Study on Enhancing Contrast Effect of CTP Plate in Developing Process

High contrast is an important characteristic of photographic materials for printing. This article focuses on the effect of four chemical development inhibitors on the contrast of silver salt diffusion transfer type CTP plate. The results show that thiosalicylic acid, mercaptobenzothiazole, nitro When benzimidazole and benzotriazole are used alone, the contrast of the plate is increased to varying degrees; when thiosalicylic acid is used together with nitrobenzimidazole, a high contrast effect is obtained. The calculations give the gamma values ​​for each inhibitor's optimal concentration. In addition, studies of the physical development process using linear CCD technology show that the addition of inhibitors increases the difference between the development induction period and the development rate at different exposure levels. , thereby enhancing the contrast.

With the rapid development of information science and technology, computer-to-plate (CTP) has been increasingly paid attention by the printing industry. Among them, the silver salt plate material realized by the principle of silver salt diffusion and transfer reversal has received widespread attention. The plate has a high printing quality and printing rate, the lipophilicity of the image area and the hydrophilicity of the non-image area should have obvious boundaries. The previous study shows that the density of the physical development silver in the image area is increased and the silver image is enhanced. Adsorption of hydrophobic organics on the surface is conducive to improving the oleophilicity of the plate surface. Therefore, improving the contrast of the physical development silver on the surface of the plate is an important issue for improving the properties of the plate. The method of obtaining high contrast in chemical development is usually Lith. Development, iridium development, iodine ion infection development and addition of inhibitors, but there are relatively few reports on the image contrast in the physical development process. This article focuses on the study of several chemical development inhibitors during the physical development of the silver salt diffusion transfer system to improve the CTP version The effect of material contrast has been achieved with good results and given from a dynamic point of view Explain step.

1 Experimental section

1.1 Plate preparation

Monodisperse cubic AgCl emulsions were prepared by a double injection method. The emulsion particles were between 0 2 and 0 4 μm. The emulsions were physically and chemically ripened. The carbon black anti-halo containing the developer was coated on the plastic coated paper base first. The layer is coated with an AgCl emulsion layer sensitized by a green dye, and finally, a physical layer of a metal sulfide is applied on the surface of the plate. The plate is exposed with a landscape CGG exposure apparatus for 1 second, and the color temperature is 3200K. .

1.2 Development Conditions

The main components of the development activation solution were: potassium hydroxide, anhydrous sodium sulfite, uracil, etc. The inhibitors were 6-nitrobenzimidazole, thiosalicylic acid, benzotriazole, mercaptobenzothiazole. For 25°C.

1.3 Experimental Principles and Methods

For the silver salt diffusion transfer type computer-to-plate plate, the silver halide grains in the image area are not exposed when the developed developer is developed. The silver halide particles are dissolved by the complexing agent and the complexed silver ions diffuse to the surface of the plate. The physical developing core layer is catalytically developed into physical developing silver and has a strong reflection effect on light; the silver halide particles in the non-image area are developed by the developer due to exposure, and the chemical developing silver is left in the gelatin layer, and the light is With strong absorption and low reflectivity, this experiment uses silver to monitor the physical development process with different reflectivity of light. The CCD device used in the experiment is described in the previous [11,12]. Through 2048 monitoring units. The one-dimensional linear CCD monitors the development process of eight different exposure stages in the wedge simultaneously. The light source uses red safety light, and the incident light intensity remains constant during the experiment.

2 Results and Discussion

2.1 CCD monitored physical development process

In the experiment, the CCD was used to collect the reflected light intensity data from the surface of the plate during development. After computer processing, a three-dimensional image was obtained as shown in Fig. 1. The X-axis is the CCD detection unit, corresponding to different exposure levels, from left to right. , Exposure increases; Z-axis is the reflected light intensity of the detected surface of the plate, according to the previous study, the reflected light intensity is proportional to the density of the resulting physical development silver; Y-axis is the time axis, close to the time of two measurements The interval is 0 2s.

It can be seen from Fig. 1 that the reflected light intensity on the surface of the plate shows a gradient change: the AB segment is a weakly exposed zone. This zone mainly takes place in the physical development process, and the physical development silver that is exposed on the surface of the plate is generated, and the reflected light intensity gradually rises. High; The CD segment is a strongly exposed zone where chemical development takes place. Chemically-developed silver is generated in the gelatin layer and absorbs light. There is no or little physical development of silver on the surface, so the reflected light intensity drops rapidly, and then the basic Invariable; BC segment is medium intensity exposure zone, due to the competition of physical development and chemical development, a certain amount of physical development silver is generated on the surface, so the reflected light intensity is medium intensity, which is intermediate transition stage. It should be noted that In the present system, the silver image (physical development silver) obtained by development in the unexposed area or the weakly exposed area has a high density, and the silver image (physical developing silver) obtained in the strongly exposed area has a low density, and the image obtained by the chemical development process is On the contrary, in order to more conveniently represent the development process, FIG. 2 and FIG. 3 can be obtained by processing FIG. 1. Among them, FIG. 2 shows the change of the reflected light intensity with time of different CCD detection units, representing various exposures. The physical development kinetics.

Figure 1 Three-dimensional view of the physical development process

The exposures corresponding to numbers 1 to 8 are sequentially increased by .tI for the physical development induction period and Imax for the corresponding maximum reflected intensity. From Fig. 2, the important information such as the development induction period and the development rate can be clearly obtained. Fig. 3 shows the end of development. The reflected light intensity at each exposure level corresponds to the photosensitive characteristic curve of the physical development silver (positive image) on the plate material. Through its slope, it is also possible to obtain the performance parameters such as the contrast ratio of the plate material. This article will mainly be based on the kinetic curves and The photosensitivity curve was used to study the effect of the inhibitor on the properties of the plate.

Figure 2 Physical development curve of each exposure level Figure 3 Physical development silver sensitivity curve