US 3615418 A
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Unite States Patent Inventors William J. Staudenmayer Pittsiord;
James C. Fleming, Rochester, both of N.Y. 835,223
June 20, 1969 Oct. 26, 197 l Eastman Kodak Company Rochester, N.Y.
Appl. No. Filed Patented Assignee HIETEIROGENEOUS DYE-BINDER PHOTOCONDUCTIVE COMPOSITIONS 13 Claims, No Drawings U.S. Cl 96/l.6, 96/1 .5, 96/1 .7, 252/501, 260/37, 260/40 Int. Cl G03g 5/06 Field of Search 96/L6, 1.7,
 References Cited UNITED STATES PATENTS 3,250,615 5/1966 Van Allen et a1... 96/l.7
Primary Examiner-George F. Lesmes Assistant Examiner-John C. Cooper, 11] Attorneys-W. H. J. Kline, J. R. Frederick and T. Hiatt lilllETlEMUGlENlEQlUS lDit'E-IMNIDEM lPHQTUCUNDUCTlll/lli CQMPUMTHQNS This invention relates to electrophotography and to photoconductive elements and structures useful in electrophotography. in addition, this invention relates to means for preparing electrophotographic elements.
Electrophotographic imaging processes and techniques have been extensively described in both the patent and other literature, for example U.S. Pat. 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; 3,220,831; 3,220,833 and many others. Generally, these processes have in common the steps of employing a normally insulating photoconductive element which is prepared to respond to imagewise exposure with electromagnetic radiation by forming a latent electrostatic charge image. A variety of subsequent operations, now well known in the art, can then be employed to produce a permanent record of the image.
One type of photoconductive insulating structure or element particularly useful in electrophotography utilizes a composition containing a photoconductive insulating material dispersed in a resinous material. A unitary electrophotographic element is generally produced in a multilayer type of structure by coating a layer of the photoconductive composition onto a film support previously overcoated with a layer of conducting material or the photoconductive composition may be coated directly onto a conducting support of metal or other suitable conducting material. Such photoconductive compositions have shown improved speed and/or spectral response, as well as other desired electrophotographic characteristics when one or more photosensitizing materials or addenda are incorporated into the photoconductive composition. Typical addenda of this latter type are disclosed in U.S. Pat. Nos. 3,250,615, 3,141,770 and 2,987,395. Generally photosensitizing addenda to photoconductive compositions are incorporated to effect a change in the sensitivity or speed a particular photoconductor system and/or a change in its spectral response characteristics. Such addenda can enhance the sensitivity of an element to radiation at a particular wavelength or to a broad range of wavelengths where desired. The mechanism of such sensitization is presently not fully understood. The phenomenon, however, is extremely useful. The importance of such effects is evidenced by the extensive search currently conducted by workers in the art for compositions and compounds which are capable of photosensitizing photoconductive compositions in the manner described.
Usually the desirability of a change in electrophotographic properties is dictated by the end use contemplated for the photoconductive element. For example, in document copying applications the spectral electrophotographic response of the photoconductor should be capable of reproducing the wide range of colors which are normally encountered in such use. if the response of the photoconductor falls short of these design criteria, it is highly desirable if the spectral response of the composition can be altered by the addition of photosensitizing addenda to the composition. Likewise, various applications specifically require other characteristics such as the ability of the element to accept a high surface potential, and exhibit a low dark decay of electrical charge. it is also desirable for the photoconductive element to exhibit high speed as measured in an electrical speed or characteristic curve, a low residual potential after exposure and resistance to fatigue. Sensitization of many photoconductive compositions by the addition of certain dyes selected from the large number of dyes presently known has hitherto been widely used to provide for the desired flexibility in the design of photoconductive elements in particular photoconductor-containing systems. Conventional dye addenda to photoconductor compositions have generally shown only a limited capability for overall improvement in the totality of electrophotographic properties which cooperate to produce a useful electrophotographic element or structure. The art is still searching for improvements in shoulder and toe speeds, improved solid area reproduction characteristics, rapid recovery and useful electrophotographic speed from either positive or negative electrostatic charging.
A high speed heterogeneous" or aggregate" photoconductive system was developed by William A. Light which overcomes many of the problems of the prior art. This aggregate composition is the subject matter of copending application Ser. No. 804,266, filed Mar. 4, 1969, and entitled Novel Photoconductive Compositions and Elements. The addenda disclosed therein are responsible for the exhibition of desirable electrophotographic properties in photoconductive elements prepared therewith. However, use of the pyrylium type sensitizing dyes described therein generally results in a coating dope which has a time dependent viscosity. Thus, the resultant photoconductive layers formed from such coating dopes can vary from batch to batch. The quality of an image produced with an electrophotographic element is related to the thickness uniformity of the photosensitive layer of such an element. Accordingly, there is a need in the art for means of obtaining high speed photoconductive compositions which can be coated uniformly.
it is, therefore, an object of this invention to provide the art of electrophotography with novel photoconductive compositions which can be uniformly coated. i
it is another object to provide a novel means for preparing high speed photoconductive coatings having uniform physical properties.
These and other objects and advantages of the invention will become apparent from the following description of the invention.
It has been discovered that when the heterogeneous or aggregate photoconductive compositions of William A. Light are prepared using certain salts of various pyrylium, selenapyrylium and thiapyrylium dyes improved uniformity of physical properties is obtained. in particular, when the dye salts used have an inorganic anion with an anionic radius at least as large as that of hexafluorophosphate, the resultant coating dope has a viscosity which is substantially independent of time. This property results in coated layers which are substantially uniform in thickness and in surface properties. The heterogeneous compositions of this invention are prepared from the above hexafluorophosphate dye salts and an electrically insulating polymeric material. The compositions thus formed can be used as photoconductors or as sensitizers for other photoeonductors.
The present aggregate photoconductive compositions can be prepared by several means; however, one particularly useful means is the dye first" technique described in copending Gramza and Qwens U.S. application Ser. No. 816,831, filed Apr. 16, 1969 and entitled Method For The Preparation 01 Photoconductive Compositions." The essential feature of this dye first method is that the sensitizing dye or dyes used are substantially completely dissolved in a suitable solvent prior to the addition of any other materials. After first dissolving the dye, the polymeric material is subsequently added with suitable stirring to dissolve the polymer. The combined solution is then coated on a suitable support which results in the formation of a separately identifiable multiphase composition, the heterogeneous nature of which is generally apparent when viewed under at least 2500K magnification, although such compositions may appear to be substantially optically clear to the nalced eye. There can, of course, be a macroscopic heterogeneity. Suitably, the dye-containing aggregate in the discontinuous phase is predominatly in the size range of from about 0.01 to 25 microns. However, it should be noted that when the heterogeneous compositions of the invention are used to sensitize a particulate photoconductor, such as zinc oxide, another discontinuous phase will be present which may not fall within this size range.
in general, the heterogeneous compositions of the present invention are multiphase organic solids containing dye and polymer. The polymer forms an amorphous matrix or continuous phase which contains a discrete discontinuous phase as distinguished from a solution. The discontinuous phase contains a significant portion of the dye present and generally a predominant portion of the dye present is in this discontinuous phase. The dye in the discontinuous phase can be considered as being in particulate form; however, that phase need not be comprised wholly of dye. It is believed that in some instances the discontinuous phase may be comprised of a co-crystalline complex of dye and polymer; however, it is also believed that all of the aggregates which can be formed in accordance with the method of this invention are not necessarily comprised of dye and polymer. Preferably, substantially all of the dye present in this system is in the discontinuous phase. When the present compositions are used in conjunction with an organic photoconductor, the resultant photoconductive composition generally contains only two phases as the photoconductor usually forms a solid solution with the continuous polymer phase. On the other hand, when the present multiphase compositions are used in conjunction with a particulate photoconductor, three phases may be present. In such a case, there would be a continuous polymer phase, a discontinuous phase containing dye as discussed above and another discontinuous phase comprised of the particulate photoconductor. Of course, the present multiphase compositions may also contain additional discontinuous phases.
Another feature characteristicof the heterogeneous compositions of this invention 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 dyepolymer solid solution formed of similar constituents. The new absorption maximum characteristic of the aggregates of this invention .is not necessarily an overall maximum for this system as this will depend upon the relative amount of dye in the aggregate state. Such an absorption maximum shift in the formation of multiphase heterogeneous systems for the present invention is generally of the magnitude of at least about m lf mixtures of dyes are used, one dye may cause an absorption maximum shift to a long wavelength and another dye may cause an absorption maximum to a shorter wavelength. In such cases, formation of the heterogeneous compositions can more easily be identified by viewing under magnification.
It is believed that the improved results obtained in accordance with the present invention may be a result of the size of the inorganic anions used along with the irregular shape of these anions. The size and possibly the shape of the anion appear to have a considerable influence on solubility properties which in turn results in extended stability of the coating dope. The hexafluorophosphate anion, for example, has a distorted octahedral shape; whereas, for example, the perchlorate and fluoroborate anions disclosed in the Light application above are regular tetrahedrons. Thus, anions suitable for use in the present invention would include inorganic anions having an anionic radius at least as large as that of hexafluorophosphate and also having an irregular shape. For purposes of comparison, the anionic radius can be approximated by adding internuclear distances,
lnteratomic Distances. Supplement, L, E. Sutton (Ed), I965 as determined by X-ray techniques on the anion in question. and the Van der Walls radius of the peripheral atom. For example, the B-F internuclear distance in BFzis 1.42 A. and the Van der Waals radius ofF is L35 A. giving a total of2.77 A. as the approximate radius ofBF; Using the above method, the following table is thus obtained:
Particularly useful results are obtained using anions of the formula QF: wherein Q is a Group VA element (other than nitrogen) in accordance with the Periodic Table of the Elements (Handbook of Chemistry and Physics, 4lst Edition, pp. 448-449 and includes antimony, arsenic and phosphorus.
Sensitizing dyes and electrically insulating polymeric materials are used in forming these heterogeneous compositions. Typically, pyrylium dyes, including pyrylium, thiapyrylium and selenapyrylium dye salts are useful in forming such compositions. Such dyes include those which can be represented by the following general formula:
inter-atomic Distances, Supplement, L.E. Sutton (Ed), I965) wherein R", R, R, R", and R can each represent (a) a hydrogen atom; (b) and alkyl group typically having from 1 to 15 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, amyl, isoamyl, hexyl, octyl, nonyl, dodecyl, etc., (c) alkoxy groups like methoxy, ethoxy, propoxy, butoxy, amyloxy, hexoxy, octoxy, and the like; and (d) aryl groups including substituted aryl groups such as phenyl, 4-diphenyl, alkylphenyls as 4-ethylphenyl, 4-propylphenyl, and the like, alkoxyphenyls as 4-ethoxyphenyl, 4-methoxyphenyl, 4-amyloxyphenyl, 2-hexoxyphenyl, Z-methoxyphenyl, 3,4-dimethoxyphenyl, and the like, B -hydroxyalkoxyphenyls as Z-hydroxyethoxyphenyl, 3-hydroxyethoxyphenyl, and the like, 4- hydroxyphenyl, halophenyls, as 2,4-dichlorophenyl, 3,4- dibromophenyl, 4-chlorophenyl, 3,4-dichlorophenyl, and the like, azidophenyl, nitrophenyl, aminophenyls as 4- diethylaminophenyl, 4-dimethylaminophenyl, and the like, naphthyl; and vinyl substituted aryl groups such as styryl, methoxystyryl, diethoxystyryl, dimethylaminostyryl, l-butyl- 4-p-dimethylaminophenyll, 3-butadienyl, B-ethyl-4- dimethylaminostyryl, and the like; where X is a sulfur, oxygen or selenium atom; and Z is an inorganic anion having an anionic radius at least as large as that of hexafluorophosphate and having an irregular shape. In addition, the pair R and R as well as the pair R and R can together be the necessary atoms to complete an aryl ring fused to the pyrylium nucleus. Table 2 below gives a partial listing of typical members of the dlmethylaminophenyll-2 e-methoxyphenyl rsphenylthiapyrylium hexafluorophosphalc l2 4-(4-dimethylaminophcnyl)-2(4-rnethoxyphenyl)-6- 5 (4-methylphenyl)pyrylium hexafluoroarsenate l3 4-(4-diphenylaminophcnyl)-2.6-
diphenylthinpyrylium hexafluorophosphate l4 2,4L6-triphenylpyryliurn hexafluorophoaphme l5 4-(4-methoxyphenyl)-2.6-diphenylpyrylium hexafluoroantimonate l l6 4-(2,4-dichlorophenyl)-2,fi-diphcnylpyrylium hcxafluorophosphate l7 4-(3,4-dichlorophenyl)-2,6-diphcnylpyrylium hcxafluorophosphatc l8 2,6-bis(4-rnethoxyphenyl) hphenylpyryliurn hexafluoroarsenate l9 fi-( l-methoxyphcnyl )-2,4-diphenylpyrylium l henafluoroarscnate 2-(3,4-dichlorophenyl)-4-(4-mcthoxypl1enyl)-6- phcnylpyryliurn hexafiuorophosphate 2l Z-( l-amyImtyphcnyI)'2,6-bis( Lelhylphcnyl )pyrylium hettafluorophosphate 22 4 (4-arnyloxyphenyl)-2,6-bis(4- methoxyphenyllpyrylium hexufluorophosphate 23 2,4,6-triphenylpyrylium hexafluoroarsenate 24 2,6'bis(4-ethylphcnyl)-4-(4- methosyphcnynpyrylium hexnfluorophosphate 25 2,6-bis(4-cthylphenyl)-4-(4- methoxyphenyhpyryliurn hexafluoroantimonate 25 26 t5-(3A-diethoxystyryl)-2,4-diphenylpyryliurn hcxafluorophosphate 27 0343,l-diethoxy-flamylstyryl)-2,4diphenylpyrylium hexafluoroantimonatc 23 -(4-dimcthylamino-fl-ethylstyryl)-2,4- diphenylpyrylium hexafluoroantimonale 29 6-( l-mamyl-4-p-dimcthylaminophcnyll ,3-
butadienyl)-2.4-dlpl1enylpyryliurn hemafluoronntimonatc 30 2,fi'bifl4-metho1ryphenyl)-4-phenylthiapyrylium hexafluorophosphate 3i 4-(2.4-dichlorophcnyl)-2,fi-diphcnylthiapyrylium hexailuorophosphate 32 2,4,6-tris(4-methoxyphenyl)thiapyrylium hexafluorophosphate 33 2,6bis(4ethy|phenyll-4'phcnylthiapyrylium hcxafluorophosphatc 34 4-(4-amyloxyphenyl)-2,6-bis(4 ethylphenyhthiapyrylium hexafluorophosphatc O 35 fi-t l-dimethylaminostyryl) 2.4-diphenylthiapyrylium hexnl'luorophosphatc 36 2.4,(v-triphenylthiapyrylium hexafluorophosphate 372,4,6- triphenylthiapyrylium hexal'luoroarsennte 38 4-(4-methoxyphenyl) 2,B-diphenylthiapyrylium hcxnl'luoroantimonate 39 2,4,fi-triphenylthiapyrylium hexafluoroantimonate 40 2-( l-arnyloxyphenyl)-4,6-diphenylthiapytyllum hexafluoroantimonate 41 4-[4-amyloxyphcnyl)-2,6-bis(4- methoxyphenyl)thiapyrylium hexafluorophosphate 42 2,6-bis(4-t:thylphenyl)-4-(4 mcthoxyphenyl)thiapyryliurn hexafluorophosphate 43 4-anisyl2.6-bis(4-n-amyloxyphcnyl)thiapyryliurn hexafluoroarsenatc 44 Z-[fiLfi-bisl l-dimethylaminophenyhvinylenc1-4.6- diphenyllhinpyrylium hcxafluorophofiphate 45 6-(fl-ethyl-wdimethylarninostyryl)-2.4- diphcnylthiapyrylium hexal'luorophosphute 46 3-( idimethylaminophenyhnaphthfl2,l-
b)selenapyrylium hcxafluorophosphale 47 H4-dimethylaminostyryl)-2-(4- mcthoxyphenyl)benzolbselenapyrylium 6O hexafluorophosphate 48 2,6-di(4-diethylaminophcnyll-lphcnylsclenapyrylium hexafluorophosphate 49 44A-dirnelhylarninophenyl)-2-(4-cthoxyphenyl)-l5- phcnylpyryllum hcxafluorophosphale Particularly useful dyes in forming, the feature aggregates are pyrylium dye salts having the formula:
l RY --R2 Q Fs wherein:
R and R; can each be phenyl radicals, including substituted phenyl radicals having at least one substituent chosen from alkyl radicals of from one to six carbon atoms and alltoxy radicals having from one to six carbon atoms;
R can be an alkylamino-substituted phenyl radical having from one to six carbon atoms in the alkyl moiety, and including dialkyamino-substituted and haloxalkylamino-substituted phenyl radicals;
X can be an oxygen or a sulfur atom: and
Q is a Group VA element such :as antimony, arsenic, phosphorus, etc.
Electrically insulating, film-forming polymers useful for the formation of electrophotographic compositions containing the aggregate photoconductive compositions made by this invention include polycarbonates and polythiocarbonates, polyvinyl ethers, polyesters, poly-cz-olefins phenolic resins, and the like. Mixtures of such polymers can also be used. Such polymers include those which function in the formation of the aggregates as well as functioning as binders which [hold the photoconductive compositions to a suitable support. Typical polymeric materials from these classes are set out in table 3.
TABLE 3 Number Polymeric Material 1 polystyrene 2 poly(vinyltolucne) 3 poly(vinylnnisole) 4 polychlorostyrene 5 polya-mcthylstyrene 6 polyacenaphthalene 7poly(vinyl isobutyl ether) 8poly(vinyl cinnamate) 9 polytvinyl henzoatv) l0poly(vinyl naphthoatc) ll poly(vinyl carbuzole) l2 poly(vinylenc carbonate) l3 poly(vinyl pyridine) l4 poly(vinyl metal) 15 poly(vinyl butyral) l6 poly(ethyl methacrylatc) l7 poly(butyl melhacrylate) l8 p0ly(styrenc-co-butadicne) l9 poly(styrcne-co-rnethyl rncthacrylate) 20 poly(styrene-co-ethyl acrylate) Zl poly(styrene-co-acrylonitrile) 22 poly(vinyl chloride-co-vinyl acetate) 23 poly(vinylidene chloride-co-viny| acetate) 24 poly(4,4'-isopropylidenediphenyl-co4,4- isopropylidenedicyclohexyl carbonate) 25 poly[4,4"isopropylidenebis(2,6
dibromophenyhcarbonare] 26poly[4,4'- isopropylidenebis(2,6- dichlorophenyhcarbonate) 27 poly[4,4'-isopropylidenebis(2,6-dirnelhylphcnyllcarbonate] 28 poly(4,4'-isopropylidenediphenyl-co-l ,4-cyclohexyldimethylicarbonate) 29 poly(4,4-isopropylidenediphenyl terephrhalate-coisophthalate) 30 poly(3,3-ethylenedioxyphenyl thiocarbonate) 3 l poly(4,4-isopropylidenediphcnyl carbonate-coterephthalale) 32 poly(4,4'-isopropylidcnediphenyl carbonate) 33 poly(4,4'-isopropylidenediphenyl thiocarbonate) 34 poly(2,2-butanebis-4-phcnyl carbonate) 35 poly(4.4-luopropylldcmedlphmnyl carbonate-biochttthylene oxide) 36 poly(4.4'-lsopropylidenediphenyl carbonate-blocktelramethyleneoxidc) 37 poly[ 4,4'-isopropylidenebis( 2- methylphenyllcarbonuto] 38 poly(4,4-isopropylidenediphenyl-co-l.4-phcnylenc carbonate) 39 poly(4.4'-isopropylidenediphcnyl-co-l ,J-phenylene carbonate) 40 poly(4,4-isopropylidenediphenyl-co-4,4'-diphenyl carbonate) 41 poly (4,4'-isopropylidenediphcnyl-co-4.4-
oxydiphcnyl carbonate) poly( 4,4'-isopropylidenediphenyl-co-4,4-
carbonyldiphenyl carbonate) 43 poly(4,4'-isopropylidenediphenyl-co-4,4-
ethylenediphenyl carbonate) 44 po|yl4,4"methylenebis(Z-methylphenyllcarbonate] 45 poly[ l ,l -(p-brornophenylethane )bis(4-phenyl) carbonate] 46 polyl4,4'-isopropylidenediphenyl-co-sulfonyl bia 4- phenyllcarbonate] 47 poly] l, l -cyclohexane bis( 4-phenyl )carbonate] 48 poly(4,4-iropropylidenediphenoxydimethylsilane) 49 poly[4,4'-isopropylidene bis(2-chlorophenyl) carbonate] 50 poly]a,a,a:',a' -tetramethyl-p-xylylene biaH-phenyl carbonate 5 I poly(hexafluoroisopropylidenediA-phenyl carbonate) 52 poly(dichlorotetrafluoroisoproplidenedi-4-phenyl carbonate) 53 poly(4,4-isopropylidenediphenyl-4,4-
impropylidenedibenzoate) 54 polyt4,4'-isopropylidenedibenzyl-4,4'-
isopropylidenedibenzoate 55 poly(4,4'-isopropylidenedil -naphthyl carbonate 56 poly(4,4'-isopropylidene bis(phenoxy-4-phenyl sulfonate)] $7 acetophenone-formaldehyde resin 58 polyl4,4'-isopropylidene bis(phenoxyethyl)-coethylene terephthalate] 59 phenol-formaldehyde resin 60 polyvinyl acetophenone 6l chlorinated polypropylene 62 chlorinated polyethylene 63 poly(2,6-dimethylphenylene oxide) 64 poly(neopentyl-Z,6-naphthalenedicarhoxylate 65 poly(ethylene terephthalatc-co-isophthalate) 66 poly( l ,4-phenylene-cl,3-phenylene succinatc) 67 polyt4,4'-lsopropylidenediphenyl phenylphosphonate) phenylcarboxylate) 69 oly( l ,4-cyclohexanedimethyl terephthalate-coisophthalate) 70 polyttetramethylene succinate) 7l pcly(phenolphthalein carbonate) 72 poly(4,-chloro-l,3-phcnylene carbonate) 73 poly(2methyll,3-phenylene carbonate) 74 poly( l ,l-bi-Z-naphthyl thiocarbonate) 75 polytdiphenylmethane bis-4-phenyl carbonate) 76 poly[2,Z-(3-methylbutane)bis-4-phenyl carbonate] 77 poly[2,2-(3,3-din1ethylbutane)bis-4-phenyl carbonate] 78 poly l,l-[ l-( l -naphthyl)]bis-4-phenyl carbonate 79 poly]2.2-(4-methylpentane)bis--t4- merhylpentane )bis-phenyl carbonate] 80 poly]4,4'(2-norbornylidene)diphenyl carbonate] Bl poly]4,4'-(hexahydro-4,7-methanoidan-5-ylidcne) diphenyl carbonate] 82 poly(4,4-isopropylidenediphenylcarbonate-blockoxytctramethylene) Especially useful polymers for forming the heterogenous compositions in accordance with the present method are com pounds numbered 28, 30-47, 49, 51, 53, 54 and 76-82 as listed in table 3 above.
Included among the preferred polymers used in the present method for preparing the multiphase heterogeneous compositions, including copolymers, are those linear polymers having the following recurring unit:
Rs R4 R1 w g,
R and R when taken separately, can each be a hydrogen atom, an alkyl radical such as methyl, ethyl, propyl, isopropyl, butyl, tertiary butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl and the like including substituted alkyl radicals such as trifluoromethyl, etc., and an aryl radical such as phenyl and naphthyl including substituted aryl radicals having such substituents as a halogen, alkyl radicals of from one to five carbon atoms, etc; and R, and Rs. when taken together, can represent the carbon atoms necessary to form a cyclic hydrocarbon radical including cycloalkanes such as cyclohexyl and polycycloal- 8 kanes such as norbornyl, the total number of carbon-atoms in R, and R, being up to 19;
R and R, can each be hydrogen, and alkyl radical of from one to five carbon atoms or a halogen such as chloro, bromo, iodo, etc; and
R is a divalent radical selected from the following:
Among the hydrophobic carbonate polymers particularly useful in the present method of forming aggregate compositions are polymers comprised of the following recurring unit:
each R is a phenylene radical including halo substituted phenylene radicals and alkyl substituted phenylene radicals; and R, and R are as described above. Such compositions are disclosed, for example, in US. Pat. Nos. 3,028,365 and 3,317,466. Preferably, polycarbonates containing an alkylidene diarylene moiety in the recurring unit such as those prepared with Bisphenol A and including polymeric products of ester exchange between diphenylcarbonate and 2,2-bis-4- hydroxyphenyl propane are useful in the practice of this invention. Such compositions are disclosed in the following US. Pat. Nos. 2,999,750; 3,038,874; 3,038,879; 3,038,880; 3,106,544; 3,106,545; 3,106,546; and published Australian Pat. Specification No. 19575/56.
The present heterogeneous compositions are electrically insulating in the dark such that they will retain in the dark and electrostatic charge applied to the surface thereof. In addition, as mentioned above, the present compositions are also photoconductive. This term has reference to the ability of such compositions to lose a retained surface charge in proportion to the intensity of incident actinic radiation. in general, the term photoconductive" as used to describe the present heterogeneous compositions means that the amount of incident radiation energy in meter-candle-seconds required to cause a l00-volt reduction in retained surface potential is not greater than about ZOO-meter-candle-seconds.
The heterogeneous compositions of this invention are typically coated as a photoconductor or as a sensitizer onto a conventional conducting support such as paper (at a relative humidity above 20 percent) including paper made more conductive by various coating and/or sizing techniques or carrying a conducting layer such as a conducting metal foil, a layer containing a semiconductor dispersed in a resin, a conducting layer containing the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer such as disclosed in US. Pat. Nos. 3,007,901 and 3,262,806, a thin film of acuum deposited nickel, aluminum, silver, chromium. etc, a conducting layer as described in US. Pat. No. 3,245,833, such as cuprous iodide, and like kinds of conducting materials. Such conducting materials can be coated in any well-known mmo'l 7 manner such as doctor-blade coating, swirling, dip-coating, spraying, and the like. Other supports, including such photographic film bases as poly-(ethylene terephthalate), polystyrene, polycarbonate, cellulose acetate, etc, bearing the above conducting layers can also be used. The conducting layer can be overcoated with a thin layer of insulating material selected for its adhesive and electrical properties before application of a photoconducting layer. Where desired, however, the photoconducting layer can be coated directly on the conducting layer where conditions permit to produce the unusual benefits described herein.
When the present multiphase compositions are used as photoconductive compositions, useful results are obtained by using the described dyes in amounts of from about 1 to about 50 percent by weight of the coating composition. When the present multiphase compositions are used as sensitizers for photoconductive coatings, useful results are obtained by using the described dyes in amounts of about 0.001 to about 30 percent by weight of the photoconductive coating composition, although the amount used can be widely varied. The upper limit in the amount of photoconductive composition present in a sensitized layer is determined as a matter of individual choice and the total amount of any photoconductor used will vary widely depending on the material selected, the electrophotographic response desired, the proposed structure of the photoconductive element and the mechanical properties desired in the element. Lesser amounts of the present feature compositions can be utilized as sensitizing amounts to increase the speed sensitivity of other photoconductors than amounts that would be used if the feature material were the only photoconductor present.
Coating thicknesses of a photoconductive composition containing the feature material of the invention can vary widely. More generally, a wet coating in the range from about 0.0005 inch to about 0.05 inch on a suitable support material is used in the practice of the invention. The preferred range of wet coating thickness is found to be in the range from about 0.002 inch to about 0.030 inch.
The present invention can readily be used for enhancing the sensitivity and extending the spectral range of sensitivity of a variety of organic photoconductors and inorganic photoconductors including both N- and P-type photoconductors. For example, the present invention can be used in connection with organic, including organo-metallic, photoconducting materials which have little or substantially no persistence of photoconductivity. Representative organo-metallic compounds are the organic derivatives of Group lllA, IVA, and VA metals such as those having at least one amino-aryl group attached to the metal atom. Exemplary organo-metallic compounds are the triphenyl-p-dialkylaminophenyl derivatives of silicon, germanium, tin and lead, the trip-dialkylaminophenyl derivatives of arsenic, antimony, phosphorus, bismuth, boron, aluminum, gallium, thallium and indium. Useful photoconductors of this type are described in copending Goldman and Johnson U.S. Pat. application Ser. No. 650,664, filed July 3, 1967 and Johnson application Ser. No. 755,71 1, filed Aug. 27, 1968.
An especially useful class of organic photoconductors is referred to herein as organic amine photoconductors. Such organic photoconductors have as a common structural feature at least one amino group. Useful organic photoconductors which can be spectrally sensitized in accordance with this invention include, therefore, arylamine compounds comprising (1) diarylamines such as diphenylamine, dinaphthylamine, N ,N'-diphenylbenxidene, N-phenyl-lnaphthylamine, N-phenyl -2-naphthylamine, N,N'diphenyl-p-phenylenediamine, 2 carboxy-5-chloro -4- methoxydiphenylamine, panilinophenol, N ,N'-di-2-naphthyl-p-phenylenediamine, those described in Fox U.S. Pat. No. 3,240,597, issued Mar. 15, l966,and the like, and (2) triarylamines including (a) non polymeric triarylamines, such as triphenylamine, N,N,N'-N'- tetraphenyl-m-phenylenediamine, 4-acetyltriphenylamine, 4- hexanoyltriphenylamine, 4-lauroyltriphenylamine, 4-hexyltriphenylamine, 4dodecyltriphenylamine, 4,4'-bis(diphenylamino)benzil, 4,44,4-bis(diphenylamino)benzophenone and the like, and (b) polymeric triarylamines such as poly[N,4 li Vu*"-"" ,N'-triphenylbenzidine)], polyadipyltriphenylamine, polysebacyltriphenylamine, polydecamethylenetriphenylamine, poly-N-(4-vinylphenyl)diphenylamine, poly-N-(vinylphenyl- 01,01- dinaphthylamine) and the like. Other useful amine-type photoconductors are disclosed in U.S. Pat. No. 3,180,730issued Apr. 27, 1965.
Useful photoconductive substances capable of being sensitized in accordance with this invention are disclosed in Fox U.S. Pat. No. 3,265,496,issued Aug. 9, 1966, and include those represented by the following general formula:
fltflli wherein T represents a mononuclear or polynuclear divalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, binaphthyl, etc.), or a substituted divalent aromatic radical of these types wherein said substituent can comprise a member such as an acyl group having from one to six carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, ethoxy, propoxy, pentoxy, etc.), or a nitro group; M represents a mononuclear or polynuclear monovalent aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), or a substituted monovalent aromatic radical wherein said substituent can comprise a member, such as an acyl group having from one to about six carbon atoms (e.g., acetyl, propionyl, butyryl, etc.), an alkyl group having from one to about six carbon atoms (e.g., methyl, ethyl, propyl, butyl, etc.), an alkoxy group having from one to about six carbon atoms (e.g., methoxy, propoxy, pentoxy, etc.), or a nitro group; Q can represent a hydrogen atom, a halogen atom or an aromatic amino group, such as MNH-; b represents an integer of from one to about 12;and R represents a hydrogen atom, a mononuclear or polynuclear aromatic radical, either fused or linear (e.g., phenyl, naphthyl, biphenyl, etc.), a substituted aromatic radical wherein said substituent comprises an alkyl group, an alkoxy group, an acyl group, or a nitro group, or a poly (4-vinylphenyl) group which is bonded to the nitrogen atom by a carbon atom of the phenyl group.
Polyarylalkane photoconductors are particularly useful in producing the present invention. Such photoconductors are described in U.S. Pat. No. 3,274,000, French Pat. No. l,383,46l and in copending application of Seus and Goldman titled photoconductive Elements Containing Organic photoconductors,Ser. No. 627,857, filed Apr. 3,1967.These photoconductors include leuco bases of diaryl or triaryl methane dye salts, l,l,1 triarylalkanes wherein the alkane moiety has at least two carbon atoms and tetraarylmethanes. there being substituted an amino group on at least one of the aryl groups attached to the alkane and methane moieties of the latter two classes of photoconductors which are nonleuco base materials.
Preferred polyarylalkane photoconductors can be represented by the formula:
J-(I1E G wherein each of D, E and G is an aryl group and J is a hydrogen atom, an alkyl group, or an aryl group, at least one of D, E and G containing an amino substituent. The aryl groups attached to the central carbon atom are preferably phenyl groups, although naphthyl groups can also be used. Such aryl groups can contain such substituents as alkyl and alkoxy typically having one to eight carbon atoms, hydroxy,
halogen, etc. in the ortho, meta or para positions, ortho-substituted phenyl being preferred. The aryl groups can also be joined together or cyclized to form a fluorene moiety, for example. The amino substituent can be represented by the formula wherein each L can be an alkyl group typically having one to eight carbon atoms, a hydrogen atom, an aryl group, or together the necessary atoms to form a heterocyclic amino group typically having five to six atoms in the ring such as morpholino, pyridyl, pyrryl, etc. At least one of D, E, and G is preferably p-dialkylaminophenyl group. When J is an alkyl group, such an alkyl group more generally has one to seven carbon atoms.
Representative useful polyarylalkane photoconductors inbis( 4-diethylamino)tetraphenylmethane 4',4"-hls(beuylethylam lno)-2',2"-
dimethyltriphenylmethnne 4,4"-bis(diethylamino )-2,2"- diethoxytriphenylmethane 4.4'-bis(dimethylamino )-l l l -triphenylethane l-( 4-N,N-dimethylaminophenyl)- l l -diphenylethane 4-dimethylaminotetraphenylmethane 4-diethylaminotetraphenylmethane Another class of photoconductors useful in this invention are the 4-diarylaminc-substituted chalcones. Typical compounds'of this type are low molecular weight nonpolymeric ketones having the general formula:
wherein R, and R, are each phenyl radicals including substituted phenyl radicals and particularly when R, is a phenyl radical having the formula:
where R and R are each aryl radicals, aliphatic residues of one to 12 carbon atoms such as alkyl radicals preferably having one to four carbon atoms, or hydrogen. Particularly advantageous results are obtained when R is a phenyl radical ineluding substituted phenyl radicals and where R, is diphenylaminophenyl, dimethylaminophenyl or phenyl.
Other photoconductors which can be used with the present aggregate compositions include rhodamine B, malachite green, crystal violet, phenosafranine, cadmium sulfide, cadmium selenide, parachloranil, benzil, trinitrofluorenone, tetranitrofluoroenone etc.
The following table 5 comprises a partial listing of US. Patents disclosing a wide variety of organic photoconductive compounds and compositions which can be improved with respect to speed, sensitivity, and/or regeneration when incor porated into the feature compositions and elements of this invention.
TABLE 5 Inventor US. Pat. No.
Hoegl et al. 3,037,861 Sues et al. 3,04l.l65 Schlesinger 3,066,023 Bethe 3,072,479 Klupfel et al. 3,047,095 Neugebauer et al. 3,l l2,l97 Cassiers et al. 3,l33,022 Schlesinger 3,l44,633 am v7.11223 3; Sues et al. 3,I27,266 Schlesinger 3,l30,046 Cassiers 3,131,060 Schlesinger 3,l39 338 Schlesinger 3,139,339 Cassiers 3,l 40,946 Davis et al. 3,l4l,770 Ghys 3,148,982 Cassiers 3,l55,503 Cassiers 3,158,475 Tomunek 3,l6l.505 Schlesinger 3,l63,$30 Schlesinger 3,163,5Jl Schlesinger 3,163,532 Hoegl 3,l69,060 Stumpf 3,174,854 Klupfel et al. 3.l80,729 Klupfel et al. 3,l80,730 Neugebauer 3,l89,477 Neugebauer 3,206,306 Fox 3,240,597 Schlesinger 3,257,202 Sues et al. 3,257,203
Sues et al. 3,257,104 FOX 3,265,496 Kosche 3,265,497
Noe et al. 3,274,000
The compositions of the present invention can be employed in photoconductive elements useful in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the xerographic process. In a process of this type, an electrophotographic element held in the dark is given a blanket electrostatic charge by placing it under a corona discharge to give a uniform charge to the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial dark insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconductive layer is then selectively dissipated from the surface of the layer by imagewise exposure to light by means of a conventional exposure operation such as, for example, by a contact-printing technique, or by lens projection of an image, and the like, to thereby form a latent electrostatic image in the photoconductive layer. Exposing the surface in this manner forms a pattern of electrostatic charge by virtue of the fact that light energy striking the photoconductor causes the electrostatic charge in the light struck areas to be conducted away from the surface in proportion to the intensity of the illumination in a particular area lld The charge pattern produced by exposure is then developed or transferred to another surface and developed there, i.e., either the charged or uncharged areas rendered visible, by treatment with a medium comprising electrostatically responsive toner particles. The developing electrostatically responsivc particles can be in various forms such as small particles of pigment or in the form of small particles comprised of a colorant in a resinous binder. A preferred method of applying such dry toners to a latent electrostatic image for solid area development is by the use of a magnetic brush. Methods of forming and using a magnetic brush toner applicator are described in the following US. Pat. Nos. 2,786,439; 2,786,440; 2,786,441; 2,811,465; 2,874,063; 2,984,163; 3,040,704; 3,117,834; and Reissue 25,779.1Liquid development of the latent electrostatic image can also be used. In liquid development the developing particles are carried to the imagebearing surface in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature, for example, US. Pat. No. 2,907,674 and in Australian Pat. No. 2 12,315.
in dry developing processes, the most widely used method of obtaining a permanent record is achieved by selecting a developing particle which has as one of its components a lowmelting resin. lileating the powder image then causes the resin to melt or fuse into or on the element. The powder is, therefore, caused to adhere permanently to the surface of the photoconductive layer. in other cases, a transfer of the electrostatic charge image formed on the photoconductive layer can be made to a second support such as paper which would then become the final print after development and fusing. Techniques oithe type indicated are well lrnown in the art and have been described in a number of US. and foreign patents, such as US. Pat. Nos. 2,297,691 and 2,551,582 and in RCA Review" l/oi. (1954) pages 469-484.
The following examples are included for a further understanding of the invention. Example 1 Several coating compositions are prepared by first dissolving a sensitizing dye in a solvent mixture comprising 60 percent dichloromethane and 40 percent 1,1 ,Z-trichloroethanc in accordance with the dye first technique described in the Gramta application (supra). After dissolution of the dye, about 6 grams of poly-(4,4(-isoprupyllidenedlphenyl carbonate) resin and about 4 grams of 4,4'-benzylidenebis(ll,l ldiethyl-m-toluidine) photoconductor are added to the solution. lvlild agitation is used in dissolving the resin and photoconductor. The resulting coating dopes are measured for viscosity and then stored for a period of up to 4 days with additional viscosity measurements being made during the storage period. This procedure is repeated several times using various concentrations of different salts containing the 4-(4- dirnethylaminophenyl)-2,o-diphenylthiapyryliurn cation. Table 6 below shows the results of this test. The percentage of dye salts shown is on a weight basis of the total solids added to the coating solvent. The viscosity values shown are in terms of centipoises.
Example 2 lid This procedure of example 1 is repeated again using 3 percent by weight of the tetrafluoroborate salt of the above thiapyrylium compound. Aher formation of the coating dope, it is sheared in a mixing blender for a period of 1 hour and the viscosity is measured and found to be 55 cps. After 2 days, the viscosity increases to 305 cps, thus showing that shearing of the coating dope apparently enhances the viscosity buildup. Next, two similar coatings are prepared using 3 percent and 4 percent, respectively, of the hcxafluorophosphate salt of the above thiapyrylium compound in accordance with the present invention. The two dopes are sheared for 1 hour and the viscosity is measured immediately and after a period of 2 days. No substantial increase in the viscosity is seen with the latter compositions.
Example 3 Three coating compositions are prepared by first dissolving a sensitizing dye in the solvent mixture ofexample 1. After dissolution of the dye, the polymer and photoconductor of example l are added to the solution followed by mild agitation to promote the dissolution of the resin and photoconductor. Each of the three coating compositions is then wet coated on a conducting support which is comprised of a high-vacuum evaporated nickel iilm coated on a poly(cthylene tcrephthalate) film base. Each coating is allowed to dry and when dry, has a thickness of about 10 microns. Each resultant electrophotographic element is then electrostatically charged under a corona source until the surface potential, as measured by an electrometer probe, reaches about 600 volts. The charged surface is exposed to light from a 3,000 li. tungsten source modulated by a stepped density gray scale. All exposures are made through a short wavelength pass interference filter having 30 percent transmittance at 600 nm. The exposure causes reduction of the surface potential of the element under each step of the gray scale from its initial value V to some lower potential V, the exact value of which depends upon the amount of exposure received by the area. The actual positive or negative speed of the photoconductive composition can then be expressed in terms of the reciprocal of the exposure required to reduce the surface potential to any fixed arbitrarily selected value. Unless otherwise stated, the actual positive or negative speed is the numerical expression of 104 divided by the exposure in meter-candle-seconds required to reduce the 600-volt charge surface potential to a value of 500 volts (IOU-volt shoulder speed) or to a value of 50 volts (50- volt toe speed). Element A contains 3 percent by weight of the total solids added of 4-(4-dimethylaminophenyl)-2,6-diphcnylthiapyrylium fluoroborate sensitizing dye, Element 18 contains 3 percent by weight of 4(4-dimethylaminophenyl)-2,6- diphenylthiapyrylium perchlorate and Element C contains 3 percent by weight of 4-(4-dimethylaminophenyl)-2,6-diphenylthiapyryliurn hexafluorophosphate sensitizing dye. The positive and negative shoulder and toe speeds of each of these ele- The procedure of example 2 is repeated again to form three separate coating dopes A, id and C. After formation of the slopes, they are allowed to stand for several days prior to coating. The dopes are then coated as in the preceding example to form electrophotographic elements 1, 2 and 3, respectively. Upon drying, the surfaces of the three elements are examined closely. Elements l and 2 are found to be streaky and not entirely uniform in appearance, whereas, element 3 has a photoconductive surface which is substantially free of streaks and appears to be uniform throughout. Element 3 is then given a surface charge by exposure to a corona source in darkness,
imagewise exposed and developed with a developer comprised of iron carrier particles and black toner material comprised of a resin binder and a colorant. The resultant image is of good quality and appears to be free of defects resulting from coating discontinuities.
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 effected within the spirit and scope of the invention.
1. A heterogeneous photoconductive composition for use in electrophotography comprising in a multiphase state (a) at least one dye selected from the group consisting of pyrylium, selenapyrylium and thiapyrylium dye salts having an inorganic anion containing a Group VA element other than nitrogen, said anion having an anionic radius at least as large as that of hexafluorophosphate and (b) an electrically insulating, filmforming, polymeric material having an alkylidene diarylene moiety in the recurring unit, said composition having a discontinuous phase comprised of a combination of said dye and polymeric material, and a continuous phase composed of said polymeric material, said composition having a wavelength range of radiation absorption different from the wavelength range of absorption of a composition comprising a substantially homogeneous combination of said dye and polymeric material.
2. A composition as described in claim 1, wherein the dye has the formula:
R, and R are aryl radicals selected from the group consisting of phenyl and substituted phenyl having at least one substituent selected from the group consisting of an alkyl radical of from one to six carbon atoms and an alkoxy radical of from one to six carbon atoms;
R, is an alkylamino-substituted phenyl radical having from one to six carbon atoms in the alkyl moiety;
X is selected from the group consisting of sulfur and oxygen;
Q is a Group VA element other than nitrogen.
3. A heterogeneous photoconductive composition for use in electrophotography comprising in a multiphase state (a) at least one dye selected from the group consisting of the hexafluorophosphate salt of a pyrylium dye and the hexafluorophosphate salt of a thiapyrylium dye and (b) an electrically insulating, film-forming, polymeric material having an alkylidene diarylene moiety in the recurring unit, said composition containing a discontinuous phase comprised of a combination of said dye and polymeric material, and a continuous phase composed of said polymeric material, said composition having a wavelength range of radiation absorption different from the wavelength range of absorption of a composition comprised of a substantially homogeneous combination of said dye and polymeric material.
4. A composition as described in claim 3 wherein the dye has the formula:
R, and R, are aryl radicals selected from the group consisting of phenyl and substituted phenyl having at least one substituent selected from the group consisting of an alkyl radical of from one to six carbon atoms and an alkoxy radical of from one to six carbon atoms;
R; is an alkylamino-substituted phenyl radical having from one to six carbon atoms in the alkyl moiety; and
X is selected from the group consisting of sulfur and oxygen.
5. A photoconductive composition as described in claim 3 wherein the dye is selected from the group consisting of 4-(4- dimethylaminophenyl)-2,6-diphenylthiapyrylium hexafluorophosphate, 4-(4-dimethylaminophenyl)-2 -(4-ethoxyphenyl)-6-phenylthiapyrylium hexafluorophosphate, 4-(4- dimethylaminophenyl)-2,6-diphenylpyrylium hexafluorophosphate and 4-(4-dimethylaminophenyl)-2-(4- ethoxyphenyl)-6-phenylpyrylium hexafluorophosphate.
6. A sensitized photoconductive composition comprising a photoconductor dispersed in a heterogeneous two-phase organic solid of dye and polymeric material, said solid having a continuous phase of said polymeric material and a discontinuous phase comprising a combination of (a) said polymeric material having an alkylidene diarylene moiety in a recurring unit and (b) at least one dye having the formula:
R and R, are aryl radicals selected from the group consisting of phenyl and substituted phenyl having at least one substituent selected from the group consisting of an alkyl radical of from one to six carbon atoms and an alkoxy radical of from one to six carbon atoms;
R is an alkylamino-substituted phenyl radical having from one to six carbon atoms in the alkyl moiety; and
X is selected from the group consisting of sulfur and oxygen.
7. A composition as described in claim 6 wherein the photoconductor is an organic material selected from the group consisting of a triarylamine, an organic derivative of a Group lllA metal having at least one aminoaryl radical attached to the metal atom, an organic derivative of a Group lVA metal having at least one aminoaryl radical attached to the metal atom, an organic derivative of a Group VA metal having at least one aminoaryl radical attached to the metal atom, a 4diarylamino-substituted chalcone and a polyarylalkane.
8. A photoconductive composition as described in claim 6 wherein the polymeric material is a carbonate resin.
9. A photoconductive composition as described in claim 8 wherein the photoconductor is an organic photoconductor and wherein the dye is selected from the group consisting of 4- (4-dimethylaminophenyl)-2,fi-diphenylthiapyrylium hexafluorophosphate, 4-(4-dimethylaminophenyl)-2-(4-ethoxyphenyl)-6-phenylthiapyrylium hexafluorophosphate, 4-(4- dimethylaminophenyl)-2,-diphenylpyrylium hexafluorophosphate and 4-(4-dimethylaminophenyl)-2-(4- ethoxyphenyl)-6-phenylpyrylium hexafluorophosphate.
10. A photoconductive composition as described in claim 7 wherein the polymeric material is a polycarbonate resin having an alkylidene diarylene moiety in the recurring unit and wherein the dye is selected from the group consisting of 4-(4- dimethylaminophenyl)-2,-diphenylthiapyrylium hexafluorophosphate, 4-(4-dimethylarninophenyl)-2-(4-ethoxyphenyl)-6-phenylthiapyrylium hexafluorophosphate, 4-(4- dimethylaminophenyl)-2,6-diphenylpyrylium hexafluorophosphate and 4-(4-dimethylaminophenyl)-2-(4- ethoxyphenyl)-6-phenylpyrylium hexailuorophosphate.
II. A photoconductive composition as described in claim 10 wherein the .polymeric material is poly(4,4'isopropylldenediphenyl carbonate) and wherein the photoconductor is 4,4'-benzylidenebls-(N,N-diethyl-m-toluidine).
12. In an electrophotographic process wherein an electro- 13 An electrophotographic element comprising a support static charge pattern is formed on aphotoconductive element, having thereon a photoconductive layer comprised of the the improvement wherein said element has a layer of the composition described in claim 6. photoconductive composition as described in claim 6. s 1, I: