The present invention relates to a two-component diazotype material, composed of a support and a light-sensitive layer which is applied thereto and contains a polymeric binder, a diazonium salt, a coupler, an acid stabilizer and conventional additives.
It is known that cellulose esters are used as the polymeric binders in diazotype materials. Due to their good film-forming and optical properties, their heat stability and their good compatibility with diazonium salts and couplers, these esters have proved so advantageous that they are frequently quoted and used almost exclusively in practice. A disadvantage of these compounds is, however, an insufficient layer adhesion to polyester film, and this can be made adequate only with the assistance of suitable, additionally applied adhesive layers. Adhesive layers are applied, for example, in a special operation using trichloroacetic acid and silica or polyvinylidene chloride.
It is also known that polyvinyl acetate can be used as the binder (U.S. Pat. No. 2,405,523). Polyvinyl acetate has the advantage that its adhesion to polyester surfaces is somewhat better. As a thermoplastic, however, polyvinyl acetate has the great disadvantage that the sensitized layers have a strong tendency to become embossed and to stick during processing.
It is also known that copolymers of vinyl acetate and maleic acid or crotonic acid are distinguished by useful adhesion on polyester surfaces (German Auslegeschrift No. 1,065,724). These polymers can be applied from an aqueous-alkaline solution, but they are also detached again by aqueous alkali with equal ease. Moreover, these layers tend to stick.
The curing of adhesive layers or lacquer layers composed of a mixture of vinyl acetate/crotonic acid copolymers and, for example, urea/formaldehyde resins is also known (German Pat. No. 1,062,111 and German Auslegeschrift No. 1,461,260). In this way, their alkali solubility is reduced but not fully eliminated.
On the other hand, the more a lacquer layer has been cured, the more difficult it is to sensitize this layer, since during the diffusion process, the diazonium salts and the coupler penetrate into the layer to a lesser extent. Thus, the degree of curing of the layer is an additional important factor with regard to its suitability in diazo printing layers.