Laser engraving flexible version

The drying process of traditional flexographic printing plates is extremely cumbersome and time consuming. It goes through the following process steps:

· Plate cutting (according to the size of the negative image, select the appropriate layout size)

·Back exposure of the plate (used to determine the embossing depth of the graphic part of the plate after drying, the longer the back exposure time, the smaller the relief depth; otherwise, the greater the relief depth)

· Frontal exposure (tear off the surface protective film of the printing plate, and close the emulsion surface of the negative plate on the negative plate to the photosensitive surface of the printing plate, and then expose the plate to expose the photosensitive material to cross-link and harden)

Developing (using organic solvents to dissolve photosensitive material in unexposed areas, forming grooves)

·Drying (rinsing the developed plate, sticky and soft, need to be dried under hot air to volatilize the solvent inside the plate)

Detachable post-treatment (The method can be to remove the adhesiveness of the resin by ultraviolet irradiation of the plate for a period of time or chemical solvent dissolution to increase the smoothness and hardness of the plate surface)

·Post-exposure (a full, uniform exposure of the dried plate to completely cross-link the uncured resin inside the plate without deforming the ink or solvent, improving the plate's resistance to printing)

The LEP (Laser Engraved plate) technology developed by BASF in Germany will bring a profound revolution to the current field of flexo printing plates. It uses laser technology to directly sculpt a flexographic printing plate that can be printed on the machine, developed on the plate material developed by the company. This technology is a successful application of computer to plate in the field of flexo plate making. It uses a computer output signal to control the scanning of the CO2 laser beam on a special printing plate material, and vaporization of the material molecules of the laser scanning part forms a concave non-graphic image, while the non-laser scanning part of the printing plate will form a graphic printing plate. section.

The comparison between the traditional flexographic drying process and the CTP process is shown in Figure 1.

From the above comparison, it is not difficult to see that LEP has the following advantages: 1. It greatly simplifies the process steps, thereby saving a lot of labor productivity and prepress consumables in this process, saving production costs; 2. As The solvent development step is omitted in this production process, which is in line with the current thinking of environmental protection; 3. After using LEP technology, the platemaking cycle is significantly shortened; 4. The entire workflow is based on all-digital, and therefore reduced 5. Occurrence of errors; 5. Using printing plates directly produced by LEP technology, the registration is more accurate when printing.

In order to gradually mature the LEP technology, people have made arduous efforts in the research and development of laser technology and flexible printing plates. After many years of unremitting exploration, Germany BASF has produced a plate made of special materials such as nyloprint WS. This is an ideal flexo plate. Its surface hard layer is particularly suitable for tubes, cups, cans and other printing. After many companies actually used it, people found that using CO2 laser and nyloprint WS plate direct laser engraving plates can ensure the quality of the output flexible printing plate.

To be able to engrave flexographic plates directly on the nyloprint WS original, first attach the nyloprint WS original firmly to the roller and prepare the prepress data on the prepress workstation. This is followed by RIP's explanation. Finally, it is transmitted to the laser front end in the TIFF format over the LAN, and the engraving process is controlled by the computer.

The CO2 laser used has a wavelength of 10 000 nm and an output power of 250 W. The drum rotates at a high speed of 2 m/s and the stepping motor has an accuracy of 20 μm in the axial direction. When the exposure resolution is 1 270 dpi, carving a set of four-color A4 format plates takes 70 minutes. Observing the difference between the traditional printing plate dots and the laser-engraved nyloprint WS printing plate dots under an electron microscope, we found that the engraving dots were significantly steeper than the conventional dots and edges, the dots were round and the diameter was about 30 μm. At the same time, it was discovered through printing that the prints printed by such plates have high contrast and low dot gain. FIG. 2 is a dot plot of 48 lpi screen dots and 10% dot size under an electron microscope. The figure on the left shows the dot plot of the traditional printing plate, and the picture on the right shows the laser engraved nyloprint WS plate dot plot.

Laser-engraved plates can get a larger, reproducible tuning range. We know that when we use the original 120 lpi screen with 360 lpi anilox roller, the traditional rubber plate can reproduce the tone range from 15% to 80%, while the resin plate can reproduce the tone range of 5 % ~ 95%; nyloprintWS provided by BASF has better copying performance, it can copy out less than 5% of the dots; therefore, it is ideal for brightly reproduced images, the printing quality is greatly improved than before, and it is ideal for printing. A fine gradient.

BASF also offers another printing plate, nyloflex LD. The plate is made from a new type of polyester material with a Shore hardness of 65A. It overcomes the disadvantages of stickiness in the rubber plate and the edge of the plate that can be easily melted. Therefore, it has great competitiveness in the current flexible plate consumable market.

People did the following experiments: people glued a nyloflex LD plate to a sleeve (the sleeve is actually a tube, sleeved on a roller, it exists as a pad of the printing plate), and then the wavelength is 10 000 nm. CO2 laser direct engraving of the printing plate, the output function is still 250 w, the exposure resolution is still 1270 dpi, and the 4 color A4 format printing plate engraving time is also 70 min. After the plate has been engraved, remove the dust that may be present on the plate with a warm towel to obtain the following dot pattern, see Figure 3.