1 Introduction
Currently, CTP is one of the hottest technical topics. There are different solutions for CTP imaging pixel shape. Creo (Crio), the largest supplier of CTP systems in the global market, prefers square outlets. Most other suppliers support round or oval outlets. In addition, the network size of the FM network imaging is the use of a dot diameter of 10μm or 20μm is also a focus of attention.
In order to give readers more detailed information, German Printer magazine conducted an interim survey of nine suppliers of CTP systems and answered key questions about different programs.
. Agfa, Fujifilm, and Heidelberg provide internal drum and external drum systems (also platform-style).
. Creo and Dainippon Screen represent external drum technology.
. Esko-Graphis and Krause only manufacture inner drum systems.
. Lithotech distributes the outer drum system. Its products can use not only infrared diodes but also violet laser diodes, whose beams can be separated.
. Löscher can rotate its outer drum with 64 or 128 infrared diodes in the drum.
The current problems are concentrated on the inner drum and outer drum CTP systems. In a flatbed system, the distance between the light source and the mirror group and the printing plate is equivalent to the distance of these components in the inner drum system. In principle the transport of the plate on the platform can be compared with the movement of the inner drum middle mirror group along the Y axis.
The answers from Agfa, Fujifilm, and Heidelberg are neutral because these companies have a variety of products and it doesn't matter which one they sell. Agfa and Fujifilm's technology can use different light source or heat source imaging plates. The answer from other manufacturers is to choose their company's technology.
Conducting an interim survey of these nine suppliers should not be seen as a preference for them because other suppliers have adopted the same technology and the results of their surveys may be repeated.
Basysprint uses UV light for traditional plate imaging, so it is no longer being investigated. Most CTP systems that use argon ions and Nd:YAG lasers in internal drum recorders are also not taken into consideration because violet laser diodes are the best choice. Unfortunately, Agfa gave up on the questionnaire. His reason was that Agfa, as a manufacturer and supplier of complete CTP system solutions, only paid attention to its quality, cost, and efficiency. Japan Screen Corporation also gave up the questionnaire survey.
2 Quality is the symbiosis between people and technology
The CTP system, like other equipment, is the result of market demand, and it is also achievable by contemporary design and manufacturing technologies, and the cost will not exceed the range that can be tolerated. However, any kind of technology is tolerant.
In the CTP system, when four plates are imaged sequentially (mostly 1m in width), the repeatability is only within 5μm. This quality level exceeds the level of automotive manufacturing and is 500μm when welding 5m long body steel panels.
However, each CTP system has its own tolerances, as well as advantages and disadvantages. If many diodes are positioned in an external drum system, will the distance of such scan lines be accurate? Will no visible defects be present? Is the heat release consistent with all diodes? The light sources and plates in the inner drum system Does the distance between them lead to loss of resolution? What is the risk of failure of the only violet laser diode? What parameters should be checked when errors are displayed along with the exposed strip? Is this only a diode energy problem? Failure at Regeneration, Development Temperature, or Speed ​​Through Rate? Perhaps the free-hand plates introduced at this year's drupa show can fundamentally eliminate development issues.
However, there are standards and specifications for printing plates and printing. The fine detailing of the printing plate on the printing plate shows nothing. The dot must show its stability when printed in large quantities.
3 questions
Question 1: When an external drum CTP system uses an infrared laser diode (830 nm) to image a thermal plate, discussions about square and circular laser spots (imaging pixels) are controversial. What are the advantages and disadvantages of different points in terms of the following criteria?
Question 1.1: What is the shape of the halftone dot?
Creo: According to our opinion, it is not enough to observe the geometry of the dots. In general, this cannot be discerned from the plate or the printed sheet. The theoretical dots in the images and graphics shown in the book are virtually impossible to produce. As a representative of the square points, we pointed out that although the square dot technology is screened with suitable dots, we never compared this dot shape as an important advantage with other dot shapes. Our technical advantage is in other aspects. This created an impression in the discussions that began with outsiders. This allowed us to regard our point of view as an advantage and adapt it to the needs of the market. This is the situation in the past. This is not the case now.
Esko-Graphis: The transfer of offset ink from the plate to the paper via the blanket does not affect the dot quality of the CTP system.
Fujifilm: The screen dot will produce the best profile when screened at 15°, 45°, and 75°. A square point will result in a stepped grade, with only the angle at 0° (yellow version) being the best. These theoretical differences are irrelevant in printing, because the definition and shape of the dot change from the plate to the paper when the blanket is transferred to the paper, depending on the printing conditions. The difference between a square dot and a dot is between the two, and it cannot be seen on paper.
Heidelberg: Circles or squares have virtually no effect on the quality of halftone dots.
Krause: The GATF research on this subject was reported in detail in the German Journal of Printing. Whether the dot shape, the version is mounted on the outer drum or the inner drum has no effect on the whole process. The dot shape is affected by the RIP technique much more than the recorder beam distribution. The advantages of the inner drum system are: simple optical path and flexible resolution suitable for the dot size.
Question 1.2: What is a uniform energy distribution with sharp edges?
   Creo: The energy distribution has no reference to the geometry of the dots.
Esko-Graphics: Plate sensitized emulsions “weld†numerous dots forming a network. The edge sharpness of this dot is produced by the sensitizing emulsion of the printing plate by absorbing laser energy. Different shapes have no effect on edge definition.
Fujifilm: Energy distribution and edge definition are factors that depend on different environmental factors - plate and chemistry, not on laser spot. The Gaussian curve distribution has no disadvantages for the square points, because making the printing dots does not use the flatness of the curve (see Figure 1).
Heidelberg (complex question 1.2~1.5): The ideal square energy distribution is not available. The ideal energy distribution of a square point is approximately trapezoidal in realistic imaging techniques - the trapezoid of a dot (constrained by diffraction) is Gaussian. The steepness of the curve in both dot and square points depends primarily on the quality and adjustment of the optical system. In actual comparison, the trapezoid (square) energy distribution curve is better than the Gaussian distribution curve (dot). Therefore, although the process variation of the Gaussian curve distribution is theoretically large, the stability of the entire system, including the recorder, the printing plate and the development always determine the quality of the edge definition of the printing plate's network point. Heidelberg's experience shows that both types of points are equally suitable for imaging all dot systems.
Krause: Different printing plate coatings (silver halide, polymer, thermal) have different ink absorption properties. Compared with the silver halide plates, the heat-sensitive silver dots have a higher dot gain rate, especially in fine meshes. Whether this issue is affected by the beam distribution is inconclusive.
Löscher: The manufacturer of thermal media points out that the main advantage of thermal imaging lies in the dual performance of the printing plate. When sufficient energy reaches the plate coating, only the negative plate image or the positive plate coating will be damaged. This means that the Gaussian energy distribution has no effect on the thermal plate. The plate only subtracts enough energy from the Gaussian energy distribution.
Question 1.3: What is the quality of imaging?
Creo: Only geometric dots are not responsible for the image quality.
Esko-Graphics: There is no difference between dots and square points on the plate.
Fujifilm: The square dots do not have much edge-to-edge definition on the plate, and even if there is a slight advantage, they disappear through the blanket. Therefore, there is no difference or difference from the dot.
Question 1.4: Does it use FM and fine mesh imaging?
Esko-Graphics: Fine dot dot quality for fine mesh and dot mesh for FM network, because its size can be changed according to the resolution of Esko-Graphics' inner drum CTP system (1200, 1270, 1800, 2400, 2540, 3200dpi ).
Fujifilm: There is no difference in printing.
Krause: Fine mesh can be imaged on all plate coatings. The quality of the FM network depends mainly on the resolution of the printing plate. With stepless adjustment of resolution, single beam systems can be optimally matched to plate resolution.