Process for forming color filter

A process for forming a color filter, which comprises patternwise exposing a black-and-white silver halide emulsion layer of a photographic material comprising a support having thereon at least one black-and-white silver halide emulsion layer, developing the photographic material with a developing solution containing a color dye developer to form a pattern containing a color dye for a pattern containing at least one dye, and removing remaining silver and/or silver halide. The patternwise exposure and color coupler containing development steps can be repeated using different color couplers to produce patterns with additional color dyes.

BACKGROUND OF THE INVENTION 
This invention relates to an improvement in a process for forming a color 
filter according to a silver salt photographic process. 
A process for forming a color filter using a coupler-in-developer type 
color developing process is described in Japanese Patent Application No. 
78313/78 (corresponding to U.S. patent application Ser. No. 52,704, filed 
June 28, 1979, now U.S. Pat. No. 4,271,246) by some of the same inventors 
herein. This color filter-forming process fundamentally comprises 
subjecting to a first patternwise exposure a black-and-white silver halide 
emulsion layer of a photographic material comprising a support having 
thereon at least one black-and-white emulsion layer, developing the 
photographic material with a coupler-in-developer color-developing process 
wherein the color developer contains a color coupler to form a pattern 
containing the first color dye and, after final color development, 
conducting a silver-removing processing. Further, after formation of the 
first color pattern, similar steps are repeated to form another pattern 
containing a second color dye, and so on, thus forming at least two color 
patterns. 
This process provides the advantage that a color filter can be obtained 
much less expensively as compared to known color filters using an 
interference filter or those obtained by dyeing a relief of a high 
molecular weight polymer material with a dye. 
However, color filters obtained by this process described in Japanese 
Patent Application No. 78313/78 have the defect that they have spectral 
characteristics which are not as sharp as those of known interference 
filters or the like. That is, as is shown in FIG. 1, when transmittance is 
plotted as the ordinate and wavelength as the abscissa, the change in 
transmittance of, for example, a yellow filter over the transmittance 
range of from about 0% to about 90% is not as sharp as indicated by curve 
A. 
SUMMARY OF THE INVENTION 
As a result of intensive investigations to remove the above-described 
defect while maintaining the above-described advantages of the former 
application, the inventors have discovered that a color filter with sharp 
spectral characteristics can be obtained by patternwise exposing a 
photographic material comprising a support having thereon at least one 
black-and-white silver halide emulsion layer, and developing the 
photographic material in a developing solution containing a dye developer. 
Dye developers are known and are usually used in an instant photographic 
process. However, such instant photographic process utilizes the 
phenomenon that, when exposed silver halide is developed, the dye 
developer is oxidized and becomes non-diffusible, whereas unreacted dye 
developer in the unexposed portions becomes diffusible on development due 
to its alkali-soluble properties and is transferred to an image-receiving 
layer, thus forming an image of dye molecules diffused from the unexposed 
portions (diffusion transfer process). Therefore, a dye developer is used 
to obtain positive images. On the contrary, in the present invention the 
diffusion transfer process is not employed, but a pattern composed of dye 
and silver formed in the imagewise exposed portions of a silver halide 
emulsion layer, i.e., negative image dye, is used to form images. Thus, 
the two processes are absolutely different from each other. And, according 
to the present invention, a novel effect of providing a color filter with 
sharp spectral characteristics as shown in FIG. 1, curve B, is produced 
through simple steps. In addition, another novel effect of providing a 
color filter having excellent fading resistance and heat resistance is 
produced. Further, considering the fact that coupler-in-developer type 
color developers require a coupling reaction and therefore dyes to be used 
are limited only to those which readily undergo such a coupling reaction, 
dye developers provide the effect of permitting dyes with good spectral 
characteristics to be freely selected and the selection of dyes with good 
fading resistance and heat resistance is facilitated. The fading 
resistance and heat resistance as well as the above-described spectral 
characteristics are extremely important in applying the resulting color 
filter, for example, to a camera tube. In the case of, for example, 
applying the color filter to a planar plate for a camera tube or further 
forming thereon a photosensitive layer, the color filter of the present 
invention can be heated. Still further, deterioration of the color filter 
can be avoided even when it is used for a long time for a camera tube. 
Therefore an object of the present invention is to provide a process for 
inexpensively forming a color filter suitable for use in, for example, a 
color camera tube or solid state camera devices. 
Another object of the present invention is to provide a color filter having 
sharp spectral characteristics. 
These objects are attained by a process for forming a color filter, which 
comprises 
subjecting to a first patternwise exposure a black-and-white silver halide 
emulsion layer of a photographic material comprising a support having 
thereon at least one black-and-white silver halide emulsion layer, 
developing the photographic material with a developing solution containing 
a first color dye developer and, if necessary, conducting again the 
patternwise exposure and development with a different color dye developer 
to form a second color pattern and so on thus forming a pattern containing 
at least one dye, and 
removing remaining silver and/or silver halide as a final step.

In these drawings, reference numeral 20 designates a support, 21 a silver 
halide emulsion layer, and 30 and 40 photomasks. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention will be described in more detail by reference to the 
accompanying drawings. 
FIG. 2 shows one embodiment of a photographic material to be used in the 
present invention, wherein a fine-grain black-and-white silver halide 
emulsion layer 21 is provided on a support 20. A subbing layer may be 
provided if necessary on the support. 
Where support 20 itself forms a support of an optical filter, the support 
must be transparent to visible light but, in the case of initially forming 
a color filter layer on the support and then transferring it onto another 
transparent support, a semi-transparent or opaque support may be used as 
well as a transparent support, because it is used only as a temporary 
support. And, as to shape of the support, the support may have a plate 
shape, a sheet shape, or a film shape. Suitable materials for the support 
which can be used, for example, include synthetic resins such as 
polyethylene terephthalate, polystyrene, polycarbonate, cellulose acetate, 
etc., glass, quartz, sapphire, and the like. The support itself may have 
other functions; for example, it may also function as a planar plate of a 
camera tube. 
The subbing layer to be provided, if desired, in the present invention is a 
layer of a material that strongly adheres to both support 20 and silver 
halide emulsion layer 21. Suitable materials which can be used for the 
subbing layer are gelatin, albumin, casein, cellulose derivatives, starch 
derivatives, sodium alginate, polyvinyl alcohol, polyvinyl pyrrolidone, 
polyacrylic acid copolymer, polyacrylamide, etc. The thickness of the 
subbing layer is desirably as thin as possible, i.e., about 0.01 to 1 
.mu.m, preferably 0.05 to 0.5 .mu.m. 
Suitable silver halide emulsions which can be coated on the support 
directly or via the subbing layer are known emulsions obtained by 
dispersing silver halide in a water-soluble binder. In the present 
invention, fine-grain emulsions are particularly preferable; for example, 
a so-called Lippmann emulsion having a mean silver halide grain size of 
about 0.1 .mu.m or less is preferred. The weight ratio of silver halide to 
water-soluble binder is within the range of from about 1:6 to 8:1. 
Exemplary silver halides which can be used are silver chloride, silver 
bromide, silver iodide, silver chlorobromide, silver bromoiodide, silver 
chloroiodide, silver chlorobromoiodide, etc. Illustrative water-soluble 
binders are gelatin, albumin, casein, cellulose derivatives, agar-agar, 
sodium alginate, sugar derivatives, polyvinyl alcohol, polyvinyl 
pyrrolidone, polyacrylamide, etc. If desired, a compatible mixture of two 
or more of these binders can be used. The dry thickness of silver halide 
emulsion layer 21 is preferably within the range of about 0.8 to about 10 
.mu.m. 
A antihalation backing layer may be provided, if desired, on the back side 
of the support 20 to the thus formed photographic material. 
This photographic material is subjected to imagewise exposure 34 
corresponding to the first color pattern of a multi-color optical filter, 
for example, a yellow striped or mosaic pattern, through a photomask 30 as 
shown in FIG. 3. Conventional photomasks can be used. For example, a 
chromium mask comprising a glass plate 31 having provided thereon 
light-intercepting portions 32 composed of chromium forming imagewise 
transparent pattern 33 corresponding to the first color pattern can be 
used. Suitable light sources to be used upon exposure can be any source 
that emits light of a wavelength to which the silver halide emulsion layer 
is sensitive. For example, a light source emitting white light can be 
used. The so-called contact exposure wherein uniform irradiation is 
conducted with the photomask superposed on the emulsion layer 21 as shown 
in FIG. 3 can be used. Also, a projection exposure wherein an image is 
exposed using a lens system can be employed. 
The thus exposed photographic material is then subjected to development 
using a first dye developer. For example, when developing the photographic 
material in a developing solution containing a yellow dye developer, 
pattern 35 composed of the yellow dye and silver grains is formed in the 
exposed portions. In the case of forming a mono-color filter containing 
the dye pattern obtained by this first development, silver in the pattern 
35 is bleached away or, after re-halogenation, the remaining silver halide 
is removed, after completion of the first development. Thus, for example, 
a yellow filter is obtained. The step to be conducted after completion of 
the first development uses a bleach-fixing solution known in the field of 
color photography, which reduces the steps to only one step. 
Where a second dye pattern in addition to the first dye pattern is to be 
formed, silver is bleached away or re-halogenated followed by washing with 
water, after completion of the first development, and, if desired, dried. 
Then, as is shown in FIG. 4, a second pattern, for example, a cyan color 
pattern, is imagewise exposed in the same manner as described above using 
a second photomask 40 across the yellow pattern 34. The photomask 40 may 
be the same chromium mask as described hereinbefore, which comprises a 
transparent support 41 having thereon a light-intercepting chromium 
pattern 42 and an imagewise transparent pattern 43 corresponding to the 
second color pattern. The thus exposed photographic material is then 
subjected to development using a second dye developer. For example, when 
this photographic material is developed in a developing solution 
containing a cyan dye developer, a pattern 44 composed of the cyan dye and 
silver is formed across the already formed yellow pattern 34. After 
completion of the second development, silver is removed in the same manner 
as described above by bleaching or re-halogenating followed by removal of 
the remaining silver halide. Thus, a filter wherein yellow and cyan 
patters cross each other is obtained. 
A third dye pattern and so on may be formed, if desired, in the same 
manner. In the present invention, it is necessary for the silver and/or 
unused silver halide to be removed at least after formation of the final 
pattern. That is, in the case of forming a pattern of a dye alone, it is 
necessary in the present invention to remove silver and unused silver 
halide after formation of the final pattern and, in the case of forming a 
color filter containing silver grains in part of the pattern, it is 
necessary to remove unused silver halide. 
The dye developer-containing developing solution which is used in the 
present invention is an alkaline aqueous solution (pH: about 9 or more, 
preferably 10.5 to 13) of an alkali-soluble dye developer capable of being 
oxidized by development to become insoluble and fixed in the silver image 
portions. To this aqueous solution are added a pH-adjusting agent or a 
buffering agent such as sodium hydroxide, sodium carbonate, sodium 
phosphate, etc.; an anti-fogging agent such as potassium bromide, etc.; an 
organic solvent for increasing the solubility of the dye developer (e.g., 
dimethylformamide, methyl ethyl ketone, etc.); and the like. 
In the present invention, any conventional dye developer known in the art 
can be used, such as those described in, for example U.S. Pat. Nos. 
2,983,605, 2,983,606, 2,992,106, 3,047,386, 3,076,808, 3,076,820, 
3,077,402, 3,126,280, 3,131,061, 3,134,762, 3,134,765, 3,135,604, 
3,135,605, 3,135,606, 3,135,734, 3,141,772, 3,142,565, 3,173,906, 
3,183,090, 3,218,164, 3,230,082, 3,230,083, 3,230,086, 3,239,339, 
3,245,790, 3,309,199, 3,246,985, 3,320,063, 3,320,083, 3,347,672, 
3,347,673, 3,453,107, 3,579,334, 3,482,972, and 3,563,739; Australian Pat. 
No. 220,279; German Pat. No. 1,036,640; British Pat. Nos. 804,971, 
804,973, 804,974, and 804,975; Belgian Pat. Nos. 554,935 and 568,344; 
Canadian Pat. Nos. 579,038 and 577,021; French Pat. No. 1,168,292; etc. 
Suitable specific dye developers which can be incorporated in the 
respective developing solutions include the following: 
##STR1## 
Pattern 34 containing a yellow dye and pattern 44 containing a cyan dye are 
thus formed in a regularly arranged form wherein the two patterns cross 
each other at a certain angle. (When the second dye development is 
conducted after re-halogenating patternwise silver formed by the first dye 
development, the crossed portions appear green.) The two patterns may 
cross each other at a right angle or may be arranged in a closely parallel 
manner or in a mosaic manner without crossing. 
In removal of silver grains, a bleaching solution used for ordinary color 
photographic processing is employed and, as an oxidizing agent, potassium 
ferricyanide, dichromate, EDTA complex salt, etc., are illustrative. For 
the purpose of re-halogenation, for example, potassium bromide is added. 
On the other hand, the fixing agent for silver halide can be a 
conventionally well known optional silver halide solvent (for example, 
sodium thiosulfate, sodium thiocyanate, etc.), and a solution containing 
such a fixing agent may further contain, if necessary, a preservative 
(e.g., sodium sulfite), a pH buffer (e.g., boric acid), a pH-adjusting 
agent (e.g., acetic acid), a chelating agent, etc. 
Also, as one of the above-described silver-removing processings, a 
mono-bath bleach-fixing solution, for example, a mixed solution of 
potassium ferricyanide and sodium thiosulfate or a mixed solution of 
iron-EDTA and sodium thiosulfate can be used. 
The present invention is now described in more detail by reference to the 
following examples. 
EXAMPLE 1 
1,400 ml of a silver bromide emulsion (mean particle size of silver halide: 
about 0.06.mu.) was prepared in a conventional manner using 50 g of 
geletin and 188 g of silver bromide. 0.25 g of 
4-methyl-2,3-diethoxythiazolocarbocyanine iodide was added to the emulsion 
to optically sensitize the emulsion to light of a wavelength of 510 nm to 
530 nm. Then, the resulting emulsion was coated on a borosilicate glass 
disc of a diameter of 1 inch and a thickness of 2.5 mm in a dry thickness 
of about 3 .mu.m to prepare a photographic light-sensitive material. This 
photographic light-sensitive materisl was exposed to white light (emitted 
from a tungsten lamp) through a closely superposed chromium mask for 
forming a stripe filter having transparent portions of a width of 25 .mu.m 
with a pitch of 50 .mu.m, immersed for 2 minutes in a 5% formaldehyde 
aqueous solution to pre-harden, then washed for 3 minutes with water, 
followed by developing in a developing solution having the following 
formulation (23.degree. C., 2 minutes). 
______________________________________ 
Dye-Developing Solution 
______________________________________ 
Dye Developer Y-1 2 g 
Anhydrous Sodium Sulfite 
5 g 
Sodium Hydroxide 0.4 g 
Sodium Sulfate 30 g 
Tolylhydroquinone 3 g 
Dimethylformamide 10 ml 
Water 1 liter 
______________________________________ 
After washing with water for 5 minutes, the sample was bleached in a 
bleaching solution having the following formulation (20.degree. C., 2 
minutes). 
______________________________________ 
Bleaching Solution 
______________________________________ 
Potassium Ferricyanide 100 g 
Potassium Bromide 30 g 
Water 1000 ml 
______________________________________ 
After washing with water for 2 minutes, the sample was processed in a 
fixing solution of the following formulation (20.degree. C., 2 minutes). 
______________________________________ 
Fixing Solution 
______________________________________ 
Sodium Thiosulfate 240 g 
Sodium Sulfite 3 g 
Glacial Acetic Acid 5 ml 
Potassium Alum 6 g 
Water 1000 ml 
______________________________________ 
After washing with water for 10 minutes, the sample was dried. Thus, a 
yellow stripe filter of a stripe width of 25 .mu.m was obtained. 
EXAMPLE 2 
The same type of photographic material as described in Example 1 was 
exposed, pre-hardened and developed in the same manner as described in 
Example 1, then bleached in the same manner as described in Example 1 
whereby a stripe pattern of a mixture of yellow dye and silver halide was 
obtained. After washing with water for 5 minutes, the sample was dried. 
Then, the sample was further exposed through a chromium mask having 
stripes of the same width and the same pitch as in Example 1 while the 
chromium mask was positioned such that its transparent portions obliquely 
crossed the above stripes of the mask used in Example 1, and developed in 
a dye-developing solution of the following formulation. 
______________________________________ 
Dye-Developing Solution 
______________________________________ 
Dye Developer C-3 1.5 g 
Anhydrous Sodium Sulfite 
5 g 
Sodium Hydroxide 0.4 g 
Sodium Sulfate 30 g 
Tolylhydroquinone 2.5 g 
Dimethylformamide 10 ml 
Water 1000 ml 
______________________________________ 
After washing with water for 5 minutes, the photographic material was 
bleached, washed, fixed, washed, and dried in the same manner as described 
in Example 1 to obtain a filter wherein yellow and cyan stripes cross each 
other. 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.