WO1995002850A1

WO1995002850A1 - The use of ultra-thin, tabular, photosensitive grains for the purpose of increasing the sensitivity of a photographic emulsion

Info

Publication number: WO1995002850A1
Application number: PCT/US1993/012449
Authority: WO
Inventors: George M. Sawyer
Original assignee: Sawyer George M
Priority date: 1993-07-12
Filing date: 1993-12-29
Publication date: 1995-01-26
Also published as: AU6227194A

Abstract

The invention is the use of ultra-thin, tabular, light-sensitive grains in a Photographic emulsion for the purpose of increasing the sensitivity of films and plates. Silver halide is the preferred light-sensitive material. It is surprising that by using a fixed weight of light-sensitive material, tabular grains produce an emulsion that is more sensitive than when spherical grains are used, and the emulsion becomes more sensitive as the diameter-to-thickness ratio (aspect ratio) of the tabular grains increases. A consequence of using the ultra-thin, light-sensitive grains of the invention is increased covering power. This consequence has a profound economic advantage. An example is given where, by using the ultra-thin tabular grains of the invention, only one tenth as much silver is required. The teachings of the invention apply to emulsions on photographic films and plates both with and without a reflective backing.

Description

THE USE OF ULTRA-THIN, TABULAR, PHOTOSENSITIVE GRAINS FOR THE PURPOSE OF INCREASING THE SENSITIVITY OF A PHOTOGRAPHIC EMULSION.

CROSS REFERENCE TO RELATED APPLICATIONS:

This application is related to the following U.S. patent Application Nos. 07/737,889 Filed 07/25/91, 07/784,611 filed 10/29/91 and 07/784,612 Filed 10/29/91 and to my U.S. Patent 4,178,181

BRIEF SUMMARY OF THE INVENTION

The invention is the use of ultra-thin, tabular, light-sensitive grains in a photographic emulsion for the purpose of increasing the sensitivity of films and plates. Silver halide is the preferred light-sensitive material. This invention was described, but not claimed, in an original U.S. Application filed April 21, 1966. That Application described many inventions, and the invention described within is one of them.

It is surprising that by using a certain weight of light-sensitive material, tabular grains produce an emulsion that is more sensitive than when spherical grains are used, and the emulsion becomes more sensitive as the diameter- o-thickness ratio (aspect ratio) of the tabular grains increases.

A consequence of using the ultra-thin, light-sensitive grains of the invention is increased covering power. This consequence has a profound economic advantage. An example is given where, by using the ultra-thin tabular grains of the invention, only one tenth as much silver is required. Formulas and graphs are presented that describe the relative sensitivities of emulsions in terms of the thickness and diameters of the characteristic grains . They show that maximum diameters and minimum thicknesses yield maximum sensitivity. For a given graininess (resolution) of a photographic film (in a direction parallel to the film plane) a formula is given which determines the maximum diameter of the characteristic grains.

To a person skilled in the art, the teachings of the invention apply to emulsions on photographic films and plates both with and without a reflective backing.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a pixel in a cross section of an ordinary photograph.

Fig. 2 shows a Pixel in a cross section of a Lippmann color photograph.

Fig. 3 shows a cross section of a Lippmann color photograph.

Fig. 4 shows a cross section of a photosensitive element used in ordinary photography.

Fig. 5 shows a cross section of a photosensitive element used in the Lippmann method of color photography.

Fig. 6 shows a pixel in a cross section of a photosensitive element used in the Lippmann method of color photography.

Fig. 7 shows an oblique view of what happens when one goes from prior art to the invention revealed. Fig. 8 shows a photosensitive grain in a cross section of a photosensitive element used in the prior art Lippmann method of color photography where spherical grains are used.

Figs. 9 and 10 show an oblique view of 4 low sensitive grains joined to make a large more sensitive grain.

Figs. 11, 12A, and 12B show formulas.

Fig. 13 is a diagram showing how relative sensitivities of emulsions depend on the characteristic grain thickness and aspect ratio.

Fig. 14 is a diagram showing how relative sensitivities of emulsions depend on the characteristic grain thickness and diameter.

Fig. 15 overlays Fig. 13 and shows territories claimed by the instant invention.

Fig. 16 also overlays Fig. 13, and on it is shown territory disclosed by U. S. Patent No. 4,434,226.

BACKGROUND OF THE INVENTION

NOTATION

Features on the figures are identified by four digit numerals. As an example, the numeral 0102 refers to Fig. 1, item 02, which is a pixel.

REFERENCES

(Lipton, 1965) Lipton, L. (1965), The Perfect Color Film, Popular Photography, p. 64, 98, 99. (Mees,1937) Mees, C. E. Kenneth, (1937), Photography, New York, MacMillan. p. 63, 64. (Mees,1942) Mees, C. E. Kenneth, (1942), The Theory of the Photographic Process, First Ed., New York, MacMillan. p. 34, 35. (Mees,1954) Mees, C. E. Kenneth, (1954) , The Theory of the Photographic Process, 2nd Ed., New York: MacMillan. p. 23, 34, 35. (Mees,1966) Mees, C. E. Kenneth, and James, T. H., (1966), The Theory of the Photographic Process, Third Ed., New York, MacMillan. p. 35, 36, and the paper cover jacket. (James, 1948) James, T. H., and Higgins, G. C. (1948) Fundamentals of Photographic Theory, New York, p.14,15,18-21. (Sibley) 427 F.2d 833 and 839, 166 USPQ at 24

DEFINITIONS

The projected (or "projective") area is the area of the grain when seen through a microscope and the grain rests on a flat surface, as on a microscope slide. The grains are commonly hexagonal, triangular, spherical, or rod shape in outline when viewed through a microscope.

The diameter of a grain is the diameter of the circle whose area is equivalent to the area of the grain when the grain rests on a flat surface, as on a microscope slide.

A tabular grain, a flat grain, or a pancake shaped grain all mean essentially the same thing, and they have in common (1) two prominent opposite sides, (2) the sides are flat, (3) the sides are parallel, (4) they have diameters that are greater than their thickness.

The aspect ratio of a tabular grain is the diameter divided by the thickness. The sensitivity of an emulsion is measured by the area that becomes opaque (black) upon exposure and development.

The relative sensitivity (RS) of an emulsion comprised of grains is equal to the diameter squared divided by the thickness of the characteristic grains, where the dimensions are in nanometers. Thus, for a spherical grain with a diameter of 50 nanometers, the RS is equal to 50 times 50 divided by 50 equals 50. When the characteristic grain has a diameter of 100 and a thickness of 25 nanometers, the RS is equal to 100 times 100 divided by 25 equals 400.

The cases considered within are where the grains are spread over a large enough area that no grain covers another. The probability of being exposed depends on the projected area of each grain. The exposing light levels are low.

Gabriel Lippmann invented, in 1891, a process of color photography that produced the first fixed color photographs from nature. His process required the interference of light waves.

The Lippmann process of color photography produces color in a photograph for a different reason than color is produced in an ordinary photograph. The Lippmann process produces color by partially reflecting layers within a pixel, whereas, ordinary photography produces color by dye within a pixel.

In a pixel of an ordinary color photograph, dye is uniformly distributed throughout the pixel. Fig.l is a cross section 0101 of an ordinary photograph. The pixel 0102 is shown with dye 0103 filling the pixel.

In a pixel of a Lippmann color photograph, a plurality of partially reflecting layers is present. Thus, a pixel is required to be structured. Fig. 2 is a cross section 0201 of a Lippmann photograph. The pixel 0202 is shown with partially reflecting layers 0203 (3 in this case) . This requirement for structure in a Lippmann photograph pixel is a unique requirement to this process and is a requirement that does not exist in ordinary photography.

Fig. 3 also shows a cross section of a Lippmann photograph 0301. The emulsion layer 0302, a base layer 0303, a light absorbing layer as black paint 0304, illumination sources 0305 and 0306, the eyes of an observer 0307 and 0308, partially reflecting layers 0309 within a violet reflecting pixel, and partially reflecting layers 0310 within a red reflecting pixel are shown.

The partially reflecting layers are farther apart when the pixel is red 0310 than when the pixel is violet 0309. Thus, color is achieved by controlling the spacing between the partially reflecting layers of the photograph. This exact spacing automatically happens when the unique Lippmann photosensitive element (sensitized plate) is exposed.

The photosensitive element used in ordinary photography and the photosensitive element used in the Lippmann process of color photography are compared in Fig. 4 and Fig 5.

Fig. 4 shows the photosensitive element 0401 used in ordinary photography wherein an emulsion layer 0402, a base layer 0403, and exposing radiation 0404 on a pixel 0405 are also shown.

Fig. 5 shows the photosensitive element 0501 used in the Lippmann method of color photography wherein an emulsion layer 0502, a base layer 0503, a reflecting layer 0504, and exposing radiation 0505 on a pixel 0506 are also shown.

During exposure, what happens within the emulsion layer and within the two pixels is quite different.

In the ordinary element of Fig 4, the exposing radiation 0404 is partially absorbed by the photosensitive emulsion layer 0402 and what is not absorbed passes through. Thus, on purpose, light travels through the emulsion layer in one direction only, and as a result, light uniformly exists throughout the emulsion pixel 0405 during exposure, except for what is absorbed.

In the Lippmann element of Fig. 5, the exposing radiation 0505 is partially trapped by the photosensitive emulsion layer 0502 and what is not trapped is purposely reflected by the reflecting layer 0504, and the reflected radiation thus travels in the opposite direction to the incident radiation. The incident and reflected radiation interfere with each other because of their wave nature. Thus, on purpose, light travels through the emulsion layer in opposite directions. Within the emulsion layer, as a consequence, an interference pattern occurs in the form of planes of lightness separated by planes of darkness. The orientation of these planes is parallel to the film plane. An enlargement of the pixel 0506, within the emulsion layer 0502 of Fig. 5, is shown as Fig. 6.

Fig. 6 shows the emulsion layer 0502, the pixel 0506, and planes of lightness 0601 and planes of darkness 0602. The planes of lightness 0601 result in metallic silver particles after development and for this reason the planes 0601 are shown in the figure as rows of especially dark spots. The purpose of the photosensitive emulsion layer 0502 is to record these planes of lightness and of darkness.

When the photosensitive emulsion layer 0502 is photosensitive because of the presence of photosensitive grains dispersed within it, the grains must be small enough to resolve the planes of lightness and darkness. This resolution requirement is in a direction perpendicular to the film plane. It is to be noted that this direction is in contrast to the ordinary way of measuring film resolution. The ordinary way of measuring resolution for sensitized materials is in a direction parallel to the film plane. Thus, the resolution requirement that is necessary to make a Lippmann photosensitive element 0501 work does not apply to ordinary film 0401; in fact, a single photosensitive grain could conceivably fill the entire pixel 0405 of the ordinary photosensitive element 0401.

Because the distance between the planes of lightness 0601 is ultra small, the largest photosensitive grains that can be used to resolve them are ultra small. (From a resolution standpoint, it is obvious that the grains can be smaller than the largest size.) One of the photosensitive emulsion layers that Lippmann used was of silver halide. One may ask, "What is the diameter of the ultra small photosensitive grains of silver halide required for recording the visible spectrum?" For recording violet (at 400 nm) the grain sized can be about 50 nm or less and for red (at 700 nm) the grain sizes can be 87 nm or less. The rule is, "The diameter of the spherical photosensitive grains used must be about l/8th of the shortest wavelength of radiation to be recorded, or less." This rule is supported by a theoretical study. Thus, for photographing the visible spectrum of from 400 to 700 nm, the diameters of the spherical grains that can be used are about 50 nm or less.

(Lipton,1965, p. 98) "Naturally the grains of the film must be smaller than the shortest wavelength of light (violet) or the shape of the wave cannot be recorded."

(Mees, 1954, p. 23) "Lippmann made extremely fine-grained emulsions....When photographed by means of the electron microscope, emulsions of this general type are found to be made up of spherical grains with an average diameter of approximately 50 millimicrons." (Note: "millimicron" is identically the same as "nanometer" or "rim.")

(Mees, 1954, p. 34) "The well resolved grains" (of the Lippmann method) "were accurately spherical, and more than a thousand were classified for size....the average particle diameter is only 45 millimicrons." (The graph that goes with this text shows that 91 % of all the grains were between 20 and 60 nanometers in diameter.) (Mees, 1942, p. 34, 35) "Lippmann made extremely fine-grained emulsions... When photographed by means of the electron microscope they appear similar to the grains of ordinary emulsions, with a diameter of approximately 10 to 50 millimicrons. "

(James, 1948, p.14) "Some of them" .... (the grains of the Lippmann emulsion) "are only 10 to 15 millimicrons in diameter and the majority lie between 20 and 40 millimicrons."

All of the references fit the description, "The average diameter of the spherical grains is about 50 nanometers or less."

One may ask, "What is the spacing (peak to peak) of the planes of lightness 0601 when the exposing radiation has a wavelength of 400 nm? The spacing for the planes of lightness is the wavelength of light (400 nm) divided by two times the refractive index. The refractive index for gelatin and many other dispersing materials is about one and one half.) The spacing is thus 133 nm. While the resolution for ordinary photographic film is considered very high when it is 400 lines per millimeter (in a direction parallel to the film plane) , the resolution requirement for the ultra small 133 nm spacing is 7,500 lines per millimeter (in a direction perpendicular to the film plane) .

It is known that the largest spherical grains that can be used in the Lippmann process are ultra small, because the process won't work if the grains are larger than this. It is also well known that small grains mean low sensitivity. There seemed no hope for increasing the sensitivity of the emulsion by increasing the grain size.

(Lipton,1965, p. 98, 99) "....The distance between the rows of grains" (planes) "corresponds to color. Naturally, the grains must be smaller than the shortest wavelength of light or the shape of the wave cannot be recorded. So we need a very fine grained film, which will be a very slow film....Today if someone resurrected the Lippmann process, ....But in all likelihood, this will never happen because of the difficulty of increasing the speed of the ultra-fine-grain emulsion..."

DETAILED DESCRIPTION OF THE INVENTION

I have discovered a solution to this problem of insensitivity and revealed the discovery by describing the solution in the Specification of U.S. Application for Patent dated April 21, 1966, Application No. 544,275. This is the living ancestor of the instant application. The solution was described, but not claimed, in 1966. Patent No. 4,178,181 issued in 1979 on one of the inventions described in the specification (that was not related to sensitivity) . This instant application claims the described (in 1966) method of increasing the sensitivity. The invention, herein discussed, is a general solution to the never ending quest for more sensitivity from the same amount of silver, and is a particular solution to the insensitivity problem that existed for the 77 years since Lippmann invented the process (1893-1966) .

Because the requirement that the grain size be ultra small in a direction perpendicular to the film plane and because I saw no such requirement for ultra smallness in a direction parallel the film plane, I discovered that a larger and more sensitive grain could be made if the required smallness in a direction perpendicular to the film plane was maintained, but that the grains are made larger in a direction parallel to the film plane. This is shown in Fig. 7. The discovery was disclosed in the original application of 1966 as follows:

"Large grains and faster speed may be achieved while maintaining grain thinness in a direction perpendicular to the film surface by using grains that are flattened like pancakes; the flattened grains are parallel to the film surface." (Page 26, line 29, through page 27, line 4, of original Disclosure. It can also be seen in U. S. Patent No. 4,178,181 column 12, lines 42-47.)

I submit that the term "tabular" is essentially equivalent to the term "pancakes" in describing the shape of photosensitive grains because they both (1) have two prominent opposite surfaces, (2) said surfaces are flat, (3) said surfaces are parallel, and (4) the diameters of said surfaces are greater than the distance between them.

It is well known that the Lippmann Process of color Photography is extraordinarily slow, that a layered photosensitive element can be used that includes a reflecting layer, of liquid mercury, and an emulsion layer comprising a dispersing medium and photosensitive grains. The photosensitive grains comprise grains characterized as being spherical in shape. The spherical grains comprise grains having diameters (and thickness) of about 50 nanometers and less, when photographing the visible spectrum, and account for essentially 100 percent of the total projection area of all the photosensitive grains. Within the emulsion layer, during exposure, the interference patterns of light waves are required to be present.

It is well known that the photosensitive grains of silver bromide of ordinary photographic films are chiefly triangles and hexagons and their thickness is never more than one-fifth of their diameter [aspect ratio never less than 5:1] and usually not more than one tenth [aspect ratio usually more than 10:1] . (Mees, 1937, p. 64) Also, nothing is apparently remarkable about grains where the aspect ratios are 20:1 or more as shown on the decorative jacket of the reference "Mees,1966". Also, their diameters vary from 0.25 micron to 5 microns. (Mees,1937, p. 64) Also, in the wet emulsions the grains are in every direction, but, after the emulsion has been coated on the film base and dried, it contracts to about one fifteenth or one-twentieth of its thickness, which naturally flattens all the grains as the contraction occurs, so that in the dry film they are parallel or nearly parallel to the face of the emulsion. (Mees, 1937, p. 64)

A later publication (later than the 1966 filing date) confirms the advantage of flat grains. "Flat "T-grain" silver halide crystals....have a higher surface-to-volume ratio than conventional pebble-like crystals; this increases sensitivity without sacrificing fine grain." (High Technology, April, 1983, p. 87) "For purposes of correlation with the photographic characteristics of an emulsion, it is more convenient to use the total projection area of all the grains of each size group instead of simply the size distribution." (James, 1948, p.15)

It is also well known, that when the teachings of the invention are considered in view of the Lippmann Process of Color photography (1) there is a cap on the maximum thickness (or diameter) of the spherical grains that depends on the wavelength of the exposing radiation, (2) the thickness of the tabular grains is tied to the thickness of the spherical grains, (3) the cap on the maximum thickness of the tabular grains is tied to the wavelength of the exposing radiation, (4) there is no stated (stated within the invention disclosure in the Specification) minimum thickness of the tabular grains, (5) there is no stated maximum diameter of the tabular grains as this depends on the required resolution of the film in a direction parallel to the film plane, (6) there is no stated limitation on the wavelength of the exposing radiation although the range would be assumed to include the range of wavelengths for which photosensitive grains are known to be sensitive that would include the range from ultra violet through infra red to 1200 nanometers, and that it is well known that photographic films are sensitive to electrons and X-rays, (7) there is no statement in the teachings of the invention that would preclude the teachings of the invention from obviously being considered for use in ordinary photography wherein limitations peculiar to interference photography (as the presence of a reflecting layer and the required presence of interference patterns of light waves during exposure) would be dropped, (8) there is no statement in the teachings of the invention that restrict the photosensitive grains to silver halide, (9) the aspect ratios of pancakes can be over 300, and (10) any amount of the improved grains of the invention that are used in order to improve the sensitivity of the photosensitive element in which they are used is beneficial, and (11) statements of improved grain abundance can be recited in terms of grain diameters of projected areas.

PREFERRED EMBODIMENTS OF THE INVENTION

EMBODIMENT NO.l

In photography, a layered photosensitive element of improved sensitivity comprising

a. a reflecting layer, and

b. an emulsion layer comprising a dispersing medium and photosensitive grains, c. wherein said photosensitive grains comprise grains characterized as being tabular in shape, d. wherein said grains characterized as being tabular in shape have thicknesses of less than 50 nanometers have average aspect ratios greater than 1 :1 and account for at least 50% of the total projected area of said photosensitive grains, and e. within said emulsion layer the interference patterns of light waves are required to be present during exposure.

Further, instead of 50%, other percentages as 10%, 25%, 70% or 90% could be stated, thus illustrating that any added amount of the improved grains that is used is beneficial, the more the better, and that other grains, not of the improved design, may also be present. Instead of aspect ratios of greater than 1:1, they could be greater than 2:1, 4:1, 8:1, 10:1, 12:1, 15:1, 20:1, 50:1,100:1, or 300:1 or more, because the greater the aspect ratios, the greater the emulsion sensitivity. Instead of thicknesses of less than 50 nanometers, claims could be written stating (1) 87 nanometers if the recording light with a wavelength of 700 nanometers is used; here, the territory claimed is shown in Fig. 15 as the area enclosed within the points 1901, 1911, 1912,1904, and 1901, (2) 150 nanometers if the recording light with a wavelength of 1200 nanometers is used; here, the territory claimed is shown in Fig. 15 as the area enclosed within the points 1901, 1905, 1906, 1904, and 1901.

The remarkable increase of sensitivities of emulsions that employ tabular grains for the purpose of increasing the sensitivity is illustrated by comparing an emulsion with spherical grains of 50 nm in diameter (plotted on Fig. 14 as 1800 with an aspect ratio of 1 :1, thickness and diameter are the same) to the following:

(1) When an emulsion of tabular grains of thickness of 50 nm and with aspect ratios of only 2:1 (diameters of 100 nm) is used, it is found that the sensitivity is increased by a factor of 4. This is plotted on Fig. 14 as 1801.

(2) When an emulsion of tabular grains of thickness of 5 nm and with aspect ratios of 10:1 (diameters of 50 nm) is used, it is found that the sensitivity is increased by a factor of 10. This is plotted on Fig. 14 as 1802.

(3) When an emulsion of tabular grains of thickness of 10 nm and with aspect ratios of 10:1 (diameters of 100 nm) is used, it is found that the sensitivity is increased by a factor of 20. This is plotted on Fig. 14 as 1803.

(4) When an emulsion of tabular grains of thickness of 300 nm and with aspect ratios of 2:1 (diameters of 600 nm) is used, it is found that the sensitivity is increased by a factor of 24. This is plotted on Fig. 14 as 1804.

(5) When an emulsion of tabular grains of thickness of 10 nm and with aspect ratios of 60:1 (diameters of 600 nm) is used, it is found that the sensitivity is increased by a factor of 720. This is plotted on Fig. 14 as 1805.

(6) When an emulsion of tabular grains of thickness of 12 nm and with aspect ratios of 100:1 (diameters of 1200 nm) is used, it is found that the sensitivity is increased by a factor of 2400. This is plotted on Fig. 14 as 1806.

The above 6 examples were determined by using the formula given in Figures 11, 12A and 12B, wherein the inherent relationship of an emulsion's sensitivity is given in terms of the thickness, diameter, and aspect ratios of the photosensitive grains used.

The teachings of the invention would obviously be considered for use in ordinary photography wherein limitations peculiar to interference photography (as the presence of a reflecting layer and consequently the presence of interference patterns within the emulsion layer during exposure) are deleted. When paragraphs "a" and "e" are deleted (limitations peculiar to interference photography) the following results:

EMBODIMENT NO. 2.

In photography, a layered photosensitive element of improved sensitivity comprising b. an emulsion layer comprising a dispersing medium and photosensitive grains, c. wherein said photosensitive grains comprise grains characterized as being tabular in shape, d. wherein said grains characterized as being tabular in shape have thicknesses of less than 50 nanometers have average aspect ratios greater than 1 :1 and account for at least 50% of the total projected area of said photosensitive grains.

However, the limitation within the above "less than 50 nanometers" originated because of a requirement in interference photography, a requirement that does not apply to ordinary photography. Because EMBODIMENT NO. 2 is not limited to interference photography, but applies to ordinary photography, the "50 nanometers" could be larger, as 100, 200, 300, etc. When EMBODIMENT NO. 2 is rewritten to use an arbitrarily larger number, as 300, the following results: EMBODIMENT NO. 3.

b. an emulsion layer comprising a dispersing medium and photosensitive grains, c. wherein said photosensitive grains comprise grains characterized as being tabular in shape, d. wherein said grains characterized as being tabular in shape have thicknesses of less than 300 nanometers have average aspect ratios greater than 1 :1 and account for at least 50% of the total projected area of said photosensitive grains.

A more limiting case in point is the limitation in the above claim "aspect ratios greater than 1 :1." A more confining limitation than "1 :1" is "aspect ratios greater than 8:1, and progressively more confining are the aspect ratios of 10:1,12:1, 20:1, 50:1, 100:1 and all fall within the limitation "aspect ratios greater than 1 :1." When "8:1" is substituted into EMBODIMENT NO. 3, the following results:

EMBODIMENT NO. 4.

b. an emulsion layer comprising a dispersing medium and photosensitive grains, c. wherein said photosensitive grains comprise grains characterized as being tabular in shape, d. wherein said grains characterized as being tabular in shape have thicknesses of less than 300 nanometers have an average aspect ratio greater than 8:1 and account for at least 50% of the total projected area of said photosensitive grains.

To focus on "an emulsion layer" where the title is "a high aspect ratio tabular grained photosensitive emulsion, " where "high aspect ratio" is_,defined as an aspect ratio of greater than 8:1, one may name the emulsion in conformity with the previous embodiment. In view of the foregoing, the following results:

EMBODIMENT NO. 5.

A high aspect ratio tabular grain photosensitive emulsion comprising a dispersing medium and photosensitive grains, wherein tabular photosensitive grains having a thicknesses of less than 300 nanometers that have an average aspect ratio of greater than 8:1 account for at least 50% of the total projected area of said photosensitive grains.

It is well known that a "photosensitive emulsion" can be a "silver halide emulsion," that "photosensitive grains" can be of "silver bromoiodide grains," and that "tabular photosensitive grains" can be "tabular silver bromoiodide grains." Making these substitutions, EMBODIMENT NO. 5 becomes:

EMBODIMENT NO. 6.

A high aspect ratio tabular grain silver halide emulsion comprising a dispersing medium and silver bromoiodide grains, wherein tabular silver bromoiodide grains having a thicknesses of less than 300 nanometers that have an average aspect ratio of greater than 8:1 account for at least 50% of the total projected area of said silver bromoiodide grains.

EMBODIMENT NO.6 does not have the limitation "and a diameter of 600 nanometers." The effect of this limitation is to reduce some of the territory otherwise covered. It is to be noted that the diameter is not independent from the aspect ratio and thickness; (a) when a diameter and thickness are given, only one possible value of the aspect ratio results; (b) when a diameter and the aspect ratio are given, only one possible value of the thickness results. Hence, when a particular diameter is given, the line representing this diameter may be plotted on a graph where the coordinates are thickness and aspect ratio. A point on the line representing a diameter of 600 nanometers is shown in Fig. 14 at 1805. Dotted curves showing aspect ratios of 8 and 20 are also shown on Fig. 14.

EMBODIMENT NO. 7

In a Lippmann light-sensitive element, used in the Lippmann method or making colored photographs by the interference of light waves, comprising

(a) a layered assembly which includes a light-sensitive layer and a parallel reflecting layer, and

(b) wherein the light-sensitive layer contains light-sensitive silver halide grains within a transparent material, the improvement for increasing the sensitivity of the Lippmann element, wherein said light-sensitive grains are

(c) flat, and

(d) the thickness of said grains is maintained in a direction perpendicular to the assembly layers, and

(e) the flat sides of said grains are essentially parallel to the assembly layers.

EMBODIMENT NO. 8

A layered light-sensitive element including a light-sensitive emulsion layer and a reflecting layer wherein:

(a) interference patterns produced by light waves are present within the light-sensitive emulsion layer during exposure; and

(b) the light-sensitive emulsion layer contains light-sensitive grains wherein said grains comprise at least one silver salt: and

(c) upon exposure, the light-sensitive grains record the interference patterns; wherein the improvement is

(d) the shape of the said light-sensitive grains is characterized as being flat. It is well known that when the Lippmann method of color photography used a light-sensitive layer comprising a silver halide emulsion, that the shape of the grains was characterized as being spherical and that the diameters of said spherical grains were about 50 nanometers or less.

EMBODIMENT NO. 9

(b) the light-sensitive emulsion layer contains light-sensitive grains: and

(d) the shape of the said light-sensitive grains is characterized as being flat.

Embodiment No. 9 is the same as Embodiment No. 8, except the grain composition limitation has been dropped.

EMBODIMENT NO.10

A method for increasing the sensitivity of a light-sensitive element by making a light-sensitive element comprised of a multiplicity of very thin emulsion layers, and an emulsion support, wherein said multiplicity of very thin emulsion layers contain light-sensitive grains, wherein said light-sensitive grains are characterized as being flat, comprising the steps of:

(a) providing an emulsion support;

(b) forming a multiplicity of very thin emulsion layers, each of essentially the same composition, on the emulsion support.

EMBODIMENT NO. 11

The method of Claim No. 10, wherein the emulsion is applied in successive layers by spraying.

EMBODIMENT NO. 12

A process for increasing the sensitivity of a layered light-sensitive element Which Includes a light-sensitive layer containing light sensitive grains in a transparent material, and a support layer for the light-sensitive layers, where the improvement includes the steps of

(a) using light-sensitive grains that are characterized as being flat, and

(b) exposing the light-sensitive element to light.

TERRITORIES COVERED BY PREFERRED EMBODIMENTS

Fig. 13 is a plot of the Relative Sensitivities of Emulsions Using Tabular Grains. The information plotted thereon applies to both photosensitive elements that comprise a reflecting layer (interference photography) and those that do not (ordinary photography) . The relative sensitivity curves connect points that are determined from the formula that relates relative sensitivity to grain thickness and aspect ratio. Here, Relative Sensitivity is equal to the aspect ratio squared multiplied by the thickness (in nanometers) . The dimensions of Relative Sensitivity values are in nanometers.

Fig. 14 is a plot of the Relative Sensitivities of Emulsions Using Tabular Grains. The information plotted thereon applies to both photosensitive elements that comprise a reflecting layer (interference photography) and those that do not (ordinary photography) . The relative sensitivity curves connect points that are determined from the formula that relates relative sensitivity to grain thickness and grain diameter. Here, Relative Sensitivity is equal to the diameter (in nanometers) squared divided by the thickness (in nanometers) The difference in Figs. 13 and 14 is that the horizontal axis is aspect ratio in Fig. 13 and diameter in Fig. 14.

Fig. 15 is an overlay of Fig. 13. On it are shown the territories covered by the preferred embodiments, as follows:

Preferred Embodiments 1 and 2 cover territory bounded by the points 1901, 1902, 1903, 1904, and 1901.

Preferred Embodiment No. 3 covers territory bounded by the points 1901, 1907, 1908, 1904, and 1901. Preferred Embodiments Nos. 4, 5, and 6 cover territory bounded by the points 1909, 1910, 1908, 1904, and 1909.

Fig. 16 is an overlay of Fig. 13 and on it is shown the territory claimed by U. S. Patent No. 4,434,226, Claim #1. This claim is bounded by the points 2001, 2002, 2003, 2004, 2005, and 2001. The line 2001, 2005, and 2004 is the line representing a grain diameter of 600 nanometers.

Comparing Fig. 16 with Fig 15 (which are both overlays of Fig. 13 and are plotted on the same scale) , it can be readily seen that U.S. Patent No. 4,434,226, claim 1 overlaps territory claimed by the Preferred Embodiment Nos. 1, 2, 3, 4, 5 and 6.

WHY FLAT GRAINS ARE MORE SENSITIVE THAN SPHERICAL ONES

Any widening at all of the grains (leaving the thickness fixed) increases the sensitivity. This is explained in an illustrative example as follows: In Fig. 9, 4 cubical grains are first shown, and then these 4 grains are joined making a single flat grain. The cubical grains simulate spherical grains and the single flat grain is one of the many flat grains of the emulsion with improved sensitivity.

The flat grain has four times the sensitivity of all four of the cubic grains together. This may be explained as follows. The four small grains together have the same area to intercept light as the one large grain. Therefore, if there is just enough light for one developable speck to be initiated on the large grain, there is just enough light for one developable speck to be initiated on the four small grains together, but the speck will be on just one of the four grains. When the emulsions containing these grains are developed, the developable speck spreads over the entire grain. Then, the entire large grain turns black, but only one of the small grains turns black. Therefore, more black (opacity) is produced by the light that was trapped by the single large grain than by the collection of the four separate small grains. In fact, there is four times as much black produced. Therefore, film using the large grains illustrated in Fig. 9 has four times the sensitivity of film using the small grains. Thus, the equation relating the relative sensitivities is the square of the ratio of the diameters. Here, it is assumed that both the small and large grains have the same thickness.

While the preceding paragraph considers the case of going from an equidimensional grain to a tabular grain, the same relationship applies in going from tabular grains of one diameter to tabular grains of a larger diameter (holding the thickness constant). This case is illustrated in Fig. 10.

The analyses within this document assumes that the same total weight of photosensitive grains per unit area of film is used, that the light levels are low, and the ability of a grain to become exposed depends directly on the grain's projected area.

When the grains are made thinner, as half as thin as before, then the same weight of photosensitive material produces twice as much surface to trap light, and an emulsion results that has twice the sensitivity as before.

Equations that provide relative sensitivity values of different emulsions using the same photosensitive material, but different characteristic grain dimensions, follow.

"Relative Sensitivity" (RS) equals the diameter squared divided by the thickness. The "aspect ratio" (AR) is defined by the diameter divided by the thickness. See Figs. 11, 12A, and 12B. The dimensional units of Relative Sensitivity are in nanometers, when the dimensions of the grains are in nanometers.

Relative sensitivities of emulsions using tabular grains are shown on Fig. 14, where the grain diameter vs thickness is shown, and on Fig. 13, where the grain aspect ratio vs thickness is given.

When designing a film with for maximum sensitivity, Fig. 14 is most conveniently used. One first determines the maximum grain diameter that can be tolerated from the standpoint of conventional resolution requirements and then makes the thickness of the grains as thin as possible.

MAXIMUM DIAMETER OF TABULAR GRAINS.

The maximum diameter of the characteristic grains used depends upon the minimum resolution required of the film. This resolution is measured in lines per millimeter in a direction parallel to the film plane. This maximum diameter is determined by the expression: 370 divided by the required resolution (in lines per millimeter) .

For example, a photosensitive element (ordinary photographic film is a "photosensitive element") is required to have a minimum resolution of 100 lines per millimeter. Determine the maximum diameter of the characteristic tabular grains of the emulsion. Answer: the maximum diameter is 370 divided by 100 equals 3.7 microns. This is just on the ragged edge. The smaller the diameter of the characteristic grains, the higher the resolution. (But when the grain diameters are reduced, the sensitivity suffers.)

COVERING POWER, IMAGE LAYER THICKNESS, AND PROCESSING TIME

A consequence of using the ultra-thin, light-sensitive grains of the invention is increased covering power. This consequence has a profound economic advantage. An illustrative example is given below where, by using the ultra-thin tabular grains of the invention, only one tenth as much silver is required.

Consider 3 cases. Case #1, the reference case. The grains are characterized as being spherical in shape with 1.0 micron diameters.

Case #2.

The grains are characterized as being spherical in shape with 0.1 micron diameters. Case #3.

The grains are characterized as being tabular in shape with 1.0 micron diameters and 0.1 micron thicknesses.

In Case 2, although the total projective area of all the grains is 10 times that of Case #1, the relative sensitivity is only one tenth that of Case #1. ^'

In Case 3, the total projective area of all the grains is 10 times that of Case #1, and the relative sensitivity is ten times that of Case #1. It follows that in order for Case #3 to have the same relative sensitivity as Case #1, only one tenth of the amount of light-sensitive material is needed. When the light-sensitive material is a silver halide, one tenth of the amount of silver is needed. As an additional advantage, the image layer can be made correspondingly thinner, and as a consequence, the processing time reduced.

HISTORY OF FLAT GRAINS IN THE U. S. PATENT OFFICE

It is of historical interest that the discovery that flat grains could be used for the purpose of increasing the sensitivity of a photosensitive element was kept secret in the U. S. Patent and Trademark Office between April 21, 1966, and December 11, 1979, when U. S. Patent #4,178,181 issued against the application filed April 21, 1966. This 1966 application described, but did not claim, the instant invention. This issued patent was in connection with interference photography, but on a different invention than the enclosed.

A data base search was made of U. S. Patents that have issued between 1963 and July 1992, that contain the words "aspect" and "silver" and "ratio." Results follow:

Between 1963 and December 7, 1975, no applications were filed that resulted in U. S. Patents.

On December 8, 1975, an application was filed that resulted in U. S. Patent No. 4,063,951 that issued on December 20, 1977. this patent is a process for making a silver halide emulsion that exhibits high contrast on exposure and development using tabular grains. Over 50% of the total projected area of all the grains is represented by grains having equivalent diameters of about 1100 nm or greater and their aspect ratios are stated to be between 1.5:1 and 7:1. (The 7:1 ratio is viewed as being "unrealistically high" in U. S. Patent No. 4,434,226.) the outlines of these tabular grains are rectangles or squares. The word "sensitive does not appear in the specification or claims. This patent was assigned to Ciba Geigy.

(On December 11, 1979, U. S. Patent No. 4,178,181 issued with an application date of April 21, 1966, revealing flat grain use for sensitivity increase. )

On Nov. 12, 1981, 14 applications were filed that resulted in 14 U. S. Patents. They were assigned to Eastman Kodak Company.

In 1982, 4 applications were filed that resulted in 4 U. S. Patents. They were assigned to Eastman Kodak Company. In 1983, 2 applications were filed that resulted in 2 U. S. Patents. They were assigned to Eastman Kodak Company.

In 1984, 1 application was filed that resulted in 1 U. S. Patent. It was assigned to Eastman Kodak Company.

From 1985 through June, 1992, none known.

Claims

I CLAIM :

1. In photography, a layered photosensitive element of improved sensitivity comprising a. a reflecting layer, and b. an emulsion layer comprising a dispersing medium and photosensitive grains, c. wherein said photosensitive grains comprise grains characterized as being tabular in shape, d. wherein said grains characterized as being tabular in shape have thicknesses of less than 50 nanometers have average aspect ratios greater than 1 :1 and account for at least 50% of the total projected area

Of said photosensitive grains, and e. within said emulsion layer the interference patterns of light waves are required to be present during exposure.

2. In photography, a layered photosensitive element of improved sensitivity comprising b. an emulsion layer comprising a dispersing medium and photosensitive grains, c. wherein said photosensitive grains comprise grains characterized as being tabular in shape, d. wherein said grains characterized as being tabular in shape have thicknesses of less than 50 nanometers have average aspect ratios area Of said photosensitive grains.

3. In photography, a layered photosensitive element of improved sensitivity comprising

4. In photography, a layered photosensitive element of improved sensitivity comprising

5. A high aspect ratio tabular grain photosensitive emulsion comprising a dispersing medium and photosensitive grains, wherein tabular photosensitive grains having a thicknesses of less than 300 nanometers that have an average aspect ratio of greater than 8:1 account for at least 50% of the total projected area of said photosensitive Brains.

6. A high aspect ratio tabular grain silver halide emulsion comprising a dispersing medium and silver bromoiodide grains, wherein tabular silver bromoiodide grains having a thicknesses of less than 300 nanometers that have an average aspect ratio of greater than 8:1 account for at least 50% of the total projected area of said silver bromoiodide grains.

7. In a Lippmann light-sensitive element, used in the Lippmann method of making colored photographs by the interference of light waves, comprising

(a) a layered assembly which includes a light-sensitive layer and a parallel reflecting layer, and (b) wherein the light-sensitive layer contains light-sensitive silver halide grains within a transparent material, the improvement for increasing the sensitivity of the Lippmann element, wherein said light-sensitive_, grains are

(c) flat, and

(d) the thickness of said grains is maintained in a direction perpendicular to the assembly layers and

8. A layered light-sensitive element including a light-sensitive emulsion layer and a reflecting layer wherein:

(b) the light-sensitive emulsion layer contains light-sensitive grains wherein said grains comprise at least one silver salt : and

(c) upon exposure, the light-sensitive grains record the interference patterns; wherein the improvement is (d) the shape of the said light-sensitive grains is characterized as being flat.

9. A layered light-sensitive element including a light-sensitive emulsion layer and a reflecting layer wherein:

(b) the light-sensitive emulsion layer contains light-sensitive grains: and

10. A method for increasing the sensitivity of a light-sensitive element by making a light-sensitive element comprised of a multiplicity of very thin emulsion layers, and an emulsion support, wherein said multiplicity of very thin emulsion layers contain light-sensitive grains, wherein said light-sensitive grains are characterized as being flat, comprising the steps of:

(a) providing an emulsion support; (b) forming a multiplicity of very thin emulsion layers, each of essentially the same composition, on the emulsion support.

11. The method of Claim No. 10, wherein the emulsion is applied in successive layers by spraying.

12. A process for increasing the sensitivity of a layered light-sensitive element which includes a light-sensitive layer containing light sensitive grains in a transparent material, and a support layer for the light-sensitive layers, where the improvement includes the steps of

(a) using light-sensitive grains that are characterized as being flat, and

(b) exposing the light-sensitive element to light.

13. A layered light-sensitive element, including a light-sensitive emulsion layer and a reflecting layer, wherein:

(b) the light-sensitive layer contains light-sensitive grains; and