Sensitizing a mixture of silver halide and lead halide by heat
United States Patent 11 1 [none et a1.  
 1 1 SENSITIZING A MIXTURE OF SILVER HALIDE AND LEAD HALIDE BY HEAT [75] Inventors: Eiichi lnoue; Hiroshi Kokado, both of Tokyo; lsamu Shimizu, Kanagawa; Shuichi Ohtsuka, Tokyo, all of Japan [73] Assignee: Fuji Photo Film Co., Ltd.,  
 Kanagawa, Japan [22] Filed: Mar. 12,1973  
 [21] Appl. No.: 340,631  
 1451 Apr. 1, 1975 Primary Examiner-Norman G. Torchin Assistant Examiner-Won H. Louie, Jr.  
 Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, Zinn &amp; Macpeak Elm/c111 [30] Foreign Application Priority Data 57 ABSTRACT Mar. 14, 1972 Japan 47-25884 The Sensitivity of a mixture of lead halide and silver halide to radiation is improved by annealing the mix 52 11.5. C1 96/88, 96/108, 252/1 me prior to exposure. [51] 1nt.Cl G03c 1/00, G03c 1/28 1581 Field 61 Search 96/108, 88 14 h m Z r -n1; Flgures SENSITIZING A MIXTURE OF SILVER I-IALIDE AND LEAD HALIDE BY HEAT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for raising the sensitivity ofa mixture of lead halide and silver halide to radiation.  
 2. Description of the Prior Art Heretofore, photographic images have been formed by exposing a light-sensitive material such as a silver halide emulsion, a diazotype light-sensitive composition or the like to light, and subjecting the exposed material to development, fixation and like processing. In particular. the method of using a silver halide emulsion can be said to be an excellent recording method since it provides a image with high sensitivity and high resolving power.  
  However. in any of the conventional recording methods chemical or physical processings are required to obtain images, and. since the material is sensitive to visible light and light in the vicinity of the visible light, these recording materials must be handled in a dark place before the formation of an image.  
  Recording methods absolutely different from the abovedescribed methods have, of course, been reported. For example. M. R. Tubbs has described in &#34;The Journal of Photographic Science&#34; 17. I62 169, a recording method using a thin film material comprising metal halide compounds or chalcogen compounds.  
 According to this report. when irradiated with visible light or ultraviolet light having a wave-length of less than 5.200 A. at l60- 220C a vacuum deposited lead iodide film changes from yellowish orange to colorless at the irradiated areas. and when a metal silver film and a lead iodide film laminated on a support is exposed to light at l J/cm at room temperature. there can be obtained an image with a resolving power of more than I ,u. If the resulting image is not covered with, e.g., a cover film. it will be deteriorated.  
  The inventors previously suggested a method of recording images without conducting chemical or physical processing (Japanese Patent Application No. 41 186.71 l. According to this method, an image can be obtained by imagewise providing a crystalline layer or a dispersion layer of a metal halide with energy of an intensity satisfying the formula;  
 I) kl&#34; wherein D represents density, k is a constant, and 1 represents the energy of the intensity.  
  However. the above-described metal halide compounds have the defect that the sensitivity thereof to energy is extremely low.  
 SUMMARY OF THE INVENTION As a result of extensive investigations to improve the above defect. the inventors reached the present invention where the sensitivity of a mixture of one or more lead halides and one or more silver halides to radiation is increased by annealing the mixture.  
  The present invention will be described in greater detail below BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 are curves showing the change in optical density (D) versus the amount of irradiation on the recording materials, the recording materials being prepared using a mixture of lead iodide and silver iodide.  
 DETAILED DESCRIPTION OF THE INVENTION As the lead halides which can be used there can be illustrated lead iodide, lead chloride, lead bromide, etc., and, as the silver halides which can be used there can be illustrated silver iodide, silver bromide, etc.  
  The proportion of lead halide to silver halide varies depending upon the kind&#39;and combination of lead halides and silver halides used. For example, in the case of lead iodide and silver bromide. the proportion of silver iodide is preferably 40 &#39;60 mol percent. This range, while representative of preferred proportions for the lead halides/silver halides in general, is not limitative as all ratios of lead halides to silver halides can be used in the present invention.  
  A mixture of lead halide and silver halide can be prepared, for example, as follows. In the case of a mixture of lead iodide and silver iodide, silver nitrate and lead acetate ofa desired molar ratio is dissolved in an aqueous solution at about C, a solution of potassium iodide is added dropwise thereto, and the precipitate formed is filtered out, washed and&#39;dried in a vacuum oven.  
  The annealing, the most characteristic feature of the present invention. will now be explained.  
  The annealing temperature is above room temperature, preferably in the range of from 50 to 600C, more preferably 50 to 450C. The annealing time varies depending upon the annealing temperature employed, but what is essential is to conduct the annealing for enough time to complete annealing, i.e.. the heat treatment is conducted to such a degree that the X-ray diffraction pattern of the mixture of lead halide and silver halide changes after annealing from-that before annealing. In the case of conducting the heat treatment at an elevated temperature. e.g.. near the upper and of the range above, it is preferred to conduct annealing in an inert gas atmosphere, such as argon, nitrogen, helium, etc., or under vacuum to prevent the oxidation of lead halide and/or silver halide due to the humidity and oxygen in the air. 7 z  
  The annealing time can, of course, be set as that at which the diffraction pattern change discussed above is noted. For most embodiments annealing will take from about /2 how to about 24 hours, though if one wished to use appropriate apparatus shorter and longer periods could be used. As an example of a typical anneal, the temperature is 300C and annealing is for 3 to 6 hours.  
  The sensitivity ofthe mixture to radiation is markedly improved by conducting the above-described annealing.  
  The mixture of lead halide and silver halide obtained by the present invention which has high sensitivity to radiation is used as a vacuum deposited film formed by vacuum deposition on a support such as paper, plastic film. glass plate, etc.. for example at 10&#34;&#34;mmHg, or is used as a dispersed layer coated on a support after dispersion in a suitable binder such as a hydrophilic or hydrophobic resin (e.g., gelatin, gelatin derivative, cellulose derivative. polyvinyl compound. acrylamide polymer. etc.  
  While not overly critical. for best results with a vacuum deposited layer the thickness thereof is usually A to 3 better yet 500 to 1,000A, and with a binder layer the thickness is l/J. to 200 1, better yet 10 to 20 41.. In the dispersed layer embodiment, the weight parts ratio of mixture to binder is preferably 10:1 to 1:10, most preferably about 1:1. The use of much less mixture will sometimes lead to insufficient photosensitive material being present, while greater amounts are not required. If the mixture is in massive form, it can be crushed prior to addition to the binder.  
  The exact size of particles used in the binder layer embodiment is not overly important, and the rule is that the smaller the particles, the higher the resolving power, and the larger the particles, the lower the resolving power. Generally, balancing all factors, the size will be less than 10g, and most preferably less than lu.  
  Since a light-sensitive material having higher sensitivity to radiation can be obtained the amount of irradiation necessary to yield an image can be reduced.  
  The present invention will now be illustrated in greater detail below by several examples.  
  The elements of the present invention shown in the Examples were exposed with light of a wavelength of 250mm to 750nm. The intensity of exposing light can vary greatly depending upper the exposure time, etc., but is usually 1 X 10 to 3 X 10 mW/cm e.g., light from a high pressure mercury lamp, xenon lamp, lasers such as ruby pulse lasers, argon lasers, He-Ne lasers, a tungsten lamp, etc.  
 Example 1 Five (5) mixtures of crystals of lead iodide and silver iodide containing 1 mol percent, mol percent, 30 mol percent, 60 mol percent or 90 mol percent of silver, respectively, were precipitated as described below, filtered out, washed, vacuum dried and then annealed at 300C for 5 hours in an argon gas atmosphere. Each of the resulting products was dispersed in a tetrahydrofuran solution of polyvinyl chloride so that the mixed crystals were present in an amount of 1 mg per 1 g of polyvinyl chloride. Each of the resulting dispersions was applied to a glass plate in a thickness of about 50 p. to give recording materials A, B, C, D and E. The resulting materials thus prepared were irradiated with a mercury lamp of 3.44 mW/cm The relationship between the change in optical density and the irradiation amount is shown in FIG. 1.  
  From FIG. I, it can be seen that the thus prepared recording materials have high sensitivity, and that the highest sensitivity is obtained when the silver iodide content is 60 mol percent.  
  These results also show the usefulness of the present invention over a wide range of mixing ratios, e.g., 1 mol percent to 90 mol percent. This range is not, of course, limitative.  
  Of course, as with most chemical inventions, a preferred mixing ratio does exist, i.e., silver halide of about mol percent to about 80 mol percent is preferred, with, correspondingly, 80 mol percent to 20 mol percent lead halide. Outside the above range, the sensitivity is lowered, and thus, while useful, is non-preferred.  
 Precipitation technique Silver nitrate in an amount of 0.002 moles. 0.02 moles, 0.06 moles, 0.12 moles and 0.18 moles and lead acetate in an amount of 0. 198 moles. 0.18 moles, 0.14 moles. 0.08 moles and 0.02 moles, respectively, were mixed and then dissolved in 1 liter of water, the mixtures being produced and kept at 80C. Then. an anhydrous solution of 0.5 moles/liter of potassium iodide was produced, and 0.5 liter thereof added to each solution kept at C while agitating and maintaining at 80C. The time of addition was 5 minutes.  
 Example 2 Four (4) mixtures of lead iodide and silver iodide (containing 30 mol percent of silver halide) prepared in the manner described in Example 1 were annealed in air at 50C and in argon gas atmosphere at l50300 and 450C, respectively, and each applied to a glass plate support in the same manner as in Example 1 to prepare recording materials F, G, H and 1. Each of the resulting recording materials were irradiated with a ruby laser (634.3 mp. wave-length, 30 MW maximum output and 15 n-sec half value width). The change in optical density versus amount of irradiation is shown in FIG. 2.  
  As is apparent from FIG. 2, recording material H annealed at 300C for 5 hours had the highest sensitivity.  
  While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.  
 What is claimed is:  
 l. A method for raising the sensitivity of a mixture oflead halide and silver halide to radiation, which mixture comprises from 20 percent to 80 mol percent lead halide with, correspondingly, 80 to 20 mol percent silver halide, which method comprises annealing said mixture prior to exposure to irradiation, thereby increasing the sensitivity of said mixture to irradiation; wherein said annealing is conducted in the absence of oxygen at a temperature of from 50 600C for a period of time of from about V2 to about 24 hours.  
  2. The method of claim 1 where the temperature is 50 to 450C.  
  3. The method of claim 1 wherein the mixture is in the form of a vacuum deposited layer.  
  4. The method of claim 1 where the mixture is in the form of a dispersion in a binder.  
  5. The method of claim 1 wherein the silver halide is silver iodide. silver bromide or a mixture thereof and the lead halide is lead iodide, lead chloride, lead bromide or a mixture thereof.  
  6. The method of claim 1 where the annealing is conducted in an inert gas atmosphere to prevent the oxidation of lead halide and/or silver halide due to humidity and oxygen.  
  7. The method of claim 1 where the annealing is conducted undcr vacuum to prevent the oxidation of lead halide and/or silver halide due to humidity and oxygen.  
  8. The method of claim I where the lead halide is lead iodide.  
  9. The method of claim 1 where the lead halide is lead chloride.  
  10. The method of claim 1 where the lead halide is lead bromide.  
  11. The method of claim I where the silver halide is silver iodide.  
  12. The method of claim 1 where the silver halide is silver bromide.  
  13. The method of claim 1 where exposure is to irradiation of an intensity of l X 10&#34; to 3 X 10 mW/cm 14. The method of claim I where the silver halide is silver iodide and the lead halide is lead iodide.