Flexographic printing refers to the use of a flexographic printing plate to transfer ink through an anilox roller, which belongs to gravure printing. Flexo printing (hereinafter referred to as flexo printing) originated in Germany at the beginning of the 20th century. In recent years, the performance of the photosensitive resin plate has been continuously improved and stabilized, greatly improving the resolution and dot reproducibility of the printing plate (up to 1-95. %); Modern high-tech applications such as electronic plate engraving and digital plate making are possible with flexo printing to realize high-color overlay; laser engraving anilox technology enables the engraving line to reach a high precision of 1000 lines/in. Accurately control the amount of ink to be printed, and can print 300 lines/in color gradation drafts. The quality of the printed product is close to that of offset printing; Water-based mimeograph ink, UV (ultraviolet) flexo ink UV/EB (ultraviolet/electron beam) ) The successful development and widespread application of the mimeograph ink has enabled the ink to develop rapidly. Now, flexo printing has become one of the major printing methods.
This article focuses on a more comprehensive analysis of flexographic presses in order to promote the development of flexographic technology in China.
First, the principle of flexographic printing Flexographic use of fluid ink strong. The ink is transferred from the ink fountain roller and the anilox roller to the graphic part of the printing plate and is inked. Then the pressure roller applies the printing pressure, the ink on the printing plate is transferred to the printing material, and the dried surface is finally dried. Finish the printing process (see Figure 1)

Second, the category of the printing press of the flexo printing machine is the core of the flexo printing machine. The arrangement of the printing section directly affects the operation performance, the quality of the printing product, the printing speed and the applicable scope of the printing. According to the arrangement of the printing part, the flexo press can be divided into three types: cascade, satellite, and aircrew.
1. Laminated flexo laminating flexo presses (as shown in Figure 2), sometimes called stacking flexo presses. The individual printing units are stacked one above the other, arranged at one or both ends of the main wallboard of the printing machine, or various printing units are installed on the rack. Each printing unit is rotated by a gear mounted on the main wall plate. Stacked mikes can print 1-8 colors, but usually 6 colors.
Stacked presses have four advantages:
* The paper path of the web can be changed, that is, the use of guide rollers to change the path of the material to pass through, and the positive and negative sides can be printed at one time. In addition, the color number conversion is extremely convenient.
* Printed parts have good accessibility, easy to adjust, replace and clean.
* Can make 360 ​​degree registration. Each color printing unit can be individually engaged and separated so that other printing units continue printing.
* Wide range of applications, can print a variety of substrates. Its main drawback is indirect multi-gear transmission. Overprinting accuracy in multi-color printing is not high, and it can only be used for general prints.
2. The satellite flexo press (shown in Figure 3) of the satellite flexo press sometimes becomes a common impression cylinder flexo press. Each printing unit is mounted between two wall panels around a common impression cylinder. The printing material is color-coded around the common impression cylinder. Because the gears are directly driven, no matter if it is a paper or film, even if no special control device is added, it is possible to overprint very accurately, and the printing process is stable, and it is often used to print color products. It has been predicted that satellite flexo will be the new mainstream of flexographic printing in the 21st century. Its main drawbacks are:

* Wait until one time passes through the printing press, only one-sided printing can be completed. Although the other side of the printing can be printed by the guide roller, since the course of the tape is too long, its tensile deformation is increased and uneven, and it is very difficult to achieve double-sided printing image registration. Therefore, on a satellite flexographic press, one sheet of film is used, and after printing, it is sealed by a vertical hot air to make a packaging bag with both sides of the pattern.
* The distance between the printing units is too short, and the ink is easy to pick up when the ink is dry. In recent years, UV and UV/EB flexo printing inks developed by UV or UV/EB light can be instantaneously dried to solve the dirt problem.
3. Unit type flexo printing machine The unit type flexo printing press consists of a printing press unit which is connected to each other and horizontally arranged by a common power shaft. The structure diagram is shown in Figure 4. As shown.

The unit type flexographic press supports only one printing unit for each additional version, so the unit type flexographic press can be designed to accommodate different drum heads. Its advantages are:
* The assembly of the unit is easy and the post-press processing is easy.
* Suitable for short live printing.
* Through the guide roller to change the running path of the tape, one-sided printing can be achieved.
Third, the characteristics of the flexo press The reason why the flexo press uniform development, in addition to the technical breakthroughs in the plate, ink, its own characteristics is an important reason to attract users.
1, the machine structure is simple, and thus easy to operate, and easy maintenance. The price of a flexographic printer with the same function is about 30-50% of an offset or gravure printer.
2. The genetic material has strong adaptability. From 0.22mm plastic film to corrugated cardboard after 10mm, satisfactory printing effect can be obtained.
3, the imprinting force is small, about 19.6-39.2N/cm2, especially printed on substrates such as corrugated paper which can not withstand excessive pressure.
4. The low printing cost is mainly due to the low price of the machine, the low cost of plate making, the low paper loss rate during the printing process, and the cost of production is 30-50% cheaper than gravure printing.
5, printing quality is good. The use of an anilox ink roller short ink inking system not only simplifies the structure of the inking system but also enables the quantitative control of the film thickness. The breakthrough in high-performance photosensitive resin technology has greatly improved the resolution and dot reproducibility of the printing plate (up to 1-95%). Flexo printing can achieve a 300-line/in color gradation printing. The printing effect can be compared with offset printing and gravure printing.
IV. Flexo Press Structures A flexo press consists of 4 parts, namely unwinding feeding parts, printing parts, drying parts and rewinding receiving parts. In modern flexo presses, there are generally tension control, edge position control, register control, print observation and other measurement and control devices and mechanical condition monitoring and fault diagnosis systems. In addition, in order to expand the scope of application, some flexographic printing machines are also equipped with glazing, laminating, bronzing, slitting, die cutting, punching, screen printing, and gravure printing units to become flexo-printing production lines. .
1. The printing speed of the unwinding-feeding part flexo printing machine generally reaches 150m/min (or even higher). Under normal operating conditions, the unwinding feeding device must be installed in order to reduce the number of stoppages and the waste of the reel material. The simplified structure is shown at 5A. The function of the unwinding feeding device is to unwind the rolled printing material, continuously and stably convey the printing material to the printing part, and control the speed, tension and lateral position of the printing material before the printing material reaches the first printing part. The unwinding feed member has a feed roll holder and a set of guide rollers, and the feed roll holder is arranged in a straight line on the printing member. The reel rack has electric or hydraulic components to control the lift. Generally, the axis of the paper roll is locked by pneumatic components, and the detector is installed at the end of the paper roll.

● tension control system. The unwinding feeding part is also equipped with a digitally controlled electromagnetic brake tension system. The structure of the tension control system for unwinding the feeding part and flexo press is shown in FIG. 6 . He can make the best tension control for different substrates and is not affected by dust and dirt. The tension compensation control adopts a loop-type self-detection system. When the diameter of the web decreases, the tension of the paper (or film) can be continuously maintained to be stable.

● Drive roller. The unwinding feed member is also mounted with a drive roller mechanism as shown in FIG. 5C. The drive roller is an easily adjustable, variable-speed feed roller that controls the speed at which the web smoothly enters the printing press and, together with the web braking device, produces unwinding tension of the web to accommodate different substrates (cards Production of paper, tissue, plastic film, etc., while ensuring that the web maintains the correct longitudinal position.

● Floating roller. The floating roller structure of the unwinding feed member is shown in Figure 5D except that the fluctuation of the unwinding tension can be reduced, and the down time when replacing the roll is shortened to improve the use efficiency of the flexographic printing machine: most flexographic printing machines have Equipped with continuous reel changer, it is very important for the floating roller to connect the material roll without stopping the machine.
● Edge position control system: The high-end flexo press unwinding feeding device is also equipped with an edge position control system. The structural sketch is shown in Figure 5B. One edge position control system is installed in front of the printing unit, and the other edge position control system Installed in front of the die table. This design keeps the roll in place throughout the entire production process.

2. Printed parts Printed parts are the core of a flexo press and use a short ink inking system. There are two ink rollers, even an ink roller with a squeegee, which can achieve uniform and quantitative ink transfer from the ink to the printing plate surface.
At present, the typical printing unit used by a flexo press is shown in diagram 7. In this system, the anilox ink transfer roller is supplied by the ink fountain rubber roller, and the function of the ink fountain roller is to transmit sufficient ink to the anilox roller (abbreviation anilox roller). The combination of the squeegee fish anilox roller allows the flexo printer to adapt to a variety of viscosity inks, resulting in better print quality under higher factors. When the printing speed is increased, although the dynamic pressure on the surface of the anilox roller is increased, the squeegee is pressed against the surface of the anilox roller. Therefore, the amount of ink delivered by the ink system is independent of the dynamic pressure of the ink and is almost insensitive to the viscosity. The amount of ink transferred by the anilox roller mainly depends on the ink storage system (the volume of the ink roller holes of the anilox roller) and the ink separation between the anilox roller and the plate surface, regardless of the operating speed of the ink transfer system. This short ink inking system can keep constant the amount of ink delivered at various speeds, so the flexo press is capable of high-speed printing and high-precision color dot printing.

(1) Flexo printing machine anilox roller.
The anilox roller is the transfer roller of the flexographic printing machine. The surface has recessed ink cavities or mesh groove lines for controlling the amount of ink transported during printing, as shown in FIG. The use of anilox rollers not only simplifies the structure of the inking system, but also controls the thickness of the ink layer, providing an important guarantee for improving the quality of printed products. It is hailed as the heart of a flexo press.
1, the type of anilox roller.
The early use of the anilox roller was a mechanically engraved copper roller and chrome plated on the copper roller to increase wear resistance and increase ink carrying capacity.
Modern anilox rollers use laser-engraved ceramic roller technology. Both anilox rollers have better ink transfer performance, but ceramic anilox rollers are expensive. In the printing of high-precision network cable version, the printing speed reaches 200m \ min, the ceramic anilox roller can show its wear-resistant, heat-resistant advantages, but the practice has proved that: the ceramic roller's ink hole is easy to plug, application must note

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