US3396016A - Development and coating of new zinc oxide photoconducting recording systems - Google Patents

Description

United States Patent 3,396,016 DEVELOPMENT AND COATING OF NEW ZINC OXIDE PHOTOCONDUCTING RE- CORDING SYSTEMS James R. Olson, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Aug. 4, 1965, Ser. No. 477,307 12 Claims. (Cl. 96-1.8)

This invention relates to electrophotography, particularly to novel photoconductive insulating layers and electrophotographic plates comprising such layers and their use in electrophotography.

Electrophotographic plates comprising various particulate photoconductors dispersed in electrically insulating binders were described by Middleton in US. Patents No. 2,663,636 patented Dec. 22, 1953 and No. 3,121,006 patented Feb. 11, 1964. Plates comprising photoconductive layers of zinc oxide dispersed in electrically insulating resin binders were described by Young and Greig in RCA Review, December 1954, .pp. 469-484 and in US. Patents No. 3,052,539 and 3,052,540, both patented Sept. 4, 1962. Photoconductive insulating layers comprising a particulate photoconductor, as described in the prior art generally comprise, as an insulating binder for the photoconductor, an electrically insulating synthetic polymeric resin such as silicone resins, metha-crylate resins, various polyester resins, polystyrenes, and the like. While some nonpolymeric compounds have been suggested as binders for this use, generally the photoconductive insulating layers produced with binders of nonpolymeric materials have been less satisfactory for one or several of various reasons such as poor electrical insulating quality, poor adhesion, reduced photographic speed, incompatibility with photosensitizing dyes, discoloration, and the like.

An object of the present invention is to provide photoconductive elements for use in electrophotography having a novel photoconductive insulating layer comprising a particulate photoconductor such as zinc oxide in a nonpolymeric binder. Another object is to provide photoconductive elements for use in electrophotography having especially favorable electrical and photographic properties. Electrophotographic elements in accordance with the present invention, in specific embodiments, will have one or more of the advantages of favorable photographic speed, favorable electrical dark resistivity, favorable dark decay properties, relatively favorable economy of manufacture, and favorable surface appearance.

The present invention provides electrophotographic elements having a photoconductive insulating layer which comprises a particulate photoconductor such as zinc oxide dispersed in a nonpolymeric vehicle selected from sucrose esters, bisphenols, and mixtures of members of those respective classes of compounds with each other and with certain other nonpolymeric materials. In addition to a particulate photoconductor and the binder, the photoconductive layers prefer-ably will contain sensitizing amounts of photographic sensitizing dyes to increase the photographic speed and to broaden the spectral sensitivity of the photoconductor. A particular advantage of certain photoconductive layers made with nonpolymeric binders of the present invention is that a variety of eflective photosensitizing dyes can be used compatibly in the photoconductive layer without adverse effect upon their sensitizing function by the binder materials. Another advantage of certain preferred electrophotographic elements in accordance with the present invention is that the photoconductive insulating surface retains its electrical resistivity at high relative humidities. Electrophotographic prints made on preferred elements in accordance with the present invention compare favorably in quality with photoconductive zinc oxide elements presently available commercially for use in electrophotography.

A first class of compounds which may be used as 'binders in accordance with the present invention is the class of organic compounds called bisphenols. This class of compounds can be characterized by the following formula:

wherein X represents a single bond, a single atom, or a bivalent organic radical, and R and R may represent hydrogen or radicals substituted for hydrogen at any of the carbon atoms on the respective rings. X may represent a bivalent organic radical having an ylidene carbon atom. Specific examples of bisphenols useful within the scope of the invention include:

4,4-sulfamyl diphenol 1,3-(4-hydroxyphenol) propane p,p'-biphenol 3,3-dipropy1-(p,p-diphenol) 4,4'-oxydiphenol diresorcyl sulfide 4,4-sulfonyl diphenol 2,2'-dihydroxy benzophenone 2,2-4,4-tetrahydroxybenzophenone 2,2-dihydroxy-4-methoxybenzophenone 2,2-dihydroxy-4,4-dimethoxy benzophenone 2,2-dihydroxy-4-n-octyloxybenzophenone 4,4-dihydroxy-3,3'-dinitrobenzophenone 1,3-'(4-hydroxyphenyl)propane 2,2'( ethane diylidene d initrilo)diphenol a,a-(ethylene dinitrilo di-o-cresol bis (2-hydroxyphenyl methane bis (4-hydroxyphenyl)methane bis(2,6-di-t-butyl-4-hydroxyphenyl)methane 1 l-bis (4-hydroxyphenyl ethane 1, l-bis (4-hydroxyphenyl -2-methyl propane 1, l-bis (4-hydroxyphenyl -3 -methyl butane 1 ,'1-bis(4-'hydroxyphenyl) -n-butane 2,2-bis(4-hydr-oxyphenyl)propane 2,2-bis( 4-hydroxyphenyl)butane 2,2-bis (4-hydroxyphenyl) -3-methyl butane 2,2-bis (4-hydroxyphenyl) pentane 2,2-bis (4-hydroxyphenyl) -4-rnethyl pentane 2,2-bis/(4-hydroxyphenyl)hexane 2,2-bis (4-hydroxyphenyl) nonane 2,2-bis(3-t-butyl-4-hydroxyphenyl)propane 3,3bis(4-hydroxyphenyl)pentane bis 4-hydroxyphenyl phenyl methane bis (4-hydroxyphenyl) naphthyl methane bis(4-hydroxyphenyl)-4-methylphenyl methane bis(4-hydroxyphenyl)-2-hydroxymethylphenyl methane bis (4-hydroxyphenyl) -2-chlorophenyl methane bis(4-hydroxyphenyl) -2,4-dichlorophenyl methane bis (4-hydroxyphenyl -4-chlorophenyl methane bis (4-hydroxyphenyl -3,4-dichlorophenyl methane bis(4-hydroxyphenyl) -2-carboxyphenyl methane bis 3-methyl-4-hydroxyphenyl) phenyl methane bis (4-hydroxyphenyl) diphenyl methane 1,1-bis(4-hydroxyphenyl) -1-phenyl ethane 1, 1-bis(4-hydroxyphenyl) -1-(4-methylphenyl) ethane 1, l-bis(4-hydroxyphenyl)-l-naphthyl ethane 1,l-bis(4-hydroxyphenyl)-1-(3-fluorophenyl) ethane 1,1-bis(4-hydroxyphenyl) -1-(4-fiuorophenyl)ethane 1,1-bis(4-hydroxyphenyl)-1-(3,4,5-trifiuorophenyl) ethane 1,1-bis(4-hydroxyphenyl)-1-(3 -chlorophenyl)ethane seasons 3 1, 1-bis(4-hydroxyphenyl)-1-(4-chlorophenyl)ethane 1, l-bis(4-hydroxyphenyl)-1-(3 ,4-dichlorophenyl) ethane 1,1-bis 4-hydroxyphenyl l -(2,5-dichlorophenyl ethane l, l-bis 4-hydroxyphenyl -1 (4-bromophenyl ethane 1, l-bis 3-methyl-4-hydroxyphenyl -1- (4-chlorophenyl) ethane 1,1-bis(3-methyl-4-hydroxyphenyl)-1-(3,4-dichlorophenyl) ethane 1,1-bis(3 ,5 -dichloro-4-hydroxyphenyl 1- 3,4-dichlorophenyl ethane 1, 1-bis(4-hydroxyphenyl)1-phenyl pentane and the like.

The class of bisphenols includes esters containing more than one bisphenol moiety, for example, the diester obtained by condensing two moles of 4,4-bis(4-hydroxyphenyl)-pentanoic acid with the glycol C36H72(OH)2.

A preferred embodiment using a bisphenol singly as a binder for zinc oxide photoconductive coatings is described in Example I.

EXAMPLE I One gram of 2,2-bis (4-hydroxyphenyl)pentane was dissolved in 6.75 grams acetone and 3.5 grams of photoconductive zinc oxide (Type XX78, New Jersey Zinc Co.) sensitized with 1.O mole Bromophenol blue and 0.84 lO mole anhydro-3,3-di-;3-carboxyethyloxacarbocyanine hydroxide per mole of zinc oxide was added to the solution. The mixture was milled by a steel roll inside a steel cylinder for minutes and then the mixture was spread on a support with a scraper bar having a .0O4-inch slit. The coating was dried by evaporation in air overnight. A coherent coating was obtained which was flexible and the surface had good resistance to chalking by abrasion. The finished coated element was tested to determine dark resistivity of the insulating layer as indicated by initial charge potential (V dark decay as indicated by the charge potential on the surface /2 minute after charging (V and photographic speed as determined by a standardized charging, exposing, and developing procedure. This sample showed the following test results: V 340 volts, V 190 volts, speed, 204.

By the procedure described in Example I, sample electrophotographic elements were made using other bisphenols listed above as binders. Test results varied among the various samples but all of the samples exhibited properties of some utility in electrophotography.

A second class of compounds which may be used as binders in accordance with the present invention is sucrose esters, for example, esters formed by condensation of sucrose with monocarboxylic organic acids. Examples of sucrose esters are sucrose octa-acetate, sucrose benzoate, sucrose diacetate hexaisobutyrate, sucrose benzoate isobutyrate, and the like.

A preferred embodiment having a sucrose ester used singly as a binder is described in Example II.

EXAMPLE u A sample electrophotographic element was made by the procedure described in Example I but using one gram sucrose benzoate isobutyrate instead of the bisphenol. The finished sample had a relatively soft photoconductive insulating layer. The sample was tested for electrophotographic properties with the following results: V 415, V 330, speed, 104.

Samples were made as in Example II but using the other sucrose esters mentioned above, singly, as binders for the respective samples. All of the samples were tested and exhibited useful electrophotographic properties.

Especially preferred binder compositions comprise a mixture of nonpolymeric compounds comprising a mixture of a bisphenol with a sucrose ester. We have found that as a binder for the photoconductive coating, the mixture of a sucrose ester and a bisphenol produces a finished photoconductive insulating coating having electrical properties superior to those made with either of the binder EXAMPLE III Twenty grams sucrose diacetate hexaisobutyrate and 20 grams 1,1-bis(4-hydroxyphenyl)-l-(4-chlorophenyl) ethane were dissolved in 250 grams acetone. This solution was mixed with 140 grams Florence Green Seal 8 zinc oxide sensitized as in Example I. The mixture was ballmilled for 21 hours, then coated by extrusion hopper on Riegel brand electrically conductive paper, Type KR39XE. The coating was dried by air heated to about 62-68 C. Finished samples were dark adapted in air of 50 percent relative humidity at 74 F. overnight before testing. The samples were tested as in Example I. Results: V 370 volts, V 275 volts, speed, 250.

Two component binder mixtures consisting of a sucrose ester and a bis-phenol were made using various sucrose esters and various bisphenols in varied combinations. Electrophotographic elements were made using these binder mixtures. These elements were made by the method described in Example III. The proportion of sucrose ester in the respective binder mixes was varied from as little as 25 percent by Weight to as much as percent by weight with the remaining proportion of the binder mix being a selected bisphenol. The weight ratio of zinc oxide to binder mix in various coatings was varied from 3:1 to 4:1 in preferred embodiments and may be varied from about 1:1 to about 6:1 in some embodiments. Useful electrophotographic elements were obtained in all cases and especially good results were obtained using sucrose octa-acetate as the sucrose ester and using 4,4'-(2- norbornylidene)-bis(2,6-dichlorophenol) as the bisphenol component. However, it should be emphasized that all of the two component sucrose ester-bisphenol binder mixtures tested produced elements having electrophotographic utility.

Coatings were made using three and four component binder mixtures comprising a sucrose ester with two or three other components all selected from other sucrose esters, biphenols, and rosin. Best results were obtained using sucrose octa-acetate as one of the components with a bisphenol as one of the other components. A preferred embodiment of a three component binder comprising sucrose octa-acetate, a bisphenol and rosin is described in the following example.

EXAMPLE IV Thirty-two and one-half grams sucrose octa-acetate, 5 grams rosin and 2.5 grams 1,1-bis(4-hydroxyphenyl)- 1-(4-chlorophenyl)ethane were dissolved in 250 grams acetone. The solution was added to grams zinc oxide (Florence Green Seal 8), sensitized as in Example I. The mixture was ballmilled, coated, and dried and the electrophotographic element was tested, all as described in Example III. Test results: V 450 volts, V 380 volts, speed, 164.

A four component binder was used in the following example.

EXAMPLE V Thirty grams of sucrose octa-acetate with 2.5 grams rosin, 5 grams sucrose diacetate hexaisobutyrate and 2.5 grams of 4,4-(2-norbornylidene)bis(2,6-dichlorophenol) were dissolved in 250 grams acetone and the solution was added to 140 grams zinc oxide (Florence Green Seal 8, New Jersey Zinc Co.), sensitized as in Example I. The

dispersion was ballmilled, coated, dried and tested as described in Example III. Test results were: V 440 volts, V 355 volts, speed, 104.

The foregoing examples describe particulate, sensitized zinc oxide as a preferred photoconductor but the present invention in its broader aspects contemplates elements having other particulate photoconductors similarly dispersed in the novel binders. For example, we might use other particulate photoconductors of the kinds described in the aforementioned US. patents. The examples above describe use of certain preferred spectra sensitizing dyes but this invention in its broader aspects contemplates use of other suitable sensitizers in the novel photoductive coatings. For example, a photoconductive insulating layer in accordance with the invention might incorporate other sensitizing compounds of the various kinds described in the aforementioned patents. Similarly, our novel photoconductive insulating layers may be coated on any supports suitable for making electrophotographic elements, for example, on supports 'of kinds described in the aforementioned patents.

In testing the plates for electrophotographic properties, we employed conventional corona discharge apparatus and methods for imposing a uniform charge on the insulating surface, and employed standard densitometry apparatus and methods for photographic exposure. Development was 'by cascade development with commercial n-type electroscopic developer.

A particular advantage with preferred embodiments of the invention is the considerable reduction in weight of the element which can be obtained by making coatings of about 2.0 gm. per sq. ft. and which will still have suitable electrophotographic properties. This coating is about /3 lighter than many of the zinc oxide-resin coatings of prior art and the reduction in copy weight is appreciable.

The invention has been described in considerable detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. An electroph-otographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconductor dispersed in a non-polymeric binder, which binder comprises from 25 to 100% 'by weight of sucrose ester, the remainder of said binder being non-polymeric organic material.

2. An electrophotographic element comp-rising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate ph'otoconductor dispersed in a non-polymeric binder, which binder consists essentially of a sue-rose ester.

3. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer com-prising a particulate photoconductor dispersed in a non-polymeric binder, which binder consists essentially of a bisphenol.

4. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconductor dispersed in a non-polymeric binder, which binder compriies a mixture of a sucrose ester and a bisphenol.

5. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconductor dispersed in a non-polymeric binder consisting of at least 25 percent by weight of sucrose octa-acetate, at least five percent by weight of a bisphenol and the remainder of non-polymeric organic material.

6. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconductor dispersed in a non-polymeric binder which comprises at least 25% by weight of sucrose octa-acetate.

7. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconductor dispersed in a non-polymeric binder consisting of at least 25 by weight of sucrose octa-acetate, at least 5% by weight of 4,4 ('2 norbornylidene)bis(2,6-dichlorophenol) and the remainder of rosin.

8. In an electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer which comprises a particulate photoconductor dispersed in an insulating film-forming vehicle, the improvement wherein said insulating vehicle consists essentially of at least 25% of a sucrose ester and the remainder of at least one material selected from sucrose esters, bisphenols, and rosin.

9. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconduc-tor dispersed in a non-polymeric binder comprising at least 25 sucrose ester, the remainder of said binder consisting essentially of at least one non-polymeric material selected from the group consisting of sucrose esters, bisphenols, and rosin.

10. An electrophotographic element comprising a support and coated thereon a photoconductive electrically insulating layer comprising a particulate photoconductor dispersed in a non-polymeric binder comprising at least 25% sucrose octa-acetate, the remainder of said binder consisting essentially of at least one material selected from the group consisting of sucrose esters, bisphenols, and rosin.

11. The electrophotographic element defined in claim 9, said particulate photoconductor being photoconductive zinc oxide.

12. The electrophotographic element defined in claim 10, said particulate photoconductor being photoconductive zinc oxide.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. C. COOPER, Assistant Examiner.

Claims (1)

1. 9. AN ELECTROPHOTOGRAPHIC ELEMENT COMPRISING A SUPPORT AND COATED THEREON A PHOTOCONDUCTIVE ELECTRICALLY INSULATING LAYER COMPRISING A PARTICULATE PHOTOCONDUCTOR DISPERSED IN A NON-POLYMERIC BINDER COMPRISING AT LEAST 25% SUCROSE ESTER, THE REMAINDER OF SAID BINDER CONSISTING ESSENTIALLY OF AT LEAST ONE NON-POLYMERIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF SUCROSE ESTERS, BISPHENOLS, AND ROSIN.