Thermal CTP Plate] Plate Composition and Imaging Principle

The basic components of a thermally cross-linked CTP plate are a frosted aluminum plate base and a photographic layer.

①Photographic layer

The photographic layer (thickness of about l μm) consists of linear phenolic resin and hydroxymethyl phenolic resin, deacidifying agent, infrared absorbing dye (IR dye) and so on.

Resin

Depending on the role of the resin in the thermal plate, it can be broadly categorized into acid or thermal cross-linking resins, acid or thermal decomposition resins, hot-melt resins and film-forming resins. Thermal plates are preferred for their storage stability and alkali resistance.

③ Cross-linking agent

The essence of cross-linking agent is to accelerate the thermal cross-linking reaction through active functional groups. There are many types of cross-linking agents, such as phenolic hydroxyl compounds, aromatic aldehydes, amino resins, isocyanate compounds, carboxylic acids, halogenated compounds, epoxy compounds, aziridines, imides, melamine and so on.

④ Development gas pedal

Development accelerators can increase the development speed of plates and generally include low molecular weight polyphenol compounds or cyclic anhydrides. The principle is that since low molecular weight phenol or hypophosphite acts as a dissolution accelerator, it increases the dissolution rate of linear phenolic resins and produces more hydrophilic percolation points.

⑤ Stabilizers

In order to improve the storage stability of the thermal version, it is necessary to add acidic compounds such as benzoic acid and naphthoic acid.

⑥ Infrared absorber

There are many kinds of infrared absorbers used in thermal CTP plates, which can be pigments or dyes, and the performance of different infrared absorbers varies greatly. For example, carbon black has the advantage of a wide range of absorption wavelengths, but the image contrast after exposure is small and not easy to distinguish; phthalocyanine dyes are easily soluble in a variety of solvents and compatible with a variety of resins to form a uniform light and heat conversion layer. Therefore, the selection of infrared absorber should consider a variety of factors to determine the final performance.

⑦ Photoreleasing Acid

Photo-releasing acid has developed rapidly in recent years, mainly sulfonates, other esters, organochlorines, diazotypes, alicyclic ethers, etc., most of which have been used in thermal CTP plates. In order to improve the working performance of the bright room of the thermal plate, the non-white light sensitive thermal releasing acid agent is getting more and more attention. Recently, some companies have introduced photoluminescent acids into infrared-absorbing dyes and polymers, thus greatly improving the sensitivity of plates.

Photodetachable acid is a cationic polymerization initiator that decomposes to form a strong protonated acid when exposed to heat or light, which triggers a carbon cation polymerization reaction, a technique known as chemical addition.

Once the photoreceptor 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 photographic layer reaches a certain value (threshold), the deacidifying agent (potential acid) decomposes to produce acid, which acts as a catalyst, and the resin undergoes cross-linking (latent image) to a certain extent, and then high temperature (i.e., preheating required for the process) is applied to accelerate the cross-linking reaction of the resin layer in the exposed part, so that the image does not dissolve in the alkaline developer solution during the development process, and a clear image is obtained after the development process. It also enhances the solvent resistance of the film layer in the image part so that it is not easily dissolved by the wetting solution or other solvents.