Hot melt technology and Azura chemical-free plate
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CTP technology has been developed for nearly 10 years, and the plate technology has always been the core of CTP. At present, there are three main types of mature plate technology, photosensitive silver salt plate, photosensitive photopolymer plate and thermal plate. These three types of plates have excellent performance for different printing market needs. Compared with the traditional film making, there are great progress in printing quality, printing durability, and ease of handling.
These three types of plates that are common in the market can be called traditional CTP plates. Why do you say this? It is because they need chemical developer treatment after exposure. There are three main effects on the chemical treatment of developing syrup. First, the impact on the quality of the print, the change in the washing conditions directly affects the reproduction accuracy of the dots. Second, the impact on the environment, the chemical waste liquid generated in the process needs to be treated before it can be discharged. Third, the cost has been increased.
The free processing plate is one of the development directions of CTP plate. Compared with traditional systems, the processing-free system is superior to traditional systems in terms of print quality, environmental protection, and cost reduction. AGFA's Azura plate is based on Thermofuse technology and is a chemical-free plate that is actually put into production. This article will explore the principles of hot melt technology and some of the characteristics of Azura chemical-free plates.
Development of thermal plates
Thermal plates have undergone three generations of development, preheated plates, preheat-free plates and disposable plates.
The first generation of thermal version is a negative version, using pre-development preheating technology, and the plate structure is aluminum plate base and heat-sensitive coating. At 830 nm laser exposure, the acid catalyst in the coating promotes cross-linking of the resin in the coating to form a latent image. Before development, the plate material forms a sufficient cross-linking reaction at a high temperature of about 140oC, which is a graphic part of the printing plate. The unexposed portion does not react at high temperatures. At the time of development, the unexposed portion was dissolved in the alkaline developing solution, and the exposed plate was a blank portion of the printing plate. After rinsing, apply a protective gel or baking plate to the plate.
The second-generation thermal plate is a positive version, eliminating the preheating process. The principle of the plate material is that the heat-sensitive coating on the plate base is ink-repellent and insoluble in alkaline syrup. After exposure, the coating absorbs energy, increases solubility, and dissolves in alkaline syrup. The exposed portion is dissolved during development to form a blank portion of the printing plate. The non-exposed portion is retained as the graphic portion of the plate. After development, it is generally cleaned and glued, and then printed on the machine. Most of the media currently used by users of thermal CTP are second-generation thermal plates.
The development goal of the third generation of thermal plate technology is to avoid processing. The process-free plate technology can be divided into three categories, thermal ablation technology, polarity conversion technology and hot melt technology.
The thermally ablated plate material is generally double coated, the bottom layer is an ink receptive layer, and the upper layer is a hydrophilic layer. During exposure, the laser energy ablates the hydrophilic layer to expose the ink-repellent layer to form a graphic image. The unexposed portion remains hydrophilic and is in the blank of the layout.
Thermal ablation technology does not perform well in successful commercial applications, and there are two main factors that constrain the development of this technology. One is how to deal with the dust formed by ablation, and the other is the printability. The dust and debris generated after ablation affects the accuracy of the optical part of the platesetter and has an impact on health and the environment. This technology requires an additional dust treatment recovery unit. In terms of printing performance, the blank parts of the traditional PS plate and CTP plate are frosted and oxidized aluminum plate base, which has good hydrophilicity and printing durability. The blank part of the thermal ablation plate is a hydrophilic coating, and its ink balance control ability and printing durability are not ideal.
The polarity conversion technology is a single-layer coating, and the drug film layer is hydrophilic (or lipophilic). After exposure, the polarity of the drug film layer changes to be oleophilic (or hydrophilic). The exposed portion is the plate graphic (or blank). This technology plate can be directly printed on the machine without any treatment after exposure. The factors that constrain the development of this technology are still printability. The ink part is coated with a drug film, and the printing control and the printing durability are greatly restricted, and there is still a large distance for real large-scale commercial application.
Hot melt technology is the technology of the real commercial application of the third generation of disposable processing plates. The blank part of the printing plate is the aluminum base after the frosting and oxidation treatment, instead of the coating of the film, the printing suitability is no different from the ordinary plate.
Principle of hot melt technology
Hot melt technology is one of the development directions of CTP plate material. It is the patented technology of AGFA. The basic principle is that the plastic glue particles have a heat fusion effect after exposure, and are condensed on the surface of the plate to form a graphic.
The hot melt technology plate is coated with plastic particles coated on a hydrophilic medium (aluminum plate base). When not exposed, the individual plastic polymer particles are closely packed and fixed by a stable water-soluble binder to prevent fusion. The hot melt technology plate has good storage properties and can be stored for more than 2 weeks in a 50oC environment.
After the plate is exposed, the plastic particles are fused together at a high temperature to form a graphic image.
The plastic particles are precisely designed to ensure a stable ink-repellent layer after exposure and fusion, and remain stable under the action of printing syrup (cleaning solution, alcohol and other solvents). The smaller the particles, the less energy is required for heat fusion.
The unfused plastic particles are cleaned to reveal an aluminum plate base, which is a blank portion of the plate. There are many ways to clean. One of them is the direct cleaning by the water roller of the printing press. This method is used by AGFA's Thermolite plate. The Azura plate based on the same principle is rinsed with glue to ensure a clean and thorough cleaning. On the other hand, the protective glue is applied to the surface of the plate to protect the plate.
Aluminum plate base in hot melt technology
Compared with other process-free technology plates, the most important feature of hot melt technology is the direct use of hydrophilic aluminum plate as the hydrophilic layer of the printing plate, which has excellent performance in printing suitability and printing durability.
More than 90% of the plates currently use aluminum plates. The aluminum plate base is generally subjected to electrode sanding, anodizing, sealing treatment, and the like, and then coated to form a printing plate.
Azura chemical-free plate
Azura chemical-free plates are made by hot melt technology. After exposure, the glue can be directly printed on the machine.
The Azura plate is composed of a plate base and a drug film layer, and the plate base is subjected to sanding, oxidation, sealing and the like. The drug film layer is a plastic particle which is adsorbed on the surface of the plate by a water-soluble material.
When exposed, the plastic particles of the image forming portion undergo a thermal fusion reaction to melt and bond.
After exposure, the glue is used to clean the layout, and the unexposed portions of the plastic particles are washed away by water to expose the plate base to form a blank portion of the layout. The particles in the exposed portion have been fused and adsorbed on the surface of the substrate.
It can be seen from the above process that the Azura plate is exposed to the printing process without any chemical treatment, and only needs to be cleaned and glued, which greatly simplifies the processing, and has the following characteristics.
ü No need to develop chemicals, reduce costs
ü No water circulation system, no waste liquid discharge, more environmentally friendly
ü True binary imaging, the quality of the dot is not affected by changes in laser energy, concentration of the solution, temperature, speed, etc.
ü Simplified production process
ü Direct printing on aluminum plate, no hydrophilic coating is required, the printing suitability is exactly the same as ordinary plate, no need for any adjustment in the printing workshop
ü High resistance to printing
ü The printing plate has strong resistance to printing chemicals
The Azura plate has made its debut at Drupa last year and currently has a large number of customers. This plate is now available for almost all CTP devices with 830nm lasers. In China, some customers have adopted Azura plates, and it is believed that this plate will bring another revolution in the field of prepress.