Reproducible PS Edition with Photocatalyst and Inkjet Technology

1 Photocatalyst found in Japan

It has been found that photocatalysts represented by titanium oxide have oxidative decomposition ability and strong hydrophilicity once they encounter sunlight or fluorescent light. In recent years, photocatalyst products using this property have been commercialized in a wide range of fields and the market has grown rapidly. Photocatalyst was discovered in Japan (Bendo Fujishima effect in 1967). Its product market is mainly formed and developed in Japan. It can be said that it is an original technology from Japan.

To promote the full development and popularization of photocatalyst technology, at the Kanagawa Institute of Science and Technology, Fujikura, the chairman of the "father of photocatalyst", provided funding to operate the photocatalyst open laboratory and photocatalyst museum. At the same time, it also conducted basic research and applied research, and conducted joint research and development with companies. Among them, a joint research and development was carried out with Tokyo Ohka Kogyo Co., Ltd., namely, "development of offset printing with photocatalyst using PS version".

2 Photocatalyst characteristics

Photocatalysts are defined as substances that, by absorbing light energy, do not change by themselves but can cause various chemical reactions. The most widely used photocatalyst is titanium oxide. Studies have found that titanium oxide has oxidative decomposition and strong hydrophilic properties under light (sunlight, fluorescent light) irradiation. Oxidative decomposition ability can be illustrated by comparison with photosynthesis in plants. Photosynthesis is the chlorophyll in the leaves absorbs energy from sunlight, synthesizes organic matter (starch) with water and carbon dioxide, and then discharges oxygen; while photocatalysts such as titanium dioxide absorb sunlight and other light energy and decompose organic matter into water and carbon dioxide. That is to say, photosynthesis and photocatalyst elicit an entirely opposite reaction. Chlorophyll can also be said to be a kind of photocatalyst.

The oxidative decomposition function of the photocatalyst can be used to decompose and remove odor or voc gas, remove the discharged nitrogen oxides to achieve air purification, or remove organic impurities in the water pool to achieve water purification, and can also be used for viruses, Antibacterial sterilization of bacteria and other microorganisms.

In addition, the photocatalyst also exhibits another property, namely its affinity with water under light conditions - super hydrophilicity. That is, under the light conditions of the photocatalyst, the water on the surface of the photocatalyst will expand into a thin water film. To make the mirror non-fogging or dirty, the mirror is coated with titanium oxide. Under light conditions, the water will go under the oil and float up and be washed away with the water.

The use of this super-hydrophilic property has led to a number of applications, such as the waterproof spray coating for automotive rearview mirrors, dirt-repellent coatings for building or residential exterior walls and window panes, and anti-dirty roofing materials (tents).

At present, application research and development are being carried out in a wide range of fields by utilizing the oxidative decomposition ability and super-hydrophilic properties of photocatalysts. The Kanagawa Institute of Science and Technology and Tokyo Shiwak Co., Ltd. have joined hands to develop the application of offset printing by utilizing the performance of photocatalysts.

3 Application on Offset Printing Ps Edition

Ordinary offset printing is performed on a photo resist-coated anodized alumina plate (PS plate) using a film to form an image from a hydrophilic portion and a water repellent portion. Offset printing is to install the PS version on the printing plate cylinder, and the ink is transferred to the blanket cylinder for printing by passing the hydrophilic part of the printing plate onto the water and flooding the part.

The offset printing plate making process develops and coats the gum after exposure. In this process, the developing solution and the gum waste solution are generated and need to be processed. In addition, the ps plate after printing is discarded because it cannot be reused, resulting in a large amount of discarded aluminum plates.

Using the titanium oxide photocatalyst's oxidative decomposition ability and superior hydrophilic properties, Kanagawa and Tokyo Ohka Chemical Co., Ltd. have conducted research and development of the "photocatalyst offset printing version" that can be reused for the PS version. First, using the traditional PS production process and film, photocatalyst hydrophilic / water-repellent image production test. The specific process is as follows: Firstly, an anodic alumina plate is coated with a titanium oxide photocatalyst coating to replace the original photoresist; then a layer of self-organizing monomolecular film sam composed of a water-repellent organic substance is formed thereon. Self assembled monolayer). Next, a printing plate was used to expose it by ultraviolet irradiation. The film allows the ultraviolet light to pass through the sam component below the part to be decomposed and removed under the action of the photocatalytic oxidation decomposition mechanism to expose the titanium oxide coating. The titanium oxide coating shows extremely strong hydrophilic properties. In addition, the sam portion of the printing plate that shields the ultraviolet rays by the printing plate is left as it is, and becomes a water repellent portion. In this way, an image having hydrophilicity/water repellency obtained by the photocatalyst is formed.

In this process, the conventional development and gluing process after exposure has been unnecessary, and no corresponding waste liquid will be produced.

For the selected printing test pattern, a print test with lithographic printing under the same conditions gave a positive result: printing using this printing plate was completely successful and feasible.

Next, the scope of the test was expanded and a printing press test of the web mill was performed. The test used a 570 mm x 309 mm size plate, and a single color printing test with a resolution of 45 lines/inch was performed. In the 5000-page printing test conducted, good print quality was obtained.