Offset printing plate cylinder analysis

2.4 Plate cylinder

1. The role of the plate cylinder.

(1) Ink part of the graphic and text, non-graphic part of the water, and make it stable, that is, the ink and water balance, which is the key to guarantee the quality of the print (on the ink and ink balance after the Syria).

(2) It is possible to compensate for errors in the platen and upper plate. The platen and upper plate sometimes cannot ensure that the alignment of the picture and text is completely consistent with the rule. Therefore, an adjustment mechanism must be installed on the plate when the plate is skewed or multiple. When the position of the color printing plate is inconsistent, it can be corrected, that is, before and after the adjustment, left and right adjustment.

(3) The ability to change the front and rear position of the graphic text When the graphic text advances or lags behind the paper and needs to be adjusted, it can be achieved by changing the front and rear positions of the plate cylinder. This is commonly referred to as the use of a roller. It is best not to use a roller under normal circumstances. If it is used, it must be returned to its original position after use.

(4) The length of the print can be changed The change of the print length is also often required in the printing process, mainly because the paper is stretched back and forth. For multi-color printing, the subsequent overprinting often requires lengthening of the print. To solve this problem, the thickness of the liner is reduced below the platen roller, so that the transferred print lengthens. A sheet of 0.1 mm thick paper causes a deformation of 0.1 × 2 × 3.14 = 0.628 (mm), which is approximately six times the thickness of the paper. This number is the maximum deformation of the tail of the paper, from the mouth to the tail of the paper. The length of the blot was gradually increased from 0 to 0.628 mm.

(5) It can make up for the paper's throwing and collecting angle. When the paper throws angle and angle, the overprint of the paper's back corners will be inaccurate. The plate's back plate clamp is equipped with the plate's stretching and compressing mechanism. Make the back corner of the plate consistent with the paper's throwing angle, so that the back corner overprint is accurate.

(6) To change the printing pressure, when the thickness of the liner below the printing plate changes, the printing pressure will change, so that the printing pressure can be adjusted by changing the thickness of the liner.

2. The composition of the plate cylinder and the role of various components.

The plate cylinder is generally composed of a printing plate, a pad, a plate mechanism, a plate-making mechanism, and a cylinder body. The role of the plate cylinder described above is manifested by these parts.

(1) The first effect in Plate 1 is actually the role of the plate. There are two reasons for leaving a sip during the printing process: There is a part of the front mouth of the printing plate that needs to be installed in the plate clamp. There is no meaning in the stencil printing in this part. 2 The front plate of the plate has a large impact immediately after it is in contact with the water roller and the ink roller. It is extremely unstable. Therefore, it is necessary to use a water roller, where the ink roller has a cushioned place where the graphic text is not transferred well. Taken together these two factors, the front of the printing plate must have a graphic without drying, that is, gargle. From the point of view of the printing plate, the smaller the better the squash of the printing plate is, the less the product is required to pass through the mouth (such as lines, words, etc.), the higher the required product, the larger the stencil of the printing plate ( Color printing). There are sometimes five points to note when making printing plates: 1 The size of the mouth must be the same, the same plate must be the same, the set of plates must be the same, and the center must be centered. Each plate must be centered. Sun; 3 printing plate surface has no dirty spots, whether the picture has no hair or paste version of the place; 4 out of the network is complete; 5 whether the sun is not the wrong place (especially more than two sun products).

(2) The liner of the liner plate is higher than the liner inside the blanket cylinder, that is, the surface needs a higher flatness. The general equipment is equipped with a special offset printing paper, if there is no special offset printing paper, Other papers may be used instead, but relative slippage should also be taken into consideration when selecting offset papers. Under normal circumstances can use offset paper, kraft paper or cloth paper. The selection of these offset papers also has the effect of making trace amounts of processing errors on the back of the printing plate and the surface of the plate cylinder body. However, this is not the main role. Some existing equipment can use standard media without offset paper, which greatly improves the speed of the previous version. When printing, in order to compensate for the deformation of the print, it is also necessary to change the thickness of the pad, add paper or reduce paper, but it must be carefully calculated, and the change of the general print length is also approximately 6 times the thickness of the added paper. . The imprinting of the paper is shortened and the length of the subtractive imprint is longer.

(3) The second role in the plate mechanism 1 is the role of the plate mechanism. The printing plate needs to be installed inside the platen mechanism so that the printing plate and the roller surface are in a relatively stationary state. When the printing plate is installed incorrectly or when it is oblique, it can be adjusted by the adjusting mechanism inside the clip. This adjustment is generally to correct the printing plate. There are two ways to do this: One is the front and rear panels, and the other is the left and right top panels. No matter which method is used, the corresponding surface needs to be released.

When pulling the plate forward or backward, if you pull it in the direction of the mouth, you need to loosen the top plate screw on the tip and vice versa. When the pull-up version is relatively large, it must be taken care that all screws are subjected to a uniform force. This will prevent local stress concentration on the edge of the plate and cause cracking at the place.

When the top and left top plates are left and right, be sure to choose a top screw as the hinge, and loosen the rest of the screws. The left and right top plates can sometimes be replaced by front and rear pull plates.

When installing the printing plate, be sure to ensure that the position of the printing plate is flush, because many devices are equipped with positioning devices. There are special positioning pegs on the plate clamps, and there are special positioning marks on the rollers. The former is based on the latter, because the positioning marks on the roller cannot be adjusted, and the position of the plate clamp relative to the roller is not always the same. The printing plate needs to be punched with a special punching device, and the printing plate needs a special hanging nail. If it can ensure that all the positioning relationships are accurate, then printing does not require any adjustment, and the overprinting requirements can be achieved. Even if the difference is poor, it is usually less than 0.10mm. Another important role of the plate mechanism is to make up for the paper's throw or angle (this device is normally mounted on the lower grip). You must borrow both sides of the top plate screw when using.

If you make up for the left-hand throw of the paper, tighten the right screw so that it is tight against the drum, and then adjust the center of the dedicated mechanism. However, it should be noted that this amount of compensation is very small.

(4) When the plate-drawing mechanism prints, if the crosshairs of the plate have been parallel (front and rear, left and right), but not overlapped, the adjustment mechanism on the re-adjustment plate clamp is very inconvenient, and the pull plate mechanism is very fast. And accurate. The plate-drawing mechanism can also slightly change the front, rear, left and right positions of the graphic on the paper. The plate-drawing mechanism includes two sets of axial (lateral or left-right) and circumferential (longitudinal or front-rear) mechanisms. The axial pull plate must move the roller axially, that is, there must be a device to move the roller axially. The circumferential pull plate must move the periphery of the drum. Changing the relative position of the plate cylinder and the blanket cylinder can only be achieved by changing the meshing relationship of the gears. Therefore, a mechanism must be used to drive the gears of the drum. Overview The analysis above is that the axis of the drum is the axis of the drum, and the axis of the gear is drawn in the circumferential direction. If the rollers and gears are thrown away, the working principle of the two pull mechanisms should be exactly the same. It should be noted that after using the machine, you can use the pull plate mechanism, especially the circumferential pull plate mechanism. Pulling during operation can make the roller or gear continuous movement, which can prevent sudden impact. The limit device of the pull plate mechanism must be absolutely reliable, otherwise it is easy to pull out the gear and cause a machine accident.

There are two types of pull plate mechanisms currently used, manual and electric. Manually is generally used for two-color machines, four-color machines are generally used for electric (individual also has manual). The layout mechanism of different devices differs in terms of structure.

(5) drum body. The requirements of the drum of the plate cylinder and other cylinders are basically the same, and will not be described in detail here.