Talking about Flexible Photosensitive Resin Plate

In addition to paper, the printing market includes the printing of cardboard, plastic film, composite packaging materials, corrugated cardboard, gold, silver foil and other packaging materials. This requires a new type of printing process, flexo printing, that can meet many printing requirements. Therefore, flexographic printing came into being, and it has developed rapidly in a short period of 30 years.

The first element of flexographic printing is the need to have a flexographic plate that meets the printing requirements of various carriers. In response to this request, a variety of flexographic printing presses of the same size, multi-color printing, and multi-function on-line operation have followed. A variety of flexo printing inks and auxiliary equipment have also been delivered to the market, which has led to the promotion and development of the flexo printing market. Here, the author talks about the characteristics and performance of flexible media.

Advantages of Flexible Plate in Printing Process

In the printing process, offset, gravure, and plates used in traditional letterpress are made of salted metal or hard plastic. Flexible printing plates are soft and flexible. The advantages of such a printing plate in the printing process are as follows:

1. Flexible printing plates are soft and flexible photosensitive resin materials, which are unique in the printing process. The plate becomes letterpress, so it can be inked on the plate and then transferred directly to the print carrier. (Anilox roller is rich in ink) This transfer is the most direct and simple method in the printing process, and it is easily mastered and accepted by people.
2. Because the flexographic printing plate is soft, it can adapt to various soft and hard printing carriers during the printing process. For example: Although there are corrugated marks on the surface of corrugated cardboard, plastic films are light and soft, but they can be directly printed. This is not possible with other printing methods.
3. The flexographic printing ink printing method is extremely simple. Only one or two ink rollers (one of the anilox rollers) supply ink to the printing plate to meet the need of ink supply. Therefore, the printing mechanical structure is much simpler (no ink and ink balance). The requirements and complex mechanisms of more than 10 uniform ink rollers). It is easier to manufacture six-color and eight-color machines, more economical, and more convenient to operate.
4. The use of photosensitive resin plate, the plate making method is also more convenient and cheaper than gravure plate making, especially after the flexible plate material can be directly plated by CTP, it can also obtain high-precision and high-quality printing materials, which can meet the needs of society.
5. Multi-functional online production saves time. Reducing the site can also reduce labor, save investment and raw materials, and reduce production costs.
Many advantages have led to the development of flexographic printing, especially in packaging and printing.

Flexible plate structure and use steps

In the field of modern flexo printing technology, the earliest listed resin version was in the late 1950s, and was the Cyre I version released by DuPont. But the truly sensitized flexible resin plate was in the mid-1970s. Since then, various types of flexible photosensitive resin plates have been rapidly developed and research and production projects for flexible plates have been carried out in Shanghai, Henan, Tianjin, and Beijing. In the early 1990s, the G and S flexible plates of the Shanghai Institute of Printing Technology began to enter the market and have been marketed until now. After foreign companies in the United States DuPont. Germany's BASF (NYLOFLEX), Japan's COSMOLIGHT, and Asahi Kasei have introduced various flexographic plates in succession. Their structural and physical shapes are mostly the same. Fig. 1A shows the profile of a conventional flexographic plate. .

As can be seen from Figure 1A, the flexographic plate has a total of 5 layers. The photosensitive layer, the base substrate, and the protective film are the main bodies of the plate. The procedure for using it is as follows (see Figure 2):

1. Back exposure: (Fig. 2-1) The back of the printing plate (substrate faces the light source) is exposed with an ultraviolet light source to form the substrate of the printing plate and improve the photosensitivity of the printing plate. The length of the back-exposure time also depends on the thickness of the plate and the depth of the plate pattern, about 5 to 120 seconds.
2. Remove the protective film: (Fig. 2-2) Remove the protective film on the front side of the plate first. At this time, the anti-adhesive layer remains on the plate, and the negative picture and the surface of the plate can not be adhered when they are in close contact with each other.
3. Main exposure: (Fig. 2-3) Put a negative film on the front of the plate, cover the vacuum film, and then vacuum. Exposure can be performed when the film and the plate are in close contact. The purpose of exposure is to transfer the graphic on the film to the plate. The length of time depends on the graphic format and plate thickness, and the exposure time is about 4 to 15 minutes.
4. Washing: (Fig. 2-4) The exposed plate is fed to a processor. The resin of the unexposed part of the plate material is washed away, and the cured resin after exposure remains on the plate surface, thereby forming a flexible relief plate, so that the plate material can be adapted to the printing plate type required for printing, and the protruding part can be printed in ink. The washing time is about 6 minutes.
5. Drying: (Fig. 2-5) Dry and solidify the washed printing plate for about 2 to 3 hours.
6. Detackling: (Fig. 2-6) The surface of the printing plate is irradiated with an ultraviolet light source to remove the tackiness of the printing plate surface, which is generally 4 to 12 minutes.
7. Post-exposure: (Figure 2-6) The plate is irradiated with an ultraviolet light source to complete the final hardness of the plate. After setting, the plate can be used for printing, generally 10 to 12 minutes.

The length of operation of each process above needs to be grasped separately according to the depth of the graphic plate and the different requirements of the hardness of the plate. This is the key to making the plate.

Regarding CTP, its plate structure is basically the same as that of a film using a film, and only a layer of carbon black film or foil is added under the protective film on the surface of the photosensitive layer, as shown in Fig. 1B. Show.

The difference between the two is mainly in the third step: the main exposure. After removing the plate protection film, the plate can be mounted on the vacuum drum of the digital imaging device, prepress data of the image processing system. Digitally controlled laser heads were burned to remove the carbon black film on the plate, exposing the part of the image needed for printing, and then performing the main exposure. At this point without negative film and vacuum, exposure.

Due to carbon black film and photosensitive layer closely. After printing and rinsing, the dots on the printing plate are clearly outlined, especially the fine 1% dots can also be displayed to meet the requirements of rich layers. The other steps are the same for both plates. $Page break $

Flexible photosensitive resin plate types and performance

Due to the variety of types of printing carriers covered by flexographic printing, the requirements and methods of printing on different carriers are not the same. Therefore, different hardness, different shades, different thicknesses and even different ink suitability are needed to meet the printing requirements. To this end, regardless of the company's production of flexible media have more than 10 models of flexible media for users to choose.

At present, the flexible photosensitive resin plate can be mainly divided into two categories: plate for negative plate making and plate for laser digital plate making (CTP). In the two types of plates, they are divided into hard and soft plates.
Hard plates are suitable for: corrugated paper pre-printing, beverage boxes, folding cartons, film printing. Printing of carriers such as trademark envelopes and flexible packaging.

Soft plate material is suitable for printing on multi-layer paper bags, corrugated board direct printing, kraft paper, cardboard, etc.

In addition to the above media, there is also a moderate hardness that can be mounted on offset lines for UV field coating and is a suitable plate for water-based varnish and UV varnish applications. All or part of the coating can be applied to the prints.

In the above-mentioned classified media, in order to clarify the performance of various media, each has its own technical indicators and characteristics, the specific content is described as follows:

1. The scope of application of plates: for example, corrugated paper. Flexible packaging, trademarks, plastic films, in-mold labels, etc.
2. Plate features: such as plate anti-ozone resistance, applicable ink type, exposure latitude, printable fine lines and high-resolution dots, sharp continuous tone blending, text depth range, and printing life.
3. Substrate film thickness: generally between 0.12 ~ 0.25mm, this layer of film is to prevent flexographic expansion and deformation of the basic guarantee.
4. Plate thickness (mm): usually 1.14,1.7,2.28,2.54,2.84,3.18,3.94,6.35,7.00 and other specifications, now the level version With a majority of 1.14 and 1.7, a majority of corrugated board 3.94 was used.
5. Plate size (cm): 45.7 × 76.2, 76.2 × 101, 6, 90 × 120, 106.7 × 152.4. 106.7×203.2. 127 × 203.2, etc. These dimensions refer to the sheet size when the plate is supplied, which is set by the plate material production company. Among them, the large size is mainly used for direct printing of corrugated cardboard.
6. Plate hardness: before and after exposure exposure in two kinds, with Shore hardness, before exposure is about 20 degrees to 40 degrees, after exposure 35 degrees to 65 degrees. The soft layered version has a higher hardness of about 65 degrees, and the corrugated board has a lower flex degree of 35 to 40 degrees.
7. Plate image parameters: dot range 2% to 95%, 1% to 98% (CTP). Independent line dot 0.15mm, thin line 0.1mm, graphic depth 0.75 ~ 1.1mm and 2.5 ~ 3.5mm (corrugated thick plate) and so on.
8. Use light source: UV 300~400nm.
9. Explicitly shows the exposure, washing and drying time.
10. Washing solvent: Cyrel version is tetrachloroethylene - butanol and so on.
After these performance indicators are clarified, the user can select according to the requirements of the printed matter, so that the plate can meet the requirements better.

Outlook

After nearly 10 years of development, China's flexo printing has already reached a certain scale. The supply chain of printing equipment has also been initially formed, which is very beneficial to the further development of flexo printing. In particular, with the promotion of the printing process, flexible photosensitive resin plates will certainly achieve greater breakthroughs. Looking forward to the future, if the media can achieve results in the following aspects, it will attract more users and expand the flexo printing market faster. This is our common desire. Specific content includes:

1. The further promotion and application of flexo plate making. Flexo plate making made the flexo printing site reach 200 lines/inch, the tone level increased from 2%~95% to 1%~98%, and the quality of flexographic printing also gained a lot. progress. In 2003, China's flexographic snowscape pattern and its participation in the international quality assessment of the US FTA won the bronze medal, which fully proved the advantages of the CTP plate making. This is a breakthrough in China's flexo printing products in the international competition, and inspired the confidence and determination of the flexo printing industry. According to reports, Shanghai Xinhua Precision Plate Co., Ltd. also introduced 1~2 sets of more than 2m in 2004