Gravure printing plate technology development

Gravure printing is a magic printing process. Although the process is simple, the printed images are rich in layers and colorful. Sharpness is good. high quality. The only challenge is the difficulty of making gravure cylinders. The first copper plated gravure cylinder was introduced in 1446. It has been a few hundred years since its inception. With the development of science and technology, the gravure plate making technology has become more and more advanced, and it has become increasingly complex. During the period has experienced a number of development stages. The earliest advent was the hand-engraved gravure, and later there were needle gravure, gravure gravure, etched gravure, and direct engraving intaglio. The core problem and the most basic principle of the various kinds of gravure platemaking processes are the imaging methods adopted, whether it is engraving or etching on the surface of the copper layer.

Requirements for gravure platemaking technology

People who have experienced erosion in the gravure platemaking era know that the etching and plate making process is quite complicated. Moreover, in the etching and plate making, a lot of expensive materials and equipment are needed, and many of the process steps have to be completed by manual operation. Many are subject to the subjective factors of the operator. Compared with the etching platemaking process, the electronic engraving plate making process is too simple, and it can also realize the digital control of the process. The operation is simple and the quality is reliable. At present, no-film carving has been realized, and it is no longer necessary to scan original information and data information. The electric carving needle can be directly driven and controlled, and the engraving process can be controlled by software.

The electronic engraving process greatly simplifies the production process of the gravure cylinder. The production efficiency has been improved, and the quality of the plate cylinder and the reliability of the plate making process have also been greatly improved. In addition, because many chemicals that are harmful to the human body have been abandoned, the working environment has not only been improved, but also better for the health of the operators. For example, the gravure printing platen used in the printing and printing of books can produce two color separation pages per person per shift, but with an active K6 Klischograph engraving machine, it can produce 150 color separations per person per shift. page. The same is true in the field of packaging and printing, and the electronic engraving method has greatly improved the platemaking efficiency.

In the future no matter what re-embossed platemaking technology will emerge, in order to gain recognition and great development, we must meet certain conditions, namely whether we can guarantee the quality of the upgraded cylinder, production efficiency and process reliability, which is also a measure of each The important criteria for the advanced nature of new processes and new technologies. If the process cannot be simplified, new processes cannot satisfy people's needs.

Electronic engraving plate making technology

Normally, some references refer to the gravure as a continuous tone printing, that is to say when the ink is transferred from the web of the plate cylinder to the substrate, the true natural gray value can be obtained. Because the gravure ink is as thin as water, it is transparent on the surface of the substrate and has a filtering effect on the light, similar to the performance of the silver salt layer in the photographic film.

At the end of the 19th century, with the development of photographic technology, people put forward higher requirements for the continuous printing of images. The first proposed mesh tuning theory for continuous tone screening is that the gray value of the image is represented by dots of different area sizes. This method has been used up to now, but the way of original manuscript has been greatly affected. change. The original was a non-contact screen, which was later replaced by a contact screen. Now it is done by a RIP (raster image processor). Usually, any value between 0 and 255 is used to represent the gray value of the image, and then RIP transforms into dots of different shapes, sizes, and positions.

The electronic engraving gravure process is obviously much simpler than the plate imaging process of embossing, offset printing and flexo printing. The value corresponding to the gray value of the original image can be directly transmitted to the electronic engraving machine, and the diamond engraving needle is controlled to carry out engraving on the surface of the copper layer. Moreover, the area and depth of the engraved cell can be changed. It is worth mentioning that , Electronic Engraving With the simple adjustment of the tone curve, high-quality gravure plate cylinders suitable for specific printing conditions (including printing presses, inks, paper, etc.) can be obtained.

As described above, it is very important to use the gray value data to control the electric engraving needle to achieve an exact match with the gravure mesh tone image. In other words, the perfect combination of electronic engraving and gravure printing process has greatly improved the reliability of the process and the quality of the plate cylinder, which is incomparable with etching gravure (including traditional gravure and direct screen gravure).

It is worth mentioning that, unlike offset printing, in the reproduction of text and lines, electronic engraving cannot achieve finer reproduction than the selected number of engraving lines, which limits the reproduction quality of text and lines. In recent years, HELL has improved the dynamic control of electric engraving needles and developed HQH software, which can effectively eliminate the "jaggies" of small yin and yang lines. Also, in many cases, gravure text is softer and easier to read than offset printing. However, there is no doubt that packaging printing has higher requirements for the quality of gravure printing. People hope that the quality of text and lines can be further improved.

Due to the many limitations of the traditional gravure platemaking process, HELL has set new goals with its 40 years of experience in the field of plate making, and it is necessary to further improve the platemaking process and quality of gravure cylinders. In order to achieve this goal, what kind of protection can be provided from the technical point of view? The following briefly describes the imaging technology of the gravure cylinder.

Traditional gravure platemaking technology

The traditional photogravure, also known as "shadow edition," completely relies on changes in the depth of the cell site to represent the tone level. For this purpose, the carbon paper must be screened and continuously sun-treated with carbon screens and continuous sun-shading images, and the area size of the carbon paper should be the same depending on the permeability of the etching solution. Different depths of cyberspace.

From the above, we can easily see that the traditional gravure platemaking process is more complicated and has many steps. There are 11 steps from preparation of carbon paper to corrosion. Therefore, the predictability and repeatability of the process are relatively poor. For example, the depth of corrosion of the cell and the control of the wall are very difficult. However, what is more difficult is the control of the bright tuning part. The bright tuning requires that the depth of corrosion of the net is very shallow and cannot exceed 1 μm, but it is really difficult to achieve.

At the same time changing the area and depth of the mesh can solve this problem, but it must be done twice for carbon paper. The depth of the cell site is controlled by one imaging with continuous tone pictures. Secondary imaging uses the same original screen, so that the depth and area of ​​the mesh can be changed at the same time.

The emergence of such gravure platemaking technology marks a step forward in the reproduction of bright and dark tone. However, the inherent instability of carbon paper and corrosion is still a problem. After all, the process is too complicated and difficult. control. With the advent of electronic engraving technology, the electric carving needle can easily and precisely engrave the cells of different area sizes and different depths. Am Art is simple, has high consistency and high reliability, and gradually replaces the traditional gravure.

Photographic direct screen plate making technology

In addition to traditional photogravure, direct photogravure processes have also been around for a long time, especially in package gravure applications. Photographic Direct Screening The basic principle of the gravure platemaking process is that after the platen has been plated with copper and polished, it is coated with a photosensitive layer, exposed and then imaged, and then the copper layer is etched.

The photosensitive layer was first coated on the copper layer of the platen roller and exposed with a high-pressure mercury lamp. Later laser etching technology emerged. Instead of film, the image data directly controls the fine laser beam imaging on the photosensitive layer. There have been two kinds of digital imaging platemaking methods: one is coating photosensitive film. Before the etching, the exposed photosensitive layer needs to be developed to expose the copper layer of the graphic part; the other is to use a special thin coating as the laser ablation layer, and the laser beam can directly The protective coating is completely ablated and the copper layer is exposed. Therefore, it is possible to directly perform the etching without developing treatment, but it is necessary to increase the energy of the laser beam.

Regardless of whether the imaging process is digital or traditional screening film, the dot structure of the area change is only created on the coating, and the depth information cannot be reflected. Corroding the exposed part of the copper layer is a rather backward process. If the operator momentarily neglects to perform the same level of corrosion on the exposed part of the copper layer, the continuous tone characteristic of the image cannot be expressed. With this type of printing plate, lines and text can be reproduced well, but the image is less effective because the image contains rich tone levels and requires a high level of depth.

In addition, the photographic direct-screening process has a disadvantage that the process is complicated and has many steps, which greatly reduces the reliability of the platemaking process. In general, the more links passed, the worse the reliability of the process. Why do you say this? Because the overall reliability of the entire plate making process is bound to be affected by all aspects and steps, if the entire platemaking process is divided into S steps To complete, the reliability of each step is 98%, so the total reliability of the platemaking process is only 90%, that is to say 10% of the produced roller may be waste, and the scrap rate of the electronic engraving process is Much lower, generally not even 2%.

In short, compared with the electronic engraving platemaking process, all the photo-gravure direct-gravure and gravure plate-making processes (even with digital imaging technology are no exception) have three fundamental problems: the imaging method is not suitable for high-quality printing. The disadvantages of the corrosion process itself and the complex process steps.

Engraving the zinc layer directly with a laser beam

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