US2967105A - Photosensitive sheet - Google Patents

Description

United States Patent 2,967,105 PHOTOSENSITIVE SHEET Robert A. Peters, New York, N.Y., assignor to Stupa gorporatlon, New York, N.Y., a corporation of New 7 ork This invention relates to a photosensitive sheet on which a positive or a negative reproduction may be formed upon photographic exposure to light of significantly greater intensity than sunlight but which can be exposed to sunlight before or after such high intensity photographic exposure without adverse color change, and to methods of preparing and using such photosensitive sheets.

Heretofore the bromides and iodides of heavy metals such as silver and gold have been the preferred photosensitive materials by reason of their ready decomposition under the influence of light. Ferrocyanide compounds have been employed for blueprints but have required an aqueous development. Certain organic compounds such as diazo materials have been sufiiciently sensitive to ultraviolet light to be suitable for oflice rcproductions. These diazo papers have generally had the disadvantage of requiring development. under the influence of ammonia gas or equivalent reagent. Altho there have been certain proposals in the patent literature relating to diazo papers which provide prints upon exposure to ultraviolet light and without any kind of development whatsoever, there has been no widespread tommercial use of the photographic paper requiring no development.

In accordance with the present invention a photographic image is formed upon a suitably prepared photosensitive sheet under the influence of light having an intensity significantly greater than that of sunlight. After the formation of such photographic image, and without development step it can be handled in a normal manner without being extremely sensitive to fading or other color changes attributable to the action of sunlight. The composition of the photosensitive sheet is such that the photosensitive components are capable of forming two kinds of decomposition products. One of the decomposition products is black or similar dark color and the other decomposition product is white, pale yellow, transparent, and/or otherwise contrasting to the dark color of the other decomposition product. If the photosensitive sheet is designed to provide a negative, so that the decomposition product resulting from the high intensity illumination is dark colored, then the exposure of the photosensitive sheet to sunlight does not bring about the formation of any dark colored material. The negative image resulting from the high intensity exposure can be subjected to sunlight for an indefinite period of time but to the extent that the sunlight brings about any decomposition of the photosensitive components of the negative no fading of the negative results by reason 0. the substantially white color and/or transparency of the decomposition product from exposure to light of the intensity of sunlight.

In certain embodiments of the present invention the photographic sheet comprises organometallic compounds as the photosensitive component. Under the influence of light, and particularly under the influence of ultraviolet light the chemical bond between a carbon of an organic group and the metal of the organometallic compound and/or the bond between two metal atoms'of an organometallic compound containing a plurality of metal atoms is broken. This light-induced breaking of a bond in an organometallic forms reactive fragments which can participate in the formation of decomposition products. The composition of the photographic sheet can comprise material tending to form transparent and/or white decomposition products if the rate of photochemical decomposition of the organometallic compound is slow but capable of forming dark colored decomposition products if the rate of decomposition of the organometallic compound is-sufiiciently rapid.

In preferred embodiments of the present invention the photographic sheet contains three reactive ingredients, namely, bis(tricyclohexyllead), an organic'sulfur compound, and an organic oxygen compound. It is possible that the decomposition product resulting from the high intensity illumination partake of the nature of lead sulfide, a dark colored material. It is possible that the photo decomposition product from low intensity exposure partake of the nature of lead oxide which is of a pale yellow color. However, the beneficial results of the present invention are useful without regard to the correctness of this theoretical explanation of the phenomena.

It has been noted that oflice reproduction prints or engineering prints should comply with requirements such as:

(1) Good prints should be obtainable by moderately short exposures of about 10 second. Oflice print exposures are ordinarily within the range of from 5 seconds (short) to about 30 seconds (long). An exposure of about 2 seconds, altho very short for office reproduction prints, is still of a very much higher order of magnitude than the of a second or of a second or other brief exposure required in motion picture photography.

(2) The image resulting in the office print should provide sufiicient contrast between the dark and. light portions that no difliculty would be encountered in reading the print.

(3) Neither the light nor the dark portions of the oflice print should undergo any change making them less readable after prolonged exposure to sunlight.

(4) The unexposed paper should be sufliciently resistant to aging that periods of the magnitude of six months to a year between manufacture and exposure could cause no significant difliculty.

An oflice reproduction paper must not only provide a moderately short exposure; adequate contrast, sunlight stability and storage stability, as respectively outlined previously, but it must provide the oflice reproduction at a low cost competitive with the diazo reproductions. Only a single molecule is photochemically decomposed by one quantum of light in the ordinary photochemical decomposition. If the reaction mechanism involves the formation of free radicals, the free radical fragments are capable of participating in a chain reaction providing a many fold increase in the number of atoms elfected by a single quantum of light. Thus a mixture of hydrogen and chlorine may be inert in the dark but exploded by exposure to a small amount of light. The light dissociates the chlorine molecule into chlorine atoms and the chlorine atom is a free radical initiating a chain reaction. Benzoyl peroxide decomposes under the influence of ultraviolet light to form free radicals which can participate in chain reactions.

Some of the earliest and most detailed work concerning the nature of free radicals and their capacity for bringing about chain reactions resulted from the thermal decomposition of organometallic compounds but there have been few studies of the photochemical decomposition of organometallic compounds.

Bis(tricyclohexyllead) (CH13)3Pb-Pb(C I'In) is a solid which is somewhat sensitive to sunlight but which Patented Jan. 3, 1961' 3 can be stored in subdued light. Earlier workers sometimes called this compound tricyclohexylplumbane.

In the development of the present invention certain novel measurements were made which helped to prove the feasibility of a photographic sheet sensitive only to high intensity light. It is helpful to understand the results of exposing solutions of hexacyclohexyldiplumbane to ultra violet light at various distances from a blueprinting lamp. A saturated solution of hexacyclohexyldiplumbane in cyclohexane was prepared. A series of cuvettes, each containing 4 ml. of the saturated solution, were positioned at various distances from a lamp and were exposed for 30 minutes to a blueprinting lamp of sufficient intensity to be designated as a 60 watt per inch lamp. The sample of solution positioned 8 inches from the lamp underwent a photographic decomposition to form a white precipitate. The sample positioned 7 inches from the lamp formed a precipitate which had a slight gray color. The sample of 4 ml. of the saturated solution in the cuvette positioned 6 inches from the lamp underwent a decomposition resulting in a dark brown precipitate. A conspicuously black precipitate formed in the sample positioned 5 inches from the lamp. There appeared to be crystals of metallic lead in the precipitate in the cuvette positioned one inch from the lamp. These prolonged exposures of the solution of the organome'tallic compound to high intensity ultraviolet light demonstrated not merely that the color of the decomposition product was dependent upon the intensity of light but also that a very great change of color resulted from a relatively small change in the intensity of light within what can be designated the critical range of intensity. Thus the intensity at 6 inches was only about or 178% of the intensity at 8 inches. These novel measurements made it appropriate to formulate the goal of an oflice reproduction paper which would form white decomposition products upon prolonged exposure to ultraviolet light content of bright sunlight but which would form dark colored decomposition products upon short exposure to an ultraviolet lamp providing an intensity from about 2 to 10 times the ultraviolet intensity of sunlight.

In the development of the present invention, it was established that not only did hexacyclohexyldiplumbane possess a color change depending upon the intensity of illumination but that the compositions containing com ponents capable of reacting with the decomposition prod uct possessed the outstanding advantage of undergoing a difierent kind of photochemical decomposition under high intensity illumination than under low intensity illumination.

Sunlight does not contain significant amounts of light of X-ray wave length but it does contain significant amounts of ultraviolet light. Most materials which are sensitive to ultraviolet light are not suitable for use in photographic materials by reason of their sensitivity to sunlight. The relatively low intensity of the ultraviolet light of sunlight can have elfect on most photosensitive materials over a very long period of time which is very similar to the effect of exposure to a blueprinting lamp or other high intensity ultraviolet source for a typical exposure period such as from 2 to 30 seconds. phenomena of forming decomposition products of different colors accordingto whether the light intensity is merely of the order of bright sunlight or significantly greater makes it possible to prepare ofice prints which do not fade after prolonged exposure to sunlight, notwithstanding the absence of any conventional developing Hexacyclohexyldiplumbane was prepared by a method substantially the same as that of Kranse, Ber, 54, 2060 The 4 (1921). A stirred mixture of magnesium turning: in 400 ml. of dry ethyl ether was reacted with 163 g. (1 mol) of cyclohexylbromide. The Grignard solution of bromomagnesiumcyclohexane then was slowly added to g. (0.45 mol, or a 33% excess) of lead chloride,

and thereafter the mixture was heated at reflux for from 4 to 24 hours. After hydrolysis, and evaporation of the ether, the solids were extracted with hot benzene. Hexacyclohexyldiplumbane was recovered from the hot benzene solution by several techniques, such as by precipitation upon cooling of the hot solution. Based upon the consumption of bromocyclohexane, the most expensive reactant, the average yield of hexacyclohexyldiplumbane in a series of successful preparations was greater than 50%.

Instead of using a method characterized by the Grignard reagent cyclohexylmagnesiumbromide, other methods of established ,value in the preparation of organometallic compounds can be utilized. For example, cyclohexyllithium could be reacted with lead chloride in pentane. The purified hexacyclohexyldiplumbane is a light canary yellow color.- Two forms of crystals have been identified under the microscope, one being generally hexagonal plates, and the other being of a shortfibrous nature or hair-like tubular crystals. In order to obtain optimumresults in photosensitive sheets, it is advantageous to purify the crude product by filtering the boiling benzene solution, distilling to remove about 20% of the benzene of the saturated filtrate, and allowing the thus-prepared supersaturated solution to cool to rapidly deposit high purity crystals.

EXAMPLE II A polyethylene resin was found to have an average molecular weight of about 14,000 as measured by the intrinsic viscosity technique. A coating composition was prepared by mixing about 40 ml. of boiling toluene, 10 g. of said polyethylene, and 10 g. of hexacyclohexyldiplumbane. This coating composition was spread upon about 18.5 square meters of a hard finish paper to provide a dry film of about 1 micron thickness. After the evaporation of the toluene solvent, the coating composition consisted of about equal parts by weight polyethylene and hexacyclohexyldiplumbane. The 1 micron thickness of the coating provided approximately 1.08 g./m. or about 2 pounds per 1000 square yards. The thus prepared photosensitive sheet, when exposed for 10 seconds at a distance of six inches from a blueprinting lamp (60 watts per inch) provided negatives which were dark brown in color. Thus it was established that the combination of a resin and hexacyclohexyldiplumbane provided a photosensitive coating for a sheet having attractive qualities for oflice and/or engineering prints.

EXAMPLE III The advantageous results of using a paper coated with a mixture of an organometallic compound and a resin are not limited to coatings containing polyethylene. A series of tests were conducted using various resins, and noting the effect of a change in the choice of resin.

A parallel series of tests were conducted using tetraethyllead as the organometallic compound in place of hexacyclohexyldiplumbane. Tetraethyllead contains a relatively higher concentration of lead, and only 2 g. of tetraethyllead (about 28% on an equamolar basis) were used in place of the 10 g. of hexacyclohexyldiplumbane. By reason of the high toxicity of tetraethyllead, this tetraethyllead was first adsorbed into particles of colloidal size silica powder, about 5 g. of silica powder (such as results from vapor phase hydration of silicon tetrachloride) being used to adsorb 2 g. of tetraethyllead. The 7 g. of mixture of tetraethyllead on silica were dispersed in the mixture of 10 g. of resin and 50 ml. of solvent to provide a coating composition.

The thin film of coating composition on paper was allowed to dry thoroughly. The thus prepared photosensitive sheet was exposed for seconds to the ultra-violet light of a blueprinting lamp positioned 6 inches from the paper. The results of the tests indicated the color and sunlight stability of the dark portion of the negative. Because the paper was so remote (6 inches) from the lamp, and the intensity was near the lower limit of the critical range, some of the resins effectively inhibited the development of a dark color under these conditions. However these tests provided evidence that under exposure at distances significantly less than 6 inches from the blueprinting lamp some reproduction machines provide an exposure about 1 inch or less from the lamp satisfactorily dark colors would be obtained.

In each case, the 10 g. of resin and the organolead compound were mxed with 50 ml. of solvent consisting of 40 ml. of methyl ethyl ketone and 10 ml. of toluene. After said standard exposure at the 6 inch distance, the various photosensitive papers had colors as indicated in Table 1.

formulations. Thus the weight of organometallic compound per unit area was approximately 16% as great in the photosensitive sheets using 6 parts of resin to 1 part of photosensitive compound as in the sheets having the l/ 1 ratio. Because some of the sheets being tested contained lesser amounts of the photosensitive material, the papers were exposed at a distance of 4 inches from the blueprint lamp. In some instances the exposure was longer than 10 seconds, thus indicating that a commercially satisfactory photosensitive sheet would require relatively larger amounts of activator. The codes assigned to the evaluations of the quality of the resistance to fading of the dark color resulting from the exposure to a high flux of ultra violet light were: A, excellent; B, good; C, fair; D, noticeable fading; E, troublesome fading; and F, unsatisfactory by reason of fading. Any unsatisfactory discoloration of the white portion of the negative print upon prolonged aging in direct sunlight was coded as sunlight sensitivity or SS. Data relating to selected examples of organo- Table 1 hexacyclohexyldiplumbane tetraethyllead resin color fading color fading polyvinyl chloride dark brown very slight---- light brown-.- slight. polyvinyl alcohol brow slight. yelloweopoly-PVA-PVC. light brown... some do polyrneth; lmethacr dark brown. very slight dark brown.-- Do. polyethylncrylnte d ..-.-do o.. Do. polybutylucrylate do Do. polybutylmethaerylata do do Do. ethyl cellulose brow o light brown-.. some. cellulose acetate do some..- row Do. cellulose acetobutyrate dark brown very slightlight brown-.. Do. polyacrylonitrlle.. brow some Do. buttylacrylate-cellulose acetobutymte mlxvery dark brown.. nono very slight.

ure. methyl methaerylate-cellulose acetate .----do Do.

mixture.

Using an emulsion of methylcellulose in water as the resin for the coating composition made possible the prepmetallic compounds as the photosensitive component of photosensitive sheets are set forth in Table 2.

Table 2 resin to organo-metallic ratio Compound 1/1 p.ethyleue color 3/1 p.ethylene color 2/1 PEA-CAB color 6/1 PBA-OAB color hexaeyclohexyldiplumbane dark brown, B dark brown, B dark brown, B dark brown, B. tetraethy ea dark brown, 0 brown, 0 hexaethyldi lumbnnelight rown, D light brown -.do Do. tetrapheuy ead light brown, D60.--. light brown, D60.-. light brown, 1360...- light brown, B60. hexaphenyldl lumbanedo do do Do. tetrabutylle dark yellow dark yellow, 11 brown, brown, 0. diphenylleadsulfideblack, A 88.. black, A SS... block, A SS. tetraghenyltin brown, D130. brown, D140" brown, C140. tetra uty brown, D140. ----.do Do. hexsbutyldistannane-.- brown, D110... brown, 0100.. brown, G100. hexacyelohexyldi brown, B20 brown, B20 brown, B20. dimethyltins do. 0 light brown, D20 light brown, 320.--- brown, 020. triphcnylarsenic light brown, D120... yellow, E120 yellow, 120 Ivlellow, 120. triphenylantim0ny light brown. C120..- yellow, D120-.- row'n, (2120-- ght brown, C120. tributylantlmony--- brown, C100 brown, C100..- brown, 0100.- trlphenylblsmuth brown, 030 brown, B dark, C20 brown, 020.

aration of a hexacyclohexyldiplumbane paper which had a brown color with a noticeable tendency to fade after exposure. There was a similar tendency for the brown negative resulting from the corresponding photosensitive paper prepared from tetraethyl lead and a water emulsion of methyl cellulose.

EXAMPLE IV of equal parts of polybutylacrylate and cellulose acetobutyrate was the resin used in the 2/1 and 6/1 ratio By a series of tests it was shown that important advantages are achieved by preparing the photosensitive sheet to include one'or more organometallic compounds, each compound containing one or more metals selected from the group consisting of lead, tin, arsenic, antimony and bismuth. Although many of the organometallic compounds of other metals can be decomposed by light of approprate wave length and intensity, none of such other organometallic compounds demonstrated a highly attractive combination of properties for photosensitive sheets in the tests conducted during the development of the present invention. However, there is reason to believe that organometallic compounds generally possess advantages as photosensitive compounds by reason of the phenomena that the light tends to decompose the metal-metal bond and/or organo-metallic bond preferentially to any decomposition of a carbon-carbon bond in such molecules,

7 and because the reactive fragments resulting from the photochemical decomposition of an organometallic compound are capable of reacting rapidly in a manner dependent greatly upon the flux or intensity of the ultraviolet light. Certain advantages are achieved by the use of compounds having a metal-metal bond. Certain advantages result from the use of cyclohexyl derivatives. Aromatic derivatives are decomposed by light with greater di.f-'

ficulty. Paraffinic derivatives are of intermediate photosensitivity. Novel measurements were made by taking the spectrograms of solutions of various compounds on a Beckman ultra-violet spectrophotometer. The carbon tetrachloride solutions of a series of organolead compounds were similar in the there was nearly complete transmission-for a wide band nearly complete adsorption of a wide band, with a relatively steep curve separating the two zones on the spectrogram. The wave length of 50% transmission provides an important clue to the photosensitivity of an organometallic compound. A significantly shorter ultra-violet wave length characterized tetraphenyllead than hexacyclohexyldiplumbane. Tetraethyllead had an intermediate wave length at the point of 50% opacity.

EXAMPLE V The dark color resulting from the photographic exposure may be attributable either to metallic deposit or to a reaction product which is more complex. In the development of the present invention it was established that a variety of sulfur-containing organic compounds served as activators for photographic sheets comprising organo-metallic compounds. It is not known whether the metal forms mercaptides, metal sulfides, or other metalsulfur type of materials or whether the beneficial effect is attributable to some catalytic or other phenomena. In any event, the photographic sheets containing controlled amounts of activators provide dark colors which are darker, less suseptible to fading, responsive to briefer pe- 8 cause of the desirability of marketing the photosensitive paper at a cost per square yard lower than the cost of either diazo paper or blueprint (ferrous ferricyanide) paper, it is desirable to use formulations providing an organometallic compound content per 1000 square yards corresponding to less than about one pound of metal. A minimum concentration is equivalent to about 8 ounces per 1000 square yards, and the maximum concentration (if cost is not important) may be about 20 pounds of 10 metal (a correspondingly larger amount of organo-metallic compound) per 1000 square yards.

Comparative experiments on extenders are difficult to interpret. It has been found that the effectiveness of an activator as an accelerator is similar to its effectiveness as an extender. The comparison of the accelerator effectiveness is readily interpreted.

A series of tests were made using the same general formulation, and varying the choice and concentration of the activator. All of the activators listed herein have been shown to be useful in photosensitive sheets, but under the standard comparison tests several of them show varying degrees of sunlight sensitivity. In the sunlight sensitive negative prints, the light color, instead of retaining its initial white color, underwent a darkening when exposed to bright sunlight for a prolonged period of time. The effect of aging, sometimes designated as sunlight sensitivity, is designated in Table 3. A series of papers were prepared by use of compositions consisting of: 10 g. of hexacyclohexyldiplumbane, 5 g. polybutylacrylate, 5 g. toluene (or 20 g. of the stock mixture of these proportions); 10 g. cellulose acetobutyrate, g. methyl ethyl ketone (or g. of a second stock mixture); and the specified amount of the indicated activator. The image was in all cases sufiiciently black to be commercially satisfactory, but the exposure time necessary to achieve such result was measured. The data are set forth in Table 3.

Table 3 amount of activator used in composition activator 0.1 g. 1.0 g. 10.0 g.

isecondsi aging seconds! aging seconds aging flowers of sulfur 1 darken---- 1 dark 1 darkens. z-mercapto bensothiazoline 3 slight.-." 3 all ht- 2 little.

t thlophonnl 10 yellow-...- 6 ye iow.... 5 yellows.

tetrathiuramdisultide 50 v. s1. 30 slight"-.- 20 none. potassium ethyl xanthoato- 20 darkens.-. 10 browns 10 browns. tetrathiuram tetra-sulfide--. 2o sllght---.- 20 sllght----.. 10 slight. potassium ethyl mnthoate I) darkens." 10 browns...- 10 browns. thinamharnidn 2o yellows.-.- 20 yel1ows. a0 yellows. dithiooxamide 30 do 30 do 20 Do. thioinslie aci 30 do 30 do 20 Do. potassium thlocarbon ate an blackens 20 blackeus- 15 blackens. phosphorus pentasulflde so do 20 do photo-i aflammable. diphenylthiooarbazoue 20 no change. 20 no change. 20 no change. thtosemicsrh 20 do 20 do 20 Do. 1,5 dlphenyl thiocarbohydrazide 2o yellows..-- 20 yellows--.. 10 yellows.

riods of exposure, responsive to lower concentrations of organo-metallic compound per unit area, responsive to lesser intensities of ultra-violet light and/or possessing other advantages over photosensitive sheets without such activators.

Ordinarily the main purpose of including the organic sulfur activators in the composition is for the purpose of reducing the requirements for the organo-metallic compound per unit area, but because the other efiects have been established, the term activator is more appropriate than the term extender. Organometallic compounds are generally expensive. Because of this high cost, and be- Exteusive experimentation of the type illustrated in Table 3 established that the activator should be a material containing sulfur, selenium or tellurium, and that particular advantages accrued from the use of a material have a functional group selected from the class consisting of 8, S=, S SH-,

SH -=8, -(i:8 which can also be described respectively as elemental sulfur, sulfide and polysulfide, thiol, thioether, thione (comprising also thials and thiocarboxylic groups) and dithiocarboxylic groups.

9 EXAMPLE V! In obtaining a colorless and/or white product from the photo-decomposition of organometallic compounds, the presence of oxygen, peroxides, carbon dioxide, and re- 10 bination with 100 mg. of either 2 mercaptobenzothiazoline or potassium ethyl xanthoate.

EXAMPLE VII lated materials are especially advantageous. Possibly the Although organo'metanic P l f are the F f reactive fragments resulting from the photochemical de- Q P the Present Invention P composition of an organometallic compound have a uve a be ye to aehleYe the strong tendency to react relatively slowly with any traces vantageousfombmatwn P Provtdlhg q t s 001018 of oxygen or related materials present in the environunder Influence of light havlhg ah Intensity greater ment, so that this is the predominating reaction except than suhhght, but not f flfter adversely affected by under those conditions in which the rate of photochem- Prolonged exposure Sunlight, twlthstandmg the abical decomposition of the organo-metallic compound is Sence f any chemlcal treatment fixing antil/01' so rapid that free metal and/or metal-sulfur compounds hghave an opportunity to form A positive paper 1s prepared by coating a paper with one of the several methods of obtaining a photosensi 5 a composition consisting of 10 parts of polybutylacrylate, tive sheet having an overall balance of attractive properto Ph of cellulose acetobutyrate, 5 parts o pp ties is to coat paper with a composition comprising an acetyhde, and 5 Parts of shctflhyl azide, and 75 p r of organometallic compound, a sulfur-containing activator, tetrah3fdrfurah- The P pe Is coated in e dark- T e and an oxygen-containing inhibitor. The maximum con- Paper lohded e ordmar Y camera and the Picture centration of the activator is desirably not greater than 1S talfeh three tunes t number of a h bu bs conthat of the organometauic compound The optimum vent onally used. The intense light decomposes the concentration of the inhibitor in many compositions is h e z q component of the photosensitive Sheet, P within the range from 1.0 to 10% of the concentration Vldlhg l'eeetlve fragments Combining with the copper to of the activator. The maximum concentration of inhibform a whlte background metel'lal the White Portions itor should be less than the organometallic concentration. of the p The Sheet is e e oved from the cam- In a series of tests papers were prepared using some era, and the effect Of the sunlight on the balance Of the of the formulations of Table 3, but adding measured Pflht is to form a black copper image- The Sunlight amounts of benzoyl peroxide. The composition was prebrings ehotlt the deeolhposittoh of the pp aeetylide pared by mixing: a solution consisting of 10 g. of celluexcept those areas In which the pp slleciflnaie lose acetobutyrate, 40 g. of methyl ethyl ketone, the binds the copper in a form insensitive to Sunlight. Indesignated amount of the designated activator, and the stead of pp aeetyhde, lead azide, Silver acetylide, d i d amount f b l id d 10 f h related light-sensitive metal compound which can react cyclohexyldiplumbane, 5 g. of polybutylacrylate and 5 g. with a dibasic organic acid or chelating compound to of toluene. A film about 1 mil thick was formed on form a White Compound insensitive to Sunlight may be paper. The coated paper was exposed to a blueprintin employed. Instead of succinyl azide, any light sensitive l f a ffi i i d of i e t id a reasonchelator, such as the azide of ethylenediamine tetraacetic ably black image, and thereafter the stability of the white ac d may be employed. portions of the negative print to bright sunlight was Obviously various modifications of the invention are measured. Data relating to some of these tests are shown 40 possible without departing from the scope of the invenin Table 4. tion as set forth in the appended claim.

Table 4 Quantity of Bemoyl Peroxideg. activator 10 mg. mg. 100 mg. 200 mg.

seconds aged color seconds aged color seconds aged color seconds aged color 0.1 flowers ofsuliur 2 light brown. 2 yellow brown. 2 yellow brown. 3 yellow. 1.0 sulfur 2 black 2 dark brown..- 2 dark brown 3 allow bro 10.0 do 2 .do 2 black... 3 black 3 rown. 0.1 Z-merca tobenzo 3 brown 3 tan..- 3 yellow a whim,

thlazoine. 1.0 do 3 do 3 brown. 5 tan 5 yellow, 10.0 -.d0 2 ....do 2 .do 3 yellow 5 paleyellow, 0.1 potassium ethyl 20 tan 5 tan 10 do 20 white.

xanthoate. 1.0 potassium salt of 10 brown to brown 10 brown 10 yellow.

ethgl xanthole 10.0.--.- po t sslumethyl 5 ----do 5 do 5 do to brown.

xanthoate.

The invention claimed is:

A photosensitive sheet consisting essentially of a strong backing and a photosensitive composition uniformly coated on the backing, said photosensitive composition consisting essentially of: bis(tricyclohexyllead) in a concentration from 8 ounces to 20 pounds per 1000 square yards of photosensitive sheet; an activator in a concentration within the range from 1% to of the concentration of the bis(tricyclohexyllead), said activator being selected from the group consisting of sulfur, organic thiols, organic sulfides, and salts of organic dithio- 11 carboxylic acids; and a peroxide in a concentration with- 2,095,839 in the range from 1% to 100% of the activator. 2,219,463

2,414,839 References Cited in the file of this patent 2,4 UNITED STATES PATENTS 5 1,880,503 Sheppard et a1. Oct. 4, 1932 217121996 1,897,843 Hickman et a1. Feb. 14, 1933 1,939,232 Sheppard et a1. Dec. 12, 1933 1,976,302 Sheppard et a1. Oct. 9, 1934 10 2,057,016 DeBoer et al. Oct. 13, 1936 12 Sheppard et a1. Oct. .2, 1937 Yngve Oct. 29, 1940 Schoen Ian. 28, 1947 Chalkley May 18, 1948 Baurnann et a1. July 13, 1954 Eggert Mar. 1, 1955 Elliot July 12, 1955 OTHER REFERENCES Coates: Organo-Metallic Compounds, John Wiley, NY. (1956), page 141.