| PATENT ASSIGNEE'S COUNTRY | Japan |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 09.01.2001 |
| PATENT TITLE |
Electrophotographic photoconductor and aromatic polycarbonate resin for use therein |
| PATENT ABSTRACT |
An electrophotographic photoconductor has an electroconductive support, and a photoconductive layer which is formed thereon and contains as an effective component an aromatic polycarbonate resin having a structural unit of formula (1), two structural units of formula (1) and (2), or a repeat unit of formula (3): ##STR1## wherein R.sup.1 and R.sup.2, Ar.sup.1 to Ar.sup.8, X, Y, s and n are as specified in the specification. The above-mentioned aromatic polycarbonate resin is provided with charge transporting properties. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | June 22, 1999 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. An aromatic polycarbonate resin comprising a structural unit of formula (1): ##STR1479## wherein R.sup.1 and R.sup.2, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and Ar.sup.8, which may be the same or different, are each an aryl group which may have a substituent; X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent; and s is an integer of 0 or 1. 2. An aromatic polycarbonate resin comprising a structural unit of formula (1) and a structural unit of formula (2), with a composition ratio of said structural unit of formula (1) to said structural unit of formula (2) satisfying a relationship of 0 wherein R.sup.1 and R.sup.2, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substitutent; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and Ar.sup.8, which may be the same or different, are each an aryl group which may have a substitutent; X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent; s is an integer of 0 or 1; and Y is a bivalent aliphatic group, a bivalent cyclic aliphatic group, a bivalent aromatic group, a bivalent group obtained by bonding the above-mentioned bivalent groups, or ##STR1481## in which R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently an alkyl group which may have a substituent, an aryl group which may have a substituent, or a halogen atom; a and b are each independently an integer of 0 to 4; c and d are each independently an integer of 0 to 3; and m is an integer of 0 or 1, provided that when m=1, Z is a straight-chain alkylene group having 2 to 12 carbon atoms, --O--, --S--, --SO--, --SO.sub.2 --, --CO--, ##STR1482## in which Z.sup.1 and Z.sup.2 are each a bivalent aliphatic group which may have a substituent or an arylene group which may have a substituent; and R.sup.7, R.sup.8, R.sup.9, R.sup.10, R.sup.11, R.sup.12 and R.sup.13 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms which may have a substituent, and alkoxyl group having 1 to 5 carbon atoms which may have a substituent, or an aryl group which may have a substituent, and R.sup.7 and R.sup.8 may form a carbocyclic ring or heterocyclic ring having 6 to 12 carbon atoms in combination, or may form a carbocyclic ring or heterocyclic ring in combination with R.sup.3 and R.sup.4 ; p and q are each an integer of 0 or 1, provided that when p and q represent 1, R.sup.14 and R.sup.15 are each an alkylene group having 1 to 4 carbon atoms; R.sup.16 and R.sup.17 are each independently an alkyl group having 1 to 5 carbon atoms which may have a substituent, or an aryl group which may have a substituent; e is an integer of 0 of 4; f is an integer of 0 to 20; and g is an integer of 0 to 2000. 3. The polycarbonate resin as claimed in claim 1, wherein said structural unit of formula (1) is represented by formula (4): ##STR1483## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X and s are respectively the same as defined in formula (1). 4. The polycarbonate resin as claimed in claim 3, wherein said structural unit of formula (4) is represented by formula (6): ##STR1484## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X and s are respectively the same as defined in formula (4). 5. The polycarbonate resin as claimed in claim 4, wherein said structural unit of formula (6) is represented by formula (8): ##STR1485## wherein R.sup.1, R.sup.2, X and s are respectively the same as defined in formula (6); and R.sup.18 and R.sup.19, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substitutent. 6. The polycarbonate resin as claimed as claim 2, wherein said structural unit of formula (1) is represented by formula (4): ##STR1486## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X and s are respectively the same as defined in formula (1). 7. The polycarbonate resin as claimed in claim 6, wherein said structural unit of formula (4) is represented by formula (6): ##STR1487## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X and s are representively the same as defined in formula (4). 8. The polycarbonate resin as claimed in claim 7, wherein said structural unit of formula (6) is represented by formula (8): ##STR1488## wherein R.sup.1, R.sup.2, X and s are respectively the same as defined in formula (6); and R.sup.18 and R.sup.19, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent. 9. An aromatic polycarbonate resin comprising a repeat unit of formula (3): ##STR1489## wherein R.sup.1 and R.sup.2, which may be the same or different, are each a hydrogen atom, and alkyl group which may have a substituent, or an aryl group which may have a substituent; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and Ar.sup.2, which may be the same or different, are each an aryl group which may have a substituent; X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent; s is an integer of 0 or 1; n is an integer of 2 to 5000; and Y is a bivalent aliphatic group, a bivalent cyclic aliphatic group, a bivalent aromatic group, a bivalent group obtained by bonding the above-mentioned bivalent groups, or ##STR1490## in which R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently an alkyl group which may have a substituent, an aryl group which may have a substituent, or a halogen atom; a and b are each independently an integer of 0 to 4; c and d are each independently an integer of 0 to 3; and m is an integer of 0 or 1, provided that when m=1, Z is a straight-chain alkylene group having 2 to 12 carbon atoms, --O--, --S--, --SO--, --SO.sub.2 --, --CO--, ##STR1491## group which may have a substituent or an arylene group which may have a substituent; and R.sup.7, R.sup.8, R.sup.9, R.sup.10, R.sup.11, R.sup.12 and R.sup.13 are each independently a hydrogen atom, a halogen atom, and alkyl group having 1 to 5 carbon atoms which may have a substituent, an alkoxyl group having 1 to 5 carbon atoms which may have a substituent, or an aryl group which may have a substituent, and R.sup.7 and R.sup.8 may form a carbocyclic ring or heterocyclic ring having 6 to 12 carbon atoms in combination, or may form a carbocyclic ring or heterocyclic ring in combination with R.sup.3 and R.sup.4 ; p and q are each an integer of 0 or l, provided that when p and q represent 1, R.sup.14 and R.sup.15 are each an alkylene group having 1 to 4 carbon atoms; R.sup.16 and R.sup.17 are each independently an alkyl group having 1 to 5 carbon atoms which may have a substituent, or an aryl group which may have a substitutent; e is an integer of 0 to 4; f is an integer of 0 to 20; and g is an integer of 0 to 2000. 10. The polycarbonate resin as claimed in claim 9, wherein said repeat unit of formula (3) is represented by formula (5): ##STR1492## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, s, X, Y and n are respectively the same as defined in formula (3). 11. The polycarbonate resin as claimed in claim 10, wherein said repeat unit of formula (5) is represented by formula (7): ##STR1493## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, s, X, Y and n are respectively the same as defined in formula (5). 12. The polycarbonate resin as claimed in claim 11, wherein said repeat unit of formula (7) is represented by formula (9): ##STR1494## wherein R.sup.1, R.sup.2, s, X, Y and n are respectively the same as defined in formula (7); and R.sup.18 and R.sup.19, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent. |
| PATENT DESCRIPTION |
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. In addition, the present invention also relates to the above-mentioned aromatic polycarbonate resin with charge transporting properties. 2. Discussion of Background Recently organic photoconductors (OPC) 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) is a film-shaped layer comprising 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 is fragile and has a low tensile strength. Such lowering of the mechanical strength of the CTL causes the wearing of the photoconductor or forms scratches and cracks on 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 transporting 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 photoconductor. 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 clarified, 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 2,2-bis(4-hydroxyphenyl)propane (hereinafter referred to as bisphenol A) to react with 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. The electrophotographic process is one of the image formation processes, through which the surface of the photoconductor is charged uniformly in the dark to a predetermined polarity, for instance, by corona charge. The uniformly charged photoconductor is exposed to a light image to selectively dissipate the electric charge of the light-exposed area, so that a latent electrostatic image is formed on the photoconductor. The thus formed latent electrostatic image is developed to a visible image by a developer comprising a coloring agent such as a dye or pigment, and a binder agent such as a polymeric material. Fundamental characteristics required for the photoconductor used in such an electrophotographic process are: (1) chargeability to an appropriate potential in the dark, (2) minimum dissipation of electric charge in the dark, and (3) rapid dissipation of electric charge when exposed to light. However, the conventional photoconductive materials are not always satisfactory in light of the above-mentioned fundamental characteristics for the photoconductor and the mechanical durability. 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 show high photosensitivity and high durability. A second 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 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 comprising a structural unit of formula (1): ##STR2## wherein R.sup.1 and R.sup.2, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and Ar.sup.8, which may be the same or different, are each an aryl group which may have a substituent; and s is an integer of 0 or 1, and when s=1, X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent. In the above-mentioned photoconductor, the structural unit of formula (1) may be represented by the following formula (4): ##STR3## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8 and X are the same as those previously defined in formula (1). Further, the structural unit of formula (4) may be represented by formula (6): ##STR4## wherein R.sup.1, R.sup.2 , Ar.sup.5, Ar.sup.8 and X are the same as those previously defined in formula (1). To be more specific, the structural unit of formula (6) may be represented by formula (8): ##STR5## wherein R.sup.1, R.sup.2 and X are the same as those previously defined in formula (1); and R.sup.18 and R.sup.19, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent. The first 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 having the aforementioned structural unit of formula (1) and a structural unit of the following formula (2), with the composition ratio of the structural unit of formula (1) to the structural unit of formula (2) satisfying a relationship of 0 wherein Y is a bivalent aliphatic group, a bivalent cyclic aliphatic group, a bivalent aromatic group, a bivalent group obtained by bonding the above-mentioned bivalent groups, or ##STR7## in which R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are each independently an alkyl group which may have a substituent, an aryl group which may have a substituent, or a halogen atom; a and b are each independently an integer of 0 to 4; c and d are each independently an integer of 0 to 3; and m is an integer of 0 or 1, and when m=1, Z is a straight-chain alkylene group having 2 to 12 carbon atoms, --O--, --S--, --SO--, --SO.sub.2 --, --CO--, ##STR8## in which Z.sup.1 and Z.sup.2 are each a bivalent aliphatic group which may have a substituent or an arylene group which may have a substituent; and R.sup.7, R.sup.8, R.sup.9, R.sup.10, R.sup.11, R.sup.12 and R.sup.13 are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 5 carbon atoms which may have a substituent, an alkoxyl group having 1 to 5 carbon atoms which may have a substituent, or an aryl group which may have a substituent, and R.sup.7 and R.sup.8 may form a carbocyclic ring or heterocyclic ring having 6 to 12 carbon atoms in combination, or may form a carbocyclic ring or heterocyclic ring in combination with R.sup.3 and R.sup.4 ; p and q are each an integer of 0 or 1, when p and q represent 1, R.sup.14 and R.sup.15 are each an alkylene group having 1 to 4 carbon atoms; R.sup.16 and R.sup.17 are each independently an alkyl group having 1 to 5 carbon atoms which may have a substituent, or an aryl group which may have a substituent; e is an integer of 0 to 4; f is an integer of 0 to 20; and g is an integer of 0 to 2000. Furthermore, 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 en effective component an aromatic polycarbonate resin having a repeat unit of formula (3): ##STR9## wherein R.sup.1, R.sup.2, Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.5, Ar.sup.6, Ar.sup.7, Ar.sup.8, X and Y are the same as those previously defined in formulas (1) and (2); and n is an integer of 2 to 5000. In the above-mentioned photoconductor, the repeat unit of formula (3) may be represented by the following formula (5): ##STR10## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X, Y and n are the same as those previously defined in formula (3). Further, the repeat unit of formula (5) may be represented by the following formula (7): ##STR11## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X, Y and n are the same as those previously defined in formula (5). To be more specific, the repeat unit of formula (7) may be represented by the following formula (9): ##STR12## wherein R.sup.1, R.sup.2, R.sup.10, R.sup.15, X, Y and n are the same as those previously defined in formulas (8) and (2). The second object of the present invention can be achieved by an aromatic polycarbonate resin comprising a structural unit of formula (1): ##STR13## wherein R.sup.1 and R.sup.2, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and Ar.sup.6, which may be the same or different, are each an aryl group which may have a substituent; and s is an integer of 0 or 1, and when s=1, X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent. In the above-mentioned polycarbonate resin, the structural unit of formula (1) may be represented by the above-mentioned formula (4), preferably formula (6), and further preferably formula (8). the second object of the present invention can also be achieved by an aromatic polycarbonate resin comprising the aforementioned structural units of formulas (1) and (2), with the composition ratio of the structural unit of formula (1) to the structural unit of formula (2) satisfying a relationship of 0 Furthermore, the above-mentioned second object of the present invention can also be achieved by an aromatic polycarbonate resin comprising a repeat unit of formula (3): ##STR14## wherein R.sup.1, R.sup.2, Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.5, Ar.sup.6, Ar.sup.7, Ar.sup.8, X and Y are the same as those previously defined in formulas (1) and (2); and n is an integer of 2 to 5000. In the above-mentioned aromatic polycarbonate resin, the repeat unit of formula (3) may be represented by the aforementioned formula (5), preferably formula (7), and more preferably formula (9). BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the invention and may of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: FIG. 1 is a schematic cross-sectional view of a first example of an electrophotographic photoconductor according to the present invention. FIG. 2 is a schematic cross-sectional view of a second example of an electrophotographic photoconductor according to the present invention. FIG. 3 is a schematic cross-sectional view of a third example of an electrophotographic photoconductor according to the present invention. FIG. 4 is a schematic cross-sectional view of a fourth example of an electrophotographic photoconductor according to the present invention. FIG. 5 is a schematic cross-sectional view of a fifth example of an electrophotographic photoconductor according to the present invention. FIG. 6 is a schematic cross-sectional view of a sixth example of an electrophotographic photoconductor according to the present invention. FIGS. 7 to 9 are IR spectra of aldehyde compounds respectively synthesized in Preparation Example 1-1 to 1-3, taken by use of a KBr tablet. FIGS. 10 to 13 are IR spectra of aminostilbene compounds respectively synthesized in Preparation Examples 2-1 to 2-4, taken by use of a KBr tablet. FIGS. 14 to 16 are IR spectra of diol compounds (hydroxystilbene compounds) respectively synthesized in Preparation Examples 3-1 to 3-3,taken by use of a KBr tablet. FIGS. 17 to 24 are IR spectra of aromatic polycarbonate resins according to the present invention, respectively synthesized in Examples 1-1 to 1-8, taken by use of a cast film. DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrophotographic photoconductor according to the present invention comprises a photoconductive layer comprising: (i) an aromatic polycarbonate resin comprising at least a structural unit with the charge transporting properties, represented by formula (1), (4), (6) or (8), (ii) an aromatic polycarbonate resin consisting of a structural unit with the charge transporting properties, represented by (1), (4), (6) or (8), (iii) an aromatic polycarbonate copolymer resin comprising a structural unit with the charge transporting properties, represented by formula (1), (4), (6) or (8), and a structural unit of formula (2) for imparting other properties than the charge transporting properties to the obtained resin, and (iv) an aromatic polycarbonate alternating copolymer resin comprising a repeat unit with the charge transporting properties, represented by formula (3), (5), (7) or (9). Those aromatic polycarbonate resins, which are novel compounds, have charge transporting properties and high mechanical strength, so that the electrical, optical and mechanical characteristics required for the charge transport layer of the photoconductor are satisfactory when the polycarbonate resins are used therein. As previously mentioned, the aromatic polycarbonate resin of the present invention comprises the structural unit of formula (1): ##STR15## wherein R.sup.1 and R.sup.2, which may be the same or different, are each a hydrogen atom, and alkyl group which may have a substituent, or an aryl group which may have a substituent; Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and Ar.sup.8, which may be the same or different, are each an aryl group which may have a substituent; and s is an integer of 0 and 1, and when s=1, X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent. It is preferable that the structural unit of formula (1) be represented by the following formula (4): ##STR16## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8 and X are the same as those previously defined in formula (1). Further, the structural unit of formula (4) may be represented by formula (6): ##STR17## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8 and X are the same as those previously defined in formula (1). To be more specific, the structural unit of formula (6) may be represented by formula (8): ##STR18## wherein R.sup.1, R.sup.2 and X are the same as those previously defined in formula (1); and R.sup.18 and R.sup.19, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an aryl group which may have a substituent. In addition, the polycarbonate resin of the present invention comprises the repeat unit of formula (3): ##STR19## wherein R.sup.1, R.sup.2, Ar.sup.1, Ar.sup.2, Ar.sup.3,Ar.sup.4, Ar.sup.5, Ar.sup.6, Ar.sup.7, Ar.sup.8, X and Y are the same as those previously defined in formulas (1) and (2); and n is an integer of 2 to 5000. It is preferable that the repeat unit of formula (3) be represented by the following formula (5): ##STR20## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X, Y and n are the same as previously defined in formula (3). Further, the repeat unit of formula (5) may be represented by the following formula (7): ##STR21## wherein R.sup.1, R.sup.2, Ar.sup.5, Ar.sup.8, X, Y and n are the same as those previously defined in formula (5). To be more specific, the repeat unit of formula (7) may be represented by the following formula (9): ##STR22## wherein R.sup.1 1, R.sup.2, R.sup.18, R.sup.19, X, Y and n are the same as those previously defined. Those aromatic polycarbonate resins according to the present invention 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 of the present invention can be produced by the ester interchange between a diol compound having the charge transporting properties, represented by the following formula (10), (11), (12) or (13) and a bisarylcarbonate compound, or by the polymerization of the above-mentioned diol compound with a halogenated carbonyl compound such as phosgene in accordance with solution polymerization or interfacial polymerization, or by the polymerization of the above-mentioned diol compound with a bischloroformate compound derived from a diol compound in accordance with solution polymerization or interfacial polymerization. ##STR23## wherein R.sup.1 and R.sup.2, Ar.sup.1 to Ar.sup.8, R.sup.18 and R.sup.19, and X are the same as those previously defined in formulas (1) and (8). In addition to the phosgene, trichloromethyl chloroformate that is a dimer of phosgene, and bis(trichloromethyl carbonate that is a trimer of phosgene are usable as the hologenated 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. Those conventional synthesis methods are described in the reference, such as "Handbook of Polycarbonate Resin" (issued by the Nikkan Kogyo Shimbun Ltd.). When a diol of the following formula (14) is employed in combination with the diol of formula (10), (11), (12) or (13) with the charge transporting properties in the course of the polymerization, there can be produced a copolymer polycarbonate resin with improved mechanical characteristics. In this case, a plurality of kinds of diol compounds represented by formula (14) may be employed. OH--Y--OH (14) wherein Y is the same as that previously defined in formula (2). In such a synthesis method, the amount ratio of the diol represented by formula (10), (11), (12) or (13) which is provided with the charge transporting properties to the diol of formula (14) can be selected within a wide range in light of the desired characteristics of the obtained aromatic polycarbonate resin. Further, a variety of copolymers, such as a random copolymer, an alternating copolymer, a block copolymer, a random alternating copolymer, or a random block copolymer can be obtained according to the polymerization procedure. For instance, a random copolymer comprising the structural unit of formula (1), (4), (6) or (8) and the structural unit of formula (2) can be obtained when the diol of formula (10), (11), (12) or (13) with the charge transporting properties and the diol of formula (4) are uniformly mixed prior to the condensation reaction with the phosgene. A random block copolymer can be obtained by adding several diols in the course of the polymerization reaction. Further, an alternating copolymer comprising a repeat unit of formula (3), (5), (7) or (9) can be produced by carrying out the condensation reaction of a bischloroformate compound derived from the diol of formula (14) with the diol having the charge transporting properties, represented by formula (10), (11), (12) or (13). In such a case, the above-mentioned alternating copolymer comprising a repeat unit of formula (3), (5), (7) or (9) can be similarly produced by carrying out the condensation reaction of a bischloroformate compound derived from the diol of formula (10), (11), (12) or (13) with the diol of formula (14). Further, a random alternating copolymer can be produced by employing a plurality of bischloroformate compounds and diol compounds in the course of the aforementioned condensation reaction between the bishcloroformate compound and the diol. 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 high-speed stirring operation or addition of an emulsifying material. As a base for preparing the aforementioned alkaline aqueous solution, 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 ion exchange water are preferably employed for the preparation of the above-mentioned alkaline aqueous solution. Examples of the organic solvent used in the above-mentioned interfacial polymerization are alphatic halogenated hydrocarbon solvents such as dichloromethane, 1,2-dichoroethane, 1,2-dichloroethylene, trichloroethane, tetrachloroethane and dischloropropane; aromatic halogenated hydrocarbon solvents such as chlorobenzene and dichlorobenzene; and mixed solvents thereof. Further, aromatic hydrocarbon solvents such as toluene, xylene and ethylbenzene, and aliphatic hydrocarbon solvents such as hexane and cyclohexane may be added to the above-mentioned solvents. Of those organic solvents, the aliphatic halogenated hydrocarbon solvents and aromatic halogenated hydrocarbon solvents, in particular, dichloromethane and chlorobenzene are preferable in the present invention. Examples of the catalyst used in the preparation of the polycarbonate resin are 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 a catalyst used in the interfacial polymerization include trimethylamine, triethylamine, tri-n-propylamine, tri-n-hexylamine, N,N,N',N'-tetramethyl-1,4-tetramethylene-diamine, 4-pyrrolidinopyridine, N,N'-dimethylpiperazine, N-ethylpiperidine, benzyltrimethylammonium chloride, benzyltriethylammonium chloride, tetrmethylammonium chloride, tetraethylammonium bromide, phenyltriethyl-ammonium chloride, triethylphosphine, triphenylphosphine, diphenylbutylphosphine, tetra(hydroxymethyl)phosphonium chloride, benzyltriethlphosphonium chloride, benzyltriphenylphosphonium chloride, 4-methylpyridine, 1-methylimidazole, 1,2-diemthylimidazole, 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 bishcloroformate are placed in the reaction system, any of the above-mentioned catalysts may be added thereto. To control the molecular weight of the obtained polycarbonate resin, it is desirable to employ a terminator as a molecular weight modifier for 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. Specific examples of the movalent 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 p-methylbenzoic acid, p-tert-butylbenzoic acid, p-butoxybenzoic acid, p-octyloxbenzoic 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 as the terminators. Of those terminators, the monovalent aromatic hydroxy compound, in particular, phenol, p-tert-butylphenol, or p-cumylphenol is preferable. It is preferable that the aromatic polycarbonate resin for use in the photoconductor of the present invention 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 in order to improve the mechanical properties of the obtained polycarbonate resin. Any compounds having 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 agent 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'-hydroxphenyl)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. To prevent the oxidation of the diol in the alkaline aqueous solution, an antioxidant such as hydrosulfite may be used in the interfacial polymerization reaction. 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 bishcloroformate compound, or the phosgene (or dimer and trimer thereof) is added to the above prepared mixture. In this case, tertiary amine compounds such as trimethylamine, trimethylamine and tripropylamine, and pyridine can be used as the deacidifying agent. 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. In addition, the same molecular weight modifier and branching agent as those employed in the interfacial polymerization can be used. The reaction temperature of the solution polymerization is generally in the range of 0 to 40.degree. C. In this case, the 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 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 molecular weight modifier and 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. 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, and then subjected to the preparation of the photoconductive layer of the electrophotographic photoconductor according to the present invention. The previously mentioned "Handbook of Polycarbonate Resin" (issued b 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) for use in the polycarbonate resin according to the present invention will now be explained in detail. In the formula (1), the alkyl group represented by R.sup.1 and R.sup.2 is a straight-chain or branched alkyl group having 1 to 5 carbon atoms. The above alkyl group may have a substituent such as a halogen atom, or a phenyl group which may have a substituent of a straight-chain or branched alkyl group having 1 to 5 carbon atoms. Specific examples of the above alkyl group represented by R.sup.1 and R.sup.2 include methyl group, ethyl group, n-propyl group, isopropyl group, tert-butyl group, sec-butyl group, n-butyl group, isobutyl group, trifluoromethyl group, benzyl group, 4-chlorobenzyl group, and 4-methylbenzyl group. As the aryl group represented by R.sup.1, R.sup.2, Ar.sup.5 and Ar.sup.6, there can be employed phenyl group, naphthyl group, and bisphenylyl group. The aryl group may have as a substituent the above-mentioned substituted or unsubstituted alkyl group. Specific examples of the aryl group represented by R.sup.1,R.sup.2, Ar.sup.5 and Ar.sup.6 include phenyl group, 4-methylphenyl group and 4'-methyl-4-biphenylyl group. As the substituted or unsubstituted arylene group represented by Ar.sup.1, Ar.sup.2, Ar.sup.3, Ar.sup.4, Ar.sup.6, Ar.sup.7 and X, the bivalent groups derived from the substituted or unsubstituted aryl group defined in the description of R.sup.1, R.sup.2, Ar.sup.5 and Ar.sup.8. Specific examples of the alkylene group represented by X include methylene group, ethylene group, 1,3-propylene group, 2,2-propylene group and 1,1-cyclohexylene group. In other formulas than the formula (1), the same examples as defined in the description of formula (1) can be employed so long as the symbol such as R.sup.1, R.sup.2 or Ar.sup.1 for use in the formula is identical. Specific examples of the diol compound represented by formula (10), which is a raw material for the preparation of the polycarbonate resin according to the present invention, are shown in TABLE 1. The previously mentioned hydroxystilbene compounds and aminostilbene compounds for use in the present invention, which are remarkably effective as photoconductive materials in the electrophotographic photoconductor, are optically or chemically sensitized with a sensitizer such as a dye or Lewis acid. In particular, the hydroxystilbene compounds and aminostilbene compounds effectively function as charge transport materials in a function-separating type electrophotographic photoconductor where an organic or inorganic pigment serves as a charge generation material. In this case, there can be employed as the sensitizer triarylmethane dyes such as Methyl Violet and Crystal Violet; xanthene dyes such as Rose Bengale, Erythrosin and Rhodamine B; thiazine dyes such as Methylene Blue; and 2,4,7-trinitro-9-fluorenone and 2,4-dinitro-9-fluorenone. In addition, specific examples of the charge generation material used in the above-mentioned function-separating photoconductor include organic pigments, for example, an azo pigment such as C.I. Pigment Blue 25 (C.I. 21180), C.I. Pigment Red 41 (C.I. 21200) and C.I. Basic Red 3 (C.I. 45210), a phthalocyanine pigment such as C.I. Pigment Blue 16 (C.I. 74100), an indigo pigment such as C.I. Vat Brown 5 (C.I. 73410) and C.I. Vat Dye (C.I. 73030), and a perylene pigment such as Algol Scarlet B and Indanthrene Scarlet R (made by Bayer Co., Ltd.); and inorganic pigments such as selenium, selenium-tellurium, cadmium sulfide, and .alpha.-silicon (amorphous silicon). Furthermore, a variety of materials such as a polycarbonate resin, polyester resin, polyurethane resin and epoxy resin can be obtained by deriving from the hydroxyl group of the above-mentioned hydroxystilbene compound. In other words, the hydroxystilbene compound for use in the present invention is considered to be useful as an intermediate for the preparation of those materials, in particular, the aromatic polycarbonate resin of the present invention. The previously mentioned aldehyde compound represented by formula (19), which is a raw material for the aminostilbene compound of formula (15) will now be explained in detail. ##STR1430## wherein Ar.sup.3, Ar.sup.4, Ar.sup.6 and Ar.sup.7, which may be the same or different, are each an arylene group which may have a substituent; Ar.sup.5 and R.sup.8, which may be the same or different, are each an aryl group which may have a substituent; and s is an integer of 0 or 1, and when s=1, X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent. To be more specific, the following aldehyde compounds of formulas (21) and (22) are usable for the preparation of the aminostilbene compounds in the present invention. ##STR1431## wherein Ar.sup.5 and Ar.sup.8, which may be the same or different, are each an aryl group which may have a substituent; R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35 and R.sup.36, which may be the same or different, are each a hydrogen atom, an alkyl group which may have a substituent, or an alkoxy group which may have a substituent; and s is an integer of 0 or 1, and when s=1, X is --O--, --S--, --SO--, --SO.sub.2 --, --CO--, a straight-chain, branched or cyclic alkylene group having 1 to 12 carbon atoms, or an arylene group which may have a substituent. In the above formulas (21) and (22), specific examples of the alkyl group represented by R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35 and R.sup.36 are lower alkyl groups such as methyl group, ethyl, group, propyl group, and butyl group; and specific examples of the alkoxy group represented by R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35 and R.sup.36 are lower alkoxyl groups such as methoxy group, ethoxy group, and propoxy group. Further, the above-mentioned alkyl group may have a substituent such as phenyl group, a halogen atom, an alkoxyl group or an aryloxy group. The aldehyde compound of formula (19) for use in the present invention is obtained by formylation of a diamine compound, to be more specific, by allowing a diamine compound of the following formula (23) to react with a Vilsmeier reagent to produce an immonium salt intermediate, and the obtained immonium salt is subjected to hydrolysis. ##STR1432## wherein Ar.sup.3 to Ar.sup.8, and X are the same as those previously defined in formula (19). The aforementioned Vilsmeier reagent for use in the present invention can be prepared by the conventional method, that is, by allowing an amide compound such as N,N-dimethylformamide (DMF) or N-methylformanilide (MFA) to react with an acid halide such as phosphoryl chloride, phosphoryl bromide, oxalyl chloride, phosgene, thionyl chloride, triphenylphosphine-Br, or hexachlorotriphosphazatriene in an amount equivalent to the above amide compound. The Vilsmeier reagent may be added in a stoichiometric amount to the diamine compound of formula (23), preferably in an amount of 2 mole or more to one mole of the diamine compound. For producing the aldehyde compound of formula (19) for use in the present invention, the Vilsmeier reagent which has been previously prepared is allowed to react with the diamine compound of formula (23) in a proper solvent. Alternatively, the above-mentioned acid halide is added dropwise to a solution in which the diamine compound of formula (23) and the above-mentioned amide compound are dissolved, thereby carrying out the reaction as generating the Vilsmeier reagent. In the above reaction for the preparation of the aldehyde compound, an inert aromatic hydrocarbon such as benzene, chloroform, dichloroethane, and o-dichlorobenzene are usable as the reaction solvents. Further, the above-mentioned amide compounds may be used as the reaction solvents as they are. The reaction temperature is generally in the range of 0 to 150.degree. C., preferably in the range of 20 to 80.degree. C. The immonium salt thus generated by the above-mentioned reaction between the diamine compound and the Vilsmeier reagent is subjected to hydrolysis in water or an alkaline aqueous solution, so that the aldehyde compound represented by the formula (19) is derived. In this case, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium acetate, or potassium acetate can be used as the alkaline aqueous solution. Likewise, the previously mentioned aldehyde compounds of formulas (21) and (22) can be obtained by formulation of the following diamine compounds of formulas (24) and (25), respectively. ##STR1433## wherein Ar.sup.5, Ar.sup.8, R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35, R.sup.36, and X are the same as those previously defined. Specific examples of the thus prepared aldehyde compound of formula (22) are shown in TABLE 3. TABLE 3 |
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