Influencing Factors Of Photographic Properties Of Hydrophilic Photothermographic Materials

In recent years, significant advances were made in technology of photothermographic (PTG) materials, and wide application was realized in medical films fields. However, there were still some problems needing to be further studied, such as different kinds of unknown influence factors of photographic properties of PTG materials. In this dissertation the influence factors of photographic properties of PTG materials using polyvinyl alcohol as hydrophilic binder and in situ or ex situ AgX as light sensitive elements were measured and the mechanisms were in detail investigated by means of IR spectra, soak tests and differential scanning calorimetry (DSC) and so on. The main results were summarized as follows:1. Effects of pH and pAg on photographic properties of PTG materials. Effect of pH on pAg of varies of PTG dispersions and the joint influences of pH and pAg on photographic properties of PTG materials were studied. It showed that pAg of PTG dispersions increased with the increment in pH. The maximal sensitivity of PTG materials was achieved while the pH was in the range of 7.0-7.5, which was possible due to the changes in latent image formation of AgBr affected by pAg, the concentration of silver complex and activity of organic developer determined by pH and pAg.2. Effects of metal ions on photographic properties of PTG materials. The impacts of Ca²⁺, Ba²⁺, Pb²⁺ and Zn²⁺ on photographic properties and storage stability were researched. The results showed that the sensitivity and fog of PTG materials were all decreased with increasing amount of different kinds of metal ions. In addition, in the aging experiment the photographic properties of PTG materials were affected by the four metal ions. Studies on mechanism showed that the decrease in sensitivity and fog of PTG materials might be caused by the decrement in latent image formation efficiency of AgBr grains and the dropping of transference speed of Ag⁺ in thermal developing process.3. Effect of triphenylphosphine (Ph3P) on photographic properties of PTG materials. The impacts of Ph3P on photographic properties of PTG materials were studied and the mechanisms were investigated by IR and DSC technologies etc. The results indicated that the sensitivity of PTG materials firstly ascended and then descended with the amount of Ph3P, while the fog density was still kept zero; and when the ratio of Ph3P/AgSt was 0.1:1 the sensitivity came to a head. The possible mechanisms for Ph3P were that Ph3P not only affected the latent image formation by the reaction of Ph3P with AgBr but also the thermal developing process of PTG materials caused by the combination of Ph3P with silver stearate (AgSt) and then the decreased phase transition temperature of AgSt.4. Effect of 2-mercaptobenziminazole (MBM) on photographic properties of PTG materials. The influences of the amount of MBM on photographic properties of PTG materials were studied and the mechanisms were also investigated based on the measurement of the structure and thermal behaviors of modified AgSt by means of IR, TG and DSC etc. The results revealed that the sensitivity of PTG materials increased at the beginning and decreased later, and the maximum could be obtained when MBM/AgSt was equal to 0.05:1, which might be resulted from the decline in phase transition temperature of AgSt modified by a small amount of MBM that was beneficial to thermal developing process while large amount of AgMBM formed on the surface of AgSt with increasing MBM blocked thermal development proceeding.5. Effect of carboxylate doped AgBr on photographic properties of PTG materials. The sensitivity of PTG materials was enhanced to a certain extent by the cubic AgBr grains doped with carboxylate and that was further raised by the surface chemical sensitization to the doped cubic AgBr grains. When the mole ratio of doped AgBr to AgSt was 0.25, the maximal sensitivity of PTG materials was obtained. That was to say, the high efficiency of latent image formation as to doped AgBr resulted in the increment in the relative sensitivity of PTG materials, and the thermal development process of PTG materials still followed Klosterboer-Rurledge's"sphere of influence"model.6. Effect of in situ AgX on photographic properties of PTG materials. Photographic properties and after processing stability under room light illumination of PTG materials using in situ AgBr or AgI as light sensitive element were studied. It was found that PTG materials had an optimum amount of in situ AgBr or AgI. The thermally processed unexposed PTG sample using in situ AgI was of better light stability than that of PTG sample using in situ AgBr.