DE69225736T2 - Electrophotographic photosensitive member, electrophotographic apparatus, device unit and facsimile device using the same - Google Patents

Description

Field of the invention

The present invention relates to an electrophotographic photosensitive member, and more particularly to an electrophotographic photosensitive member consisting of a protective layer containing a specific resin and a photosensitive layer containing a specific compound. The present invention also relates to an electrophotographic apparatus, an apparatus unit and a facsimile machine to which such an electrophotographic photosensitive member is applied.

Related prior art

An electrophotographic photosensitive member must of course have sensitivity, electrical characteristics and optical characteristics necessary for the electrophotographic process. More specifically, a photosensitive member which is repeatedly used is brought into a state in which external electrical and mechanical forces caused during the steps of corona charging, image-wise exposure, development with a toner, transfer to paper and cleaning are directly and repeatedly applied to the surface of the photosensitive member, and therefore it must withstand these external forces. A photosensitive member must particularly exhibit resistance to abrasion and/or cracks caused on its surface by sliding contact with other components during the steps of transfer and cleaning, deterioration of the photosensitive member and potential characteristics due to ozone generated during the step of corona charging, etc. In view of another problem that a toner tends to deteriorate during the repeated steps of development To deposit a toner and clean the surface of a photosensitive element, good cleanability is also required.

In order to satisfy the above-mentioned conditions imposed on photosensitive members, it has been attempted to provide a surface protective layer containing resin as a main component over a photosensitive layer. For example, Japanese Patent Application Laid-Open Nos. 56-42863 and 53-103741 propose the use of a protective layer containing curable resin as a main component to improve hardness and abrasion resistance.

The documents which are equivalent to earlier European patent applications within the meaning of Articles 54(3) and (4) EPC are further discussed below.

EP-A 0 425 224 discloses an electrophotographic element comprising a photoconductive layer and a protective layer coated thereon containing a resin formed by curing certain acrylic compounds. The photosensitive layer contains a charge transport material and the citation refers in this respect to various documents of the patent literature comprising a very large number of groups of organic photoconductive compounds. In one example of this citation a certain hydrazone compound is used.

In EP-A 0 460 558, an electrophotographic photosensitive member is formed by arranging a photosensitive layer and a protective layer in this order on an electrically conductive support, the protective layer being formed from a resin obtained by polymerizing curable acrylic monomer having at least three acrylic groups. As an example of a charge transport substance to be used for the charge transport layer of the photosensitive layer, Example 5 of this document a compound corresponding to the comparative compound example No. (1)-24 shown below was used. Its melting point is therefore 139.0 to 140.0 ºC.

EP-A 0 464 749 discloses an electrophotographic photosensitive member comprising a photoconductive support and a photosensitive layer coated thereon in the form of a resinous layer obtained by polymerizing a certain phosphazene polyene compound. An additional protective layer formed from an acrylic resin is not used in the system of this citation.

However, in the case of using such a curable resin as a surface protective layer, particularly in the case where an underlying photosensitive layer is an organic photosensitive layer which also contains resin as a main component, it has been found that contraction caused by curing the curable resin may cause cracks in the protective layer and/or the photosensitive layer, thereby causing defects in a copied image.

Furthermore, obtaining a higher quality image requires not only that the protective layer of the photosensitive member have properties such as high hardness and excellent abrasion resistance, but also that the protective layer itself have an appropriate resistance. If the resistance of the protective layer is too high, an increase in the so-called residual potential occurs, that is, an accumulation of electric charges in the protective layer by the repeated electrophotographic process of charging and exposure. This results in unstable image quality because the potential is not kept constant during repeated use of the photosensitive member. On the other hand, if the resistance is too low, an electrostatic latent image tends to migrate in the direction of the plane, resulting in a problem such as blurring or feathering. To solve these problems For example, Japanese Laid-Open Patent Application No. 57-30843 proposes adjusting the resistance of a protective layer by adding a metal oxide in the form of fine electrically conductive particles to the protective layer.

However, it has been found that the protective layer and/or the photosensitive layer may crack even in the case of using this proposed protective layer if a curable resin is used as the resin for the protective layer and an organic photosensitive layer is used as the photosensitive layer.

In view of a recent increase in demand for higher image quality and higher durability, investigations and research have been conducted to develop an electrophotographic photosensitive member which has higher durability and can stably provide a higher quality image.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrophotographic photosensitive member which can suppress the occurrence of cracks in the photosensitive member during the formation of a protective layer, exhibits high durability and is free from image defects.

It is another object of the present invention to provide an electrophotographic photosensitive member which can maintain high image quality without accumulation of residual potential by repeated electrophotographic process.

It is still another object of the present invention to provide an electrophotographic apparatus, an apparatus unit and a facsimile machine to which such an electrophotographic photosensitive member is applied.

More specifically, the present invention consists in an electrophotographic photosensitive member comprising a conductive support, a photosensitive layer and a protective layer, wherein the protective layer contains resin formed by curing a photocurable acrylic monomer, and the photosensitive layer contains, as a charge transport material, at least one compound selected from the group consisting of (A), (B) and (C) below:

(A) Styryl compounds having a structure expressed by the following formula (1) and a melting point not higher than 135 ºC:

wherein Ar¹ and Ar² are aromatic ring groups, Ar³ is a divalent aromatic ring group or a divalent heterocyclic group, R¹ is an alkyl group or an aromatic ring group, R² is a hydrogen atom, an alkyl group or an aromatic ring group and n₁ is 1 or 2, wherein R¹ and R² may be joined together to form a ring when n₁ = 1;

(B) Triarylamine compounds having a structure expressed by the following formula (2) and a melting point not higher than 150ºC:

wherein Ar⁴, Ar⁵ and Ar⁴ each represents an aromatic ring group or a heterocyclic group;

(C) Hydrazone compounds having a structure expressed by the following formula (3) and a melting point not higher than 155 ºC is:

wherein R3 is a hydrogen atom or an alkyl group, R4 and R5 are alkyl groups, aralkyl groups or aromatic ring groups, n2 is 1 or 2 and A is an aromatic ring group, a heterocyclic group or -CH=C(R6)R7 (wherein R6 and R7 are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R6 and R7 are not both simultaneously hydrogen atoms)

The present invention further consists in an electrophotographic apparatus, an apparatus unit and a facsimile machine to which the above-mentioned electrophotographic photosensitive member is applied.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows an example of a schematic arrangement of an electrophotographic apparatus to which an electrophotographic photosensitive member of the present invention is applied.

Fig. 2 shows an example of a block diagram of a facsimile machine to which the electrophotographic photosensitive member of the present invention is applied.

DETAILED DESCRIPTION OF THE INVENTION AND EMBODIMENTS

A protective layer contained in an electrophotographic photosensitive member of the present invention contains resin obtained by curing a photocurable acrylic monomer (hereinafter referred to as "acrylic monomer of the present invention").

As an attempt to use curable acrylic resin in a protective layer of a photosensitive element, for example, Japanese Patent Application Laid-Open No. 61-5253 and No. 1-178972 explain the use of thermosetting acrylic resin. However, when such thermosetting acrylic resin is coated on an organic photosensitive layer and cured under heating, a curing agent, an acrylic monomer, an acrylic oligomer, etc. are forced to migrate into the photosensitive layer during the temperature raising process and react with charge transport materials and/or charge generation materials, thereby causing disadvantages such as a reduction in sensitivity and an increase in residual potential.

As a result of conducting various studies in view of the above, the inventors have found that these disadvantages can be eliminated by using the photocurable acrylic monomer.

The resin obtained from the photocurable acrylic monomer also has sufficient hardness, which is one of the important properties required for the protective layer.

Examples of the acrylic monomer of the present invention are listed below, but not in a limitative sense.

In the above formulas, R and R' are given by the following formulas:

The resin used in the present invention may be obtained from two or more photocurable acrylic monomers or may be mixed with other types of resins such as polyester, polycarbonate, polyurethane, acrylic resin, epoxy resin, silicone resin, alkyd resin and copolymer of vinyl chloride and vinyl acetate.

When the acrylic monomer of the present invention is cured, an optical initiator (or photoinitiator) is used. The amount of the optical initiator added is preferably in a range of 0.1 to 40 mass% based on the total mass of the acrylic monomer, and more preferably in a range of 0.5 to 20 mass%. Examples of the optical initiator used are listed below, but not in a limiting sense. Isopropyl or Isobutyl Methyl Ethyl

From the point of view of adjusting the resistance of the protective layer, the protective layer within the scope of the present Invention preferably conductive particles, e.g. metal oxide particles, in a dispersed state.

Examples of such conductive metal oxide particles are particles of zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin-doped indium oxide, antimony-doped tin oxide and zirconium oxide. These metal oxides may be used singly or in a mixed form consisting of two or more kinds. Two or more kinds of metal oxides may be mixed together in the form of a solid solution or a melt. The content of metal oxide particles in the present invention is preferably in a range of 5 to 90 mass% based on the total mass of the protective layer, and more preferably in a range of 10 to 90 mass%. If the content of metal oxide particles is less than 5 mass%, the resistance value of the protective layer may be too high. If it is larger than 90 mass %, the resistance value tends to be lower than a value required for the surface layer of the photosensitive member, resulting in a reduced charging ability and causing pinholes.

When conductive particles are dispersed in the protective layer, the particle size is preferably smaller than the wavelength of the incident light in order to prevent the incident light from being scattered by the dispersed particles. In general, the number-average particle size is preferably less than 0.3 µm. The smaller the particle size of the dispersed particles, the more difficult it is to disperse the particles to be dispersed. It is therefore preferable in the present invention to use a photocurable acrylic monomer having three or more functional groups per molecule or a photocurable acrylic monomer in which the number of functional groups per unit mass is not less than 0.004 mol/g. The larger number of functional groups per molecule is also preferable from the viewpoint of hardness because the resin structure is more likely to become three-dimensional.

In order to further improve the dispersibility, adhesiveness and environmental resistance, any of various coupling agents and/or antioxidants may also be added to the protective layer in the present invention.

The thickness of the protective layer in the context of the present invention is preferably in a range from 0.1 to 10 µm and especially in a range from 0.5 to 7 µm.

The protective coating can be applied by any of methods such as spray coating, jet coating and dip coating.

As mentioned above, in the case of providing a protective layer on an organic photosensitive layer using a curable resin, the protective layer and the photosensitive layer tend to easily be cracked.

Although the exact mechanism of the manner in which the photosensitive member cracks during the application and curing of the protective layer has not yet been clarified, it is undoubtedly believed that a contraction of the layer caused during the curing of the protective layer is involved in the mechanism, and it is easy to imagine that such cracks are also attributable to the structure of the curable monomer for the resin used in the protective layer. In particular, it is believed that the greater the number of functional groups in the monomer per molecule, that is, the greater the number of functional groups in the monomer per unit mass, the more likely the cracks are to occur. However, as mentioned above, the photocurable acrylic monomer as the monomer for the resin used in the protective layer has a higher hardness with an increase in the number of functional groups in the acrylic monomer per molecule or per unit mass, and it is in this case superior in terms of properties such as scratch resistance and resistance to cracking is improved. In addition, in the case where conductive particles are dispersed in the protective layer, the dispersibility is improved as the number of functional groups in the photocurable acrylic monomer increases. Consequently, the advantage obtained by using the photocurable acrylic monomer having the larger number of functional groups as the monomer for resin used in the protective layer is remarkable, and the invention of a method for forming a protective layer on an organic photosensitive layer by using such a resin without causing cracks is very useful.

In view of the above, the inventors have conducted various studies and researches and, as a result, have made the present invention based on the finding that by providing a protective layer of the present invention on a photosensitive layer containing a charge transport material having a specific structure and melting point, a photosensitive member can be prevented from cracking.

More specifically, the present invention consists in an electrophotographic photosensitive member comprising a conductive support, a photosensitive layer and a protective layer, wherein the protective layer contains resin formed by curing a photocurable acrylic monomer, and the photosensitive layer contains at least one compound selected from the group consisting of (A), (B) and (C) below:

(A) Styryl compounds having a structure expressed by the following formula (1) and a melting point not higher than 135 ºC is:

wherein Ar¹ and Ar² are aromatic ring groups, Ar³ is a divalent aromatic ring group or a divalent heterocyclic group, R¹ is an alkyl group or an aromatic ring group, R² is a hydrogen atom, an alkyl group or an aromatic ring group and n₁ is 1 or 2, wherein R¹ and R² may be joined together to form a ring when n₁ = 1;

(B) Triarylamine compounds having a structure expressed by the following formula (2) and a melting point not higher than 150ºC:

wherein Ar⁴, Ar⁵ and Ar⁴ each represents an aromatic ring group or a heterocyclic group;

(C) Hydrazone compounds having a structure expressed by the following formula (3) and a melting point of 2.0 not higher than 155 ºC:

wherein R3 is a hydrogen atom or an alkyl group, R4 and R5 are alkyl groups, aralkyl groups or aromatic ring groups, n2 is 1 or 2 and A is an aromatic ring group, a heterocyclic group or -CH=C(R6)R7 (wherein R6 and R7 are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R6 and R7 are not both simultaneously hydrogen atoms).

In the formula (1), Ar¹ and Ar² each represent an aromatic ring group such as phenyl, naphthyl and anthryl. Ar³ is a divalent aromatic ring group or a divalent heterocyclic group which can be obtained by removing two hydrogen atoms from an aromatic ring such as benzene, naphthalene and anthracene or from a heterocycle such as thiophene and furan. R¹ is an alkyl group such as methyl, ethyl, propyl and butyl or an aromatic ring group such as phenyl and naphthyl. R² is an alkyl group such as methyl, ethyl, propyl and butyl, an aromatic ring group such as phenyl and naphthyl or a hydrogen atom.

Ar¹, Ar², Ar³, R¹ and R² may each have substituents. Examples of possible substituents include an alkyl group such as methyl, ethyl, propyl and butyl; an alkoxy group such as methoxy, ethoxy and propoxy; an aryloxy group such as phenoxy and naphthoxy; a halogen atom such as fluorine, chlorine and bromine or a disubstituted amino group such as dimethylamino, diethylamino and diphenylamino. When n₁ = 1, Furthermore, R¹ and R² may be linked directly or via an atom such as carbon, sulfur and oxygen to form a ring.

In the formula (2), Ar⁴, Ar⁵ and Ar⁴ each represent an aromatic ring group such as phenyl, naphthyl, anthryl, pyrenyl, fluorenyl, phenanthryl, 9,10-dihydrophenanthryl and fluorenonyl or a heterocyclic group such as pyridyl, quinolyl, dibenzothienyl, dibenzofuryl, N-methylcarbazole, N-ethylcarbazole and N-tolylcarbazole.

The aromatic ring groups or the heterocyclic groups of Ar⁴, Ar⁵ and Ar⁶ may each have substituents thereof. Examples of possible substituents include an alkyl group such as methyl, ethyl, propyl and butyl; an aralkyl group such as benzyl, phenethyl and naphthylmethyl; an alkoxy group such as methoxy, ethoxy and propoxy; an aryloxy group such as phenoxy and naphthoxy; a halogen atom such as fluorine, chlorine and bromine; an aromatic ring group such as phenyl and biphenylyl; a diarylamino group such as diphenylamino and ditolylamino; a dialkylamino group such as dimethylamino and diethylamino; a diaralkylamino group such as dibenzylamino and diphenethylamino; an alkylaralkylamino group such as e.g. benzylmethylamino and benzylethylamino; a nitro group or a hydroxyl group.

In the formula (3), R3 is an alkyl group such as methyl, ethyl and propyl, or a hydrogen atom. R4 and R5 each represent an alkyl group such as methyl, ethyl and propyl, an aralkyl group such as benzyl and phenethyl, or an aromatic ring group such as phenyl, naphthyl and anthryl. Note that R4 and R5 may be connected to form a ring. n2 is 1 or 2. R4 and R5 each may have substituents thereof. Examples of possible substituents include an alkyl group such as methyl and ethyl; an alkoxy group such as methoxy and ethoxy; or a halogen atom such as fluorine, chlorine and bromine.

A is an aromatic ring group such as phenyl, naphthyl, anthryl and pyrenyl; a heterocyclic group such as thienyl, furyl, N-methylcarbazole and N-ethylcarbazole or -CH=C(R⁶)R⁷ (wherein R⁶ and R⁷ are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R⁶ and R⁷ are not both hydrogen atoms at the same time). These aromatic ring groups and heterocyclic groups may have substituents. Examples of substituents include an alkyl group such as methyl and ethyl; an alkoxy group such as methoxy and ethoxy; a halogen atom such as fluorine, chlorine and bromine; a dialkylamino group such as dimethylamino and diethylamino; a diaralkylamino group such as dibenzylamino and diphenethylamino or a diarylamino group such as diphenylamino and di-(p-tolyl)-amino.

Below are listed styryl compounds having the structure expressed by the formula (1) and their melting points. Of the compound examples, Nos. (1)-1 to (1)-22 are styryl compounds having a melting point not higher than 135 ºC used in the present invention, while Nos. (1)-23 to (1)-40 are styryl compounds having the structure expressed by the formula (1) but whose melting points are higher than 135 ºC, so that they are outside the scope of the present invention. It should be understood that the types of styryl compounds usable in the present invention are of course not limited to the following examples.

Below are triarylamine compounds having the structure expressed by formula (2) and their melting points Of the compound examples, numbers (2)-1 to (2)-45 are triarylamine compounds with a melting point not higher than 150 °C used in the present invention, while Nos. (2)-46 to (2)-72 are triarylamine compounds having the structure expressed by the formula (2) but whose melting points are higher than 150 °C, so that they are outside the scope of the present invention. It should be understood that the kinds of triarylamine compounds usable in the present invention are of course not limited to the following examples.

Below are hydrazone compounds having the structure expressed by formula (3) and their melting points Of the connection examples, Nos. (3)-1 to (3)-27 Hydrazone compounds with a melting point, which is not higher than 155 °C used in the present invention, while Nos. (3)-28 to (3)-47 are hydrazone compounds having the structure expressed by the formula (3) but whose melting points are higher than 155 °C, so that they are outside the scope of the present invention. It should be understood that the kinds of hydrazone compounds usable in the present invention are of course not limited to the following examples.

In the present invention, the photosensitive layer of the electrophotographic photosensitive member may have either a single-layer structure in which a charge generation material and a charge transport material are contained in the same layer, or a layered structure in which a charge transport layer containing a charge transport material and a charge generation layer containing a charge generation material are functionally separated from each other.

Now, the photosensitive layer having the layered structure will be described. The arrangement of the photosensitive layer having the layered structure is classified into two types, one of which is formed by layering the charge-transport layer over the charge-generation layer and the other of which is formed by layering the charge-generation layer over the charge-transport layer.

The charge transport layer used in the present invention is formed by at least one of the compounds (A), (B) and (C) as a charge transport material is dissolved in resin exhibiting film-forming ability, using a suitable solvent to prepare a coating solution, and then applying and drying the coating solution. As such a resin, in addition to the resin obtained by curing the acrylic monomer of the present invention, any kind of resin which has been conventionally used for the charge transport layer can be used, and includes, for example, polyester, polycarbonate, polymethacrylic acid and polystyrene. The thickness of the charge transport layer is preferably in a range of 5 to 40 µm, and more preferably in a range of 10 to 30 µm. In the present invention, any suitable charge transport materials other than the compounds (A), (B) and (C) can be further added to the charge transport layer.

The charge generation layer in the present invention is formed by dispersing a charge generation material in a binder resin to prepare a dispersion solution, and then applying and drying the dispersion solution. As such a binder resin, the resin of the present invention obtained by curing acrylic monomer can be used, and includes, for example, polyvinyl butyral, polystyrene, polyvinyl acetate, acrylic resin, cellulose acetate and ethyl cellulose. Examples of the charge generation material include azo pigments such as Sudan red and Dian blue; quinone pigments such as pyrenequinone and anthathrone; quinocyanine pigments; perylene pigments; indigo pigments such as indigo and thioindigo; azulenium salt pigments or phthalocyanine pigments such as copper phthalocyanine and titanyl phthalocyanine. The thickness of the charge generation layer is preferably not greater than 5 µm and in particular in a range of 0.05 to 2 µm.

Next, the photosensitive layer having a single-layer structure is described. The photosensitive layer having a single-layer structure is formed, by preparing a solution in which at least one of the compounds (A), (B) and (C) and the charge generation material are dissolved and dispersed in the above-mentioned resin, and then coating and drying the solution. The thickness of the photosensitive layer having a single-layer structure is preferably in a range of 5 to 40 µm, and more preferably in a range of 10 to 30 µm.

The conductive support for use in the present invention may be made of any material as long as it exhibits conductivity, and the material includes, for example, a metal or alloy such as aluminum, chromium, nickel, stainless steel, copper and zinc; a composite material formed by overlaying a plastic film with a metal film such as aluminum and copper; another composite material formed by coating a plastic film with aluminum, indium oxide, tin oxide and the like by vacuum deposition; or a metal, plastic film, paper and the like on which a conductive layer has been provided by applying a conductive material (alone or together with a suitable binder resin).

Examples of the conductive material used in this conductive layer include powder, foil and fiber of a metal such as aluminum, copper, nickel, and silver; a conductive metal oxide such as antimony oxide, indium oxide and tin oxide; a high molecular conductive material such as polypyrrole, polyaniline and high molecular electrolyte; carbon black, graphite powder and an organic or inorganic electrolyte or conductive powder whose surface is coated with any of these conductive materials.

Although the conductive support may be in the form of a drum, sheet, belt or the like, the support is preferably formed in any desired shape that is optimal for the electrophotographic apparatus in which it is used.

In addition, an undercoat layer may be provided which is interposed between the conductive support and the photosensitive layer. The undercoat layer acts as a barrier layer for controlling the injection of charges at the interface between itself and the photosensitive layer and/or as a bonding layer therebetween. The undercoat layer is mainly composed of binder resin, but may contain any of the above-mentioned metals and alloys or oxides and salts thereof and surfactants. Examples of the binder resin constituting the undercoat layer are polyester, polyurethane, polyacrylate, polyethylene, polystyrene, polybutadiene, polycarbonate, polyamide, polypropylene, polyimide, phenolic resin, acrylic resin, silicone resin, epoxy resin, urea resin, allyl resin, alkyd resin, polyamideimide, nylon, polysulfone, polyallyl ether, polyacetal and butyral resin. The layer thickness of the underlayer is preferably in a range of 0.05 to 7 µm and especially in a range of 0.1 to 2 µm.

Each of the above-mentioned layers can be formed by using vapor deposition and coating. Above all, the coating method is preferable because it can form many different layers from thin to thick with different compositions. The coating method includes, for example, dip coating, spray coating, jet coating, bar coating, doctor blade coating and roll coating.

The electrophotographic photosensitive member of the present invention is applicable not only to electrophotographic copying machines but also to a wide field of electrophotography such as laser beam printers, cathode ray tube printers, light emitting diode printers, liquid crystal printers, facsimile machines and laser printing machines.

Fig. 1 shows an example of the schematic arrangement of a transfer electrophotographic apparatus in which an electrophotographic photosensitive member of the present invention is applied.

In Fig. 1, 1 denotes a drum-shaped electrophotographic photosensitive member of the present invention which serves as an image carrier and is driven to rotate in the direction of an arrow at a prescribed peripheral speed around a shaft la. While making one revolution, the photosensitive member 1 is uniformly charged to a prescribed positive or negative potential on the peripheral surface and then subjected to optical image-wise exposure L (such as slit exposure and laser beam scanning exposure) at an exposure section 3 by an image-wise exposure device (not shown). Through the above-mentioned steps, an electrostatic latent image corresponding to the exposure image is formed on the peripheral surface of the photosensitive member in sequence.

Thereafter, the electrostatic latent image is developed by a developing device 4 using toner, and the developed toner image is transferred by a transfer device 5 in sequence between the photosensitive member 1 and the transfer device 5 in synchronism with the rotation of the photosensitive member 1 onto the surface of a transfer material P fed from a paper feed device (not shown).

The transfer or image receiving material P with the image transferred thereon is separated from the surface of the photosensitive element and introduced into an image fixing device 8 to fix the image, whereupon it is printed out outside the device as a reproduction product (copy).

After the image transfer, the surface of the photosensitive member 1 is cleaned by a cleaning device 6 to remove the remaining toner and the charges, which remain on the surface are removed by a pre-exposure device 7, whereupon the image formation is repeated.

As the means 2 for uniformly charging the photosensitive member 1, a corona charging means is generally often used. Also, as the transfer means 5, a corona charging means is generally often used. The electrophotographic apparatus may be arranged such that at least two of the above-mentioned components such as the photosensitive member, the developing means and the cleaning means are combined into a device unit which is detachably attached to the device body. For example, it is also possible to combine the photosensitive member 1 and the cleaning means 6 into a single device unit and to detachably attach the unit to the device body by a guide means such as rails arranged in the device body. In this case, further, the charging means and/or the developing means may be built into the device unit.

In the case where the electrophotographic apparatus is applied as a copying machine or a printer, the optical image-wise exposure L is carried out by receiving the light reflected from or passed through an original or by directly reading the original to convert it into an electric signal and then performing scanning with a laser beam driving a light emitting diode array or driving a liquid crystal shutter array in response to the electric signal.

In the case where the electrophotographic apparatus is used as a printer for a facsimile machine, the optical image-wise exposure L is carried out to to print data. Fig. 2 shows an example of this case in the form of a block diagram.

A control device 11 controls an image reading part 10 and a printer 19. The entire control device 11 is controlled by a central processing unit 17. The data read from the image reading part 10 are transmitted to a remote data station (partner station) via a transmission circuit 13. The data received from the remote data station (partner station) are transmitted to the printer 19 via a reception circuit 12. An image memory 16 stores prescribed image data therein. A printer control unit 18 controls the printer 19. A telephone is designated by 14.

The image data received from a line 15 (i.e. the image data received from a remote data station connected via the line) are demodulated by the receiving circuit 12, decoded by the central processing unit 17 and then stored in sequence in the image memory 16. When the image data of at least one page has been stored in the image memory 16, an image-wise recording of this page takes place. The central processing unit 17 reads the image data of a page from the image memory 16 and transmits the decoded image data of a page to the printer control unit 18. When the image data of a page is received from the central processing unit 17, the printer control unit 18 controls the printer 19 so that the recording of the image data of this page is carried out.

Note that the CPU 17 receives the image data of the next page during recording by the printer 19.

In this way, the reception and recording of images is carried out.

The present invention is further described by the following examples.

example 1

10 parts of an alcohol-soluble copolyamide resin (weight average molecular weight: 29,000) and 30 parts of a methoxymethylpolyamide-6 resin (weight average molecular weight: 32,000) were dissolved in a mixed solvent of 260 parts of methanol and 40 parts of butanol. The mixture was coated onto a glass substrate by dipping to form a 1 µm thick undercoat layer.

10 parts of the above-mentioned styryl compound example (1)-4 as a charge transport material was dissolved together with 10 parts of a polycarbonate (weight average molecular weight: 46,000) in a mixed solvent of 20 parts of methylene chloride and 40 parts of chlorobenzene. This solution was coated on the above-mentioned undercoat layer by dipping and dried at 120 °C for 60 minutes to form a charge transport layer having a layer thickness of 18 µm.

Four parts of a bisazo pigment represented by the following formula, 2 parts of a polyvinyl butyral (butyralization degree: 68%, weight average molecular weight: 24,000) and 34 parts of cyclohexanone were dispersed for 12 hours by a sand mill apparatus using glass beads having a diameter of 1 mm.

Then, a dispersion liquid for a charge generation layer was prepared by adding 60 parts of tetrahydrofuran (THF) into the above-mentioned dispersed mixture. The dispersion liquid was applied to the above-mentioned charge transport layer by spraying and then dried at 80 °C for fifteen minutes to form a charge generation layer having a layer thickness of 0.20 µm. to form a photosensitive layer having a layered structure.

Then, 60 parts of the above-mentioned acrylic monomer compound example (20), 30 parts of ultrafine tin oxide particles having an average particle diameter of 400 Å before dispersion, 2 parts of 2-methylthioxanthone as a photoinitiator, 100 parts of toluene and 200 parts of Cellosolve were dispersed by the sand mill for 48 hours.

A layer was formed on the photosensitive layer by jet coating using the dispersion liquid and then dried. A protective layer was obtained by curing with light using a high pressure mercury lamp with an intensity of 8 mW/cm2 for 20 seconds. The layer thickness of the protective layer was 4 µm. The dispersion in the liquid mixture for the protective layer was good and its surface was uniform without unevenness.

The photosensitive member thus formed was observed with a transmission microscope with backlight at an angle of 15º to check the extent of cracks that had occurred. The evaluation was carried out with three ranks of , Δ and ×, with the microscope judging based on the appearance or occurrence of cracks in the entire field of view at 10x magnification. Δ means "no cracks", Δ means "not more than five relatively small cracks of not more than 1 cm" and × means "more than five cracks or one or more than one layer crack of more than 1 cm".

A similar evaluation was carried out on photosensitive members prepared with other styryl compounds listed in Table 1. The evaluation results are also shown in Table 1. TABLE 1

As shown in Table 1, as the melting point of the charge transport substance decreases, the occurrence of cracks also decreases and becomes zero at and below 135 ºC.

Example 2

A coating material for a conductive layer was prepared by dispersing 50 parts of a conductive titanium oxide powder coated with tin oxide containing 10% antimony oxide, 25 parts of phenol resin, 20 parts of methyl cellosolve, 5 parts of methanol and 0.002 part of silicone oil (polydimethylsiloxanepolyoxyalkylene copolymer, average molecular weight: 3000) for two hours by the sand mill device using the glass beads having a diameter of 1 mm. The coating material was coated on an aluminum cylinder (30 mm Ø x 260 mm) by dipping and evaporated for thirty minutes at 140 ºC. In this way, a conductive layer with a layer thickness of 20 µm was formed.

Then, an undercoat layer was formed by the same method as in Example 1, and thereon, a photosensitive layer and a protective layer were sequentially coated by the same method as in Example 1 except that the above-mentioned styryl compound example No. (1)-17 was used as the charge transport material, to obtain a photosensitive member.

The electrophotographic photosensitive member thus formed was mounted in a positive development copying machine, in which a 1.5 second cycle of charging, exposure, development, transfer and cleaning processes was repeated. Electrophotographic characteristics were evaluated under ordinary temperature and ordinary humidity, and as a durability test, image formation was repeated 10,000 times.

Results are shown in Table 2. As shown in Table 2, the photosensitive member of Example 2 exhibited a sensitivity and residual potential equivalent to those of a photosensitive member of Comparative Example 1 without a protective layer while maintaining stable images without unevenness and black spots. The photosensitive member of the present invention also provided the stable images without causing image deterioration such as a black streak, i.e., an image defect in the form of a black band.

Examples 3 to 7

Photosensitive members were prepared in the same manner as in Example 2 except that the above-mentioned styryl compound examples Nos. (1)-7, (1)-9, (1)-13, (1)-16 and (1)-20 were used as the charge transport material and the above-mentioned monomer examples (2), (7), (13), (15) and (18), respectively, and evaluated in a similar manner.

Results are shown in Table 2.

Example 8

A conductive layer and an underlayer were provided on an aluminum cylinder in the same manner as in Example 2.

4 parts of a bisazo pigment represented by the following formula, 2 parts of a polyvinylbenzal (benzalization degree: 80%, weight average molecular weight: 11,000) and 30 parts of cyclohexanone were dispersed for 20 hours by the sand mill apparatus using the glass beads of 1 mm ∅

Then, a dispersion liquid for a charge generation layer was prepared by adding 60 parts of methyl ethyl ketone into the above-mentioned dispersed mixture.

The dispersion liquid was applied to the above-mentioned undercoat layer by spraying and then dried at 80 °C for fifteen minutes to form a charge generation layer having a layer thickness of 0.20 µm.

10 parts of the above-mentioned styryl compound example (1)-21 as a charge transport material were then mixed together with 10 parts of a polycarbonate (weight average molecular weight: 25,000) dissolved in a mixed solvent of 20 parts of methylene chloride and 40 parts of chlorobenzene. This solution was coated on the above-mentioned charge generation layer by dipping and dried at 120 ºC for 60 minutes to form a charge transport layer having a layer thickness of 15 µm.

An electrophotographic photosensitive member was obtained by forming a protective layer on the charge transport layer in the same manner as in Example 2.

The electrophotographic photosensitive member thus formed was mounted in a laser printer for reversal development, in which a 1.5 second cycle of charging, laser exposure, development, transfer and cleaning processes was repeated. Electrophotographic characteristics were evaluated at ordinary temperature and pressure, and as a durability test, image formation was repeated 10,000 times.

Results are shown in Table 2.

Example 9

Layers up to the photosensitive layer were formed in the same manner as in Example 8. Then, a liquid mixture of 20 parts of the above-mentioned acrylic monomer example (21), 30 parts of methanol, 50 parts of methoxypropanol and 2 parts of 2-methylthioxanthone as a photoinitiator was coated on the photosensitive layer by dipping and dried at 60 °C for one hour. After drying, it was subjected to light curing with the high pressure mercury lamp in the same manner as in Example 1 to obtain a protective layer. The layer thickness of the protective layer was 0.8 µm. The obtained photosensitive member was evaluated in the same manner as in Example 8.

Results are shown in Table 2.

Examples 10 to 12

Photosensitive members were prepared in the same manner as in Example 2 except that their charge transport materials were prepared from the following mixtures, and evaluated in a similar manner.

Example 10: Styryl compound example No. (1)-15: 50 parts, No. (1)-29: 50 parts

Example 11: Styryl compound example No. (1)-3: 20 parts, No. (1)-30: 80 parts

Example 12: Styryl compound example No. (1)-21: 60 parts, No. (1)-31: 40 parts

Results are shown in Table 2.

Comparison example 1

A photosensitive member was prepared in the same manner as in Example 2 except that no protective layer was formed and evaluated in a similar manner. Results are shown in Table 2. As shown in Table 2, the photosensitive member of Comparative Example 1 initially showed good electrophotographic properties, but after the durability test of 300 sheets, it was difficult to form good images therewith due to abrasion of the surface of the charge generation layer.

Comparison example 2

A photosensitive member was prepared in the same manner as in Example 2 except that the binder resin in the protective layer was a polycarbonate resin. Using the photosensitive member, evaluation was carried out in a similar manner to Example 2.

Results are shown in Table 2.

comparative examples 3 to 5

Photosensitive members were prepared in the same manner as in Example 2 except that the above-mentioned styryl compound examples Nos. (1)-26, (1)-28 and (1)-38 were used as the charge transport material, and evaluated in a similar manner.

Results are shown in Table 2. TABLE 2

Example 13

Photosensitive members were prepared in the same manner as in Example 1 except that the triarylamine compounds shown in Table 3 were used as the charge transport material, and evaluated in a similar manner.

Results are shown in Table 3. TABLE 3

As shown in Table 3, as the melting point of the charge transport substance decreases, the occurrence of cracks also decreases and becomes zero at and below 150 ºC.

Example 14

A photosensitive member was prepared in the same manner as in Example 2 except that the above-mentioned triarylamine compound example No. (2)-18 was used as the charge transport material, and evaluated in a similar manner.

Results are shown in Table 4. As shown in Table 4, the photosensitive member of Example 14 exhibited a sensitivity and residual potential equivalent to those of a photosensitive member of Comparative Example 6 without a protective layer while maintaining stable images without unevenness and black spots. The photosensitive member of the present invention also provided the stable images without causing image deterioration such as a black streak, i.e., an image defect in the form of a black band.

Examples 15 to 19

Photosensitive members were prepared in the same manner as in Example 2 except that as the charge transport material the above-mentioned triarylamine compound examples Nos. (2)-4, (2)-17, (2)-19, (2)-30 and (2)-38 were used, respectively, and as the acrylic monomer for the protective layer, the above-mentioned monomer examples (2), (7), (13), (15) and (18) were used, respectively, and evaluated in a similar manner.

Results are shown in Table 4.

Example 20

A photosensitive member was prepared in the same manner as in Example 8 except that the thickness of the charge generation layer was 0.10 µm and that the above-mentioned triarylamine compound example No. (2)-8 was used as the charge transport material, and evaluated in a similar manner. Results are shown in Table 4.

Example 21

Layers up to the photosensitive layer were formed in the same manner as in Example 20. Then, a photosensitive element was prepared in the same manner as in Example 9 except that Compound Example No. (20) was used as the acrylic monomer, and evaluated in a similar manner.

Results are shown in Table 4.

Examples 22 to 24

Photosensitive members were prepared in the same manner as in Example 14 except that their charge transport materials were prepared from the following mixtures, and evaluated in a similar manner.

Example 22: Triarylamine Compound Example No. (2)-3: 50 parts, No. (2)-50: 50 parts

Example 23: Triarylamine compound example No. (2)-18: 20 parts, No. (2 )-53: 80 parts

Example 24: Triarylamine Compound Example No. (2)-40: 60 parts, No. (2)-57: 40 parts

Results are shown in Table 4.

Comparison example 6

A photosensitive member was prepared in the same manner as in Example 14 except that no protective layer was formed, and evaluated in a similar manner.

Results are shown in Table 4. As shown in Table 4, the photosensitive member of Comparative Example 6 showed good electrophotographic properties at the beginning, but after the durability test of 300 sheets, it was difficult to form good images due to abrasion of the surface of the charge generation layer.

Comparison example 7

A photosensitive member was prepared in the same manner as in Example 14 except that the binder resin in the protective layer was a polycarbonate resin. Using the photosensitive member, evaluation was carried out in a similar manner to Example 14.

Results are shown in Table 4.

Comparative examples 8 to 10

Photosensitive members were prepared in the same manner as in Example 14 except that the above-mentioned triarylamine compound examples Nos. (2)-53, (2)-59 and (2)-72 were used as the charge transport material, respectively, and evaluated in a similar manner.

Results are shown in Table 4. TABLE 4

Example 25

Photosensitive elements were prepared in the same manner as in Example 1, except that the hydrazone compounds listed in Table 5 were used as the charge transport material, and evaluated in a similar manner.

Results are shown in Table 5. TABLE 5

As shown in Table 5, as the melting point of the charge transport substance decreases, the occurrence of cracks also decreases and becomes zero at and below 155 ºC.

Example 26

A photosensitive member was prepared in the same manner as in Example 2 except that the above-mentioned Hydrazone Compound Example No. (3)-17 was used as the charge transport material, and evaluated in a similar manner.

Results are shown in Table 6. As shown in Table 6, the photosensitive member of Example 26 exhibited a sensitivity and residual potential equivalent to those of a photosensitive member of Comparative Example 11 without a protective layer, while maintaining stable images without unevenness and black spots. The photosensitive member of the present invention also provided the stable images without any image deterioration such as a black stripe, ie an image defect in the form of a black band, occurring.

Examples 27 to 31

Photosensitive members were prepared in the same manner as in Example 2 except that as the charge transport material the above-mentioned hydrazone compound examples Nos. (3)-4, (3)-13, (3)-15, (3)-18, and (3)-27 were used, respectively, and as the acrylic monomer for the protective layer, the above-mentioned monomer examples (2), (7), (13), (15), and (18) were used, respectively, and evaluated in a similar manner.

Results are shown in Table 6.

Example 32

A photosensitive member was prepared in the same manner as in Example 8 except that the thickness of the charge generation layer was 0.10 µm and that the above-mentioned hydrazone compound example No. (3)-19 was used as the charge transport material, and evaluated in a similar manner.

Results are shown in Table 6.

Example 33

Layers up to the photosensitive layer were formed in the same manner as in Example 32. Then, a photosensitive member was prepared in the same manner as in Example 9 except that Compound Example No. (20) was used as the acrylic monomer, and evaluated in a similar manner.

Results are shown in Table 6.

Examples 34 to 36

Photosensitive members were prepared in the same manner as in Example 26 except that their charge transport materials were prepared from the following mixtures, and evaluated in a similar manner.

Example 34: Hydrazone compound example No. (3)-7: 50 parts, No. (3)-29: 50 parts

Example 35: Hydrazone compound example No. (3)-4: 20 parts, No. (3)-28: 80 parts

Example 24: Hydrazone compound example No. (3)-11: 60 parts, No. (3)-31: 40 parts

Results are shown in Table 6.

Comparison example 11

A photosensitive member was prepared in the same manner as in Example 26 except that no protective layer was formed, and evaluated in a similar manner.

Results are shown in Table 6. As shown in Table 6, the photosensitive member of Comparative Example 11 showed good electrophotographic properties at the beginning, but after the durability test of 300 sheets, it was difficult to form good images due to abrasion of the surface of the charge generation layer.

Comparison example 12

A photosensitive member was prepared in the same manner as in Example 26 except that the binder resin in the protective layer was a polycarbonate resin. Using the photosensitive member, evaluation was carried out in a similar manner to Example 26.

Results are shown in Table 6. Comparative Examples 13 to 15 Photosensitive members were prepared in the same manner as in Example 26 except that the above-mentioned Hydrazone Compound Example Nos. (3)-32, (3)-35 and (3)-40 were used as the charge transport material, respectively, and evaluated in a similar manner.

Results are shown in Table 6. TABLE 6

As is apparent from the above, the present invention can provide an electrophotographic photosensitive member in which the photosensitive member is provided with a protective layer having high hardness and excellent durability without cracking, and in which the photosensitive member can provide high quality images without unevenness or without image defects from the beginning until after a considerable number of repeated uses.

Further, conductive microparticles may be dispersed in the protective layer in the present invention. Their excellent dispersibility and dispersion stability contribute to stable delivery of higher quality images having high transparency and durability while exhibiting no residual potential.

Claims (26)

1. An electrophotographic photosensitive member comprising a conductive support, a photosensitive layer and a protective layer, wherein said protective layer contains resin formed by curing an acrylic monomer with light, and said photosensitive layer contains as a charge transport material at least one compound selected from the group consisting of (A), (B) and (C) below: (A) Styryl compounds having a structure expressed by the following formula (1) and a melting point not higher than 135 ºC: wherein Ar¹ and Ar² are aromatic ring groups, Ar³ is a divalent aromatic ring group or a divalent heterocyclic group, R¹ is an alkyl group or an aromatic ring group, R² is a hydrogen atom, an alkyl group or an aromatic ring group and n₁ is 1 or 2, wherein R¹ and R² may be linked to form a ring when n₁ = 1; (B) Triarylamine compounds having a structure expressed by the following formula (2) and a melting point not higher than 150ºC: wherein Ar⁴, Ar⁵ and Ar⁴ each represents an aromatic ring group or a heterocyclic group; (C) Hydrazone compounds having a structure expressed by the following formula (3) and a melting point not higher than 155 ºC is: wherein R3 is a hydrogen atom or an alkyl group, R4 and R5 are alkyl groups, aralkyl groups or aromatic ring groups, n2 is 1 or 2 and A is an aromatic ring group, a heterocyclic group or -CH=C(R6)R7 (wherein R6 and R7 are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R6 and R7 are not both simultaneously hydrogen atoms). 2. An electrophotographic photosensitive member according to Claim 1, wherein said compound is (A). 3. An electrophotographic photosensitive member according to Claim 1, wherein said compound is (B). 4. An electrophotographic photosensitive member according to Claim 1, wherein said compound is (C). 5. An electrophotographic photosensitive member according to claim 1, wherein said photocurable acrylic monomer has three or more functional groups per molecule. 6. An electrophotographic photosensitive member according to claim 1, wherein said photocurable acrylic monomer has not less than 0.004 mol of functional groups/g. 7. An electrophotographic photosensitive member according to claim 1, wherein said protective layer contains conductive particles. 8. An electrophotographic photosensitive member according to claim 7, wherein said conductive particles are metal oxide particles. 9. An electrophotographic photosensitive member according to claim 1, wherein said protective layer contains an adhesive and/or an antioxidant. 10. An electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer comprises a charge generation layer and a charge transport layer. 11. An electrophotographic photosensitive member according to claim 10, wherein said electrophotographic photosensitive member comprises a conductive support, a charge generation layer and a charge transport layer arranged in this order. 12. An electrophotographic photosensitive member according to claim 10, wherein said electrophotographic photosensitive member comprises a conductive support, a charge transport layer and a charge generation layer arranged in this order. 13. An electrophotographic photosensitive member according to claim 1, wherein said photosensitive layer is a single layer. 14. An electrophotographic photosensitive member according to claim 1, wherein said electrophotographic photosensitive member has an undercoat layer interposed between said conductive support and said photosensitive layer. 15. An electrophotographic apparatus comprising an electrophotographic photosensitive member, means for forming an electrostatic latent image, means for developing an electrostatic latent image formed by said electrostatic latent image forming means, and Device for transferring a developed image to a transfer or image receiving material, wherein said electrophotographic photosensitive member comprises a conductive support, a photosensitive layer and a protective layer, wherein said protective layer contains resin formed by curing an acrylic monomer with light, and said photosensitive layer contains as a charge transport material at least one compound selected from the group consisting of (A), (B) and (C) below: (A) Styryl compounds having a structure expressed by the following formula (1) and a melting point not higher than 135 ºC: wherein Ar¹ and Ar² are aromatic ring groups, Ar³ is a divalent aromatic ring group or a divalent heterocyclic group, R¹ is an alkyl group or an aromatic ring group, R² is a hydrogen atom, an alkyl group or an aromatic ring group and n₁ is 1 or 2, wherein R¹ and R² may be linked to form a ring when n₁ = 1; (B) Triarylamine compounds having a structure expressed by the following formula (2) and a melting point not higher than 150ºC: wherein Ar⁴, Ar⁵ and Ar⁴ each represents an aromatic ring group or a heterocyclic group; (C) Hydrazone compounds having a structure expressed by the following formula (3) and a melting point not higher than 155 ºC: wherein R3 is a hydrogen atom or an alkyl group, R4 and R5 are alkyl groups, aralkyl groups or aromatic ring groups, n2 is 1 or 2 and A is an aromatic ring group, a heterocyclic group or -CH=C(R6)R7 (wherein R6 and R7 are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R6 and R7 are not both simultaneously hydrogen atoms) 16. An electrophotographic apparatus according to claim 15, wherein said compound is (A). 17. An electrophotographic apparatus according to claim 15, wherein said compound is (B). 18. An electrophotographic apparatus according to claim 15, wherein said compound is (C). 19.Device unit comprising an electrophotographic photosensitive member and at least one device selected from the group consisting of a charging device, a developing device and a cleaning device, wherein said electrophotographic photosensitive member comprises a conductive support, a photosensitive layer and a protective layer, wherein said protective layer contains resin formed by curing an acrylic monomer with light, and said photosensitive layer contains as a charge transport material at least one compound selected from the group consisting of (A), (B) and (C) below: (A) Styryl compounds having a structure expressed by the following formula (1) and a melting point not higher than 135 ºC: wherein Ar¹ and Ar² are aromatic ring groups, Ar³ is a divalent aromatic ring group or a divalent heterocyclic group, R¹ is an alkyl group or an aromatic ring group, R² is a hydrogen atom, an alkyl group or an aromatic ring group and n₁ is 1 or 2, wherein R¹ and R² may be linked to form a ring when n₁ = 1; (B) Triarylamine compounds having a structure expressed by the following formula (2) and a melting point not higher than 150ºC: wherein Ar⁴, Ar⁵ and Ar⁴ each represents an aromatic ring group or a heterocyclic group; (C) Hydrazone compounds having a structure expressed by the following formula (3) and a melting point not higher than 155 ºC: wherein R³ is a hydrogen atom or an alkyl group, R⁴ and R⁵ are alkyl groups, aralkyl groups or aromatic ring groups, n₂ is 1 or 2 and A is an aromatic ring group, a heterocyclic group or -CH=C(R⁶)R⁷ (wherein R⁶ and R⁷ are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R⁶ and R⁷ are not both simultaneously hydrogen atoms), wherein said unit carries said electrophotographic photosensitive member and said at least one means selected from the group consisting of a charging means, a developing means and a cleaning means together and is detachably mounted on an apparatus body. 20. Device unit according to claim 19, wherein said compound is (A). 21. Device unit according to claim 19, wherein said connection is (B). 22. Device unit according to claim 19, wherein said connection is (C). 23. Facsimile machine with an electrophotographic device and a device for receiving image data from a remote data station, wherein said electrophotographic apparatus has an electrophotographic photosensitive member, wherein said electrophotographic photosensitive member comprises a conductive support, a photosensitive layer and a protective layer, wherein said protective layer contains resin formed by curing an acrylic monomer with light, and said photosensitive layer contains as a charge transport material at least one compound selected from the group consisting of (A), (B) and (C) below: (A) Styryl compounds having a structure expressed by the following formula (1) and a melting point not higher than 135 ºC is: wherein Ar¹ and Ar² are aromatic ring groups, Ar³ is a divalent aromatic ring group or a divalent heterocyclic group, R¹ is an alkyl group or an aromatic ring group, R² is a hydrogen atom, an alkyl group or an aromatic ring group and n₁ is 1 or 2, wherein R¹ and R² may be linked to form a ring when n₁ = 1; (B) Triarylamine compounds having a structure expressed by the following formula (2) and a melting point not higher than 150ºC: wherein Ar⁴, Ar⁵ and Ar⁴ each represents an aromatic ring group or a heterocyclic group; (C) Hydrazone compounds having a structure expressed by the following formula (3) and a melting point not higher than 155 ºC: wherein R3 is a hydrogen atom or an alkyl group, R4 and R5 are alkyl groups, aralkyl groups or aromatic ring groups, n2 is 1 or 2 and A is an aromatic ring group, a heterocyclic group or -CH=C(R6)R7 (wherein R6 and R7 are hydrogen atoms, aromatic ring groups or heterocyclic groups, provided that R6 and R7 are not both hydrogen atoms at the same time). 24. A facsimile apparatus according to claim 23, wherein said connection is (A). 25. A facsimile apparatus according to claim 23, wherein said connection is (B). 26. A facsimile apparatus according to claim 23, wherein said connection is (C).