US3912507A

US3912507A - Polyrhodanine photoconductive materials

Info

Publication number: US3912507A
Application number: US366910A
Authority: US
Inventors: Juergen H H Keller; Robert H Sprague
Original assignee: Itek Corp
Current assignee: Northrop Grumman Guidance and Electronics Co Inc
Priority date: 1973-06-04
Filing date: 1973-06-04
Publication date: 1975-10-14
Anticipated expiration: 1992-10-14

Abstract

New compositions comprising polyrhodanines with three or more rhodanine rings are described. These compositions can be used as pigment-type photoconductors by dispersing them in insulating binders, or as dyes.

Description

United States Patent 11 1 Keller et al.

[ 1 Oct. 14,1975

[ POLYRHODANINE PHOTOCONDUCTIVE MATERIALS [75] Inventors: Juergen H. H. Keller, Chelmsford;

Robert H. Sprague, Carlisle, both of 21 Appl. No.: 366,910

[52] US. Cl. 96/l.5; 96/1.6; 96/1.7; 96/139; 260/3067 R [51] Int. Cl. G03G 5/06 [58] Field of Search 96/1.5, 1.6, 1.7

[56] References Cited UNITED STATES PATENTS 3,047,384 7/1962 Jones et a1. 96/l.7 3,110,591 11/1963 Stewart 96/1.7 3,140,283 7/1964 Depoarter et 96/1.5 X 3,155,503 11/1964 Cassiers et a1. 96/l.5 3,507,649 4/1970 Hensley 96/l.7 3,507,692 4/1970 Ghys et al.. 96/1.5 X 3,563,735 2/1971 Emmi 96/1.7 3,647,433 3/1972 Contais 96/1.5 X 3,658,522 4/1972 Endo et a1. 96/1.6 X 3,687,946 8/1972 Yao 96/1.6 X 3,719,480 3/1973 Brantly 96/1.5 X 3,743,638 7/1973 Webster et a1... 96/1.7 X 3,748,128 7/1973 McNally 96/1.5 X 3,759,931 9/1973 Brown et a1. 96/1.7 X 3,772,281 11/1973 Tubuko et a1. 96/l.6 X

3,782,935 1/1974 Yao 96/1.6 X 3,796,573 3/1974 Jones 3,839,327 10/1974 Yao 96/1.5 X

FOREIGN PATENTS OR APPLICATIONS 45-32756 10/1970 Japan 96/1.6

964,875 7/1964 United Kingdom.... 964,877 7/ 1964 United Kingdom.... 1,226,892 3/1971 United Kingdom....

45-2879 1/1970 Japan 96/1.7

OTHER PUBLICATIONS Dye-sensitized Photoconductive Compositions, 10015, Research Disclosures, Product Licensing 1ndex, Aug. 1972, pp. 4951.

Sprague et a1., Dye Sensitization of Photosensitive Titanium Dioxide, Photographic Science & Engineering, Vol. 14, No. 6, Nov.-Dec., 1970, pp. 401-406.

Primary Examiner-Roland E. Martin, Jr.

Assistant Examiner-John R. Miller Attorney, Agent, or Firm-Homer 0. Blair; Robert L. Nathans; David E. Brook [57] ABSTRACT New compositions comprising polyrhodanines with three or more rhodanine rings are described. These compositions can be used as pigment-type photoconductors by dispersing them in insulating binders, or as dyes.

1 Claim, No Drawings POLYRHODANINE PHOTOCONDUCTIVE MATERIALS BACKGROUND OF THE INVENTION SUMMARY OF AN EMBODIMENT OF THE INVENTION In one embodiment, the invention comprises new compositions of matter comprising polyrhodanine dyes having three or more rings therein. These polyrhodanine dyes can be coated upon suitable electrically conducting substrates with or without binders to form photoconductive coatings. One suitable insulating binder is polystyrene.

Whereas most known organic photoconductors are colorless compounds and require added sensitizing dyes for sensitivity to visible light, the polyrhodanine dyes described herein are colored. Therefore, they are sensitive to visible light without added sensitizers. Also, the polyrhodanine photoconductors described herein have high sensitivities and low dark decay.

DESCRIPTION OF THE INVENTION The polyrhodanines described herein are formed by reacting a rhodanine, including N-alkyl or aryl rhodanines, with an ester such as methyl-p-toluene sulfonate at elevated temperatures. The reaction proceeds stepwise, the quaternary salt being formed first reacting with another molecule of rhodanine followed by quaternization of this dinuclear product which then further condenses giving a series of products.

The polyrhodanine compositions of this invention can be represented by the following structural formula:

0 R o R o R ll l l l ll l 'l l \T I l H c c=o s s s wherein:

n equals 1, 2, 3 or 4; and,

R represents hydrogen; C -C alkyl including unsubstituted, substituted and/or unsaturated alkyls; aryl; or aralkyl.

More specifically, these light-sensitive compositions can be represented by the following structural formulas:

R CO R N/ co R H2C c=c I N Ci I s c=o s S Polyrhodaninc I co R \ co /R CO R N me I N co C=C I N c=c l N S l s c=o S S Polyrhodanine II co R N co R H ,C l N co R c=c I N co R c=c I N s l N s I s c=c s s Polyrhodanine Ill co R N CO R HZC N co R l \N' co R S C=C N l s c=c l N S c=c i Polyrhodanine IV One use for some of the polyrhodanine dyes described and claimed herein is as photoconductive compositions. For example, polyrhodanine compositions having five or six rings have been found to be photoconductive. Such photoconductive compositions are useful in preparing electrophotographic elements.

In preparing electrophotographic elements using polyrhodanine photoconductors of this invention, the dye compositions may be formulated and coated with or without a binder. When a binder is employed, the compound is dispersed in a solution of binder and solvent and then after thorough mixing, the composition is coated on an electrically conducting support in a well known manner such as swirling, spraying, doctor blade coating, etc. By electrically conducting, is meant a resistivity of about 10 ohm-centimeters or lower, and preferably of about 10 ohm-centimeters or lower.

Suitable binders comprise polymers having fairly high dielectric strength and good electrically insulating characteristics. By electrically insulating," is meant a resistivity of ohm-centimeters or higher, and preferably of about 10 ohm-centimeters or higher.

Examples of specific suitable binder materials in clude: styrene-butadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soya-alkyd resins; poly(vinyl chloride); poly( vinylidene chloride); vinylidene chloride; acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate; vinyl chloride copolymers; poly(vinyl acetals), such as poly(vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(n-butylmethacrylate), poly(isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenol-formaldehyde resins; ketone resins; polyamide; polycarbonates; etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyl resins can be prepared according to the method described in U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for uses in the photoconductive layers of the invention are sold under such trade names as Vitel PE- 101, Cymac, Piccopale 100, and Saran F-220. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, 2- butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers. e.g., tetrahydrofuran, or mixtures of these solvents, etc.

Where a binder is used, it is satisfactory to have pigment/binder ratios of from 2/1 to about 1/4. Preferably, the pigment/binder ratio is from about 1/1 to about U2.

The coating thickness of polyrhodanine dyes in solution can vary widely. In general, thicknesses, before drying, from about 0.0005 to about 0.01 inches should be suitable. Preferably, the wet coating thicknesses are from about 0.0015 to about 0.006 inches.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of the electrically conducting supports, for example, paper (at a relative humidity above 20%); aluminum-paper laminates; metal foils such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass and galvanized plates; regenerated cellulose and cellulose derivatives; certain polyesters, es-

pecially polyesters having a thin electroconductive layer (e.g., cuprous iodide) coated thereon; etc. Suitable supporting materials can also include the humidity-independent conducting layers of semiconductors dispersed in polymeric binders, as described in U.S. Pat. No. 3,112,192.

The elements of the present invention can be employed in any of the well known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an image-bearing transparency by a conventional exposure operation such as, for example, by contact-printing technique, or by lens projection of an image, etc., to form a latent image in the photoconducting layer. By exposure of the surface in this manner, a charge pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust, e.g., powder, a pigment in a resinous carrier, i.e., toner, or a liquid developer may be used in which the developing particles are carried in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature in such patents, for example, as U.S. Pat. No. 2,297,691, and in Australian Pat. No. 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has as one of its components, a low-melting resin, it is possible to treat the developed photoconductive material with heat and cause the powder to adhere permanently to the surface of the photoconductive layer. In other cases, a transfer of the image formed on the photoconductive layer can be made to a second support, which would then become the final print. Techniques of the type indicated are well known in the art and have been described in a number of U.S. and foreign patents, such as U.S. Pat. Nos. 2,297,691 and 2,551,582, and in RCA Review, vol. 15, 1954, pp. 469-484.

Also, these polyrhodanines are dyes, usually from yellow to blue in color. As such, they can be used, for example, to dye fibers, or to spectrally sensitize photosensitive systems to visible light.

The polyrhodanines described herein can also be used as dopants to raise the sensitivity of lower sensitivity photoconductors. This use is described in more detail in my copending application, Ser. No. 366,906, filed June 4, 1973, now U.S. Pat. No. 3,877,937. These polyrhodanines have particularly beneficial results when small amounts are intimately dispersed with organic, pigment-type photoconductors as described in my copending application, Ser. No. 366,907, filed June 4, 1973. The teachings from both of my abovementioned copending applications are hereby expressly incorporated by reference.

The following examples further illustrate the inven tion.

EXAMPLE 1 Preparation of Polyrhodanine I Ten grams of N-ethylrhodanine were mixed with 20 grams of methyl-t-toluenesulfonate and heated to 150C. After reaching 150C, the reaction mixture turned darker rapidly and the temperature rose to 200C. without further application of heat. The reaction mixture was left standing for minutes, during which time the temperature fell to 160C. The mixture was further cooled to 20C., stirred with ether, decanted and treated with several further portions of ether until a heavy, sticky residue remained. This residue was stirred with 350 ccs. of absolute ethanol, heated and left standing overnight at room temperature. The next morning the solution was filtered with suction and the solid product was washed with ethanol. 4.2 grams of a solid product were obtained; this product was a mixture of polyrhodanine compounds I, ll,'llI and IV.

The ethanol filtrate was concentrated to 150 ccs. at which time crystals started to form in the boiling solution. The mixture was cooled and the product filtered off to yield 2.1 grams of yellow crystals, with an absorption maximum in Cresol at 450 nm. The crystals were extracted with 7x200 ccs. of boiling methanol. The extracts were combined and chilled. Crystals formed and were filtered off. A small amount of an impurity, having an absorption maximum at 494 nm., was removed by dissolving in 300 ccs. in boiling acetone and treatment with four consecutive portions of Norite A. The acetone solution was concentrated to 50 cc. and cooled. On filtration, Polyrhodanine I was obtained as yelloworange crystals. M.P. 269271C. D-max: 1.24 in pyridine, l/l10,000 at 424 nm. (430 in Cresol).

EXAMPLE 2 I Preparation of Polyrhodanine II The 4.2 grams of original crystal product in Example 1 were extracted with 4X50 ccs. of hot acetone to remove most of Polyrhodanine I which was still present in this mixture, as shown by a curve, which indicated absorption maxima in cresol at 430, 495, 550 and 610 nm. 3.8 grams remained undissolved, of which 3.5 grams were extracted with 250 ccs. of boiling pyridine. The solution was cooled and the crystals that formed were filtered off to yield 0.8 grams of Polyrhodanine II. D-max: 0.78 in pyridine, l/210,000 at 470 nm. (495 in Cresol EXAMPLE 3 Preparation of Polyrhodanine Ill The solid material remaining after extraction with boiling pyridine in Example 2 was further extracted with 4X50 ccs. of boiling pyridine. Only a very small amount went into solution. After standing overnight in the refrigerator, the solution was filtered, and 0.015 grams of a light purple dye, polyrhodanine III, was obtained having an absorption maximum at 550 nm. in

Cresol.

EXAMPLE 4 Preparation of Polyrhodanine IV 0.5 grams of the material still undissolved after Example 3 was extracted with 50 ccs. of Cresol at 150l60C. The remaining residue was stirred with acetone and filtered, and then thoroughly washed with acetone to remove all the Cresol. 0.2 grams polyrhoda- 5 nine IV were obtianed as a dark purple material, having an absorption maximum at 610 nm. in Cresol.

EXAMPLES 5 and 6 Preparation of Electrophotographic Plates Electrophotographic plates containing polyrhodanine pigment-type photoconductors as described herein were prepared as follows.

50 mg. of pigment was dispersed in one-half cc. of a 10% solution of polystyrene in tetrahydrofuran. This solution was coated onto a 0.006 inch grained aluminnm plate by means of a Bird applicator to give a 0.003 inch wet thickness. The plate was dried for a minimum of 30 minutes at 100C. before testing for dark decay and sensitivity on an electrostatic testing apparatus. This apparatus rotated the plate under a corona charger until the surface potential (measured on an oscilloscope) reached 500 volts. The charging current was shut off and the percent drop in voltage after seconds was recorded (dark decay). The plate was then recharged to 500 volts and exposed to a 15 watt tungsten light source held 2 inches from the sample. Percent drop in voltage in 3 seconds was recorded as sensitivity. 1f 100% discharge, or amounts approaching 100% occurred in less than 3 seconds, the charge exposure cycle was repeated using a 0.5, 1.0 or 2.0 neutral density filter between the sample and the light source.

The following table presents dark decay and sensitivity data for various polyrhodanine photoconductors, determined according to the above procedure.

TABLE Ex. Polyrhodanine No. Photoconductor Dark Decay Sensitivity 5 Ill 15 100-2 sec.

30(l) 6 IV 70 lOO-l sec.

"1.() neutral density filter What is claimed is: 1. A photoconductive composition comprising a photoconductive polyrhodanine dispersed in an electrically insulating binder and having a pigment to binder ratio of from about 2/1 to about 1/4, said photoconductive polyrhodanine being represented by the following structural formula:

O R O R O R l 1 l1 1 l N ("N HA 2 1 (i=0 S S S wherein:

n equal 1, 2, 3 or 4; and, R represents hydrogen; C C alkyl; aryl; or aralkyl.

Claims

1. A PHOTOCONDUCTIVE COMPOSITION COMPRISING A PHOTOCONDUCTIVE POLYRHODANINE DISPERSED IN AN ELECTRICALLY INSULATING BINDER AND HAVING A PIGMENT TO BINDER RATIO OF FROM ABOUT 2/1 TO ABOUT 1/4, SAID PHOTOCONDUCTIVE POLYRHODANINE BEING REPRESENTED BY THE FOLLOWING STRUCTURAL FORMULA: