JPH0545898A - Image forming method - Google Patents

Abstract

PURPOSE:To allow the formation of a copied image having excellent image quality without generating a transfer memory by providing >=5.3eV ionization potential on a charge transfer layer. CONSTITUTION:The electrostatic latent image is formed on a photosensitive body and a toner of the same polarity as the polarity of the electrostatic latent image is stuck to the electrostatic latent image to form the toner image. This toner image is transferred to copying paper by applying the charge of the polarity reverse from the polarity of the toner to the rear surface of the copying paper. This photosensitive body is the separated function type photosensitive body formed with a conductive substrate, a charge generating layer and the charge transfer layer in this order in such a case. This charge transfer layer is so constituted as to have >=5.3eV ionization potential. The ionization potential refers to the value obtd. as the integration of the compsn. constituting the charge transfer layer and does not refer to the ionization potential of a specific constituting material. The range of the ionization potential is regulated by the combination of a binder resin, charge transfer material and other additives, etc., which are the compsn. of the charge transfer layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method using a reversal developing method in a laser printer or the like.

[0002]

2. Description of the Related Art Conventionally, a bias potential having the same polarity as that of an electrostatic latent image formed on a photoconductor is applied to the surface of a developing sleeve to adhere toner having the same polarity as the electrostatic latent image to the electrostatic latent image. Inverse development for developing the electrostatic latent image has been performed.

In such reversal development, the toner attached to the electrostatic latent image is applied to the back surface of the copy paper by the transfer charger, and a charge having a polarity opposite to the charge polarity of the toner is applied to the copy paper. The toner image is transferred to form an image. (At this time, the photoconductor portion corresponding to the copy paper portion is referred to as the "paper passing portion").

When the copy charger is charged by the transfer charger, a system is adopted in which the transfer charger operates in synchronization with the supply timing of the copy paper to charge the copy paper, but the charging is started from just the leading end of the copy paper. However, it is very difficult systematically to charge only the copy paper. Normally, as shown in FIG. 2, the photoconductor portion corresponding to the portion before the leading edge of the copy paper (“non-sheet passing portion”) is used. ") (Portion (a) in the figure), the charge charged by the transfer charger is applied to the photoconductor. More specifically, the case of performing reversal development by negatively charging the photoconductor will be described with reference to FIG. 3 showing the history of changes in the photoconductor surface potential. The photosensitive member used in FIG. 3 is a function-separated type photosensitive member in which a conductive substrate, a charge generation layer, and a charge transport layer are laminated in this order, and has negative chargeability. The front end portion of the paper is usually a non-image portion, and the surface potential after charging is maintained. When the photoconductor approaches the transfer area, the non-sheet passing portion receives a positive charge by the transfer charger. Here, the charge transport layer has a function of transporting positive charges so that a negative electrostatic latent image can be formed. Therefore, the positive charge imparted by the transfer unit moves inside the photoconductor according to the ionization potential of the charge transport layer of the photoconductor, and the interface between the charge transport layer and the charge generation layer or the charge generation layer and the conductive substrate Accumulated at the interface of. Therefore, the apparent surface potential largely swings to the positive potential side. On the other hand, in the paper passing portion, since it is not affected by the positive charge by the charger,
After the toner transfer, the surface potential at the paper passing portion is attenuated to almost zero. In this state, in order to repeat the next copying process, even if a negative charging charge is uniformly applied by the charger, in the non-sheet passing portion, part of the accumulated charge as described above is charged. Since the charges are canceled, the surface potential is lowered (ΔV ₀ ) as compared with the paper passing portion. Further, when the portion that was the non-sheet passing portion (the portion shown in FIG. 2A) in the previous copying is exposed, the surface potential becomes lower (ΔVi) than the portion that was the sheet passing portion. The developing potential of this portion is apparently increased, and the positively charged toner is further attached to the portion. Therefore, in the second copying, the phenomenon of thickening of characters (referred to as "transfer memory") occurs in the non-sheet passing portion.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object thereof is to provide an image forming method in which a transfer memory does not occur.

[0006]

That is, according to the present invention, an electrostatic latent image is formed on a photoconductor, and toner having the same polarity as the electrostatic latent image is adhered to the electrostatic latent image to form a toner image. Then, in the image forming method of transferring the toner image onto the copy paper by applying an electric charge having a polarity opposite to that of the toner to the back surface of the copy paper, the photoreceptor is a conductive substrate, a charge generation layer, and a charge transport layer in this order. The formed function-separated type photoreceptor is characterized in that the charge transport layer has an ionization potential of 5.3 eV or more.

By adopting the constitution of the photoconductor, the transfer memory in the reversal development can be effectively prevented. The photoreceptor according to the present invention comprises at least a charge generation layer and a charge transport layer laminated in this order on a conductive substrate.

The charge transport layer has an ionization potential of 5.3 eV or more, preferably 5.5 eV or more, more preferably 5.5 to 6.0 eV. In the present invention, the ionization potential of the charge transport layer means a value obtained as the total composition of the charge transport layer, and does not mean the ionization potential of a specific constituent substance. If the ionization potential is smaller than 5.5 eV, the charge having the opposite polarity to the charge applied at the time of transfer moves in the charge transport layer and accumulates in the photoconductor. Cannot be prevented. Further, there is a problem that the charge transport layer is likely to be oxidized and the characteristics of the photoconductor are likely to be deteriorated. On the other hand, when the ionization potential is higher than 6.0 eV, although the effect of preventing the occurrence of the transfer memory is effective, the adverse effect of the decrease in the sensitivity of the photoconductor becomes larger and the image deterioration is accompanied.

In order to adjust the ionization potential of the charge transport layer to the above range, it can be adjusted by a combination of the composition of the charge transport layer, such as a binder resin, a charge transport material and other additives.

Generally, as the charge transport material, a hydrazone compound, a pyrazoline compound, a styryl compound, a triphenylmethane compound, an oxadiazole compound, a carbazole compound, a stilbene compound, an enamine compound, an oxazole compound, a triphenylamine compound, a tetraphenylbenzidine compound. It is preferable to select various compounds such as azine compounds and the like, which have a high ionization potential of the charge transport material itself. However, although the butadiene-based compound or the pyrazoline-based compound tends to have a relatively low ionization potential, the ionization potential is also affected by the substituent, so the type of the substituent is also taken into consideration and the charge transport material is You have to choose. As the substituent, an electron-accepting group such as a nitro group or a halogen atom tends to increase the ionization potential.

The binder resin constituting the charge transport layer does not affect the ionization potential as much as the charge transport material, and is therefore electrically insulating, and is a known thermoplastic resin or thermosetting resin. , photocurable resin, it is possible to use a photoconductive resin, as measured by itself, 1 × 10 ¹²
Any material having a volume resistance of Ω · cm or more can be used. Specifically, saturated polyester resin, polyamide resin, acrylic resin, ethylene-vinyl acetate copolymer, ion-crosslinked olefin copolymer (ionomer), styrene-butadiene block copolymer, polycarbonate,
Vinyl chloride-vinyl acetate copolymer, cellulose ester, polyimide, thermoplastic agent such as styrene resin, epoxy resin, urethane resin, silicone resin, phenol resin, melamine resin, xylene resin, alkyd resin,
Thermosetting resin such as thermosetting acrylic resin, photocurable resin,
Examples thereof include photoconductive resins such as polyvinylcarbazole, polyvinylpyrene, polyvinylanthracene, and polyvinylpyrrole.

As an additive to be added to the charge transport layer, the addition of an antioxidant is effective for adjusting the ionization potential, and the addition of the antioxidant makes it possible to increase the ionization potential. The antioxidant may be added in a generally used amount.

Next, a method of manufacturing a laminated type photoreceptor in which the charge transport layer of the present invention is used and a charge generation layer and a charge transport layer are laminated on a conductive substrate will be described.

As the conductive support, aluminum,
A foil or plate of silver, iron, nickel or the like in the form of a sheet or a drum, or a material obtained by attaching these metals to a plastic film or the like by vacuum deposition, electroless plating or the like, a conductive polymer, indium oxide, A layer in which a conductive compound layer such as tin oxide is similarly formed by coating or vapor deposition on a support such as paper or a plastic film can be used.

When forming the charge generation layer on such a conductive support, the charge generation material is vapor-deposited or plasma polymerized on the conductive support, or the charge generation material is dissolved in an appropriate resin. It is dispersed in the above solution, and this dispersion is applied on a conductive support and dried to form the film. The charge generation layer has a thickness of 4 μm.
m or less, preferably 2 μm or less.

As the charge generating material, a bisazo pigment,
Triarylmethane dye, thiazine dye, oxazine dye, xanthene dye, cyanine dye, styryl dye, pyrylium dye, azo pigment, quinacridone pigment, indigo pigment, perylene pigment, polycyclic quinone dye Organic substances such as pigments, bisbenzimidazole pigments, indathlon pigments, squalium salt pigments, azulene pigments, phthalocyanine pigments, selenium, selenium, etc.
Inorganic substances such as tellurium, selenium alloys such as selenium and arsenic, cadmium sulfide, cadmium selenide, zinc oxide, amorphous silicon, etc. can be used. Any material may be used as long as it can generate charge carriers.

The binder resin used in the charge generation layer is
The same kind of material that can be used for the charge transport layer described above can be used.

In providing the charge transporting layer on the charge generating layer formed as described above, a binder resin selected, a charge transporting substance, and a desired and more suitable additive are appropriately added according to a conventional method. It is dissolved in a suitable solvent, the coating solution is coated on the charge generation layer, and dried. In this case, the thickness of the charge transport layer is 3 to 50 μm, preferably 5 to 20 μm.
to be m. In addition, the ratio of the charge transport material contained in the charge transport layer is 1 part by weight of the binder resin.
0.2 to 2 parts by weight, preferably 0.3 to 1.3 parts by weight.

Further, in forming the charge generation layer or charge transport layer using the binder resin, halogenated paraffin, polychlorinated biphenyl,
Plasticizers such as dimethylnaphthalene, dibutylphthalate, 0-terphenyl, chloranil, tetracyanoethylene, 2,4,7-trinitrofluorenone, 5,6-dicyanobenzoquinone, tetracyanoquinodimethane, tetrachlorophthalic anhydride, An electron-withdrawing sensitizer such as 3,5-dinitrobenzoic acid or a sensitizer such as methylpyoret, rhodamine B, cyanine dye, pyrylium salt and thiapyrylium salt may be used. Furthermore, it is also possible to appropriately use an antioxidant, an ultraviolet absorber, a dispersion aid, an anti-settling agent and the like.

As described above, the addition of the antioxidant to the charge transport layer is an effective additive for increasing the ionization potential.

The photoconductor obtained as described above can be mounted on the printer shown in FIG. 1 for use.

The printer shown in FIG. 1 is provided with a photosensitive drum (1) which is an electrostatic latent image carrier at the center thereof, and this drum is rotationally driven in the clockwise direction in the figure by a driving means (not shown). A corona charger (2), a developing device (3), a transfer charger (4), a cleaning device (5) and an eraser (6) are sequentially arranged around the photosensitive drum (1). An optical system (7) is arranged above the photoconductor drum (1), and this optical system includes a semiconductor laser generator, a polygon mirror, a toroidal lens, a half mirror, a spherical mirror, and a folding back in a housing (71). A mirror, a reflection mirror, etc. are arranged, and an exposure slit (72) is formed on the floor of the housing (71). From this, a photoconductor drum (passage is provided between the charger (2) and the developing device (3). The image can be exposed to 1). A timing roller pair (81), an intermediate roller (82), and a paper feed cassette (83) are sequentially arranged on the right side of the photosensitive drum (1) in the drawing, and the paper feed cassette (83) includes a paper feed roller (81). 8
4) is facing. Further, a fixing roller pair (91) and a paper discharge roller pair (92) are sequentially arranged on the left side of the photosensitive drum (1) in the figure, and a paper discharge tray (93) is arranged on the arrangement roller pair (92). Facing.

Each of the above-described parts includes a printer body (1
It is installed in 0). The main body (10) is a lower unit (1
01) and an upper unit (102), and comprises the above-mentioned charger (2), developing device (3), cleaning device (5), eraser (6), optical system (7), timing roller pair (81). Upper roller and intermediate roller pair (8
The upper roller (2), the paper feed roller (84), the upper roller of the fixing roller pair (91), the paper discharge roller pair (92), and the paper discharge tray (93) are all provided in the upper unit (102). .. In this upper unit, the end on the paper feed side can be opened and closed up and down around the shaft rod (103) provided at the left end of the printer in the figure, which enables jam processing and various maintenance. There is.

The photoconductor drum (1) is the above-mentioned function-separated type organic photoconductor described in the production method. Also,
The toner used in the developing device (3) is of a negative charging type, and this toner is stored in the developing device (3) and reverse development is performed under a developing bias of -300V.

According to this printer, the surface of the photosensitive drum (1) is uniformly charged (-600 V) to a predetermined potential by the charger (2), and the charged area is image-exposed from the optical system (7) to cause fog. The light portion is attenuated to about -50V and an electrostatic latent image is formed. The electrostatic latent image thus formed is developed into a toner image by the developing device (3), and is transferred to the transfer area facing the transfer charger (4).

On the other hand, the transfer sheet is pulled out from the sheet feeding cassette (83) by the sheet feeding roller (84), reaches the timing roller pair (81) through the intermediate roller pair (82), and then on the drum (1). It is sent to the transfer area in synchronization with the toner image. Thus, in the transfer area, the transfer charger (4) transfers a toner image on the drum (1) onto the transfer paper by applying a positive charge having a polarity opposite to the charging polarity of the toner from the back surface of the transfer paper, and the transfer paper is fixed. It reaches the roller pair (91), where the toner image is fixed, and then it is ejected to the paper ejection tray (93) by the paper ejection roller pair (92). After the toner image is transferred to the transfer paper, the toner remaining on the photosensitive drum (1) is cleaned by the cleaning device (5), and the residual charge is erased by the eraser (6). The system speed of the printer (the peripheral speed of the photosensitive drum 1) is 3.5 cm / sec.

The present invention will be described below with reference to examples.
In the examples, “part” means “part by weight”.

[0028]

【Example】Example 1  Metal-free phthalocyanine 2 parts, butyral resin (BX-
1; Sekisui Chemical Co., Ltd.) 2 parts tetrahydrofuran 400 parts
It was dispersed with a sand grinder together. The resulting dispersion
Apply the coating solution on an aluminum tube with a dry film thickness of 0.2 μm.
So as to form a charge generation layer.

Next, the following chemical formula:

[Chemical 1] A solution prepared by dissolving 70 parts of a hydrazone compound represented by and 70 parts of a polycarbonate resin (K-1300; manufactured by Teijin Chemicals Ltd.) in 400 parts of methylene chloride is formed on the charge generation layer so that the dry film thickness becomes 20 μm. Coating was performed to form a charge transport layer. In this way, a laminated photoreceptor having two layers was obtained.

[0030]Example 2  In Example 1, the substitution of the compound represented by the chemical formula 1
Instead, the following chemical formula

[Chemical 2] Example 1 except that the hydrazone compound represented by
In the same manner as described above, a laminated photoreceptor having two layers was obtained.

[0031]Example 3  In Example 2, instead of metal-free phthalocyanine
Titanium phthalocyanine is used, and the charge transport layer is hindered.
Amine amine antioxidant (Mark LA62; ADEKA EAR
Gust Co.) was added in the same manner as in Example 2 except that 4 parts were added.
Then, a laminated photoreceptor having two layers was obtained.

[0032]Comparative Example 1  In Example 1, the substitution of the compound represented by the chemical formula 1
Instead, the following chemical formula

[Chemical 3] A laminated photoreceptor having two layers was obtained in the same manner as in Example 1 except that the butadiene compound represented by

[0033]Comparative example 2  In Example 1, instead of metal-free phthalocyanine
Using titanyl phthalocyanine for
Instead of things

[Chemical 4] Example 1 except that the hydrazone compound represented by
In the same manner as described above, a laminated photoreceptor having two layers was obtained.

[0034]Example 4  In Example 1, instead of the compound of Chemical formula 1,
In the charge transport layer, the hydrazone compound represented by
Hindered phenolic antioxidant (irganox
565; manufactured by Ciba Geigy Co.) except that 14 parts were added.
A laminated photoreceptor having two layers was obtained in the same manner as in Example 1.

[0035]Example 5  In Example 1, the dry thickness of the charge generation layer was 0.4 μm.
m, instead of the hydrazone compound represented by Chemical formula 1,
following:

[Chemical 5] Example 1 except that the hydrazone compound represented by
In the same manner as described above, a laminated photoconductor having two layers was obtained.

[0036]Example 6  In Example 5, the hindered pheno in the charge transport layer.
14 parts of diol-based antioxidant (Irganox 1076)
Laminate consisting of two layers in the same manner as in Example 5 except that the layers were added.
A photoconductor was obtained.

[0037]Toner manufacturing example  100 parts by weight of A type polyester resin and carbon bra
5 parts by weight of CK MA # 8 (manufactured by Mitsubishi Kasei Co., Ltd.),
Bontron S-34 (manufactured by Orient Chemical Industry Co., Ltd.)
3 parts by weight and Viscor TS-200 (Sanyo Kasei Co., Ltd.
A publicly known composition of 2.5 parts by weight
Kneading, crushing and classifying by means of an average particle size of 10 μm,
Toner in which 80% by weight is distributed in a particle size range of 7 to 13 μm
Particles are manufactured and the toner particles are treated with a hydrophobic agent as a fluidizing agent.
Of silica (Tanolux 500 manufactured by Tarco)
5% by weight was added, and the mixture was stirred with a homogenizer.

[0038]Evaluation  The feelings obtained in Examples 1 to 6 and Comparative Examples 1 and 2.
A surface analyzer (AC-
1; manufactured by Riken Keiki Co., Ltd.). In addition, these photoconductors
Mounted on the laser printer explained in Fig. 1,
Perform a copy test using the toner described above, and transfer memory
Occurrence of was observed. Run the observation results as follows.
I attached it. ⊚: No memory was found and the image quality was excellent.
It ◯: No memory is found. Δ: Some memory is observed, but there is no problem in practical use
Yes. ×: Memory is generated.

The above results are summarized in Table 1.

[Table 1]

[0040]

The photoconductor of the present invention can form a copied image having no transfer memory and excellent in image quality.

[Brief description of drawings]

FIG. 1 is a diagram showing the schematic configuration of a laser printer.

FIG. 2 is a diagram for explaining the mechanism of transfer memory generation from the viewpoint of the apparatus configuration.

FIG. 3 is a diagram for explaining a mechanism of generation of a transfer mechanism from the viewpoint of a photoreceptor surface potential.

[Explanation of reference symbols] 1 photoconductor drum 2 corona charger 3 developing device 4 transfer charger 5 cleaning device 6 eraser

Claims (1)

[Claims] 1. An electrostatic latent image is formed on a photoconductor, toner having the same polarity as the electrostatic latent image is adhered to the electrostatic latent image to form a toner image, and the toner image is transferred onto a copy sheet. In the image forming method of transferring by applying an electric charge having a polarity opposite to that of the toner to the back surface of the copy paper, the photoconductor is a function-separated photoconductor in which a conductive substrate, a charge generation layer, and a charge transport layer are formed in this order. An image forming method, wherein the charge transport layer has an ionization potential of 5.3 eV or more.