability, good surface treatment, strong recyclability, easy regeneration, abundant resources andreasonable price, etc,, which makes it an indisputable high-quality PS/CTP plate substrate. The average annual growth rate of China’s PS/CTP plate output from 2005 to 2011 was 21.32%. The growth rate of the domestic production from 2011 to 2015 was 11.2%. At present, China has become a net exporter of PS/ CTP plate. For PS plate making, there are two kinds of raw materials: the continuous cast-rolling strip and the ingot hot-rolled strip. The PS plate quality made of them are almost equal. For CTP pringting plates, the better choice is to use the ingot hot-rolled aluminum. In the production of CTP plates, the pure stretch straightening production line is indispensable. It plays a very important role in ensuring product flatness and performance. Up to now, many CTP plates manufacturers such as Haomei Aluminum has such production line. As for the composition of the alloy, there is still a lot of work to be done. Although the aluminum base plate used in PS/ CTP plate are 1000 series aluminum, from our work experience and metallological principles, we should regard this type of alloy as Al- Fe-Si alloys. The Fe/Si value must reach a certain ratio in order to produce high-quality aluminum sheet. It is better that the Fe/Si value is between 2.5 to 3.5. plate, of which the aluminum content is

2. What Is PS Plate PS plate, the abbreviation of "Presensitized Plate", is a a lithographic printing plate pre-coated with a photosensitive resin layer on the aluminum plate substrate. The high-quality aluminum plate for PS plate is processed by electrolytic grinding and anodizing. The PS plate features flat coating, uniform thickness, relatively good hydrophilicity, abrasion resistance, and chemical stability, so its printing resistance is very high, which is suitable for printing high, precise and fine products. The commonly used PS aluminum plate substrate is generally 1050 and 1060 aluminum sheet with H18 temper. In addition to the production of PS plates, 1060 aluminum plate is also widely used in positive PS plates, thermal CTP plates, photosensitive CTP plates, UV-CTP plates, etc. The width range of Haomei aluminum plate for PS plate making is generally 400-1600mm, and the conventional thickness is 0.10-0.50mm. The aluminum base plate should be of high surface quality and flatness. Therefore, in order to obtain a high-quality alumnum sheet, a special straightening method must be adopted after cold rolling. With an advanced straightening processing technology, Haomei aluminum plate substrate can avoid such defects like hard scratches, leveling marks, and shock marks. In addition, the electrostatic spraying technology on the matte surface makes the air between the film and the PS plate during printing smoothly drawn out, so that the vacuuming time is shortened by two-thirds compared with the PS plate without the matte surface, thereby reducing the plate making time. Advanced multi-layer sand mesh technology can help the PS plate base to improve the printing durability. It is composed of sand meshes of different sizes (large waves, medium waves, and small waves). Each size of the sand mesh shares important performance, so as to well realize the balance of printing resistane and stain resistance. How to Choose PS Plate Substrate PS plate for offset printing is made up of two parts: the photosensitive layer that forms the graphic part in printing and the aluminum plate that forms the hydrophilic blank part. It features excellent printing quality, high printing endurance, safety and low cost. The PS plate substrate is usually 1050 aluminum sheet. The thickness is 0.30mm, 0.27mm and 0.15 mm. The aluminum plate surface is not to have cracks, scratches, oil marks,etc. The gap

3. between plate and horizontal plane is less than 3mm, wave number is less than 3/m and the diagonal difference is less than 1 mm. Its qualiy has great effect on the quality of PS plate. 1. The surface quality of the aluminum plate In the making process of aluminum plate, a layer of oxide film will be formed on its surface. At the same time, the rolling oil and other impurities such as dust will inevitably remain. If it is not removed, it will directly affect the electrolytic grit shape and anodizing effect, which will finally influence the printing quality. Therefore, we must strictly control the surface quality of the aluminum sheet, that is, the defects depth of the surface and the degree of residual oil stains. 2. The flatness of the aluminum plate If the flatness of the aluminum sheet is not good or the waves aare large, the distance between the polar plate and the aluminum plate is not uniform. Then, the flow of charged between the two is different. The electric quantity of the aluminum plate above the base surface is very different, thus leading to the different electrolysis reaction. The resulting grit size is uneven. Fine sand meshes have little water storage and cannot meet the printing requirements; coarse sand meshes store a lot of water, and the blank part of the printing plate is easy to get dirty. Besides, the large waves of the aluminum base plate will result in uneven spray electrolyte volume, nozzle cracks and the damage of the pringting equipment. 3. The thickness difference of aluminum plate The relative elongation of the PS plate is restricted by the thickness of the aluminum base plate. And the thickness difference of the PS plate will inevitably lead to uneven deformation and cause inaccurate overprinting during printing. Therefore, the thickness of the PS plate should be moderate and the thickness difference should be uniform. Only in this way can it be ensured that it is strong enough and will not cause excessive deformation. CTP Printing Plates VS PS Plate With the rapid development of CTP printing technology and the the continuous decline of CTP plates price, the usage of CTP pringting plates is also rapidly catching up with the traditional PS plates. The printing has high overall requirements for plate materials. To ensure the quality of the printing plate, the apparent quality of the plate base is the prerequisite. The apparent performance of aluminum sheet

4. The CTP plates have higher requirements on the aluminum sheet such as free of cracks, corrosion pits, spots, scratches, oil marks and no slight color difference. The PS plate can ignore the above problems. The main reason is that the CTP equipment uses scanning imaging. The PS plate uses a vacuum method to make the plate and the film close. The geometric size requirements of aluminum sheet The aluminum plate thickness for CTP plate is generally 0.280mm, which is slightly thicker than that of the PS plate. The thickness of the PS plate substate is 0.270mm±0.005mm. Some printing companies also use the CTP plate of 0.275mm thickness. The thick aluminum plate is not easy to bend. The width tolerance of the CTP plate substrate is required to be ≤±0.5mm, preferably without tolerance. There are also clear requirements for the cutting quality of aluminum coils, that is, there should be no burrs and curling edge on the both sides after cutting. The longitudinal and lateral thickness tolerances of the aluminum plate base should be ≤±0.005mm. The thickness deviation will affect the plate making, and the parameters set by the CTP plate making machine are generally not allowed to be adjusted casually. The electrolytic performance requirements of aluminum sheet Because CTP printing plates are mostly used for high-end color printing, the sand mesh value of CTP plates is smaller than that of PS plates. The grit value Ra of the CTP plate is generally 0.45-0.60 μm while the grit value Ra of the PS plate is generally 0.60-0.80 μm. Haomei Aluminum has different kinds of printing plates such as PS plate wholesale, CTP plates and CTCP plate. Welcome to send inquire to dolly@alumhm.com.