Gravure Printing Process (3)

(Basic Gravure Printing) The fourth part of the role of the impression cylinder impression cylinder is used to exert pressure on the substrate material, the substrate material and the plate cylinder contact, so that the ink in the roller compartment can be transferred to the substrate On the material, print out clear-cut words and images. In addition, the impression cylinder also determines the way in which the tension is printed between the units and allows the substrate material to move on the press. The "nip" is the contact point between the impression cylinder, the substrate material and the plate cylinder. The rotation of the impression cylinder is not driven by the gear of the printing press, but is driven by the friction at the impression point. Figure 13: An impression cylinder and a plate cylinder. The design of an impression cylinder The inner core of an impression cylinder is generally composed of a steel material and is covered with a rubber layer. The diameter of the impression cylinder is not the same as the diameter of the plate cylinder. Both ends of the impression cylinder are supported by bearings, mainly to ensure that the impression cylinder can maintain its balance during the printing process and avoid large vibrations. Although the processing company of the impression cylinder can be processed according to the parameters provided by the printing press manufacturer, the following points are decided by the printing company itself: 1. The coating material should be determined according to the condition of the printing press. The most commonly used materials are: natural rubber, neoprene, nitrile rubber, and polyurethane. 2. The shape of the outer rubber layer at the joints at both ends of the impression cylinder. Second, the physical properties of the rubber layer The physical properties of the outer rubber layer include: hardness (Shore hardness), heat resistance, elasticity, heat accumulation properties, wear resistance, chemical resistance and so on. The performance of various rubber layers is shown in the table below. Different rubber properties Comparison table Characteristics Nitrile rubber Neoprene Urethane rubber Ethylene propylene Hypalon Silicon rubber Viton Natural rubber hardness (Shore hardness) 20~9020~900A ~75D30~9050~9010~8560~9030A~70D Heat resistance (0F) 195180250350300500500 Ozone-resistance PF-GEEEEEE Cutting performance FGEF-GF-GPF-GG-E Wear resistance F-GG-EEF-GGPF-GG- E-Oketone Performance PFPEP-FFPE Aromatic Compound Resistance (Toluene) GP-FF-GPPPEP Ester-Resistant Performance (Ethyl Acetate) EGFPF-GPEP Anti-Cellulite Performance FFPGGGEG Resistance to Dichloromethane Performance PPPFPFEE Alcohol Resistance G- EF-GF-GG-EG-EGEG-E Water resistance GGGEEGEE Note: P - Poor F - General G - Good E - Excellent Third, the hardness of the rubber material of the impression cylinder The hardness and hardness of the rubber material can be expressed by Shore hardness. The hardness of the rubber material can be measured using a durometer. In order to be able to precisely control the amount of ink transferred to the substrate material, it must be ensured that the substrate material is in close contact with the ink in the cells. So, in the end should choose how much hardness of rubber material is more appropriate? This depends to a large extent on the type of substrate material. The rougher and more elastic the substrate material, the greater the hardness of the rubber layer of the impression cylinder. For example, an impression cylinder with a rubber layer hardness of 90 Shore A or more is suitable for printing recycled cardboard. Under the same conditions, when printing with a larger impression cylinder, a larger printing pressure can be applied without causing deformation. If the surface of the substrate material is very smooth and its weight is lighter, a softer rubber material should be used, and the required pressure is generally smaller. If the substrate material is relatively hard and relatively smooth, it should use a relatively soft rubber material, but it should not be too soft, otherwise it will produce deformation and wrinkles, commonly used around 80 Shore hardness of the impression cylinder. If the substrate material is soft and relatively smooth, an embossing cylinder with a 70 Shore hardness is appropriate. Fourth, the size of the impression cylinder In the choice of the hardness of the rubber material, we must also take into account the size of the impression cylinder, which is also a very important factor. We all know that the reason why the ink in the cell can be absorbed is mainly due to the capillary action, which means that a vacuum must be formed at the contact area of ​​the imprint. This is very important. The contact area between the impression cylinder and plate cylinder is called "nip". In general, the rougher the surface of the sheet material, the wider the contact area should be, and the larger the required diameter of the printing cylinder, and vice versa, the smaller the diameter of the cylinder. The reason is that rough surface of the substrate is uneven, there are many "pits" can not touch the ink in the roller compartment, so in order to be able to form the necessary vacuum, you need to increase the contact area. In order to prevent the impression cylinder from bending during the application of pressure, a steel press roll has been added to many presses, especially those with very wide webs. When a high pressure is applied, if the central portion of the printed matter is white and the image is not printed, it can be concluded that the impression cylinder has undergone a bending deformation.