Barco flexo platemaking: completely digital process flow (middle)

● Make the edges of the dots more “vertical” and sharper.

● greatly enhance the reliability of printing

● No need for film, reducing dust problems

● Significantly reduced dot compensation and making it easier to control

● Perfect calibration system guarantees high precision of flexographic exposure

● Faster, easier startup and improved printing reliability

Due to the emergence of Barco's CDI, digital flexography became possible. This is an external drum exposure device with a laser of 60 watts that can be exposed directly to Cyrel DPS or DPH media. The vacuum suction device tightly adsorbs the DPS plate on the roller. Exposure roller rotation speed can be adjusted according to the resolution of the exposure and the thickness of the plate, the general exposure speed of the thin plate is 2000rpm In order to ensure a smooth operation, the roller and bearing device is on a solid marble base In order to avoid the error caused by internal and external oscillations. The 60-watt YAG light source generates an infrared laser with a wavelength of 1064 nanometers. When the laser beam breaks through the black synthetic film of the DPS or DPH plate, it generates a momentary partial flash, and the heat evaporates the local black coating.

The laser beam is excited by an Acousto optical modulator, accurate to 180.000 pixels in the circumferential direction of the roller, the horizontal positioning repeatability is 1mm, the resolution is 1050 to 4200dpi, the size of the laser pointer has two kinds, S type CDI ( The speed type) is 25 microns, and the Q type CDI (mass type) laser spot is 18 microns. YAG laser

● In order to better achieve quality assurance, BARCO's flexo platesetter uses YAG lasers to ensure that there is enough energy to penetrate the thick synthetic black film on Cyrel. This is completely different from other diode lasers. Diode laser is often used in offset printing to expose the film and PS plate. The surface of the plate and film is coated with emulsion. The low energy laser can perform exposure imaging on the plate, but in flexo, the diode laser The image quality will be very rough, because the laser energy of the diode is not enough to burn through the thick layer of Cyrel. Even if it is exposed to an image, the shape and quality of the dot are rough.

● The following figure is a comparison of the dot shapes of YAG laser and diode laser images. It is easy to see that the shape of the dots of high-energy laser imaging is good, while the low energy laser can only form coarse dots.

Auto focus:

If the surface of the plate is smooth, the diode laser may obtain a relatively stable dot shape, but in the flexo plate making process, the surface of the flexographic plate is often uneven, for example, different plates have different thicknesses, and due to the plate Its own material characteristics, the surface of the flexographic plate is rough and uneven, and the thickness is not the same. Theory and practice have produced a great difference. Diode lasers often become larger dots,

In order to avoid high dot gain, BARCO uses an auto-focus system to automatically focus the laser according to the thickness and smoothness of the media. After the application of the autofocus system, the dot gain can be well minimized. The effect is far better than the network of diode laser imaging.

Before exposure, the flexographic plate was placed on a high-speed rotating drum. The laser head was moved along the roller direction to generate laser light for exposure. The roller was made of light carbon fiber material and the entire roller weight was 40 kg. The roller, the entire high-speed system is mounted on a marble base, which is excellent for avoiding the errors caused by the external swing. The roll width is 1525×1067 mm (60×42 in). During the exposure, the rotation speed of the roll can be 2000 rpm, because the lower speed guarantees the quality. When the thick plate is exposed, the higher speed will produce larger The centrifugal force acts to detach the plate from the roller. Therefore, in order to ensure the quality, a reasonable rotation speed must be selected. When the exposure is performed at a lower resolution, the laser beam focuses to form larger dots and the energy per unit area is lower. . Appropriately turning down the speed allows the laser energy to return to the desired level.

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When the vacuum suction device is activated, the operator places the plate on the roller, the roller rotates, the suction device adsorbs the plate material on the roller, and the connection portion of the plate material is sealed with a tape to achieve vacuum. Then cover the cover and the machine begins to expose.

exposure

Compared with the traditional plate-making process, digital exposure is even easier. The surface of the flexographic plate is coated with a 3 micron thick black film. There is also a protective layer on the surface of the traditional flexographic plate. The digital plate can be seen on the black carbon film. As the peeling layer of the traditional plate material, the surface of the plate is precoated with a synthetic carbon film in a clean environment, and also avoids dust particles. The CyrelDPS plate is mounted on the CDI roller, and then the black adhesive tape is used. When the seal reaches a vacuum, the rollers begin to rotate and begin exposure. The CDI laser is then imaged through a synthetic membrane. The laser-burned smoke and particles are cleaned by a vacuum cleaner.

Under the synthetic film is a conventional photopolymer, which reacts only with the activation of a UV laser. The infrared laser does not have any effect on the digital flexographic plate. Its ultimate purpose is to create a local high energy and leave no trace after disappearing. The final image is laser burned through the synthetic membrane, leaving no material on top of the monopolymer, resulting in extremely clear results.