With the rapid development of pre-press platemaking technology, computer-to-plate technology, or CTP technology, has become a popular solution for improving the quality and efficiency of platemaking. Although some people began to study the issue of direct platemaking as early as the 1970s, Drupa'95 held in Germany in 1995 was a milestone for CTP to enter commercial applications on a scale.
First, the structure of CTP equipment Technically speaking, direct plate-making technology is a continuation of phototypesetting technology. Due to the different imaging materials, the technology used by the CTP equipment and the thermal stripper is slightly different. The imagesetter uses three technologies in its structure: inner drum technology, outer drum technology, and flat table technology. The direct platemaking equipment also uses these three technologies. However, unlike the imagesetter, the technology used in direct platemaking equipment is often related to the sensitive characteristics of the plate.
1. Inner Drum Technology The inner drum structure exposes the printing plate on the inside of the drum. When the inner drum CTP equipment is in operation, the printing plate is adsorbed on the inner wall of the drum, the rotating mirror moves along the central axis of the drum while rotating, and the laser beam in the direction of the central axis is projected at an angle of 90°. On the edition. The laser spot size is determined by the resolution requirements. The distance between the plate and the laser mirror is constant, approximately equal to the drum radius, to ensure the uniformity of the laser spot size at various parts of the plate.
The laser of the inner drum CTP device is mostly a single beam laser, and its imaging speed mainly depends on the rotating speed of the rotating mirror motor and the photosensitive speed of the printing plate. The fastest known motor at the moment is Agfa's Phoenix Photoetter Motor, which has a speed of 68,000 revolutions per minute. Other companies' products, such as Fujifilm's new Luxel series of photo-setters and plate-making machines, use a combination of two lasers and three lasers, although the turning speed is only 30,000 rpm. Times increase.
The application of inner drum technology is also limited by the speed of the printing plate. One or two years ago, the thermal version was very popular, but its imaging speed was slow, requiring the laser to stay on the plate longer. If internal drum technology is used, it is also futile for the motor to turn faster. This is also a weakness of the internal drum structure. Therefore, there were fewer direct plate-making equipments using inner drum technology, and the direct plate-making equipment of the thermal plate mostly used the outer drum structure. Now, the sensitivity of the thermal plate has changed substantially. CTP equipment using a single beam of thermal light has emerged in the market. The CTP devices of Agfa, Barco Graphics, Krause, and Purup-Eskofot use 1064 nm YAG lasers and inner drum structures. The fastest speed of these devices and the speed of external drum equipment can be higher or lower.
The intensity of the laser is also an important factor in the left and right drum technology. For example, the sensitivity of the thermal plate is low and a stronger light source is required. The Cymbolic Sciences company's approach is to use 15 lasers to focus a laser beam on a plate using a rotating mirror system, which also greatly increases the imaging speed.
Internal drum technology is a very mature technology. Most high-end imagesetters use internal drum technology. In the early stages of the appearance of CTP equipment, although drum technology was questioned, advances in technology made internal drum technology more brilliant. The emergence of violet lasers has further encouraged the trend of the popularity of drum technology. At present, most of the violet laser direct plate-making equipment on the market uses internal drum technology.
2. Outer drum technology The outer drum structure is to install the printing plate outside the drum. The direction of the laser beam is perpendicular to the axis of the drum. During imaging, the platen is rotated by the drum, and the direction of movement of the laser head is parallel to the axis of the drum. Inner laser equipment has a long laser path because the laser light goes from the center of the drum to the circumference. In contrast, the light path of the outer drum equipment is very short. Since the drum is unbalanced and shakes when it is rotated after the plate is mounted, a tremor sensor should be installed to ensure that the distance from the laser head to the plate remains exactly the same as the drum rotates.
Due to the low sensitivity of the thermal plate, the use of single beam laser imaging is very slow, so the outer drum technology generally uses multiple laser technologies to increase the imaging speed. Some direct plate-making equipment can have up to 500 laser beams. Multi-beam laser imaging is divided into two different forms - step and spiral.
The step-by-step feature is that when a group of lasers completes imaging in the first week of the plate, that is, after the drum has rotated one revolution, the laser head moves forward and the distance it moves is the width of the group of laser beams. This method is very accurate, but it is slower because the process of starting, stopping, and restarting is constantly repeated, so it is called "stepping."
The characteristic of the spiral type is that when the plate cylinder rotates, the exposure of the laser beam on the printing plate presents a trajectory from the beginning to the end of the plate which is a non-stopping spiral. This movement makes the laser beam's trajectory not parallel to the edge of the page's starting point. There is a small angle called the "offset."
3. Comparison of Inner Drum and Outer Drum Types For the inner drum type structure, since a laser beam is used, the offset amount is too small to be ignored. Even with Fujifilm's new Luxel series of imagers using three lasers, the offset is not large. The outer drum structure uses multiple lasers. The more laser beams are used, the greater the offset. The low resolution offset is higher than the high resolution offset when imaging. Some drum-type imagesetters adopt the civilian spiral imaging method and use more than 500 laser beams. The offset is 500 times that of the inner drum imageetter using a single laser beam. Such large offsets will of course affect the formation of dots. To avoid the effect of offset on image quality, the offset of the image must be adjusted electronically. Many CTP platesetter systems on the market today have automatic compensation for offsets.
The advantage of the outer drum structure is that it is very suitable for thermal imaging. Thermal plates are generally less sensitive. This requires that the laser beam has a longer dwell time at each pixel to ensure that there is enough energy to image the plate. This type of dwell time is a single beam. The laser light path of the laser and inner drum structure is very short, and the exposure efficiency is relatively high.
In addition, the outer drum structure can use multiple lasers, a feature that is used in super-large-format direct platemaking equipment. At present, most of the super large-format direct platemakers in the market adopt the outer drum technology and use multiple laser beams to increase the imaging speed.
The outer drum technology needs to pay attention to the uniform density of the laser beam. The use of multiple lasers requires that the optical system of the equipment be able to ensure that the density of each laser is the same, and that inconsistent density results in banding on the plate. This does not occur in inner drum structures that use a single beam of laser light. However, this does not matter for using a thermal plate because the thermal plate does not suffer from overexposure.
Then there is the problem of rotational speed. Outside the drum structure of the drum, its rotation speed is very important for the normal operation of the equipment. For systems that use fewer laser beams, such as devices that use eight lasers, the operating speed of the rollers must exceed 1,000 rpm; for systems that use more laser beams, such devices that use FD YAG laser sources have 480 beams that use infrared light. The device of the laser diode light source has 240 lasers, and its rotation speed is relatively slow, ranging from 70 to 140 rpm. Even so, due to the large inertia of the plate when the drum is rotating, the technical requirements for fixing the plate to ensure its safety are high. In this case, multiple fixed clamps are required to secure the plate firmly to the roller.
4. Platform-type technology Platform-type direct plate-making equipment is much simpler than roller-structured equipment. Automatically or manually, it is easy to mount and unload plates, and most punching systems can be easily used on a platform-style device. Platform technology is divided into single beam laser systems and multiple beam laser systems.
Single-Beam Laser Systems Most flat-panel systems use a rotating mirror system that refracts a single beam of laser light at the plate surface. In a single-beam laser system, the plate is moved forward on the platen, and its direction of movement is perpendicular to the laser scanning direction. The time it takes for the lobe to move a pixel distance is consistent with the time it takes for the laser to scan the plate from left to right. Because the single beam laser reciprocates in the transverse direction of the printing plate during the scanning process, the distance from the lens to the plate is constantly changing. In order to ensure uniform exposure spot size and shape, the laser beam must be focused on the plate by a special lens. This also limits the scanning width of the laser, so the width of the platen of such equipment is not very wide.
The platform-type single-beam laser system has a fast imaging speed and has the fastest automatic plate-up and unloading technology. However, due to the scanning width limitation, it is currently mainly applied to commercial printing production of newspapers, small format, and medium format. If a single-beam laser system is to be used to produce wider-format devices, one option is to use multiple laser heads to combine multiple sets of data. This is a multibeam laser system.
Multi-beam laser systems Some company's products also use a platform-type structure, which increases the size of the plates that can be processed while maintaining fast automatic plate-up and unloading techniques.
Barco Graphics products use 5 to 6 laser heads, each of which consists of 3 to 5 lasers. When used, these laser beams are optically and digitally combined to generate a laser line, which greatly increases the imaging speed and imaging area.
Second, laser technology of CTP equipment Laser technology used by CTP equipment is related to printing plate. In addition to the use of different lasers whose visible wavelengths range from 400 to 700 nm, ultraviolet and infrared light are also used. In the past, CTP equipment has been widely used lasers:
Argon ion laser, blue, visible laser at 488 nm.
FD-YAG laser, blue-green, 532nm visible laser.
He-Ne laser, red laser, visible laser at 630nm.
Laser diode (low energy), red laser, visible laser at 670 nm.
Laser diode (high energy), infrared laser for thermal technology, 830nm. The wavelength of the infrared laser diode is generally between 780 and 900 nm.
Neodymium Yttrium Aluminum Garnet Laser (Nd YAG), High-energy infrared laser for thermal imaging, 1064 nm.
Frequency-doubled yttrium aluminum garnet laser (FD YAG), green, visible laser at 532 nm.
Recently, more popular 400-450nm violet lasers have emerged. At the same time, the CTP equipment using the ordinary PS version of the UV light source is also attracting attention.
1. The thermal technology lmprinta'97 exhibition is a major sign of plate making technology towards CTP technology, its main tendency is thermal imaging.
The biggest benefit of the thermal plate is that the image quality is guaranteed because it is a binary plate and it has only two states: imaged and unimaged. Unlike silver salt and photopolymerized CTP plates, this plate does not underexpose or produce images. In this way, the requirement for exposure accuracy is not as good as the quality of the photosensitive plate. The exposure control is also very precise and the washing equipment is very mature.
In fact, there is no significant difference in quality between the silver salt, photopolymer, and thermal plates. The photopolymerization version has a maximum screening accuracy of 200 lpi, which is sufficient for most situations. Exposure to high-quality CTP systems using silver salt can reach 300 lpi or even higher.
The thermal plate can be operated in daylight without working under a safety light, that is, dark rooms may not be needed. Some photo-sensitive plates can also work under very bright security lights, almost in close proximity to sunlight.
In the past, the thermal plate was subjected to a pre-heating process and a flushing process. Most thermal plates need to be pre-heated in a high-energy oven before they are imaged on CTP devices. Nowadays, most new plates can eliminate the preheating process. Exemption of printing plate is also a hot topic at present. In addition to using ablation technology, there are some new technologies available, such as the mechanism version technology.
For the time being, even the latest thermal plates have sensitivity issues. Its imaging speed is lower than the photosensitive version. The advantage of the thermal plate in the future is that it is a type of plate that does not need to be processed. It can be directly printed on the machine after coming out of the CTP platesetter. They will even be used for direct plate making on the press.
2. Purple laser technology violet laser
First, the structure of CTP equipment Technically speaking, direct plate-making technology is a continuation of phototypesetting technology. Due to the different imaging materials, the technology used by the CTP equipment and the thermal stripper is slightly different. The imagesetter uses three technologies in its structure: inner drum technology, outer drum technology, and flat table technology. The direct platemaking equipment also uses these three technologies. However, unlike the imagesetter, the technology used in direct platemaking equipment is often related to the sensitive characteristics of the plate.
1. Inner Drum Technology The inner drum structure exposes the printing plate on the inside of the drum. When the inner drum CTP equipment is in operation, the printing plate is adsorbed on the inner wall of the drum, the rotating mirror moves along the central axis of the drum while rotating, and the laser beam in the direction of the central axis is projected at an angle of 90°. On the edition. The laser spot size is determined by the resolution requirements. The distance between the plate and the laser mirror is constant, approximately equal to the drum radius, to ensure the uniformity of the laser spot size at various parts of the plate.
The laser of the inner drum CTP device is mostly a single beam laser, and its imaging speed mainly depends on the rotating speed of the rotating mirror motor and the photosensitive speed of the printing plate. The fastest known motor at the moment is Agfa's Phoenix Photoetter Motor, which has a speed of 68,000 revolutions per minute. Other companies' products, such as Fujifilm's new Luxel series of photo-setters and plate-making machines, use a combination of two lasers and three lasers, although the turning speed is only 30,000 rpm. Times increase.
The application of inner drum technology is also limited by the speed of the printing plate. One or two years ago, the thermal version was very popular, but its imaging speed was slow, requiring the laser to stay on the plate longer. If internal drum technology is used, it is also futile for the motor to turn faster. This is also a weakness of the internal drum structure. Therefore, there were fewer direct plate-making equipments using inner drum technology, and the direct plate-making equipment of the thermal plate mostly used the outer drum structure. Now, the sensitivity of the thermal plate has changed substantially. CTP equipment using a single beam of thermal light has emerged in the market. The CTP devices of Agfa, Barco Graphics, Krause, and Purup-Eskofot use 1064 nm YAG lasers and inner drum structures. The fastest speed of these devices and the speed of external drum equipment can be higher or lower.
The intensity of the laser is also an important factor in the left and right drum technology. For example, the sensitivity of the thermal plate is low and a stronger light source is required. The Cymbolic Sciences company's approach is to use 15 lasers to focus a laser beam on a plate using a rotating mirror system, which also greatly increases the imaging speed.
Internal drum technology is a very mature technology. Most high-end imagesetters use internal drum technology. In the early stages of the appearance of CTP equipment, although drum technology was questioned, advances in technology made internal drum technology more brilliant. The emergence of violet lasers has further encouraged the trend of the popularity of drum technology. At present, most of the violet laser direct plate-making equipment on the market uses internal drum technology.
2. Outer drum technology The outer drum structure is to install the printing plate outside the drum. The direction of the laser beam is perpendicular to the axis of the drum. During imaging, the platen is rotated by the drum, and the direction of movement of the laser head is parallel to the axis of the drum. Inner laser equipment has a long laser path because the laser light goes from the center of the drum to the circumference. In contrast, the light path of the outer drum equipment is very short. Since the drum is unbalanced and shakes when it is rotated after the plate is mounted, a tremor sensor should be installed to ensure that the distance from the laser head to the plate remains exactly the same as the drum rotates.
Due to the low sensitivity of the thermal plate, the use of single beam laser imaging is very slow, so the outer drum technology generally uses multiple laser technologies to increase the imaging speed. Some direct plate-making equipment can have up to 500 laser beams. Multi-beam laser imaging is divided into two different forms - step and spiral.
The step-by-step feature is that when a group of lasers completes imaging in the first week of the plate, that is, after the drum has rotated one revolution, the laser head moves forward and the distance it moves is the width of the group of laser beams. This method is very accurate, but it is slower because the process of starting, stopping, and restarting is constantly repeated, so it is called "stepping."
The characteristic of the spiral type is that when the plate cylinder rotates, the exposure of the laser beam on the printing plate presents a trajectory from the beginning to the end of the plate which is a non-stopping spiral. This movement makes the laser beam's trajectory not parallel to the edge of the page's starting point. There is a small angle called the "offset."
3. Comparison of Inner Drum and Outer Drum Types For the inner drum type structure, since a laser beam is used, the offset amount is too small to be ignored. Even with Fujifilm's new Luxel series of imagers using three lasers, the offset is not large. The outer drum structure uses multiple lasers. The more laser beams are used, the greater the offset. The low resolution offset is higher than the high resolution offset when imaging. Some drum-type imagesetters adopt the civilian spiral imaging method and use more than 500 laser beams. The offset is 500 times that of the inner drum imageetter using a single laser beam. Such large offsets will of course affect the formation of dots. To avoid the effect of offset on image quality, the offset of the image must be adjusted electronically. Many CTP platesetter systems on the market today have automatic compensation for offsets.
The advantage of the outer drum structure is that it is very suitable for thermal imaging. Thermal plates are generally less sensitive. This requires that the laser beam has a longer dwell time at each pixel to ensure that there is enough energy to image the plate. This type of dwell time is a single beam. The laser light path of the laser and inner drum structure is very short, and the exposure efficiency is relatively high.
In addition, the outer drum structure can use multiple lasers, a feature that is used in super-large-format direct platemaking equipment. At present, most of the super large-format direct platemakers in the market adopt the outer drum technology and use multiple laser beams to increase the imaging speed.
The outer drum technology needs to pay attention to the uniform density of the laser beam. The use of multiple lasers requires that the optical system of the equipment be able to ensure that the density of each laser is the same, and that inconsistent density results in banding on the plate. This does not occur in inner drum structures that use a single beam of laser light. However, this does not matter for using a thermal plate because the thermal plate does not suffer from overexposure.
Then there is the problem of rotational speed. Outside the drum structure of the drum, its rotation speed is very important for the normal operation of the equipment. For systems that use fewer laser beams, such as devices that use eight lasers, the operating speed of the rollers must exceed 1,000 rpm; for systems that use more laser beams, such devices that use FD YAG laser sources have 480 beams that use infrared light. The device of the laser diode light source has 240 lasers, and its rotation speed is relatively slow, ranging from 70 to 140 rpm. Even so, due to the large inertia of the plate when the drum is rotating, the technical requirements for fixing the plate to ensure its safety are high. In this case, multiple fixed clamps are required to secure the plate firmly to the roller.
4. Platform-type technology Platform-type direct plate-making equipment is much simpler than roller-structured equipment. Automatically or manually, it is easy to mount and unload plates, and most punching systems can be easily used on a platform-style device. Platform technology is divided into single beam laser systems and multiple beam laser systems.
Single-Beam Laser Systems Most flat-panel systems use a rotating mirror system that refracts a single beam of laser light at the plate surface. In a single-beam laser system, the plate is moved forward on the platen, and its direction of movement is perpendicular to the laser scanning direction. The time it takes for the lobe to move a pixel distance is consistent with the time it takes for the laser to scan the plate from left to right. Because the single beam laser reciprocates in the transverse direction of the printing plate during the scanning process, the distance from the lens to the plate is constantly changing. In order to ensure uniform exposure spot size and shape, the laser beam must be focused on the plate by a special lens. This also limits the scanning width of the laser, so the width of the platen of such equipment is not very wide.
The platform-type single-beam laser system has a fast imaging speed and has the fastest automatic plate-up and unloading technology. However, due to the scanning width limitation, it is currently mainly applied to commercial printing production of newspapers, small format, and medium format. If a single-beam laser system is to be used to produce wider-format devices, one option is to use multiple laser heads to combine multiple sets of data. This is a multibeam laser system.
Multi-beam laser systems Some company's products also use a platform-type structure, which increases the size of the plates that can be processed while maintaining fast automatic plate-up and unloading techniques.
Barco Graphics products use 5 to 6 laser heads, each of which consists of 3 to 5 lasers. When used, these laser beams are optically and digitally combined to generate a laser line, which greatly increases the imaging speed and imaging area.
Second, laser technology of CTP equipment Laser technology used by CTP equipment is related to printing plate. In addition to the use of different lasers whose visible wavelengths range from 400 to 700 nm, ultraviolet and infrared light are also used. In the past, CTP equipment has been widely used lasers:
Argon ion laser, blue, visible laser at 488 nm.
FD-YAG laser, blue-green, 532nm visible laser.
He-Ne laser, red laser, visible laser at 630nm.
Laser diode (low energy), red laser, visible laser at 670 nm.
Laser diode (high energy), infrared laser for thermal technology, 830nm. The wavelength of the infrared laser diode is generally between 780 and 900 nm.
Neodymium Yttrium Aluminum Garnet Laser (Nd YAG), High-energy infrared laser for thermal imaging, 1064 nm.
Frequency-doubled yttrium aluminum garnet laser (FD YAG), green, visible laser at 532 nm.
Recently, more popular 400-450nm violet lasers have emerged. At the same time, the CTP equipment using the ordinary PS version of the UV light source is also attracting attention.
1. The thermal technology lmprinta'97 exhibition is a major sign of plate making technology towards CTP technology, its main tendency is thermal imaging.
The biggest benefit of the thermal plate is that the image quality is guaranteed because it is a binary plate and it has only two states: imaged and unimaged. Unlike silver salt and photopolymerized CTP plates, this plate does not underexpose or produce images. In this way, the requirement for exposure accuracy is not as good as the quality of the photosensitive plate. The exposure control is also very precise and the washing equipment is very mature.
In fact, there is no significant difference in quality between the silver salt, photopolymer, and thermal plates. The photopolymerization version has a maximum screening accuracy of 200 lpi, which is sufficient for most situations. Exposure to high-quality CTP systems using silver salt can reach 300 lpi or even higher.
The thermal plate can be operated in daylight without working under a safety light, that is, dark rooms may not be needed. Some photo-sensitive plates can also work under very bright security lights, almost in close proximity to sunlight.
In the past, the thermal plate was subjected to a pre-heating process and a flushing process. Most thermal plates need to be pre-heated in a high-energy oven before they are imaged on CTP devices. Nowadays, most new plates can eliminate the preheating process. Exemption of printing plate is also a hot topic at present. In addition to using ablation technology, there are some new technologies available, such as the mechanism version technology.
For the time being, even the latest thermal plates have sensitivity issues. Its imaging speed is lower than the photosensitive version. The advantage of the thermal plate in the future is that it is a type of plate that does not need to be processed. It can be directly printed on the machine after coming out of the CTP platesetter. They will even be used for direct plate making on the press.
2. Purple laser technology violet laser
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