Magnetic Printing Technology and Mechanical Discussion--Flexo Printing (2)

2. The main body of flexographic printing presses

The inking mechanism of the flexographic printing press is relatively simple, but the surface structure of the transfer roller is more complicated than the transfer roller (or transfer roller) used in the printing machine used in other printing methods.

The flexographic printing press consists of a transmission part, a paper feeding part, a printing part, a drying part, and a main device such as a guide roll and a rewinding part. The mechanical transmission portion is similar to the rotary mechanism of the gravure web press, and will not be described below.

(1) The paper feeding section places the printing materials to be printed, and the printing materials to be printed are smoothly and accurately fed to the printing section for printing according to the embossing characteristics of the printing machine, collectively referred to as the feeding section.

The paper feeding section of the flexographic printing press has two forms of sheet feeding and web feeding.

1 Single-sheet feeders The printing materials are single-sheet (sheet) forms, such as paper, cardboard, corrugated cardboard, curved cardboard, thin cardboard (E-type corrugated), etc. Automatic feeding device.
The flexible sheet feeding method has two forms of jet feeding and vacuum suction feeding.

2 The coil conveying device The function of the coil conveying device is to smoothly input the roll-shaped printing material to be printed into the printing portion to complete the graphic printing process.

In the printing process, the diameter of the coil gradually becomes smaller, so that the operating conditions change continuously, and the tension also changes continuously as the diameter of the coil changes.

The continuous changes in the tension of the web not only make it impossible to control the elongation of the easily stretched printing film, the conveying cannot be smoothly adjusted, but also has a serious impact on the printing color printing, so that the printing cannot meet the quality requirements.

The most important condition for the web during the transport process is to control the tension of the web so that the web of the input printing unit maintains a stable degree of tension.

The basic structure of all kinds of different types of coil conveying devices is the same. They are composed of a conveying shaft, a tension control device, a coil axial adjustment device and various guide roller systems.

a. The web feed shaft is the horizontal axis of the web to be printed. Conveyor shaft cone sleeve type and cylinder type two. The web conveying shaft of the low-speed flexographic printing press with a printing speed lower than 50m/min adopts a conical sleeve structure. When it is used, the steel mandrel is inserted into the paper tube in the middle of the coil, and both ends are fixed with a tapered sleeve, and then used. Nuts locked. The high-speed flexographic printing press uses a cylinder-type conveying shaft. When it is used, the mandrel of the gas cylinder device is inserted into the intermediate paper tube of the coil, and then a high-pressure gas flow of 4 kg or more is input, so that the mandrel expands and expands, and the coil is fixed. The pneumatic conveying shaft is easy to operate, saves time and effort.

b. Tension Control Device The role of tension control device is to control the roll substrate without changing the diameter, maintain a certain degree of tension, and prevent the substrate from wrinkling, breaking and skewing.

Tension control devices are divided into manual controllers and automatic controllers. Low-speed flexographic printing presses commonly use manual controls to adjust the web tension. During use, with observation and experience, according to the conveying condition of the coil, the control panel on the manual controller is used to change the tightness of the contact between the friction plate in the tension control device and the coil shaft, and adjust the operation of the coil. Tension size. The manual controller is installed on one side of the reel rack. The automatic tension controllers at both ends of the coil are divided into two types, magnetic powder and oil pressure, depending on the structure. The magnetic powder tension controller automatically adjusts the tension of the web as the diameter of the web changes. The hydraulic tension controller automatically adjusts the tension according to the vertical change of the web and automatically measures the web. The automatic tension controller has the same tension on both ends of the web.

c. Coil Axial Adjustment System Roll material placed on the feed shaft often does not fit the printed position of the layout correctly. In the normal operation of the printing press, displacement sometimes occurs, affecting the correct reproduction of the graphic. Therefore, it must be adjusted by the axial (left and right) adjustment system. The axial adjustment of the web is generally controlled manually.

(2) Printing part The printing part of the flexographic printing press determines the performance of the whole machine.

1 Ink Transfer System The ink transfer system of the flexographic printing press has two types of ink delivery system: the two-roll ink transfer system and the squeegee ink transfer system.

a. Two-roller ink transfer system Two-roller ink transmission An ink transfer system consisting of an ink feed roller and an ink transfer roller is called a two-roll ink transfer system.
The ink roller is immersed in the ink tank to adhere the ink to the surface. When contacted with the transfer roller, the ink layer is transferred to the transfer roller; the transfer roller receives the ink layer during the contact with the transfer roller, and is During the contact of the plate cylinder, the ink layer is coated on the graphic portion of the surface of the plate cylinder, as shown in Figure 2-43.

The surface of the initial ink transfer roller and the transfer roller was wrapped with a rubber layer. With the appearance of the metal reticulation, an anilox roller was used instead of the rubber transfer roller to transfer the ink better. The dual-roll transfer system is suitable for low-speed flexographic printing presses.

b. Squeegee Ink Transfer System The ink transfer system of the reverse squeegee between the ink feed roller and the transfer roller is called the squeegee ink transfer system, as shown in Figure 2-44. The ink system was developed on the basis of a two-roll system.

During the printing process, the ink on the surface of the anilox roller is scraped with a doctor blade. The gap between the squeegee and the anilox roller determines the ink transfer roller thickness.

When the squeegee is in use, it is closely attached to the ink transfer roller. When not in use, the squeegee should be reversed to leave the surface of the anilox roller.

It is simpler and more practical to directly rotate the anilox roller in the ink tank instead of using the ink transfer roller's ink transfer system, as shown in Figure 2-45.

2 Imprinting system consists of the following components.

a. Plate-printing drum The plate-printing drum is a cylindrical body made of alloy steel, which is made by precision machining and undergoes dynamic balance processing. It is not easily deformed. Its surface has a standard scale for loading and unloading printing plates.

The plate cylinder is placed in fixed bearings at both ends of the frame and is in contact with the impression cylinder to complete the printing process. Both ends of the drum are respectively equipped with vertical and horizontal adjustment mechanisms to adjust the vertical and horizontal alignment of the printing plate patterns, respectively, to ensure overprint accuracy of the various color graphics.

The circumferential length of each set of plate cylinders of a flexographic printing press must meet the specifications (length) of the printed product. That is to say, different types of substrates require a certain size of plate cylinder to match. In order to allow the printer to print products of different specifications without restriction, each flexographic printing mechanism has a variety of plate cylinders of different circumferential lengths (different diameters). The serialization of plate cylinders makes the flexibility of the printing presses and the printing plate exchanges convenient.

b. Embossing cylinder The embossing cylinder, also known as the printing cylinder, is a cylinder that supports the printing material in contact with the printing plate cylinder to generate printing pressure and complete the printing process.

The structure of the impression cylinder of the imprinting type printing press is relatively complicated, and its diameter is more than 1m, which is 4 to 5 times that of other types of printing presses.

The embossing cylinder of the co-imprinting printing press is re-wound from the steel plate, and after static balance treatment, the eccentricity error is kept within the allowable range. Both ends support high-precision bearings and can rotate freely. Some co-compression type impression cylinders are designed with an automatic temperature control system, which is circulated by hot water to control the temperature of the surface of the impression cylinder. In order to prevent the temperature of the surface of the impression cylinder from rising too high, an additional cooling water circulation system may be provided for adjustment, and it is generally preferable to control it at about 30°C.

The impression cylinder of a tandem or laminate type flexographic printing press is made of alloy steel as a cylinder body, is made by finishing, and is subjected to dynamic balance processing. The diameter of the impression cylinders of each printing unit is equal and fixed, and the configuration is relatively simple.