US3540914A

US3540914A - Pressure sensitive record sheets employing indole substituted pyromellitides

Info

Publication number: US3540914A
Application number: US821540*A
Authority: US
Inventors: Chao-Han Lin
Original assignee: NCR Corp
Current assignee: Appvion LLC; NCR Voyix Corp; National Cash Register Co
Priority date: 1967-01-30
Filing date: 1969-01-24
Publication date: 1970-11-17
Anticipated expiration: 1987-11-17
Also published as: FR1554989A; US3491117A; GB1161651A

Description

1910 CHAD-HAN LIN 3,540,914

PRESSURE SENSITIVE RECORD SHEETS EMPLOYING INDOLE SUBSTITUTED PYROMELLITIDES Original Filed Jan. 30, 1967 FIG. I

BASE-SHEET OF RECORD MATERIAL COATED ON THE REAR WITH MINUTE PRESSURE-RUPTURABLE CAPSULES CONTAINING LIQUID SOLUTION OF CHROMOGENIC MATERIAL DEVELOPABLE ON CONTACT WITH AN ELECTRON ACCEPTING MATERIAL OF THE LEWIS- ACID TYPE TO COLORED FORM RECEIVING SURFACE OF UNDERSHEET COATED WITH 2: DEL1E$;EONACCEPTING MATERIAL OF THE LEWIS- FIG. 2

nun-union;fi aggggggggggg INVENTOR CHAO-I-IAN LIN United States Patent 3,540,914 PRESSURE SENSITIVE RECORD SHEETS EMPLOYING INDOLE SUBSTITUTED PYROMELLITIDES Chao-Han Lin, Dayton, Ohio, assignor to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Original application Jan. 30, 1967, Ser. No. 612,497, now Patent No. 3,491,117, dated Jan. 20, 1970. Divided and this application Jan. 24, 1969, Ser. No. 821,540

Int. Cl. B41m /22 US. Cl. 11736.2 29 Claims ABSTRACT OF THE DISCLOSURE Pressure sensitive record unit and method of marking employing chromogenic material of normally colorless form having structural formulae:

CIS CONFIGURATION 0 R1 R2 II 5 4 3 0/ 1y \0 TRANS CONFIGURATION where R R R and R consist of substituted and unsubstituted indolyl radicals and dialkylaminophenyl radi cals such that at least two indolyl radicals are present in a cis relationship in compounds having a cis configura tion and in a trans relationship in compounds having a trans configuration; said material assuming a colored form upon contact with a Lewis acid molecule. Examples of these novel compounds include 3,5-bis(p-diethylaminophenyl) 3 ,5 -bis( 1,2-dimethylindol-3-yl pyromellitide and 3 ,7-bis(1,2-dimethylindol-3 -yl) pyromellitide.

This is a division of application Ser. No. 612,479 filed Jan. 30, 1967, now US. Pat. No. 3,491,117.

This invention pertains to novel chromogenic compounds for use in pressure sensitive record material and to an improved mark-forming manifold system incorporating these novel chromogenic compounds. More specifically, this invention pertains to indolyl derivatives of pyromellitic acid which have the form of substantially colorless, i.e. white or slightly colored solids, or approach being colorless when in liquid solution, but which may be converted to dark-colored forms upon reactive contact with acidic material. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by eliecting localized reactive contact between the chromogenic material and the acidic material on or in such a web or sheet, such material being brought thereto by transfer, or originally there in situ, the desired reactive contact forming dark-colored materials in the intended image areas.

Pressure-sensitive, mark-forming systems of the prior art include that disclosed in application for Letters Patent No. 392,404, filed Aug. 27, 1964, by Robert E.

3,540,914 Patented Nov. 17, 1970 Miller and Paul S. Phillips, Jr., now abandoned. The latter application provides a marking system of disposing on and/or within sheet support material the unreacted mark-forming components (at least one of which is a polymeric material) and a liquid solvent in which each 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 the application of pressure causes a breach or rupture of the barrier in the area delineated by the pressure pattern. The markforming components thereby are brought into reactive contact, producing a distinctive mark.

It is an object of this invention to provide new and improved substances having chromogenic properties which may be incorporated in a web or coated onto the surface of a web to provide a novel manitolding unit, and which are useful in carrying out improved methods of marking involving reactive contact with a color-acti vating material to develop dark-colored materials in areas where marking is desired.

It is another object of this invention to provide modified compounds, based upon the cis and trans-bis and tetrakis dimethylindolyl pyromellitides, which are substantially colorless, or slightly colored, oliering a new and improved variety of chromogenic characteristics, and developing novel dark-colored substances upon contact with color-activating materials.

It is a further object of this invention to provide a new and improved mark-forming system which has the form of disposing within a web or upon the surface of a web or sheet support material unreacted chromogenic material which is capable of being reactively contacted with an acidic material to produce a dark-colored substance, thus providing marks having desirable color intensity and hue.

In accordance with this invention, there is provided a novel substantially colorless or slightly colored chromogenic compound having the structural formula:

CIS CONFIGURATION t w C C TRANS-CONFIGURATION where R R R and R consist of substituted and unsubstituted indolyl radicals and dialkylaminophenyl radicals such that at least two indolyl radicals are present in a cis relationship in compounds having a cis configuration and in a trans relationship in compounds having a trans configuration.

Examples of the novel compounds of this invention include:

cis-3,5-bis-(p-diethylaminophenyl) 3,5 bis (1,2-dimethylindol-3-yl)-pyromellitide having the structural formula:

Trans 3,7 bis (p-diethylaminophenyl)-3,7-bis-(1,2- dimethylindol-3-yl)-pyromellitide having the structural formula:

Trans 3,3,7,7 tetrakis (1,2 dimethylindol 3-yl)- pyromellitide Cis 3,3,5,5 tetrakis (1,2-dimethylindol 3 yl)- pyromellitide O CHz-N N-CHa CH3 L CH:

U O n /5\ a 3 CHa O6\ /20 CHa 3 7 1 (3H 2 p CH3 In accordance with another feature of this invention, a new composition of matter comprises the dark-colored substance having a resonant form developed by contact of a color-activating material with one of the above-mentioned chromogenic compounds. The color-developing or -activating material is an acidic substance for converting the chromogenic compound to the resonant form.

The method of marking of this invention, i.e., by desveloping a dark-colored material from substantially colorless or slightly colored chromogenic compounds comprises providing a chromogenic compound selected from among the above-mentioned compounds and bringing such chromogenic compound into reactive contact in areas where marketing is desired with an acidic coloractivating substance to produce a dark-colored resonant form of the chromogenic compound by the action thereon in said areas of the said acidic substance.

The acidic materials employed in this invention can be any compound within the definition of a Lewis acid, i.e., an electron acceptor. Preferably, acidic organic polymers such as phenolic polymers are employed as the acidic material. The novel chromogenic materials exhibit the advantage of improved color stability when reacted with such phenolic polymers. The solution formation of the solid particles of polymeric material in the same solvent with the substantially colorless chromogenic compounds allows penetration of the color into the support sheet, if .porous, e.g., paper, so that the colored form of the chromogenic material sinks into the body of the sheet and is not merely on the surface of the sheet. This feature protects against erasure of recorded data by attrition of the surface of the record sheet.

Reference is to be taken to the drawings. FIG. 1 is a diagrammatic representation of a two-sheet unit manifold, a perspective in which the bottom surface of the overlying is supplied on the surface or near it with a multiplicity of minute pressure-rupturable microcapsules, each containing a droplet. Each droplet contains a solution of the basic chromogenic component. An acidic component, such as an acid clay or a phenolic polymeric material lies within the lower web or sheet or upon the upper surface of the lower web or sheet. A colored mark is made by the use of a stylus, a type character, or other pressurewriting means applied to the two-sheet unit manifold.

The encapsulated droplets are released on the rupture of the capsules in writing operations, as shown in FIG. 2. The liquid of the released droplets is transferred in the pattern of the data configuration to the top of the underlying sheet. The top of the underlying sheet is coated or impregnated with a material reactant with the chromogenie material, e.g., a phenolic polymer material having an acid-reacting OH group. The drawings show capsules on the over sheet containing a liquid solution of chromogenic material. However, the capsules can contain the polymeric phenolic material in liquid solution and the top surface of the under-sheet may be supplied with the chromogenic material in particulate form. The improvement in the system is the chromogenic compound which is the novel substance of the instant invention.

Referring again to FIG. 1 comprising an upper web or sheet having the chromogenic material dispersed with in or upon in a contiguous juxtaposition, it is possible to incorporate the chromogenic material in a solid, crystalline-state in a binder material so that the chromogenic material may be transferred from the upper web or sheet upon the application of pressure from a stylus to deposit some of the chromogenic material on a surface carrying a color-activating polymeric material. Preferably, the chromogenic substance is dissolved in a solvent and minute droplets of the solution of the chromogenic material are encapsulated in minute, pressure-rupturable capsules. Obviously, many other arrangements, configurations and relationships of the solvent and the mark-forming materials, with respect to their encapsulation and location on the supporting sheet or webs can be envisioned. Such arrangements are thoroughly described in the aforementioned application S.N. 392,404 to Miller et al., and need not be repeated herein.

It is noted that the polymeric mark-forming components should have a common solubility with the chromogenic material in at least one liquid solvent when the acid-reacting material is a phenolic or other organic acidic polymer.

It is also noted that in a single system several chromogenic materials may be used with the same or different polymeric materials. Several polymeric materials can be reactively contacted with a single chromogenic compound or with a mixture of chromogenic compounds.

As mentioned above, the solvent is maintained in physical isolation in minute droplets until such time as it is released by application of pressure. This may be accomplished by several known techniques, but preferably isolation is maintained by individual encapsulation of the solvent droplets in a microcapsule according to the procedures described, for example, in US. Pat. No. 2,712,507, issued to Barrett K. Green on July 5, 1955; 2,730,457, issued to Barrett K. Green and Lowell Schleicher on Jan. 10, 1956; 2,800,457, issued to Barrett K. Green and Lowell Schleicher on July 23, 1957; and 2,800,458, issued to Barrett K. Green on July 23, 1957, reissued as Reissue Pat. No. 24,899 on Nov. 29, 1960. The microscopic capsules, when disposed within or upon a supporting web as a multiplicity in contiguous juxtaposition, are rupturable by pressure, such as normal marking pressures utilized, for example, in writing or typing operating.

The material or materials chosen as the wall material of the microcap sule, in addition to being pressure rupturable, must be inert with respect to the contents of the capsule and the other mark-forming components so that the wall material remains intact under normal storage conditions until such time as it is released by the application of marking pressure. Examples of such wall materials are gelatin, gum arabic and many others thoroughly described in the aforementioned patents.

For use in record material, the capsule size should not exceed 50 microns in diameter. Preferably, the capsules should be smaller than microns in diameter.

The acidic organic polymeric material useful in this invention include phenolic polymers, phenol acetylene polymers, maleic acid-rosin resins, partially or wholly hydrolyzed styrene-maleic anhydride copolymers and ethylene-maleic anhydride copolymers, carboxy polymethylene and wholly or partially hydrolyzed vinyl methyl ether maleic anhydride copolymer and mixtures thereof;

Phenolic polymers found useful include alkylphenol acetylene resins, which are soluble in common organic solvents and possess permanent fusibility in the absence of being treated by cross-linking materials. A specific group of useful phenolic polymers are members of the type commonly referred to as novolacs (as sold by Union Carbide Corp., New York, N.Y.), which are characterized by solubility in common organic solvents and which are,

in the absence of cross-linking agents, permanently fusible. Generally, the phenolic polymer material found useful in practicing this invention is characterized by the presence of free hydroxyl groups and the absence of groups such as methylol, which tend to promote infusibility or cross-linking of the polymer, and by their solubility in organic solvents and relative insolubility in aqueous media. Again, obviously, mixtures of acidic materials can be employed.

Resoles, if they are soluble, may be used, though subject to change in properties upon aging.

A laboratory method useful in the selection of suitable phenolic resins is the determination of the infra-red absorption pattern. It has been found that phenolic resins showing an absorption in the 3200-3500 cmregion (which is indicative of the free hydroxyl groups) and not having an absorption in the 1600-1700 cm.- region are suitable. The latter absorption region is indicative of the desensitization of the hydroxyl groups and, consequently, makes such groups unavailable for reaction with the chromogenic materials.

The preparation of the phenolic formaldehyde polymeric materials for practicing this invention is described in Industrial and Engineering Chemistry, volume 43, pages 134 to 141, January 1951, and a particular poly- 6 mer thereof is described in Example 1 of US. Pat. No. 2,052,093, issued to Herbert Honel on Aug. 25, 1936, and the preparation of the phenol-acetylene polymers is described in Industrial and Engineering Chemistry, vol. 41, pages 73 to 77, January 1949.

The preparation of the maleic anhydride copolymers is described in the literature, such as, for example, one of the maleic anhydride vinyl copolymers, as disclosed in the publication, Vinyl and Related Polymers, by Calvin E. Schildknecht, second printing, published April 1959, by John Wiley & Sons, Incorporated. See pages 65 to 68 (styrene-maleic anhydride copolymer), 628 to 630 (vinyl methyl ether-maleic anhydride copolymer), and 530 to 531 (ethylene-maleic anhydride copolymer).

When the acidic material is one of the aforementioned organic polymers, the liquid solvent chosen must be capable of dissolving the mark-forming components. The solvent may be volatile or non-volatile, and a single or multiple component solvent may be used which is wholly or partially volatile. Examples of volatile solvents useful in the afore-described basic chromogen-acidic polymer are toluene, petroleum distillate, perchloroethylene, and xylene. Examples of non-volatile solvents are high-boiling point petroleum fractions and chlorinated biphenyls.

Generally, the solvent chosen should be capable of dis solving at least 0.3%, on a weight basis, of the chromogenic material, and about a 3-5%, on a weight basis, of the polymeric material to form an efficient reaction. However, in the preferred system, the solvent should be capable of dissolving an excess of the polymeric material, so as to provide every oportunity for utilization of the chromogenic material and, thus, to assure the maximum coloration at a reaction site.

A further criterion of the solvent is that it must not interfere with the mark-forming reaction. In some instances, the presence of the solvent may interfere with the mark-forming reaction or diminish the intensity of the mark, in which case the solvent chosen should be sufficiently vaporizable to assure its removal from the reaction site after having, through solution, brought the markforming components into intimate admixture, so that the mark-forming contact proceeds.

Since the mark-forming reaction requires an intimate mixture of the components to be brought about through solution of said components, one or more of the markforming components may be dissolved in the isolated solvent droplets, the only requirement being that at least one of the components essential to the mark-forming reaction be maintained isolated until reactively contacted with the other.

In the usual case, the mark-forming components are so chosen as to produce a mark upon application of pressure at room temperature (20 to 25 degrees contigrade). However, the present invention includes a system in which the solvent component is not liquid at temperatures around room temperature but is liquid and in condition for forming solutions only at elevated temperatures.

The support member on which the components of the system are disposed may comprise a single or dual sheet assembly. In the case where all components are disposed on a single sheet, the record material is referred to as a self-contained system. Where there must be a migration of the solvent, with or without mark-forming component, from one sheet to another, the record material is referred to as a transfer system. (Such a system may also be referred to as a two-fold system, in that at least two sheets are required and each sheet includes a component, or components, essential to the mark-forming reaction.) Where a copious amount of the colored reaction product in liquid form is produced on a surface of one sheet, it may produce a mark by transfer to a second sheet as a colored mark.

In the preferred case, where microcapsules are employed, they may be present in the support material either disposed therethroughout or as a coating thereon,

or both. The capsules may be applied to the sheet material while still dispersed in the liquid vehicle in which they were manufactured, or, if desired, separated and the separated capsules thereafter dispersed in a solution of the polymeric component (for instance, 30 grams of water and 53 grams of a l aqueous solution of polyvinyl methyl ether maleic anhydride) to form a coating composition in which, because of the inertness of the solution and the capsules, both retain their identity and physical integrity. When this composition is disposed as a film on the support material and dried, the capsules are held therein subject to rupture to release the liquid contained. This latter technique, relying on the inertness of the microcapsule and the dispersing medium of the film-forming mark-forming component, allows for a method of preparing a sensitive record coating with the capsules interspersed directly in a dry film of the polymeric material as it is laid down from the solution. A further alternative is to disperse in a liquid medium one or more mark-forming components, insoluble therein, and disperse in said medium the insoluble micfocapsules, with the result that all components of the mark-forming system may be disposed on or within the support sheet in the one operation. Obviously, the several components may be applied individually.

The respective amounts of the several components will vary, depending primarily upon the nature of the materials and the architecture of the record material unit. Suitable lower amounts include, in the case of the chromogenic material, about .005 to .075 pound per ream (a ream in this application meaning five hundred (500) sheets of 25" x 38" paper, totaling 3,300 square feet); in the case of the solvent, about 1 to 3 pounds per ream; and in the case of the polymer, about /2 pound per ream. In all instances, the upper limit is primarily a matter of economic consideration.

In the instance where the mark-forming components are interspersed throughout a single support sheet material (so-called self-contained unit), the following technique or procedure has been found useful:

The slurry of capsules may be applied to a wet web of paper as it exists on the screen of a Fourdrinier paper machine, so as to sink into the paper web a distance depending on the freeness of the pulp and the Water content of the web at the point of application.

The capsules may be placed directly in the paper or in a support sheet. Not only capsule structures, but films which hold a multitude of droplets for local release in an area subject to pressure are included. (See US. Pat. No. 2,299,694 which issued Oct. 20, 1942, to B. K. Green.)

With respect to the acidic organic polymeric component, a solution thereof in an evaporable solvent is introduced into twice as much water and agitated while the evaporable solvent is blown off by an air blast. This leaves an aqueous colloidal dispersion slurry of the polymeric material, which may be applied to the paper so as to leave a surface residue, or the slurry may be applied to paper at the size-press station of a paper-making machine by roller. In another method of making a polymersensitized sheet, the water-insoluble polymer is ground to the desired particle size in a ball mill with water, preferably With a dispersing agent, such as a small quantity of sodium silicate. If a binder material of hydrophilic properties is ground with the phenolic material, the binder itself may act as a dispersant. If desired, an amount of binder material of up to 40%, by weight, of the employed amount of the polymeric material may be added to the ball-milled slurry of materials, such binder materials being of the paper coating binder class, including gum arabic, casein, hydroxyethylcellulose, and latex (such as styrenebutadiene copolymer). If desired, oil absorbents in the form of fullers earths may be added to the polymeric material particles to assist in retaining, in situ, the liquid droplets to be transferred to it in data-representing configuration, for the purpose of preventing bleeding of the print.

Another way of applying the chromogenic or polymeric material individually to a single sheet of paper is by immersing a sheet of paper in a 1% to 10% solution of the material in an evaporable solvent. Obviously, this must be done alone for each reactant, because if the other reactant material were present, it would result in a premature coloration over the sheet area. A dried sheet with one component then may be coated with a solution of the other component, the solvent of which is a non-solvent to the already supplied component.

The polymeric material may be dissolved in ink composition vehicles to form a printing ink of colorless character and, thus, may be used to spot-print a proposed record sheet unit sensitized for recording in a reactionproduced color in those areas by application of a solution of the chromogenic material.

In the case of phenolic polymer, a printing ink may be made of up to 75% weight, of the phenolic polymeric material in a petroleum solvent to a viscosity suitable for printing purposes. The relative amounts of components to be used are the most convenient and economical amounts consistent with proper visibility of the recorded data. The resolution of the recorded data is, among other things, dependent on particle size, distribution and amount of particles, liquid solvent migration, chemical reaction elfciency, and other factors, all of which are things that may be worked out empirically by one familiar with the art, and which do not determine the principle of the invention, which, in part, involves means of enabling the bringing into solution, by marking pressure, of two normally solid components in a common liquid solvent component held isolated as liquid droplets, preferably in marking-pressure-rupturable capsules having film walls, or else held isolated in a continuous marking-pressurerupturable film as a discontinuous phase.

In the base-acid color system of this invention the acidic mark-forming component(s) reacts with the basic chromogenic material(s) to effect distinctive color formation or color change. In a multi-sheet system in which an acidic organic polymer is employed, it is desirable to include other materials to supplement the reactants. For example, kaolin can be added to improve the transfer of the liquid and/or the dissolved materials between the sheets. In addition, other materials such as bentonite, attapulgite, talc, feldspar, halloysite, magnesium trisilicate, silica gel, pyrophyllite, zinc sulfate, zinc sulfide, calcium sulfate, calcium citrate, calcium phosphate, calcium fluoride, barium sulfate and tannic acid can be included.

Various methods known to the prior art and disclosed in the aforementioned application S.N. 392,404 to Miller et al. and United States patent application S.N. 420,193 to Phillips et al. can be employed in coating compositions of the mark-forming materials into their supporting sheets. An example of the compositions which can be coated onto the surface of an underlying sheet of a twosheet system to react with the capsule coating on the underside of an overlying sheet is as follows:

Coating composition: Percent by weight EXAMPLE I Preparation of bis-(diethylaminophenyl) -(l,2-dimethylindol-3-yl) pyromellitide 9.0 grams of N,N-diethylaniline, milliliters of benzene, and 5.5 grams of pyromellitic dianhydride were stirred under ice-cooling. 16.0 grams of aluminum chloride were slowly added. Stirring was continued for one hour under ice-cooling, and at a temperature of 35 C. to 42 C. for two hours. A complex formed in the reaction vessel. 100 milliliters of 3 normal hydrochloric acid was added to decompose the complex. A solid precipitated out of solution and a benzene layer formed in the reaction mixture; both were separated from the solution. The solution pH was adjusted to 2.7 by the addition of ammonium hydroxide to precipitate a yellow solid exhibiting a weight of 6.9 grams. The crude product was a mixture of two isomeric ketoacids having the following structures:

2.6 grams of the product prepared above, 1.45 grams of 1,2-dimethylindole, and 20 milliliters of acetic anhydride were heated in a 50 milliliter beaker on a hot plate. A solution was formed, but a solid precipitated out of solution after 5 minutes. The filtrate was set aside for use in the procedure delineated in Example II.

' The precipitate was dissolved in 120 milliliters of benzene and then concentrated to 25 milliliters whereupon a yellow solid exhibiting a weight of 0.4 gram precipitated out of solution. The solid was further purified by repeatedly dissolving said solid in benzene, concentrating the solution, and precipitation with petroleum ether to obtain one of the isomers of bis-(p-diethylaminophenyl)- bis-(1,2-dimethylindol-3-yl) pyromellitide exhibiting a melting point of above 300 C. A benzene solution of the product turned blue when contacted with attapulgite clay coated on paper and a bluish green when contacted with a phenolic polymer coated on paper.

EXAMPLE II Preparation of the second isomer of bis- (p-diethylaminophenyl) -bis- 1,2-dimethylindol-3-yl) pyromellitide The filtrate from the procedure of Example I and the washings of the precipitate of Example I were combined and heated for minutes to slightly less than the boiling point of the solution. The filtrate was then poured into 100 milliliters of water, ammonium hydroxide was added to adjust the alkalinity, and the mixture stirred for 30 minutes. A precipitate formed. The precipitate was sequentially purified by precipitation from a benzene solution with petroleum ether to yield the second isomer of bis-(p-diethylaminophenyl) bis (1,2-dimethylindol-3- yl) pyromellitide which exhibited a melting point range of 255257 C. A benzene solution of the product turned blue both when contacted with attapulgite clay coated on paper and with a phenolic polymer coated on paper.

EXAMPLE III Preparation of tetrakis-(1,2-dimethylindol-3-yl) pyromellitide 3.2 grams of pyromellitic dianhydride, 5.0 grams of 1,2-dimethylindole, and 40 milliliters of benzene were stirred under ice-cooling. 4.4 grams of aluminum chloride was slowly added to the reaction mixture. After 10 minutes of stirring, the ice-bath was replaced with a water bath and the temperature of the water bath was raised to 52 C. After an additional 30 minutes of stirring, 2.5 milliliters of acetic anhydride was added. Stirring at 52 C. to 60 C. was continued for another 30 minutes time increment. 100 milliliters of 3 normal hydrochloric acid was added and the reaction mixture was heated. A solid which had formed was collected, washed with water, and treated with dilute ammonium hydroxide and filtered.

The solution was treated with activated charcoal, whereupon the solution appeared to be a red color. Upon acidification of the red solution a purple solid exhibiting a weight of 2.6 grams precipitated out of solution. The crude product was a mxiture of two isomeric acids having the following structures:

CH3 CH3 1.0 gram of the purple solid, 0.8 gram of 1,2-dimethylindole, and acetic anhydride were heated for 20 minutes. The reaction mixture was diluted with water and made alkaline with ammonium hydroxide, whereupon a solid product, one of the isomers of tetrakis-(1,2-dimethylindol 3-yl) pyromellitide, exhibiting a weight of 1.4 grams precipitated out of solution. A benzene solution of the product turned purple when contacted with attapulgite clay coated on paper and purple with a phenolic polymer coated on paper.

What we claim is:

1. A pressure sensitive record unit comprising:

:(a) support web or sheet material,

(b) mark-forming components and a pressure-releasable liquid solvent for said mark-forming components arranged in contiguous juxtaposition and supported by said sheet material,

(c) said mark-forming components comprising at least one chromogenic compound selected from the group consisting of:

and mixtures thereof, where R R R and R consist of 1,2-dialkylindol-3-yl and p-dialkylaminophenyl, wherein alkyl has less than 5 carbon atoms such that at least two indolyl radicals are present in a cis relationship in compounds having a cis configuration and in a trans relationship in compounds having a trans configuration; and an electron-accepting material of the Lewis acid type reactive with said chromogenic material to produce a mark; which components upon pressure-release of the liquid solvent are brought into reactive contact in the released solvent.

2. The record unit of claim 1 wherein at least one of the mark-forming components is maintained in isolation from the other mark-forming components prior to the release of the solvent.

3. The record unit of claim 1 wherein the liquid solvent is present as the nucleus of a microcapsule.

4. The record unit of claim 1 wherein the chromogenic material is dissolved in the isolated liquid solvent prior to pressure release.

5. The record unit of claim 1 wherein the mark-forming components and the isolated liquid solvent are present in a single support sheet.

6. The record unit of claim 1 wherein at least one member selected from the group consisting of the mark-forming components and the liquid solvent is present in a support sheet other than the support sheet having the remaining members of the group.

7. The record sheet material of claim 1 where the electron-accepting material of the Lewis acid type comprises a clay.

8. The record sheet material of claim 1 where the electron-accepting material of the Lewis acid type comprises an organic'polymer.

9. The record sheet material of claim 1 where the electron-accepting material of the Lewis acid type comprises a phenolic polymer.

10. The record sheet material of claim 1 where the chromogenic compound comprises 3,5-bis-(p-diethylaminophenyl -.3 ,5 -bis- 1 ,2-dimethylindol-3-yl) pyromellitide.

11. The record sheet material of claim 1 where the chromogenic compound comprises 3,7-bis-(p-diethylaminophenyl 3,7-bis-(1,2-dimethylindoh3-yl) pyromellitide.

12. The record sheet material of claim 1 where the chromogenic compound comprises 3,3,7,7-tetrakis-(1,2-dimethylindol-3-yl) pyromellitide.

13. The record sheet material of claim 1 where the chromogenic compound comprises 3,3,5,5-tetrakis-(l,2- dimethylindol-3-yl) pyromellitide.

14. A mark-forming record sheet system comprising: A first web or sheet having on one surface a transfer coating which contains as a finely dispersed phase a plurality of minute, pressure-rupturable, capsules containing as an inner phase a solvent vehicle; a second web or sheet having an adherent coating upon its surface or dispersed within said web or sheet, said first and second webs or sheets being maintained disposed together in face-to-face relationship with said respective transfer and adherent coatings in contiguity with each other; a first coating constituent in the form of a substantially colorless or slightly colored chromogenic material which includes a chromogenic compound selected from the group consisting of and mixtures thereof, where R R R and R consist of 1,2-dialkylindol-3-yl and p-dialkylaminophenyl, wherein alkyl has less than 5 carbon atoms such that at least two indolyl radicals are present in a cis relationship in compounds having a cis configuration and in a trans relationship in compounds having a trans configuration; and a second constituent in the form of an electron-accepting material of the Lewis acid type; one of said constituents being dissolved in said solvent liquid vehicle present as the inner phase of the plurality of minute pressure-rupturable capsules in the transfer coating on or within said first web or sheet, and the other of said coating constituents being bonded to said second web in said adherent coating thereon but being accessible to other materials coming into contact with portions of the adherent coating, where by upon local impact and rupture of said capsules, releasing said liquid vehicle containing one coating constituent from at least some of the capsules onto said contiguous adherent coating, reactive contact is effected between said two constituents to produce a dark-colored material by the action of said electron-accepting material of the Lewis acid type upon said chromogenic material to effect color change in said chromogenic compound to said colored form.

15. The mark-forming record sheet of claim 14 in which the electron-accepting material of the Lewis acid type comprises a clay.

16. The mark-forming record sheet of claim 14 in which the electron-accepting material of the Lewis acid type comprises an organic polymer.

17. The mark-forming record sheet of claim 14 in which the electron-accepting member of the Lewis acid type comprises a phenolic polymer.

18. The mark-forming record sheet of claim 14 in which the chromogenic material includes the compound 3,5- bis-(p-diethylaminophenyl) 3,5-bis-(1,2-dimethylindol-3-yl) pyromellitide.

19. The mark-forming record sheet of claim 14 in which the chromogenic material includes the compound 3,7-bis-(p-diethylaminophenyl) 3,7-bis (1,2-dimethylindol-3-yl) pyromellitide.

20. The mark-forming record sheet of claim 14 in which the chromogenic material includes the compound 3,3,7,7-tetrakis-(1,2-dimethylindol-3-yl) pyromellitide.

21. The mark-forming record sheet of claim 14 in which the chromogenic material includes the compound 3,3,5 ,5 -tetrakis-( 1,2-dimethylindol-3-yl) pyromellitide.

22. The method of marking on a substrate by developing dark-colored materials from chromogenic compounds comprising: providing as at least one substituent a colorless or slightly colored chromogenic compound selected from the group consisting of C l O O and mixtures thereof, where R R R and R consist of 1,2-dialkylindol-3-yl and p-dialkylaminophenyl, wherein alkyl has less than 5 carbon atoms such that at least two indolyl radicals are present in a cis relationship in the compound having a cis configuration and in a trans relationship in a compound having a trans configuration; and bringing said chromogenic compound into contact, in areas on said substrate sheet where marking is desired, with an electron-accepting material of the Lewis acid type to produce marks in said areas of a dark-colored material formed by the action of said electron-accepting material on said chromogenic compound.

23. The method of claim 22 in which the electronaccepting material of the Lewis acid type is a clay.

24. The method of claim 22 in which the electronaccepting material of the Lewis acid type is an organic polymer.

25. The method of claim 22 in which the electron- References Cited Izigiepting material of the Lewis acid type is a phenolic UNITED STATES PATENTS ymer.

26. The method of claim 22 in which at least one chro- 2,505,486 1950 mogenic compound is 3,5-bis-(p-diethylaminophenyl)-3,5- 5 3,244,549 4/ 1966 Farnham t a1. bis-(1,2-dimethylindol-3-yl) pyromellitide, 3,268,537 8/ 966 G l at al- 27. The method of claim 22 in which at least one chro- 3,336,337 1967 GQ ue mogenic compound is 3,7-bis-(p-diethylaminophenyl)-3,7- 3,455,721 7/ 1969 h p et bis-(1,2-dimethylindol-3-yl) pyromellitide. 3,491,117 1/ 1970 L111- 28. The method of claim 22 in which at least one chro- 10 Y mogenic compound is 3,3,7,7 tetrakis-(1,2-dimethylindol- MURRAY KATZ Pnmary Exammer 3-yl) pyromellitide.

29. The method of claim 22 in which at least one chromogenic compound is 3,3,5,5-tetrakis-(1,2-dimethylindol- 117 -36.2, 36.8, 155 3-y1) pyromellitide. 15