CA1284492C - Photoconductive phthalocyanine pigments, electrophotographicelements containing them and a method of use - Google Patents

Abstract

PHOTOCONDUCTIVE PHTHALOCYANINE PIGMENTS, ELECTROPHOTOGRAPHIC ELEMENTS CONTAINING THEM
AND A METHOD OF USE
Abstract of the Disclosure Near infrared sensitive photoconductive elements are made from fluorine-substituted titanyl-phthalocyanine pigments which can be dispersion coated.

Description

~ 28449;~

PHOTOCONDUCTIVE PHTHALOCYANINE PIGMENTS, ELECTROPHOTOGRAPHIC ELEMENTS CONTAINING THEM
AND A METHOD OF USE
Field of the Invention 5Th$s invention relates to phthalocyanine plgments snd more particularly to novel photo-conductive fluorine-substituted titanyl phthalo-cyanine pigments, to photoconductive elements contsining them and to a method of forming electrophotographic imsges with Cuch elements..
Back~round of the Invention Electrophotographic imaging processes employ a photoconductive element comprising an insulating photoconductive layer disposed on an electrically conductive support. Photoconductive layer~ have in the pa~t contained various inorganic photoconductors such as amorphous selenium, cadmium sulfide or lead oxide or organic photoconductors such as polyvinyl carbazole and aryl amine compounds. While m~ny of the common photoconductors have good electrophoto-graphic sensitivity in the wavelength range from ultraviolet to red, their sensitivity in the near infrared range above about 700 nm is not sufficiently high for use with diode laser~ which currently are of great importance in recording techniques.
In lieu of the more commonly used photo-conductors it has been sugge~ted that certain metal phthalocyanines which absorb in the near infrared region be employed. For example, U.S. Patent 4,426,434 ~uggests a photoreceptor having an evaporsted film of chloroaluminum phthalocyanine or chloroaluminum monochlorophthalocyanine. It is said that such compounds have high photosensitivity in the near infrared region. Unfortunately, such compounds, as well a~ many other phthalocyanines, evidently are not readily dispersible in coating Eormulations and, 8~9~2 to deposit them as photoconductive layers, the expensive procedure of vacuum evaporation must be used .
The patent to Tanikawa, U.S. 4,458,004 dated July 3, 1984 discloses an optical recording medium containing 8 fluorine-~ub~tituted phthalocyanine. A
structural formula in the patent shows a central ~ymbol M which is said to represent, smong many other things, titanium oxide. The patent does not suggest, however, that any of the indicated phthalocyanines are photoconductive or that they can be dispersion coated to form photoconductive layers of low granularity. No method of prepsration of the phthalocyanines ia mentioned.
SummarY of the Invention In accordance with the present invention new photoconductive phthalocyanine pigments are provided which not only have hlgh electrophotographic ~ensitivity in the near infrared region but, in addition, are resdily dl~per~ible in polymeric binders and have extremely low granularity when disper~ed in the polymeric binder of a photo-- conductive layer. Photoconductive elements can be prepared with these novel phthalocyanines by the relatively inexpensive procedure of dispersion coating. The resulting near infrared-~ensitive photoconductive elements provide excellent image resolution because of the small particle slze and dispersability of the photoconductive phthalocyanine compounds. Also, because they can be deposited on a substrste by dispersion coating, it is pos~ible to make single layer and inverted multilayer photocon-ductive elements with the novel phthalocyanine pigments of the invention.
The novel pigments of the invention are photoconductive titanyl phthalocyanlnes having ` -~2 8~

fluorine substitution in one or more of their csrbocyclic rings. The near infrared sensitive photoconductive elements of the invention comprise an electrically conductive substrate and a photo-conductive layer comprising a binder resin and aphthalocyanine as described, and especially such an element whereln the phthalocyanine of the photo-conductive layer is deposited by dispersion coating.
The method of the invention comprises electrostatically charging a photoconductive element of the type described, exposing it to a pattern of near infrared radiation and developing the resulting charge pattern.
Detailed DescriPtion 15 The photoconductive titanyl fluoro-phthalocyanine pigments of the invention can be prepared by the reaction of a fluorine-substituted phthalonitrile with a titanium chloride in 8 hot ~olvent, as illu~trated below, wherein the letter n represents an integer from 1 to 4.

/-~ /CN ~ -~ /
Fn ~ I~ + TiCla ~ i~"i!"l >~,~< ,i!~ ~i Fluorophthalonitrile /-;F
n Titanyl Fluorophthalocyanine Since the fluorine ~ub~tituted phthalo-nitrile molecules which have fewer than four fluorine 3S ~ubstituents can combine with each other in different ~patial configurations, the reaction product will be ~28~9~

a mixture of isomeric titanyl fluorophthalocyanines.
When tetrafluoro phthalonitrile is the starting material, only one isomer forms, i.e., titanylhexa-decyl fluorophthalocyanine.
Although the maximum benefits of the invention have been found with pigments of formula I, wherein the phthalocyanine is synthesized from a slngle fluoro-substituted phthalonitrile, the invention also includes novel fluorine substituted titanyl phthalocyanines in which not all of the aromatic rings have fluorine aub~tituents or do not have an equal number of fluorine substituents.
Non-uniformly substituted compounds of this type can be made by reacting titanium trichloride with two or more phthalonitriles, one of which is a fluorophthalonitrile as illustrated above, and the other or others of whlch are of the formula ~-~ / CN
~./ ~ CN

wherein R can be hydrogen, a halogen such as fluorine, chlorine or bromine, iodine or a hydrocarbon radical such as lower alkyl, e.g., methyl, ethyl, isopropyl and t-butyl, and n is an integer from 1 to 4.
When the titanyl phthalocyanine having fluorine ring ~ubstitution is made in this manner by the reaction of two or more phthalonitriles the reaction product will contain a mixture of substituted oxotitanium phthalocyanines. This mixture will include phthalocyanines in which as few as one of the aromatic rings is fluorine substi-tuted. Thus, while phthalocyanines having only fluorine substituents, and those being equal in number on each aromatic ring, are preferred pigment~

~2~3449~

of the invention, photoconductive fluorine-substituted-titanyl phthalocyanines which are non-uniformly substituted are slso within the scope of the invention and have valuable qualities such as good dispersability in coating compositions.
Before using the fluoro titanylphthalo-cyanine pigment as a near infrsred sensitive electrophotographic charge generation compound, it is sub~ected to a treatment which purifies it, modifies its crystalline form and reduces the particle size.
The resulting novel pigment is photocon-ductive. By this is meant that in the dark the pigment is electrically insulating but when exposed to actinic radiation in the near infrared region, it becomes electrically conductive. More specifically, the dark resistivity is greater than 10 1 ohm-cms at 25C and is rapidly reduced several orders of magnitude when exposed to actinic radiation in the near infrared region (700-900 nm) at an intensity of 5 to 30 erg~/cm /sec T~plcally, a ch~rged photo-conductor discharges by at least 50 volts within 10 seconds when exposed to such radiation. For the more sensitive pigments of the invention, e.g., the tetrafluoro species, the conductivity upon exposure to near infrared radiation is such that a photoconductive element containing the pigment in its charge generation layer can be discharged from -500 volts to -100 volts in one second at an exposure of 7 ergs per cm and a wavelength of 830 nm.
One useful procedure for rendering the pigment photoconductive is called "acid-pasting". It involves dissolving the pigment, after extraction purification with a solvent such ag dimethyl-formamide, in cold concentrated mineral scid, preferably sulfuric acid. The solution is poured into ice water to reprecipitate the phthalocyanine ~X84~92 compound. The precipitate is washed free of acid with water, then with methanol and then is dried.
The resulting purified pigment when dispersed in a blnder resin has a substantially smaller particle size than the crude pigment and is highly sensitive to radiation in the near infrared region.
The photoconductive elements of the invention comprise an electrically conductive substr~te having disposed on it a photoconductive layer containing a titanyl fluoro phthalocyanine compound I. The phthalocyanine compound can be deposited on the conductive substrate as the sole component of the photoconductive layer or in admixture with other components such as a resin binder, a coating aid, other photoconductive compounds, chemical sensitizers and ~pectral sensitizing dyes and pigments.
Although the photoconductive elements of the lnvention can have only a single photoconductive layer, the preferred photoconductive elements are multilayer (also called multiactive) elements having a charge generation layer and at least one charge transport layer. The configurations and general principles of multilayer elements have been described in the prior art, for example, in the patent to Berwick et al, U.S. 4,175,960. When employed in multilayer photoconductive elements in accordance with the present invention, the titanyl fluoro phthalocyanine compound is placed in the charge generation layer.
The photoconductive elements of the invention are used according to the method of the invention to make electrophotographic images, as in diode laser recording. In the method, the photocon-ductive element s electro~tatically charged, e.g.,by corona treatment, to a voltage, for example, of ~28~9`2 500 to 600 volts negative or positive. Then it is exposed to a pattern of near infrared irradiation, causing chsrge to dissipate in the exposed regions.
The resulting charge pattern on the photoconductive element ls developed by contsct with a positively or negstively charged toner. Suitable developers include liquid and dry developers which are well known in the art. Such liquid developers comprise disper~ion of pigmented polymeric toner particles in 10 8 volatile insulating liquid such as an isoparaffinic hydrocarbon. Useful dry developers include both ~ingle component and two-componen~ developers, the latter comprising, for example, a mixture of magnetic carrier psrticles and powdered toner particles composed of a pigmented thermoplastic resin.
The preparation of ~ specific titanyl fluoro-phthalocyanine, namely, the compound titanyl 2, 9, 16, 23-tetrafluorophthalocyanine and its isomers, will illustrate how compounds of the invention and their precursors can be made The tttanyl tetrafluorophthslocy~nine compound can be prepared by the reaction of 4-fluorophthalonitrile with titanium trichloride in l-chloronaphthalene at 210-215C. The synthesis of 4-fluorophthalonitrile as the precursor for the polyfluorinated phthalocyanine starts with 3,4-dimethylaniline and is shown in the following ~eries of reactions:

~ 28~9Z

,!~ /CH3 i) NsN02/HCl !~ /CH3 /C6H6 11) HBF4 i!~ ~ BF3~N2) /-~ /CH3 ~ o ~ il~ ~I~ ~

o urea / ~ / NH /-~ /CONH2 15 - 1l i \ NH 3 ~ ll I
l; F/ ~ \CONH2 o SOC12/DMF ~~ /CN
-- ~ U
~ ~ ~CN
Dlazotizatlon (i) and converslon (ii) to the tetrafluoroborate followed by pyrolysis in benzene of that derlvative (Balz-Schleman reactlon) glves 3,4-dimethylfluorobenzene, Thls is oxldlzed by aqueous potasslum permanganate to 4-fluorophthallc acid, monopotasslum salt. Vacuum dlstillation of the latter in the precence of sulfuric acid yields 4-fluorophthsllc anhydride. Treatment of the anhydride with urea in boillng chlorobenzene yields the imide which is converted with concentrated ammonium hydroxlde to the dlamlde. Flnally, dehydratlon of the diamide with thionyl chloride ln dimethylformamide glve~ 4-fluorophthalonitrlle, The followlng example descrlbe~ the use of 4-fluorophthalonltrlle, prepared a~ de~cribed above, ~28449~

_g_ to prep~re a polyfluoro phthalocyanine compound of the invention.
ExsmPle 1: PreParation of TitanYl TetrafluoroPhthalocYanine 4-Fluorophthalonitrile (38.7 g, 0.267 mole) and 20.7 g (0.134 mole) of titanium trichloride was ~uspended in 200 ml l-chloronaphthalene and heated to 210-215C (oil bath) and maintained for 2 l/2 hours at thi~ temperature. The reaction mixture was cooled slightly, the dark solid was collected, washed with acetone and methanol. After drying, the dark blue solid (34 g) was ~lurried twice in refluxing dimethyl-formamide, filtered hot each time and washed with acetone yielding a pigment having an x-ray diffractogram peak (2e) of 7.4.
The next example illustrates the acid pasting procedure which purifies, reduces the particle size snd modifies the crystalline form of the phthalocyanlne pigment~.
ExamPle 2 - Acid Pastin~ of TitanYl FluoroPhthalocYanine The blue solid of Example 1 was dissolved in 300 ml of concentrated sulfuric acid with cooling, stirred for one hour at room temperature, and filtered through a medium frit Buchner funnel. The acid filtrate was added to 2 liters of ice and water mixture with stirring. The bright blue solid that separated was collected, washed free of acid with water, then reqlurried in 500 ml of boiling water.
The phthalocyanine was collected by hot filtration and air-dried to give 26.4 g of pigment having an x-ray diffractogram peak (2~) of 6.8.
Calcd- for C32Hl2F4N8Ti (648-4) C~
59.2; H, 1.88; F, 11.7; N, 17.3; Ti, 7.38. Found:
C, 59.0; ~, 1.7; F, 11.3; N, 17.3; Ti, 6.9.

~2:8449~

The photoconductive elements of the invention preferably sre made from the 6.8 form of the pigment, as made in Example 2, or from a mixture of the 6.8 and 7.4 forms. Such a mixture can be obtained if the 6.8 form is dlspersed in an organic solvent .
To prepare a photoconductive element of the invention from a titanyl fluorophthalocyanine pigment, the pigment is disper~ed in a solution of a binder resin such as a polycarbonate resin. To achieve homogeneity the dispersion is milled for sn extended time, e.g., for several days, in a ball mill or other homogenizing apparatus. After diluting the milled dispersion to a suitsble viscosity for coating and after blending in a coating aid such as a silicone surfactant, the dispersion is coated on a conductive substrate. The latter, for example, can be a nlckel-coated polyethylene terephthalate film.
The coating is dried, e.g., by heating mildly for a few minutes.
The resulting charge generation layer is overcoated with a di~persion of a charge transport compound or compounds in a binder resin. This coating is then dried to provide a relatively thicker charge transport layer.
The next example describes preparation of multilayer photoconductive elements containing phthalocyanine pigments of Examples 1 and 2.
Example 3 - MultilaYer Photoconductive Element Containin~ TitanYl FluoroPhthalocYanine Pi~ment Pigments prepared as described in Examples 1 and 2, which are referred to as [~4-F)4Pc]TiO, were incorporated in the following formulation:

-` ~L28~49;;~

1.75 g High moleculsr weight polycsrbonate binder resin poly(oxycarbonyloxy-1,4-phenylene (l-methylethylidene)-1,4-phenylene) in solution in a solvent mixture of 1,1,2-trichlorometh~ne (40 g) and dichloromethane (26 g) 0.18 g [(4-F)4Pc]Tio 9.56 g Dichloromethane solvent 2 drops 1~ Solution of silicone surfsctant in dichloromethane (DC510 ~urfsctant of Dow Chemical Co . ) To form a coating dispersion this formula-tion was placed in a glas-~ container with 30 g of zirconia beads, shaken for three hours in a paint ~haker ~nd sep~r~ted from the be~ds. The dispersion was then coated a~ a charge generation layer on a subbed, nickelized conductive poly(ethylene terephthal~te) film support. The coated film was cured for 30 minutes in an 80C. oven, yielding a dried charge generation layer of 1.5 ~m thickness.
This thin layer was then overcoated with a thicker layer of an organic charge transport layer containing 35 percent 1,1-bis(4-di-~-tolylaminophenyl) cyclohexane and 65 percent of a polyester binder in a solvent mixture consisting of 60 parts by weight dichloromethsne And 40 part~ 1,1,2-trichloro-ethane, the polye ter being poly(4,4'-[2-norborn-ylidene]bi~phenylene terephthalate-co-azelate) 60l40. The re~ulting multilayer element was cured for two hours in a 60C oven.
Tests were m~de of multilayer elements prepared a~ in Example 3 using the crude pigment of Example 1 and the ~cid pasted-pigment of Example 2..

~28~49Z

Re~ult~ are given in the following table.

Electricsl Maximum Pigment Pl~ment Charscteristics Optical Psrticle Vo Dark decsY DensltY Size (~m) Exsmple 1 -220 v.
Exsmple 2 -500 v. 9.4v/sec. 2.5 <1.0 The dsts ~how that the scid-pasting treatment of Example 2 yields a pigment of very small particle size and improves the electrical propertie~
of the element.
When corona treated to a negative charge, the element containing the non-acid-pasted pigment (Example 1) wsq messured to be only about -220 volts (VO). The element cont~ining the acid-pasted pigment (Example 2) dlscharged from -500 to -100 volts when exposed to radiation of 830 nm st 7.0 ergs/cm . Dark decay was only 9.4 volts/sec.
ExamPle 4 - TitanYl HexadecYlfluoroPhthalo-cYanine (F16Pc)TiO
The reaction of tetrafluoro phthslonitrile with TiC13 by the procedure of Exsmple 1 yields the pigment, titsnyl hexafluorophthslocyanine. The sb~orption ~pectrum of this compound qhows a ~-msx st 728 nm, which i~ hypsochromsticslly shifted sbout 100 nm from the ~-msx of 826 nm exhibited by the titsnyl tetrsfluorophthslocyanine compound of Example 1. Although the electricsl snd dsrk dec~y characteristics of the tetrafluoro pigment were quperior to those of the hexsdecylfluoro species, the scid-pssted hexcadecylfluoro pigment i~ neverthele~s u~eful as a near infrs-red sensitive photoconductor snd its di~perssbility in binder resins is good.

The example~ have illustrsted the prepara-tion of a multilayer photoconductive element of the lnvention in which the charge transport layer is coated over the charge generation layer which s contain~ a titanyl fluorophthalocyanine pigment and is contiguou~ to the conductive ~ubstrate. Also within the ~cope of the invention are "inverted"
multiactive photoconductive elements in which a charge transport layer or layers are contiguous to the conductive support and a charge generation layer is coated over the charge trangport layer or layers.
Thia configurstion is preferred, for example, when it i9 desired to charge the photoconductive element po~itively in~tead of negatively. It is also advantageou~ in reducing the formation of white ~pots in the image which are caused by electrical breakdown in the development ~tage. Further, it i~ u eful in lmproving the uniformity of charge acros~ the ~urface of the photoconductive element or, in other word~, improvlng the electricsl granularity of the element.
The next example, de~cribes such an inverted element in which a charge generating layer containing a titanyl tetrafluorophthalocyanine compound is coated over the charge tran~port layer. 5 ExamPle 5 - Inverted Multilaver Photoconductive Element The pigment, titanyl tetrafluorophthalo-cyanine, (3.0 g) of Example 2 and 9.0 g of poly(oxycarbonyloxy-1,4-phenylenebicyclo~2.2.1]
hept-2-ylidene-1,4-phenylene) binder resln were di~persed in 81 g of 1,1,2-trichloroethane solvent.
The dispersion was milled for three days in a grinding mill. The milled di~persion wag then diluted with 360 g of dichloromethane and filtered to provide pigment concentrate. Thig concentrate wa~

2 8 4 ~ 9 incorporated in a dispersion for the charge generating layer having the following composition:
4.0 g Polycarbonate binder re~in 2.0 g Tri-p-tolylamine photoconductor 32.0 g Dichloromethane coating solvent 11.0 g 1,1,2-Trichloroethane coating ~olvent 151.0 g Phthalocyanine pigment concentrate 0.03 g Silicone ~urfactant coating aid (Dow DC510, a trademark of the Dow Chemical Company) For the charge transport layer a liquid disper~ion of the following formulation was prepared:
172.5 g Polycarbonate binder resin (Lexan 145 polycarbonate, a trademark of the General Electric Company, which i~ identified as poly(oxycarbonyl--oxy-l,4-phenylene (-l-methylethyl-idene)~~l,4-phenylene) 7.5 g Poly(ethylene--co-neopentylene terephthalate) polyester binder resin 120.5 g Tri-p-tolylamine photoconductor 1680.0 g Dichloromethane 420.0 g 1,1,2-trichloroethane 0.3 g Silicone surfactant coating aid (DC510) The inverse multilayer element wa~ prepared by coating the indicated charge tran-~port layer liquid dispersion on a nickel-coarted subbed poly(ethylene terephthalate~ film ~upport at 1.5 g/ft2 (16.15 g/m2) dry coverage and drying the coating. The charge generating layer wa~ then formed by coating the indicated charge generating layer liquid di~per~ion over the charge transport layer at 0.2 g/ft2 (2.15 g/m2) dry coverage and drying the coating.

.~

128~

The inverse lsyer e~ement of this example when tested in comparison with an element having the same pigment but the standard layer configuration had less electr~csl breakdown (as shown by reduction in image white spots after liquid development) and lower electrical granularity.
Although the examples have described pigments made from 4-fluoro and tetrafluoro phthalonitr$1es, any of the fluorine-substituted phthalonitriles are suitable precursors. Hence compounds of the invention include all of those represented by formula I wherein n is an integer of 1, 2, 3 or 4. For those in which n is leQs than 4, the fluorine can be substituted at any po~ition on the phthalonitrile ring. All of the resulting titanyl fluorophthalonitrile pigments of the invention have near infra-red sensitivity and di~persability ~o that photoconductlve elements can be made from them by dlspersion coatlng.
The patent to Scozzafava et al, U.S.
4,514,481 dlscloses electrophotographlc layers that contain an electron donor and an electron trans-porting compound such as certain 4H-thiopyran-l,l-dloxides. It has been found~ in accordance with the present invention, that these electron transporting compounds are unexpectedly beneficial when used in a multilayer photoconductive element of the present invention which can be positively charged for imaging. These elements have high ~ensit$vity in the near infrared reglon and low dark decay, making them especially useful in laser or LED-based prlnters.
One disadvantage of the $nverted layer configuration of multllayer photoconductor 1~ that the thin charge generation layer is on top of the element and may be sub~ect to abras~on a~ the element is used repeatedly in a series of lmaging cycle~.

~Z84~9i~

This, of course, shortens the life of the photoconductive element. By using an electron transporting compound, as described herein, the charge transport lsyer can be the top layer which is coated over the charge generation layer. This protects the thinner and more critically lmportant charge generation layer from abrasion as the element is reused, and yet the element csn be positively charged.
The following examples illustrate electro-photographic elements containing an electron trans-porting compound.
ExamPle 6 - Photoconductive Element ContaininQ a 4 H-ThioPvran-4-one-1~1-dioxide A photoconductive element was prepared substsntially as in Exsmple 3 except that the charge transport layer contalned 30 percent by weight of the compound 4-dicyanomethylene-2,6-diphenyl-4H-thiopyran-4-one-1,1-dioxlde in the polye~ter blnder.
The charge generatlon layer contained tltanyl tetrafluorophthalocyanlne in a polycarbonate blnder as in Example 3. The conductlve layer was an aluminum plate.
ExamPle 7 Another multilayer element was prepared as ln Example 6 except that the electron transportlng compound was 4-dicyanomethylene-2,6-di- = tolyl-4H-thiopyran-l,l-dioxide and the conductlve layer was a nickel-coated polymeric film.
ComParative ExamPle - AQQre~ate Chare Generation Laver A multilayer element like that of Example 6 was prepared except that, lnstead of tltanyl fluoro-phthalocyanine, an aggregate photoconductor as in Berwick et al U.S. 4,175,960 was used ln the charge generation layer.

9~

The photoconductive elements of Exsmple 6 and 7 and the comparative example were charged to 500 volts positive and exposed to radiation sufficient to discharge the element to 250 volts. The exposure for S Examples 6 and 7 was at 830 nm and for the compara-tive example was at 680 nm, that being within the region of sensitivity of the aggregate photo-conductor. The relative quantities of exposure required to discharge each element to 250 volts are listed in the table below, an arbitrary value of 100 being assigned to the quantity of exposure for the compsrative example. The table also shows the residual voltage ~VtOe) of each element after full irradiation.
TABLE
Residual Dark Relative Voltage Example Decay Exposure TOE
No. (V/sec) (-500V -250V~
6 4 12.1 40 7 4 14.0 44 Comp. 5 100* 124 Example *arbitrarily assigned a value of 100 for comparison The results show that when the thiopyran-dioxide electron transporting compounds were used with a titanyl fluorophthalocyanine charge generator in accordance with the invention (Examples 6 and 7), the exposure required to discharge the photoconductor from VO = 500 volts to 250 volts was about one eighth the exposure required for the same degree of discharge of the aggregate-type photoconductor u~ed with the same class of electron transporting compound. The table also shows that upon complete radiation the elements of the inven~ion discharged to -- ~ 2~449;~

voltages of 40 and 44 while the residual voltage for the element having a different charge generation layer was discharged only to 124 volts. These results demonstrate an unexpected cooperation of the tltanyl fluorophthalocysnine layer and the electron transportlng layer in the multilayer photoconductive elements of the invention.
When using an electron transport compound in a multilayer element of the invention having a conductive layers which is electron in~ecting, e.g., nickel, it may be de~irable to place a thin barrier layer between the conductive layer and the charge generation layer to prevent dark discharge. The barrier layer can be a non-conductive polymer such as a polyester or other materials disclosed in U.S.
4,175,960.
One of the advantages of the novel phthalocyanine pigments of the invention is that becau~e of their ~ensltivity to radiation in the near infrared region of the spectrum they can be used in photoconductive element~ which record the radiation of diode la~er~. They are not limited to that use, however. They can be used in adm$xture with charge generation compounds having sensltivlty, e.g., to visible light to provide photoconductive elements that have a broad range of sensitivity including the visible light range and near infrared.
The charge generation layer which contain~
the novel phthalocyanine pigmentC can have a thickness within a wide range depending upon the degree of photosensitivity desired. Thicknes~
affects photosensitivity in two opposite ways. As thickness increases a greater proportion of actinic radiation is absorbed by the layer, but there is a greater likelihood of a charge carrier being trapped and thus not contributing to image formation. These . ~LZ~34~

two factors must be balanced in selecting an appropriate thickness. A thickness in the range of sbout 0.05 ~m to 6.0 ~m is preferred for maximum photosensitivity. At thicknesses much below 0.05 ~m the rsdiatlon absorption is inadequate and at thlcknesses much sbove 6.0 ~m, the trapping of charge carriers becomes excess$ve.
A~ indicated in the examples and as disclosed in U.S. 4,175,960, the charge trsnsport layer in 8 multilayer element is thicker than the charge generation layer. Its thickness can be of the order of 3 to 40 ~m, preferably, 5 to 30. It can be several times thicker than the charge generation layer, e.g., 2 to 20 times thicker.
Although the examples have illustrated specific charge transport layer materials, the charge transport layer can be monomeric or polymeric orgsnic photoconductors or inorganic materials which can transport chsrge carrler~ generated ln the charge generatlon layer. Comblnations may be used. Most charge tran~port materials preferentially ~ccept and transport either positive charges (holes) or negative charges (electrons), although materials are known which will transport both positive and negative charges. Transport materials with a preference for conduction of positive charge carriers are called p-type transport materials and those with a preference for conduction of negative charges are called n-type.
Variouo p-type organic charge transport materials can be used in the charge transport layer in accordance with the present invention. Representa-tive p-type organic photoconductive materials include:
1. Carbazoles includlng carbazole, N-ethyl carbazole, N-isopropyl carbazole, N-phenyl carbazole, halogenated carbazoles, various polymeric carbazole materisls such B9 poly(vinyl carbazole) halogenated poly(vinyl carbazole), and the like.
2. Arylamines including monoarylamines, dlsrylamines, trlsrylam$nes, as well as polymeric arylamlnes. ExQmples of aryl~mine photQconductors include the non-polymeric triphenylamines illustrated in Klupfel et 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 radicals 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 3,567,450 issued March 2, 1971; the triarylamines in which at least one of the aryl radicsls in substituted by an active hydrogen-containing group, as described in Brantly et al U.S.
Patent No 3,658,520 i~sued Aprll 25, 1972; ~nd trltolylamlne.

3. Polyarylslkanes of the type described in Noe et al U.S. Patent 3,274,000 issued September 20, 1966; Wilson U.S. Patent No. 3,542,547 issued November 24, 1970 and in Rule et al U.S. Patent No.
3,615,402 is~ued October 26, 1971. Preferred polyarylalkane photoconductors can be represented by the formula:
D
J-C-E
G
wherein D and G, which may be the ~ame or different, represent aryl groups and J and E, which may be the same or different, represent a hydrogen atom, an alkyl group, or an Pryl group, at least one of D, E

~28~9~

and G containing an amino substituent. An especially useful polyarylalkane photoconductor which may be employed 8S the charge tran~port material is a polyarylalkane having the formula noted above wherein J and E represent a hydrogen atom, an aryl group, or an alkyl group and D and G represent substituted aryl groups having 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 substituted aryl such as a tolyl group. Additional information concerning certain of these latter polyarylalksnes may be found ln Rule et al U.S. Patent No. 4,127,412 lssued November 28, 1978.

4. Strong Lewis bases such as aromatic compounds, including aromatically un~aturated heterocyclic materials which are free of strong electron withdrawing groups.
Such aromatic Lewis bases include tetra-phenylpyrene, l-methylpyrene, perylene, chrysene, anthracene, tetraphene, 2-phenyl naphthalene, azapyrene, fluorene, fluorenone, l-ethylpyrene, acetyl pyrene, 2,3-benzochrysenes, 3,4-benzopyrene, 1,4-bromopyrene, phenylindole, polyvinyl carbazole, polyvinyl pyrene, polyvinyl tetracene, polyvinyl perylene, and polyvinyl tetraphene.

5. Other useful p-type charge-transport materials include the p-type organic photoconductors, including metallo-organo material~, known to be useful in electrophotographic processes, such a~ any ~Z8~

of the organic photoconductors described in Research Disclosure, Vol. 109, May 1973, pages 61-67, paragraph IV (A) ~2) through (13) which are p-type photoconductors. (Research Disclosure is published by Industrial Opportunities Limited, Havant, Hflmp~hlre, PO9 lEF, United Kingdom.) Representative of n-type charge-transport materials are strong Lewis acids such as organic and metallo-organic compounds containing one or more aromatic, including aromatically unsaturated hetero-cyclic compounds having an electron withdrawin8 substituent. These are considered useful because of their electron accepting capability. Typical electron withdrawing substituents include cyano and nitro groups; sulfonate groups; halogens Quch as fluorine chlorine, bromine, and iodine; ketone groups; ester groups; acid anhydride groups; and other acid groups such a~ carboxyl and quinone group~. Example~ of ~uch n-type aromatlc Lewis ~cids having electron withdrawlng ~ub~tituent~ include phthalic anhydride, tetrachlorophthalic anhydride, benzil, mellitic anhydride, S-tricyanobenzene, picryl chloride, 2,4-dinitrochlorobenzene, 2,4-dinitro-bromobenzene, 4-nitrobiphenyl, 4,4'-dinitrobiphenyl, 2,4,6-tri- nitroanisole, trichlorotrinitrobenzene, trinitro-o-toluene, 4,6-dichloro-1,3-dinitrobenzene, 4,6-dibromo-1,3-dinitrobenzene, p-dinitrobenzene, chloranil, bromanil, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitrofluorenone, trinitroanthracene, dinitroacridene, tetracyanopyrene, dinitroanthra-quinone, and mixture~ thereof.
Other useful n-type charge transport material~ are conventional n-type organic photo-conductors, for example, complexes of 2,4,7-trinitro-9-fluorenone and poly(vinyl carbazole).
Still other useful n-type organic and metallo-organo ~449;~

photoconductive materials lnclude any of the n-type organic photoconductive materials known to be useful in electrophotographic processes such as any of those described in Research Disclosure, Vol. 109, May 1973, page~ 61-67, paragraph IV(A) (2) through (13).
A ~ingle charge transport layer or more than one can be employed. Where a aingle charge transport layer i~ employed it can be either a p-type or an n-type material.
Where it is intended that the charge generation layer be exposed to actinic radiation through the charge transport layer, it is preferred that the charge transport layer have little or no ab~orption in the region of the electromagnetic spectrum to which the charge generation layer responds, thus permitting the maximum amount of actinic radiation to reach the charge generation layer. Where the charge transport layer is not in the path of exposure, thls consideration does not apply.
When solvent coating the layer~, a film-forming polymeric binder can be employed. The binder may, if it is electricslly insulating, help to provide the element with electrical in~ulatlng characteriatics. It al~o is useful (a) in CatinB
the layer, (b) in adhering the layer to an ad~acent layer, and (c) when it is a top layer, in providlng a smooth, easy to clean, wear resistant -~urface.
When a polymeric binder i~ employed in either the charge generation or charge transport layer, the optimum ratio of charge generation or charge transport material to binder may vary widely depending on the particular binder and charge transport msterials. In general, uaeful re~ùlts are obtained wherein when the amount of actlve charge generation or charge tran~port material contained ~ 2~3~492 within the layer varies within the range of from about 2 to sbout 90 weight percent based on the dry weight of the layer.
Representative materials which may be employed as binders in the charge generation and charge transport layers are film-forming polymers having a fairly high dielectric strength and good electrically insulating properties. Such binders include, for example, styrene-butadiene copolymers ;
polyvinyl toluene-styrene copolymers; styrene-alkyd resins; silicone-alkyd resins; soys-alkyd resins;
vinylidene chloride-vinyl chloride copolymers;
poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; vinyl acetste-vinyl chloride copolymers; poly(vinyl acetals), suchas poly(vinyl butyral); nitrated polystyrene;
polymethylstyrene; isobutylene polymers; polyesters, such as poly[ethylene-co-alkylenebis(alkylene-oxyaryl)phenylenedicarboxylate]; phenolformaldehyde reslns; ketone resins; polyamides; polycarbonates;
polythiocarbonates; polytethylene-co-isopropylidene-2,2-bis(ethyleneoxyphenylene)terephthalate];
copolymer~ of vinyl haloacrylates and vinyl acetate such as poly(vinyl-m-bromobenzoate-co-vinyl acetate);
and chlorinated poly(olefins), such as chlorinated poly~ethylene).
Binder polymers should provide little or no interference with the transport of charge carriers through the layer. Examples of binder polymers which are e~pecially useful in p-type charge transport layers include styrene-containing polymers, bisphenol A polycarbonates, phenol-formaldehyde resins, polyesters such as poly~ethylene-co-isopropylidene-2,2-bis(ethyleneoxy-phenylene)]terephthalate, and copolymers of vinyl haloacrylates and vinylacetate ~28~

such ag poly(vinyl-m-bromobenzoate-co-vinyl acetate).
The charge generation and charge transport layers can also contain other addenda such as leveling sgents, surfactants and plasticizers to enhance or improve various physical properties of the layer. In addition, various addenda to modify the electrophotographic re~ponse of the element can be incorporated in the charge transport layer. For IO example, contrast control materials, such as certain hole-trapping agents and certain easily oxidized dyes can be incorporated. Such contrast control materials are described in Research Disclosure, Vol. 122, June 1974, p. 33, in an article entitled "Additives For Contra3t Control In Organic Photoconductor Compositions and Elements".
When the charge generation layer or the charge transport layer i8 ~olvent coated, the components are di~solved or di~persed in a liquid together with the binder, if one ls employed, and other sddenda. Useful liquids include aromatic hydrocarbons such a~ benzene, naphthalene, toluene, xylene and mesitylene; ketones such as acetone and butanone; halogenated hydrocarbons such as methylene chloride, chloroform and ethylene chloride; ethers including cyclic ethers such as tetrahydrofuran and ! ethyl ether; and mixtures thereof.
A variety of electrically conducting supports can be employed in the elements of this invention, such as for example, paper (at a relative humidity above 20 percent); aluminum-paper laminates;
metal foils such as aluminum foil, zinc foil, etc.;
metal plates such as aluminum, copper, zinc brass and galvanized plates; vapor deposited metal layers such as silver, chromium, nickel, sluminum and the like coated on paper or conventional photographic film 2 ~ ~ ~ 9 Z

bsses such as poly(ethylene terephthalate), cellulo~e acetate, polystyrene, etc. Such conducting materials as chromium, nickel, etc. can be vacuum deposited on transpsrent fllm supports ln sufficlently thln layers to allow electrophotographlc elements prepared therewith to be exposed from either side. An especl~lly useful conductlng support can be prepared by costing a support material such as poly(ethylene terephthalate) with a conducting layer containlng a semlconductor dlspersed ln a resin. Such conducting layers both with and without electrical barrier layers sre described in U.S. Patent 3,245,833 by Trevoy, l~sued April 12, 1966. Other useful conducting lsyers include compositions consisting essentislly of sn intimate mixture of at least one protectlve lnorganic oxide and from 30 to 70 percent by weight of at least one conducting metal, e.g., a vacuum-depo~lted cermet conducting layer as described ln Ra~ch U S. Patent No. 3,880,657 i~sued April 2g, 1973. ~ikewi~e, a sultable conductlng coating can be prepared from the ~odium ~alt of a carboxyester lactone of maleic anhydride and a vinyl scetste polymer. Such conducting layers and methods for their optimum preparation and u~e are disclosed in U.S. Patent 3,007,901 by Minsk issued November 7, 1961 and 3,262,807 by Stermsn et al lssued July 26, 1966.
The v~rlous lsyers of the element can be coated directly on the conducting substrate. In some cases, lt may be desirable to use one or more intermedi~te subbing lsyers over the conducting substrate to improve adhe~lon between the conducting substrste and overlylng layers or to act as an electrlcal barrler layer a9 descrlbed in Dessauer U.S. Patent 2,940,348. Such subbing layers, if used, typicslly have a dry thicknes~ in the range of about ~28~L92 0.01 to about 5 ~m. Typical subbing layer materials include film-forming polymers such as cellulose nitrate, polyesters, copolymers of poly(vlnyl pyrrolidone) snd vinylacetste, and various vinylidene chloride-containing polymers including two, three and four component polymer~ prepared from a polymerizable blend of monomers or prepolymers containlng at least 60 percent by weight of vinylidene chloride. Representative vinylidene chloride-containing polymers include vinylidene chloride-methyl methacrylate-itaconic acid terpolymers as disclosed in U.S. Patent No.
3,143,421. Various vinylidene chloride containing hydro~ol tetrapolymer which may be used include tetrapolymers of vinylidene chloride, methyl acrylate, acrylonitrile and acrylic acid as disclosed in U,S. Patent No, 3,640,780. Other useful vinylidene chloride-containing copolymer~ include poly(vinylldene chloride-methyl acrylate), poly(vinylidene chlorlde-methacrylonitrile), poly-(vinylidene chloride-acrylonitrile), and poly-(vinylidene chloride-acrylonitrile-methyl acrylate).
Other subbing material~ include the so-called tergels described in Nadeau et al U.S. Patent 3,501,301 and the vlnylidine chloride terpolymers described in Nadeau U.S. patent 3,228,770.
One e~pecially useful subbing layer i~ a hydrophobic film-forming polymer or copolymer free from any acid-containing group, such as a carboxyl group, prepared from a blend of monomers or pre-polymers, each of said monomers or prepolymers containing one or more polymerizable ethylenically unssturated group~. Useful materials include many of the above-mentioned copolymer5, and in addition, the following: copolymers of polyvinylpyrrolidone and ~z~

vinyl acetate, poly(vinylidene chloride-methyl methacrylate), and the like.
Optlonal overcoat layers can also be used if desired. For example, to improve surface hardness and resi~tance to abrasion, the surface layer of the element of the invention can be coated with one or more electrically insulating, organic polymer coating~ or electrically insulating, inorganic costings. A number of such coatings are well known in the art. Typical overcoats are described for example, in Re~earch Disclosure, "Electrophotographic Elements, Materials and Processes", Vol. lO9, p. 63, Psragraph V, May 1973.
While the novel photoconductive elements are useful in electrophotography, they can al~o be used in other arts, ~uch as in solar cell~, where photocon-ductive elements are employed.
This invention has been de~cribed in detail wlth certaln preferred embodiment~ thereof, but it will be understood that variatlons and modifications can be effected within the spirit and scope of the invention.

Claims (21)

1. A photoconductive titanylphthalo-cyanine pigment having fluorine ring substitution.

2. A pigment according to claim 1 having at least one fluorine substituent on each carbocyclic ring thereof.

3. A pigment according to claim 1 having one fluorine substituent on each carbocyclic ring thereof.

4. A pigment according to claim 2 wherein the compound is titanyl 2,9,16,23-tetrafluoro-phthalocyanine.

5. A pigment according to claim 1 wherein the compound is titanyl hexadecylfluorophthalocyanine.

6. A pigment according to claim 3 having an x-ray diffractogram peak (2.THETA.) of 6.8°.

7. A pigment accordlng to claim 4 having an x-ray diffractogram peak (2.THETA.) of 7.4°.

8. A plgment accordlng to clslm 3 whlch ls mixture of the 6.8° and 7.4° forms.

9. A photoconductlve element comprising an electrically conductive substrate and a photo-conductive layer, said photoconductive layer comprising a binder resin and a pigment of claim 1.

10. A photoconductive element according to claim 9 which is a multilayer element comprising at least one charge generation layer and at least one charge transport layer.

11. A photoconductive element according to claim 10 wherein the charge generation layer is contiguous to the conductive substrate and a charge transport layer is the surface layer and contains a 4H-thiopyran-1,1-dioxide compound as an electron transport compound.

12. An element according to claim 11 wherein said electron transport compound is 4-dicyano-methylene-2,6-di-phenyl-4H-thiopyran-1,1-dioxide.

13. An element according to claim 11 wherein said electron transport compound is 4-dicyanomethy-lene-2,6-di-m-tolyl-4H-thiopyran-1,1-dioxide.

14. A photoconductive element according to claim 10 wherein a charge transport layer is contiguous to the conductive substrate and the charge generation layer is the surface layer.

15. A photoconductive element according to claim 9 wherein the layers containing said phthalocyanine pigment are formed by dispersion coating.

16. A photoconductive element according to claim 10 wherein the layers containing said phthalocyanine pigment are formed by dispersion coating.

17. A photoconductive element according to claim 9 wherein the phthalocyanine pigment before incorporation in the element has been subjected to acid treatment, the acid treatment compriaing diaaolving the pigment in cold concentrated mineral scid, adding the scid solution to cold water to reprecipitate the phthalocyanine compound, washing the precipitate free of acid and drying the washed precipitate.

18. A photoconductive element according to claim 14 wherein the charge generation layer is formed by coating on a support a dispersion obtained by milling the binder resin with the acid-treated phthalocyanine pigment.

19. A photoconductive element comprising sn electrically conductive substrate and a photo-conductive layer which contains a pigment according to claim 6.

20. A photoconductive element comprising an electrically conductive substrate and a photo-conductive layer which contains a pigment according to claim 8.

21. A method of forming an electrophoto-graphic image which comprises electrostatically charging a photoconductive element according to claim 9, exposing the charged element to a pattern of near infrared radiation and developing the resulting charge pattern on the photoconductive element.