Thermal version technology
There are currently three main types of digital printing technology: silver halide technology, high-sensitivity technology, and the latest thermal technology. Silver halide technology includes a silver halide diffusion transfer version, visible laser light, and light waves between blue and red. Based on this technology, Agfa introduced two aluminum-based digital direct printing plates, Litoostar plus and Silver Lith SDB, to the market. Dupont-hausen launched a polyester-based digital direct printing plate and the red-colored Setprint-HN-LL version.
Polaroid launched a silver salt composite technology, CTX technology, which is coated with silver halide technology and emulsion on the PS plate that is sensitive to ultraviolet light.
Agfa launches a photopolymerizable offset printing plate, Ozasol N90A version, which is also a digital direct printing plate, with fast light sensitivity, green and blue.
Recently, a new type of digital offset printing plate has appeared on the market, which is called the thermal plate. The sensitivity range of the thermal version is 830 ~ 1064 nm, or even wider. Its printing plate technology includes melting, ablation, transfer, cross-linking, photoelectron decomposition, etc. Regardless of which of the above techniques is used for imaging, the printing plate is obtained after development. Due to different plate materials, some need to undergo wet processing.
1. Chemical insolubility
By laser heating, the polymer in the active layer is cross-linked, resulting in chemical insolubility, forming a negative image. After exposure to IR, the acid is generated by heating, which catalyzes the chemical cross-linking of the polymer binder, so that the exposed area is selectively cross-linked . The pre-heating program can achieve a sufficiently high degree of cross-linking after multi-molecular reaction. Therefore, to obtain a high printing process, such a plate can be obtained by using traditional wet processing and post-baking plates after the preheating process. The tolerance of preheating is smaller, and the controllability of the heating box is better.
2. Physical insolubility
This technology is to generate physically insoluble substances by heating the active layer. The active layer contains a uniformly dispersed thermoplastic polymer latex particles, which can quickly dissolve, but after IR-laser exposure, the thermoplastic polymer particles are thermally coalesced to inhibit the solubility of the polymer layer, and the dual performance of such particles results High-quality images. The advantage of this technology is that it has a bright room and stable quality. At the same time, it can output and image images of the inner and outer drum printing plates. It belongs to the printing board. Wet the plates after wet processing, and get a high-print version. Agfa's RD-9 plate has a photosensitive wavelength range of 830 to 1100 nm, and has both internal and external drum recording imaging technology, but it has not yet been commercialized.
3. Chemical dissolution
This technology is that the active layer is heated to produce chemically dissolved substances without heating, and a positive plate is obtained, which is completely brightened. The plate is baked after wet processing, and the printing process is high. The active layer can use acid resin as the basis, the solubility of this layer increases during thermal imaging. If red line-absorbed species is added as a dissolution inhibitor to this layer, the exposed area will be selectively removed.
4. Heat sensitive ultraviolet mask
The technology senses visible light and uses IR-rays for imaging exposure, so that the ultraviolet absorbing layer is no longer soluble in the alkaline developer, thus acting as a lower layer ultraviolet mask. The other form is through the infrared-absorbing UV-absorbing layer, which is exposed to heat and etch to image the bottom UV-sensitive layer. However, its disadvantage is that the process is complicated and requires two parts to completely or incompletely remove the UV mask layer.
5. Physical mask for heat
This technology was pioneered by Agfa and is a new type of heat-sensitive positive plate named Thermostar. It is the structure of the physical mask layer that is heated by high-energy laser to change its structure. After the carbon or IR dye in the protective layer absorbs IR light, the infrared light energy is converted into heat, and the heat energy makes the temperature in the active layer rise sharply. It reaches 400 ° C or higher to complete the exposure. The specific temperature is determined by the thermal diffusion coefficient of the layer, exposure time, layer thickness and thermal diffusion coefficient of the adjacent layer. At the same time, the thin active layer can withstand the expansion caused by the light pulse, and the volume and thickness of the layer have increased The laser energy used for the two exposures at the same time can complete the ablation reaction in the layer.
Due to the high IR light absorption capacity of this version of the protective layer, it can also generate high temperatures for relatively low exposure levels to cause physical deformation of the protective layer. This physical deformation can not only effectively wet the exposed part of the plate surface with the alkaline developing solution, but also quickly penetrate the protective layer and enter the bottom layer to effectively dissolve the bottom layer and dissolve faster than the non-exposed area. The alkaline protective film acts as a mask. Obviously, its surface and interfacial tension are important parameters for processing.
It is concluded from this that the technology uses different effects of physical developers for imaging, this unique non-ablation process is before harmful volatile compounds have been formed in the layer, or before some components in the layer have not degraded It has been imaged. As the compound components in the layer are processed, they will not pollute the environment. Therefore, the use of the above technology can reduce the risk, and at the same time, it can eliminate the need for vacuum cleaning equipment and the laser ablation technology needs to be equipped with vacuuming facilities in the imaging area. [next]
6. Non-ablation characteristics of imaging technology
Ablation includes evaporation and decomposition of the infrared photosensitive layer. In the meantime, physical and chemical changes have occurred in the layer. When this layer is used as a protective layer, the ablated material evaporates into the air. In most cases, a part of it is in the form of powder and is redeposited on the surface of the material. This may further affect the imaging of the material, especially if the ablation degree is too high. After the whole layer is evenly colored, the powder can be easily wiped off to make the layer thinner and the chemical density becomes smaller. This ablative media can distinguish the quality by eyes, and can also be tested by instruments.
Classification of thermal plates
So far, at least six thermal plates have entered the market, and it is necessary to find a way to classify them.
(1) negative thermal plate
Including cross-linked optically sensitive polymer plates. Both Kodak Polygraphics' Thermal 830 plates and Fujifilm's Brillia LH-NI fall into this category. This plate is only imaged on the external drum plate-making machine. The printing performance of the negative plate is amazing. Without baking, the plate can guarantee 250,000 prints. According to reports, a printing factory has printed 700,000 prints without baking, and after baking, the printing volume can exceed 2 million.
(2) Yangtu Thermal Plate
It is a cross-linked optically sensitive polymer plate. It requires less laser beam power and is suitable for inner-drum direct plate-making machines. No preheating is required, but it needs to be processed, and the printing volume can be improved after baking. Horsell's Electra DC is one of them, in addition to Agfa's ThermalStar 830 and 1064, Fuji's Brillia LH-PG (1064nm), Lastra Extreme 830, Plurimetal Cygnus and Toray CTP Waterless 830, these plates are printed in 15 From 10,000 to 200,000 copies, Electra DC can exceed 1 million copies after baking.
(3) No processing thermal plate
It is composed of aluminum base coated with ink-receptive layer, hydrophilic layer and protective layer, and can be printed without developing treatment. In addition to the Presstek production so far, this year Kodak Polylight will also have products available. There are two shortcomings of the untreated plate material. First, the hydrophilic layer must be strong enough to achieve high print volume, which requires that this layer should be as thick as possible, but it also increases the difficulty of removing the melting impurities. The second is that these plates cannot be baked to increase the printing volume, because the baked plate will completely burn off the hydrophilic layer, and the printing information will be lost.
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