CA1072806A - Multi-active photoconductive element i - Google Patents

Abstract

MULTI-ACTIVE PHOTOCONDUCTIVE ELEMENT I

Abstract of the Disclosure A multi-active photoconductive insulating element having at least two layers comprising a charge-generation layer and an organic photoconductor-containing charge-transport layer is disclosed. The charge-generation layer contains a continuous polymeric phase having dispersed therein a co-crystalline complex composed of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one pyrylium-type dye salt.

Description

~ield of the invention This invention relates to electrophotography and particularly to an improved photoconductive insulating element for use in various electrophotographic processes.
Background of the Invention Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature, for example, U.S. Patent Nos. 2,221,776; 2,277,013;

2,297,691; 2,357,809; 2,551,582; 2,825,814; 2,833~648; 3~220,324;
o 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing a photoconductive insulating element which is prepared to respond to imagewise exposure with e:Lectromagnetic radiation by forming a latent electrostatic charge image. A variety o~ subsequent operations, now well-known in the art, can then be employed to produce a permanent record of the charge image.
Various types o~ photoconductive insulating elements are known ~or use ln electrophotographic Lmaglng processes. In many conventional elements, the active components oP the photocon- , `
ductive insulating composition are contained in a single layer composition. This composition is typically affixed, ~or example, to ~ conductive support during the electrophotographic imaging process.

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Among the many different kinds of photoconductive compositions which may be employed in typical single active layer photoconductive elements are inorganic photoconductive materials such as vacuum evaporated selenium, particulate zinc oxide dispersed in a polymeric binder, homogeneous organic photo-conductive compositions composed of an organic photoconductor i` ;

30 solubilized in a polymeric binder, and the like. ,`
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~ Z806 Other especially useful photoconductive insulating compo-sitions which ma~ be employed in a single active layer photocon-ductive element are the high-speed heterogeneous or aggregate photo-conductive compositions described in Light, U.S. Patent 3,615,~14 issued October 26, 1971 and Gramza et. al., U.S. Patent

3,732,180 issued May 8, 1973. These aggregate-containing photoconductive compositions have a continuous electrically insulating polymer phase containing a finely-divided, particulate, co-crystalline complex of (i) at least one pyrylium-type dye salt and (ii) at least one polymer having an alkylidene diarylene group in a recurring unit.
In addition to the various single active layer photo-conductive insulating elements such as those described above, various "multi-active-layer" photoconduc-tive insulating elements, i.e., those having more than one active layer have been described in the art. One useful t~pe of "multi-active-layer" photoconductive element is described in Hoesterey, U~S. Patent 3,165,405 issued January :L2, 1965, at column 2, lines 6-20 thereof. As descri.bed in this patent, pho-toconductivity is achieved by applying a uniform positive charge to the surface of an element containing two layers of zinc oxide, a sensitized ~-` zinc oxide bottom layer and an unsensitized zinc oxide upper layer, and then exposing the sensitized bottom layer to a pattern of activating radiation. Photoconductivity is -produced in the element by the electrical interaction of the two zinc oxide layers. The sensitized zinc oxide bottom layer generates photoelectrons, i.e. negative charge carriers, and injects these charge carriers into the`unsensitized zinc oxide . . .
30 upper layer which accepts and transports these charge carriers to the positlvely charged surface of the photoconductive element.

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The concept o~ using two or more active layers in a photo-conductive insulating element, at least one of the layers designed primarily ~or the photogeneration of charge carriers and at least one other layer designed primarily for the transportation of these generated charge carriers, has been discussed in the patent literature. Such multi-active-layer photoconductive elements are sometimes referred to hereinafter simply as "multi-active" photoconductive elements. In addition to the above-noted Hoesterey patent, a partial listing of representative patents discussing or at least referring to "multi-active"
photoconductive elements includes: Bardeen, IJ.S. 3,041,166 issued June 26~ 1962 ; Makino, U.S. 3,394,001 issued July 23, 1968; Makino et. al. U.S. 3,679,~o5 issued July 25, 1972;
Hayaski et. al., U.S. 3,725,058 issued April 3, 1973; Canadian patent 930,591 issued July 2~, 1973; and Canadian patents;
932,197 - 199 issued ~ugust 21, 1973; and British Patents 1,337,228 and 1, 343,671.
~lthough there has been a fairly extensive description of specific types of multi-active photoconductive insulating ~ -elemen-ts in the literature, various shortcomings still exist in these elements so that there is a need to investigate alternative kinds of multi-active elements. For example, the multi-active elèments described in the aforementioned Hoesterey patent suffer -from the disadvantages of using generally low speed and difficult to clean zinc oxide materials in bo-th active layers of the element. Other multi-active elements such as those described ` in Canadian patents 930,591 and 932,199 appear to be primarily`` designed for use in a positive charging mode of operation and therefore may -not generally be suitable ~or use in an electro-20 photographic process in which a negative charging mode is ' employed. Furthermore~ the type o~ multi-active-elements described in U.S. Patents 3,041~166; 3,394,001; 3,725,058 and Canadian Patent 930,591~ which employs contiguous organic and lnorganic ~, . .

~ 806 active layers, presents the problem of obtaining g~od adhe610n between two layers of substantially disslmilar mat~rials ln a unitary element.
In addition to the above-noted problems and ~hort-comings associated with prior art m~lti-active photoconductive elements, it should be noted that, to applicant's knowledge~
the art, to date, h~s generally disclo6ed no type of multi-active photoconductive element which uses and takes advantage of the above-mentioned high-speed aggregate photoconductive compositions described in Light, U.S. Patent 3,615,414, except as may be described in Seus, U.S. Patent -3,591,374 issued July 6, 1971. The aforementioned Seus patent describes a photoconductive element employing an aggregate photo-conductive composition overcoated with a solution of a sen6itizing dye of the type useful in preparing the initial aggregate photo-conductive composition, ie., a pyryliu~-type dye salt, whereby the overcoated dye imbibes into and interacts with the aggregate photoconductive composition to provide~ an increaæe in electro-photographic speed of the resultant aggregate composition. In this regard, it is also noted th~t, Mey, Canadian Serial No.
239,052 filed November 5, 1975, describes a type of multi-active photoconductive element which includes a layer employing the aggregate photoconductive cmmpositions described in U.S.
3~615~414 together with an inorganic photoconductor-containing layer.
Becau~e of the commercial need ~or improved ~ggregate photoconductive compositions, particularly those exhlbiting one or more of the following properties: easier cleaning, ~reater resistance to wear and abrasion, improved panchromatic response, improved resistance to electrical ~atigue, and higher electro-photographic speeds, it would be advantageous to develop new types of multi-acti~e element~ which employ ~nd improve on-the exi~ting aggregate photoconductive compo~itions.

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t~R{~6 Summary of the Invention In accord with the present invention there is providedan improved multi-active photoconductive insulating element having at least two layers comprising an organic photoconductor-containing, charge-transport layer in electrical contact with an aggregate, charge-generation layer. A primary feature of the improved multi-active element of the present invention resides in the aggregate~ charge-generation layer which contains a con-tinuous, electrically insulating polymer phase and a discontinuous phase comprising a finely-divided, particulate co-crystalline complex of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one pyrylium-type dye salt. :
In accord with a particularly useful embodiment of the invention relating to multi-active photoconductive elements sensitive to visible light, i.e., light in the region of from about 400 to 700 nm, the aggregate charge-generation layer is characterized by havlng its princlpal absorption band o~ radiation in the visible region of -the spectrum within -the range of from about 520 nm to about 700 nm.
The organic charge-transport layer used in the m~llti-active elements of the invention contains no particulate, co-crystalline complex and no pyrylium-type dye salt. The charge~
transport layer is essentiall~ an organic composltion. It is in eIectrical contact with the charge-generation layer and contains at least one organic photoconductor as the charge-transport material which is capable o~ accepting and transporting injected charge carriers ~rom the charge-generation layer.

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In accord with those par-ticularly useful embodiments of the invention wherein the multi-active element is sensitive to visible light, it is advantageous to select the organic photoconductor(s) contained in the charge-transport layer from organic photoconductive materials whose principal absorption band occurs in a region of the spectrum below about 475 nm., preferably below about 400 nm. In accord with this embodimen-t, the charge-transport layer is insensitive or, at most, only partially sensitive to visible light. In this embodiment of the invention, the charge-transport layer is substantially transparent (i.e., transmits and does not absorb), as well as substantially insensitive, to visible light so that e~posure of the charge-generation layer may be made through the charge-transport layer, if necessary or desirable.
In accord with another embo~iment of the invention, the charge-transport layer may be colored or opaque so that it transmits only a portion of or no radiation capable of activating the charge-generation layer. In this embodiment of the invention, exposure of the charge-generation layer to activating radiation is advantageously made by exposing the surface of the generation layer which is opposite the charge-transport layer so that activating radiation for the charge-generation layer need not pass through the charge-transport layer before contacting the charge-generation ~ -layer.
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Another important feature o~ the invention resides in the finding that extremely high-speed photoconductive elements can be obtained by controlling the thickness of the charge-transport and charge-generation layers. That is, it has been found that an especially useful embodiment of the multi-active photoconductive element of the invention may be provided using a relatively -thin charge generation layer contiguous to a charge-transport layer having a dry thickness from about 5 to about 200 times that of the charge-generation layer. In accord with this embodiment, a particularly high-speed multi-active photoconductive element is obtained using an element having a charge-generation layer having a dry thickness less than about 5.0 microns, and preferably within the range of from about 0.5 to about 2.0 microns. However, as illustrated hereinafter, multi-active elements containing charge-transport layers which have a dry thickness less than that of the charge-generation layer may also be used.
It should be understood that the multi-active photoconductive element of the invention may be employed as the light-sensitive electrical image-forming member in a variety of electrophotographic processes,including transfer electrophotographic processes,employing a reusable photo~ 31~. :
conductive element; non-transfer electrophotographic processes wherein a final visible image is formed on a _8-.

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non-reusable photoconductive element; the so-called TESI processes (i.e., Transfer of ElectroStatic Images) such as described by R.M. Schaffert in the book entitled Electrophotography, at ~ 87-96, The Focal Press, New York (1965); etc. For convenience and purposes of illustration, the multi-active photoconductive element of the invention will be described herein with reference to its use in conventional electrophotographic processes in which an electrostatic charge image is formed at or near the surface of the photoconductive element by employing the now well known steps of (a) applying a uniform electrostatic charge to the top surface of the photoconductive insulating element in the absence of activating radiation while the bottom surface of the element is maintalned at a suitable reference potential,thereby creating an electric field through the photoconductive element and (b) imagewise exposing the photoconductive element to activating radiation. However, it will be appreciated b~ those familiar wlth the art that the multi-actlve element of the invention may a:Lso be advantageously employed in a wide variety of other known electrophotographic processes.
In accord with the various embodiments of the present ~-invention, the above-described multi-active photoconductive element may be emplo~ed in electrophotographic processes using either positive or negative charging of the photoconductive element.- Typically, when the multi-active photoconductive element is employed in an electrophotographic process, the element is affixed, either permanently or temporarily, on a conductive .
support~ In such case, by àppropriate selection of the charge~
transport material in the charge-transport layer, the multi~
active element is capable of providing useful electrostatic 30 charge images when used in either a positive or negative ---charge mode, regardless of whether the charge-generation layer `~ or the charge-transport layer is located adjacent the conductive support. However, in accord with certain preferred embodiments .. . .
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of the invention, when ~he element is to be used in a positive charging mode~ it is par~icularly advan~ageous to place the charge-~ransport layer adjacen~ to the conductive support.
And, when it is desired to use the multi-ac~ive element in a negative charging mode, it is par~icularly advantageous to place the charge-generation layer adjacen~ the conductive support.
In accord with an especially useful embodiment of the invention, wherein the charge-generation layer of the multi-active element is adjacent to a conductive support, the overcoated charge-transport layer comprises a homogeneous composition of an electrically-insulating polymeric binder and solubilized therein one or more p-type organic photoconductors which are transparent to radiation which activates the charge-generation la~er.
B~lef` 3escrlptlon of the Drawln~s FIG. 1 represents a cross-sectlonal vlew o~ a mul-tl-active photoconductive insulating element 14 of the present invention applied to the surface of a conductive layer 11 wherein charge-generation layer 10 is in electrical contact with conducting layer 11. ~lthough not shown in FIG. 1, one or more optional subbing layer(s) to improve adhesion and/or to modify current flow (e.g. -an electrical barrler layer) may be used between conducting layer - ~-11 and charge-generation layer 10. In FIG. 1 charge-transport -layer 12 is the upper layer of the multi-active photoconductive In FIG. 2 another embodlment of the multl-actlve element 14 of the present lnventlon is shown whereln the charge-trans-port layer 12 ls in electrical contact wlth conducting layer 11.
Agaln~an optional subblng layer between conductlng layer 11 and charge-transport layer 12 may be present, if desired. In this embodlment of the lnventi~n, the charge-generation layer 10 serves as the upper layer of the multi-active photoconductl~e element. -.

--10'7'~8 FIGS. 3a-3d, 4a-4d, 5a-5d and 6a-6d represen~
diagrammatically the different modes of electrical operation which are believed to occur in the multi-active elements of the invention.
FIG. 7 represents a modification of the various modes of operation represented in FIGS. 3a-3d and 4a-4d wherein exposure of the multi-active element of the ,1 -invention is e~fected without having the activating radiation for the charge-generation layer pass through lO the charge-transport layer. t~

Description o~ the Pre~erred Embodiments Before proceeding with a detailed description of the various materials which ma~ be employed in the multi-activephoto- -conductive insulating element of the invention, a description of the electrical interaction and function ~f the charge-transport !
and charge-generation la~er used in the multi-active photoconductive !
element described herein will be help~ul to gain a better under-standing of the present invention. Accordingl~, a description of ~- -the electrical operation occurring in the multi-active photocon-ductive element of the invention when employed in a conventional !~
; electrophotographic imaging process is presen-ted with reference to the attached FIGS.
The charge-transport layer used in the present invention, ~
as its name implies, is a composition which, in the presence of ~ -an electrical ~ield~ accepts the charge carriers injected into i-t b~ the charge-generation la~er and transports~ i.e. conducts, the charge carriers through the bod~ of the charge-transport layer to -the surface thereof. The electrical force driving the charge carriers through the transport layer is supplied by an electric ~ield such as a potential difference applied across -the multi-active `
photoconductive element. Such an electrical driving force may be -11- , - . ,.- . . . . - ~;; - , .. ,........ - - .~ - , . :

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es-tablished, for example, in conventional electrophotographic imaging processes in which the multi-active photoconductive element may be employed, by at least ~mporarily af~ixing the element to a conductive substrate maintained at a given re~erence potential and applying a uniform electrostatic charge of opposite polarity to the surface of the multi-active element in the absence o~ activating radiation.
The term "activating radiation" as used in the present specif~cation is defined as electromagnetic radiation which is capable o~ generating electron-hole pairs in the charge-generation layer upon exposure thereof. Thus, when ~he charge-generation layer is exposed to activat~ng radiation, charge carriers, i.e. electron-hole pairs, are photogenerated therein. In accord with those preferred embodiments of the invention wherein the charge-transport layer is wholly or partially transparent to activating radiation, the charge-transport layer is insensit:Lve or at least relatively insensitive to activating radiation (compared to the charge-generation layer) and therefore generates no or relatively few charge carriers (compared ~o the number of charge carriers produced by the charge-generation layer) upon exposure to activating radiation.
The uniform electrostatic charge applied to the surface of the multi-active element is held at or near the surface due to the electrical insulating properties of the multi-active element in the absence o~ activating radiation. As illustrated in Figs. 1 and 2, either the charge-generation layer 10 or the charge-transport layer 12 may be used as the sur~ace layer o~ the photoconductive element of the invention~ and these layers are in electrical contact with one another so that charge carriers generated in the charge-generation layer can flow into the charge-transport layer. The electrical resistivity of the multi-active phokoconductive insulating element of the inven-tion (as measured ~ .

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across the charge--transport layer and -the charge-generation layer in the absence of activating radiation and any other radiation to which the charge -transport layer may be sensitive) should be at least about 109 ohm-cms. at 25C. In general, it is advantageous to use multi-active elements having a resistivity several orders of magnitude higher than 101 ohm-cms., for example, elements having an electrical resistivity greater than about 1014 ohm-cms. at 25C.
Having described some of the general functions and characteristics of the charge-transport and charge-generation layer hereinabove, it should be pointed out that there are actually four different modes of operation possible with the element of the present invention using conventional electro-photographic ~echniques, depending upon the particular composition of the charge-transport layer used in a speciflc multi-active embodiment. Although, as explained hereinafter, the present invention has been found to provide higher sensitivity and more efficient operation in certain of these modes of operation ; than in other o~' these modes, it is possible to use the present invention in each o~ these four different modes.
Referring now to Fig. 1 wherein charge-generation layer 10 is adjacent conducting layer 11~ two modes of operation are possible depending upon whether the element is subjected to an initial uniform negative electrostatic charge or to an initial uniform positive electrostatic charge. These two differen~t modes of operation are presented diagrammatically in Figs. 3a-3d and 4a-4d.

In Fig. 3a the multi-active photoconductive element 14, in the absence of activating radiation, is given an initial uniform negative charge 15 with respect to an equipotential reference 3 potential 20 at which conducting layer 11 is maintained. In : . .

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Fig. 3b, element 1)~ is exposed to activatirlg radiation 16. As a result, as indicated in Fig. 3b, the activating radiation passes through the charge-transport layer 12 which is substantially transparent and insensitive to this radiation and contacts the particulate co-crystalline complex 18 located in charge~generation layer lO. Assuming now that activating radiation 16 represents a single photon of light, the electrical process which occurs as radiation 16 strikes a single particle of the co-crystalline complex is illustrated in Fig. 3c.
In Fig. 3c, upon exposure of particle 18 ~ith radiation 16, charge carriers, i.e. an electron-hole pair 19, are photogenerated b~ particle 18 which is sensitive to ac-tivating radiation 16. Due to the electrical ~ield which is present in multi-active element 14, between conductive la~er 11 and the surface of charge-transport layer 1~, the photogenerated charge carriers will now begin to mi~rrate through the multi-actlve photoconductive element. The hole will be electrically attracted to the uniform negative electrostakic charge 15 at the surface of charge-transport layer 12; whereas ~0 the electron will migrate toward conducting layer ll which is maintained at positive reference potential 20 relative to the uniform negative electrostatic charge 15. Once this .. , . . .,~,v ~` migration is complete, the original negative uniform charge 15 applied to the surface of layer 12 is effectively neu-tralized at the point of exposure to activating ray 16. This is caused by the migration of the hole to the surface of charge-transport layer 12 at the point where activating ray 16 passes through charge-transport layer 12.
As a result, as shown in Fig. 3d, à~ter exposure the ` 3O multi-active photoconductive element 14 has an electrostatic charge pattern 15 at or near its sur~ace ~hich corresponds .... ____ ._ ._.. -. .

~ 14-to -the pa-ttern of activating radiation to which the element was exposed. This charge pattern may then be developed by conventional electrophotographic techniques3 or it may be transferred to another dielectric element to be developed at a later time.
The second mode of operation to which the multi-aCtiVe photoconductive element 14 in Fig. 1 may be subjected is illustrated diagrammatically in Figs. 4a through 4d. Thls process is quite similar to that illustrated in Figs. 3a through 3d, except that the uniform electrostatic charge 15 applied to charge-transport layer 12 has a positive polarity with respect to the reference potential 20 at which conducting layer 11 is maintained. Accordingly, as indicated in Figs. 4a-4d, when the exposure of co-crystalline complex particles 18 to activating radiation 16 causes the photogeneration of charge carriers; the hole migrates to conductive layer 11 arld the electron migrates to the surface of charge~transport ; layer 12. As indicated in Fig. 4d, the net result Or this mode of operation is the formation of a positive electrostatic charge pattern 15' at or near the surface of charge-transport layer 12 which corresponds to the pattern of activating radiation 16 to which multi-active element 14 was exposed.
The two modes of operation associated with the multi-active photoconductive element of Fig. 2 are analogous to that described hereinabove with reference to Fig. 1. In this case, however, as shown in Fig. 2, the position of the charge-transport layer 12 and the charge-generation layer 10 .
are reversed. Thus, in Figs. 5a-5d and 6a-6d the uniform electrostatic charge which is applied to the surface of multi-active photoconductive element 14 is applied to charge~
generation layer 10, rather than to charge-transport layer 12.

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Turning now specifically to Figs. 5a-5d, a mode of operation for the element of Fig. 2 is illustrated wherein`
the charge-generation layer 10 is given a uniform electro-static charge 15 of negative polarity relative to the reference potential 20 at which conducting layer 11 is maintained. Thus, an electrical field is set up within multi-active element 14 of Fig. 5a. In Fig. 5b, the element bearing the uniform negative polarity electrostatic charge 15 is exposed to activating radiation 16. As a result, as shown in Fig. 5c, co-crystalline complex particles 18 are contacted by activating radiation 16 and photogenerate electron-hole pair 19 charge carriers. The hole migrates to the surface of charge-generation layer 10 due to the negative polarity of electrostatic charge residing at this surface, and the electron migrates through charge-transport layer 12 to the inter~ace between conducting layer 11 and charge-transport layer 12. Thus, as shown in Fig. 5d, as a result oP uniform negative electrostatic charge 15 and the exposure to aetivating radiation 16~ a negative electrostatie eharge image pattern 15 is formed at or near the sur~aee of eharge-generation layer 10.
The remaining mode of operation for the multi-aetive photoeonduetive element of the present invention having the struetural eon~iguration shown in Fig. 2 is illustrated in Figs. 6a-6d. This eleetrostatie image-forming pxoeess is similar to that described above with respeet to Figs. 5a-5d, exeept that in Figs. 6a-6d the uniform electrostatie eharge 15 applied to the surfaee of eharge-generation layer 10 has a positive pola~it~ as indieated in Fig. 6a. For this reason~
in Figs. 6b and 6e when aetivating radiation 16 strikes 30 eo-crystalline complex particles 18 to photogenerate electron- ~ `
hole pair 19 charge carrlers, the hole and the electron migrate in directions opposite to that depicted in Fig. 5c.
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Thus, in Fig 6c the electron migrates to the surface of charge- -generation layer 10, and the hole migrates through charge-transport layer 12 to the interface of conducting layer 11 and charge-transport layer 12. As a result, as shown in Fig. 6d, there is ~ormed a positive electrostatic image pattern 15' at or near the sur~ace o~ charge-generation layer 10 corresponding to the original activating radiation exposure pattern.
Although the present invention has been explained in terms of several differing modes of electrical operation, as outlined briefly hereinbefore, it shall be noted that certain multi-active elements may be employed in more than one mode of operation. For example, certain transport layers are capable of transporting both holes and electrons, so that a multi-active element of the invention using such a transport layer may be capable of all four of the above-described modes of operation.
In the four modes of operation illustrated in Figs. 3a-3d and 4a-4d, exposure of the multi-active element is achieved by exposing the charge generation layer 10 through the charge-transport layer 12. Accordingly, in these particular embodiments of the invention the charge-transpo~tlayer must be wholly or at least partially transparent to acti~ating ~ radiation 16 Howe~er, in accord with a modlfication of the present `: invention illustrated in Fig. 7, it is possi~le to use a charge-.; transport layer 12 which is partially or wholly opaque to - activating radiation 16 in the modes of operation illustrated in Fig. 3a-3d. This can be done, as illustrated in Fig. 7, by employing as conducting support 11, a conducting support 3 which is transparent to radiation 16 so that radiation 16 can expose charge-generation layer 10 without having to first pass through charge-transport layer 120 :; :

~7Z8~i l'he multi-active elements of the invention, particularly certain preferred embodiments thereof such as that illus~rated in Figs. 3a-3d, offer distinct advantages over conventional single layer aggregate photoconductive compositions as described in Light, U.S. 3,615,414.
Among others, it has been found that although conventional single layer aggregate compositions may be made to have varying thicknesses, best results are usually obtained with fairly thin layers having a dry thickness on the order of up to about 15 microns. As aggregate layers thicker than about 15 microns are used, speed losses are encountered because the negative charge carrier appears to have a transport range limitation of about 15 microns.
However~ it would be advantageous to increase the thick-ness of conventional aggregate photoconductive layers beyond 15 microns so that one could take advantage of the theoretical reduction in the amount of exposure light required to discharge the layer. This theoretical reduction in the amount of required exposure light is the result of the decrease in capacitance and the corresponding reduction in the surrace charge density which would occur by increasing the thickness of the -aggregate photoconductive layer.
The multi-active elements of the present ;~ invention as illustrated in Figs. 3a-3d are readily prepared having thicknesses above 15 microns without .
- encountering any problem associated with negative charge carrier range limitations. This is because the charge-generation layer which contains the aggregate 30 composi-tion in the multi-active element of the invention ¦~

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~ 8~6 can be, and preferably is, a relatively thin layer having a thickness less than 5 microns, whereas the charge-transport layer can be, and preferably is, a relatively thick layer. Using a multi-active element having these structural characteristics in a negative charging mode as shown in Figs. 3a-3d, one can obtain the advantage of using a relatively thick photoconductive layer while r avoiding the range limitations of the negative charge carriers in conventional single layer aggregate photo-10 conductive elements.
It has also been found that conventional slngle layer aggregate compositions tend to exhibit a change in thelr pos:ltive charge carrier transport capability as the elements are aged. For example, it is known that conven-tional aggregate compositions, when subjected to normal room light temperature aging, exhibit a gradual improvement in ~ :
the transport of positive charge carriers until a constant value ls reached after about 100 to 400 hours. In contrast, the multi-active elements of the present invention, at 20 least in certain embodiments thereo~, exhibit improved positive charge carrier transport, both when freshl~
prepared and when aged, in comparison to conventional single layer aggregate compositions. ~.
In addition, certain embodiments of the invention having the structure shown in Fig. 1 provide a reusable photoconductive element which is significantly easier to ` clean and much less subject to deterioration and wear than are conventional reusable single layer aggregate photocon-ductive elements. This advantage is particularly applicable 30 to those embodiments of the invention wherein the charge-trans-port layer is a homogeneous composition comprising one or more organic photoconductors solubilized in a polymeric binder.

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The charge-transport layer used in the multi-acti~e element of the present invention is essentiall~ an organic material-containing composition free from all inorganic photo-conductors, i.e., photoconductors such as zinc oxide composed solel~ of inorganic molecules. The term "organici', as used herein, refers to both organic and metallo-organic materials.
The charge-transport layer used in the present invention contains as the active charge-transport material one or more organic photoconductors capable of accepting and transporting charge carriers generated by the charge-generation layer. The charge-transport layer is ~ree of the above-mentioned co-crystalline complex and any pyrylium-type dye salt. Useful charge-transport materials can generally be divided into two classes depending upon the electronic charge-transport properties of the material. That is, most charge transport materials generally will preferentially accept and transport either positive charges, i.e. holes, or negative charges, i.e. electrons, generated by the charge-generation layer. Of course, there are many materials which will accept and transport either positive charges or negative charges; however, even these "amphoteric"
materials generally, upon closer investigation, will be found to ; possess at least a slight preference for the conduction of either positive charge carriers or negative charge carriers.
Those materials whlch exhibit a preference for the conduction of` positive charge carriers are referred to herein as "p-type" charge-transport materials, and those materials which exhibit a preference for the conduction of negative charge ; carriers are referred to herein as "n type" charge-transport materials.
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The capability of a given organic photoconductor to accept and transport charge carriers generated by the charge-generation layer used in the multi-active elements of the invention can be conveniently determined by coating a layer of the particular organic photoconductor under consideration for use as a charge-transport material (e.g. a 5 to 10 micron thick layer containing about 30 weight percent or more of the organic photoconductive material together with up to about 70 weight percent of a binder, if one is used), on the surface of a charge-generation layer (eOg., a 0.5 to 2 micron aggregate charge-generation layer such as that described more specifically in Example 2 hereinafter) which is, in turn, coated on a conducting substrate. The resultant unitary element may then be subjected to a conventional electrophotographic processing sequence including (a) applying a uniform electrostatic charge to the surface of the layer to be tested ~or charge-transport properties in the absence of activating radiation while the conducting substra-te is maintained at a suitable reference potential thereby creating a potential dif-ference, V~ across the element of, for example, about + 200-600 volts, (b) exposing the charge-generation layer of the resultant element to activating radiation, ~or example, 680 nm. light energy of 20 ergs/cm.2, and (c) determining the change in the magnitude of the charge initially applied to the element caused by the exposure to activating radiation, i.e., calculating the change in potential difference, ~.V, across the element as a result of the exposure. If the particular organic photoconductor under consideration as a charge-transport material possesses no charge-transport capability, then the ratio of the quantity V0 to the quantity VO - ~ , i.e., the ratio V0 : (VO - ~V)~ will~ to a `30 good approximation, equal the ratio of the sum of the physical thicknesses of the charge-transport layer~ TCt, and -the charge-.... .
generation layer, Tcg, to the physical thickness of the charge-generation layer by itself (i.e. Tcg ), i e.~ the ratio , ,, -: : - - ~, ~7~8(~6 (TCt -1- Tcg) Tcg . That is, VO:(VO_ ~V) - (Tct-~Tcg) Tcg-If, on the other hand, the particular organic photoconductor under consideration possesses charge-transport capability then the ratio VO:(VO - ~V) will be greater than the ratio (TCt + Tcg) Tcg, i-e-, VO (VO - ~V) ~ (Tct ~ Tcg ) Tcg -If, as is often the case, a binder is employed in the charge-transport layer when the above-described charge-transfer determination is made, care should be taken to account for any charge-transport capability exhibited by the charge-transport layer which may be imparted solely by the binder, rather than by -the particular organic photoconductor being evaluated. For exam-ple, certain polymeric materials,particularly certain aromatic- or heterocyclic-group-containing polymers have been found to be capable of accepting and transporting at least some of the charge carriers which are inJected to it by an adJacent charge-generation layer. For this reason, it is advantageous when evaluating various organic photoconductor materials for charge-transport p~operties to employ a binder, if one ls needed or desired, which exhibits little or no charge transport capability with respect to charge carriers generated by the charge~generation layer of the present invention, for example, a poly(styrene) polymer.
As explained above, among the organic photoconductors which have been found especially preferred as charge-transport materials in the present invention are materials wholly or partially transparent to9 and therefore insensitive or substantially insensitive to, the activating radiation used in the present invention. Accordingly, if desired, exposure of the charge-generation layer can be ef~ected by activating radiation which ;~

30 passes through the charge-transport layer before impinging on the generation layer. The organic photoconductors preferred for use .

~ - -22-.. . . ~ . ....... ... ....... . . .
.... . - . . ..

~ 8~6 as charge-transport materials in the charge transport layer do not~
in fact, function as photoconductors in the present invention because such materials are insensitive to acti~rating radiation and, therefore, do not generate electron-hole pairs upon exposure to activating radiation; rather, these materials serve to transport the charge carriers generated by the charge-generation layer.
In most cases (except as noted hereinafter with respect to FIG. 7), the charge-transport materials which are prepared for use in a -multi-active element of the invention which is sensitive to lO visible light radiation are organic photoconductors whose ;
; principal absorption band lies in a region of the spectrum below about 475 nm. and preferably below about l~oo nm. The phrase "organic p~lotoconductors whose principal absorption band is belo~
about L~oo nm. 'l refers herein to photoconductors wh-lch are both colorless and transparent to visible light, i.e., do not absorb visible light~ ~hose ma~erials which exhibit little or no absorptlon above 475 nm. but do e~hibit some absorption of radlation in the 400 to 475 nm. region will exh:ibit a yellow coloration but will remain transparent to visible light in the 1~75 to 700 nm.
region of the visible spectrum.
. .
Of course, as noted earlier, where the multi-active element of the invention is exposed to activating radiation as illustrated in Fig. 7, i.e., where the charge-generation layer it is exposed without having to expose through the charge-transport layer, it is possible to use organic photoconductive materials in the charge-transport layer which are highly colored or opaque.
An example of such a multi-active element is illustrated herein-after in Example 7 wherein a charge-transport material comprising a mixture of poly(vinyl carbazole)and 2,4,7-trinitro-9-~luorenone is employed. Such a mixture is highly colored having a deep orange :

~'7Z~

coloration and is opaque over a substantial portion of the visible spectrum.
In some cases, where one employs3 for example, a charge-generation material having a peak absorp-tion to visible light within the range of from abou~t 520 - 700 nm., it may be desirable to employ as the charge-transport material a material exhibiting at least some absorption of radiation in the region of the spectrum e~tending ~rom about 400 nm. to about 520 nm. In such case, one can expose the resultant element to visible light through the transport layer and use the transport layer as (1) a charge-transport material for the charge carriers generated b~ the charge-generation layer in response to that portion o~ the visible light in the 520 - 700 nm. range and (2) a partial charge-generatlon material for that portion of the visible light below the 520 nm. region with respect to which the charge-generation layer exhibits onl~r minimal sen~itivity.
Another useful criteria which has been found helpful in characterizing those charge-transport materials which seem to operate most effectively in the multi-active element o~ the invention is the finding that, to date, the more useful charge-transport materials are organic photoconductive materials whichexhibit a hole or electron drift mobility greater than about 10-9 cm.2/volt-sec.,pre~erably greater than about 10 6cm2/volt-sec.
Various p-type organic charge transport materials may be used in the charge transport layers of the present invention.
As noted, these materials have the capability of conducting positive charge carriers in~ected therein. Any of a variety of organic photoconductive materials which are capable of transport-ing positive charge carriers may be employed. A partial listing of representative p-type organic photoconductive materials 3 encompasses:
` -.. -iV~ 6 1. carbazole materials inc]uding carbazole, N-ethyl carbazole, N-isopropyl carbazole, N-phenylcarbazole, halogenated carbazoles, various polymeric carbazole materials such as poly(vinyl carbazole) halogenated poly(vinyl carbazole), and the like. ;;

2. arylamine-containing materials including monoaryl-amines, diarylamines, triarylamines, as well as polymeric arylamines. A partial listing o~ specific arylamine organic photoconductors include the particular non-polymeric triphenylamines illustrated in Klup~el et.al., U.S. Patent No. 3,180,730 issued April 27, 1965; the polymeric triarylamines described in Fox U.S. Patent No. 3,240,597 issued March 15, 1966; the triarylamines having at least one of the aryl radical~ substituted by either a vinyl radical or a vinylene radical having at least one active hydrogen-containing group as described in Brantly et.al., U.S. Patent No. 3,567,450 issued March 2, 1971; the triarylamines in which at least one of the aryl radicals is substituted by an active hydrogen-containing group as described in Brantly et. al. -U.S. Patent No. 3,658,520 issued April 25, 1972; and tritolylamine. - `:
:-'.
3. polyarylalkane materials of the type described in Noe et. al., U.S. Patent No. 3,274,ooo issued ..:: :.

September 20, 1966; Wilson; U.S. Patent No. 3,542,547 :~
issued November 24, 1970; Seus et. al., U.S. Patent i No. 3,542,544 issued November 24, 1970, and in ;~,' ' ` - . .
Rule et. al., U.S. Patent No. 3,615,402 issued ::

' :::- - ~ ' -: - : - , ... .... . . . .

~ 806 \

October 26~ 1971. Prererred polyarylalkane photoconductors can be represented by the ~ormula:

. J-C-E
G

wherein D and G, which may be the same or different, represent aryl groups and J and E~
which may be the same or difrerent, represent a hydrogen atom, an alkyl group, or an aryl group~ at least one of D, E and G containing .~-an amino substituent. An especially use~ul .:
polyarylalkane photoconductor which may be employed as the charge transport materlal is a polyarylalkane having the rormula noted above wherein J and E re.present a hydrogen atom, an aryl group, or an alkyl group and D and G
represent substituted aryl ~roups havlng as a substituent thereof a group represented by the formula:

R . ..
-N

~ R .
wherein R represents an unsubstituted aryl group . : `

such as phenyl or an alkyl æubstituted aryl such :
as a tolyl group. Additlonal lnformation con- .
.:
: cerning certain of these latter polyarylalkane .~ materials may be found in ~ule et al~ copending -Canadian Patent Application, Serial No. 242,182 filed December 18, 1975, and entitled "Photocon-.,:. .;..: . :.
ductlve Polymer and Photoconductlve Compositionsand Elements Containing Same".

4. strong Lewis base materials such as various aromatic ~: -including aromatical-ly unsaturated heterocyclic- ~.~
. .
containing materials which are free of trong ~ ~ :

-26_ .: .

~ 2806 electron withdrawing groups. A partial listing of such aromatic Lewis base materials includes tetraphenylpyrene, l-methylpyrene, perylene, chrysene, anthracene, tetraphene, 2-phenyl naphthalene, azapyrene, fluorene, fluorenone, l-ethylpyrene, acetyl pyrene, 2,3-benzochrysene, 3,4-benzopyrene, 1,4-bromopyrene, and phenyl-indole, polyvinyl carbazole, polyvinyl pyrene, polyvinyl tetracene, polyvinyl perylene, and polyvinyl tetraphene.

5. other useful p-type charge-transport materialsWhich may be employed in the present invention are any of the p-type organic photoconductors, including metallo-organo materials, known to be useful in electro-photographic processes, such as any of the organic photoconductive materials described in Research ~isclosure, Vol. lO9, May 1973, pages 61-67, ~
paragraph IV (A) (2) through (13) which are p-type ;
photoconductors.

Representative of typical n-type charge-transport ` materials whlch are believed to be useful are strong Lewis acids such as organic, includlng metallo-organic, materials containing one or more aromatic, including aromatically unsaturated hetero-cyclic, materials bearing an electron withdrawing substituent.
These materials are considered useful because of their character-- istic electron accepting capability. Typical electron withdrawing substituents include cyano and nitro groups; sulfonate groups;
halogens such as chlorine, bromine, and iodine; ketone eroups;
. .

l~)'YZ8~i ester groups; acid anhydride groups; and other acid groups such as carboxyl and quinone groups. A partial listing of such represent-at~ve n-type aromatic Lewls acid materials havin~ electron ~lth-draw~ng substituents lnclude phthalic anhydride, tetrachloro-phthalic anhydride, benzil, mellitic anhydride, S-trlcyanobenzene, picryl chloride, 2,4-dinitrochlorobenzene, 2,4-dlnitrobromo-benzene~ l~-nitrobiphenyl, 4,4-dinitrobiphenyl~ 2~4,6-trinltro-anisole, trichlorotrinitrobenzeneg trinltro-0-toluene, 4,6-dichloro-1,3-dinitrobenzene, 4,6,-dibromo-1,3-dlnitrobenzene, P-dinitrobenzene, chloranil, bromanll, 2,4,7-trinikro-9-fluorenone, 2,4,5,7-tetranitrofluorenone, trinltroanthracene, dinltroacrid~ne, tetracyanopyrene, dinitroanthraquinone, and mixtures thereo~.
As suggested above,other use-rul n-type charge-transport materlals which may be employed in the present inven~lon are conventional n-type organlc photoconductors, ~or example, complex-es of 2,4,6-trinltro-9-fluorenone and poly(vinyl carbazole) provide useful n-type charge-transport material6. Still other n-type organic, including metallo-org~no, photoconductl~e materials useful as n-type charge-transport materials ln thè :
present invention are any of the organic photoconductlve materials known to be useful in electrophotographic processes Euch as any ~ -of the materials descrlbed in Research Disclosure, ~ol. 109, May 1973, pages 61-67, paragraph IV tA) (2) ~hrough (13) ~hich : are l~-type photoconductor~.
As noted earller hereln, in accord ~ith an e~pe~ally preferred embodiment o~ the present lnvention, the organlc photoconductlve materlals useful herein as charge-transport materials are advantageously those materials ~hleh e~hibit ll~tle : ~:
or no photosensitivlty to radiat~on withln the ~avelen th range .

' : :':
~ ,~, i.~ , .
., . , - .. , ~ :

1~'728~6 to which the charge-generation layer is sensitive, i.e.~
radiation which causes the charge-generation layer to produce electron-hole pairs. Thus, in accord with a preferred embodiment of the invention wherein the multi-acti~e element of the invention is to be exposed to visible electromagnetic radiation, i.e., radiation within the range of from about 400 to about 700 nm., and wherein the charge-generation layer contains a co-crystalline complex of the type described in greater detail hereinafter which is sensibive to radiation within the range of from about 520 nm.
to about 700 nm.; it is advantageous to select as the organic photoconductive material to be used in the charge-transport layer, an organic material which is photosensitive to light outside the 520 - 700 nm. region of the spectrum, preferably in the spectral region below about 475 nm. and advant;ageously below about 400 nm.
Xn this regard, the above-described arylamine and polyarylalkane p-type organic photoconductors have been ~ound especially useful as charge-transfer materials.
The charge-~ransport layer may consist entirely of the charge-transport materials described hereinabove~ or, as is more usually the case, the charge-transport layer may contain a mixture of the charge-transport material in a suitable film- .~.~.rr.
forming polymeric binder material. The binder material mayj if it is an electrically insulating material, help tp provide the charge-transport layer with electrical insulating characteristics, and it also serves as a film-forming material useful in(a)coating ~e charge-transport layer, (b) adhering the charge~transport layer- to an adjacent substrate, and (c) providing a smooth~ easy to clean, and ~ear resistant sur~ace. Of course, in instances where the charge--transport material may be conveniently applied without a separate binder, ~or example, where the charge-transport .

~ . .

~.~'7'~8~

material is itsel~ a polymeric material~ such as a polymeric arylamine or poly(~inyl carbazole), there may be no need to use a separate polymeric binder. However, even in man~ o~
these cases, the use o~ a polymeric binder may enhance desirable ph~sical properties such as adhesion, resistance to cracking, etc.
Where a polymeric binder material is employed in the charge_transport layer, the optimum ratio o~ charge-transport material to binder material may vary widely depending on the particular polymeric binder(s) and particular charge-transport material(s) employed. In general, it has been found that, when a binder material is employed, use~u:L results are obtained wherein the amount of active charge-transport material contained within the charge-transport layer varies within the range of ~rom about 5 to about 90 weight percent based on the dry weight of the charge-transport layer.
A partlal listing of representative materials which may be employed as binders in the charge-t.ransport layer are film-forming polymeric materials having a fairly high dielectric 20 strength and good electrically insulating properties. Such .
binders include styrene-butadiene copolymers, polyvinyl toluene- :
styrene copolymers; styrene-alkyd resins; silicone-alkyd resins; .
. soya-alkyd resins; vinylidene chloride-vinyl chloride copolymers; ::
~. poly(vinylidene chloride); vinylidene chloride-acrylonitrile .

.
; ,' .

I ,.....

1 . , ' .

, ~

.... .
. ~3~

.
`

~'7~V6 copolymers; vinyl acetate-vinyl chloride copolymers; poly(vlnyl acetals), such as poly(vinyl butyral); nitrated polystyrene;
poly~.ethylstyrene; isobutylene polymers; polyesters, such as poly[ethylene-co-alkylenebis(alkyleneoxyaryl) phenylenedicarboxyl-ate]; phenolformaldehyde resins; ketone resins; polyamides;
polycarbonates, polythiocarbonates; poly[ethylene-co-isopropylid-ene-2,2-bis(ethyleneoxyphenylene)terephthalate]; copolymèrs of vinyl haloarylates and vinyl acetate such as poly(vinyl-m- ~-~lcJmobenzoate-co-vinyl acetate)i chlorinated poly(olefins)~
s~ch as chlorinated poly(ethylene); etc. ~ethods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in Gerhart VS patent 2,361,019, issued October 24~ 1~44 and Rust US patent 2,258,423, issued October 7, 1941. Sultable - resins of the type contemplated for use in the charge transport layers Or the invention are sold under such tradenames as VITEL
PE-101, CYMAC , ptccopale~l00, Sara~ F-220, and LEXAN 145. Other types o~ binders which can be used in charge transport layers include such materials as para~fin, mineral waxes, etc, as well ~O as combinations of binder ~,ateri21s.
In general, it has been found that polymers containlng aromatic or heterocyclic Eroups are most effective as the binder materials for use in the cha.6e transport layers because these pol~ .ers, b~ irtue o~ their heteroc~Jclic or aro~.a~ic ~roups~ tend to pro~ide little or no interference ~ith the transport o~ charæe carriers throu~h the layer. Hetero-cyclic or aro~.atic-contair.in~ pol~.ers which are especially `

-.
: . . . ~ .. .. . . . .
.

~ 8~

useful in p-type charge-transport layers include styrene-containing polymers, bisphenol-A polycarbonate polymers, phenol-formaldehyde resins, polyesters such as poly[ethylene-co-isopropylidene-2,2-bis(ethyleneoxyphenylene)] terephthalate,.and copolymers of vinyl haloarylates and vinylacetate such as poly(vinyl-m-bromobenzoate-co-vinyl acetate).
The charge-transport layer may also contain other addenda such as leveling agents, surfactants, plasticizers, and the like to enhance or improve various physical properties of the charge-transport layer. In addition, various addenda to modify the electrophotographic response of the element may be incorporated in the charge-transport layer. For example, various eontrast control materials, such as certain hole-trapping agents and .
eertain easily oxidized dyes ma~ be incorporated in the charge-transport layer. Various sueh eontrast control ma-terials are described in Research Disclosure, Volume 122, June, 197~, p. 33, ln an artiele entitled ~Additives for Contrast Control in Organic Photoe~nductor CompoFitions end Elements" ~ :

r.

, .

,~ ' .

. ' ' ' .
. - ' . - ` - ~ ' . .. ... ' " .: " .. ' : .' ' .' : ' . .

~ 80~i The thickness of the charge-transport layer may vary.
It is especially advantageous to use a charge-transport layer which is thicker than that of the charge-generation layer,with best results generally being obtained when the charge-transport layer is from about 5 to about 200 times, and partlcularl~ 10 to 40 times,as thick as the charge-generation layer. ~ useful thickness for the charge-gensration layer is within the range of ~rom about 0.1 to about 15 microns dry thickness, particularly from about 0.5 to about 2 microns. However~ as indicated hereinafter, good results can also be obtained using a charge-transport layer which is thinner than the charge-generation layer.
The charge-transport layers described herein are typically applied to the desired substrate by coating a liquid dispersion or solution containing the charge~transport layer components. Typically, the liquid coating vehicle used is an organic vehicle. Typical organic coating vehicles include 1) ~romatic hydrocarbons such as benzene, naphthalene, etc.~ including substituted aromatic hydrocarbons such as toluene, xylene, mesitylene, etc.;
2) Ketones such as acetone, 2-butanone, etc.;
3) Halogenated aliphatic hydrocarbons such as methylene chloride~ chloroform, ethylene chloride, etc.;
4) Ethers including cyclic ethers such as tetrahydro-furan, ethylether, 5) Mixtures of the above.
` The charge-generation layer used in the present invention comprises a layer of the heterogeneous or aggregate composition as described in Light, U.SO Patent 3,615,414 issued October 26, 1971. These aggregate compositions have a multi~
phase structure comprising (a) a discontinuous phase of at least ~ - .

'' ~

- : .
. .

Z~
..
one particulate co-crystalline compound or complex o~ a pyrylium-type dye salt and an electrically insulating, film-~orming polymeric material containing an alkylidene diarylene group as a recurring unit and (b) a continuous phase comprising an electrically insulating film-~orming polymeric material. Optionally~ one or more charge_transport material(s) may also be incorporated in this multiphase structure. Of course, these multi-phase compositions may also contain other addenda such as leveling agents, surfactants, plasticizers, contrast control materials and the like to enhance or improve various physical properties or electro-photographic response characteristics of the charge-generation layer.
The aggregate charge_transport composition may be prepared by several techniques, such as, for example, the so-called "dye ~irst" technique described in Gramza et. al., U.S.
` Patent 3,615,396 issued October 26, 1971. Alternatively, these compositions may be prepared by -the so-called "shearing" method described in Gramza, U.S. Patent 3,615,415 issued October 26, 1971.
Still another method of preparation involves preforming the ~inel~-divided aggregate particles such as is described in Gramza et. al., U.S. Patent 3,732,180 and simply storing these pre~ormed aggregate particles until it is desired to prepare the charge-transport layer. At this time, the pre~ormed aggregate particles may be -~
dispersed in an appropriate coating vehicle toge-ther with the - desired film-~orming polymeric material and coated on a suitable substrate to ~orm the resultant aggregate charge_generation composition.
In any case, by whatever method prepared, the aggregate composition exhibits a separately identifiable multi-phase ~ . . .

., ,.

~ 80~

structure. The heterogeneous nature of this multi-phase composition is generally apparent when viewed under magnification, although such compositions may appear to be substantially optically clear to the naked eye in the absence of magnification.
There can, of course, be microscopic heterogeneity. Suitably, the co-crystalline complex particles present in the continuous phase of the aggregate composition are finely-divided, tha-t is, typically predominantly in the size range of from about 0.01 to about 25 microns;
The terms "co-crystalline complex" or"co-crystalline compound"are used interchangeably herein and have reference to a co-crystalline compound which contains dye and polymer molecules co-crystallized in a single crystalline structure to form a regular array of molecules in a three-dimensional pa-ttern. It is this particulate co-crystalline material dispersed in the continuous polymer phase of the aggregate charge-generation layer ~hich, upon belng exposed to activating radiation in the presence of an electric field, generates electron-hole pairs in ~he multi-active photoconductive elements of the present invention.
~ nother ~eature characteristic of conventional hetero-geneous or aggregate compositions such as those described in U.S. Patents 3,615~414 and U.S. Patent 3,732,180 is that the wavelength of the radiation absorption maximum characteristic of such compositions is substantially shifted from the wavelength of the radiation absorption maximum of a substantially homogeneous dye-polymer solid solution formed ~ similar constituents. - ;
The new absorption maximum characteristic of the aggregate composition is not necessarily an overall maximum for the , .

30 system as this will depend on the relative amount of dye in - `

the aggregate. The shift in absorption maximum which occurs : :

, - . . . .. ...

~ 6 due to the formation of the co-crystalline complex in conventional aggregate compositions is generally of the magnitude of at least about lO nanometers.

A further advantageous feature of the heterogeneous or aggregate compositions contained in the charge-generation layer of the multi-active element of the invention is that these compositions have been found to be an excellent emitter o~ both hole and electron charge carriers. Hence, the charge-generation layer used in the invention can be used to inJect charge carriers into either n-type or p-type charge transport materials to result in a highly efficient multi-active photoconductive element.

.... . . ..... . .. . .. _ .
As suggested earlier herein, those charge-generation layers which have been found especially advantageous for use in those embodiments of the invention relating to visible light sensitive multi-active elemen~s are charge-genqration layers containing a particulate aggregate material having lts principal absorption band of radiation in the v~isible region of the spectrum within the range of from about 520 nm. to about 700 nm.
The pyrylium type dye salts useful in preparing the 20 co-crystalline complex contained in the charge-generation layer :
o~ the present invention includes pyrylium, bispyrylium, thia-pyrylium, and selenapyrylium dye salts; and also salts o~
pyrylium compounds containing condensed ring systems such as salts of benzopyrylium and napthopyrylium dyes are useful in forming such compositions. Typical pyrylium-type dye salts from these classes which are usefuI in ~orming these co-crystalline complexes are disclosed in Light, U.S. Patent 3,6l5,4lL~ noted above.
.:, . `
. -' ~ .

. . . ~ , . ,.. :; ~ . ., lU'^~Z~3~6 Particularly useful pyrylium-type dye salts which may be employed in forming the co-crystalline complex are salts having the formula: 3 . ~ .
Z- .
Rl R2 wherein:
Rl and R2 can each be phenyl groups, including sub-stituted phenyl groups having at least one substituent chosen from alkyl groups of from 1 to about 6 carbon atoms and alkox~ groups having from 1 to about 6 carbon atoms;
R3 can be an alkylamino-substituted phenyl group hav-ing from 1 to 6 carbon atoms in the alkyl group, and including ` d:~alkylamino-substituted and haloalkylamino-substituted phenyl groups;
X can be an oxygen, selenium, or a sulfur atom; and Z is an anionic function, including such anions as -.
perchloride~ ~luoroborate, iodide, chloride, bromide, sulfate, . periodate, p-toluenesulfonate, hexafluorophosphate, and the like.
The ~ilm-~orming polymer used in forming the co-crystalline complex contained in the charge-generation layer r~
used in the present invention may include any of a variety of film-forming polymeric materials which are electrically insula-ting and have an alkylidene diarylene group in a recurring unit such as those linear polymers, including copolymers, containing the following group in a recurring unit: ::

R!6 R4 7 ... -~
~ . . ..
~ -37-. - . . - -- . . . . . . .....

;'Z~

wherein:
R4 and R5, when taken separately, can each be a hydro-gen atom, an alkyl group having from one to about 10 carbon atoms such as methyl, ethyl, isobutyl, hexyl, heptyl, octyl, nonyl, decyl, and the like including substituted alkyl groups such as trifluoromethyl, etc., and an aryl group such as phenyl and naphthyl, including substituted aryl gr~ups having such substituents as a halogen atom, an alkyl group of from 1 to about 5 carbon atoms, etc.; and R~ and R5, when taken together, can represent the carbon atoms necessary to complete a saturated cyclic hydrocarbon group including cycloalkanes such as cyclohexyl and poly-cycloalkanes such as norbornyl, the total number of carbon atoms in R~ and R5 being up to about 19;
R6 and R7 can each be hydrogen, an alkyl group of from 1 to about 5 carbon atoms, e.g., or a halogen such as chloro, bromo, iodo, etc.; and ; R8 is a divalent group selec-ted from the following: ;
O ' S O ' o ' " " , " 11 ~ .
-O-C-O ,-O-C-O- , -C-O- , -C-O-CH2. ,.
~ .
0 CH3 0 ,, -C-0-CH- , -CH2-0-C-0- , and -0-P-0-0~ '~ ' ' ;'' Polymers especially useful in forming the agg~egate crystals are hydrophobic carbonate polymers containing the follo~ing group in a recurring unit:

.' ;'' .
-38- ~

.. ~ , .

~ 8~6 "
-R-C-R-O-C-O-wherein:
Each R is a phenylene group including halo substituted phenylene groups and alkyl substituted phenylene groups; and R4 and R5 are as described above. Such compositions are disclosed, for example, in U.S. Patent Nos. 3~o28,365 and 3,317,466.
Pre~erably polycarbonates containing an alkylidene diarylene moiety in ~he recurring unit such as those prepared with Bisphenol A and including polymeric products of ester exchange betwee~ diphenylcarbonate and 2,2-bis-(4-hydroxyphenyl)propane ~re use~ul in the practice of this invention. Such compositions are dlsclosed in the ~ollowing U.S. Patents: U.S. 2,999,750 by Miller et. al., issued September 12, 1961; 3,o38,874 by Laakso et. al., issued June 12, 1962; 3,o38,879 by Laakso et. al., issued June 12, 1962; 3,o38,880 by Laakso et. al., issued June 12, 19~2; 3,106,544 by Laakso et. al., issued October 8, 1963;
` 3,106~545 by Laakso et. al., issued October 8, 1963, and ` 3,106,546 by Laakso et. al., issued October 8, 1963. A wide ,~, range o~ ~ilm-~orming polycarbonate resins are useful, with -completely sa-tisfactory results being obtained when using commercial polymeric materials which are characterized by an inherent ~iscosity o~ about 0.5 to about 1.8.
` ~le ~ollowing polymers of ~able A are included among the materials use~ul in the practice o~ this invention:

, .
~ _39-. ` , .
. ~ .

..... .. . .

~28~6 TABLE ~
.
Polymeric material Number:
1 ---- Poly(4-4'-isopropylidenediphenylene-co-1-4-cyclohexylenedimethylene carbonale).
2 ---- Poly(ethylenedioxy-3 3 3'-phenylene thiocarbonate).
3 ---- Poly(4,4'-isopropylidenediphenylene carbonate-co-terephthalate).
lO4 ---- Poly(4-4'-isopropylidenediphenylene - -carbonate).
5 ---- Poly(4,4'-isopropylidenediphenylene thiocarbonate).

6 ---- Poly(4,4'-sec-butylidenediphenylene carbonate).

7 ---- Poly(4,4'-isopropylidenediphenylene carbona~te-block-oxyethylene).

8 ---- Poly(l~,4'-isopropylidenediphenylene carbonate-block-oxytetramethylene).
209 ---- Poly ~ -isopropylide~ebis(2-methyl-phenylene)-carbonate .
10 ---- Poly(4,4'-isopropylidenediphenylene-co-1,4-phenylene carbonate).
11 - - - - Po ly ( 4,4'-i~opropylidenediphenylene-co-1,3-phenylene carbonate).
12 ---- Poly(4,4'-isopropylidenediphenylene-co-4,4'-diphenylene carbonate).
13 ---- Poly(4,4'-isopropylidenediphenylene-co-4,4'-oxydiphenylene carbonate).
3014 ---- Poly(4,4'-isopropylidenediphenylene-co-4,4'-carbonyldiphenylene carbonate).
15 ---- Poly(4,4'-isopropylidenediphenylene-co-4,4'-ethylenediphenylene carbonate).
1~ ---- Poly[4,4'-methylenebis(2-methyl-phenylene)carbonate].
17 ---- Poly[1,1-(p-bromophenylethylidene)bis(1 ,4-phenylene)carbonate].

-~0-.

.
- , : ', . . , ' :' . . ' ., ' '. ' .
,' ~ 8~6 TABLE A Cont.

. _ Polymeric material Number:
- Poly[4,4'-isopropylidenediphenylene-co-4,4-sulfonyldiphenylene)carbonate].
19 ---- Poly[4,4'-cyclohexylidene(L~-diphenylene) carbonate].
20 ---- Poly[4,4'-isopropylidenebis(2-chloro-phenylene) carbonate].
lO21 ---- Poly(4,4'-hexafluoroisopropylidene-diphenylene carbonate). --~
22 ---- Poly(4,4'-isopropylidenediphenylene 4,4'-isopropylidenedibenzoate).
23 ---- Poly(4,4'-isopropylidenedibenzyl 4,4'-isopropylidenedibenzoate).
2l~ ---- Poly[4,L~'-(1,2-dimethylpropylidene)di- ~-phenylene carbonateJ.
25 ---- Poly[l~ '-(1,-2,2-trimethylpropylidene)di-phenylene carbonate].
; 2026 ---- Poly~4,4'-[1-(~-naphthyl)ethylidene]dî-phenylene carbonate~.
27 ---- Poly[4,4'-(1,3-dimeth~lbutylidene)di-phenylene carbonate~.
28 -~-- Poly[4,4'-(2-norbornylidene)diphenylene~ -carbonate].
29 ---- Poly[4,4'-(he~ahydro-4,7-methanoindan-5-ylidene)diphen,lene carbonataJ. ~ ~"

.. . .
~' .
, ~ .

~ 8~

The film-forming electrically insulating polymeric material used in forming the continuous phase of the aggregate charge-generation layer of the present invention may be selected from any of the above-described polymers having an alkylidene diarylene group in a recurring unit. In fac-t, best results are generally obtained when the same polymer is used to form the co-crystalline complex and used as the matrix polymer of -the continuous phase of the aggregate composition. This is especially true when the aggregate particles are formed in situ as the aggregate composition is being formed or coated such as described in the so-called "dye-first" or "shearing" me-thods described above. Of course, where the partieulate eo-erystalline eomplex is preformed and then later admixed in the coating dope which is used to coat the aggregate composition, it is unneeessary for the polymer of the eontinuous phase to be Ldentical to the polymer eontained in the co-crystalline complex itsel~. In such ease, other kinds o~ film-~orming, electrically insulating materials wh:Leh are well-known in the polymeric coating art may be employed. However~ here to it is often desirable to use a film-forming electrically insulating polymer which is structurally similar to that of the polymer contained in the co~erystalline complex so that the various eonstituents of the eharge-generation layer are relatively eom~
patible with one another for purposes of, for example, eoating.
If desired, it may be advantageous to ineorporate other kinds of eleetrieally insulating film-forming polymers in the aggregate eoating dope~ for example~ to al-ter various physical or eleetrieal ` properties, sueh as adhesion, of the aggregate eharge-generation layer.
~:' .~:
"
-'' -, : . - . . :

~07'~8~6 The amount of the above-described pyrylium type dye salt used in the aggregate charge-generation layer may vary. Use~ul results are obtained by employing the described pyrylium-type dye salts in amounts o~ ~rom about 0.001 -to about 50 percent based on the dry weight of the charge-generation layer. When the charge-generation layer also has incorporated therein one or more charge-transport materials, useful results are obtained by using the described dye salts in amounts of from about 0.001 to about 30 percent by weight based on the dry weight o~ the charge-generation layer, although the amount used can ~ary widely depending upon such ~actors as individual dye salt solubility, the polymer contained in the continuous phase, additional charge transport materials, the electro-photographic response desired, the mechanical properties desired, etc. Similarly, the amount of dialkylidene diarylene group-containing polymer used in the charge-gener-ation layer o~ the multi-acti~e elements of the invention ~-.
may varyO Typically, the charge-generation la~er contains arl amount of this polymer within the range of ~rom about 20 to about 98 weight percent based on the dry weight o~ the charge-generation layer, although larger or smaller amounts . /.-~.
may also be used.

- : : . .

~0~80~

~ s noted abo~e, it has been found advantageous to incorporate one or more charge-transport materials in the aggregate composition. Especially useful such materials are organic, including metallo-organic, materials which can be solubilized in the continuous phase of the aggregate composition.
By employing these materials in the aggregate composition, it has been found that the resultant sensitivity of the multi-active photoconductive element o~ the present invention can be enhanced. Although the exact reason for this enhance-ment is not completely understood, it i-s believed that the charge-transport material solubilized in the continuous phase of the charge-generation layer aids in transporting the charge carriers generated by the particulate co-crystalline complex of the charge-generation layer to the charge-transport layer and thereb~ prevents recombination of the charge carriers, ie., the electron-hole pairs, in the charge-generation layer.
If a char-ge-transport material is incorporated in the charge-generation layer of the multi active element of the inven-tion as is described above,~the particular material selected shoul~ - -be electronically compatible with the charge-transport material used in the charge-transport layer. That is, if an n-type charge-transport material is used in the charge-transport layer, then an n-type charge-transport material should be incorporated in the aggregate charge-generation composition. Similarly, if a p-type charge-transport material is used in the charge-transport . ~ .
layer of the present in~ention, then a p-type charge-transport ~ material should be incorporated in the aggregate charge-`~ genera-tion layer o~ the element.

` The kinds o~ charge-transport materials which may be incorporated in the charge~generation layer include any of the charge-transport materials described above ~or use in the charge-~ .
-4~-: ' .. .

-1~'7'~80~

generation layer. ~s is -the case with the charge-transport layer, if a charge-transport material is incorporated in the aggregate charge-generation layer~ it is preferred (although not required) that the particular material selected is one which is incapable of generating any substantial number of electron-hole pairs when exposed to activating radiation ~or the co-crystalline complex of the charge-generation layer. In this regard, however, it has been found advantageous in accord with certain embodiments of the invention to incorporate a charge-transport material in the aggregate charge-generation layer which, although insensitive to activating radiation for the co-crystalline complex, e.g.
visible light in the 520-700 nn region, is sensitive to, or is capable of sensitizing the co-crystalline complex to, visible light in the L~oo-520 nm. region of the visible spectrum.
When a charge transport material is incorporated in the charge-generation layer, the amount which is used may vary depending on the particular material, its'compatibility, for example, solubili-ty in the continuous polymeric binder of the charge-generation layer, and the like. Good results have been 20 obtained using an amount of charge-tran6port material in the ;~
charge-gener~tion layer within the range of from about 2 to about 50 weight percent based on the dry weight of -t.he charge-generation layer. Larger or smaller amounts may also be used.
. .., .

... . . ,...... . , : ~ . .
. .

~7Z8~

The multilayer photoconductive elements of the invention can be affixed, i~ desired, directly to a conducting substrate. In some cases, it may be desirable to use one or more intermediate subbing layers between the conducting substrate to improve adhesion to the conducting substrate and/or to act as an electrical barrier layer between the multi-active element and the conducting substrate as described in Dessauer, U.S. Patent 2,940,348. Such subbing layers, if used, typically have a dry thickness in the range of about 0.1 to about 5 microns. Typical subbing layer materials which may be used include film-forming poly-mers such as cellulose nitra~e3 polyesters, copolymers of poly(vinwl pyrrolidone) and vinylacetate, and various vinylidene chloride-containing polymers including two, three and four component polymers prepared ~rom a polymerizable blend of monomers or prepolymers cohtaining at least 60 percent by weight of vinyl:Ldene chloride. A partial 11st of representative vinylidene chloride-containing polymers includes vinylidene chloride-methyl methacrylate-itaconic acid terpolymers as dis-closed in U.S. Patent 3,143,421. Various vinylidene chloride containing hydrosol tetrapolymers which may be used include tetrapolymers of vinylidene chloride, methyl acrylate~
acrylonitrile, and acrylic acid as disclosed in U.S. Patent No. 3,640,708. A partial listlng of other useful vinylidene chloride-containing copolymers includes poly(vinylidene chloride-methyl acrylate), poly(vinylidene chloride-methacrylonitrile), poly(vinylidene chloride-acrylonitrile), and poly(vinylidene chloride-acrylonitrile-meth~l acrylate). Other useful subbing ; materials include ~he so-called tergels which are described in Nadeau et al. U.S. Patent No. 3,501,301.
', .

-~6-%8V~i One especially useful subbln~ layer whl~h may be employed in the multi-active element of the lnvention is a hydrophobic film-forming polymer or c~polymer free from any acld-containing group, such as a carboxyl group~ prepared ~rom 3 blendof monomers or prepolymer~, each of ~ald monomers or prepolymer~
containing one or more polymerizable ethylenically unsaturated groups. A partial listing of such useful materials includes many of the above-mentioned copolymers, and, in addition, the following polymers: copolymers of polyvinylpyrrolidone and vinyl acetate, poly(vinylidene chloride-methyl methacrylate), and the like.
Optional overcoat layers may be used in the present invention~ if desired. For example, to improve surface hardness and resistance to abr3siong the ~ur~ace layer Or the multiactive element of the invention may be coated with one or more electrically insulatlng, organic polymer coatings or electrically insulatlng, lnorganic coatings. A number o~ such coatings are well known ln the art and accordingly extended di~cussion ~hereof i~
~G unnecessary. Typical useful such overcoats are descrlbed, -.
for example, in Research Disclosure, "Electrophotographic Elements, Materials, and Processes"~ Volume 109, page 63, :
Paragraph V, May~ 1973.
The multi-~cti~e elements of the invention may be ~f~ixed, ~
i~ desired, to a ~ariety o~ electri~ally conduct~ng support~.for : :
example ~ paper ( at a relative humid~ty abovc 20 perc~nt );

:

. - . ', .
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.

-l~q'~8~

aluminum-paper laminates; metal foilQ such as aluminum ~oil, zinc ~oil, etc.; metal plates9 ~uch as aluminum, copper, zinc, brass and galvanized plates; vapor deposited metal layer~
such as 9 ilver, nickel, aluminum and the like coated on p~per or conventional photogr~phic film ba~eq such as cellulose acetate, poly-qtyrene, etc. Such conductinæ material~ as nickel can be vacuum deposited on transparent film ~upport3 in sur-ficiently thin layers to allow electrophotographic alement~
prepared therewith to be expoqed from either ~ide of such ele-ments. An especially useful conducting ~upport c~n be preparedby coating a ~upport material ~uch as poly(e$hylene terephthal~te) with a conducting layer containing a semiconductor dispersed in a resin. Such conducting layers both with and without electrical barrier layers are described in U.S. P~tent 3,245,833 by Trevoy, iQ~ued April 120 1966. Other useful conducting layers include compositions consistin~ essentially of an intimate mixture of at least one protective inorganic oxide and from about 30 to about 70 percent by weight of at least one conducting metal, e.g., a vacuum-deposited cermet conducting layer as described in Rasch, CanadianSerial No. 228,670 filed ~une 6, 1975. Likewise, a suit~ble conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a ~inyl acetate polymer. Such kinds of conducting layers and methods ~or their optimum preparation and use are disclosed in U.S. 3,007,901 by Minsk, issued November 7, 1961 and 3,262,807 by Sterman ~t.
issued July 26~ 1966.

.

~ . . . . ' .

lOq'~8~6 The following examples are presented herein merely to illus-trate, not to limit, the present invention.

Element A of the Invention A multi-active photoconductive element of the invention was made in the following manner: 10 g of Bisphenol A
polycarbonate (inherent viscosity 2.70 in 1,2-dichloroethane) and 1 g of 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium perchlorate were dissolved in 405 ml of dichloromethane by lO stirring the solids into the solvent for 4 hours at room temperature. The resulting solution was sheared in a water jacketed Waring Blender for 30 minutes. The water in the jacket -of the blender was maintained at 50C.during shearing. The sheared dope was coated at a coverage of 1.08 g/m~2 on a conducting substrate using an extrusion hopper. The dried coating was overcoated with toluene at the rate of 21.6 ml/m.2 to con~ert it to an aggregated photoconductive layer of the type described in Light, U.S, Patent 3,615,l~1L~. Ne~t, 6 g of poly~tyrene and L~ g of tri-p-tolylamine were dissolved in 65 ml of toluene 20 by stirring the solids in the solvent for 4 hours at room temperature. A multi-active element was then prepared by ~ -overcoating the above-described aggregated organic photo-conductor layer with the aforementioned polystyrene solution at a coverage of lO.8 g/m.2 using an extrusion hopper. ` `
Element B_(Prior Art) :
~ For purposes o~ comparison, a conventional single r layer aggregate photoconductive element was made in the following manner: 70 g of Bisphenol A polycarbonate and 1.4 g of 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyrylium `
30 perchlorate were dissolved in 474 ml of dichloromethane by stirring the solids in the solvent for 4 hours at room " temperature, The resulting solution was sheared in a water - ~ -jacketed Waring Blender for 30 minutes. The water in the jacket of the blender was maintained at 15 C.during shearing.

_~g _ .

~ 8~

A~ter shearing, 1.39 g of tri-p-tolylamine and 12.5 g of a dye solution (solution prepared by dissolving 0.6 g of 4-(4-dimethyl-aminophenyl)-2,6-diphenylthiapyrylium perchlorate in 203 ml of dichloromethane) were added to 36.1 g ofthe sheared solution.
The resulting mi~ture was stirred for 1 hour at room temperature using a magnetic stirrer. The resultant solution was coated at .015 cm. wet thickness on a conducting substrate.
Comparison of Element A and Element B
CroSS~sectional photomicrographs of Elements A and B above were taken. The pictures indicated that Element A
consisted of an aggregate layer less than 1~ thick overcoated ~ -with a polystyrene/tri-p-~ol~lamine layer of lO~ in thickness.
Single layer Element B was 10~ in thickness. The spectro-photometric transmission characteristics of Elements A and B
were also measured. Element A absorbed 90% of the incident radiation at 680 nm; Element B absorbed 92% of the incident rRdiation at 680 nm. The electrophotographic speeds measured for Elements A and B at 680 nm. indicated that Element A was about 2-3 times faster than Element B.

' 20 E~AMPLE 2 Coating ~ormulations for a multi-active element ` of the invention were prepared as follows: `
Char~e-Transport La~er Bisphenol A polycarbonate60.0 g Tri-tolylamine 40.0 g Chloroform 566.7 g Charge-Genera~ion La~er Bisphenol A polycarbonate30.96 g 4 ( 4-dimeth~laminophenyl)-2,6-3 diphenylthiapyrylium perchlorate 5.45 g Methylene chloride 1940.00 g . .
.
.
.

: . ~

~ 8~6 The charge-transport layer using the indicated solvent and binder modifications of this example was prepared in a manner similar to the transport layer described in Example 1 except that the polycarbonate and chloroform were stirred together ~or 12 hours prior to the addition of the tritolylamine. The final transport layer dope was then stirred an additional two hours and coated from an extrusion hopper at20.5 g solids/m , after passage through a 5~ in-line filter, at the rate o~ 5 cm./sec., onto a charge-generation layer (prepared as described below). The charge-generation layer was prepared by first dissolving the thiap~r~lium salt in methylene chloride and stirring ~or 12 hours before adding the Bisphenol A polycarbonate. The dope was then ~iltered through a Honeycomb Fulflow El7Rl-4C2 filter and coated from an extrusion hopper at l.08g/m.2 on a 0.4 optical density vacuum-deposited nickeled rilm support which had been subbed with a vi3lylidene chloride (83 weight ~) methyl acr~late 15 we~ght ~) itaconic acid (2 weight ~) terpolymer. Complete aggregation o~ this layer was obtained by application thereto of a toluene overcoat applied at 43.2 ml/m2. Cross-sectional photo-microgr~phs confirmed a ~inal dry thickness for the multi-active element Or this example of 20~ consisting of l-2~ charge- .. ~ir ' ' ' " ~"
generation layer as base with an 18-19f~ charge transport l~yer.

" ' , '. ':

. ... : .. . .: . . .. .:: . . .. . . . .. .. .. . .. .

~7~8~6 The electrophotographic performance of this multi-active element is shown in Table 1 in terms of relative sensitivity measurements using as a control a heterogeneous or aggregate photoconductive element of the type described in Light, U.S.
Patent 3,615,414 referred to earlier herein. The control photoconductive element of Table 1 was composed of a 10 micron thick (dry thickness) aggregate photoconductive layer coated on a conductive ~ilm support. The aggregate photoconductive layer of the control element, when coated and dried, had a composition identical to Element B of Example 1.

The relative sensitivity measurements reported in this and the following examples are relative electrical sensitivity measurements. The relative electrical sensitivity measures the ;
speed of a given photoconductive element relative to other elements typically within the same test group o~ elements. The relative sensitivity values are not absolute sensitivity values.
; ~lowever, relative sensitivity values are related to absolute sensltivity values. The relative electrical sensitivity is a dimensionless number and is obtained simply by arbitrarily assigning a value, Ro, to one particular absolute sensitivity of one particular photoconductive control element l~e relative sensitivity Rn, o~ any other photoconductive element, n~ relative to this value, Ro, may then be calculated as follows:
Rn = (An)(R/Ao) wherein An is the absolute electrical sensitivity (in ergs/cm.2) of n, Ro is the sensitivity value arbitrarily assigned to the control element, and Ao is the absolute electrical sensitivity (measured in ergs/cm.2) of the control element.

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10~80 The multi-active element of this example was similar to that described in Example 2, except that a 1~ thick charge-generation layer was used with a lOfL thick charge-transport layer. Table 2 indicates the relative sensitivity exhibited by both fresh and aged samples of this element, and the residual voltage (i.e., V0 - ~V) remaining on the surface of the multi-active element after exposure to visible light ener~y (~ = 680 nm.) of 20 ergs/cm.2.

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This example demonstrates the relative sensitivity advantages provided by utilization of thicker multi-active photoconductive elements of the invention and illustrates that negative charge carrier range limitations do not affect the sensitivity of the thicker elements.
A series of multi-active elements, Elements C-~ of Table 3, we~ prepared having a charge-transport la~er and charge-generation layer composition as ~ollows:
Charge~Transport Layer Polystyrene 60.0 g Tri-tolylamine 40.o g Toluene 566.7 g aharge-Genera~ion La~er _ _ L~ -dimethylaminophenyl)-2,6-di]?henyl thiapyrylium perchlorate10.50 g Bisphenol A polycarbonate61.92 g Methylene chloride 3568.oo g The charge-generation la~er ~as prepared and coa~ed .
as in Example 2. The charge-transport layer ~as prepared and coated similar to Example 2, except using a flow rate at -~

9.7 g solids/m. from the extrusion hopper, The final thickness of the dried multi-active photoconductive elements varied from

10~ to 22~ as shown in Table 3. .. r.. ~

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~ 8~6 EXAMPLE 5 ~ -A series of multi-active photoconductive elements, Elements Nos. I-VIII, o~ the present invention were prepared using a variety of different charge-transport layers. Each element had an identical 1-2f~thick aggregated photoconductive layer as the charge-generation layer prepared in a manner similar to that described in Example 2. Each of the different charge-transport layers prepared in this example were about 8 in dry thickness and consisted of 40 weight percent transport material and 60 weight polymeric binder. Fresh (:i.e., unaged) and aged samples of each element were tested.
The specific composition Or the charge-transport layer and the relative sensitivit~v measurements of each of the multi-active elements prepared in this example are presented herein in Table 4 .

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As previously noted, the multi-active photoconductive elements of the invention which contain a p-type transport material in the charge-transport layer work most efficiently when negatively charged, unless the order of the charge-generation layer and charge-transport layer is reversed in which case the element then functions best under positive charging. In this example, a multi-active element of the .
invention wasprepared having a charge-transport layer of about 10 microns thickness and a charge-generation layer of about 1 micron thickness. The composition of each of these layers was identical to that of the transport and generation layers described in Example 1. However, in this example, a positive charging mode wasused and the order Or the transport layer and ~eneration layerwasreversed. That is, the transport layer was coated contiguous to the conducting substrate and the generation layer wasthe surface layer. The structure and mode of operation used to test this elementwas identical to that described in Fig. 6a-6d. Using this positive charge mode o~
operation, it was found that the multi-active element of this example required an exposure intensity of 37 ergs/cm2 of' ~ = 600nm. light to discharge from +500 volts to +100 volts.

EXA~IPLE 7 _ In this example a multl-active element o~ the in-vention was prepared containing an n-type charge-transport material in the charge-transport la~er. This charge~transport layer was then coated over an aggregate charge~generation la~er carried on a ~ransparènt conductive support. The resultant multi-active element was ~ound to produce use~ul ..

` .

~t)~ 806 electr~sta~ic image patterns ~hen subjec~ed to ~he mode o~
electrical opera~ion illustrated diagramatically in Fig. L~a - 4d, namel~ use of an initial uni~orm positive surface potential. However, in this particular example, due to the relative opacity o~ the charge ~ransport layerj e~posure o~
the elemen-t was made through the transparent conducting support as shown in Fig. 7.
rhe composition of the charge-trarlsport coating dope used in this example was as follows:

Charge-Transport Layer Coating Composition Poly(vinylcarbazole) 1.4 g 2,4,7-trinitrofluorenone (TNF) 0.6 g ChlorofoIIll 31.3 g The coolposition of the nggre~ate charge-genera-tion layer and the trallsparcnt conductive support used in this exaluple was tllo sallle as thnt desori~ed for -the mlllti-lctive ele~nen-t of ~.Yaluple 2. The preparation and coating procedure for the above-noted charge-transport co~ting cou1position was as follows: The poly(vinylcarbazole) was dissolved in the chloro-form over 3 hours under stirring and the TNF then added. After an additional 30-mirlute stirring, the charge-transport coating coulposition was applied over the charge-generation layer via a handcoatillg procedure utilizing a 6 mil, fixed edge knife.
After drying for 3 minutes at 37.8C., the resultant multi-active photoconductive film element was cured for 1 hour at 54C. and rested in the dark for ~8 hours. A sample O.e this filul was then charged to +500 volts and subjected to rea~

illumination (~ =680Ilm). The sample film was discharged from +500 to ~100 volts with 13~0 ergs/cm2 of activating radia-tion ()\=~;8011UI).

~t~ 6 -Although most multi-active photoconductive elements of the invention have a relatively thin charge-generation layer and a relatively thick charge-transport layer, the multi-active element of the invention will also function well, albeit with a somewhat reduced sensitivity, using a thick charge-generation layer over-coated with a relatively thin charge-transport layer. The multi-active element o~ this example comprises a 12~ charge-generation layer and a 1~ charge--transport layer prepared as follows:
Charge-Transport Layer Bisphenol-A-polycarbonate (Lexan~ 145 purchased from G.E. Co.) 48.o g Bis-(4-diethylamino)tetraphenylmethane 32.0 g Chloroform 1253.6 g Char~e-Generation Layer -Part A

4- (4- dimethylaminophenyl)-2~6-diphenylthiapyrylium hexa~luoro-phospha-te ` 14, L~ g Dichloromethane 882.o g 1,1,2-trichloroethane 436.o g Bisphenol-A-pol~carbonate (Lexa ~ 145 purchased from G.E.Co.) 102.4 g Part B
Dichloromethane 662.3 g 1,1~2-trichloroethane 283.9 g Bis-(4-diethylamino)tetraphenyl-methane 96.o g To form the charge-generation layer of this example, the hexafluorophosphate thiapyrylium salt was dissolved in the solvent mix of Part A for 12 hours under magnetic stirring whereupon the Le~an~ 145 was added in two por-tions, 15 minutes . .

~ 6 apar-t. I'he solution was then stirred an additional 3 hours, sheared for 0.5 hours in a Waring type blender and exactly one half of the sheared solution added to Part B - a solution of bis-(4-diethylamino)tetraphenylmethane in 1,1,2-trichloroethane and dichloromethane. The dope was filtered and coated at

12.9 g/m similar to Example 2 on a suitable conductive substrate to form a 12~ dry thickness charge-generation layer.
The charge-transport layer was formulated similar to Example 2 and coated at 1. o8 g/m2 over the above-described charge-generation layer to form a 1~ dry thickness transport layer. The multi-active element of this example exhibited improved relative sensitivity over that obtainable with a comparable single-layer aggregate photoconductive element.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be e~fected within the spirit and scope of the invention.

,.,~: :;

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Claims (37)

We Claim:

1. A photoconductive insulating element having at least two layers comprising a charge-generation layer in electrical contact with a charge-transport layer, (a) said charge-generation layer comprising a continuous, electrically insulating polymer phase and dispersed in said continuous phase a discontinuous phase comprising a finely-divided, particulate co-crystalline complex of (i) at least one polymer having an alkyli-dene diarylene group in a recurring unit and (ii) at least one pyrylium-type dye salt, which co-crystalline complex, upon exposure to activat-ing radiation for said complex,generates and injects charge carriers into said charge-transport layer, (b) said charge-transport layer being an organic composition free from said co-crystalline complex and said pyrylium-type dye salt, and comprising as a charge-transport material an organic photo-conductive material which accepts and transports injected charge carriers from said charge-generation layer.

2. A photoconductive insulating element as defined in Claim 1 wherein said charge-transport layer comprises a polymeric binder and a p-type organic photoconductive charge-transport material.

3. A photoconductive insulating element as defined in Claim 1 wherein said charge-transport layer comprises a polymeric binder and an n-type organic photoconductive charge-transport material.

4. A photoconductive insulating element having at least two layers comprising a charge-generation layer contiguous to a charge-transport layer, (a) said charge-generation layer comprising a charge transport material in solid solution with a continuous, electrically insulating polymer phase and dispersed in said continuous phase a discontinuous phase comprising a finely-divided, particulate co-crystalline complex of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one pyrylium-type dye salt, which co-crystalline complex, upon exposure to activating radiation for said complex, generates and injects charge carriers into said charge-transport layer, (b) said charge-transport layer being an organic composition insensitive to said activating radiation and free from said co-crystalline complex and said pyrylium-type dye salt, said charge-transport layer comprising as a charge-transport material an organic photoconductive material which accepts and transports charge carriers from said charge-generation layer.

5. A photoconductive insulating element as defined in Claim 4 wherein said charge-transport material comprises a p-type organic photoconductive charge-transport material.

6. A photoconductive insulating element as defined in Claim 4 whereln said charge-transport material contained in said charge-generation layer comprises an n-type organic photo-conductive charge-transport material.

7. A photoconductive insulating element having at least two layers comprising a charge-generation layer in electrical contact with a charge-transport layer, (a) said charge-generation layer having a dry thickness less than about 15 microns and comprising a continuous electrically insulating polymer phase and dispersed in said continuous phase a discontinuous phase comprising a finely-divided particulate co-crystalline complex of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one thiapyrylium dye salt, which co-crystaline complex, upon exposure to radiation within the range of from about 520 to about 700 nm., generates and injects charge carriers into said charge-transport layer, (b) said charge-transport layer being an organic composition free from said co-crystalline complex and any pyrylium-type dye said and comprising as a charge-transport material an organic photoconductive material having a principal absorption band below about 475 nm.
which accepts and transports injected charge carriers from said charge-generation layer.

8. A photoconductive insulating element as defined in Claim 7 wherein said charge-generation layer comprises an organic photoconductive charge-transport material in solid solution with said continuous phase, said transport material being electronically compatible with the transport material contained in said charge-transport layer.

9. A photoconductive insulating element as defined in Claim 7 wherein said charge-transport layer has a dry thickness greater than that of said charge-generation layer.

10. A photoconductive insulating element as defined in Claim 7 wherein said charge-transport layer has a dry thickness less than that of said charge-generation layer.

11. A photoconductive insulating element having at least two layers comprising a charge-generation layer in electrical contact with a charge-transport layer, (a) said charge-generation layer having a dry thickness within the range of from about 0.5 to about 15.0 microns and comprising a p-type organic photoconductive charge-transport material in solid solution with a continuous, electrically insulating polymer phase and dis-persed in said continuous phase a discontinuous phase comprising a finely-divided, particulate co-crystalline complex of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one thiapyryl-ium dye salt, which co-crystalline complex, upon exposure to radiation within the range of from about 520 to about 700 nm., generates and injects charge carriers into said charge-transport layer, (b) said charge-transport layer being an organic composition having a dry thickness within the range of from about 5 to about 200 times that of said charge-generation layer and free from said co-crystalline complex and any pyrylium-type dye salt, said charge-transport layer comprising as a p-type charge-transport material an organic photoconductive material having a principal absorption band below about 400 nm. which accepts and transports injected charge carriers from said charge-generation layer.

12. A photoconductive insulating element as defined in Claim 11 wherein said charge-transport material contained in said charge-generation layer and in said charge-transport layer is a p-type organic photoconductor selected from the group consisting of carbazole, photoconductive materials, arylamine photoconductive materials, and polyarylalkane photo-conductive materials.

13. A photoconductive insulating element as defined in Claim 11 wherein said charge-transport material contained in said charge-transport layer is a p-type arylamine organic photoconductor.

14. A photoconductive insulating element as defined in Claim 11 wherein said charge-transport material contained in said charge-transport layer is a p-type polyarylalkane photo-conductor having the formula wherein J and E, which are the same or different, represent a hydrogen atom, an alkyl group, or an aryl group; and D and G, which are the same or different represent substituted aryl groups having as a substituent thereof a group represented by the formula wherein R represents an unsubstituted aryl group or an alkyl substituted aryl group.

15. A photoconductive insulating element as defined in Claim 11 wherein said charge-transport material contained in said charge-transport layer is tritolylamine.

16. A photoconductive insulating element having at least two layers comprising a charge-generation layer contiguous to a charge-transport layer, (a) said charge-generation layer having a dry thickness within the range of from about 0.5 to about 5.0 microns and comprising a p-type organic photoconductive charge-transport material in solid solution with a continuous electrically insulating polymer phase and dis-persed in said continuous phase a discontinuous phase comprising a finely-divided particulate co-crystalline complex of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one thiapy-rylium dye salt, which co-crystalline complex, upon exposure to radiation within the range of from about 520 to about 700 nm., generates and injects charge carriers into said charge-transport layer, (b) said charge-transport layer being an electrically insulating organic composition having a dry thickness within the range of from about 10 to about 40 times that of said charge-generation layer, said charge-transport layer being free from said co-crystalline complex and any pyrylium-type dye salt and comprising as a p-type charge-transport material an organic photoconductive material having a principal absorption band below about 400 nm. which accepts and transports injected charge carriers from said charge-generation layer.

17. A photoconductive insulating element as defined in Claim 16 wherein said charge-transport material contained in said charge-generation layer and in said charge-transport layer is a p-type organic photoconductor selected from the group consisting of carbazole photoconductive materials, arylamine photoconductive materials, and polyarylalkane photoconductive materials.

18. A photoconductive insulating element as defined in Claim 16 wherein said charge-transport material contained in said charge-transport layer is a p-type arylamine organic photo-conductor.

19. A photoconductive insulating element as defined in Claim 16 wherein said charge-transport material contained in said charge-transport layer is a p-type polyarylalkane photo-conductor having the formula wherein J and E, which are the same or different, represent a hydrogen atom, an alkyl group, or an aryl group; and D and G, which are the same or different represent substituted aryl groups having as a substituent thereof a group represented by the formula wherein R represents an unsubstituted aryl group or an alkyl substituted aryl group.

20. A photoconductive insulating element as defined in Claim 16 wherein said charge-transport material contained in said charge-transport layer is tritolylamine.

21. A photoconductive insulating element having at least two layers comprising a charge-generation layer contiguous to a charge-transport layer, (a) said charge-generation layer having a dry thickness less than about 15.0 microns and comprising a p-type organic photoconductive charge-transport material having a principal absorption band below about 475 nm. in solid solution with a continuous electrically in-sulating polymer phase and dispersed in said continuous phase a discontinuous phase com-prising a finely-divided particulate co-crystalline complex of (i) at least one polymer having an alkylidene diarylene group in a recurring unit and (ii) at least one thiapyrylium dye salt, which co-crystalline complex, upon exposure to activating radiation within the range of from about 520 nm. to about 700 nm., generates and injects charge carriers into said charge-transport layer, (b) said charge-transport layer being an electrically insulating organic composition having a dry thickness within the range of from about 10 to about 40 times that of said charge-generation layer, said charge-transport layer being free from said co-crystalline complex and any pyrylium-type dye salt, and comprising an electrically insulating polymeric binder and, in solid solution with said binder, a p-type organic photoconductive charge-transport material having a principal absorption band below about 475 nm. and which accepts and transports injected charge carriers from said charge-generation layer.

22. A photoconductive insulating element as defined in Claim 21 wherein said p-type organic photoconductive material contained in said charge-generation layer and in said charge-transport layer is an arylamine organic photoconductor.

23. A photoconductive insulating element as defined in Claim 21 wherein said electrically insulating polymer phase of said charge-generation layer and the electrically insulating polymeric binder of said charge-transport layer comprise the same polymeric materials.

24. A photoconductive insulating element comprising (a) a conductive support, (b) a polymeric subbing layer overcoating said support, (c) a charge-generation layer overcoating said subbing layer, and (d) a charge-transport layer overcoating said generation layer, (i) said charge-generation layer comprising a continuous, electrically insulating polymer phase and dispersed therein a discontinuous phase comprising a finely-divided particulate co-crystalline complex of (1) at least one polymer having an alkylidene diarylene group in a recurring unit and (2) at least one pyrylium-type dye salt, which co-crystalline complex, upon exposure to activating radiation for said complex generates and injects charge carriers into said charge-transport layer, (ii) said charge-transport layer being an organic composition in electrical contact with said charge-generation layer, said charge-transport layer being free from said co-crystalline complex and said pyrylium-type dye salt, said charge-transport layer comprising as a charge-transport material an organic photoconductive material which accepts and transports injected charge carriers from said charge-generation layer.

25. A photoconductive insulating element as defined in Claim 24 wherein said subbing layer has a dry thickness in the range of from about 0.1 to about 5 microns and comprises a film-forming polymer.

26. A photoconductive insulating element as defined in Claim 24 wherein said subbing layer comprises an electrical barrier layer.

27. A photoconductive insulating element as defined in Claim 24 wherein said subbing layer has a dry thickness in the range of from about 0.1 to about 5 microns and comprises a film-forming polymer comprising a polymerized blend of monomers or prepolymers containing at least 60 percent by weight of vinylidene chloride.

28. A photoconductive insulating element as defined in Claim 24 wherein said subbing layer comprises a hydrophobic, film-forming polymer and has a dry thickness in the range of from about 0.1 to about 5 microns, said polymer being free of any acid-containing groups and comprising a polymerized blend of monomers or prepolymers, each possessing one or more polymerizable ethylenically unsaturated groups.

29. A photoconductive insulating element as defined in Claim 25 wherein said polymer is a polyester.

30. A photoconductive insulating element comprising (a) a conductive support, (b) a polymeric subbing layer overcoating said support, (c) a charge-transport layer overcoating said subbing layer, and (d) a charge-generation layer overcoating said transport layer, (i) said charge-generation layer comprising a continuous, electrically insulating polymer phase and dispersed therein a discontinuous phase comprising a finely-divided, particulate co-crystalline complex of (1) at least one polymer having an alkylidene diarylene group in a recurring unit and (2) at least one pyrylium-type dye salt, which co-crystalline complex, upon exposure to activating radiation for said complex, generates and injects charge carriers into said charge-transport layer, (ii) said charge-transport layer being an organic composition in electrical contact with said charge-generation layer, said charge-transport layer being free from said co-crystalline complex and said pyrylium-type dye salt, said charge-transport layer comprising as a charge-transport material an organic photoconductive material which accepts and transports injected charge carriers from said charge-generation layer.

31. A photoconductive insulating element as defined in Claim 30 wherein said subbing layer has a dry thickness in the range of from about 0.1 to about 5 microns and comprises a film-forming polymer.

32. A photoconductive insulating element as defined in Claim 30 wherein said subbing layer comprises an electrical barrier layer.

33. A photoconductive insulating element as defined in Claim 30 wherein said subbing layer has a dry thickness in the range of from about 0.1 to about 5 microns and comprises a film-forming polymer comprising a polymerized blend of monomers or prepolymers containing at least 60 percent by weight of vinyli-dene chloride.

34. A photoconductive insulating element as defined in Claim 30 wherein said subbing layer comprises a hydrophobic, film-forming polymer and has a dry thickness in the range of from about 0.1 to about 5 microns, said polymer being free of any acid-containing groups and comprising a polymerized blend of monomers or prepolymers, each possessing one or more polymer-izable ethylenically unsaturated groups.

35. A photoconductive insulating element as defined in Claim 31 wherein said polymer is a polyester.

36. A photoconductive insulating element comprising (a) a conductive support, (b) a charge-generation layer overcoating said support, and (c) a charge-transport layer overcoating said generation layer, (i) said charge-generation layer comprising a continuous, electrically insulating polymer phase and dispersed therein a discontinuous phase comprising a finely-divided particulate co-crystalline complex of (1) at least one polymer having an alkylidene diarylene group in a recurring unit and (2) at least one pyrylium-type dye salt, which co-crystalline complex, upon exposure to activating radiation for said complex, generates and injects charge carriers into said charge-transport layer, (ii) said charge-transport layer being an organic composition in electrical contact with said charge-generation layer, said charge-transport layer free from said co-crystalline complex and said pyrylium-type dye salt, said charge-transport layer comprising as a charge-transport material an organic photoconductive material which accepts and transports injected charge carriers from said charge-generation layer.

37. A photoconductive insulating element comprising (a) a conductive support, (b) a charge-transport layer overcoating said support, and (c) a charge-generation layer overcoating said transport layer, (i) said charge-generation layer comprising a continuous, electrically insulating polymer phase and dispersed therein a discontinuous phase comprising a finely-divided, particulate co-crystalline complex of (1) at least one polymer having an alkylidene diarylene group in a recurring unit and (2) at least one pyrylium-type dye salt, which co-crystalline complex, upon exposure to activating radiation for said complex generates and injects charge carriers into said charge-transport layer, (ii) said charge-transport layer being an organic composition in electrical contact with said charge-generation layer, said charge-transport layer being free from said co-crystalline complex and said pyrylium-type dye salt, said charge-transport layer comprising as a charge-transport material an organic photoconductive material which accepts and transports injected charge carriers from said charge-generation layer.