Wired processing helper - rotary screen printing unit

Nowadays, consumers are increasingly demanding product packaging. In order to respond to this market demand, packaging designers and packaging and printing companies are actively seeking appropriate solutions. Screen printing can be regarded as effective. Solution: This paper analyzes and discusses the application of rotary screen printing units in connection processing.

Why Rotary Screen Printing

There are many classification methods for screen printing. According to the structure of the screen printing plate, it can be divided into flat screen printing and rotary screen printing. Rotary screen printing is a type of rotary screen printing. In practical applications, it is also the first choice for many printing companies.

Due to the thick ink layer and strong hiding power of screen printing products, the application in the field of labels and packaging printing is becoming more and more widespread.

In addition, the structure of the rotary screen printing unit is very simple, flexible, and adaptable, and it can easily form a combined printing with a narrow-width or wide-width rotary printing press adopting a modular design structure.

Combination rotary screen printers have rapidly exceeded the scope of their original pressure-sensitive label printing applications. In order to obtain unique printing effects that can be provided by screen printing, narrow web companies started to use screen printing units such as screen printing to print white or other colors as the background on film and foil substrates. The use of offset printing, flexo printing, or gravure printing to overprint color logos and logos greatly enhances the product's grade and added value.

Now we can see rotary screen printing units on flexographic, web offset, and gravure machines. Of course, the added value of screen printing units varies in different printing processes. Since screen printing can provide a very thick ink layer (which can be up to 260 μm), rotary screen printing units are often used for printing with stereoscopic three-dimensional effects and Braille labels, and the like. The use of a rotary screen printing unit to print UV varnish can result in a very high gloss or embossing effect; rotary screen printing metal ink can also replace the traditional hot stamping process, and the cost is lower, and it will not cause pollution to the environment; High-density printing, such as RFID (RF1D) printing and magnetic printing, rotary screen printing is an ideal choice; for the printing of fluorescent inks, dye-sublimation inks and other specialty inks, rotary screen printing is also very suitable s Choice.

Deep knowledge of rotary screen printing unit

In rotary screen printing, a mesh screen cylinder with a mesh is covered with ink. When the roll substrate is in contact with a rotating plate cylinder, the ink is pressed by a squeegee located inside the cylinder. The ink was allowed to pass through the mesh on the screen plate and transferred to the substrate material. We can control the thickness of the ink layer transferred to the substrate by selecting a screen plate of different mesh sizes (which can now be 400 mesh/inch or more) and adjusting the printing pressure.

The screen printing platemaking process is also relatively simple: First, the screen plate is coated with a liquid water-based emulsion to block all the meshes, and then the screen plate is dried in a drying oven; Positive prints with printed images are wrapped around screen-printed rollers coated with emulsions and exposed to UV light (since the screen plates are generally drum-shaped, it is necessary to rotate the screen cylinders). After the exposure is completed, the screen plate is rinsed in an automatic processor, and the unexposed emulsion is rinsed away, leaving the mesh part of the graphic part.

After the above steps, the plate cylinder can be printed on the machine. Different from flat screen printing, the squeegee in the rotary screen printing is fixed inside the plate cylinder. Before the printing, the inside of the roller is filled with ink. During the printing, the screen plate roller rotates and the squeegee is rotated. Under the effect of pressure, the ink is printed on the printing material; after the printing is completed, the printing plate can be cleaned and stored by the corresponding post-press equipment for use in reprinting. The emulsion layer of some screen-printed plates (such as some of Stork's screen plates) can also be peeled off and then used for coating and imaging. The number of reuses can be as high as 10-20 times. Obviously this is very important. The cost-effectiveness. We can make a small calculation. If the price of a plate cylinder is 3,000 yuan, the screen plate cost of each printing can be reduced to 150 yuan at the most by repeated use.

Rotary screen printing speeds usually range from 75 to 150 ft/min, but if printing thicker ink layers, the speed will be slower; if the intermediate drying time is longer, the speed of rotating screens can reach 150 to 350 ft. /minute. In fact, the running speed of the rotary screen printer itself is not limited (it can be up to 600 feet/minute), and the real limiting factor is the ink and its drying performance.

Rotary screen printing and flexographic printing profitable combination

Screen makers, printer manufacturers, and ink manufacturers all recognize the many advantages of rotary screen printing and the ability to process the wiring in flexographic printing. Especially in UV flexo printing, due to the instantaneous curing properties of UV inks, many problems related to ink drying are solved, and the open design of modern flexo presses makes it easy to rotate screen printing units. Embedded into the production process.

According to reports, Stork in Charlotte and several suppliers of narrow-web printing equipment have developed a new, lower-cost dro-in subsystem that works on the principle of An anilox roller inking system and a plate cylinder in a unit in a flexographic printing system are replaced by a set of rotary screen printing units. This new printing unit functions as another "impression cylinder" because The original UV lamp setting and register control are still used, so basically no extra tuning time is brought.

The effect and role of ink

Rotary screen printing inks are mostly UV-curable inks that use a UV light source for curing, but there are also solvent-based inks that use hot air to dry them. For example, conductive silver inks used in the "antennas" of printed RFID tags are solvent-based inks. Ink, which uses a hot air drying method.

In order to strengthen the status of rotary screen printing in UV flexo printing, ink manufacturers have not ceased the research and development of new inks at all times. In foreign countries, many ink companies such as Sun Chemical, Akzo Nobel and Flint Ink, and Deco-Chem in Mashawaka, Indonesia, are all working hard to research and develop UV inks for combination of flexographic and rotary screen printing. An RSF silicone-free ink for rotary screen printing. Domestic ink manufacturing companies should learn from foreign companies and strengthen technical exchanges and cooperation with foreign companies. They may also consider intensifying research and development in this area and lay the foundation for their superior position in fierce market competition.

We know that in order to increase the viscosity of the ink in screen printing and prevent the generation of bubbles, the defoamer with a higher content of silicone is generally added to the ink, but this will also bring about other problems. For example, when ink is used to make a base, when overprinting the flexo ink, due to the presence of silicone resin, overprinting and cracking may occur easily. However, if silicone is not added, ink viscosity and bubbles are insufficient. Too many problems, it is difficult to reach equilibrium in these two aspects, there is always a certain contradiction between each other, and this has always been a major problem faced in the flexographic printing on thin film printing materials. In fact, this issue has not yet been satisfactorily resolved. Davis of Deco-Chem Company believes that RSF ink has more application prospects for flexo printing of metal thin films with a certain thickness and finish, because RSF ink can solve the white spot, noise, fish that had been tried before without using silicone ink. Eyes and other performance defects, but due to the absence of silicone resin, the gloss of the ink layer after printing may be worse.

From the analysis of this paper, it can be concluded that due to the flexibility of the rotary screen printing unit and the unique printing effect of screen printing, the combination of rotary screen printing units can bring higher printing products With the added value, with the emergence of new materials and the improvement of process technology, rotary screen printing will surely be adopted by more and more printing companies, and its scope of application will also expand.

Source: Printing Technology

Wen/Liu Binqiang (Xi'an University of Technology), Qian Junhao (Jiangnan University)