Waterless offset printing technology has been adopted in digital imaging machines for printing machinery. Waterless offset printing technology, new materials for printing plates and inks have been continuously introduced, and traditional printing technologies combined with digital technologies will make new contributions to the modern printing industry.
Problems and progress
1. Avoid the problems of ink and water balance
The hardest part of offset printing is to achieve the correct ink-water balance. Too much water can wrinkle the paper and thin the ink film transferred to the paper. Too little water can make the ink uncontrollable and transfer to the non-graphic area. The ink-to-ink ratio also affects the viscosity of the ink. In the case of multi-color printing, there is also a problem of how to control the post-printing ink to superimpose the previously printed ink. It is not easy to achieve the correct ink-water balance. The balance of ink and ink is influenced by various factors such as temperature, humidity, paper type, and printing speed. Waterless offset printing brings many benefits because there is no ink-ink balance. Waterless offset technology has been invented for 40 years. The early “dryography†system emerged in early 1970. Although the dryography system can be used in the laboratory, it does not work in the field. The first practical waterless offset printing technology was introduced by the Japanese Toray company at Drupa International Printing Exhibition in 1977, but Toray had not been ready to bring its waterless offset products to market. Two years after Drupa'77 was held, Toray's waterless offset printing plate was finally sent to the user. Toray media use silica gel instead of water as the oil repellent component (the area can become the ink receiving area when the silicon layer is removed during plate making). Toray plates are more expensive, about 2-4 times more expensive than traditional offset plates. This plate is easily damaged, is easily scratched, and quickly corrodes during the printing process.
2. Need to increase investment
One of the major problems with waterless offset printing is temperature control. The viscosity of the ink varies with temperature and is only rejected by silicon in a narrow range of viscosity. During the printing process, the ink will heat up due to the friction between the ink rollers. When the temperature rises to a certain degree, the ink viscosity will become thin and the printing plate will become dirty. If there is no self-cooling effect, perhaps the same problem will occur on a conventional offset press. The self-cooling effect causes the ink roller to pick up fine water droplets from the plate. The water droplets float on the ink film and return to the ink roller. When the water evaporates, the ink is cooled. One solution to stabilize the ink viscosity is to use special inks, which maintain a constant viscosity over a wide temperature range; another trick is to use thicker inks during the long live printing process. The real solution, however, is to pump coolant through internal tubes on some of the rollers to stabilize the ink temperature. This method will add considerable cost to the new press, which is a purely expensive modification to the old press. In any case, this method can use the same ink and the same operating technology for the short live and long live.
3. Advantages of waterless offset printing
Because there is no water to weaken the ink film, waterless offset printing on the printed page can have a higher ink density, so the print image has a larger color city; a four-color waterless offset proof, looks like on the traditional offset printing machine Printed six-color print job. Other benefits of waterless offset printing include shorter print setup times and less paper waste (this is especially important for digital short-duration digital imaging), there is no problem with the removal of excess dampener additives, and the pressroom There are only a few volatile organic compounds in the air. In order to be able to use waterless offset printing, it is now more and more common to equip the aforementioned cooling rollers even on conventional printing presses. This fact shows that the use of waterless offset printing can still be accepted by users even though the running costs have increased.
4. Several waterless offset printing new technologies
In Drupa 2000, the following new technologies are inseparable from on-press printing and CTP technology.
*Toray has introduced a thermal CTP waterless offset printing plate and claims to be free of waterless plates.
* Kodak Polychrome Graphics (KPG) introduced a thermal CTP waterless version but did not disclose detailed specifications.
*Presstek, Adast and Xerox partnered to launch PAX waterless offset printing presses, using Presstek's PearlDry plate, on-machine imaging, and automatic plate change technology to achieve rapid print job preparation.
* Heidelberg and Sun Chemical demonstrated a water-based (oil-free) single fluid ink that requires the use of a temperature control roll and a special printing plate. This ink is also environmentally friendly.
*Flink Ink demonstrated its new Single fluid ink, which can be applied to ordinary aluminum or polyester plates with no need for temperature control. The company claims that the ink can be shipped in one year. The industry believes this ink is promising.
Toray Launches CTP Plate
As mentioned above, Toray Corp. first developed a waterless offset printing system. Since 1979, Toray's water-free printing plates have seen many improvements. At least 100,000 impressions are available on sheetfed presses and up to 30 on rotary presses. Wan Yin. This shows that the plate life is not a problem for most of India. Using an ordinary UV lamp vacuum platen, the plate can be exposed with an ordinary negative film. UV light breaks the chemical link between the silicon layer and the underlying polymer (also used in the positive version, where the UV light is to enhance chemical bonding), and after chemical soaking, gently brush off unlinked silicon. Toray waterless version needs to be treated with its own chemicals. Plates are vulnerable to damage due to scratches on the silicon layer, and the plates are also more expensive than traditional ones. Waterless offset printing plates in Japan are approximately 2 times more expensive than traditional offset printing plates. Times, it is said that in Europe even 6 times more expensive. For this reason, Toray's waterless offset technology has not been promoted in printing plants, regardless of the benefits of waterless offset printing.
1. To the thermal
In 2000, Toray developed to thermal CTP. Introduced the Toray CTP waterless offset plate that is sensitive to the 830nm infrared laser. As with earlier designs, its CTP waterless plate was coated with a layer of polymer on an aluminum plate and a silicon layer on top of the polymer. The laser burns through the polymer to release the polymer from the silicon layer, which is then brushed away. Toray said that the price of the new CTP anhydrous plate varies with different markets, but on average it is about twice as expensive as the existing thermal CTP plate.
2. Soon there is no need to deal with media
Toray also talked about its free handling of the “CG†media technology, which does not require any chemical treatment of chemicals other than rinsing with water. The “CG†plate needs slightly more 830nm laser energy than the CTP waterless offset plate (Compared with 150～200mJ/cm2 of CTP waterless offset plate, the sensitivity of CG plate is 300mJ/cm2). , but can be applied to most existing thermal platesetters, price or shipping schedule has not yet been specified.
PAX waterless offset in flash
The PAX DI press was exhibited at Drupa 2000. The PAX DI press is a product jointly developed by Presstek, Adast and Xerox, and is therefore abbreviated as PAX. PAX is an eight-page sheet-fed direct-machine platen offset press with four, five, or six colors. Presstek offers PearlDry Plus polyester plate and laser direct imaging system, Adast is responsible for printing machine design and processing, and Xerox is responsible for marketing.
PAX is fully adapted to the needs of short-lived printing that requires fast job conversion. Inside each plate cylinder, there is a roll of plate material, which is wound on a roll. The roll is also inside the plate cylinder. The plate roll is rotated forwards to allow the plate to be replaced. Like the outer drum plateetter, the image was burned on the plate by the 870 nm laser. To increase plate speed, the plate cylinder can be run separately from the rest of the press so that the plate cylinder can be turned faster. Each drum has 32 lasers, exposed at a resolution of 2540 dpi, and the plate making time is more than 4 minutes; at 1270 dpi, it only takes more than 2 minutes. At the same time, the press operator can load paper for the next job and fill in a job ticket form. From the last sheet of the last job to the first available sheet of the next job, the total plate replacement time does not exceed 10 minutes. The positioning problem is ensured by the on-machine imaging technology. The ink uniformity problem can be pre-set by the RIP, and there is no adjustment of the ink balance.
Only a few sheets can be prepared for the print job after the change. In one demonstration, one can see that when the third sheet is printed, the quality of the printed image can be within the tolerance of the densitometer. PAX is suitable for printing several different versions of documents. Since each cylinder can be separated from the printing system individually, several sets of cylinders can print the same version of the content, while other cylinders print different versions of the information. For example, a five-color printer, three color groups can print the same version of the content, and the other two color groups can be used as a black-and-white printing color group, one printed in English, the other printed in French. The PAX printing machine can also perform double-sided printing. A five-color printing machine can print one side of four colors and the other side of a single color printing, and can print one side of the two-color, the other side of the three-color printing, from a printing format to The other form takes only 20 seconds.
KPG Introduces Thermal Dry Plate
KPG introduced Thermal Waterless thermal offset printing plate, which is resistant to printing of 200,000 impressions. The required laser power is the same as the first-generation thermal CTP plate at 830 nm. This version uses a silicon layer as the oil repellent material. Unfortunately, the company did not provide information such as price and delivery schedules.
Waterless offset ink
When most successful waterless offset systems use special plates, 3 companies are developing special inks. In fact, only one type is a true waterless offset ink, but all three ink products have the advantage of eliminating the need to adjust the ink balance when printing.
The United States Gauss Company had demonstrated single-fluid (single fluid) inks at Print 97, and the technical details were kept confidential. The concept is that traditional oil-based inks are emulsified with water. The emulsification process is achieved by a device that is mounted on a printing press and resembles a stirrer. The emulsified emulsion (pigmented mayonnaise) is then added to the ink roller of the printing press. When it reaches the printing plate, the emulsion separates into components of water and oil. Gauss did not demonstrate its single fluid ink technology at Drupa 2000, but it is said that the technology is still under development and was tested in a newspaper in the fall of 2000. Gauss has already registered "SingeFluid" as a registered trademark.
Heidelberg cooperated with Sun Chemical to develop a water-based ink. Technically speaking, this product does not belong to waterless ink but is an oil-less ink. However, like waterless inks, this ink avoids ink balance problems and it also has environmental benefits.
Heidelberg's inks require a silicon-containing plate to allow the non-imaged areas to repel ink. In addition, it also requires the printer to have a temperature control roll, but instead of a chill roll, this ink needs to heat the roll to 35°C and evaporate the excess water from the ink by heat, when the ink is attached to the plate, the final The total moisture content is 1% to 2%. Although this temperature value is not very strict, it can be varied within the range of 10°C but it must be controlled. If the water evaporates too much, the ink will dry on the ink roller; if the water evaporates too little, the printing plate will tend to be dirty when printed. It is said that the ink will be heated to dry at 40°C, and if dried, it will have water resistance. When the ink is hot enough to dry immediately, it is not necessary to spray (the press is usually done with talcum powder on the newly printed sheet to prevent the ink on the surface of the sheet below the sheet from picking up the back of the sheet). . After 5 minutes, the degree of drying of the ink allowed the printer to carry the sheet by hand; after 15 minutes, the ink was dry enough to allow the printer to fold the sheet. In addition to the environmental benefits, water-based inks perform as well as the printer expects, have the same viscosity and viscosity as conventional inks, and produce the same maximum solid ink density on the page. At first, its price may be twice that of waterless offset inks now, but in the future its price will depend on the amount of ink produced.
Flint Ink's most impressive is Flint Single fluid ink. It can be used with conventional aluminum plates on ordinary uncooled printing presses.