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., that is, "development of a PS plate for offset printing with photocatalyst."
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 contaminants 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 PS Plate
Ordinary offset printing is performed by using a film on anodized aluminum plate (PS plate) coated with photoresist, and an image is formed by a hydrophilic portion and a water repellent portion. Offset printing is to install the PS plate onto the plate cylinder, and the ink is transferred to the blanket cylinder for printing by passing the hydrophilic part of the printing plate against the water and the water repellent 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, PS plates after printing are discarded because they cannot be reused, resulting in a large amount of discarded aluminum plates.
Using the titanium oxide photocatalyst's oxidative decomposition ability and super-hydrophilic properties, Kanagawa and Tokyo Ohka Co., Ltd. have carried out research and development of "photocatalyst offset PS plates" that can be reused for PS plates. First, a photocatalyst hydrophilic/water repellent image production test was conducted using a conventional PS plate making process and a film. 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 self-organized 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 UV to pass through the SAM component under the photocatalyst to be decomposed and removed under the action of the oxidative decomposition mechanism of the photocatalyst to expose the titanium oxide coating. The titanium oxide coating shows extremely strong hydrophilic properties. In addition, the SAM of the printing plate portion that shields the ultraviolet rays by the printing plate remains 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.
4 Application of Inkjet Technology - Non-filming of Photocatalyst Offset Printing Plates
At present, the computerization process in the printing field is advancing. By digitizing the data, the plate making process is allowed to enter the so-called CTP stage where the printing plate is scanned directly by the computer to produce a printing plate. As a result, the traditionally used printing plate is eliminated, and the plate making process is greatly reduced, which leads to the realization of short delivery period and cost reduction.
In the second step, with the aim of CTP, the non-filming of the photocatalyst offset printing plate was discussed. The process is that, after the titanium oxide photocatalyst coating and the SAM self-organizing monomolecular film layer are coated on the printing plate, the water-based ink is sprayed on the printing plate to form an image by using an inkjet method to replace the original film. Under the irradiation of ultraviolet rays, the SAM on the printing plate which is not sprayed with the aqueous ink is decomposed by the action of the photocatalyst to remove and expose the photocatalyst layer to become a hydrophilic portion. The part of the printing plate that is sprayed with water-based ink retains the SAM because the water-based ink shields the ultraviolet rays. Next, the aqueous ink was removed by washing with water to prepare a photocatalyst type printing plate having hydrophilicity/water repellency. Using this printing plate (plate size 570 mm x 309 mm), a color printing test was conducted on a proofer of a printing factory, and a good printing effect was obtained.
5 PS version recycling
The third step is to discuss the purpose of this technology - the recycling of the PS version. The PS plate used in the aforementioned color printing test was thoroughly irradiated with ultraviolet rays to completely remove the SAM layer on the surface thereof. Then, SAM was again applied to form an ink jet image to form an aqueous ink image, followed by irradiation with ultraviolet rays, followed by washing with water to produce a regenerated PS plate, which was then sent to a printing plant for a color print test. The results of the test confirmed that the print quality of the reprinted plate was exactly the same as the new print quality. This achieves the construction of practical goals.
6 for practical use
Compared with the conventional PS plate, the photocatalyst PS plate developed this time has simplified the plate-making process, reduced the amount of waste liquid, and can also be used for regeneration. Therefore, the photocatalyst PS plate is used as a printing process with low cost. This is expected to be associated with technologies that significantly reduce the environmental load. In addition, this technology is no different from the now popular CTP process. The use of an inkjet printer eliminates the need for an expensive laser exposure machine, resulting in low equipment investment and easy purchase.
The current problems are the number of reproductions of the PS plate, and the service life problems caused by the wear of the PS plate during the printing process. These problems are now being resolved.
PS version of the base material - aluminum printing capacity is poor, has become an unfavorable factor of recycling, so it is currently developing titanium plate-based PS version. The surface of the titanium metal plate is treated by heat treatment or anodization, and a photocatalyst layer of titanium oxide is formed on the surface of the titanium metal plate. This titanium-based PS plate has now been made. Using this titanium-based PS plate, the same printing test and rejuvenation test as above were performed, confirming that it can be used for printing and laying the foundation for its technology. It can be expected that the number of recycling of photocatalyst PS plates can also be greatly improved.
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., that is, "development of a PS plate for offset printing with photocatalyst."
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 contaminants 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 PS Plate
Ordinary offset printing is performed by using a film on anodized aluminum plate (PS plate) coated with photoresist, and an image is formed by a hydrophilic portion and a water repellent portion. Offset printing is to install the PS plate onto the plate cylinder, and the ink is transferred to the blanket cylinder for printing by passing the hydrophilic part of the printing plate against the water and the water repellent 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, PS plates after printing are discarded because they cannot be reused, resulting in a large amount of discarded aluminum plates.
Using the titanium oxide photocatalyst's oxidative decomposition ability and super-hydrophilic properties, Kanagawa and Tokyo Ohka Co., Ltd. have carried out research and development of "photocatalyst offset PS plates" that can be reused for PS plates. First, a photocatalyst hydrophilic/water repellent image production test was conducted using a conventional PS plate making process and a film. 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 self-organized 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 UV to pass through the SAM component under the photocatalyst to be decomposed and removed under the action of the oxidative decomposition mechanism of the photocatalyst to expose the titanium oxide coating. The titanium oxide coating shows extremely strong hydrophilic properties. In addition, the SAM of the printing plate portion that shields the ultraviolet rays by the printing plate remains 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.
4 Application of Inkjet Technology - Non-filming of Photocatalyst Offset Printing Plates
At present, the computerization process in the printing field is advancing. By digitizing the data, the plate making process is allowed to enter the so-called CTP stage where the printing plate is scanned directly by the computer to produce a printing plate. As a result, the traditionally used printing plate is eliminated, and the plate making process is greatly reduced, which leads to the realization of short delivery period and cost reduction.
In the second step, with the aim of CTP, the non-filming of the photocatalyst offset printing plate was discussed. The process is that, after the titanium oxide photocatalyst coating and the SAM self-organizing monomolecular film layer are coated on the printing plate, the water-based ink is sprayed on the printing plate to form an image by using an inkjet method to replace the original film. Under the irradiation of ultraviolet rays, the SAM on the printing plate which is not sprayed with the aqueous ink is decomposed by the action of the photocatalyst to remove and expose the photocatalyst layer to become a hydrophilic portion. The part of the printing plate that is sprayed with water-based ink retains the SAM because the water-based ink shields the ultraviolet rays. Next, the aqueous ink was removed by washing with water to prepare a photocatalyst type printing plate having hydrophilicity/water repellency. Using this printing plate (plate size 570 mm x 309 mm), a color printing test was conducted on a proofer of a printing factory, and a good printing effect was obtained.
5 PS version recycling
The third step is to discuss the purpose of this technology - the recycling of the PS version. The PS plate used in the aforementioned color printing test was thoroughly irradiated with ultraviolet rays to completely remove the SAM layer on the surface thereof. Then, SAM was again applied to form an ink jet image to form an aqueous ink image, followed by irradiation with ultraviolet rays, followed by washing with water to produce a regenerated PS plate, which was then sent to a printing plant for a color print test. The results of the test confirmed that the print quality of the reprinted plate was exactly the same as the new print quality. This achieves the construction of practical goals.
6 for practical use
Compared with the conventional PS plate, the photocatalyst PS plate developed this time has simplified the plate-making process, reduced the amount of waste liquid, and can also be used for regeneration. Therefore, the photocatalyst PS plate is used as a printing process with low cost. This is expected to be associated with technologies that significantly reduce the environmental load. In addition, this technology is no different from the now popular CTP process. The use of an inkjet printer eliminates the need for an expensive laser exposure machine, resulting in low equipment investment and easy purchase.
The current problems are the number of reproductions of the PS plate, and the service life problems caused by the wear of the PS plate during the printing process. These problems are now being resolved.
PS version of the base material - aluminum printing capacity is poor, has become an unfavorable factor of recycling, so it is currently developing titanium plate-based PS version. The surface of the titanium metal plate is treated by heat treatment or anodization, and a photocatalyst layer of titanium oxide is formed on the surface of the titanium metal plate. This titanium-based PS plate has now been made. Using this titanium-based PS plate, the same printing test and rejuvenation test as above were performed, confirming that it can be used for printing and laying the foundation for its technology. It can be expected that the number of recycling of photocatalyst PS plates can also be greatly improved.
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