CA1062074A - Sensitizing phthalocyanine compositions with aldehyde substituted perylene derivatives - Google Patents

Abstract

Photoconductive compositions containing phthalocyanine pigments and at least one spectral sensitizer compound of the formula wherein R, R1 and R2 are independently selected from hydrogen or alkyl of 1-3 carbon atoms. The weight ratio of phthalocyanine pigments to spectral sensitizer in the photoconductive compositions can range from about 2:1 to about 1:2. These compositions are useful in electrophotographic articles and methods.

Description

10~;~074 BACKGROUND OF THE INVENTION `
Field of the Invention - This invention relates to a com-position, an article and a method employing said article. More specifically, this invention concerns an improvement in both ~ , the spectral sensitivity and a reduction in the induction period of phthalocyanine/resinous binder compositions used in electro-photographic plates and imaging methods.
_scription of the Prior Art - The formation and develop-ment of images on the imaging surfaces of photoconductive materials by electrostatic means is well known. The best known of the commercial processes, more commonly known as xerography, involves forming a latent electrostatic image on the imaging surface of an imaging layer by first uniformly electrostatically .$' charging the surface of the imaging layer in the dark, followed by exposing this electrostatically charged surface to a light and shadow image. The light struck areas of the imaging layer are thus rendered relatively conductive and the electrostatic charge selectively dissipated in these irradiated areas. After the photoconductor is exposed, the latent image on this image bearing surface is rendered vis~ble by development with finely divided colored electroscopic materials, known in the art as "toner". This toner will be principally attracted to those areas on the image bearing surface having a polarity of charge opposite to the polarity of charge on the toner particles. -The developed image can then be read or permanently affixed to the photoconductor where the imaging layer is not to be reused. This later practice is usually followed with respect to the binder-type photoconductive films (e~g. zinc oxide/
insulating binder resin) where the photoconductive imaging layer is also an integral part of the finished copy, U. S. Patents 3,121,006 and 3,121,007.

~ ~.

~06Z074 `: -:

In so called "plain paper" copying systems, the latent image can be developed on the imaging surface of the reusable photoconductor or transferred to another surface, such as a sheet of paper, and thereafter developed. When the latent image is developed on the imaging surface of a reusable photo-conductor it is subsequently transferred to ano*her substrate and then permanently affixed thereto. Any one of a variety of well known techniques can be used to permanently affix the toner image to the copy sheet, including overcoating with ~
transparent films, and solvent vapor or thermal fusion of the toner particles to the supportive substrate.
In the above "plain paper" copying systems, the -materials used in the photoconductive layer should be prefer-- ably capable of rapid switching from insulating to conductive to insulating ~tate in order to permit cyclic use of the ~maging surface. The failure of a material to return to its relatively insulating state prior to the succeeding charging/
imaging sequence will result in a decrease in the maximum charge acceptance of the photoconductor. This phenomenon, commonly referred to in the art as "fatigue" has in the past been avoided by the selection of photoconductive materials possessing rapid switching capacity. Typical of the ;~ material suitable for use in such a rapidly cycling imaging system includes anthracene sulfur, selenium, and mixtures thereof (U. S. Patent 2,297,691); selenium being preferred because of its superior photosensitivity.
In addition to anthracene, other organic photocon-ductive materials, such as phthalocyanine pigments (U. S. Patent 3,816,118) and poly~N-vinylcarbazole) ~U. S.
Patent 3,037,861) have been disclosed as suitable for use in electrophotography. Until recently, none of the above , ~ .. ..

organic materials have received serious consideration as an alternative to such inorganic photoreceptors as selenium, due to problems inherent in their fabrication or due to their relative lack of speed and broad spectral sensitivity in the visible region of the electromagnetic spectrum. Phthalocyanine pigments, for example, lack substantial photoresponse at the low end of the visible spectrum and also suffer from the inherent disadvantages of relatively slow photodischarge and a relatively long induction period. In order to attempt to improve the more efficient utilization of incident light, the spectral sensitization of phthalocyanine has been attempted.
Conventional sensitization with dyestuffs has proven less than satisfactory since the absorption coefficient of phthalo-cyanine is simply too great in the spectral region where sensitization is sought and thus precludes incident light from reaching the conventional color sensitizers.
SUMMARY OF THE INVENTION
In accordance with one aspect of this invention there is provided a photoconductive composition consisting essential-ly of a dispersion containing particles of phthalocyaninepigment, a film-forming insulating binder resin and particles of at least one spectral sensitizer compound of the formula CHO.

. ~1` .
~.
wherein R, Rl and R2 are independently selected from hydrogen or alkyl of 1-3 carbon atoms.

The weight ratio of phthalocyanine pigments to spectral -- 106~74 ; ~
sensitizer in the above composition should preferably be in the range from about 2:1 to about 1:2. The relative concen- `-tration of phthalocyanine pigments in the composition will vary depending upon the electronic properties of the resinous binder but preferably ranges from about 0.1 to 50 weight percent.
In the event that the resinous binder is electronically inert (that is incapable of substantial transport of charge carriers of either polarity) the concentration of phthalocyanine pigment must be at least 30, and preferably, about 50 percent by weight.
Where the binder is electronically active (that is capable of transport of charge carriers of at least one polarity) the concentration of phthalocyanine pigment can be substantially reduced since interparticulate contact of such pigments is no longer necessary to transport charge carriers generated upon photoexcitation of the composition since that function -is now performed by the binder matrix.
In accordance with another aspect of this invention there is provided an electrophotographic imaging member wherein the photoconductive insulating layer consists essential-ly of a dispersion containing particles of phthalocyanine ;-pigment, a film forming insulating binder resin and particles of at least one spectral sensitizer compound of the formula indicated above.
In accordance with another aspect of this invention there is provided an electrostatographic imaging method that comprises providing an imaging member of the type indicated above and forming a latent electrostatic image on said imaging member by initially sensitizing the imaging member to a positive potential in the dark followed ~y selective exposure of the sensitized layer to image information, the wavelength of light used in projection of said image information being anywhere within the range of the visible 74 :~
spectrum.

DESCRIPTIO~ OF THE I~VENTIO~
INCLUDING PREFERRED EMBODIMENTS
The photoconductive composition af this invention can be prepared by simply dispersing the appropriate pro-portions of phthalocyanine pigment, spectral sensitizer and film-forming insulating binder resin in a fluid medium and casting or coating the resulting dispersion on a self-sup-porting (preferably conductive) substrate.
The phthalocyanine pigments suitable for use in this composition include any of the metal-free or metal-containing phthalocyanine pigments available in the art. The polymorphic form of a pigment is not believed to be a factor in practising this invention. In one of the embodiments of this invention, the sen~itizer compound can be added to the alpha form of the phthalocyanine pigment prior to its conversion to the corres-ponding beta polymorph; Phthalocyanine pigments are generally readily commercially available and where unavailable can be prepared by techniques and with apparatus disclosed in both the technical and patent literature, see Moser and Thomas, PhthalocYanine Compounds, ACS Monograph Series, Reinhold Publishing Corporation, New York City (1963); U. S. Patent 3,492,309--synthesis of metal-free phthalocyanine; U. S.
Patent 3,492,308--synthesis of metal-free phthalocyanine; U. S.
Paten~ 3,509,146--synthesis of phthalocyanine and heterocyclic analogues thereof; U. S. Patent 3,657,272--synthesis of the X-form of metal-free phthalocyanine; U. S. Patent 3,594,163--method for converting the alpha form of phthalocyanine to the X-polymorph; and U. S. Patent Re 27,117 (original, U. S.
Patent 3,357,989)--synthesis of the X-form of metal phthalocyanine.

106~074 `
:

The sensitizers of the photoconductive composition can be any one or combination of compounds having the structural formula previously set forth. Sensitizers which are especially suitable for use in this composition include 3-perylenecarbox-aldehyde, and the lower alkyl homologues thereof. Sensitizer compounds of the type referred to hereinabove can be prepared by techniques described in literature or by standard modifica-tion of published procedures. In the preferred embodiments of this invention, the weight ratio of sensitizer to phthalocyanine pigment is about 1:1. At such concentrations, the spectral response of the composition is essentially flat and the induc- -~
tion period (the interval between illumination and photoresponse) is shortened in comparison to unsensitized composition.
Any of the insulating binders commonly used in prepara-tion of electrophotographic imaging members are suitable for use in this invention. Representative of such binder materials '~
are the poly(olefins), poly(styrene), poly(methylmethacrylate), poly(vinylchloride), poly(siloxane), the poly(vinylcarbazoles), poly(vinylpyrene), mixtures--e.g. U. S. Patent 3,640,710--, blends and copolymers thereof. A number of the above binders are commercially available and where unavailable can be pre-pared by techniques disclosed in the literature.
As indicated previously, the various components of the photoconductive composition can be associated with one another by conventional means and techniques. As is generally appre-ciated, the concentration of phthalocyanine that must be present within the composition to render it photoresponsive can vary depending upon the electronic properties of the other materials also present within the composition. For example, 106;~074 ~,, as little as about 0.1 weight percent phthalocyanine pigment is sufficient to render a composition photoresponsive provided charge carriers generated upon photoexcitation are not trapped within the composition but retain sufficient mobility to be capable of movement under the influence of an applied electric field.
The transport of such mobile carriers within a typical photoconductive composition can be accomplished by the photo-generator material, (through interparticulate contact) or by 10 the polymeric matrix or by other materials also contained with-in the composition. In order for the phthalocyanine pigments to perform both carrier generation and transport functions, they must be present within the photoconductive composition in a concentration of at least about 30 percent by weight and pre-erab1y about 50 percent by weight. As the concentration of phthalocyanine pigments increases substantially in excess of about 50 percent by weight, the charge storage capacity of the resulting photoconductive composition will decline. This increase in dark conductivity of the photoconductive composi-20 tion can be remedied by simply overcoating the photoconductivecomposition with a suitable material. Such overcoatings can either provide shallow trapping of the sensitizing charge (as described in U. S. Patent 2,901,348) or be sufficiently insu-lating so as to be capable of an independent charge storage function (similar to the overcoatings used in U. S. Patents 3,234,019; 3,653,064; and 3,708,291).
In order for the matrix containing the photoconduc-tive pigment to participate in or assume the entire charge transport function of the photoconductive composition, it must 30 also be photoresponsive (preferably outside the range of -~06~074 ~'.

spectral response of the photoconductive pigment). Represen-tative of the binder materials, which can be used as transport mat:rices, include the poly(vinylcarbazoles) and poly(vinyl-pyrene).
As indicated previously, once having combined the phtha-locyanine pigment, the sensitizer compound, and insulating bind- :
er resin in the proper relative proportions, the resulting mixture can be solvent cast or coated on a suitable substrate.
Both the phthalocyanine pigment and the spectral sensitizer 10 should preferably be insoluble in such casting solvents. Any ~ -of the conductive substrates traditionally used in preparation of electrophotographic imaging members can be coated with the above described photoconductive composition. Representative of materials suitable for use as conductive substrates in electro-photography include aluminum, chromium, brass, nickel, stain-less steel, metallized plastic films, metal-coated plastic films (aluminumized Mylar ) and tin oxide coated glass plates (NESA
glass).
The amount of composition transferred to the conduc-tive substrate can vary within the range of thicknesses general-ly disclosed for electrophotographic imaging members. For example, in conventional electrophotographic imaging systems, the thickness of the photoconductive layer can range from as thin as about 0.1 microns to an excess of about 60 microns.
Thicker layers, on the order of about 150 to about 200 microns, are traditionally used in xeroradiographic imaging members.
Where the photoconductive layer is overcoated with a dielectric film, the photoconductive layer need not itself be insulating provided that the overcoating in combination with the photo-conductive layer is capable of sustaining a sensitizing surfacecharge.

* trade marks .

11~6'~074 The Examples which follow further define, describe and illustrate the compositions, articles and methods of this invention. Apparatus and techniques used in preparation and evaluation of such electrophotographic imaging members are standard or as hereinbefore described. Parts and percentages appearing in such Examples are by weight unless otherwise indicated.
EXAMPLE I
Preparation of the 3-perylenecarboxaldehyde -About 22 grams N-methylformanilide is initially dis- , solved in 40 milliliters o-dichlorobenzene, the vessel contain-ing the above solution partially immersed in a water bath (bath temperature less than 25C) and 22 grams phosphorus oxychloride introduced into the flask by dropwise addition. About 20 grams of perylene is stirred into the above solution and the resulting mixture heated on a steam bath for twelve hours (temperature of contents of vessel 90-95C). The contents of the flask are thereafter poured into a second vessel containing 100 grams sodium acetate dissolved in 250 milliliters water.
The organic liquid phase of the mixture is separated from the aqueous phase by steam distillation. Crude aldehyde is there-after precipitated from aqueous solution and the solids re-crystallized from acetic acid and from benzene. The solids ~;
thus obtained are further extracted in a soxhlet extractor with 30-60 pet ether. The material remaining in the extrac-tion thimble is 3-perylenecarboxaldehyde mp 230C; yield 9.5 grams.
A photoconductive composition is now prepared accord-ing to the procedures described in U. S. Patent 3,640,710.

The following ingredients are added to a ball-milling jar one-third full of half inch diameter flint pebbles and roller ~06;~)74 . .
milled for about 20 hours at 140 rpm:
* . .
4.8 parts Chlorowax - 70 LP (a chlorinated paraffin, available from Diamond Shamrock Corp.) 4.8 parts alkyd-acrylate resin (Arotap EP8911-7-7 available from ADM Chemicals) ; 1.6 parts silicone resin ( Silicone Resin Sr-82 , available from General Electric Corp.) 0.7 parts alpha metal free phthalocyanine (available from BASF Corp.) 0.7 parts 3-perylenecarboxaldehyde - prepared as described above.
During this ball-milling procedure, the phthalocyanine pigment is converted from the alpha to the beta polymorph.
The above composition is separated from the flint pebbles by filtration through a 200 mesh nylon screen, the viscosity of the dispersion adjusted (if necessary, by the addition of toluene, to within a viscosity range of from about 150 to about 175 centipoise - measured at 24C on a Brookfield RVK viscom-eter, No. 2 spindle, speed setting - 50), and the recovered dispersion draw-down coated with a #22 wire on a 5 mil alumi-num sheet. The resulting coating is force air dried for 60 seconds at 125C to minimize settling of the particulates within the binder. Dry film thickness of the coating is estimated at about 6 to 7 ~m. Spectral response character-istics of this composition are shown in Fig. 1.

EXAMPLE I I--V
The procedures of Example I are repeated except for the addition of the following dyes to the composition in place of 3-perylenecarboxaldehyde.
EXAMPLE NO. DYE-STUFF
_ II Rhodamine B (2 mg dye/0.7 g pigment) * trade marks -12-106'~074 III Erythrosin Y(2 mg dye/0.7 g pigment) IV Napthol Red B (0.3 g dye/0.7 g pigment) V Indofast Yellow (.03 g dye/0.7 g -pigment) Evaluation of the spectral response characteristics of the above dye sensitized composition indicate no increase in sensitivity at the low end of the visible spectrum. Moreover, the dye sensitized compositions tend to show a decrease in spectral sensitivity of the composition at the upper end of the visible spectrum.
EXAMPLE VI
The electrophotographic plate prepared as described in Example I is now uniformly sensitized to a positive potential of approximately 600 volts by charging with a corona electrode, exposed to image inormation by projecting a color transparency onto said plate with white light from a distance of about 25 centimeters; thereby forming a latent image on the surface of -said plate. This latent image is rendered visible by develop-ment with Xerox 364 toner (a carbon'black pigmented styrene/n-butylmethacrylate resin). The toner image is thereafter trans-ferred to an untreated sheet of paper and any toner residues remaining on the plate removed by wiping the plate with a soft cotton cloth. The toner image is fixed to the copy sheet by standard thermal fusion techniques. The copy has good contin-uous tone quality indicating that the plate is sensitive to image information throughout substantially the entire visible spectrum.

. - ~ . - . .

~06~074 EXAMPLE VII
A series of phthalocyanine photoconductive binder layers are prepared from one part by weight X-metal free B phthaocyanine, one part by weight polyester resin (PE-20 g available from Goodyear Chemicals) and one part by weight perylene and a number of its analogues. The table which ~ollows compares the photoresponsiveness of these sensitized films at 498 nm to the photoresponsiveness of an unsensitized film at the same wavelength. The photoresponsiveness of the unsensitized film is assigned a sensitivity value of 1 and, therefore, films having values in excess of 1 are regarded as more photoresponsive and films having ~alues less than 1 are regarded as less photoresponsive. The other comments in this table reflect upon the suitability of such se~sitized compositiong in an electrophotgraphic imaging system.
SENSITIVITY
SE~SITIZER FACTOR COMME~TS
, a) perylene 1.8 absorption coefficient at 500 nm relatively low b) 3-perylene 3,5 carboxaldehyde , c) 3-perylene 0.5 low charge acceptance, carboxylic acid . persistent photo-currents d) 3,9-perylene(bis) 1.0 aldehyde .

e) 3,9-perylene(bis) 1.0 - carboxamide .
30f) 3,9-perylene(bis) 0,3 low charge acceptance hydroxymethyl 106~074 SENSITIVITY
SENSITIZER FACTOR COMMENTS

g) 3,9-perylenedicarbox- 0.8 anilide - ~ -, h) perylene-3-cyano-9- 1.1 carboxamide Ac is shown in the above table, the sensitization of a phthalocyanine binder composition with perylene and its analogues can produce significantly different photoresponse in the resulting composition. Most notible is the dramatic increase between the sensitization of the binder layer with perylene and 3-perylenecarboxaldehyde.

, ,

Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A photoconductive composition consisting essentially of a dispersion containing particles of phthalo-cyanine pigment, a film forming insulating binder resin and particles of at least one spectral sensitizer compound of the formula wherein R, R1 and R2 are independently selected from hydrogen or alkyl of 1-3 carbon atoms the relative weight ratio of phthalocyanine pigment to spectral sensitizer being within the range of 2:1 to 1:2 and the relative concentration of phthalocyanine pigment to binder within the composition ranging from about 0.1 to about 50 weight percent.

2. The composition of Claim 1 wherein the phthalo-cyanine pigment is the X-form of metal free phthalocyanine.

3. The composition of Claim 1 wherein the phthalo-cyanine pigment is the X-polymorph of a metal containing phthalocyanine.

4. The composition of Claim 1 wherein the insulat-ing binder is photoconductive.

5. The composition of Claim 1 wherein the spectral sensitizer is 3-perylenecarboxaldehyde.

6. The composition of Claim 1 wherein the spectral sensitizer is a homologue of 3-perylenecarbox-aldehyde.

7. An electrophotographic imaging member wherein the photoconductive insulating layer consists essentially of a dispersion containing particles of phthalocyanine pigment, a film forming insulating binder resin and particles of at least one spectral sensitizer compound of the formula wherein R, R1 and R2 are independently selected from hydrogen or alkyl of 1-3 carbon atoms the relative weight ratio of phthalocyanine pig-ment to spectral sensitizer being with the range of 2:1 to 1:2 and the relative concentration of phthalocyanine pig-ment to binder in the photoconductive insulating layer ranging from about 0.1 to about 50 weight percent.

8. The imaging member of Claim 7 wherein the phthalocyanine pigment is the X-form of metal free phthalo-cyanine.

9. The imaging member of Claim 7 wherein the phthalocyanine pigment is the X-polymorph of a metal con-taining phthalocyanine.

10. The imaging member of Claim 7 wherein the insulating binder is photoconductive.

11. The imaging member of Claim 7 wherein the spectral sensitizer is 3-perylenecarboxaldehyde.

12. The imaging member of Claim 7 wherein the spectral sensitizer is homologue of 3-perylenecarboxaldehyde.

13. An electrostatographic imaging method com-prising:
(a) providing an electrophotographic imaging member having a photoconductive insulating layer consisting essentially of a dispersion containing particles of phthalo-cyanine pigment, a film forming insulating resin binder and particles of a spectral sensitizer compound of the formula wherein R, R1 and R2 are independently selected from hydrogen or alkyl of 1-3 carbon atoms the relative weight ratio of phthalocyanine pigment to spectral sensitizer being in the range of 2:1 to about 1:2 and the relative concentration of phthalocyanine pigments to binder in the photoconductive insulating layer ranging from about 0.1 to about 50 weight percent; and (b) forming a latent electrostatic image on said imaging member by initially sensitizing the imaging member to a positive potential in the dark followed by selective exposure of the sensitized layer to image information, the wavelength of light used in projection of said image infor-mation being anywhere within the range of the visible spectrum.

14. A photoconductive composition according to Claim 1 consisting essentially of a dispersion containing particles of phthalocyanine pigment, a film-forming insulating binder resin which is incapable of substantial transport of charge carriers and particles of at least one spectral sensitizer compound of the formula set forth in Claim 1, the relative concentration of phthalocyanine pigment to binder within the composition ranging from about 30 to about 50 weight percent.

15. The composition of Claim 14, wherein the phthalocyanine pigment is the X-form of metal-free phthalo-cyanine.

16. The composition of Claim 14, wherein the phthalocyanine pigment is the X-polymorph of a metal-containing phthalocyanine.

17. An electrophotographic imaging member according to Claim 7 wherein the photoconductive insulating layer consists essentially of a dispersion containing particles of phthalocyanine pigment, a film-forming insulating binder resin which is incapable of substantial transport of charge carriers and particles of at least one spectral sensitizer compound of the formula set out in Claim 7, the relative concentration of phthalocyanine pigment to binder in the photoconductive insulating layer ranging from about 30 to about 50 weight percent.

18. An electrostatographic imaging method accord-ing to Claim 13 wherein in step (a) there is provided an electrophotographic imaging member having a photoconductive insulating layer consisting essentially of a dispersion containing particles of phthalocyanine pigment, a film-forming insulating resin binder which is incapable of substantial transport of charge carriers and particles of a spectral sensitizer compound of the formula set out in Claim 13, the relative concentration of phthalocyanine pigment to binder in the photoconductive insulating layer ranging from about 30 to about 50 weight percent.

19. A photoconductive composition according to Claim 1, wherein the phthalocyanine pigment is in the form of a dispersion containing particles of phthalocyanine pigment, the film-forming insulating binder resin is capable of trans-port of charge carriers, and the spectral sensitizer is in the form of particles.

20. An electrophotographic imaging member accord-ing to Claim 7, wherein the photoconductive insulating layer consists essentially of a dispersion containing particles of phthalocyanine pigment, a film-forming insulating binder resin which is capable of transport of charge carriers and particles of at least one spectral sensitizer compound of the formula set out in Claim 7.