Photographic material containing a novel DIR-compound

Abstract: Photographic elements and processes are described which employ compounds capable of releasing, as a function of silver halide development, a deactivatable development inhibitor to provide a combination of desirable sensitometric results. The deactivatable development inhibitor has the structure: wherein X is methylene; and R is alkyl of 1 to 4 carbon atoms.

Description: This invention relates to a color photographic element containing a photographic compound, such as a coupler, which releases a deactivatable development inhibitor moiety during processing. Images are commonly obtained in the photographic art by a coupling reaction between the development product of a silver halide color developing agent (i.e., oxidized aromatic primary amino developing agent) and a color forming compound commonly referred to as a coupler. The dyes produced by coupling are indoaniline, azomethine, indamine or indophenol dyes, depending upon the chemical composition of the coupler and the developing agent. The subtractive process of color formation is ordinarily employed in multicolor photographic elements and the resulting image dyes are usually cyan, magenta and yellow dyes which are formed in or adjacent to silver halide layers sensitive to radiation complementary to the radiation absorbed by the image dye; i.e., silver halide emulsions sensitive to red, green and blue radiation. The various ways recognized in the photographic art for improving the quality of such images produced in color photographic silver halide materials include the improvement or graininess, sharpness and color tonal rendition of such images by the use of compounds capable of providing a diffusible development inhibitor moiety as a function of silver halide development. The patent and technical literature contains many references to compounds, generally referred to as DIR-compounds, which can be used for the above described purposes. Representative compounds are described in the following patents: U.S. Patents 3,227,554; 3,701,783; 3,615,506; 3,617,291; 3,379,529; 3,620,746; 3,384,657; 3,733,201; 4,248,962 and 4,409,323. It has been recognized that DIR-compounds, including those disclosed in the above representative patents, have in common the shortcoming that they comprise development inhibitor moieties which, after their release can diffuse out of the photographic material being processed, and accumulate in the processing solution. Such accumulation, commonly referred to as "seasoning", causes a loss of speed in color photographic materials subsequently processed in the solution. Some measures taken to overcome this problem have required a more frequent exchange of processing solutions, as well as limiting the quantity and/or restricting the selection of inhibitor releasing compounds incorporated in the photographic material. Such measures are undesirable for reasons of economy and freedom of design. Yet another approach to overcoming the seasoning problem is described in U.K. Patent 2,099,167. This involves design of the development inhibitor molecule so that soon after contact with the processing solution, it is converted to a species which is inactive as a development inhibitor. While this patent describes this modification as applicable to all known development inhibitor classes, most of those described and exemplified are triazoles. For many applications, mercaptotetrazoles are a preferred class of inhibitors. However, those few mercaptotetrazole inhibitors which are shown in U.K. Patent 2,099,167, as well as in subsequent applications such as EP Application 0,167,163 and Japanese Kokai 205150/83, are inadequate from the standpoint of interimage effect and sharpness. In addition, development inhibitors exemplified in the '167 patent are dependent upon the presence of a catalyst for their conversion into an inactive species in a reasonable period of time. European Specification A-0 242 685 describes compounds which can release a photographically useful group on silver halide development and which contain a hydrazide group. A photographic element containing compound 28 thereof is disclaimed from the present claims. It would be desirable to provide compounds that release mercaptotetrazole development inhibitors which give high interimage effects and good sharpness, yet which are converted to an inactive species in the developer solution without the need for a catalyst. In accordance with our invention, there is provided a photographic element comprising a support bearing a silver halide emulsion and a photographic compound which, as a function of silver halide development, releases a development inhibitor having one of the structures: with the proviso that the photographic compound is not a hydrazide compound capable of releasing a 1-(n-propyloxy-carbonylmethyl)-5-mercaptotetrazole. According to a preferred embodiment, the photographic compound from which the inhibitor is released is a photographic coupler. The inhibitors of formula I can be released from any of the compounds from which inhibitors have been released in the art. Typically, the compound contains a carrier group from which the inhibitor is released either directly or from an intervening timing group which is first released from the carrier group. Carrier groups useful in DIR-compounds of this invention include various known groups from which the development inhibitor moiety can be released by a variety of mechanisms. Representative carrier groups are described, for example, in U.S. Patent No. 3,227,550 and Canadian Patent No. 602,607 (release by chromogenic coupling); U.S. Patent Nos. 3,443,939 and 3,443,940 (release by intramolecular ring closure); U.S. Patent Nos. 3,628,952, 3,698,987, 3,725,062, 3,728,113, 3,844,785, 4,053,312, 4,055,428 and 4,076,529 (release after oxidation of carrier); U.S. Patent No. 3,980,479, U.K. Patent Nos. 1,464,104 and 1,464,105 and U.S. Patent No. 4,199,355 (release unless carrier is oxidized); and U.S. Patent No. 4,139,379 (release after reduction of carrier). A timing group can be employed which serves to join the development inhibitor moiety to the carrier moiety and which, after its release from the carrier, is cleaved from the development inhibitor fragment. Such timing groups are described, e.g., in U.S. Patents Nos. 4,248,962; 4,409,323 and Japanese Patent Publication No. 87/0189037. The development inhibitor moiety can be present in the DIR-compound as a preformed species or it can be present in a blocked form or as a precursor. For example, a preformed development inhibitor may be attached to either the carrier or the timing group via a non-inhibiting function, or the development inhibiting function may be blocked by being the point of attachment or blocked by a hydrolyzable group. When the DIR-compound is an inhibitor releasing developing agent of the type disclosed, for example, in U.S. Patent 3,379,529, the development inhibitor group is imagewise released as a result of silver halide development by the developing agent, optionally in the presence of an auxiliary developing agent. When the DIR-compound is a hydroquinone compound of the type described, for example, in European Patent Application 0,167,168, the development inhibitor is imagewise released by a redox reaction in the presence of an oxidized developing agent. When the DIR-compound is a coupler, the development inhibitor group is imagewise released by a coupling reaction between the coupler and oxidized color developing agent. The carrier moiety can be any coupler moiety employed in conventional color photographic couplers which yield either colored or colorless products on reaction with oxidized color developing agents. Both types of coupler moieties are well known to those skilled in the art. It will be appreciated that, depending upon the particular carrier moiety, the particular developing agent and the type of processing, the development reaction product can be colored or colorless and diffusible or nondiffusible. Thus, it may or may not contribute to image density. Representative compounds included within the scope of the invention include the following: The compounds employed in this invention can be prepared by synthetic procedures well known in the art. Generally, this involves first attaching the timing group, if one is to be a part of the compound, to the appropriate carrier moiety or a derivative thereof, followed by the attachment of the appropriate derivative of the inhibitor group to form the desired DIR-compound. Alternatively, the timing group can be attached to the carrier group after first combining the timing and inhibitor groups by an appropriate reaction. In the absence of a timing group, the inhibitor group is attached to the carrier moiety or a derivative thereof directly. The inhibitor fragment can by synthesized according to the scheme shown in J. Heterocyclic Chem., 15, 981 (1978). Illustrative syntheses are shown in the Examples which follow. One advantage offered by compounds of the invention is that they provide inhibitor moieties having a combination of characteristics that afford improved color photographic, sensitometric and processing results. Such improved sensitometric results include enhanced image sharpness and color tonal rendition. Improved processing results include uncontaminated color developing solutions resulting from the absence therein of accumulated active development inhibitor molecules. We have found that the logarithm of the partition coefficient (Log P) is a good measure of the strength of the inhibitor and its mobility to provide interimage effects. Log P is the logarithm of the partition coefficient of a species between a standard organic phase, usually octanol, and an aqueous phase, usually water. The color photographic element is a polyphasic system, and a photographic inhibitor released in such a system can partition between these various phases. Log P can serve as a measure of this partitioning, and can be correlated to desirable inhibitor properties such as inhibition strength and interimage effects. Inhibitor moieties of this invention with Log P values below 0.50 have been found to be too weak as inhibitors, although they may have useful interimage properties; while moieties with Log P values above 2.10, and especially above 2.25, have poor interimage properties although they have adequate inhibitor strength. The Log P values used in this specification are, unless otherwise indicated, calculated using the additive fragment techniques of C. Hansch and A. Leo as described in "Substituent Constants for Correlation Analysis in Chemistry and Biology", Wiley, New York, 1979, using the computer program "MedChem", version 3.32, Medicinal Chemistry Project, Pomona College, Claremont, CA (1984). Where measured values of Log P are provided, such as in the examples infra, they are measured by the techniques cited in A. Leo, C. Hansch, and D. Elkins, Chem. Rev., 71, 525 (1971); see, for example, R. Livingston, "Physico Chemical Experiments", third editions, Macmillan, New York, 1957, pp. 217 ff. Briefly, the material to be evaluated is dissolved in octanol. An equal volume of water or aqueous buffer of appropriate pH is added and the vessel shaken vigorously for 2 min. The mixture is centrifuged, and aliquots taken from both layers. The aliquots are analyzed by hplc (liquid chromatography) by comparison to sample of known concentration, and Log P calculated from the log of the ratio of the amount in the octanol phase to the amount in the aqueous phase. The DIR compounds can be used and incorporated in photographic elements in the way that DIR compounds have been used in the past. The photographic elements can be single color elements or multicolor elements. Multicolor elements contain dye image-forming units sensitive to each of the three primary regions of the visible spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer, e.g., as by the use of microvessels as described in Whitmore U.S. Patent 4,362,806 issued December 7, 1982. In the following discussion of suitable materials for use in the emulsions and elements of this invention, reference will be made to Research Disclosure , December 1978, Item 17643, published by Industrial Opportunities Ltd., Homewell Havant, Hampshire, PO9 1EF, U.K. This publication will be identified hereafter by the term "Research Disclosure". The silver halide emulsions employed in the elements of this invention can be either negative-working or positive-working. Suitable emulsions and their preparation are described in Research Disclosure Sections I and II and the publications cited therein. Suitable vehicles for the emulsion layers and other layers of elements of this invention are described in Research Disclosure Section IX and the publications cited therein. In addition to the couplers generally described above, the elements of the invention can include additional couplers as described in Research Disclosure Section VII, paragraphs D, E, F and G and the publications cited therein. These couplers can be incorporated in the elements and emulsions as described in Research Disclosure Section VII, paragraph C and the publications cited therein. The photographic elements of this invention or individual layers thereof, can contain brighteners (see Research Disclosure Section V), antifoggants and stabilizers (See Research Disclosure Section VI), antistain agents and image dye stabilizers (see Research Disclosure Section VII, paragraphs I and J), light absorbing and scattering materials (see Research Disclosure Section VIII), hardeners (see Research Disclosure Section XI), plasticizers and lubricants (See Research Disclosure Section XII), antistatic agents (see Research Disclosure Section XIII), matting agents (see Research Disclosure Section XVI) and development modifiers (see Research Disclosure Section XXI). The photographic elements can be coated on a variety of supports as described in Research Disclosure Section XVII and the references described therein. Photographic elements can be exposed to actinic radiation, typically in the visible region of the spectrum, to form a latent image as described in Research Disclosure Section XVIII and then processed to form a visible dye image as described in Research Disclosure Section XIX. Processing to form a visible dye image includes the step of contacting the element with a color developing agent to reduce developable silver halide and oxidize the color developing agent. Oxidized color developing agent in turn reacts with the coupler to yield a dye. With negative working silver halide, the processing step described above gives a negative image. To obtain a positive (or reversal) image, this step can be preceded by development with a non-chromogenic developing agent to develop exposed silver halide, but not form dye, and then uniformly fogging the element to render unexposed silver halide developable. Alternatively, a direct positive emulsion can be employed to obtain a positive image. Development is followed by the conventional steps of bleaching, fixing, or bleach-fixing, to remove silver and silver halide, washing and drying. The following examples are included for a further understanding of this invention. Compounds of this invention may be prepared by first synthesizing the inhibitor fragment according to the following scheme (see J. Heterocyclic Chem., 15, 981 (1978) and then attaching it to the carrier or to the timing group as defined hereinbefore by well-known methods. GENERAL SYNTHESIS SYNTHESIS EXAMPLES SYNTHESIS EXAMPLE I Preparation of 1-n-Propoxycarbonylmethyl-2-tetrazoline-5-thione To a stirred solution of 30 g (0.4 mol) glycine (S-1) and 45 g (0.8 mol) potassium hydroxide in a 100 ml water is added over a period of 1.5 hour 24.4 ml (0.4 mol) carbon disulfide while heating the mixture on a steambath. After an additional 6 hours, heat is removed and 100 ml ethanol is added, followed by the addition over a period of 1 hour of 24.8 ml (0.4 mol) methyl iodide. Upon standing at room temperature overnight, the mixture is concentrated and acidified with sulfuric acid, and the resulting solid is removed by filtration and washed briefly with cold water. The filtrate is extracted with ethyl acetate and concentrated to yield 32.4 g crystalline acid, (S-2), (m.p. 110-111°C on further recrystallization from toluene/ligroin). A solution of this acid (196 mmol), 7.8 g (196 mmol) sodium hydroxide and 14.3 g (220 mmol) sodium azide in 400 ml water is heated for 3 hours on a steambath, cooled, and acidified to pH 2 with hydrochloric acid. An extractive workup yields 7 g of 1-carboxymethyl-2-tetrazoline-5-thione (S-3). More product is obtained upon repeated extraction. This acid is next esterified by heating for 1.5 hour on a steambath 20 g (125 mmol) in 400 ml n-propanol and 3 ml concentrated sulfuric acid. Concentration and extractive workup give a crude product, m.p. 62-64°C, which on recrystallization from toluene/hexane yields 11.3 g of the thione S-4, m.p. 62-64°C, whose mass and nmr spectra are consistent with those of the desired ester. Elemental analysis - Calculated: C, 35.6; H, H, 5.0; N, 27.7. Found: C, 36.0; H, 4.9; N, 27.2. SYNTHESIS EXAMPLE II Preparation of Compound 18 To a stirred solution of 10.92 g (20 mmOl) Coupler (S-5) and 4.04 g (20 mmol) thione (S-4) in 150 ml dimethylformamide chilled to 5-10° C is added a solution of 3.2 g (20 mmol) bromine in 10 ml dimethylformamide. After 1 hour, the mixture is poured into ice water, and following filtration, washing and drying, a yield of 11.4 g, m.p. 133-141°C, is obtained. An acetonitrile solution is treated with Norit carbon, filtered and water added to precipitate purified product, yielding after drying 8.3 g Compound 18, m.p. 124-125°C. Elemental analysis - Calculated: C, 62.7; H, 7.3; N, 15.0; Found: C, 62.5; H, 7.2; N, 15.0. SYNTHESIS EXAMPLE III Preparation of Compound 13 Procedures described in U.S. Patent 4,248,962 (Columns 26 and 28) are used to prepare intermediate (S-6), a yellow dye-forming coupler with an attached timing group terminating in a carbamoyl chloride moiety. A solution of 24.4 g (30mmol) of S-6 and 6.06 g (30mmol) of (S-4) in 250 ml anhydrous pyridine is stirred for 16 hours under a nitrogen atmosphere. The reaction mixture is next poured into an ice/ethyl acetate mixture and carefully acidified with concentrated hydrochloric acid to pH 4 with vigorous stirring, then shaken with a brine/ethyl acetate mixture. The organic phase is separated, dried over magnesium sulfate, concentrated and purified by silica gel chromatography and a 72-hour trituration of the resulting solid with hexane. Pressing this solid on a porous plate and drying yield 7.9 g of Compound 13, m.p. 90-93°C. Elemental analysis - Calculated: C, 55.2; H, 6.9; Cl, 3.6; N, 11.4; S, 6.5. Found: C, 55.2; H, 6.6; Cl, 3.5; N, 11.3; S, 6.4. SYNTHESIS EXAMPLE IV Preparation of Compound 7 A solution of 3.21 (5 mmol) of intermediate (S-7, X=OH) and 2 ml thionyl chloride in 35 ml methylene chloride is stirred for 18 hours at room temperature, then concentrated, redissolved in heptane/methylene chloride, and reconcentrated. The resulting solid (S-8, X=Cl) is dissolved in 20 ml methylene chloride and stirred for 24 hours with a solution of 1.08 g (5 mmol) of ester (S-4-A), 0.42 g (5 mmol) sodium bicarbonate, and 0.1 g tetrabutylammonium bromide in 20 ml water. The organic phase is separated, dried, concentrated, and chromatographed on silica gel with methylene chloride. An impure fraction (0.75 g) and a purer fraction (1.51 g) are isolated after treatment with n-butanol/hexane and subsequent drying. The latter is identified as the desired Compound 7. Elemental analysis - Calculated: C, 64.3; H, 6.7; N, 10.0; S, 3.8. Found: C, 64.5; H, 7.0; N, 10.0; S, 3.3. Trace amounts of free inhibitor are removed by washing a diethyl ether solution with aqueous sodium bicarbonate solution, separating the organic phase, drying, concentrating, treating with n-butanol, and drying in vacuum for 24 hours. EXAMPLES Example I This example demonstrates advantages of the compounds of the invention with respect to interimage effects and sharpness. A set of photographic elements was prepared which had the common format shown below. The only differences between elements were the development inhibitor compound employed and the amount of development inhibitor compound required to reach a common level of response. The format is schematically represented as follows, the numbers in parentheses represent the amount of the component in mg/m² The hardener was bis(vinylsulfonylmethyl) ether. The silver bromoiodide (coating weight is that of silver) was 6.4 mol % in iodide, had an average grain size of 0.5 micrometer and had been chemically sensitized with sulfur and gold. Each of the cyan and yellow dye-forming couplers was dispersed in half its weight of dibutyl phthalate, and each DIR-coupler was dispersed in twice its weight of diethyl lauramide. The development inhibitor was released from the same compound. The development inhibitor releasing compound had the general structure: The specific inhibitors used are identified in Table I, together with the results obtained. Comparison couplers, which are identified in Table I, were from compounds shown in UK Patent Application 2,099,167A, or are compounds just outside the scope of this invention which are not specifically shown in the '167A application. The materials were processed at 38°C as follows: Step Time Color Developer 3-1/4' Stop (5% Acetic Acid) 2' Wash 2' Bleach (FeEDTA) 4' Wash 2' Fix 2' Wash 2' Color Developer Composition g/L Na₂SO₃ 4.0 4-Amino-3-Methyl-N-ethyl-N-β-hydroxylethylaniline sulfate 4.5 K₂CO₃ 37.5 NaBr 1.3 KI 0.0012 Hydroxylamine sulfate 2.0 H₂SO₄ 1.3 Each element shown in Table I was exposed through a graduated density test object and a minus blue (Wratten 12) filter and then processed as described above. Sensitometric curves were generated from the exposed and processed elements from which a contrast (γ) in each of the causer and receiver layers was measured. The ratio of γ C /γ R for an element containing a DIR compound gives an indication of where in the element the inhibitor has its predominant effect. Materials with higher values of γ C /γ R show that the inhibitor is acting more in the receiver layer than in the causer layer and thus show good interimage effects. Interimage comparisons were made at a causer layer contrast of 1. From the exposed and processed elements, CMT-35 acutance was also measured at a causer layer contrast (γ) of 1 by the techniques described and discussed in "An Improved Objective Method for Rating Picture Sharpness: CMT Acutance," by R. G. Gendron, Journal of the SMPTE, 82 , 1009-12 (Dec., 1973). The higher the CMT acutance number, the sharper the image. The numerical values obtained are reported in Table I, below. Compound # Inhibitor Structure (X=) Interimage (γ C /γ R ) Acutance (CMT 35) 1 (INV) -CH₂CO₂C₃H₇ 1.54 94.9 2 (INV) -CH₂CO₂C₃H₇-i 1.72 95.4 3 (INV) -CH₂CO₂C₄H₉ 1.32 94.4 4 (COMP) -C₄H₈CO₂C₂H₅ 1.54 95.1 5 (COMP) -C₂H₄CO₂C₄H₉ 1.09 94.6 6 (COMP) -CH₂CO₂C₅H₁₁ 1.00 93.7 7 (COMP) -C₄H₈CO₂PhCl 0.81 91.9 8 (COMP) -PhCO₂CH₂CO₂C₂H₅ 0.85 92.7 9 (COMP) -PhCO₂Ph 0.81 91.5 This data shows that 1) compounds 7, 8 and 9, which employ inhibitors from compounds 34, 91, and 95, inter alia, of the '167A application, give both poorer interimage effect and poorer sharpness than the compounds of the invention; 2) compounds 5 and 6, which are not specifically shown in the '167A application, give similar sharpness as the invention but poorer interimage; and 3) compound 4, which is not specifically shown in the ′167A application, gives similar interimage and sharpness as the invention. Example II The example evaluates the rate of decomposition, and thus the effect on seasoning, of a developer solution containing development inhibitors released from compounds of this invention compared with inhibitors outside the invention. The buildup of active development inhibitor in a developer solution has a detrimental effect on subsequent processed film. A seasoned developer solution was simulated by stirring ethyl mercaptotetrazole (EMT), another comparison inhibitor, or one of the development inhibitors of this invention into separate portions of the developer solution shown in Example I. After 15 and 60 minutes, separate exposed strips of a single-layer photographic coating were developed in the seasoned solution. Density loss, compared with the same coating processed through a non-seasoned solution, provided a measure of residual inhibitor effect. The effect of inhibitor strength was removed by normalizing the results at 60 minutes with results obtained at 15 minutes. An inhibitor which has poor seasoning characteristics will provide equal or nearly equal inhibition at both time intervals. Inhibitors exhibiting the best seasoning characteristics give the lowest percent inhibitor remaining at 60 minutes relative to the 15-minute test. The results are reported in Table II. Compound # Inhibitor Structure (X=) Residual Inhibitor (@ 60 Minutes) 1 (INV) -CH₂CO₂C₃H₇ 20 3 (INV) -CH₂CO₂C₄H₉ 33 6 (COMP) -CH₂CO₂C₅H₁₁ 66 4 (COMP) -C₄H₈CO₂C₂H₅ 93 11 (COMP) -C₂H₅ 93 These data show that compounds of the invention decompose at a much more rapid rate than compounds outside the invention. In fact, compound 4 is no better than Compound 11, an inhibitor known not to decompose. Example III A third series of experiments was conducted to determine the need for a catalyst in the processing solution to cause the inhibitor to decompose. This was done using the procedure described in Example II above, comparing color developer solutions containing hydroxylamine sulfate with those from which it had been omitted. Hydroxylamine sulfate acts as a catalyst for the decomposition of some development inhibitors. The density loss in separated strips of exposed film was compared for strips processed in the developer composition shown in Example I containing one of the inhibitors shown in Table III, with and without the hydroxylamine sulfate. The developer compositions were held for 60 minutes between addition of the inhibitor and processing of the filmstrip. The ratio of density loss with and without the catalyst is indicative of catalyst dependancy of the inhibitor. A low ratio indicates little dependancy on the presence of catalyst, while a high ratio indicates that a catalyst is required for the inhibitor to decompose. The results are shown in Table III. These data show that compounds of the invention decompose whether or not a catalyst is present. Compound 12, which employs the inhibitor released from Compound 2, 10, and 16 of the '167A application, is highly dependent on the presence of a catalyst.

Claims: A photographic element comprising a support bearing a silver halide emulsion and a photographic compound which, as a function of silver halide development, releases a development inhibitor having one of the structures: with the proviso that the photographic compound is not a hydrazide compound capable of releasing a 1-(n-propyloxy-carbonylmethyl)-5-mercaptotetrazole. A photographic element of Claim 1 wherein the development inhibitor is joined directly to the coupling position of a photographic coupler. A photographic element of Claims 1 or 2 wherein the development inhibitor is joined to the coupling position of a photographic coupler through a timing group. A photographic element of any of Claims 1 to 3 wherein the coupler is a yellow dye-forming coupler. A photographic element of any of Claims 1 to 3 wherein the coupler is a cyan dye-forming coupler. A photographic element of any of Claims 1 to 5 wherein the development inhibitor has the structure: A photographic element of any of Claims 1 to 6 wherein the coupler is contained in one or more layers of a multilayer, multicolor photographic element. A process of forming a color photographic image which comprises developing an exposed silver halide photographic element, which yields a dye image, in the presence of a development inhibitor releasing compound as defined in any of claims 1 to 7.

Inventors: DESELMS ROY CHARLES C O EASTMA, KAPECKI JON ALFRED C O EASTMAN, DESELMS, ROY CHARLES C/O EASTMAN KODAK COMPANY, KAPECKI, JON ALFRED C/O EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1988
Main classification: G03C7
IPC codes: G03C7, C07D257