CHROMOGENIC FLUORAN COMPOUNDS

Abstract: Fluoran compounds of the general formula wherein: R₁ and R₂ are each independently, lower alkyl; A is NR₃R₄ where R₃ and R₄ are each, independently, C₁ to C₁₂ alkyl, cycloalkyl, phenyl or phenyl substituted by lower alkyl or lower alkoxy; or A is a pyrrolidinyl, piperidino, morpholino or piperazino radical; are particularly suitable for use as colour formers in pressure sensitive or heat sensitive recording materials.

Description: This invention relates to chromogenic fluoran compounds and to their use as colour formers in record material. Fluorans are a well known class of chromogenic materials useful as colour formers in pressure and/or heat sensitive record material. Within the broad class there is a group of compounds having substituted amino substituents in the 3- and 7- positions and an alkyl substituent in the 6-position which have neutral (grey or black) colour forms. In particular compounds in which the 7-substituent is N -phenylamino (commonly referred to as 'anilino') e.g. as in 3-diethylamino-6-methyl-7-N-phenylaminofluoran, have proved successful as colour formers in pressure and thermally sensitive record material. Although most interest has previously been directed to compounds where the phenyl ring in the anilino group is unsubstituted, several patent specifications refer to colour formers carrying substituents on the anilino group. These include U.S. Nos. 4226912 and 4482905, which refer to a xylidino-substituent in the 7-position, U.S. Nos. 4,442,176, 4473832 and 4629800, which refer to 2,3-,2,4- and 2,5- dimethyl substituted anilino substituents in the 7-position and U.S. No. 4330713 which relate to various methyl substituents in the 7-anilino group including reference to 2,4-dimethyl, 2,4,5-trimethyl, 2,3,5,6-tetramethyl and 2,3,4,5,6-pentamethyl anilino groups. The reference to 7-xylidino substituents in U.S. Specifications Nos. 4226912 and 4482905 is not clear as it does not distinguish between a particular, unnamed, isomer and the mixture of isomers which would be obtained by using commercially available technical grade xylidene (a mixture of various of the possible isomers of xylidine) as a (notional) starting material. The present invention is based on the discovery that chromogenic fluorans having a 2,6-dialkylsubstitutedphenylamino-group in the 7-position can be particularly good neutral or grey or black colour formers. In particular they can be particularly resistant to discolouration to exposure to ambient conditions prior to contact with a suitable colour developer material, or to give coloured forms with enhanced image density and/or improved i.e. reduced background discolouration or with improved resistance to hue shifts on exposure to light. Accordingly, the present invention provides a chromogenic fluoran compound of the formula: wherein R₁ and R₂ are each independently, lower alkyl; A is a group of the formula: where R₃ and R₄ are each, independently, C₁ to C₁₂ alkyl, cycloalkyl, phenyl or phenyl substituted with lower alkyl or lower alkoxy; or A is a pyrolidinyl, piperidino, morpholino or piperazino radical. Among the more important compounds of the invention are those of the formula (I) above where R₁ and R₂ are each, independently, lower alkyl and A is -NR₃R₄ where R₃ and R₄ are each, independently, C₁ to C₁₂, cycloalkyl or phenyl. Of these compounds, those where R₁ and R₂ are each, independently, methyl, ethyl or propyl, but especially methyl or ethyl, and R₃ and R₄ are each, independently, C₁ to C₈ alkyl, cycloalkyl or phenyl, but especially lower alkyl, are particularly preferred. As used herein lower alkyl and lower alkoxy groups are those groups containing from one to four carbon atoms and cycloalkyl groups are those groups with five or six carbon atom rings. The invention is particularly directed to compounds of the formula (I) as substantially pure compounds in particular substantially free from other 3-substituted amino-6-methyl-7- N -(alkylsubstitutedphenyl)aminofluorans. The fluoran compounds of the invention can be made by condensing e.g. with concentrated sulphuric acid, a keto-acid of the formula (II) with an amine of the formula (III): where A, R₁ and R₂ are as defined above and R′ and R″ are each hydrogen or, usually lower, alkyl. Most commonly R′ will be hydrogen and R″ will be lower alkyl, particularly methyl. The intermediate keto-acids (II) are generally known compounds in fluoran synthesis. The intermediate amines III can be synthesised by reaction of an acylated phenylamine and phenyl halide followed by deacylation of the product. Two complementary reactions can achieve the desired result: where R″, R₁ and R₂ are as defined above and R‴ is lower alkyl, particularly methyl, and X is halogen, particularly bromine. The reaction is usually carried out in the presence of alkali e.g. potassium carbonate, to remove the hydrogen halide generated and typically in the presence of a catalyst such as copper (I) iodide. The chromogenic fluoran compounds of this invention are suitable for use in pressure sensitive and thermally sensitive mark forming systems. Pressure sensitive mark forming systems provide a marking system of disposing on and/or within sheet support material unreacted mark forming components and a liquid solvent in which one or both of the mark forming components is soluble, said liquid solvent being present in such form that it is maintained isolated by a pressure rupturable barrier from at least one of the mark forming components until application of pressure causes a breach of the barrier in the area delineated by the pressure pattern. The mark forming components are thereby brought into reactive contact, producing a distinctive mark. In such pressure sensitive mark forming systems the chromogenic fluoran compounds of this invention will typically be used in combination with other chromogenic compounds which individually produce marks of diferent colours so that in combination the reaction between the chromogenic materials and the acidic colour developer material produce a mark having a black perceived image. This black mark forming system constitutes a specific, subsidiary, feature of the invention. The pressure rupturable barrier, which maintains the mark forming components in isolation, preferably comprises microcapsules containing liquid solvent solution. The microcapsules are coated on a support sheet, preferably along with protective stilt material such as uncooked starch particles as disclosed in British Patent No. 1252858. The microencapsulation process utilized to make microcapsules as referred to above can be chosen from the many known in the art. Well known methods are disclosed in U.S. patent Nos. 2800457, 304129, 3533958, 3755190, 4001140 and 4100103. Any of these and other methods are suitable for encapsulating the liquid solvent containing the chromogenic compounds of this invention. The method of marking comprises providing a chromogenic fluoran compound of the present invention and bringing such chromogenic compound into reactive contact, in areas where marking is desired, with an acidic colour developer material to produce a coloured form of the chromogenic compound. The acidic materials can be any compound within the definition of a Lewis acid i.e. an electron acceptor. These materials include clay substances such as attapulgite, bentonite and montmorillonite and treated clays such as silton clay as disclosed in U.S. Patent Nos. 3622364 and 3753761, materials such as silica gel, talc, feldspar, magnesium trisilicate, pyrophyllite, zinc sulphate, zinc sulphide, calcium sulphate, calcium citrate, calcium phosphate, calcium fluoride and barium sulphate, aromatic carboxylic acids such as salicyclic acid, derivatives or aromatic carboxylic acids and metal salts thereof as disclosed in U.S. Patent No. 4022936, acidic polymeric material such as phenol-formaldehyde polymers, phenol-acetylene polymers, maleic acid-rosin resins, partially or wholly hydrolyzed styrene-maleic anhydride copolymers and ethylenemaleic anhydride copolymers, carboxy polymethylene and wholly or partially hydrolyzed vinyl methyl ether maleic anhydride copolymers and mixtures thereof as disclosed in U.S Patent No. 3672935, biphenols as disclosed in U.S. Patent No. 3244550 and addition products of a phenol and a diolefinic alkylated or alkenylated cyclic hydrocarbon as disclosed in U.S. Patent No. 4573063. Thermally sensitive mark forming systems are well known in the art and are described in many patents, for example U.S. Patent Nos. 3539375, 3674535, 3746675, 4151748, 4181771 and 4246318. In these systems basic chromogenic material and acidic colour developer material are contained in a coating on a substrate which, when heated to a suitable temperature, melts or softens to permit said materials to react, thereby producing a coloured mark. The following Examples illustrate the invention. All parts and perecentages are by weight unless otherwise stated. Examples 1 to 3 provides an illustrative synthesis of a fluoran compound of the invention. Application Examples 1 and 2 relate to testing these compounds and comparing them with the materials made in Comparative Examples 1 to 4. Example 1 3-di- n -butylamino-6-methyl-7- N - (2,6-dimethylphenyl)aminofluoran. A mixture of 14.3 g of 3-methoxy-6-acetylaminotoluene, 17.8 g of 2-bromo- m -xylene, 6.6 g of potassium carbonate, and 0.3 g of copper (I) iodide was stirred for 42 hours at 160-210°C. After the reaction mixture was cooled, 22.9 g of potassium hydroxide and 66 ml of n -amyl alcohol were added and reacted and the amyl alcohol was removed by distillation, and the remaining reaction mixture was distilled under reduced pressure to obtain 5.5 g (28 percent of theoretical yield) of 3-methoxy-6- N -(2,6-dimethylphenyl)aminotoluene. A mixture of 8.4 g of 2-(di- n -butylamino-2-hydroxybenzoyl)benzoic acid and 23 ml of concentrated sulphuric acid was cooled in an ice bath and to this was added 5.5 g of 3-methoxy-6- N -(2,6-dimethylphenyl)aminotoluene. The resulting mixture was stirred for 19.5 hours at room temperature. The mixture was poured into 130 ml of ice water. The precipitate was filtered off, washed with water, and refluxed with 60 ml of toluene and 7.0 g of sodium hydroxide dissolved in 16 ml of water for 1.5 hours. The toluene layer was separated, washed with hot water, dried and filtered. Then the toluene was removed by coevaporation with methanol under reduced pressure. The residue was recrystallized from methanol. The product, 5.6 g (43 percent of theoretical yield) of 3-di- n -butylamino-6-methyl-7- N -(2,6-dimethylphenyl)aminofluoran, was obtained as an off-white powder having a melting point of 170-172°C. The mass spectrum, H-NMR spectrum, and infra-red spectrum of this product were consistent with the named structure. Example 2 3-di- n -butylamino-6-methyl-7- N -(2,6-diethylphenyl)aminofluoran. The title compound was prepared by the general method described in Example 1 above but substituting 2-bromo-1,3-diethylbenzene for the 2-bromo- m -xylene used in Example 1. Example 3 3-diethylamino-6-methyl-7- N -(2,6-diethylphenyl)aminofluoran. The title compound was prepared by the method described in Example 2 but using 2-(4-diethylamino-2-hydroxybenzoyl)benzoic acid as the keto acid. Comparative Examples 1 to 4 The following compounds were used as Comparative Examples: 1 3-dibutylamino-6-methyl-7- N -(diethylphenyl)aminofluoran (3-dibutylamino-6-methyl-7-(diethylanilino)fluoran) 2 3-dibutylamino-6-methyl-7- N -(2,3,5,6-tetramethylphenyl)aminofluoran 3 3-dibutylamino-6-methyl-7- N -(2,4,6-trimethylphenyl)aminofluoran 4 3-dibutylamino-6-methyl-7- N -(dimethylphenyl)aminofluoran (3-dibutylamino-6-methyl-7-(xylidino)fluoran) The compounds of the Comparative Examples were made by the general method described in Example 1 but using appropriate starting materials to obtain the desired product. The compounds of the comparative Examples were selected as representing the closest available prior art. In particular fluoran compounds having a 7- N -(substituted-phenyl)amino group, including substituents at the 2- and 6- positions, as well as elsewhere, of the phenyl ring, were chosen in comparative Examples 2 and 3 were chosen in comparative Examples 2 and 3 and commercially available technical grade diethylaniline and xylidene (believed to comprise a mixture of various respective isomers) were used as starting amines for Comparative Examples 1 and 4 to give corresponding isomeric mixtures in the products. In the tests and samples record material described below references to the compounds of Examples 1, 2 and 3 are abbreviated to "E1", E2" and "E3" and to the materials of Comparative Examples 1 to 4 to "CE1". "CE2", "CE3" and "CE4" respectively. Application Example 1 The colour formers from Examples 1 to 3 of the invention and those of Comparative Examples 1 to 4 were separately incorporated into solutions with the solvents indicated in Table 1: Each colour former solution was microencapsulated by polymerization methods utilizing initial condensates as taught in U.S. Patent No. 4100103. The resulting microcapsule dispersions were mixed with a corn starch binder and wheat starch particles, the mixture was applied as an 18% solids aqueous dispersion to a paper base using a No. 12 wire-wound coating rod and the coating was dried with hot air, producing a dried coating composition as listed in Table 2. This coated sheet is hereinafter referred to as a CB sheet. The CB sheets were tested against a sheet coated with a composition comprising acid treated dioctahedral montmorillonite as an acidic developer material (hereinafter referred to as the CF sheet). Such a developer is disclosed in U.S. Patents Nos. 3,622,364 and 3753761, which are hereby incorporated by reference. Each CB sheet was coupled, coated side to coated side with a CF sheet and each rsulting CB-CF pair was imaged in a Typewriter Intensity (TI) test. After the image was allowed to fully develop overnight, the image colour properties were measured using the Hunter Tristimulus Colorimeter. The Hunter Tristimulus Colorimeter is a direct reading L, a, b instrument. L, a, b is a surface colour scale (in which L represents lightness, a represents redness-greenness and b represents yellowness-blueness) and is related to the CIE tristimulus values, X, Y and Z, as follows: The Hunter L, a, b scale was designed to give measurements of colour units of approximate visual uniformity throughout the colour solid. Thus, "L" measures lightness and varies from 100 for perfect white to zero for black, approximately as the eye would evaluate it. The chromaticity dimensions ("A" and "b") give understandable designations of colour as follows: "a" measures redness when plus, grey when zero and greenness when minus "b" measures yellowness when plus, grey when zero and blueness when minus The above described colour scales are described fully in Hunter, R.S. "The Measurement of Appearance", John Wiley & Sons, New York, 1975. As an important advantage of the present invention is to provide a colour former which produces a grey (rather than green) image initially and/or which resists the usually occurring red shift upon light exposure of the image, the "a" chromaticity dimension was used to evaluate the above described TI images. The data following was used to evaluate the redness-greenness of the image initially and after various indicated time intervals after room light exposure of the images. The parameter used was Δ a defined by: Δa = a₁ - ao where a₁ = the measured 'a'; and a o = the 'a' value of the unimaged CF sheet (background). The results set out in Table 3 were obtained: The value of Δ aInitial is the Δ a value of the image before exposure to light and represents the greyness of the initial (unexposed) image and the value of Δ a 72 -Δ aInitial represents the magnitude of the red shift upon 72 hours room light exposure of the image. From the above data it is readily apparent that images produced by the fluoran compounds of the present invention are initially nearer to grey and/or upon room light exposure shift less to red than images produced by the reference materials. Application Example 2 To further demonstrate the unexpected properties of the fluoran compounds of the present invention, the fluoran compounds of Example 2 and Comparative Example 1 were incorporated into thermally responsive record material which was subjected to typical imaging tests. Each of the record materials was produced substantially according to the procedures of U.S. patent No. 4586061, which is hereby incorporated by reference. In manufacturing the record material, a coating composition was prepared which included a fine dispersion of the components of the colour forming sytstem, polymeric binder material, surface active agents and other additives in an aqueous coating medium. The coating composition was applied as a coated layer on a paper substrate with a No. 18 wire-wound coating rod and dried, yielding a coating weight of about 5 to 6 grams per square metre of the composition listed in Table 4. The thermally sensitive record material sheets were imaged by contacting the coated sheet with a metallic imaging block at the indicated temperature for 5 seconds. The density of each image was measured by means of a reflectance reading using a Macbeth reflectance densitometer. A reading of 0 indicates no discernable image. A value of about 0.9 or greater usually indicates good image development. The densities of the images are set out in Table 5. The background colouration of the thermally sensitive record material sheets was determined initially and after ageing the sheets for 3 days and 19 days. The background colouration was measured by means of a reflectance reading using a Bausch & Lomb Opacimeter. A reading of 92 indicates no discernable colour and the higher the value the less background colouration. The background data are set out in Table 6. The thermally responsive record material samples were imaged on a Hifax 700 Group 3 facsimile machine sold by Harris/3M Document Products, 903 Commerce Drive, Oak Brook, Illinois 60521. In this imaging test a standard test sheet was employed. The test sheet has a variety of types and densities of images. After imaging each of the examples in the Hifax equipment, the reflectance density was measured in four corresponding areas of each test sheet. The density of each image was measured by means of a reflectance reading using a Macbeth Reflectance Densitometer. The densities of the images of each sample are set out in Table 7. From the data in Tables 5, 6 and 7, it is readily apparent that thermally responsive recording materials comprising the fluoran compounds of the present invention produce substantially improved image density and/or background colouration.

Claims: A chromogenic fluoran compound of the formula: wherein R₁ and R₂ are each independently, lower alkyl; A is a group of the formula: where R₃ and R₄ are each, independently, C₁ to C₁₂ alkyl, cycloalkyl, phenyl or phenyl substituted with lower alkyl or lower alkoxy; or; A is a pyrrolidinyl, piperidino, morpholino or piperazine radical. A fluoran compound as claimed in claim 1 wherein A is -NR₃R₄, where R₃ and R₄ are as defined in claim 1 and where R₁ and R₂, each independently of the other, are methyl, ethyl or propyl. A fluoran compound as claimed in claim 2 wherein R₃ and R₄ are each, independently, C₁ to C₈ alkyl, cycloalkyl or phenyl. A fluoran compound as claimed in claim 3 where R₁ and R₂ are each, independently, methyl or ethyl; and R₃ and R₄ are each, independently, C₁ - C₈ alkyl. A fluoran compound as claimed in claim 4 wherein R₃ and R₄ are each, independently, lower alkyl. A method of marking on a substrate comprising bringing into contact at least one fluoran compound as claimed in any one of claims 1 to 5, in areas on said substrate where marking is desired, with an acidic developer material to produce marks in said areas of a coloured material formed by the action of said acidic developer material on said fluoran compound. A pressure sensitive or heat sensitive recording material comprising the fluoran compound of any one of claims 1 to 5.

Inventors: BECKER, WILLIAM J., DWYER-HALLQUIST, PATRICIA, GLANZ, KENNETH D., MILLER, ROBERT E.
Applicants: ESCO  COMPANY LIMITED PARTNERSHIP
Application year: 1988
Main classification: B41M5
IPC codes: B41M5, C09B11, C07D493, C07D311