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​The composition and imaging principle of thermal CTP plate

Time:2022-09-28 Author:Huaiho

  The basic composition of the heat-crosslinking type CTP plate is a grained aluminum plate base and a photosensitive layer.

  1. photosensitive layer

  The photosensitive layer (having a thickness of about 1 μm) is composed of a novolac resin, a methylol phenol resin, an acid releasing agent, an infrared absorbing dye (IR dye), and the like.

  2. resin

  Resins can be roughly classified into acid or thermal crosslinking resins, acid or thermal decomposition resins, hot melt resins, and film-forming resins depending on their function in the thermal plate. Thermal storage plates are ideal for storage stability and alkali resistance.

  3. crosslinker

  The cross-linking agent essentially accelerates the thermosensitive crosslinking reaction by a reactive functional group. There are many types of crosslinking agents, such as phenolic hydroxyl compounds, aromatic aldehydes, amino resins, isocyanate compounds, carboxylic acids, halogenated compounds, epoxy compounds, aziridines, imides, melamines and the like.

  4. development accelerator

  The development accelerator can increase the development speed of the plate, and generally includes a low molecular weight polyphenol compound or a cyclic acid anhydride. The principle is that since the low molecular weight phenol or hypophosphorous acid increases the dissolution rate of the novolac resin and acts as a dissolution promoter, more hydrophilic percolation points are produced.

  5. stabilizer

  In order to improve the storage stability of the heat-sensitive plate material, it is necessary to add a stabilizer of an acidic compound such as benzoic acid, naphthoic acid or the like.

  6. infrared absorber

  There are many types of infrared absorbers used in the thermal CTP plate, which can be pigments or dyes, and the performance of different infrared absorbers is quite different. For example, carbon black has the advantage of wide absorption wavelength range, but the contrast of the image after exposure is small and difficult to distinguish; the phthalocyanine dye is easily soluble in various solvents and compatible with various resins to form a uniform light-to-heat conversion layer. However, the development performance is not optimal. Therefore, the choice of infrared absorber should take into account various factors and be determined by the final performance.

  7. photoacid release agent

  Photoacid release agents have developed rapidly in recent years, mainly including sulfonates, other esters, organochlorines, diazos, and alicyclic ethers, most of which have been used in thermal CTP versions. In order to improve the bright room operating performance of the thermal plate, non-white light sensitive thermal photoacid release agents have attracted much attention. Recently, some companies have introduced photoacid release agents into infrared absorbing dyes and polymers, thereby greatly increasing the sensitivity of the plates.

  The photoacid release agent is a cationic polymerization initiator which decomposes when heated or light to form a strong protonic acid, thereby initiating carbocation polymerization, a so-called chemical amplification technique.

  Once the photosensitive layer is exposed, the infrared absorbing dye first absorbs the infrared laser and then converts the light energy into heat. The temperature rises. When the temperature of the photosensitive layer reaches a certain value (threshold value), the acid release agent (potential protonic acid) is decomposed to generate acid, the acid acts as a catalyst, the resin undergoes a certain degree of crosslinking (latent image), and then the high temperature is applied (ie, the process) The preheating required on the surface accelerates the crosslinking reaction of the resin layer at the exposed portion, so that the image is insoluble in the alkaline developing solution at the time of development, and a clear image is obtained by development. At the same time, the solvent resistance of the image portion of the image layer is also enhanced, so that it is not easily dissolved by the fountain solution or other solvent.