Electrophotographic photoconductor and aromatic polycarbonate resin for use in the photoconductor

An electrophotographic photoconductor has an electroconductive support, and a photoconductive layer which is formed thereon and contains an aromatic polycarbonate resin including at least a structural unit of formula (1): ##STR1## wherein a, b, c and d are each independently an integer of 0 to 4; n is an integer of 0 or 1; and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each independently a halogen atom, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxyl group having 1 to 6 carbon atoms, or a substituted or unsubstituted aryl group, and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may each be the same or different when a, b, c and d are each an integer of 2, 3 or 4. Further, there are provided aromatic polycarbonate resins each including the structural unit of formula (1) and a structural unit with charge transporting properties.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an electrophotographic photoconductor
 comprising an electroconductive support and a photoconductive layer formed
 thereon, comprising an aromatic polycarbonate resin provided with
 mechanical strength, or both the mechanical strength and charge
 transporting properties according to the combination of structural units
 for use in the polycarbonate resin. In addition, the present invention
 also relates to aromatic polycarbonate resins with charge transporting
 properties, which are useful as the photoconductive materials for use in
 the electrophotographic photoconductor and as the materials for use in
 electronic devices such as organic electroluminescent (EL) device.
 2. Discussion of Background
 Recently organic photoconductors are used in many copying machines and
 printers. These organic photoconductors have a layered structure
 comprising a charge generation layer (CGL) and a charge transport layer
 (CTL) which are successively overlaid on an electroconductive support. The
 charge transport layer (CTL) comprises a binder resin and a
 low-molecular-weight charge transport material (CTM) dissolved therein.
 The addition of such a low-molecular-weight charge transport material
 (CTM) to the binder resin lowers the intrinsic mechanical strength of the
 binder resin, so that the CTL film becomes fragile. Such lowering of the
 mechanical strength of the CTL causes the wearing of the photoconductor or
 the formation of scratches and cracks in the surface of the
 photoconductor.
 Although some vinyl polymers such as polyvinyl anthracene, polyvinyl pyrene
 and poly-N-vinylcarbazole have been studied as high-molecular-weight
 photoconductive materials for forming a charge transport complex for use
 in the conventional organic photoconductor, such polymers are not
 satisfactory from the viewpoint of photosensitivity.
 In addition, high-molecular-weight materials having charge transporting
 properties have been also studied to eliminate the shortcomings of the
 above-mentioned layered photoconductors. For instance, there are proposed
 an acrylic resin having a triphenylamine structure as reported by M.
 Stolka et al., in "J. Polym. Sci., vol 21, 969 (1983)"; a vinyl polymer
 having a hydrazone structure as described in "Japan Hard Copy '89 p. 67";
 and polycarbonate resins having a triarylamine structure as disclosed in
 U.S. Pat. Nos. 4,801,517, 4,806,443, 4,806,444, 4,937,165, 4,959,288,
 5,030,532, 5,034,296, and 5,080,989, and Japanese Laid-Open Patent
 Applications Nos. 64-9964, 3-221522, 2-304456, 4-11627, 4-175337, 4-18371,
 4-31404 and 4-133065. However, any materials have not yet been put to
 practical use.
 According to the report of "Physical Review B46 6705 (1992)" by M. A.
 Abkowitz et al., it is confirmed that the drift mobility of a
 high-molecular weight charge transport material is lower than that of a
 low-molecular weight material by one figure. This report is based on the
 comparison between the photoconductor comprising a low-molecular weight
 tetraarylbenzidine derivative dispersed in the photoconductive layer and
 the one comprising a high-molecular polycarbonate having a
 tetraarylbenzidine structure in its molecule. The reason for this has not
 been classified, but it is suggested that the photoconductor employing the
 high-molecular weight charge transport material produces poor results in
 terms of the photosensitivity and the residual potential although the
 mechanical strength of the photoconductor is improved.
 Conventionally known representative aromatic polycarbonate resins are
 obtained by allowing a 2,2-bis(4-hydroxyphenyl)propane (hereinafter
 referred to as bisphenol A) to react with a carbonate precursor material
 such as phosgene or diphenylcarbonate. Such polycarbonate resins made from
 bisphenol A are used in many fields because of their excellent
 characteristics, such as high transparency, high heat resistance, high
 dimensional accuracy, and high mechanical strength.
 For example, this kind of polycarbonate resin is intensively studied as a
 binder resin for use in an organic photoconductor in the field of
 electrophotography. A variety of aromatic polycarbonate resins have been
 proposed as the binder resins for use in the charge transport layer of the
 layered photoconductor.
 As previously mentioned, however, the mechanical strength of the
 aforementioned aromatic polycarbonate resin is decreased by the addition
 of the low-molecular-weight charge transport material in the charge
 transport layer of the layered electrophotographic photoconductor.
 In recent years, aromatic polycarbonate resins with excellent sensitivity
 and electrical characteristics have been found as described in Japanese
 Laid-Open Patent Application 9-297419. However, at the present stage,
 those conventional aromatic polycarbonate resins are not always
 satisfactory in terms of the durability necessary for the
 electrophotographic photoconductor.
 SUMMARY OF THE INVENTION
 It is therefore a first object of the present invention to provide an
 electrophotographic photoconductor free from the conventional
 shortcomings, which can exhibit high mechanical strength and high
 durability.
 The above-mentioned first object of the present invention can be achieved
 by an electrophotographic photoconductor comprising an electroconductive
 support, and a photoconductive layer formed thereon, comprising as an
 effective component an aromatic polycarbonate resin which comprises a
 structural unit of formula (1):
 ##STR2##
 wherein a, b, c and d are each independently an integer of 0 to 4; n is an
 integer of 0 or 1; and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each
 independently a halogen atom, a substituted or unsubstituted alkyl group
 having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxy group
 having 1 to 6 carbon atoms, or an aryl group which may have a substituent,
 and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may each be the same or
 different when a, b, c and d are each an integer of 2, 3 or 4.
 In this case, it is preferable that the structural unit of formula (1) be
 in an amount of 5 wt. % or more of the total weight of the polycarbonate
 resin.
 A second object of the present invention is to provide an
 electrophotographic photoconductor capable of exhibiting both high
 mechanical strength and high sensitivity.
 The aforementioned second object of the present invention can be achieved
 by an electrophotographic photoconductor comprising an electroconductive
 support, and a photoconductive layer formed thereon, comprising as an
 effective component an aromatic polycarbonate resin which comprises a
 structural unit of formula (1) and a structural unit having charge
 transporting properties.
 In this case, it is preferable that the structural unit having charge
 transporting properties be in an amount of 5 wt. % or more, more
 preferably, in an amount of 10 to 90 wt. %, of the total weight of the
 aromatic polycarbonate resin.
 It is preferable that the aforementioned structural unit having charge
 transporting properties be represented by the following formula (2):
 ##STR3##
 wherein R.sup.5 is a hydrogen atom, an alkyl group which may have a
 substituent, or an aryl group which may have a substituent; Ar.sup.1 is an
 aryl group which may have a substituent; and Ar.sup.2 and Ar.sup.3 are
 each an arylene group which may have a substituent.
 The above-mentioned second object of the present invention can be achieved
 by an electrophotographic photoconductor comprising an electroconductive
 support, and a photoconductive layer formed thereon, comprising as an
 effective component an aromatic polycarbonate resin which comprises a
 repeat unit of formula (3) comprising the previously mentioned structural
 unit of formula (1) and structural unit of formula (2) having charge
 transporting properties:
 ##STR4##
 wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, Ar.sup.1, Ar.sup.2,
 Ar.sup.3, a, b, c, d, and n are the same as those previously defined; and
 m is an integer of 2 to 5000, which represents a degree of polymerization.
 It is also preferable that the aforementioned structural unit having charge
 transporting properties, that is used in combination with the structural
 unit of formula (1), be represented by the following formula (4):
 ##STR5##
 wherein Ar.sup.2 and Ar.sup.3 are the same as those previously defined;
 Ar.sup.4 is an arylene group which may have a substituent; and R.sup.6 and
 R.sup.7, which may be the same or different, are each an acyl group, an
 alkyl group which may have a substituent, or an aryl group which may have
 a substituent.
 The second object of the present invention can also be achieved by an
 electrophotographic photoconductor comprising an electroconductive
 support, and a photoconductive layer formed thereon, comprising as an
 effective component an aromatic polycarbonate resin which comprises a
 repeat unit of formula (5) comprising the previously mentioned structural
 unit of formula (1) and structural unit of formula (4) having charge
 transporting properties:
 ##STR6##
 wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.6, R.sup.7, Ar.sup.2,
 Ar.sup.3, Ar.sup.4, a, b, c, d, and n are the same as those previously
 defined; and m is an integer of 2 to 5000, which represents a degree of
 polymerization.
 A third object of the present invention is to provide an aromatic
 polycarbonate resin that is remarkably useful as a high-molecular-weight
 charge transport material for use in an organic electrophotographic
 photoconductor.
 The third object of the present invention can be achieved by an aromatic
 polycarbonate resin comprising a structural unit of formula (1) and a
 structural unit of formula (2), with the relationship between the
 composition ratios being 0&lt;k/(k+j)&lt;1 when the composition ratio of the
 structural unit of formula (1) is j and that of the structural unit of
 formula (2) is k:
 ##STR7##
 wherein a, b, c and d are each independently an integer of 0 to 4; n is an
 integer of 0 or 1; and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each
 independently a halogen atom, an alkyl group having 1 to 6 carbon atoms,
 which may have a substituent, an alkoxy group having 1 to 6 carbon atoms,
 which may have a substituent, or an aryl group which may have a
 substituent, and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may each be the
 same or different when a, b, c and d are each an integer of 2, 3 or 4;
 ##STR8##
 wherein R.sup.5 is a hydrogen atom, an alkyl group which may have a
 substituent, or an aryl group which may have a substituent; Ar.sup.1 is an
 aryl group which may have a substituent; and Ar.sup.2 and Ar.sup.3 are
 each an arylene group which may have a substituent.
 The third object of the present invention can also be achieved by an
 aromatic polycarbonate resin comprising a repeat unit of formula (3):
 ##STR9##
 wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, Ar.sup.1, Ar.sup.2,
 Ar.sup.3, a, b, c, d, and n are the same as those previously defined; and
 m is an integer of 2 to 5000, which represents a degree of polymerization.
 Further, the third object of the present invention can be achieved by an
 aromatic polycarbonate resin comprising the previously mentioned
 structural unit of formula (1) and a structural unit of the following
 formula (4) , with the relationship between the composition ratios being
 0&lt;k/(k+j)&lt;1 when the composition ratio of the structural unit of formula
 (1) is j and that of the structural unit of formula (4) is k:
 ##STR10##
 wherein Ar.sup.2 and Ar.sup.3 are the same as those previously defined;
 Ar.sup.4 is an arylene group which may have a substituent; and R.sup.6 and
 R.sup.7, which may be the same or different, are each an acyl group, an
 alkyl group which may have a substituent, or an aryl group which may have
 a substituent.
 The third object of the present invention can also be achieved by an
 aromatic polycarbonate resin comprising a repeat unit of formula (5):
 ##STR11##
 wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.6, R.sup.7, Ar.sup.2,
 Ar.sup.3, Ar.sup.4, a, b, c, d, and n are the same as those previously
 defined; and m is an integer of 2 to 5000, which represents a degree of
 polymerization.
 Furthermore, to be more specific, it is preferable that the previously
 mentioned structural unit of formula (4) be represented by the following
 formula (6):
 ##STR12##
 wherein e and f are each independently an integer of 0 to 5; and R.sup.8
 and R.sup.9 are each independently a halogen atom, an alkyl group having 1
 to 6 carbon atoms, which may have a substituent, an alkoxyl group having 1
 to 6 carbon atoms, which may have a substituent , or an aryl group which
 may have a substituent, and R.sup.8 and R.sup.9 may each be the same or
 different when e and f are each an integer of 2, 3, 4 or 5.
 In addition, it is preferable that the previously mentioned repeat unit of
 formula (5) be represented by the following formula (7):
 ##STR13##
 wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.8, R.sup.9, a, b, c, d,
 e, f and n are the same as those previously defined; and m is an integer
 of 2 to 5000, which represents a degree of polymerization.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The aromatic polycarbonate resin for use in the photoconductive layer of
 the electrophotographic photoconductor according to the present invention
 comprises at least a structural unit of formula (1). Alternatively, the
 aromatic polycarbonate resin is prepared in the form of a copolymer resin
 comprising the above-mentioned structural unit of formula (1) and a
 structural unit with charge transporting properties, for example, of
 formula (2) or (4). Further, according to the present invention, the
 aromatic polycarbonate resin is prepared in the form of an alternating
 copolymer resin comprising a repeat unit of formula (3) or (5).
 The previously mentioned polycarbonate resins in the form of a copolymer
 resin and an alternating copolymer resin, which are novel compounds, are
 provided with high mechanical strength and charge transporting properties.
 Therefore, those aromatic polycarbonate resins are considered to show
 satisfactory electrical characteristics, optical characteristics, and
 physical characteristics when used in a photoconductive layer of the
 electrophotographic photoconductor.
 Any of the above-mentioned aromatic polycarbonate resins are provided with
 high mechanical strength because the structural unit of formula (1) is
 employed. As a result, the photoconductor of the present invention can
 shown high durability.
 The method of producing the aromatic polycarbonate resin comprising at
 least the structural unit of formula (1) will now be explained in detail.
 The above-mentioned aromatic polycarbonate resin can be obtained by the
 method of synthesizing a conventional polycarbonate resin, that is,
 polymerization of a bisphenol and a carbonic acid derivative.
 To be more specific, the aromatic polycarbonate resin comprising the
 structural unit of formula (1) can be produced by the ester interchange
 between at least one kind of diol represented by the following formula (8)
 and a bisarylcarbonate compound, or by the polymerization of the diol of
 formula (8) with a halogenated carbonyl compound such as phosgene in
 accordance with solution polymerization or interfacial polymerization, or
 by the polymerization of the diol with a chloroformate such as
 bischloroformate derived from the diol:
 ##STR14##
 wherein a, b, c, d, n, R.sup.1, R.sup.2, R.sup.3, and R.sup.4 are the same
 as those previously defined.
 In addition to phosgene, trichloromethyl chloroformate that is a dimer of
 phosgene, and bis(trichloromethyl)carbonate that is a trimer of phosgene
 are usable as the halogenated carbonyl compounds in the above-mentioned
 polymerization. Further, halogenated carbonyl compounds derived from other
 halogen atoms than chlorine, for example, carbonyl bromide, carbonyl
 iodide and carbonyl fluoride are also employed.
 Such conventional synthesis methods are described in the reference, for
 example, "Handbook of Polycarbonate Resin" (issued by The Nikkan Kogyo
 Shimbun Ltd.).
 The photoconductive layer of the electrophotographic photoconductor
 according to the present invention may comprise as the effective component
 an aromatic polycarbonate resin which consists essentially of the
 structural unit of formula (1). In order to control the mechanical
 properties, the aromatic polycarbonate resin in the form of a copolymer
 may be prepared using the structural unit of formula (1) and other
 structural units. In this case, the structural units for use in the
 conventional polycarbonate resins, for example, the structural units as
 described in the previously mentioned reference "Handbook of Polycarbonate
 Resin" (issued by The Nikkan Kogyo Shimbun Ltd.) can be utilized as the
 copolymerizable structural units. One of the preferable copolymerizable
 structural units is a structural unit represented by the following formula
 (9):
 ##STR15##
 The starting material for the aforementioned structural unit of formula (9)
 is represented by the following formula (10):
EQU HO--O--OH (10)
 wherein X is a bivalent aliphatic group, a bivalent cyclic aliphatic group,
 a bivalent aromatic group, a bivalent group prepared by bonding the
 aforementioned bivalent groups, or a bivalent group selected from the
 followings:
 ##STR16##
 in which R.sup.10, R.sup.11, R.sup.12, R.sup.13, R.sup.13', and R.sup.13"
 are each independently an alkyl group which may have a substituent, an
 aryl group which may have a substituent, or a halogen atom; p and q are
 each independently an integer of 0 to 4; r and s are each independently an
 integer of 0 to 3; and l is an integer of 0 or 1, and when l=1, Y is a
 straight-chain alkylene group having 2 to 12 carbon atoms, a branched
 alkylene group having 3 to 12 carbon atoms, a bivalent group comprising at
 least one alkylene group having 1 to 10 carbon atoms and at least one
 oxygen atom and/or sulfur atom, --O--, --S--, --SO--, --SO.sub.2 --,
 ##STR17##
 in which Z.sup.1 and Z.sup.2 are each a substituted or unsubstituted
 bivalent aliphatic group, or a substituted or unsubstituted arylene group;
 R.sup.14, R.sup.15, R.sup.16, R.sup.17, R.sup.18, R.sup.19 and R.sup.20
 are each independently a hydrogen atom, a halogen atom, a substituted or
 unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or
 unsubstituted alkoxyl group having 1 to 5 carbon atoms, or a substituted
 or unsubstituted aryl group, and R.sup.14 and R.sup.15 may form together a
 carbon ring or heterocyclic ring having 5 to 12 carbon atoms or R.sup.14
 and R.sup.15 may form a carbon ring or heterocyclic ring in combination
 with R.sup.10 and R.sup.11 ; l' and l" are each an integer of 0 or 1, and
 when l'=1 and l"=1, R.sup.21 and R.sup.22 are each an alkylene group
 having 1 to 4 carbon atoms; R.sup.23 and R.sup.24 are each independently a
 substituted or unsubstituted alkyl group having 1 to 5 carbon atoms or a
 substituted or unsubstituted aryl group; t is an integer of 0 to 4; u is
 an integer of 0 to 20; and v is an integer of 0 to 2000.
 When Y is a bivalent group comprising at least one alkylene group having 1
 to 10 carbon atoms and at least one oxygen atom and/or sulfur atom, as
 mentioned above, the following specific examples can be employed:
 OCH.sub.2 CH.sub.2 O
 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 O
 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 O
 OCH.sub.2 CH.sub.2 CH.sub.2 O
 OCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 O
 OCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 O
 OCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 O
 CH.sub.2 O
 CH.sub.2 CH.sub.2 O
 CHE.sub.t OCHE.sub.t
 CHCH.sub.3 O
 SCH.sub.2 OCH.sub.2 S
 CH.sub.2 OCH.sub.2
 OCH.sub.2 OCH.sub.2 O
 SCH.sub.2 CH.sub.2 OCH.sub.2 OCH.sub.2 CH.sub.2 S
 OCH.sub.2 CHCH.sub.3 OCH.sub.2 CHCH.sub.3 O
 SCH.sub.2 S
 SCH.sub.2 CH.sub.2 S
 SCH.sub.2 CH.sub.2 CH.sub.2 S
 SCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 S
 SCH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 S
 SCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 S
 SCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 S
 According to the previously mentioned synthesis method, a desired aromatic
 polycarbonate resin comprising at least one structural unit of formula (1)
 and at least one structural unit of formula (9) can be provided by freely
 employing the diol of formula (8) in combination with at least one kind of
 diol represented by formula (10).
 In such a synthesis of the diol of formula (8) and the diol of formula
 (10), the amount ratio of the diol of formula (8) to the diol of formula
 (10) may be selected within a wide range in light of the desired
 characteristics of the obtained aromatic polycarbonate resin. In the
 present invention, to produce a polycarbonate resin with high mechanical
 strength, it is preferable that the amount of the structural unit of
 formula (1) be 5 wt. % or more of the total weight of the produced
 aromatic polycarbonate resin.
 As previously mentioned, there is provided an aromatic polycarbonate resin
 comprising the structural unit of formula (1) and the structural unit
 having charge transporting properties, represented by formula (2), (4) or
 (6), with the relationship between the composition ratios being
 0&lt;k/(k+j)&lt;1 when the composition ratio of the structural unit of formula
 (1) is j and that of the structural unit of formula (2), (4) or (6) is k.
 By employing such an aromatic polycarbonate resin, the photoconductive
 layer can be provided with charge transporting properties. To produce such
 a polycarbonate resin, at least one diol of the previously mentioned
 formula (8) may be used together with at least one diol with charge
 transporting properties, represented by the following formula (11), (12)
 or (13):
 ##STR18##
 wherein Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, R.sup.5, R.sup.6, R.sup.7,
 R.sup.8, R.sup.9, e and f are the same as those as previously defined.
 Furthermore, an aromatic polycarbonate resin in the form of a copolymer
 with improved mechanical properties can be produced by further adding the
 diol of formula (10) to the diol of formula (8) and at least one diol of
 formula (11), (12) or (13). In this case, one or a plurality of diols of
 formula (10) may be used.
 In the preparation of the copolymer resin, the amount ratio of the diol
 with charge transporting properties, represented by formula (11) or (12)
 and the amount ratio of the diol of formula (8) may be selected within a
 wide range in light of the desired characteristics of the obtained
 aromatic polycarbonate resin. In the electrophotographic photoconductor of
 the present invention, it is preferable that the aromatic polycarbonate
 resin comprise the structural unit of formula (1) in an amount of 5 wt. %
 or more, and the structural unit with charge transporting properties in an
 amount of 5 wt. % or more, more preferably in an amount of 10 to 90 wt. %
 of the total weight of the produced aromatic polycarbonate resin.
 Further, various kinds of copolymers, such as a random copolymer, an
 alternating copolymer, a block copolymer, a random alternating copolymer,
 and a random block copolymer can be obtained by appropriately selecting
 the polymerization procedure.
 For instance, a random copolymer comprising the structural unit of formula
 (1) and the structural unit of formula (2), (4) or (6) can be obtained
 when the diol of formula (11), (12) or (13) with charge transporting
 properties and the diol of formula (8) are uniformly mixed prior to the
 condensation reaction with the phosgene. A random block copolymer can be
 obtained by the addition of a plurality of diols in the course of the
 reaction. Further, an alternating copolymer comprising a repeat unit of
 formula (3), (5) or (7) can be produced by carrying out the condensation
 reaction of a bischloroformate compound derived from the diol of formula
 (8) and the diol having charge transporting properties, represented by
 formula (11), (12) or (13). In such a case, the above-mentioned
 alternating copolymer comprising a repeat unit of formula (3), (5) or (7)
 can be similarly produced by carrying out the condensation reaction of a
 bischloroformate compound derived from the diol of formula (11), (12) or
 (13) having charge transporting properties and the diol of formula (8).
 Further, a random alternating copolymer can be produced by employing a
 plurality of bischloroformate compounds and/or diol compounds in the
 course of the aforementioned condensation reaction.
 The interfacial polymerization is carried out at the interface between two
 phases of an alkaline aqueous solution of a diol and an organic solvent
 which is substantially incompatible with water and capable of dissolving a
 polycarbonate therein in the presence of the carbonic acid derivative and
 a catalyst. In this case, a polycarbonate resin with a narrow
 molecular-weight distribution can be speedily obtained by emulsifying the
 reactive medium through the high-speed stirring operation or addition of
 an emulsifying material.
 As a base for preparing the alkaline aqueous solution of diol, there can be
 employed an alkali metal and an alkaline earth metal. Specific examples of
 the base include hydroxides such as sodium hydroxide, potassium hydroxide
 and calcium hydroxide; and carbonates such as sodium carbonate, potassium
 carbonate, calcium carbonate and sodium hydrogencarbonate. Those bases may
 be used alone or in combination. Of those bases, sodium hydroxide and
 potassium hydroxide are preferable. In addition, distilled water or
 deionized water are preferably employed for the preparation of the
 above-mentioned alkaline aqueous solution of diol.
 Examples of the organic solvent used in the above-mentioned interfacial
 polymerization are aliphatic halogenated hydrocarbon solvents such as
 dichloromethane, 1,2-dichloroethane, 1,2-dichloroethylene,
 trichloroethane, tetrachloroethane and dichloropropane; aromatic
 halogenated hydrocarbon solvents such as chlorobenzene and
 dichlorobenzene; and mixed solvents thereof. Further, aromatic hydrocarbon
 solvents such as toluene, xylene and ethylbenzene, or aliphatic
 hydrocarbon solvents such as hexane and cyclohexane may be added to the
 above-mentioned solvents. The aliphatic halogenated hydrocarbon solvents
 and aromatic halogenated hydrocarbon solvents are preferable, and in
 particular, dichloromethane and chlorobenzene are preferably employed in
 the present invention.
 Examples of the catalyst used in the preparation of the polycarbonate resin
 include a tertiary amine, a quaternary ammonium salt, a tertiary
 phosphine, a quaternary phosphonium salt, a nitrogen-containing
 heterocyclic compound and salts thereof, an iminoether and salts thereof,
 and a compound having amide group.
 Specific examples of such catalysts are trimethylamine, triethylamine,
 tri-n-propylamine, tri-n-hexylamine,
 N,N,N',N'-tetramethyl-1,4-tetramethylenediamine, 4-pyrrolidinopyridine,
 N,N'-dimethylpiperazine, N-ethylpiperidine, benzyltrimethylammonium
 chloride, benzyltriethylammonium chloride, tetramethylammonium chloride,
 tetraethylammonium bromide, phenyltriethylammonium chloride,
 triethylphosphine, triphenylphosphine, diphenylbutylphosphine,
 tetra(hydroxymethyl)phosphonium chloride, benzyltriethylphosphonium
 chloride, benzyltriphenylphosphonium choride, 4-methylpyridine,
 1-methylimidazole, 1,2-dimethylimidazole, 3-methylpyridazine,
 4,6-dimethylpyrimidine, 1-cyclohexyl-3,5-dimethylpyrazole, and
 2,3,5,6-tetramethylpyrazine.
 Those catalysts may be used alone or in combination. Of the above-mentioned
 catalysts, the tertiary amine, in particular, a tertiary amine having 3 to
 30 carbon atoms, such as triethylamine is preferably employed in the
 present invention. Before and/or after the carbonic acid derivatives such
 as phosgene and bischloroformate are placed in the reaction system, any of
 the above-mentioned catalysts may be added thereto.
 To prevent oxidation of the diol in the alkaline aqueous solution in the
 course of the polymerization reaction, an antioxidant such as hydrosulfite
 may be used.
 The interfacial polymerization reaction is generally carried out at
 temperature in the range of 0 to 40.degree. C., and terminated in several
 minutes to 5 hours. It is desirable to maintain the reaction system to pH
 10 or more.
 In the case of the solution polymerization, the diol is dissolved in a
 proper solvent to prepare a solution of the diol, and a deacidifying agent
 is added thereto. Then, the bischloroformate compound, phosgene or the
 like is added to the above prepared mixture. In this case, tertiary amine
 compounds such as trimethylamine, triethylamine and tripropylamine, and
 pyridine can be used as the deacidifying agents.
 Examples of the solvent for use in the above-mentioned solution
 polymerization are halogenated hydrocarbon solvents such as
 dichloromethane, dichloroethane, trichloroethane, tetrachloroethane,
 trichloroethylene, and chloroform; cyclic ethers such as tetrahydrofuran
 and dioxane; and pyridine.
 The reaction temperature is generally in the range of 0 to 40.degree. C. In
 this case, the solution polymerization is generally terminated in several
 minutes to 5 hours.
 In the case where the polycarbonate resin is synthesized by the ester
 interchange method, the diol and the bisarylcarbonate are mixed in the
 presence of an inert gas, and the reaction is carried out at a temperature
 in the range of 120 to 350.degree. C. under reduced pressure. The pressure
 in the reaction system is stepwise reduced up to 1 mmHg or less in order
 to distill away the phenols generated during the reaction from the
 reaction system. The reaction is commonly terminated in about one to 4
 hours. When necessary, the antioxidant may be added to the reaction
 system. As the bisarylcarbonate compound, diphenyl carbonate, di-p-tolyl
 carbonate, phenyl-p-tolyl carbonate, di-p-chlorophenyl carbonate and
 dinaphthyl carbonate can be employed.
 To control the molecular weight of the obtained polycarbonate resin, it is
 desirable to employ a terminator as a molecular weight modifier in any of
 the above-mentioned polymerization reactions. Consequently, a substituent
 derived from the terminator may be bonded to the end of the molecule of
 the obtained polycarbonate resin.
 As the terminator for use in the present invention, a monovalent aromatic
 hydroxy compound and haloformate derivatives thereof, and a monovalent
 carboxylic acid and halide derivatives thereof can be used alone or in
 combination.
 Specific examples of the monovalent aromatic hydroxy compound are phenols
 such as phenol, p-cresol, o-ethylphenol, p-ethylphenol, p-isopropylphenol,
 p-tert-butylphenol, p-cumylphenol, p-cyclohexylphenol, p-octylphenol,
 p-nonylphenol, 2,4-xylenol, p-methoxyphenol, p-hexyloxyphenol,
 p-decyloxyphenol, o-chlorophenol, m-chlorophenol, p-chlorophenol,
 p-bromophenol, pentabromophenol, pentachlorophenol, p-phenylphenol,
 p-isopropenylphenol, 2,4-di(1'-methyl-1'-phenylethyl)phenol,
 .beta.-naphthol, .alpha.-naphthol, p-(2',4',4'-trimethylchromanyl)phenol,
 and 2-(4'-methoxyphenyl)-2-(4"-hydroxyphenyl)propane. In addition, alkali
 metal salts and alkaline earth metal salts of the above phenols can also
 be employed. Various haloformate derivatives of the above-mentioned
 aromatic hydroxy compounds can be used as the terminators.
 Specific examples of the monovalent carboxylic acid are aliphatic acids
 such as acetic acid, propionic acid, butyric acid, valeric acid, caproic
 acid, heptanic acid, caprylic acid, 2,2-dimethylpropionic acid,
 3-methylbutyric acid, 3,3-dimethylbutyric acid, 4-methylvaleric acid,
 3,3-dimethylvaleric acid, 4-methylcaproic acid, 3,5-dimethylcaproic acid
 and phenoxyacetic acid; and benzoic acids such as benzoic acid,
 p-methylbenzoic acid, p-tert-butylbenzoic acid, p-butoxybenzoic acid,
 p-octyloxybenzoic acid, p-phenylbenzoic acid, p-benzylbenzoic acid and
 p-chlorobenzoic acid. In addition, alkali metal salts and alkaline earth
 metal salts of the above-mentioned aliphatic acids and benzoic acids can
 also be employed. In addition, various halide derivatives of the
 above-mentioned monovalent carboxylic acids can be employed as the
 terminators.
 The molecular weight of the obtained aromatic polycarbonate resin can be
 freely controlled by adding any of the above-mentioned terminators in the
 course of the polymerization reaction or prior to the polymerization
 reaction.
 Furthermore, the above-mentioned terminator can be used as a protectant for
 the end group of the molecule of the obtained polycarbonate resin. By the
 addition of the terminator after completion of the polymerization
 reaction, the end group of the obtained polycarbonate resin can be
 protected and provided with various functions.
 The above-mentioned terminators may be used alone or in combination. Of
 those terminators, the monovalent aromatic hydroxy compound is preferable.
 Preferable examples of the terminators include phenol, p-tert-butylphenol,
 p-cumylphenol and phenyl chloroformate.
 In the present invention, it is preferable that the aromatic polycarbonate
 resin thus obtained have a number-average molecular weight of 1,000 to
 500,000, more preferably in the range of 10,000 to 200,000 when expressed
 by the styrene-reduced value.
 Furthermore, a branching agent may be added in a small amount during the
 polymerization reaction in order to improve the mechanical properties of
 the obtained polycarbonate resin. Any compounds that have three or more
 reactive groups, which may be the same or different, selected from the
 group consisting of an aromatic hydroxyl group, a haloformate group, a
 carboxylic acid group, a carboxylic acid halide group, and an active
 halogen atom can be used as the branching agents for use in the present
 invention.
 Specific examples of the branching agents for use in the present invention
 are as follows:
 phloroglucinol,
 4,6-dimethyl-2,4,6-tris(4'-hydroxyphenyl)-2-heptene,
 4,6-dimethyl-2,4,6-tris(4'-hydroxyphenyl)heptane,
 1,3,5-tris(4'-hydroxyphenyl)benzene,
 1,1,1-tris(4'-hydroxyphenyl)ethane,
 1,1,2-tris(4'-hydroxyphenyl)propane,
 .alpha.,.alpha.,.alpha.'-tris(4'-hydroxyphenyl)-1-ethyl-4-isopropylbenzene,
 2,4-bis[.alpha.-methyl-.alpha.-(4'-hydroxyphenyl)ethyl]phenol,
 2-(4'-hydroxyphenyl)-2-(2",4"-dihydroxyphenyl)propane,
 tris-(4-hydroxyphenyl)phosphine,
 1,1,4,4-tetrakis(4'-hydroxyphenyl)cyclohexane,
 2,2-bis[4',4'-bis(4"-hydroxyphenyl)cyclohexyl]propane
 .alpha.,.alpha.,.alpha.',.alpha.'-tetrakis(4'-hydroxyphenyl)-1,4-diethylben
 zene,
 2,2,5,5-tetrakis(4'-hydroxyphenyl)hexane,
 1,1,2,3-tetrakis(4'-hydroxyphenyl)propane,
 1,4-bis(4',4"-dihydroxytriphenylmethyl)benzene,
 3,3',5,5'-tetrahydroxydiphenyl ether,
 3,5-dihydroxybenzoic acid,
 3,5-bis(chlorocarbonyloxy)benzoic acid,
 4-hydroxyisophthalic acid,
 4-chlorocarbonyloxyisophthalic acid,
 5-hydroxyphthalic acid,
 5-chlorocarbonyloxyphthalic acid,
 trimesic trichloride, and
 cyanuric chloride.
 Those branching agents may be used alone or in combination.
 The polycarbonate resin thus synthesized is purified by removing the
 catalyst and the antioxidant used in the polymerization; unreacted diol
 and terminator; and impurities such as an inorganic salt generated during
 the polymerization. Through the above-mentioned purifying procedure, the
 polycarbonate resin is used in the photoconductive layer of the
 electrophotographic photoconductor according to the present invention. The
 previously mentioned "Handbook of Polycarbonate Resin" (issued by Nikkan
 Kogyo Shimbun Ltd.) can be referred to for such a procedure for purifying
 the polycarbonate resin.
 To the aromatic polycarbonate resin produced by the previously mentioned
 methods, various additives such as an antioxidant, a light stabilizer, a
 thermal stabilizer, a lubricant and a plasticizer can be added when
 necessary.
 The structural unit of formula (1), that is the basic structural unit for
 the preparation of the aromatic polycarbonate resin, will be now explained
 in detail.
 ##STR19##
 wherein a, b, c and d are each independently an integer of 0 to 4; n is an
 integer of 0 or 1; and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each
 independently a halogen atom, an alkyl group having 1 to 6 carbon atoms,
 which may have a substituent, an alkoxyl group having 1 to 6 carbon atoms,
 which may have a substituent, or an aryl group which may have a
 substituent, and R.sup.1, R.sup.2, R.sup.3 and R.sup.4 may each be the
 same or different when a, b, c and d are each an integer of 2, 3 or 4.
 Examples of the halogen atom represented by R.sup.1 to R.sup.4 are fluorine
 atom, chlorine atom, bromine atom, and iodine atom.
 The alkyl group represented by R.sup.1 to R.sup.4 is a straight chain,
 branched or cyclic alkyl group having 1 to 6 carbon atoms. The alkyl group
 may have a substituent such as a fluorine atom, cyano group, or a phenyl
 group which may have a substituent selected from the group consisting of a
 halogen atom and a straight chain or branched alkyl group having 1 to 5
 carbon atoms.
 Specific examples of such a substituted or unsubstituted alkyl group are
 methyl group, ethyl group, n-propyl group, iso-propyl group, t-butyl
 group, s-butyl group, n-butyl group, iso-butyl group, trifluoromethyl
 group, 2-cyanoethyl group, benzyl group, 4-chlorobenzyl group,
 4-methylbenzyl group, cyclopentyl group, and cyclohexyl group.
 Specific examples of the substituted or unsubstituted alkoxy group
 represented by R.sup.1 to R.sup.4 are methoxy group, ethoxy group,
 n-propoxy group, iso-propoxy group, n-butoxy group, iso-butoxy group,
 s-butoxy group, t-butoxy group, 2-hydroxyethoxy group, 2-cyanoethoxy
 group, benzyloxy group, 4-methylbenzyloxy group and trifluoromethoxy
 group.
 Examples of the aryl group represented by R.sup.1 to R.sup.4 are phenyl
 group, naphthyl group, biphenylyl group, terphenylyl group, pyrenyl group,
 fluorenyl group, 9,9-dimethyl-2-fluorenyl group, azulenyl group, anthryl
 group, triphenylenyl group, chrysenyl group, fluorenylidenephenyl group,
 5H-dibenzo[a,d]cycloheptenylidenephenyl group, thienyl group, benzothienyl
 group, furyl group, benzofuranyl group, carbazolyl group, pyridinyl group,
 pyrrolidyl group, and oxazolyl group.
 The above-mentioned aryl group may have a substituent such as the
 previously mentioned substituted or unsubstituted alkyl group, substituted
 or unsubstituted alkoxy group, a halogen atom such as fluorine atom,
 chlorine atom, bromine atom or iodine atom, or an amino group represented
 by the following formula:
 ##STR20##
 in which R.sup.25 and R.sup.26 are each the same substituted or
 unsubstituted alkyl group or the same substituted or unsubstituted aryl
 group as defined in the description of R.sup.1 to R.sup.4, and R.sup.25
 and R.sup.26 may form a ring together or in combination with a carbon atom
 of the aryl group to constitute piperidino group, morpholino group or
 julolidyl group.
 Further, specific examples of the compound represented by the previously
 mentioned formula (8), that is, the starting material for the structural
 unit of formula (1) are shown below.
 ##STR21##
 The structural unit of formula (9) will now be explained by referring to
 the diol of formula (10) that is the starting material for the structural
 unit of formula (9).
 In the case where X in the diol of formula (10) represents a bivalent
 aliphatic group or a bivalent cyclic aliphatic group, the representative
 examples of the obtained diol are as follows: ethylene glycol, diethylene
 glycol, triethylene glycol, polyethylene glycol, polytetramethylene ether
 glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,
 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,7-heptanediol,
 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol,
 1,12-dodecanediol, neopentyl glycol, 2-ethyl-1,6-hexanediol,
 2-methyl-1,3-propanediol, 2-ethyl-1,3-propanediol,
 2,2-dimethyl-1,3-propanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol,
 cyclohexane-1,4-dimethanol, 2,2-bis(4-hydroxycyclohexyl)propane,
 xylylenediol, 1,4-bis(2-hydroxyethyl)benzene,
 1,4-bis(3-hydroxyphenyl)benzene, 1,4-bis(4-hydroxybutyl)benzene,
 1,4-bis(5-hydroxypentyl)benzene, and 1,4-bis(6-hydroxyhexyl)benzene.
 In the case where X in the diol of formula (10) represents a bivalent
 aromatic group, there can be employed any bivalent groups derived from the
 same substituted or unsubstituted aryl group as defined in the description
 of R.sup.1 to R.sup.4.
 In addition, X represents a bivalent group selected from the following
 groups:
 ##STR22##
 wherein R.sup.10, R.sup.11, R.sup.12, R.sup.13, R.sup.13--, and R.sup.13--
 are each independently an alkyl group which may have a substituent, an
 aryl group which may have a substituent, or a halogen atom; p and q are
 each independently an integer of 0 to 4; r and s are each independently an
 integer of 0 to 3; and l is an integer of 0 or 1, and when l=1, Y is a
 straight-chain alkylene group having 2 to 12 carbon atoms, a branched
 alkylene group having 3 to 12 carbon atoms, a bivalent group comprising at
 least one alkylene group having 1 to 10 carbon atoms and at least one
 oxygen atom and/or sulfur atom, --O--, --S--, --SO--, --SO.sub.2 --,
 --CO--,
 ##STR23##
 in which Z.sup.1 and Z.sup.2 are each a substituted or unsubstituted
 bivalent aliphatic group, or a substituted or unsubstituted arylene group;
 R.sup.14, R.sup.15, R.sup.16, R.sup.17, R.sup.18, R.sup.19 and R.sup.20
 are each independently a hydrogen atom, a halogen atom, a substituted or
 unsubstituted alkyl group having 1 to 5 carbon atoms, a substituted or
 unsubstituted alkoxyl group having 1 to 5 carbon atoms, or a substituted
 or unsubstituted aryl group, and R.sup.14 and R.sup.15 may form together a
 carbon ring or heterocyclic ring having 5 to 12 carbon atoms or R.sup.14
 and R.sup.15 may form a carbon ring or heterocyclic ring in combination
 with R.sup.10 and R.sup.11 ; l' and l" are each an integer of 0 or 1, and
 when l'=1 and l"=1, R.sup.21 and R.sup.22 are each an alkylene group
 having 1 to 4 carbon atoms; R.sup.23 and R.sup.24 are each independently a
 substituted or unsubstituted alkyl group having 1 to 5 carbon atoms or a
 substituted or unsubstituted aryl group; t is an integer of 0 to 4; u is
 an integer of 0 to 20; and v is an integer of 0 to 2000.
 In the above-mentioned bivalent groups, the same substituted or
 unsubstituted alkyl group, and the same substituted or unsubstituted aryl
 group as defined in the description of R.sup.1 to R.sup.4 can be employed
 for R.sup.10 to R.sup.20 and R.sup.23 and R.sup.24.
 Examples of a halogen atom represented by R.sup.10 to R.sup.20 are a
 fluorine atom, a chlorine atom, a bromine atom and an iodine atom.
 When Z.sup.1 and Z.sup.2 each represent a substituted or unsubstituted
 bivalent aliphatic group, there can be employed any bivalent groups
 obtained by removing the hydroxyl groups from the diol of formula (10) in
 which X represents a bivalent aliphatic group or a bivalent cyclic
 aliphatic group. On the other hand, when Z.sup.1 and Z.sup.2 each
 represent a substituted or unsubstituted arylene group, there can be
 employed any bivalent groups derived from the substituted or unsubstituted
 aryl group as defined in the description of R.sup.1 to R.sup.4.
 Preferable examples of the diol of formula (10) in which X represents a
 bivalent aromatic group are as follows:
 bis(4-hydroxyphenyl)methane,
 bis(2-methyl-4-hydroxyphenyl)methane,
 bis(3-methyl-4-hydroxyphenyl)methane,
 1,1-bis(4-hydroxyphenyl)ethane,
 1,2-bis(4-hydroxyphenyl)ethane,
 bis(4-hydroxyphenyl)phenylmethane,
 bis(4-hydroxyphenyl)diphenylmethane,
 1,1-bis(4-hydroxyphenyl)-1-phenylethane,
 1,3-bis(4-hydroxyphenyl)-1,1-dimethylpropane,
 2,2-bis(4-hydroxyphenyl)propane,
 2-(4-hydroxyphenyl)-2-(3-hydroxyphenyl)propane,
 1,1-bis(4-hydroxyphenyl)-2-methylpropane,
 2,2-bis(4-hydroxyphenyl)butane,
 1,1-bis(4-hydroxyphenyl)-3-methylbutane,
 2,2-bis(4-hydroxyphenyl)pentane,
 2,2-bis(4-hydroxyphenyl)-4-methylpentane,
 2,2-bis(4-hydroxyphenyl)hexane,
 4,4-bis(4-hydroxyphenyl)heptane,
 2,2-bis(4-hydroxyphenyl)nonane,
 bis(3,5-dimethyl-4-hydroxyphenyl)methane,
 2,2-bis(3-methyl-4-hydroxyphenyl)propane,
 2,2-bis(3-isopropyl-4-hydroxyphenyl)propane,
 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane,
 2,2-bis(3-tert-butyl-4-hydroxyphenyl)propane,
 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane,
 2,2-bis(3-allyl-4-hydroxyphenyl)propane,
 2,2-bis(3-phenyl-4-hydroxyphenyl)propane,
 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,
 2,2-bis(3-chloro-4-hydroxyphenyl)propane,
 2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane,
 2,2-bis(3-bromo-4-hydroxyphenyl)propane,
 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane,
 2,2-bis(4-hydroxyphenyl)hexafluoropropane,
 1,1-bis(4-hydroxyphenyl)cyclopentane,
 1,1-bis(4-hydroxyphenyl)cyclohexane,
 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane,
 1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane,
 1,1-bis(3,5-dichloro-4-hydroxyphenyl)cyclohexane,
 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane,
 1,1-bis(4-hydroxyphenyl)cycloheptane,
 2,2-bis(4-hydroxyphenyl)norbornane,
 2,2-bis(4-hydroxyphenyl)adamantane,
 4,4'-dihydroxydiphenyl ether,
 4,4'-dihydroxy-3,3'-dimethyldiphenyl ether,
 ethylene glycol bis(4-hydroxyphenyl)ether,
 4,4'-dihydroxydiphenylsulfide,
 3,3'-dimethyl-4,4'-dihydroxydiphenylsulfide,
 3,3',5,5'-tetramethyl-4,4'-dihydroxydiphenylsulfide,
 4,4'-dihydroxydiphenylsulfoxide,
 3,3'-dimethyl-4,4'-dihydroxydiphenylsulfoxide,
 4,4'-dihydroxydiphenylsulfone,
 3,3'-dimethyl-4,4'-dihydroxydiphenylsulfone,
 3,3'-diphenyl-4,4'-dihydroxydiphenylsulfone,
 3,3'-dichloro-4,4'-dihydroxydiphenylsulfone,
 bis(4-hydroxyphenyl)ketone,
 bis(3-methyl-4-hydroxyphenyl)ketone,
 3,3,3',3'-tetramethyl-6,6'-dihydroxyspiro(bis)indane,
 3,3',4,4'-tetrahydro-4,4,4',4'-tetramethyl-2,2'-spirobi(2H-1-benzopyrane)-7
 ,7'-diol,
 trans-2,3-bis(4-hydroxyphenyl)-2-butene,
 9,9-bis(4-hydroxyphenyl)fluorene,
 9,9-bis(4-hydroxyphenyl)xanthene,
 1,6-bis(4-hydroxyphenyl)-1,6-hexanedione,
 .alpha.,.alpha.,.alpha.',.alpha.'-tetramethyl-.alpha.,.alpha.'-bis(4-hydrox
 yphenyl)-p-xylene,
 .alpha.,.alpha.,.alpha.',.alpha.'-tetramethyl-.alpha.,.alpha.'-bis(4-hydrox
 yphenyl)-m-xylene,
 2,6-dihydroxydibenzo-p-dioxine,
 2,6-dihydroxythianthrene,
 2,7-dihydroxyphenoxathine,
 9,10-dimethyl-2,7-dihydroxyphenazine,
 3,6-dihydroxydibenzofuran,
 3,6-dihydroxydibenzothiophene,
 4,4'-dihydroxybiphenyl,
 1,4-dihydroxynaphthalene,
 2,7-dihydroxypyrene,
 hydroquinone,
 resorcin,
 ethylene glycol-bis(4-hydroxybenzoate),
 diethylene glycol-bis(4-hydroxybenzoate),
 triethylene glycol-bis(4-hydroxybenzoate),
 1,3-bis(4-hydroxyphenyl)-tetramethyldisiloxane, and
 phenol-modified silicone oil.
 Further, an aromatic diol having an ester linkage produced by the reaction
 between 2 moles of a diol and one mole of isophthaloyl chloride or
 terephthaloyl chloride is also usable.
 The structural units of formulas (2) and (3) having charge transporting
 properties will now be explained in detail by referring to the diols of
 formulas (11) and (12), that is, starting materials of the structural
 units of formulas (2) and (3), respectively.
 In formula (11), R.sup.5 is a hydrogen atom, or the same substituted or
 unsubstituted alkyl group or the same substituted or unsubstituted aryl
 group as defined in the description of R.sup.1 to R.sup.4.
 In formula (11), Ar.sup.1 is an aryl group which may have a substituent.
 Specific examples of the substituted or unsubstituted aryl group
 represented by Ar.sup.1 include a monovalent group derived from a
 heterocyclic group having an amine structure, such as pyrrole, pyrazole,
 imidazole, triazole, dioxazole, indole, isoindole, benzimidazole,
 benzotriazole, benzisoxazine, carbazole and phenoxazine; and a group
 represented by the following formula (14):
 ##STR24##
 wherein R.sup.6 and R.sup.7 which may be the same or different, are each an
 acyl group, an alkyl group which may have a substituent, or an aryl group
 which may have a substituent; Ar.sup.4 is an arylene group; and w is an
 integer of 1 to 3.
 The above-mentioned aryl group represented by Ar.sup.1 may have a
 substituent, for example, the same substituted or unsubstituted alkyl
 group, the same substituted or unsubstituted aryl group as defined in the
 description of R.sup.1 to R.sup.4, or a halogen atom such as fluorine
 atom, chlorine atom, bromine atom or iodine atom.
 In formula (14), there can be employed acetyl group, propionyl group, and
 benzoyl group as the acyl group represented by R.sup.6 and R.sup.7. In
 addition, for R.sup.6 and R.sup.7, there can be employed the same
 substituted and unsubstituted alkyl group as defined in the description of
 R.sup.1 to R.sup.4.
 Furthermore, examples of the substituted or unsubstituted aryl group
 represented by R.sup.6 and R.sup.7 include the same substituted and
 unsubstituted alkyl group as defined in the description of R.sup.1 to
 R.sup.4, and a group represented by the following formula (15):
 ##STR25##
 wherein R.sup.25 is a hydrogen atom, the same substituted or unsubstituted
 alkyl group as defined in the description of R.sup.1 to R.sup.4, an
 alkoxyl group, a halogen atom, the same substituted or unsubstituted aryl
 group as defined in the description of R.sup.1 to R.sup.4, an amino group,
 nitro group, or cyano group; and B is seleceted from the group consisting
 of --O--, --S--, --SO--, --SO.sub.2 --, --CO--, and the following bivalent
 groups:
 ##STR26##
 in which x is an integer of 1 to 12; x' is an integer of 1 to 3; and
 R.sup.26 is a hydrogen atom, the same substituted or unsubstituted alkyl
 group as defined in the description of R.sup.1 to R.sup.4, or the same
 substituted or unsubstituted aryl group as defined in the description of
 R.sup.1 to R.sup.4.
 Examples of the alkoxyl group represented by R.sup.25 in formula (15) are
 methoxy group, ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy
 group, iso-butoxy group, s-butoxy group, t-butoxy group, 2-hydroxyethoxy
 group, 2-cyanoethoxy group, benzyloxy group, 4-methylbenzyloxy group and
 trifluoromethoxy group.
 Examples of the halogen atom represented by R.sup.25 in formula (15) are
 fluorine atom, chlorine atom, bromine atom and iodine atom.
 As the amino group represented by R.sup.25 in formula (15), there can be
 employed the same amino group that defined as the substituent for the aryl
 group represented by R.sup.1 to R.sup.4.
 As the arylene group represented by Ar.sup.4 in formula (14), there can be
 employed any bivalent groups derived from the same substituted or
 unsubstituted aryl group as defined in the description of R.sup.1 to
 R.sup.4.
 Similarly in formulas (11) and (12), there can be employed as the arylene
 group represented by Ar.sup.2 and Ar.sup.3 any bivalent groups derived
 from the same substituted or unsubstituted aryl group as defined in the
 description of R.sup.1 to R.sup.4.
 The structural unit of formula (6) will now be explained by referring to
 the diol of formula (13), that is, a starting material of the structural
 unit of formula (6).
 In formula (13), e and f are each independently an integer of 0 to 5; and
 R.sup.8 and R.sup.9 are each independently a halogen atom, a substituted
 or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or
 unsubstituted alkoxyl group having 1 to 6 carbon atoms, or a substituted
 or unsubstituted aryl group. When e and f are each an integer of 2 to 5,
 R.sup.8 and R.sup.9 are each the same or different.
 Examples of the above-mentioned substituted or unsubstituted alkyl group
 represented by R.sup.8 and R.sup.9, and examples of the above-mentioned
 substituted or unsubstituted aryl group represented by R.sup.8 and R.sup.9
 are the same as those defined in the description of R.sup.1 to R.sup.4.
 Examples of the halogen atom represented by R.sup.8 and R.sup.9 are
 fluorine atom, chlorine atom, bromine atom and iodine atom.
 Examples of the alkoxyl group represented by R.sup.8 and R.sup.9 are
 methoxy group, ethoxy group, n-propoxy group, i-propoxy group, n-butoxy
 group, i-butoxy group, s-butoxy group, t-butoxy group, 2-hydroxyethoxy
 group, 2-cyanoethoxy group, benzyloxy group, 4-methylbenzyloxy group, and
 trifluoromethoxy group.
 When the polycarbonate resin in the form of a copolymer comprising the
 structural unit of formula (1) and the structural unit of formula (2) is
 employed for the photoconductive layer, the charge transporting properties
 of the polycarbonate resin depend upon the content of the structural unit
 of formula (2). Therefore, it is preferable that the amount of structural
 unit having formula (2) be 5 wt. % or more, more preferably in the range
 of 10 to 90 wt. % of the total weight of the polycarbonate resin.
 According to the present invention, the aromatic polycarbonate resin can be
 provided with charge transporting properties by using the structural unit
 of formula (1) and the structural unit having charge transporting
 properties, represented by formula (2), (4) or (6) in combination. In
 order to improve the electrical characteristics and the mechanical
 characteristics, the structural unit of formula (1) and other conventional
 structural units with charge transporting properties can be used together.
 Namely, to provide such a polycarbonate resin, at least one diol
 represented by formula (8) may be subjected to polymerization together
 with at least one of the conventional diols to be described later. Further
 addition of the previously mentioned diol of formula (10) makes it
 possible to provide the polycarbonate resin in the form of a copolymer
 with improved mechanical strength. In this case, a plurality of diols
 represented by formula (10) can be employed. The amount ratio of the diol
 of formula (8) and the amount ratio of the conventional diol with charge
 transporting properties may be selected within a wide range in light of
 the desired characteristics of the obtained aromatic polycarbonate resin.
 In the present invention, the amount of the structural unit of formula (1)
 may be controlled to 5 wt. % or more, and the amount of the structural
 unit with charge transporting properties may be controlled to 5 wt. % or
 more, of the total weight of the aromatic polycarbonate resin.
 Examples of the above-mentioned conventional diol with charge transporting
 properties are as follows: acetophenone derivatives (Japanese Laid-Open
 Patent Applications 7-325409, 7-258399, 8-269183 and 9-151248),
 distyrylbenzene derivatives (Japanese Laid-Open Patent Application
 9-71642), diphenetylbenzene derivatives (Japanese Laid-Open Patent
 Application 9-127713 and 9-104746), .alpha.-phenylstilbene derivatives
 (Japanese Laid-Open Patent Applications 9-297419, 9-97424, 9-241369 and
 9-272735), butadiene derivatives (Japanese Laid-Open Patent Applications
 9-80783 and 9-235367), bydrogenated butadiene derivatives (Japanese
 Laid-Open Patent Applications 9-80784 and 9-87376), diphenylcyclohexane
 derivatives (Japanese Laid-Open Patent Applications 9-80772 and 9-110976),
 distyryltriphenylamine derivatives (Japanese Laid-Open Patent Applications
 9-222740 and 9-268226), distyryldiamine derivatives, distyryldiamine
 derivatives, diphenyldistyrylbenzene derivatives (Japanese Laid-Open
 Patent Applications 9-265197, 9-265201, 9-221544 and 9-227669), stilbene
 derivatives (Japanese Laid-Open Patent Applications 9-211877 and
 9-157378), m-phenylenediamine derivatives (Japanese Laid-Open Patent
 Applications 9-304956, 9-304957, 9-302084 and 9-302085), resorcin
 derivatives (Japanese Laid-Open Patent Applications 9-329907 and
 9-328539), and triarylamine derivatives (Japanese Laid-Open Patent
 Applications 64-9964, 7-199503, 8-176293, 8-208820, 8-253568, 8-269446,
 3-221522, 4-11627, 4-183719, 4-124163, 4-320420, 4-316543, 5-310904,
 7-56374, and 8-62864, and U.S. Pat. Nos. 5,428,090 and 5,486,439.).
 In the above-mentioned polycarbonate resin comprising the structural unit
 of formula (1) and the conventional structural unit with charge
 transporting properties, the charge transporting properties of the
 obtained polycarbonate resin depend upon the content of the structural
 unit with the charge transporting properties. It is therefore preferable
 that the amount of structural unit having charge transporting properties
 be 5 wt. % or more, more preferably in the range of 10 to 90 wt. % of the
 total weight of the polycarbonate resin.
 As previously explained, both the aromatic polycarbonate resin serving as a
 binder resin, and the aromatic polycarbonate resin having charge
 transporting properties are used in the photoconductive layer of the
 electrophotographic photoconductor.
 The embodiments of the electrophotographic photoconductor according to the
 present invention will be described later, provided that the aromatic
 polycarbonate resin having charge transporting properties is employed in
 the photoconductive layer. In the case where the aromatic polycarbonate
 resin for use in the photoconductive layer essentially consists of the
 structural unit of formula (1), in other words, when the aromatic
 polycarbonate for use in the photoconductive layer is not provided with
 charge transporting properties, a conventional low-molecular weight charge
 transport material may be contained in the photoconductive layer. By the
 addition of such a low-molecular weight charge transport material, a
 desired charge transport layer or charge transport medium can be obtained
 even though the above-mentioned polycarbonate resin for use in the
 photoconductive layer works only as a binder resin. Even when the
 polycarbonate resin of the present invention provided with charge
 transporting properties is used for the preparation of the charge
 transport medium, the above-mentioned low-molecular weight charge
 transport material may also be employed.
 Specific examples of the low-molecular weight charge-transport materials
 are as follows: oxazole derivatives, oxadiazole derivatives (Japanese
 Laid-Open Patent Applications 52-139065 and 52-139066), imidazole
 derivatives, triphenylamine derivatives (Japanese Laid-Open Patent
 Application 3-285960), benzidine derivatives (Japanese Patent Publication
 58-32372), .alpha.-phenylstilbene derivatives (Japanese Laid-Open Patent
 Application 57-73075), hydrazone derivatives (Japanese Laid-Open Patent
 Applications 55-154955, 55-156954, 55-52063, and 56-81850),
 triphenylmethane derivatives (Japanese Patent Publication 51-10983),
 anthracene derivatives (Japanese Laid-Open Patent Application 51-94829),
 styryl derivatives (Japanese Laid-Open Patent Applications 56-29245 and
 58-198043), carbazole derivatives (Japanese Laid-Open Patent Application
 58-58552), and pyrene derivatives (Japanese Laid-Open Patent Application
 2-94812).
 According to the present invention, at least one of the previously
 mentioned aromatic polycarbonate resins is contained in different ways,
 for example, in photoconductive layers 2, 2a, 2b, 2c, 2d, and 2e, as shown
 in FIGS. 1 through 6.
 In the photoconductor shown in FIG. 1, a photoconductive layer 2 is formed
 on an electroconductive support 1, which photoconductive layer 2 comprises
 the previously mentioned aromatic polycarbonate resin according to the
 present invention and a sensitizing dye, with the addition thereto of a
 binder agent (binder resin) when necessary. In this photoconductor, the
 aromatic polycarbonate resin works as a photoconductive material, through
 which charge carriers necessary for the light decay of the photoconductor
 are generated and transported. However, the aromatic polycarbonate resin
 itself scarcely absorbs light in the visible light range and, therefore,
 it is necessary to add a sensitizing dye which absorbs light in the
 visible light range in order to form latent electrostatic images by use of
 visible light.
 Referring to FIG. 2, there is shown an enlarged cross-sectional view of
 another embodiment of an electrophotographic photoconductor according to
 the present invention. In this photoconductor, there is formed a
 photoconductive layer 2a on an electroconductive support 1. The
 photoconductive layer 2a comprises a charge transport medium 4' comprising
 (i) an aromatic polycarbonate resin having charge transporting properties
 according to the present invention, optionally in combination with a
 binder agent, and (ii) a charge generation material 3 dispersed in the
 charge transport medium 4'. In this embodiment, the aromatic polycarbonate
 resin (or a mixture of the aromatic polycarbonate resin and the binder
 agent) constitutes the charge transport medium 4'. The charge generation
 material 3, which is, for example, an inorganic material or an organic
 pigment, generates charge carriers. The charge transport medium 4' accepts
 the charge carriers generated by the charge generation material 3 and
 transports those charge carriers.
 In this electrophotographic photoconductor of FIG. 2, it is basically
 necessary that the light-absorption wavelength regions of the charge
 generation material 3 and the aromatic polycarbonate resin not overlap in
 the visible light range. This is because, in order that the charge
 generation material 3 produce charge carriers efficiently, it is necessary
 that light pass through the charge transport medium 4' and reach the
 surface of the charge generation material 3. Since the aromatic
 polycarbonate resin of the present invention do not substantially absorb
 light with a wavelength of 600 nm or more, it can work effectively as a
 charge transport material when used with the charge generation material 3
 which absorbs the light in the visible region to the near infrared region
 and generates charge carriers. The charge transport medium 4' may further
 comprise the previously mentioned low-molecular weight charge transport
 material.
 Referring to FIG. 3, there is shown an enlarged cross-sectional view of a
 further embodiment of an electrophotographic photoconductor according to
 the present invention. In the figure, there is formed on an
 electroconductive support 1 a two-layered photoconductive layer 2b
 comprising a charge generation layer 5 containing a charge generation
 material 3, and a charge transport layer 4 comprising an aromatic
 polycarbonate resin with the charge transporting properties according to
 the present invention.
 In this photoconductor, light which has passed through the charge transport
 layer 4 reaches the charge generation layer 5, and charge carriers are
 generated within the charge generation layer 5. The charge carriers which
 are necessary for the light decay for latent electrostatic image formation
 are generated by the charge generation material 3, and accepted and
 transported by the charge transport layer 4. The generation and
 transportation of the charge carriers are performed by the same mechanisms
 as that in the photoconductor shown in FIG. 2.
 In this case, the charge transport layer 4 comprises the aromatic
 polycarbonate resin with charge transporting properties, optionally in
 combination with a binder agent. Furthermore, in order to increase the
 efficiency of generating the charge carriers, the charge generation layer
 5 may further comprise the above-mentioned aromatic polycarbonate resin,
 and the photoconductive layer 2b including the charge generation layer 5
 and the charge transport layer 4 may further comprise the previously
 mentioned low-molecular weight charge transport material. This can be
 applied to the embodiments of FIGS. 4 to 6 to be described later.
 In the electrophotographic photoconductor of FIG. 3, a protective layer 6
 may be provided on the charge transport layer 4 as shown in FIG. 4. The
 protective layer 6 may comprise the aromatic polycarbonate resin of the
 present invention, optionally in combination with a binder agent. In such
 a case, it is effective that the protective layer 6 be provided on a
 charge transport layer in which a low-molecular weight charge transport
 material is dispersed. The protective layer 6 may be provided on the
 photoconductive layer 2a of the photoconductor shown in FIG. 2.
 Referring to FIG. 5, there is shown still another embodiment of an
 electrophotographic photoconductor according to the present invention. In
 this figure, the overlaying order of the charge generation layer 5 and the
 charge transport layer 4 comprising the aromatic polycarbonate resin is
 reversed in view of the electrophotographic photoconductor as shown in
 FIG. 3. The mechanism of the generation and transportation of charge
 carriers is substantially the same as that of the photoconductor shown in
 FIG. 3.
 In the above photoconductor of FIG. 5, and protective layer 6 may be formed
 on the charge generation layer 5 as shown in FIG. 6 in light of the
 mechanical strength of the photoconductor.
 When the electrophotographic photoconductor according to the present
 invention shown in FIG. 1 is fabricated, at least one aromatic
 polycarbonate resin with charge transporting properties is dissolved in a
 solvent, with the addition thereto of a binder agent when necessary. To
 the thus prepared solution, a sensitizing dye is added, so that a coating
 liquid for the photoconductive layer 2 is prepared. The thus prepared
 photoconductive layer coating liquid is coated on an electroconductive
 support 1 and dried, so that a photoconductive layer 2 is formed on the
 electroconductive support 1.
 It is preferable that the thickness of the photoconductive layer 2 be in
 the range of 3 to 50 .mu.m, more preferably in the range of 5 to 40 .mu.m.
 It is preferable that the amount of aromatic polycarbonate resin with
 charge transporting properties be in the range of 30 to 100 wt. % of the
 total weight of the photoconductive layer 2. It is preferable that the
 amount of sensitizing dye for use in the photoconductive layer 2 be in the
 range of 0.1 to 5 wt. %, more preferably in the range of 0.5 to 3 wt. % of
 the total weight of the photoconductive layer 2.
 Specific examples of the sensitizing dye for use in the present invention
 are triarylmethane dyes such as Brilliant Green, Victoria Blue B, Methyl
 Violet, Crystal Violet and Acid Violet 6B; xanthene dyes such as Rhodamine
 B, Rhodamine 6G, Rhodamine G Extra, Eosin S, Erythrosin, Rose Bengale and
 Fluoresceine; thiazine dyes such as Methylene Blue; and cyanine dyes such
 as cyanin.
 The electrophotographic photoconductor shown in FIG. 2 can be produced by
 the following method:
 The finely-divided particles of the charge generation material 3 are
 dispersed in a solution in which at least one aromatic polycarbonate resin
 with charge transporting properties, or a mixture of the aromatic
 polycarbonate resin and the binder agent is dissolved, so that a coating
 liquid for the photoconductive layer 2a is prepared. The coating liquid
 thus prepared is coated on the electroconductive support 1 and then dried,
 whereby the photoconductive layer 2a is provided on the electroconductive
 support 1.
 It is preferable that the thickness of the photoconductive layer 2a be in
 the range of 3 to 50 .mu.m, more preferably in the range of 5 to 40 .mu.m.
 It is preferable that the amount of aromatic polycarbonate resin with
 charge transporting properties be in the range of 40 to 100 wt. % of the
 total weight of the photoconductive layer 2a.
 It is preferable that the amount of charge generation material 3 for use in
 the photoconductive layer 2a be in the range of 0.1 to 50 wt. %, more
 preferably in the range of 1 to 20 wt. % of the total weight of the
 photoconductive layer 2a.
 Specific examples of the charge generation material 3 for use in the
 present invention are as follows: inorganic materials such as selenium,
 selenium-tellurium, cadmium sulfide, cadmium sulfide-selenium and
 .alpha.-silicon (amorphous silicon); and organic pigments, for example,
 azo pigments, such as C.I. Pigment Blue 25 (C.I. 21180), C.I. Pigment Red
 41 (C.I. 21200), C.I. Acid Red 52 (C.I. 45100), C.I. Basic Red 3 (C.I.
 45210), an azo pigment having a carbazole skeleton (Japanese Laid-Open
 Patent Application 53-95033), an azo pigment having a distyryl benzene
 skeleton (Japanese Laid-Open Patent Application 53-133445), an azo pigment
 having a triphenylamine skeleton (Japanese Laid-Open Patent Application
 53-132347), an azo pigment having a dibenzothiophene skeleton (Japanese
 Laid-Open Patent Application 54-21728), an azo pigment having an
 oxadiazole skeleton (Japanese Laid-Open Patent Application 54-12742), an
 azo pigment having a fluorenone skeleton (Japanese Laid-Open Patent
 Application 54-228834), an azo pigment having a bisstilbene skeleton
 (Japanese Laid-Open Patent Application 54-17733), an azo pigment having a
 distyryl oxadiazole skeleton (Japanese Laid-Open Patent Application
 54-2129), and an azo pigment having a distyryl carbazole skeleton
 (Japanese Laid-Open Patent Application 54-14967); phthalocyanine pigments
 such as C.I. Pigment Blue 16 (C.I. 74100); indigo pigments such as C.I.
 Vat Brown 5 (C.I. 73410) and C.I. Vat Dye (C.I. 73030); and perylene
 pigments such as Algol Scarlet B and Indanthrene Scarlet R (made by Bayer
 Co., Ltd.). These charge generation materials may be used alone or in
 combination.
 When the above-mentioned charge generation material comprises a
 phthalocyanine pigment, the sensitivity and durability of the obtained
 photoconductor are remarkably improved. In such a case, there can be
 employed a phthalocyanine pigment having a phthalocyanine skeleton as
 indicated by the following formula (16):
 ##STR27##
 In the above formula (16), M (central atom) is a metal atom or hydrogen
 atom.
 To be more specific, as the central atom (M) in the above formula, there
 can be employed an atom of H, Li, Be, Na, Mg, Al, Si, K, Ca, Sc, Ti, V,
 Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd,
 In, Sn, Sb, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Hg, Tl, La, Ce, Pr, Nd, Pm,
 Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Th, Pa, U, Np or Am; the
 combination of atoms forming an oxide, chloride, fluoride, hydroxide or
 bromide. The central atom is not limited to the above-mentioned atoms.
 The above-mentioned charge generation material with a phthalocyanine
 structure for use in the present invention may have at least the basic
 structure as indicated by the above-mentioned formula (16). Therefore, the
 charge generation material may have a dimer structure or trimer structure,
 and further, a polymeric structure. Further, the above-mentioned basic
 structure of the above formula (16) may have a substituent.
 Of the phthalocyanine compounds represented by formula (16), an oxotitanium
 phthalocyanine compound which has the central atom (M) of TiO in the
 formula (16) and a metal-free phthalocyanine compound which has a hydrogen
 atom as the central atom (M) are particularly preferred in the present
 invention because the obtained photoconductors show excellent
 photoconductive properties.
 In addition, it is known that each phthalocyanine compound has a variety of
 crystal systems. For example, the above-mentioned oxotitanium
 phthalocyanine has crystal systems of .alpha.-type, .beta.-type,
 .gamma.-type, m-type, and y-type. In the case of copper phthalocyanine,
 there are crystal systems of .alpha.-type, .beta.-type, and .gamma.-type.
 The properties of the phthalocyanine compound vary depending on the
 crystal system thereof although the central metal atom is the same.
 According to "Electrophotography--the Society Journal--Vol. 29, No. 4
 (1990)", it is reported that the properties of the photoconductor vary
 depending on the crystal system of a phthalocyanine contained in the
 photoconductor. In light of the desired photoconductive properties,
 therefore, it is important to employ the phthalocyanine compounds each
 having the optimal crystal system. The oxotitanium phthalocyanine in the
 y-type crystal system is particularly advantageous.
 A plurality of charge generation materials with phthalocyanine skeleton may
 be used in combination in the charge generation layer. Further, such
 charge generation materials with phthalocyanine skeleton may be used in
 combination with other charge generation materials not having
 phthalocyanine skeleton. In this case, inorganic and organic conventional
 charge generation materials are usable.
 Specific examples of the inorganic charge generation materials are
 crystalline selenium, amorphous selenium, selenium--tellurium,
 seleniuim--tellurium--halogen, selenium--arsenic compound, and a-silicon
 (amorphous silicon). In particular, when the above-mentioned a-silicon is
 employed as the charge generation material, it is preferable that the
 dangling bond be terminated with hydrogen atom or a halogen atom, or be
 doped with boron atom or phosphorus atom.
 Specific examples of the organic charge generation materials that can be
 used in combination with the phthalocyanine compound include an azulenium
 salt pigment, a squaric acid methine pigment, an azo pigment having a
 carbazole skeleton, an azo pigment having a triphenyl-amine skeleton, an
 azo pigment having a diphenylamine skeleton, an azo pigment having a
 dibenzothiophene skeleton, an azo pigment having a fluorenone skeleton, an
 azo pigment having an oxadiazole skeleton, an azo pigment having a
 bisstilbene skeleton, an azo pigment having a distyryl oxadiazole
 skeleton, an azo pigment having a distyryl carbazole skeleton, a perylene
 pigment, an anthraquinone pigment, a polycyclic quinone pigment, a quinone
 imine pigment, a diphenylmethane pigment, a triphenylmethane pigment, a
 benzoquinone pigment, a naphthoquinone pigment, a cyanine pigment, an
 azomethine pigment, an indigoid pigment, and a bisbenzimidazole pigment.
 The electrophotographic photoconductor shown in FIG. 3 can be produced by
 the following method:
 To provide the charge generation layer 5 on the electroconductive support
 1, the charge generation material is vacuum-deposited on the
 electroconductive support 1. Alternatively, the finely-divided particles
 of the charge generation material 3 are dispersed in an appropriate
 solvent, together with the binder agent when necessary, so that a coating
 liquid for the charge generation layer 5 is prepared. The thus prepared
 coating liquid is coated on the electroconductive support 1 and dried,
 whereby the charge generation layer 5 is formed on the electroconductive
 support 1. The charge generation layer 5 may be subjected to surface
 treatment by buffing and adjustment of the thickness thereof if required.
 On the thus formed charge generation layer 5, a coating liquid in which at
 least one aromatic polycarbonate resin with charge transporting
 properties, optionally in combination with a binder agent, is dissolved is
 coated and dried, so that the charge transport layer 4 is formed on the
 charge generation layer 5. In the charge generation layer 5, the same
 charge generation materials as employed in the above-mentioned
 photoconductive layer 2a can be used.
 The thickness of the charge generation layer 5 is 5 .mu.m or less,
 preferably 2 .mu.m or less. It is preferable that the thickness of the
 charge transport layer 4 be in the range of 3 to 50 .mu.m, more preferably
 in the range of 5 to 40 .mu.m.
 When the charge generation layer 5 is provided on the electroconductive
 support 1 by coating the dispersion in which finely-divided particles of
 the charge generation material 3 are dispersed in an appropriate solvent,
 it is preferable that the amount of finely-divided particles of the charge
 generation material 3 for use in the charge generation layer 5 be in the
 range of 10 to 100 wt. %, more preferably in the range of about 50 to 100
 wt. % of the total weight of the charge generation layer 5. It is
 preferable that the amount of aromatic polycarbonate resin of the present
 invention 4 be in the range of 40 to 100 wt. % of the total weight of the
 charge transport layer 4.
 The photoconductive layer 2b of the photoconductor shown in FIG. 3 may
 comprise a low-molecular-weight charge transport material as previously
 mentioned.
 To produce the photoconductor shown in FIG. 4, a coating liquid for the
 protective layer 6 is prepared by dissolving the previously mentioned
 aromatic polycarbonate resin, optionally in combination with the binder
 agent, in a solvent, and the thus obtained coating liquid is coated on the
 charge transport layer 4 of the photoconductor shown in FIG. 3, and dried.
 It is preferable that the thickness of the protective layer 6 be in the
 range of 0.15 to 10 .mu.m. It is preferable that the amount of aromatic
 polycarbonate resin for use in the protective layer 6 be in the range of
 40 to 100 wt. % of the total weight of the protective layer 6.
 The electrophotographic photoconductor shown in FIG. 5 can be produced by
 the following method:
 The aromatic polycarbonate resin of the present invention, optionally in
 combination with the binder agent, is dissolved in a solvent to prepare a
 coating liquid for the charge transport layer 4. The thus prepared coating
 liquid is coated on the electroconductive support 1 and dried, whereby the
 charge transport layer 4 is provided on the electroconductive support 1.
 On the thus formed charge transport layer 4, a coating liquid prepared by
 dispersing the finely-divided particles of the charge generation material
 3 in a solvent in which the binder agent may be dissolved when necessary,
 is coated, for example, by spray coating, and dried, so that the charge
 generation layer 5 is provided on the charge transport layer 4. The amount
 ratios of the components contained in the charge generation layer 5 and
 charge transport layer 4 are the same as those previously mentioned in the
 description of FIG. 3.
 When the previously mentioned protective layer 6 is formed on the above
 prepared charge generation layer 5, the electrophotographic photoconductor
 shown in FIG. 6 can be fabricated.
 To fabricate any of the aforementioned photoconductors of the present
 invention, a metallic plate or foil made of aluminum, a plastic film on
 which a metal such as aluminum is deposited, and a sheet of paper which
 has been treated so as to be electroconductive can be employed as the
 electroconductive support 1.
 Specific examples of the binder agent used in the preparation of the
 photoconductor according to the present invention are condensation resins
 such as polyamide, polyurethane, polyester, epoxy resin, polyketone and
 polycarbonate; and vinyl polymers such as polyvinylketone, polystyrene,
 poly-N-vinylcarbazole and polyacrylamide. All the resins that have
 electrically insulating properties and adhesion properties can be
 employed.
 Some plasticizers may be added to the above-mentioned binder agents, when
 necessary. Examples of the plasticizer for use in the present invention
 are halogenated paraffin, dimethylnaphthalene and dibutyl phthalate.
 Further, a variety of additives such as an antioxidant, a light
 stabilizer, a thermal stabilizer and a lubricant may also be contained in
 the binder agents when necessary.
 Furthermore, in the electrophotographic photoconductor according to the
 present invention, an intermediate layer such as an adhesive layer or a
 barrier layer may be interposed between the electroconductive support and
 the pohtoconductive layer when necessary.
 Examples of the material for use in the intermediate layer are polyamide,
 nitrocellulose, aluminum oxide and titanium oxide. It is preferable that
 the thickness of the intermediate layer be 1 .mu.m or less.
 When copying is performed by use of the photoconductor according to the
 present invention, the surface of the photoconductor is uniformly charged
 to a predetermined polarity in the dark. The uniformly charged
 photoconductor is exposed to a light image so that a latent electrostatic
 image is formed on the surface of the photoconductor. The thus formed
 latent electrostatic image is developed to a visible image by a developer,
 and the developed image can be transferred to a sheet of paper when
 necessary.
 The photosensitivity and the durability of the electrophotographic
 photoconductor according to the present invention are remarkably improved.
 As mentioned above, the aromatic polycarbonate resin according to the
 present invention is remarkably useful as a charge transport material when
 used in combination with the charge generation material in the
 electrophotographic photoconductor, in particular, in the
 function-separating electrophotographic photoconductor. In addition to the
 above, the aromatic polycarbonate resin of the present invention can be
 preferably employed as electronic devices such as an organic
 electroluminescent device in the field of electronics.
 Other features of this invention will become apparent in the course of the
 following description of exemplary embodiments, which are given for
 illustration of the invention and are not intended to be limiting thereof.
 PREATION EXAMPLE 1
 Synthesis of Aromatic Polycarbonate Resin No. 1
 3.23 parts by weight of a diol with charge transporting properties, that
 is, Np{4-[2,2-bis(4-hydroxyphenyl)vinyl]phenyl}-N,N-bis(4-tolyl)amine,
 2.39 parts by weight of a diol serving as a comonomer, that is,
 1,3-bis(4-hydroxyphenoxy)benzene, and 0.02 parts by weight of a molecular
 weight modifier, that is, 4-tert-butyl phenol were placed in a reaction
 container with stirrer.
 The above prepared reaction mixture was dissolved with stirring in a stream
 of nitrogen under the application of heat thereto, with the addition
 thereto of an aqueous solution prepared by dissolving 2.96 parts by weight
 of sodium hydroxide and 0.06 parts by weight of sodium hydrosulfite in 40
 parts by weight of water.
 Thereafter, the reaction mixture was cooled to 20.degree. C. and vigorously
 stirred with the addition thereto of a solution prepared by dissolving
 1.76 parts by weight of bis(trichloromethyl)carbonate, namely, a trimer of
 phosgene, in 33 parts by weight of dichloromethane, thereby forming an
 emulsion. The polymerization reaction was initiated with the emulsion
 being formed.
 The reaction mixture was then stirred for 15 minutes at room temperature.
 With the addition of 0.007 parts by weight of triethylamine serving as a
 catalyst, the reaction mixture was further stirred for 60 minutes at room
 temperature. Then, a solution prepared by dissolving 0.12 parts by weight
 of phenyl chloroformate serving as a terminator in 5 parts by weight of
 dichloromethane was added to the reaction mixture, and the resultant
 mixture was stirred for 60 minutes at room temperature in order to
 continue the reaction.
 Thereafter, by the addition of 200 parts by weight of dichloromethane to
 the reaction mixture, an organic layer was separated. The resultant
 organic layer was successively washed with a 3% aqueous solution of sodium
 hydroxide, a 2% aqueous solution of hydrochloric acid, and water.
 The thus obtained organic layer was added dropwise to large quantities of
 methanol, whereby a yellow polycarbonate resin was precipitated.
 Thus, a polycarbonate resin No. 1 (in the form of a random copolymer)
 according to the present invention was obtained.
 The structural units of the polycarbonate resin No. 1 are shown in TABLE 1
 and the composition ratio of each structural unit is put beside the
 structural unit in TABLE 1, on the supposition that the total number of
 structural units is 1.
 The polystyrene-reduced number-average molecular weight (Mn) and
 weight-average molecular weight (Mw), which were measured by the gel
 permeation chromatography, were respectively 67,200 and 263,000.
 FIG. 7 shows an infrared spectrum of the aromatic polycarbonate resin No.
 1, measured from a cast film on an NaCl plate.
 The IR spectrum indicates the appearance of the characteristic absorption
 peak due to C.dbd.O stretching vibration of carbonate at 1780 cm.sup.-1.
 The glass transition temperature (Tg) of the above obtained aromatic
 polycarbonate resin No. 1 was 147.8.degree. C. when measured by use of a
 differential scanning calorimeter.
 PREATION EXAMPLE 2
 Synthesis of Aromatic Polycarbonate Resin No. 2
 The procedure for preparation of the aromatic polycarbonate resin No. 1 in
 Preparation Example 1 was repeated except that the comonomer diol of
 1,3-bis(4-hydroxyphenoxy) benzene employed in Preparation Example 1 was
 replaced by 1,4-bis(3-hydroxyphenoxy)benzene.
 Thus, an aromatic polycarbonate resin No. 2 in the form of a random
 copolymer according to the present invention was obtained.
 The structural units of the polycarbonate resin No. 2 are shown in TABLE 1.
 The polystyrene-reduced number-average molecular weight (MN) and
 weight-average molecular weight (Mw), which were measured by the gel
 permeation chromatography, were respectively 55,100 and 172,000.
 FIG. 8 shows an infrared spectrum of the aromatic polycarbonate resin No.
 2, measured from a cast film on an NaCl plate.
 The IR spectrum of the aromatic polycarbonate resin No. 2 indicates the
 appearance of the characteristic absorption peak due to C.dbd.O stretching
 vibration of carbonate at 1780 cm.sup.-1.
 The glass transition temperature (Tg) of the above obtained aromatic
 polycarbonate resin No. 2 was 139.0.degree. C. when measured by use of a
 differential scanning calorimeter.
 PREATION EXAMPLE 3
 Synthesis of Aromatic Polycarbonate Resin No. 3
 The procedure for preparation of the aromatic polycarbonate resin No. 1 in
 Preparation Example 1 was repeated except that the comonomer diol of
 1,3-bis(4-hydroxyphenoxy)benzene employed in Preparation Example 1 was
 replaced by 1,4-bis(4-hydroxyphenoxy)benzene.
 Thus, an aromatic polycarbonate resin No. 3 in the form of a random
 copolymer according to the present invention was obtained.
 The structural units of the polycarbonate resin No. 3 are shown in TABLE 1.
 The polystyrene-reduced number-average molecular weight (Mn) and
 weight-average molecular weight (Mw), which were measured by the gel
 permeation chromatography, were respectively 43,700 and 117,000.
 FIG. 9 shows an infrared spectrum of the aromatic polycarbonate resin No.
 3, measured from a cast film on an NaCl plate.
 The IR spectrum of the aromatic polycarbonate resin No. 3 indicates the
 appearance of the characteristic absorption peak due to C.dbd.O stretching
 vibration of carbonate at 1780 cm.sup.-1.
 The glass transition temperature (Tg) of the above obtained aromatic
 polycarbonate resin No. 3 was 157.9.degree. C. when measured by use of a
 differential scanning calorimeter.
 PREATION EXAMPLE 4
 Synthesis of Aromatic Polycarbonate Resin No. 4
 2.87 parts by weight of 1,3-bis(4-hydroxyphenoxy) benzene, 2.62 parts by
 weight of 1,1-bis(4-hydroxyphenyl) cyclohexane, and 0.04 parts by weight
 of a molecular weight modifier, that is, 4-tert-butyl phenol were placed
 in a reaction container with stirrer.
 The above prepared reaction mixture was dissolved with stirring in a stream
 of nitrogen under the application of heat thereto, with the addition
 thereto of an aqueous solution prepared by dissolving 3.9 parts by weight
 of sodium hydroxide and 0.06 parts by weight of sodium hydrosulfite in 40
 parts by weight of water.
 Thereafter, the reaction mixture was cooled to 20.degree. C., and
 vigorously stirred with the addition thereto of a solution prepared by
 dissolving 3.48 parts by weight of bis(trichloromethyl)carbonate, namely,
 a trimer of phosgene, in 33 parts by weight of dichloromethane, thereby
 forming an emulsion. The polymerization reaction was initiated with the
 emulsion being formed.
 The reaction mixture was then stirred for 15 minutes at room temperature.
 With the addition of 0.007 parts by weight of triethylamine serving as a
 catalyst, the reaction mixture was further stirred for 60 minutes at room
 temperature in order to continue the reaction.
 Thereafter, by the addition of 200 parts by weight of dichloromethane to
 the reaction mixture, an organic layer was separated. The resultant
 organic layer was successively washed with a 3% aqueous solution of sodium
 hydroxide, a 2% aqueous solution of hydrochloric acid, and water.
 The thus obtained organic layer was added dropwise to large quantities of
 methanol, whereby a yellow polycarbonate resin was precipitated.
 Thus, a polycarbonate resin No. 4 (in the form of a random copolymer)
 according to the present invention was obtained.
 The structural units of the polycarbonate resin No. 4 are shown in TABLE 1
 and the composition ratio of each structural unit is put beside the
 structural unit in TABLE 1, on the supposition that the total number of
 structural units is 1.
 The polystyrene-reduced number-average molecular weight (MN) and
 weight-average molecular weight (Mw), which were measured by the gel
 permeation chromatography, were respectively 44,500 and 115,000.
 FIG. 10 shows an infrared spectrum of the aromatic polycarbonate resin No.
 4, measured from a cast film on an NaCl plate.
 The IR spectrum indicates the appearance of the characteristic absorption
 peak due to C.dbd.O stretching vibration of carbonate at 1775 cm.sup.-1.
 The glass transition temperature (Tg) of the above obtained aromatic
 polycarbonate resin No. 4 was 125.3.degree. C. when measured by use of a
 differential scanning calorimeter.
 TABLE 1
 Prepara-
 tion Poly-
 Molecular
 Exam- carbonate
 Weight Tg
 ple No. Resin No. Structure of Polycarbonate Resin
 Mn Mw (.degree. C.)
 1 1
 ##STR28##
 67200 263000 147.8
 ##STR29##
 2 2
 ##STR30##
 55100 172000 139.0
 ##STR31##
 3 3
 ##STR32##
 43700 117000 157.9
 ##STR33##
 4 4
 ##STR34##
 44500 115000 125.3
 ##STR35##
 EXAMPLE 1
 [Fabrication of Photoconductor No. 1]
 (Formation of intermediate layer)
 A commercially available polyamide resin (Trademark "CM-8000", made by
 Toray Industries, Inc.) was dissolved in a mixed solvent of methanol and
 butanol, so that a coating liquid for an intermediate layer was prepared.
 The thus prepared coating liquid was coated on an aluminum plate by a
 doctor blade, and dried at room temperature, so that an intermediate layer
 with a thickness of 0.3 .mu.m was provided on the aluminum plate.
 (Formation of charge generation layer)
 A coating liquid for a charge generation layer was prepared by pulverizing
 and dispersing a bisazo compound of the following formula, serving as a
 charge generation material, in a mixed solvent of cyclohexanone and methyl
 ethyl ketone using a ball mill. The thus obtained coating liquid was
 coated on the above prepared intermediate layer by a doctor blade, and
 dried at room temperature. Thus, a charge generation layer with a
 thickness of 0.5 .mu.m was formed on the intermediate layer.
 [Bisazo compound]
 ##STR36##
 (Formation of charge transport layer)
 The aromatic polycarbonate resin No. 1 of the present invention prepared in
 Preparation Example 1, serving as a charge transport material, was
 dissolved in dichloromethane. The thus obtained coating liquid was coated
 on the above prepared charge generation layer by a doctor blade, and dried
 at room temperature and then at 120.degree. C. for 20 minutes, so that a
 charge transport layer with a thickness of 20 .mu.m was provided on the
 charge generation layer.
 Thus, an electrophotographic photoconductor No. 1 according to the present
 invention was fabricated.
 EXAMPLES 2 AND 3
 The procedure for fabrication of the electrophotographic photoconductor No.
 1 in Example 1 was repeated except that the aromatic polycarbonate resin
 No. 1 for use in the charge transport layer coating liquid in Example 1
 was replaced by the aromatic polycarbonate resins No. 2 and No. 3,
 respectively in Examples 2 and 3.
 Thus, electrophotographic photoconductors No. 2 and No. 3 according to the
 present invention were fabricated.
 EXAMPLE 4
 The intermediate layer and the charge generation layer were successively
 overlaid on the aluminum plate in the same manner as in Example 1.
 The following components were mixed to prepare a coating liquid for a
 charge transport layer:

Parts by Weight
 Low-molecular weight charge 0.47
 transport material of the following formula:
 ##STR37##
 Polycarbonate resin No. 4 0.53
 (synthesized in Preparation
 Example 4)
 Dichloromethane 5.7
 The thus prepared charge transport layer coating liquid was coated on the
 above prepared charge generation layer by a doctor blade, and dried at
 room temperature and then at 120.degree. C. for 20 minutes, so that a
 charge transport layer with a thickness of 20 .mu.m was provided on the
 charge generation layer.
 Thus, an electrophotographic photoconductor No. 4 according to the present
 invention was fabricated.
 Each of the electrophotographic photoconductors No. 1 to No. 4 according to
 the present invention fabricated in Examples 1 to 4 was charged negatively
 in the dark under application of -6 kV of corona charge for 20 seconds,
 using a commercially available electrostatic copying sheet testing
 apparatus ("Paper Analyzer Model SP-428" made by Kawaguchi Electro Works
 Co., Ltd.). The surface potential (Vm) of each photoconductor was
 measured.
 Then, each electrophotographic photoconductor was allowed to stand in the
 dark for 20 seconds without applying any charge thereto, and the surface
 potential (Vo) of the photoconductor was measured.
 Each photoconductor was then illuminated by a tungsten lamp in such a
 manner that the illuminance on the illuminated surface of the
 photoconductor was 4.5 lux, and the exposure E.sub.1/2 (lux.multidot.sec)
 required to reduce the initial surface potential Vo (V) to 1/2 the initial
 surface potential Vo (V) was measured.
 The results are shown in TABLE 2.
 TABLE 2
 Example Polycarbonate -Vm -Vo E.sub.1/2
 No. Resin No. (V) (V) (lux .multidot. sec)
 1 No. 1 -1322 -1183 1.34
 2 No. 2 -1082 -904 0.79
 3 No. 3 -1313 -1097 1.35
 4 No. 4 -1485 -1322 1.08
 COMATIVE EXAMPLE 1
 The procedure for fabrication of the electrophotographic photoconductor No.
 1 in Example 1 was repeated except that the aromatic polycarbonate resin
 No. 1 for use in the charge transport layer coating liquid in Example 1
 was replaced by an aromatic polycarbonate resin (described in Japanese
 Laid-Open Patent Application 9-297419) represented by the following
 formula:
 ##STR38##
 The weight-average molecular weight and the number-average molecular weight
 of the above-mentioned aromatic polycarbonate resin were respectively
 627,000 and 106,000.
 Thus, a comparative electrophotographic photoconductor No. 1 was
 fabricated.
 COMATIVE EXAMPLE 2
 The procedure for fabrication of the electrophotographic photoconductor No.
 1 in Example 1 was repeated except that the aromatic polycarbonate resin
 No. 1 for use in the charge transport layer coating liquid in Example 1
 was replaced by an aromatic polycarbonate resin (described in Japanese
 Laid-Open Patent Application 9-297419) represented by the following
 formula:
 ##STR39##
 The weight-average molecular weight and the number-average molecular weight
 of the above-mentioned aromatic polycarbonate resin were respectively
 207,900 and 83,600.
 Thus, a comparative electrophotographic photoconductor No. 2 was
 fabricated.
 The electrophotographic photoconductors Nos. 1 to 3 according to the
 present invention fabricated in Examples 1 to 3 and the comparative
 electrophotographic photoconductors Nos. 1 and 2 fabricated in Comparative
 Examples 1 and 2 were subjected to an abrasion test, using a commercially
 available Taber abrader with truck wheels (CS-5), made by Toyo Seiki
 Seisaku-sho, Ltd.
 The abrasion amount of each photoconductor was measured under the
 application of a load of 1 kg after 3000 rotations.
 The results are shown in TABLE 3.
 TABLE 3
 Example No. Abrasion Amount (mg)
 Example 1 0.71
 Example 2 1.80
 Example 3 1.15
 Comparative Example 1 5.20
 Comparative Example 2 4.30
 The abrasion resistance of the aromatic polycarbonate resins according to
 the present invention is considered to be superior to that of the
 conventional high-molecular weight charge transport materials when the
 results of Examples 1 to 3 are compared with those of Comparative Examples
 1 and 2. Consequently, the photoconductors of the present invention show
 high durability.
 COMATIVE EXAMPLE 3
 The procedure for fabrication of the electrophotographic photoconductor No.
 4 in Example 4 was repeated except that the aromatic polycarbonate resin
 No. 4 for use in the charge transport layer coating liquid in Example 4
 was replaced by a Z type polycarbonate resin (having a viscosity-average
 molecular weight of about 50,000).
 Thus, a comparative electrophotographic photoconductor No. 3 was
 fabricated.
 The electrophotographic photoconductor No. 4 according to the present
 invention fabricated in Example 4 and the comparative electrophotographic
 photoconductor No. 3 fabricated in Comparative Example 3 were similarly
 subjected to the above-mentioned abrasion test.
 The results are shown in TABLE 4.
 TABLE 4
 Example No. Abrasion Amount (mg)
 Example 4 4.34
 Comparative Example 3 5.05
 When the abrasion resistance of the photoconductor of Example 4 is compared
 with that of the photoconductor of Comparative Example 3, it is found that
 the photoconductor No. 4 according to the present invention is superior to
 the comparative photoconductor No. 3 employing the conventional Z-type
 polycarbonate resin.
 Further, each of the electrophotographic photoconductors No. 1 to No. 4
 according to the present invention was set in a commercially available
 electrophotographic copying machine, and the photoconductor was charged
 and exposed to light images via original images to form latent
 electrostatic images thereon. Then, the latent electrostatic images formed
 on the photoconductor were developed into visible toner images by a dry
 developer, and the visible toner images were transferred to a sheet of
 plain paper and fixed thereon. As a result, clear toner images were
 obtained on the paper. When a wet developer was employed for the image
 formation, clear images were formed on the paper similarly.
 As previously explained, the previously mentioned novel polycarbonate
 resins, for example, comprising the structural unit of formula (1) and the
 structural unit of formula (2), according to the present invention can
 provide polymeric materials with minimum mechanical abrasion. In addition,
 these polycarbonate resins can effectively function as photoconductive
 materials in the electrophotographic photoconductor. Such polycarbonate
 resins are optically or chemically sensitized with a sensitizer such as a
 dye or a Lewis acid. These resin compounds are preferably employed as
 charge transport materials in a photoconductive layer of the
 electrophotographic photoconductor, in particular, of a
 function-separating type electrophotographic photoconductor comprising a
 charge generation layer and a charge transport layer because these
 polycarbonate resins are provided with high charge transporting properties
 and high mechanical strength.
 The polycarbonate resin for use in the photoconductive layer of the
 electrophotographic photoconductor according to the present invention
 comprises as an effective component at least the structural unit of
 formula (1). Further, the aromatic polycarbonate resin used in the
 photoconductive layer comprises the structural unit of formula (1) and a
 structural unit having charge transporting properties. Furthermore, a
 polycarbonate resin in the form of a random copolymer comprising the
 structural unit of formula (1) and the structural unit of formula (2) or
 (4), and a polycarbonate resin in the form of an alternating copolymer
 comprising the repeat unit of formula (3) or (5) are employed in the
 electrophotographic photoconductors of the present invention.
 In any case, the polycarbonate resin for use in the present invention
 comprises at least the structural unit of formula (1), so that a polymeric
 material with minimum mechanical abrasion can be provided. When the
 above-mentioned polycarbonate resin is employed in the photoconductive
 layer of the electrophotographic photoconductor, the abrasion resistance
 of the photoconductor is remarkably improved. In particular, the
 polycarbonate resin in the form of a copolymer resin comprising the
 structural unit of formula (1) and the structural unit having charge
 transporting properties has excellent mechanical strength, so that the
 obtained photoconductor can exhibit high sensitivity and high durability.
 Japanese Patent Application No. 10-209554 filed Jul. 24, 1998 and Japanese
 Patent Application No. 10-212637 filed Jul. 28, 1998 are hereby
 incorporated by reference.