一ã€Waterless Offset Overview
Waterless offset printing refers to a type of lithographic printing method that uses special inks to complete printing without using aqueous solution dampening, using an ink-repelling silicone rubber layer as a blank part of the printing plate. The most fundamental feature of traditional lithographic offset printing is the use of aqueous solution dampening, which uses the principle of mutual exclusion of ink and ink to balance the ink and water on the printing plate to achieve the transfer of dots. Whether the ink is balanced in the printing process will seriously affect the printing effect. However, in actual production, it is very difficult to really achieve the ink-water balance. It is necessary for operators to fully grasp the suitability of printed materials and to standardize the operation of the printing process in production. At the same time, it is also affected by the performance of the printing equipment. In this case, waterless offset printing came into being.
As early as the end of the 1960s, the 3M company in the United States developed a waterless offset printing plate, but due to a series of technical reasons gave up further research. Japan's Toray Corporation purchased a copyrighted patent and conducted research. In 1977, it showed the world the first waterless offset printing plate. Since then, waterless offset printing plates, inks and printing equipment have been correspondingly developed. In recent years, the United States, Japan, Germany, and Switzerland have rapidly developed waterless offset printing, and have achieved considerable economic benefits. In Japan, 15% of sheet-fed four-color printing presses use waterless printing. More specifically, Japan currently has about 400 offset presses that use waterless offset printing, of which 200 are completely waterless offset presses. Another 200 units can be converted between traditional offset printing and waterless offset printing.
Second, the characteristics of waterless offset
The main difference between waterless offset printing and conventional offset printing is that no fountain solution is needed. Therefore, it has its own characteristics on the printing plate, ink and printing equipment.
1. Plates: Waterless offset plates consist of multiple layers. The substrate is an aluminum plate coated with a layer of diazo photosensitive material, and the outermost layer is a silicone layer of about 2 μm thick, which has strong ink resistance and acts as a blank portion on the printing plate. In order to make the aluminum plate and the diazo photosensitive material, the diazo photosensitive material and the silica gel layer adhere well to each other, a gluing layer made of a photosensitive diazonium compound is also coated between them.
The film used in the platemaking process may be a positive image or a negative image. Use an ultraviolet light source for exposure. If a negative image is used, the photosensitive portion is peeled off and the unexposed portion (ie, the blank portion) retains the silicone layer; if a positive image is used, the photosensitive portion is hardened, and the unexposed portion is detached to form a graphic portion. The plate making process is the same as for the PS plate. One point to emphasize here is that waterless offset printing gives a gravure plate that is different from the PS plate. In this way, in the process of ink transfer, the dot enlargement formed under the effect of the printing pressure is very small, and the faithful reproduction of the graphic and picture is basically achieved.
2. Ink: Waterless offset requires the use of specific inks. It requires a higher viscosity to ensure that no dirty plate appears (i.e., the blank does not contain ink). It also requires that the ink does not contain rough particles to prevent scratches on the protective film on the surface of the plate, and at the same time avoid the friction of the particles and reduce heat generation. The viscosity of the ink. For high viscosity anhydrous offset inks, temperature is a critical factor. Small changes in temperature can cause the ink viscosity to change greatly. For example, the viscosity of the ink at 25°C is 100-150 poise, but at 40°C the viscosity drops sharply to 30-40 poise. In actual production, inks of different viscosities are used depending on the temperature conditions. For example, the use of high-viscosity inks during the summer and the use of relatively low-viscosity inks during the winter can be used. Due to the high viscosity requirements of the ink, an effective cooling system will be the key to the success of waterless offset printing in the printing process.
3. Temperature control system on printing equipment: In the continuous printing process, due to friction and other factors will cause the plate layout temperature increases, resulting in decreased printing ink viscosity. Therefore, the temperature needs to be well controlled in waterless offset printing. In 1989, Toray developed a special temperature control system for sheetfed and web presses. This initial temperature control system has the same temperature for each process color group. However, studies have shown that inks of different colors react differently to changes in temperature. Therefore, the temperature of each printing color group needs to be controlled separately. For modified waterless offset presses, the main purpose is to control the temperature by adding hollow cylinders on a conventional offset press and applying cooling water to it. This method is called water cooling. Another cooling method is air cooling, which blows cold air to the surface of the plate cylinder to reduce the temperature of the plate.
Third, the advantages of waterless offset
The advantages of waterless offset printing are mainly focused on two aspects: one is the printing cost, and the other is the quality of printed matter.
1. Printing cost: Since there is no effect of dampening water, it does not need to spend a lot of time to achieve the best ink-water balance when printing. It speeds up the printing speed and reduces the waste of the test printing paper; because the ink can be well Drying can reduce the drying temperature of each printing color group, thereby reducing energy consumption. In the printing process, it reduces the downtime caused by changes in the ink-water balance, improves production efficiency, and achieves economic benefits.
2. Printing quality: Because of the low dot gain rate of waterless offset printing, it has good dot reproducibility, especially the details of the dark tone can be reproduced well; because there is no dampening water, it will not cause the paper's stretching deformation , Improve overprint accuracy; India ink uniform thick, bright ink; printing plate printing rate greatly improved; wide range of substrates, in addition to printing on paper, but also on the flat plastic and metal surface printing.
3. In addition to the above-mentioned advantages of quality and economy of printed materials, waterless offset printing does not contain alcohol, so it has also played a positive role in protecting the environment and preventing pollution.
IV. Development Status and Development Prospect of Waterless Offset Printing in China
From the above analysis, many advantages of waterless offset printing are unmatched by ordinary offset printing methods. Its appearance is a huge leap forward in the lithographic offset printing technology. The recognition and continuous development of the lithographic offset printing industry promotes its wider and wider application. In China, waterless offset printing is gradually being accepted by the people. A few enterprises have implemented waterless offset printing on the structural adjustment of the original offset printing equipment, and have achieved good economic benefits, which has opened up a precedent for waterless offset printing in China. . Due to the high printing quality of waterless offset printing, it is particularly suitable for printing exquisite pictures, exquisite packaging and other high-grade prints to meet the needs of the market. However, we have to face several technical problems in waterless offset printing, especially printing plates, inks and temperature control systems. The study of waterless offset printing inks is also a technical difficulty. The waterless offset printing inks currently used in China are mainly imported, and the price is much higher. However, through actual production cost analysis, it is concluded that low paper waste and high production efficiency can make up for the high costs brought about by the plate and ink. In addition, according to the actual situation of most printing companies in China, it is feasible to convert the existing offset press into a waterless offset press. The simplest method is to separate the dampening system of the existing equipment, without using a water cooling system and air cooling. Under the circumstances of the system, strictly controlling the temperature of the printing shop can achieve waterless offset printing without much investment.
A large number of researchers in China have been working on the problems of waterless offset printing. It can be predicted that the day when localization of printing plates and inks is realized is the day when waterless offset printing is flourishing in China. Waterless offset printing, as an advanced printing method, will eventually exert its tremendous advantages in people's continuous exploration, and it will occupy an irreplaceable place in the long-term development of printing.
Waterless offset printing refers to a type of lithographic printing method that uses special inks to complete printing without using aqueous solution dampening, using an ink-repelling silicone rubber layer as a blank part of the printing plate. The most fundamental feature of traditional lithographic offset printing is the use of aqueous solution dampening, which uses the principle of mutual exclusion of ink and ink to balance the ink and water on the printing plate to achieve the transfer of dots. Whether the ink is balanced in the printing process will seriously affect the printing effect. However, in actual production, it is very difficult to really achieve the ink-water balance. It is necessary for operators to fully grasp the suitability of printed materials and to standardize the operation of the printing process in production. At the same time, it is also affected by the performance of the printing equipment. In this case, waterless offset printing came into being.
As early as the end of the 1960s, the 3M company in the United States developed a waterless offset printing plate, but due to a series of technical reasons gave up further research. Japan's Toray Corporation purchased a copyrighted patent and conducted research. In 1977, it showed the world the first waterless offset printing plate. Since then, waterless offset printing plates, inks and printing equipment have been correspondingly developed. In recent years, the United States, Japan, Germany, and Switzerland have rapidly developed waterless offset printing, and have achieved considerable economic benefits. In Japan, 15% of sheet-fed four-color printing presses use waterless printing. More specifically, Japan currently has about 400 offset presses that use waterless offset printing, of which 200 are completely waterless offset presses. Another 200 units can be converted between traditional offset printing and waterless offset printing.
Second, the characteristics of waterless offset
The main difference between waterless offset printing and conventional offset printing is that no fountain solution is needed. Therefore, it has its own characteristics on the printing plate, ink and printing equipment.
1. Plates: Waterless offset plates consist of multiple layers. The substrate is an aluminum plate coated with a layer of diazo photosensitive material, and the outermost layer is a silicone layer of about 2 μm thick, which has strong ink resistance and acts as a blank portion on the printing plate. In order to make the aluminum plate and the diazo photosensitive material, the diazo photosensitive material and the silica gel layer adhere well to each other, a gluing layer made of a photosensitive diazonium compound is also coated between them.
The film used in the platemaking process may be a positive image or a negative image. Use an ultraviolet light source for exposure. If a negative image is used, the photosensitive portion is peeled off and the unexposed portion (ie, the blank portion) retains the silicone layer; if a positive image is used, the photosensitive portion is hardened, and the unexposed portion is detached to form a graphic portion. The plate making process is the same as for the PS plate. One point to emphasize here is that waterless offset printing gives a gravure plate that is different from the PS plate. In this way, in the process of ink transfer, the dot enlargement formed under the effect of the printing pressure is very small, and the faithful reproduction of the graphic and picture is basically achieved.
2. Ink: Waterless offset requires the use of specific inks. It requires a higher viscosity to ensure that no dirty plate appears (i.e., the blank does not contain ink). It also requires that the ink does not contain rough particles to prevent scratches on the protective film on the surface of the plate, and at the same time avoid the friction of the particles and reduce heat generation. The viscosity of the ink. For high viscosity anhydrous offset inks, temperature is a critical factor. Small changes in temperature can cause the ink viscosity to change greatly. For example, the viscosity of the ink at 25°C is 100-150 poise, but at 40°C the viscosity drops sharply to 30-40 poise. In actual production, inks of different viscosities are used depending on the temperature conditions. For example, the use of high-viscosity inks during the summer and the use of relatively low-viscosity inks during the winter can be used. Due to the high viscosity requirements of the ink, an effective cooling system will be the key to the success of waterless offset printing in the printing process.
3. Temperature control system on printing equipment: In the continuous printing process, due to friction and other factors will cause the plate layout temperature increases, resulting in decreased printing ink viscosity. Therefore, the temperature needs to be well controlled in waterless offset printing. In 1989, Toray developed a special temperature control system for sheetfed and web presses. This initial temperature control system has the same temperature for each process color group. However, studies have shown that inks of different colors react differently to changes in temperature. Therefore, the temperature of each printing color group needs to be controlled separately. For modified waterless offset presses, the main purpose is to control the temperature by adding hollow cylinders on a conventional offset press and applying cooling water to it. This method is called water cooling. Another cooling method is air cooling, which blows cold air to the surface of the plate cylinder to reduce the temperature of the plate.
Third, the advantages of waterless offset
The advantages of waterless offset printing are mainly focused on two aspects: one is the printing cost, and the other is the quality of printed matter.
1. Printing cost: Since there is no effect of dampening water, it does not need to spend a lot of time to achieve the best ink-water balance when printing. It speeds up the printing speed and reduces the waste of the test printing paper; because the ink can be well Drying can reduce the drying temperature of each printing color group, thereby reducing energy consumption. In the printing process, it reduces the downtime caused by changes in the ink-water balance, improves production efficiency, and achieves economic benefits.
2. Printing quality: Because of the low dot gain rate of waterless offset printing, it has good dot reproducibility, especially the details of the dark tone can be reproduced well; because there is no dampening water, it will not cause the paper's stretching deformation , Improve overprint accuracy; India ink uniform thick, bright ink; printing plate printing rate greatly improved; wide range of substrates, in addition to printing on paper, but also on the flat plastic and metal surface printing.
3. In addition to the above-mentioned advantages of quality and economy of printed materials, waterless offset printing does not contain alcohol, so it has also played a positive role in protecting the environment and preventing pollution.
IV. Development Status and Development Prospect of Waterless Offset Printing in China
From the above analysis, many advantages of waterless offset printing are unmatched by ordinary offset printing methods. Its appearance is a huge leap forward in the lithographic offset printing technology. The recognition and continuous development of the lithographic offset printing industry promotes its wider and wider application. In China, waterless offset printing is gradually being accepted by the people. A few enterprises have implemented waterless offset printing on the structural adjustment of the original offset printing equipment, and have achieved good economic benefits, which has opened up a precedent for waterless offset printing in China. . Due to the high printing quality of waterless offset printing, it is particularly suitable for printing exquisite pictures, exquisite packaging and other high-grade prints to meet the needs of the market. However, we have to face several technical problems in waterless offset printing, especially printing plates, inks and temperature control systems. The study of waterless offset printing inks is also a technical difficulty. The waterless offset printing inks currently used in China are mainly imported, and the price is much higher. However, through actual production cost analysis, it is concluded that low paper waste and high production efficiency can make up for the high costs brought about by the plate and ink. In addition, according to the actual situation of most printing companies in China, it is feasible to convert the existing offset press into a waterless offset press. The simplest method is to separate the dampening system of the existing equipment, without using a water cooling system and air cooling. Under the circumstances of the system, strictly controlling the temperature of the printing shop can achieve waterless offset printing without much investment.
A large number of researchers in China have been working on the problems of waterless offset printing. It can be predicted that the day when localization of printing plates and inks is realized is the day when waterless offset printing is flourishing in China. Waterless offset printing, as an advanced printing method, will eventually exert its tremendous advantages in people's continuous exploration, and it will occupy an irreplaceable place in the long-term development of printing.
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