US 3861919 A
Photographic copy media comprising a photoconductor have greatly increased sensitivity to activating radiation by means of amine compounds contained therein or coated thereon. It has been found that amine compounds which do not normally act to reduce reducible metal ions can be used to increase the sensitivity of a layer which is subsequently used to form a permanent image.
Description (OCR text may contain errors)
United States Patent [191 Stein Jan. 21,1975
[ A PHOTOCONDUCTOR PROCESS USING A COPY MEDIUM SENSITIZED WITH AN AMINE  Inventor:
 Assignee: Itek Corporation, Lexington, Mass.
 Filed: May 9, 1972  Appl. No.: 251,671
Related US. Application Data  Continuation-impart of Ser, No. 24,037, March 30,
Samuel H. Stein, Lexington, Mass.
 US. Cl. 96/48, 96/1.6, 96/27 R  Int. Cl G03c 5/24  Field of Search 96/27, 48, 29, 61, 1.6;
 References Cited UNITED STATES PATENTS 5/1961 Morse 96/29 10/1964 Shepard 96/64 3,274,022 9/1966 Rhoda 117/227 3,380,823 4/1968 Murray 3,392,019 7/1968 Barnes 3,652,276 2/1972 Bartlett 96/48 PD FOREIGN PATENTS OR APPLICATIONS 1,068,333 12/1969 England 96/29 Primary ExaminerNorman G. Torchin Assistant Examiner-John L. Goodrow Attorney, Agent, or FirmHomer 0. Blair; Robert L. Nathans; W. Gary Goodson 7 Claims, N0 Drawings A PHOTOCONDUCTOR PROCESS USING A COPY MEDIUM SENSITIZED WITH AN AMINE This application is a continuation-in-part application of US. Ser. No. 24,037, filed Mar. 30, 1970 now abandoned.
BACKGROUND OF THE INVENTION Data or image storage media comprising radiationsensitive materials such as titanium dioxide are described in detail in US. Pat. Nos. 3,152,903; 3,052,541; and 3,380,823. In the aforementioned US. Pat. No. 3,380,823, radiation-sensitive titanium dioxide functions as a photoconductive component of the media and exposure of said media to activating means such as radiant energy, electron beams or the like results in the storage of a reversible latent image pattern therein. The reversible latent image pattern exists for a limited time during which said pattern can be converted to an irreversible form and read out visually by contacting said pattern with a suitable image forming material, such as a chemical redox system. In the previously mentioned US. patents, the radiation-sensitive material is combined with at least one component of an image-forming material prior to exposure to activating means. For example, US. Pat. No. 3,052,541 describes a photoconductive copy media comprising a photoconductive material such as titanium dioxide in combination with a reducible metal ion such as silver ion. This copy media is exposed to activating means and then contacted with a reducing agent to produce a visible image. On the other hand, US. Pat. No. 3,152,903 discloses a system wherein the photoconductive material is used in combination with both an oxidizing agent such as silver nitrate and a reducing agent such as hydroquinone. Upon exposure to suitable activating means, a visible image is formed. One of the limitations of the abovementioned data or image storage systems is that they lack the photographic speed of systems such as silver halide. Therefore, in order to expand the possible uses of these photographic systems described in the above-mentioned patents and application, it is highly desirable to increase the photographic speed of the systems. Much research effort has been spent in trying to find ways to increase speed.
It is presently believed that the photoconductor employed in this process is a semiconductor material characterized by having electrons in one energy level capable of being raised to a different energy level by the action of activating radiation. The electrons in the raised level are not necessarily characterized by luminesence or the emission of visible radiation upon return to their initial energy level, nor are they necessarily in a conductive state. It is presently believed that these electrons can be raised to elevated energy levels and to act to transfer energy to a metallic ion such as a silver ion, which may be subsequently applied to the layer to form nucleation centers corresponding to a photographic latent image. Such a latent image is capable of being reduced or developed as is customary in the photographic art, to produce a permanently visible reduced metal or metallic silver image.
The hereinbefore described system finds acceptance as a useful and valuable way of recording an image, but it is, nevertheless characterized by requiring relatively strong illumination to produce the desired result.
SUMMARY OF THE INVENTION According to a preferred embodiment of the present invention, it has been found that a very substantial increase in photosensitivity can be imparted to photosensitive layers of a photoconductor of the type described herein by means of an amine which does not normally act to reduce metal ions in image configuration. The amine can be incorporated into a binder layer in the coating operation or may be subsequently added to the material as, for example, by dipping it into a very dilute solution of the amine. It is not intended to limit this invention to any particular chemical or physical mechanism by means by which it may operate, but one possible theoretical explanation of the mechanism is that the amine may introduce electrons into the energy levels or traps in the titanium dioxide or other photoconductor which have been emptied by the exposure to activating radiation, and that they, in this manner, prevent these electrons from returning to the original energy level, causing substantially more of the activated electrons to be effective in producing a developable latent image.
DETAILED DESCRIPTION OF THE INVENTION The invention is described in detail in conjunction with a presently preferred photoconductor species, namely titanium dioxide. The invention is not, how ever, limited to the titanium dioxide species, but instead is suitable with other photoconductors which form a latent developable image upon exposure to activating radiation. Such photoconductors include, but are not limited to zinc oxide, metal carbonyls such as chromium, tungsten and molybdenum carbonyls, lead chromate, lead molybdate, lead oxide, zinc sulfide, cadmium sulfide, chromium oxide and many others.
A simple test to determine whether or not a material is a photoconductor for the purpose of this invention is to mix the material in question with an aqueous solution of silver nitrate. Little, if any, reaction should take place in the absence of light. At the same time a control sample of an aqueous solution of silver nitrate alone is subjected to light, such as ultraviolet light. If the mixture darkens faster than the silver nitrate, alone, that material is a photoconductor.
For the purpose of comparison, all numerical data presented in the Examples was obtained by exposure in a commercially available EG&G Mark VI sensitometer and photographic sensitivity is expressed in terms of maximum density (Dmax), number of gray steps obtained in step wedge exposure in the sensitometer and the sensitivity itself. Sensitivity (80.2) is defined as the reciprocal of the exposure expressed in meter candle seconds required to give a density of 0.2 above base plus fog, and is a practical expression of response to activating radiation.
EXAMPLE 1: A photoconductor-binder coated paper was prepared by mixing together titanium dioxide in an aqueous solution of polyvinyl alcohol and coating and drying the mix on a bartya paper base. The photoconductor to binder ratio was 4:1 and the total solids in the coating mix was about 17%. The resulting coated paper can be used by known techniques to form a permanently visible record of an optical image.
In a comparative test, the coated paper was prepared and dried as above. Prior to exposure, the paper was dipped in 0.3% methanol solution of triethanol amine and air dried. After exposure in the sensitometer, the
paper was processed for seconds in 0.1N methanolic silver nitrate, drained ten seconds and developed in a conventional methanolic developer and fixed. The sensitivity (80.2) was increased from 2.34 X 10 to 5.89 X 10 Dmax was increased from about 1.00 to about 1.17 and an increase in number of steps of gray was achieved. As a secondary control test, the procedure was repeated with a dip into methanol containing no amine. After exposure and processing, this test produced results substantially like the standard paper. The paper dipped in triethanol amine was superior to untreated paper and superior to paper dipped in methanol alone.
EXAMPLE 2: A photoconductor-binder coated VI sensitometer and then dipped in a 0.3% methanolic solution of the amine for 5 seconds and drained 5 seconds. After draining to remove excess amine solution, the paper was then immersed in a 0.1N solution of methanolic silver nitrate for 20 seconds and drained to remove excess liquid. Thereafter, an intense visible image was developed, as disclosed in British Pat. No. 1,043,250, as for example, by immersing the paper in a solution of a metol type developer. Sensitivity and other properties were measured by exposure to white light and green light using appropriate filters between the source and the coated paper.
The data for Examples 4-16 are found in Table 1.
EXAMPLE 17: The procedure of Example 3 was repaper was prepared and exposed as in Example Aft peated using a series of different concentrations of triexposure, it was dipped in f hl mixed 0 IN methan0 ethanol amine. The results in Table II show an improve- ]ic Silver nitrate containing triethanol amine in an ment in sensitivity with increasing concentration of amount equivalent to 0.01N. Thereafter, it was develamine in P immersion Solutlon: however) h Oped and fixed as in Example L The Sensitivity (S02) as the amine reaches 20% the fog has increased signifiwas increased from 2.34 X 10 to 9.12 X 10*": Density camly' and gray scale were also improved. LE II EXAMPLE 3: A photoconductor-binder paper was Amine Dmux so2 prepared, incorporating triethanol amine in the photoconductor-binder coating. An aqueous dispersion 3?: i :81 was prepared containing polyacrylamide, titanium di- 10% 1:36 16.2 x 10' 0:13 oxide and triethanol amine in a 5:1 pigment binder ra- 20% X 10% tio, 14.5% total solids and 10% by weight triethanol amine based on the amount of pigment. This mix was 30 EXAMPLE 1 A photoconductopbinder Coated coated on P p and dried- The y P p was exposed paper was prepared according to Example 1. Prior to in a sensitometer and then processed by immersing in exposure, the paper was dipped in 13% methanolic methanolic silver nitrate, developing and fixing. The l ti f 1,4-bi (aminomethyl) cyclohexane and air sensitivity was increased from 2.95 X 10 to 16.2 X dried. After exposure in the sensitometer,
TABLE I EXAMPLE AMINE WHITE SENSITIVITY GREEN SENSITIVITY Step 11 No. of $0.2 Step 11 No.01 So.2 Dmax D Steps (X10 Dmax D Steps (X10 Fog 4 Control 1.10 0.68 16 3.8 0.94 0.08 8 1.4 0.08 5 4amino butyric acid 1.28 1.14 21 10.5 1.24 0.50 12 5.6 0.34 6 2-aminomethy1-3,4
dihydro ZH-pyran 1.26 1.10 19 9.6 1.13 0.23 11 3.9 0.14 7 1,6-hexane diamine 1.30 1.20 19 12.0 1.24 0.62 10 2.8 0.60 8 S-aminovaleric acid 1.26 1.08 21 13.8 1.20 0.22 14 3.7 0 14 9 N-(Z-aminoethyl) 1,3-
propanediamine 1.31 1.22 20 16.6 1.24 0.50 13 9.8 0.17 10 6-amino caproic acid 1.26 1.04 20 10.5 1.12 0.20 12 3.1 0.15 11 mxylylenediamine 1.28 1.06 20 12.0 1.20 0.60 12 3.2 0.50 12 N-(2-aminoethyl)-1,4-
butanediamine 1.29 1.06 21 13.8 1.18 0.40 14 4.7 0.28 13 N-alkyl-N-methylaniline 0.98 0.62 18 3.6 .84 0.10 9 1.5 0.10 14 1,12-diaminod0decane 1.25 1.04 21 16.2 1.14 0.42 13 6.8 0.18 15 2-(2 aminoethylamino)- ethnol .30 1.14 21 13.2 1.20 0.46 13 6.2 0.26 16 ll-uminoundecanoic acid 1 16 0.90 20 9.6 1.05 0.13 13 3.1 0.12
10; density, gray scale and other characteristics were improved, when compared to a similar coating having no amine included.
the paper was processed in 0.1N methanolic silver nitrate, drained 10 seconds and developed in a metol developer and fixed. In Table III are shown sensitometric data for procedures in which the paper was dipped in the methanolic silver nitrate for 10 and 20 seconds respectively, and developed in the metol developer for 10 and 20 seconds, respectively. For control purposes, other samples of paper designated M in Table III were exposed and processed in the above manner after being dipped in methanol (no 1,4-bis (aminomethyl) cyclohexane present). A second control, Samples designated U in Table III, consisted of samples of paper which were exposed and dipped directly into the silver nitrate solution and otherwise processed as above without any dipping prior to exposure and contacting with silver nitrate. Samples designated D in Table III represents samples dipped in a 0.3% methanolic solution of 1,4-bis (aminomethyl) cyclohexane and and dried prior to exposure and contacting with silver nitrate. As can be seen in Table III, sensitivity was greatly increased by dipping in a 1,4-bis (aminomethyl) cyclohexane, and fog could be controlled by judicious choice of processing time. Relative PS" in the table below represents relative print speed which is the exposure in meter candle seconds required to give a density of 0.6 density units base above fog. In Table III below D represents the maximum evaluated density.
TABLE III Effect of 1,4-BAMC on Sensitometry of Photoconductor Coated Paper EXAMPLE 19: The procedure of Example 3 was repeated. After exposure in the sensitometer, the paper was processed in a commercial processing machine in which both silver ion and metol developing agent are supplied from separate aqueous solutions by roller applications to the exposed sheet, which is transported through the unit at 4% inches per second. Using this procedure, the sensitivity was increased from 3.31 X to 4.35 X 10' density, gray scale and other characteristics were improved. A similar procedure was carried out using polyvinyl alcohol as the binder. In this case, the sensitivity was increased from 5.01 X 10' to 2.88 X 10 The amine can be added to the photosensitive layer in any of several ways, as illustrated in the examples. The compound can be added to the mix prior to coating on the support base. It also may be added to the layer after coating or after coating and drying as for example, by dipping or immersing the coated material in a solution containing the desired amine. It also can be added to the material after exposure to an image either by first applying the amine material and subsequently treating with one of the active agents, such as, for example, the silver nitrate. In addition, it may be added to the silver nitrate solution, or other developer, and preferably, used promptly after being freshly mixed.
Generally speaking, it has been found that the amine material can be advantageously incorporated in the photoconductor layer by mixing the amine therein prior to the coating operation. The amine may also, however, be applied as a separate coating.
According to the preferred procedure, the amine material is applied to the photoconductor layer and dried prior to subsequent exposure and processing of the material. To a large extent, however, this is a matter of commercial convenience inasmuch as the amine may be conveniently applied to the layer during the manufacturing operation resulting in a marketable product which is convenient and easy to use. If desired, however, the photoconductor material may be manufactured without the addition of an amine and the subsequent processing by the user may include treatment with the amine material as indicated. Preferably. however, the amine is used in a top layer on the photoconductor paper, film or the like, whereby optimum convenience and product acceptability may be achieved. In addition, the top coated paper increases inhibition of the metallic or silver-ion material and results in improved shelf life as compared with a product containing the amine distributed through the photoconductor layer. At worst, however, the product is not plagued by the problem of chemical reaction between the amine and silver ion during shelf storage, inasmuch as the product on the shelf prior to use does not contain silver.
It has been found that a wide variety of amines can be used in the present invention. Generally, the amine compound should be incapable of alone acting as a photographic developer for selectively reducing silver ions to silver metal on exposed portions of a copy medium comprising a photoconductor comprising titanium dioxide which has been exposed and contacted with a solution of silver ions. The amines which act as photographic reducing agents have been found to give unsatisfactory results in this invention. These amines which are suitable as photographic reducing agents are clearly defined in Mees, The Theory of the Photographic Process, third edition, Chapter 13, Page 238 wherein organic developing agents are defined as materials having the following structures:
I a4c where a and a may be OH, NI-I NHR, and wherein R is an alkyl group. When n=0 in above structures the developing agents then become H 0 NHZNHZ, Or
A wide variety of amine compounds have been found satisfactory, and generally, the most extensive information has been obtained in connection with triethanolamine (trinitriloethanol). However, if there is employed an amine that produces significant fogging in the final picture, there are several steps which can be taken to reduce or eliminate the fog, all of them favorable. For example, the amine itself can be used in a lesser quantity. If desired, one of the other ingredients can be used in smaller quantity, or development can be carried out for a shorter period of time, and excellent results have been achieved employing an amine as a means to reduce the quantity of silver nitrate required in the process.
The preferred classes of amines suitable for this invention are the following:
a. Primary and secondary amines of the structure H N CH Z-CH X wherein Z is a cyclic or acyclic alkalane or alkene group, said alkane or alkene groups preferably having 2-18 carbon atoms; and wherein X is NR CO R, OR or H; and wherein R is H or an alkyl group preferably having 1 to carbon atoms.
b. Primary and secondary amines of the class: H N- ZY wherein Y is -NHCH ZCH X; and wherein X and Z are defined as described above.
0. H N(CH ),.Q(CH ),,,X wherein X is defined above and wherein Q is an aromatic hydrocarbon and n and m are integers from O to 8 except that when the aromatic substituents of the formula of (c) are ortha or para to one another, then either n or m must be greater than zero but excluding the photographic developer materials defined above, and
d. Tertiary amines of the class: R,N (CH A) wherein A is CO R or CH OR and wherein R is CH A or (CH ),,N(CH A) wherein p is an integer from 2 to 4.
Generally, the image forming materials comprise a chemical redox system, which usually includes a reducible metal ion such as silver, copper or another metal. In conjunction with such a metal-ion containing material it is usual to employ a developer such as a photographic developer. A preferred physical developer is that disclosed in US. Pat. No. 3,157,503, incorporated herein by reference. Physical developers or electroless plating solutions may be used or, in general, any developing agent which will bring about the formation of an intense permanently visible image in the areas where the developable latent image can be formed.
The invention has been described in conjunction with the binder materials which are generally water miscible and water soluble, and the preferred embodiment of the invention does, in fact, now contemplate the use of such water miscible materials. Essentially equivalent results however, are achieved with the use of solvent soluble binder materials which are applied from an organic solvent, and with the use of emulsion type material which are applied from aqueous emulsions. This means generally that the invention is compatible with titanium dioxide-binder materials in all forms now used with photolytic recording processes.
1. In a process for recording an image pattern of activating radiation comprising exposing a copy medium comprising a photosensitive titanium dioxide which becomes activated upon exposure to activating radiation and thereby capable of causing reduction of silver ion at exposed portions of said medium upon contact with a solution of silver ions and contacting said medium with image-forming material comprising a solution of silver ions, the improvement comprising contacting the copy medium with an amine compound incapable of alone acting as a photographic developer for selectively reducing silver ion to silver metal in exposed portions of a copy medium comprising photosensitive titanium dioxide which has been exposed and contacted with a solution of silver ions in a sufficient amount to increase the photographic speed of the copy medium in the process, but not in sufficient amount to cause excessive fogging in such process and wherein the amine is at least one member selected from the following groups:
a. H N CH Z CH X wherein Z is an alkanc or an alkene moiety, said alkane or alkenc moiety having 2 to 18 carbon atoms and wherein X is NR -CO R, OR, or -H wherein R is H or an alkyl group having 1 to 10 carbon atoms;
b. H N Z Y wherein Z is as defined above; Y is NH CH Z CH X; and wherein X is as defined above;
c. H N(CH ),,Q(CH ),,,X wherein X is as defined above; Q is an aromatic hydrocarbon and n and m are integers from 0 to 8; and
d. R N--(CH A) wherein A is CO R or CH OR and wherein R is CH A or (CH ),,N(C- H A) wherein p is an integer from 2 to 4 and R is as defined above.
2. The method of claim 1, in which said titanium dioxide is finely divided titanium dioxide.
3. The method of claim 1 wherein said titanium dioxide is dispersed in a film forming binder.
4. The method of claim 2 in which the amine is at least one member selected from the group consisting of triethanol amine, 4-amino butyric acid; 2-amino ethyl- 3 ,4dihydro2H-pyran; 1,6-hexane diamine; 5- aminovaleric acid; N-( 2-aminoethyl)- 1,3,propanediamine; 6-amino caproic acid; m-
xylylenediamine; N-(Z-aminoethyl l ,4,- butanediamine; N-alkyl-N-methylaniline; 1,12diaminododecane; 2-( 2 aminoethylamino)- ethanol; ll-aminoundecanoic acid; and 1,4-bis (aminornethyl) cyclohexane.
5. The method of claim 4 wherein the amine is present in the photoconductor layer prior to exposure and the photoconductor layer is contacted subsequent to exposure with a solution of image-forming materials comprising reducible silver ions.
6. The method of claim 3 wherein the amine is triethanol amine.
7. The method of claim 3 wherein the amine is 1,4-