Thermal plate technology
There are currently three major digital printing technologies: silver halide technology, high-sensitivity technology, and the latest thermal technology. Silver halide technologies include silver halide diffusion transfer plates, visible light lasers, and light waves between blue and red. Based on this technology, Agfa introduced two aluminum-based digital direct-printing plates, Liteostar plus and Silver Lith SDB, to the market. DuPont-Hausen introduced a polyester-based digital direct-printing, red-feeling Setprint-HN-LL version.
Polaroid introduced a silver salt compounding technology, CTX Technology, which uses silver halide technology and emulsions to coat UV-sensitive PS plates.
Aikefa introduced a photopolymerized offset printing plate, Ozasol N90A Edition, which is also a digital direct printing plate, with fast speed, green and blue.
Recently, there has been a newest type of digital offset printing on the market. People call it the thermal printing version. The thermal sensitivity range of 830 to 1064 nm is even wider. Its plate technologies include melting, ablation, transfer, cross-linking, photoelectron decomposition, and the like. No matter which of the above techniques is used for imaging, the plate is obtained after further development. Due to the different types of plates, some require wet processing.
1, chemical insolubility
Through laser heat, the polymer in the active layer is cross-linked, resulting in chemical insolubility, negative image formation, acidification by IR exposure to heat, catalytic crosslinking of the polymer binder, selective cross-linking of exposed areas . The pre-heating procedure enables a sufficiently high degree of crosslinking after multiple molecular reactions. Therefore, such a printing plate can be obtained by obtaining a high printing range, using a conventional wet-processing and post-baking plate after the pre-heating process. The preheating latitude is small, and the heating box is more controllable.
2, physical insoluble
This technique generates physically insoluble materials by heating the active layer. The active layer contains a homogeneous dispersion of thermoplastic water-in-water polymer latex particles that can be rapidly dissolved, but exposed to IR-laser exposure, the thermal coalescence of thermoplastic polymer particles inhibits the solubility of the polymeric layer, and the dual properties of such particles are produced. High quality images. The advantage of this technology is bright room, stable quality, at the same time can be printed inside and outside the printing and printing of images and images, is a printed board, wet processing and then baked version, can get a high printing version. The photosensitive wavelength range of Agfa's RD-9 plate is from 830 to 1100 nm. Both internal and external drum recording imaging technology are available, but it has not yet been commercialized.
3, chemical dissolution type
This technology is used to heat the active layer to produce chemically dissolved substances, without heating, to obtain a positive plate, fully lighted, wet-processed and then baked, with a high printing distance. The active layer can be based on acid phthalate resin, and the thermal solubility of the layer increases. If a red line-absorbing species is added to the layer as a dissolution inhibitor, the exposed areas are selectively removed.
4, thermal UV mask
The technology senses visible light, and imagewise exposure is performed with IR-rays so that the UV absorbing layer is no longer soluble in the alkaline developer and thus acts as an underlying UV mask. Another form is through the infrared absorption layer of UV, exposed by thermal etching, the exposure of the underlying UV photosensitive layer imaging, but its drawback is that the process is complex, requires two processing to completely or not completely remove the UV mask layer.
5, thermal mask
This technology, pioneered by Agfa, is a new type of thermal positive plate named Thermostar. The structure is changed by heating the physical mask layer with a high-energy laser. After the carbon or IR dye in the protective layer absorbs IR light, the infrared light energy is converted into heat, and the temperature in the active layer is drastically increased by the heat energy. It reaches 400Â°C or more to complete the exposure. The specific temperature is determined by the thermal diffusivity of the layer, the exposure time, the thickness of the layer, and the 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 increase. Exposure to the two lasers used at the same time can complete the ablation reaction in the layer.
Due to the high absorption capacity of IR light on the protective layer of this plate, a relatively low exposure energy level can also generate high temperatures to physically deform the protective layer. This physical deformation can effectively not only make the alkaline developing solution wet the exposed portion of the plate, but also quickly penetrate the protective layer, enter the bottom layer, effectively dissolve the bottom layer, and dissolve faster than the non-exposed area, and the protective layer is Alkaline protective film acts as a mask, and apparently its surface and interfacial tension are important parameters for processing.
It is concluded that the technique is based on the use of different effects of physical imaging agents. This unique non-ablative process is performed prior to the formation of harmful volatile compounds in the layer, or until some of the components in the layer have not been degraded. It has been imaged. Since the compound components in the layer are treated, they do not pollute the environment. Therefore, the use of the above techniques can reduce the risk. At the same time, the laser ablation technology can also be used in the imaging area without vacuum equipment.
6. Non-ablation characteristics of imaging technology
Ablation includes the evaporation and decomposition of the infrared photosensitive layer. During this time, physical and chemical changes have taken place in the layer. When the layer is used as a protective layer, the ablated material evaporates into the air. In most cases, some of the material is powdery and redeposits on the surface of the material. This may further affect the imaging of the material, especially if the ablation degree is too high. When the entire layer is uniformly colored, the powder can be easily wiped off to make the layer thinner and the chemical density becomes smaller. Such an ablation medium can be distinguished by its quality from the eyes, and can also be tested by instruments.
Classification of Thermal Plates
To date, 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 photosensitive polymer plates. Kodak PolyVision's Hot 830 media and Fujifilm's Brillia LH-NI are all included in this category. This media is only imaged on an external drum plateetter. The printing performance of the negative image plate is surprising, and the plate will not be baked, and the plate will guarantee 250,000 marks. It has been reported that a printing plant has printed 700,000 copies without baking, and after baking, it can print more than 2 million copies.
(2) Yang Tu Thermal Plate
A cross-linked photosensitive polymer material. It requires less laser beam power and is suitable for internal drum type platesetters. It does not require preheating, but it needs to be processed. After baking, the print volume can be increased. 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. From 200,000 to 200,000 copies, Electra DC can be over 1 million after baking.
(3) No heat treatment plate
It is composed of an aluminum plate base coated with a hydrophilic layer, a hydrophilic layer and a protective layer, and can be printed without developing treatment. In addition to Presstek's production so far this year, Kodak Polystar will also have products available. There are two disadvantages to the non-treated plate material. First, the hydrophilic layer must be strong enough to achieve a high throughput. This requires that the layer should be as thick as possible, but it also increases the difficulty of removing impurities from the melting process. The second is that these plates can not be baked to increase the print volume, because the baking plate will completely burn off the hydrophilic layer and lose the printed message.
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