US3667943A

US3667943A - Quinacridone pigments in electrophotographic imaging

Info

Publication number: US3667943A
Application number: US754726A
Authority: US
Inventors: Lester Weinberger
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1968-08-22
Filing date: 1968-08-22
Publication date: 1972-06-06
Anticipated expiration: 1989-06-06
Also published as: BE737810A; GB1278702A; DE1942700A1; ES370720A1; BR6909996D0; FR2016183A1; NL6912733A; CH519183A; PL80390B1

Abstract

AN ELECTROPHOTOGRAPHIC PLATE INCLUDING A PHOTOCONDUCTIVE LAYER COMPRISING A NOVEL QUINACRIDONE PIGMENT IN A BINDER MATERIAL, SAID QUINACRIDONE PIGMENT HAVING THE FORMULA:

2,9-DI(R),3,10-BIS((2-R''-PHENYL)-CO-NH-CH2-)-5,7,12,14-

TETRAHYDRO-QUINO(2,3-B)ACRIDINE-7,14-DIONE

WHEREIN R=CH3, C2H5,OCH3, OCH2H5 OR A HALOGEN AND WHEREIN R''=AN AROMATIC, HETEROCYCLIC, ALICYCLIC OR ALIPHATIC GROUP IS DISCLOSED. METHODS OF PREPARING SAID PLATE AND OF USING SAID PLATE IN ELECTROPHOTOGRAPHIC PROCESSES ARE ALSO DISCLOSED.

Description

w States Patentfimce 3,667,943

Patented June 6, 1972 tive. For this reason, selenium has been the most commer- Q MRWE 1N a; as; assassinate Y PHOTOGRAPHIC IMAGING Lester Weinberge'r, Penfield N.Y., assignor to Xerox aspects from l l hmltanons m h Its Spectral Corporation Rochester, response is somewhat limited to the ultra-violet, blue and No Drawing. Filed Aug. 22, 1968, Ser. No. 754,726 green regwns of the spectrum and the p p o of Int. Cl, G03 5/06 vitreous selenium plates requires costly and complex pro- U.S. Cl. 96-1 PC 6 Claims cedures, such as vacuum evaporation. Also, vitreous selenium layers are only metastable in that they are readily 10 recrystallized into inoperative crystalline forms at tem- ABSTRACT OF THE DISCLOSURE peratures only slightly in excess of those prevailing in con An electrophotographic plate including a photoconducventional electrophotographic copying machines. Further, tive layer comprising a novel quinacridone pigment in a selenium plates require the use of a separate conductive binder material, said quinacridone pigment having the substrate layer, preferably with an additional barrier layer formula; deposited thereon before deposition of the selenium photo- H H O o g N\ orrzNnb dNHoH 0 O I '7 g 2 R I N R -NH yo H J v C-NH-R' wherein R=OH C H ,OCH OC H or a halogen and conductor. Because of these economic and commercial .wherein R'=an aromatic, heterocyclic, alicyclic or aliconsiderations, there have been many recent efforts tophatic group is disclosed. Methods of preparing said plate ward developing photoconductive insulating materials and of using said plate in electrophotographic processes other than selenium for use in electrophotographic plates. are also disclosed. It has been proposed that various two-component materials be used in photoconductive insulating layers used in electrophotographic plates. These consist of a photo- BACKGROUND- OF THE INVENTION v conductive insulating material in particulate form dispersed This invention relates, in general, to electrophotography in an insulating binder. Where the particles consist of a and, more specifically, to a binder plate usable in electrophotoconductive material comprising inorganic crystalline photography. compounds containing a metallic ion, satisfactory photo- It is known that images may be formed and developed graphic speed and spectral response for use in xerographic on the surface of certain photoconductive insulating maplates are obtained. However, these plates even when dyeterials by electrostatic means. The basic electrophotosensitized generally have sensitivities much lower than selegraphic process, as taught by Carlson in US. Pat. 2,297,- nium. These plates are generally considered to be non-re- 691, involves uniformly charging a photoconductive inusable since it is necessary to use such high percentages sulating layer and then exposing said layer to a light-andof photoconductive pigment in order to attain adequate shadow image which dissipates the charge on the portions sensitivity that it is diflicult to obtain smooth surfaces of the layer which are exposed to light. The electrostatic which lend themselves to efficient toner transfer and sublatent image formed on the layer corresponds to the consequent cleaning prior to reuse. An additional drawback in figuration of the light-and-shadow image. Alternatively, a the use of inorganic pigment-binder type plates is that latent electrostatic image may be formed on the plate by they can be charged only by negative and not by positive charging said plate in image configuration. This image is corona discharge. This property makes them commercially rendered visible by depositing onthe imaged layer a finely undesirable since negative corona discharge generates divided developing material comprising a colorant called much moreozone than positive corona discharge and is a toner and a toner carrier. The powdered developing magenerally more difficult to control. terial will normally be attracted to those portions of the 1 It has been further demonstrated that organic photolayer which retain a charge, thereby forming a powder conductive dyes and a wide variety of polycyclic comimage corresponding to the latent electrostatic image. pounds maybe used together with suitable resin materials Where the base sheet is relatively inexpensive, such as to form photoconductive insulating layers useful in binderpaper, the powder image may be fixed. directly to the plate type plates. These plates generally lack sensitivity levels as by heat orsolventfusing. Alternatively, the powder necessary for use in conventional electrophotographic image may betransferred to a sheet of receiving material, copying devices. In addition, these plates lack abrasion such as paper, and fixed thereon. The above general procresistance and stability of operation, particularly at eleess is also described in US. Pats. 2,357,809; 2,891,011; .vated temperatures.

and 3,079,342. In anothertype plate, inherently photoconductive poly- The photoconductive insulating layer to be elfective mers are used frequently in combination with sensitizing must be capable of holding an electrostatic charge in the dyes or Lewis acids, to form photoconductive insulating dark and dissipating the charge to a conductive substrate layers. These polymeric organic photoconductor plates when exposed to light. That variousphotoconductive ingenerally have the inherent disadvantages of high cost of sulating materials may be used in making electrophotomanufacture, brittleness, and poor adhesion to supporting graphic plates is known. Suitable photoconductive insulatsubstrates. A number of these photoconductive insulating ing materials such as anthracene, sulfur, selenium or mixlayers have thermal distortion properties which make them vtures thereof havebeen disclosed by Carlson in US. Pat. undesirable in an automatic electrophotographic appara- 2,297,691.These materials generally have sensitivity in tus which often includes powerful lamps and thermal fusthe blue or near ultraviolet, range, and all but selenium ing devices which tend to heat the electrophotographic have a further limitation of being only slightly light-sensiplate.

Thus, there is a continuing need for improved. photovaried over wide limits by selection of the appropriate reconductive insulating materials from which stable, senslsins to suit specific requirements. In this regard, these tive, and reusable electrophotographic plates can be made. photoconductive layers are superior to many heretofore SUMMARY OF THE INVENTION known binder suspensions of inorganic pigments which require a relatively high percentage of inorganic pigment It is, therefore, an ob ect of this invention to provide such that the inorganic pigment used i ll cqntmls an electfophotogfaphlc Plate devold of the above'noted the physical properties of the final photoconductive layer.

disadvantages. Since the percentage of quinacridone pigment needed is Another object of this invention is to provide electror latively low, the photoconductive plate may have a Photographic Plates having Sensitivties which extend over very hard, very smooth surface. This eliminates many of Substantial Portions of the Visible P the disadvantages of the prior pigment-binder plates which, Still another object Of this invention is 1:0 provide a 1' 6- because f the proportions of igment had a very usable electrophotographic plate having a high overall rough d abrasive f Sensitivity and high thermal Stability When compared to While any of the novel class of quinacridones having Present commercially available reusable p the above-described general formula may be used to pre- Yet aflflthaf Object of this invention is to Provide pare the photo-conductive layer of the present invention, photoconductive insulating material suitable for use in {Us preffirred to employ those i id h i R electrophotographic plates in both single use and reusable i l d f o h group consisting of CH (3 1-1 nd systems. mixtures thereof and wherein Yet another object of this invention is to provide a photoconductive insulating layer for an electrophoto- RENE O graphic plate which is substantially resistant to abrasion and has a relatively high distortion temperature.

Yet another further object of this invention is to provide since these materials are highly photosensitive and proan electrophotographic plate having a wide range of useful duce the most desirable images. physical properties. Various of the above-described novel quinacridones The foregoing objects and others are accomplish d in may be utilized alone or in combination with other comaccordance with this invention, generally speaking, by positions in any suitable mixture, dimer, trimer, oligomer, providing an electrophotographic plate having a novel polymer, copolymer or mixtures thereof.

photoconductive layer comprising a quinacridonc pigment The novel class of quinacridones of the persent invenin a resin binder, said quinacridone pigment having the foltion are prepared by a method which comprises mixing a lowing general formula: compound having the .general formula:

0 H g o R- HZNHJJ- l NHOH -R 001E 0 H g (I) 0 R oHlNnd--@ @Jinnon R Ii N R'NH0 t H CNH where R==CH C H OCH OC H or a halogen and where R=CH ,-C H 001-1 OC H or a halogen, with R'-=an aromatic, alicyclic or aliphatic group. This particu- SOCl in 'dimethylformamide and then with 2R NH lar class of quinacridone pigments as well as methods for Where R"=an aromatic, alicyclic or aliphatic amine; their preparation are fully, described in copending'appli- Any suitable organic binder resin may be used in comcation, Ser. No. 754,634, filed in the U.S. Patent Oflice bination with the novel class of quinacridones to prepare Aug. 22,1968. the photoconductive layer of this invention. In order to The above-described quinacridone-resin photoconduc be useful the resin used in the present invention should be tive layer may be deposited on any suitable supporting submore resistive than about 10 and preferably more than strate, or may be cast as a self-supporting film. The plate 10 ohms per centimeter under the conditions of electromay be overcoated with any suitable materials, if desired. photographic use. Typical resins include: thermoplastics The quinacridone-resin photoconductive layer may be including olefin polymers such as polyethylene and polyused in the formation of multi-layer sandwich configurapropylene; polymers derived from dienes such as polytions adjacent a dielectric layer, similar to that shown butyldiene, polyisobutylene, and polychloroprene; vinyl by Golovin et al., in the publication entitled A New and vinylidene polymers such as polystyrene, styrene- Electrophotographic Process, Elfected by Means of Comacrylonitrile copolyrners, acryloru'trile butadiene-styrene bined Electric Layers Doklady. Akad. Nauk SSSR vol. 55 terpolymers, polymethylmethacrylate, polyacrylatcs, poly- 129, No. 5, pages 1008-1011, N overnber- December 1959. acrylics, polyacrylonitrilc, polyvinylacetate, polyvinyl It has been found that the percentage of the particular alcohol, polyvinylchloride, polyvinylcarbazole, polyvinyl class of quinacridones described above which are required others, and polyvinyl ketoncs; fluorocarbon polymers such to produce adequate sensitivity in a plate is very low. as polytetrafluoroethylene and polyvinyldiene fluoride; Because of this, the mechanical properties of the photoconheterochain thermoplastics such as polyamides, polyesters, ductive layers are substantially determined by the proppolyurethanes, polypeptides, casein, polyglycols, polysulerties of the binder. A wide variety of resin binders may tides, and'polycarbonates; and cellulosic polymers such as be used in the present invention, varying from soft therregenerated cellulose, cellulose acetate and cellulose nimoplastics to hard cross-linked enamels. Thus, the physitrate. Also, thermosetting resins including phenolic resins;

cal properties of the final photoconductive layer may be amino resins such as urea-formaldehyde resins and melamineformaldehyde resins; unsaturated polyester resins; epoxy resins, silicone polymers; alkyd resins and furan resins. Various copolymers and mixtures of the abovementioned resins may be used where applicable. In addition to the above-noted resins, any other suitable material may be used if desired.

The quinacridone compositions of the present invention may be incorporated into the dissolved or melted binderresin by any suitable means such as strong shear agitation, preferably with simultaneous grinding. Typical methods include ball milling, roller milling, sand milling, ultrasonic agitation, high speed blending and any combination of these methods. Any suitable ratio of pigment to resin may be used. On a quinacridone-dry resin weight basis, the useful range extends from about 1:1 to about 1:40. {Best results are obtained at, and therefore the preferred range is, from about 1:4 to about 1:10. Optimum results are obtained when the ratio is about 1:4. While highest photosensitivity is obtained at pigment-resin ratios of 1:1 to 1:4, at the high concentration of pigment dark conductivity increases. The optimum balance between sensitivity and dark decay occurs at a ratio ofabout 1:4. It should be noted that the proportion of photoconductor used in the preferred range lies substantially below that used in making heretofore known inorganic photoconductive binder plates. In these known plates, satisfactory electrophotographic sensitivity is attained only when the pigment-resin ratio is at least 2: 1.

The use in the present invention of lower pigment to resin ratios represents a highly desirable advantage over the prior art since a smaller amount of the relatively expensive pigment component is required. Also, this permits very smooth adhesive coatings to be obtained because of the high binder content. The small proportion of added material has little efiect on the physical properties of the binder-resimThus, resins may be chosen having the desired softening range, smoothness, hardness, tough: ness, solvent resistance, or solubility and the like with assurance that the pigment will not affect these properties to any considerable extent.

When it is desired to coat the quinacridone-resin film on a substrate, various supporting materials may be used. Suitable materials'for this purpose include aluminum, steel, brass, metallized or tin oxide coated glass, semiconductive plastics and resins, paper and any other convenient material of bulk resistivity at the time of use v ohms-cm., or surface resistivity -10 ohms/square. The pigment-resin-solvent slurry (or the pigment-resin-melt) may be applied to conductive substrates by any of the wellknown painting or coating methods, including spraying, flow-coating, knife coating, electro-coating, Mayer bar drawdown, dip coating, reverse roll coating, etc. Spraying in an electric field may be preferred for smoothest finish and dip coating may be preferred for convenience in the laboratory. The setting, drying, and/ or curing steps for these plates are generally similar to those recommended for films of the particular binders'as usedfor other'painting applications. For example, quinacridoneepoxy plates may be cured by adding a cross-linking and stoving according to approximately about the same schedule as other baking enamels made with the. same resins photoconductive coating and preferably should beno more than 4/; the thickness of said coating. Any suitable overcoating, as for example, nitrocellulose lacquer, may be employed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples will further define various preferred embodiments of the present invention. Parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 An electrophotographic plate is prepared by initially mixing about 6 parts Pliolite 85B, a styrene-butadiene copolymer resin available from Goodyear Tire and Rubber Company, about 43 parts xylene and about 1 part of a quinacridone pigmenthaving the formula:

1 to obtain a homogeneous dispersion. After milling, the

and similar pigments for paint application. A very desirable aspect of quinacridone compositions is that they are stable against chemical decomposition at the temperature normally used for a wide variety of bake-on enamels, and therefore, may be incorporated in very hard glossy photoconductive coatings, having surfaces similar to automotive or kitchen appliance resin enamels.

The thickness of the quinacridone-binder films may be varied from about 1 to about 100 microns, depending upon the required characteristics. Self-supporting films, for example, cannot be conveniently manufactured in thickdispersion is applied to a sheet of 5 mil aluminum foil using a No. 36 wire draw-down rod. The coating is then forced air dried at about C. for about two hours. The plateisthen charged to a positive potential of about 65Q volts by means of corona discharge, as described, for example, in US. Patent 2,777,957. The charged plate is then contact exposed for 15 seconds to a film positive by means of a tungsten lamp-having a 3400 K. color temperature. The illumination level at the exposure plane is about 57 foot candles. The latent electrostatic image formed on the plate is then developed by cascading pigmentedelectroscopic marking particles over the plate, by the process described, for example, in US. Patent 2,618,- 551. The powder image developed on the plate is electrostatically transferred to a receiving sheet and heat fused thereon. The image on the receiving sheet is of good quality and corresponds to the contact exposed original. I

EXAMPLE II rnixingabout 2 parts Silicone SR-82, a methyl-phenyl silicone resin available from General Electric Company,

about 40 parts xylene, and about 1 part of a quinacnidone pigment having the formula:

can onmno@ @am. C H O N \H/ 2 5 (m4 7 H 0 -g;

This plate is positively charged to an initial potential of about 290 volts. The image resulting is of satisfactory quality. 7

EXAMPLES III-1V Two electrophotographic plates are prepared by mixing about 1 part Vinylite VYNS, a copolymer of vinyl chloride and vinyl acetate available from Union Carbide Corporation, about 10 parts diethyl ketone and about 1 part of a quinacridone pigment having the formula:

The plate is coated, cured, charged, exposed and developed as in Example I above, however, in Example III, the plate is positively charged to a potential of 480 volts and, in Example IV, the plate is charged to a negative potential of 835 volts. The resulting image is of excellent quality.

EXAMPLES V-VI 40 Two electrophotographic plates are prepared by initially mixing about 1 part of Vinylite VYNS, about 10 parts dieth-yl ketone and about 1 part of a quinacridone pigment having the formula:

0 GHzNH- potential of 630 volts. Good images result. I

EXAMPLES VIP-VIII An electrophotographic plate is prepared by initially mixing about 1 part Vinylite VYNS, about 10 parts diethyl ketone, and about 1 part of a quinacridone pigment having the formula:

N l oomcumin OCH;

The plate is coated, cured, charged and developed as in Example 1 above. However, here the plate of Example VII is charged to a positive potential of 410 volts and the plate of Example VIII is chraged to a negative potential of 605 volts. Excellent images are produced by these plates.

EXAMPLES IX-X Two electrophotographic plates are prepared by initially mixing about parts of a 10 percent solution of polyvinyl carbazole in benzene, about 5 parts cyclohexanone, and about 1 part of the quinacridone pigment of Example I. These plates are coated, cured, charged, exposed and developed as in Example -1 above. However, here the plate of Example ]X is charged to a positive potential of about 180 volts and the plate of Example X is charged to a negative potential of about 215 volts. Images of good quality are produced.

EXAMPLES XI-XIl Electrophotogranhic plates are prepared by initially mixing about 100 parts of a 10 peroentpolyviuyl carbazole solution in benzene, about 5 parts cyclohexanone and about 1 part of the quinacridone pigment of Example II. The plates are coated, cured, charged, exposed and developed as in Example I above. However, here the plate of Example XI is charged to a positive potential of about volts and the plate of Example XII is charged to a negative potential of about volts. Images of good quality result. 7 I

Although specific components in proportions have been described in the above examples relating to the use of "a novel class of quinacridone pigments in electrophotographic plates, other suitable materials, as listed above,

may be used with similar results. In addition, other materials may be added to the quinacridone pigment compositions or to the pigment-resin compositions to synergize, enhance, or otherwise modify their properties. The pigment compositions and/or the pigment-resin compositions of this invention may be dyesensitized, if desired, or may be mixed or otherwise combined with other photoconductors, both organic and inorganic.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An electrophotographic imaging process which comprises uniformly charging the surface of an electrophotographic plate comprising a self-supporting layer of an electrophotographic composition comprising a photoconductive quinacridone pigment in a binder material, said quinacridone pigment having the formula:

wherein R is selected from at least one member of the group consisting of CH C H OCH OC H and a halogen and wherein R is selected from at least one member of the group consisting of an aromatic group, a heterocyclic group, an alicyclic group and an aliphatic group, said layer having a thickness greater than about microns, and exposing said charged plate to a pattern of activating electromagnetic radiation to produce an electrostatic latent image.

2. An electrophotographic imaging process which comprises uniformly charging the surface of an electrophotographic plate comprising a support substrate having a bulk resistivity greater than about 10+ ohms-centimeter having superimposed thereon a photoconductive layer 0 ll H E wherein R is selected from at least one member of the group consisting of CH, C H OCH, OC H and a halogen and wherein R is selected from one member of the group consisting of an aromatic group, a heterocyclic group, an alicyclic group and an aliphatic group, and selectively exposing said charged plate to activating electromagnetic radiation to produce an electrostatic latent image.

3. The process as disclosed in claim 1 further including the steps of developing said latent image with electroscopic marking particles.

4. The process as disclosed in claim 2 further including the step of developing said latent image with electroscopic marking particles.

5. The process as disclosed in claim 3 wherein the imaging cycle of charging, exposing and developing is repeated at least once.

6. The process as disclosed in claim 4 wherein the imaging cycle of charging, exposing and developing is repeated at least one time.

References Cited UNITED STATES PATENTS 3,074,950 1/1963 Deuschel et al. 260279 3,121,006 2/1964 Middleton et al. 961

3,384,566 5/1968 Clark 201-181 3,386,843 6/1968 Jaife et al 106-288 FOREIGN PATENTS 1,085,680 10/1967 Great Britain.

GEORGE F. LESMES, Primary Examiner J. C. COOPER llll, Assistant Examiner US. Cl. X.R. 96---l.5