JPH10312101A - Image forming device - Google Patents

Abstract

(57) [Problem] To provide an image forming apparatus which is excellent in abrasion resistance, has a stable electric potential, and can maintain a good image even after durability. In an image forming apparatus for performing image formation by applying an image forming process including a step of charging a surface of a charged body to a charged body, the charged body has a number average molecular weight on a conductive support. A photoreceptor having a surface layer containing at least 30,000 polycarbonate resin, wherein the charging means for the charged body is charged by bringing a charging member to which a voltage is applied into contact with the charged body; A contact-type charging device that charges a body surface, and when the charging member corresponds to a non-image forming area of the member to be charged, controls the DC constant voltage of the charging member, and according to the thickness of the non-charged body layer at that time. Detecting the amount of DC current detected, and when the charging member corresponds to the image forming area of the non-charged member, the charging member is controlled to be a DC constant voltage with a DC voltage corresponding to the detected DC current amount. Characteristic image forming apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus of a type in which a voltage is directly charged.

[0002]

2. Description of the Related Art In an electrophotographic method, for example, selenium,
When an image is obtained by performing a basic process such as charging, exposure, development, transfer, fixing, and cleaning on an electrophotographic photosensitive member using cadmium sulfide, zinc oxide, amorphous silicon, an organic photoconductor, or the like. The process applies a high voltage (DC 5 to 8 KV) to the metal wire almost in the past,
Charging is performed by the generated corona. However, if allowed to proceed for image blurring or deterioration denature the surface of the photosensitive member by corona products such as ozone and NO _X during corona generating in this way, the wire - the dirt affect the image quality, image white spots and black streaks And other problems. In particular, an electrophotographic photosensitive member in which the photosensitive layer is mainly composed of an organic photoconductor,
Compared with other selenium photoreceptors and amorphous silicon photoreceptors, the chemical stability is low, and when exposed to a corona product, a chemical reaction (mainly an oxidation reaction) occurs and tends to deteriorate. Therefore, when repeatedly used under corona charging, image blurring due to the above-mentioned deterioration and a decrease in copy density due to a decrease in sensitivity tend to shorten printing resistance (copying life).

In corona charging, only 5 to 30% of the electric current directed to the photosensitive member in terms of electric power, and most of the current flows to the shield plate and is inefficient as a charging means.

To compensate for such a problem, Japanese Patent Application Laid-Open No. 57-178267 discloses a method without using a corona discharger.
JP-A-56-104351, JP-A-58-405
No. 66, JP-A-58-139156, JP-A-58-150975 and the like,
A method of contact charging has been proposed.

More specifically, a charging member such as a conductive elastic roller, a conductive elastic blade, or a conductive brush to which a DC voltage of about 1 to 2 KV is externally applied is brought into contact with the surface of the photoreceptor. Thus, the surface of the photoreceptor is charged to a predetermined potential.

Further, in order to improve the uniformity of charging,
A method has been proposed in which an AC voltage is superimposed on a DC voltage and applied to a charging member (JP-A-63-149668). In this charging method, a pulsating voltage is applied by superimposing an _AC voltage (V _AC ) on a DC voltage (V _DC ) to perform uniform charging.

In this case, in order to maintain the charging uniformity and prevent image defects such as white spots in the normal development system, black spots in the reversal development system, and fogging, the superposed AC voltage is at least twice the DC voltage. Peak potential difference (V _PP )
It is necessary to have

However, if the superimposed AC voltage is increased in order to prevent image defects, the maximum applied voltage of the pulsating voltage causes discharge breakdown at a small defective portion inside the photoconductor. In particular, in the case of a photoconductor having a low withstand voltage such as a thin film thickness of the photoconductor, this dielectric breakdown is remarkable. In this case, in the normal development method, an image becomes blank over the longitudinal direction of the contact portion, and in the reversal development method, black stripes are generated. Further, when a pinhole is generated, there is a problem that a portion of the pinhole serves as a conduction path, current leaks, and the voltage applied to the charging member drops.

Further, in the contact charging system, the charging member is in contact with the photoreceptor, so that the photoreceptor is easily worn by the charging member. For this reason, there is a disadvantage that the sensitivity of the photosensitive member is easily reduced, including the decrease in the dielectric strength described above.

As described above, in the electrophotographic apparatus using the contact charging system, the photoreceptor wears a lot, and in the case of the direct charging system in which a DC voltage is applied, particularly, the charging characteristic changes due to a change in capacity due to friction of the photoreceptor. Is greatly affected. That is,
Due to the decrease in the thickness of the photoreceptor, the DC current flowing through the charging member increases, and the surface potential of the photoreceptor increases. As a result, the development contrast increases and the density of the developed image increases. Sufficient reverse contrast was not obtained, and there was a problem that a "fog" image was obtained when the image was thinly developed with a developer.

This is because when the thickness of the photoreceptor decreases, the surface potential increases, and the bright portion potential of the surface potential also increases accordingly. Further, since the photoconductor sensitivity decreases as the film thickness decreases, the surface potential corresponding to the white document, that is, the light portion potential does not sufficiently drop. From these facts, the bright portion potential is significantly increased, and the surface potential contrast between the black document and the white document is narrowed. As a result, a sufficient development contrast cannot be obtained at the time of development, and the bright portion potential is thinly developed with the developer. The image becomes a “fog” image.

Even when this is adjusted so as not to be covered by the developing bias and the exposure lamp voltage (exposure amount of light image irradiation), it is necessary to secure a sufficiently wide adjustment range. This was a cost increase factor for power supplies.

Further, as the film thickness of the photoreceptor decreases, the surface potential increases, so that the photoreceptor is repeatedly used in a high electric field, and the deterioration of the photoreceptor is further promoted, and the life of the photoreceptor is shortened. I was

[0014]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus which is excellent in abrasion resistance, has a stable electric potential, and can maintain a good image even after running.

[0015]

According to the present invention, there is provided an image forming apparatus for forming an image by applying an image forming process including a step of charging a surface of a charged body to the charged body, wherein the charged body is electrically conductive. A photosensitive member having a surface layer containing a polycarbonate resin having a number-average molecular weight of 30,000 or more on a porous support, wherein the charging means for charging the charged member applies a voltage to a charging member to which the charged member is charged. A contact-type charging device that contacts the body to charge the surface of the body to be charged, and controls the DC constant voltage of the charging member when the charging member corresponds to a non-image forming area of the body to be charged; The amount of DC current corresponding to the thickness of the non-charged member layer is detected, and when the charging member corresponds to the image forming area of the non-charged member, the charging member is DC-controlled with a DC voltage corresponding to the detected DC current amount. Image forming apparatus characterized in that voltage control is performed. Et al constructed.

Further, the present invention comprises an image forming apparatus according to the present invention, wherein an exposure amount of light irradiation performed at the time of image formation is controlled in accordance with the detected amount of direct current.

Further, the present invention comprises the image forming apparatus of the present invention, wherein the charging member is a conductive charging member having a high resistance layer on a surface layer.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A contact charging method for charging an electrophotographic photosensitive member by bringing a charging member into contact with the electrophotographic photosensitive member is performed by discharging in a minute space near a contact portion between the photosensitive member and the charging member.

Therefore, the photoreceptor is repeatedly worn by the charging member, and the wear is promoted by the discharge. As described above, in the contact charging system, the abrasion of the photoconductor, which has not occurred in the conventional corona discharge system, is large. Also,
For this reason, there is a disadvantage that the copy life is shortened due to a decrease in charging uniformity and a decrease in sensitivity.

Therefore, in the present invention, a polycarbonate resin having a number average molecular weight of 30,000 or more is contained in the surface layer of the photoreceptor in order to improve the abrasion resistance of the surface of the photoreceptor and extend the copying life. Let me.

Furthermore, even if there is a change in the capacity of the photoconductor due to a decrease in the thickness of the photoconductor due to an increase in the number of times of image formation,
In each case, by detecting the voltage-current characteristic corresponding to the capacitance with respect to the thickness of the photoconductor, it is possible to apply the optimum correction application voltage at that time to the charging member. In addition, it is possible to perform optimal appropriate exposure on the photoconductor.

According to this, as the thickness of the non-charged body decreases, the amount of current detected when the non-image portion constant voltage is applied increases,
In order to add a voltage decrease correction to the image portion applied voltage value according to the increase amount and to add an increase in the exposure lamp voltage,
The charging process and the image formation in the optimum state are always performed.

Next, the outline of the electrophotographic photosensitive member according to the present invention will be described, but this is a typical example and does not limit the present invention.

As the conductive support, a metal cylinder such as aluminum or stainless steel, a cylindrical cylinder such as paper or plastic, a sheet or a film is used. Further, these cylindrical cylinders, sheets or films may have a conductive polymer layer or a resin layer containing conductive particles such as tin oxide, titanium oxide and silver particles as required.

Further, an undercoat layer (contact layer) having a barrier function and an adhesive function can be provided between the conductive support and the photosensitive layer. The undercoat layer is formed for improving the adhesion of the photosensitive layer, improving the coating property, covering defects on the support, improving the charge injection property from the support, protecting the photosensitive layer against electrical breakdown, and the like. Its film thickness is about 0.2 to 2 μm.

As the charge generating substance, pyrylium, thiapyrylium dye, phthalocyanine pigment, anthantrone pigment, dibenzopyrene quinone pigment, pyratron pigment, azo pigment, indigo pigment, quinacridone pigment, asymmetric quinocyanine, quinocyanine and the like can be used. Can be.

As the charge transport material, hydrazone compounds, pyrazoline compounds, styryl compounds, oxazole compounds, thiazole compounds, triarylmethane compounds, polyarylalkane compounds and the like can be used. .

The charge generation layer contains the above-mentioned charge generation substance in 0.1.
With 5 to 4 times the amount of binder resin and solvent, well dispersed by a method such as homogenizer, ultrasonic wave, ball mill, vibration ball mill, sand mill, attritor, roll mill, etc.
It is formed by coating and drying. The film thickness is preferably 5 μm or less, particularly preferably in the range of 0.01 to 1 μm.

The charge transport layer is generally formed by dissolving the charge transport material and the binder resin in a solvent, coating and drying. The mixing ratio of the charge transport material and the binder resin is 2:
It is about 1-1: 2. As the solvent, ketones such as acetone and methyl ethyl ketone, esters such as methyl acetate and ethyl acetate, aromatic hydrocarbons such as toluene and xylene, and chlorinated hydrocarbons such as chlorobenzene, chloroform and carbon tetrachloride are used. . When applying this solution, for example, a coating method such as immersion coating, spray coating, spinner coating or the like can be used, and drying is performed at 10 ° C to 200 ° C, preferably 20 ° C to 200 ° C.
It can be carried out in a range of 150 ° C. for 5 minutes to 5 hours, preferably for 10 minutes to 2 hours, under blast drying or still drying. The thickness of the formed charge transporting layer is preferably 5 to 30 μm, particularly preferably 10 to 25 μm.

Examples of the binder resin used to form the charge transport layer include acrylic resins, styrene resins, polyesters, polycarbonates, polyarylates, polysulfones, polyphenylene oxides, epoxy resins, polyurethanes, and alkyds. Resins selected from resins and unsaturated resins are preferred. In particular, polymethyl methacrylate,
Polystyrene, styrene-acrylonitrile copolymer,
Polycarbonate or diallyl phthalate resin is exemplified.

The charge generation layer or the charge transport layer may contain various additives such as an antioxidant, an ultraviolet absorber, and a lubricant.

The polycarbonate used in the present invention
The resin may be a homopolymer or a copolymer, and the constituent monomers are not limited as long as the total number average molecular weight (hereinafter abbreviated as Mn) of the polymer is 30,000 or more.

In consideration of coatability, the molecular weight is in the range of 30,000 to 200,000, particularly preferably 30,000 to 100,000.

The number average molecular weight of the polycarbonate can be measured by a general method using gel permeation chromatography (hereinafter abbreviated as GPC).

The polycarbonate may be used alone or in a blend. However, in the case of a polycarbonate having a number average molecular weight of less than 30,000, it is preferred that the content of the polycarbonate of 30,000 or more is 50% by weight or more. Such a polycarbonate can be advantageously used as a binder resin in the formation of the photosensitive layer. When the photosensitive layer is a laminated type, the polycarbonate in the present invention may be used as a binder for any of the charge generation layer and the charge transport layer, but is preferably used as a binder for the charge transport layer. preferable.

FIG. 1 shows a specific example of an image forming apparatus using the electrophotographic photosensitive member of the present invention. This apparatus includes a roller-shaped charging member 2, an image exposing unit 3, a developing unit 4, a sheet-supply roller and sheet-supply guide 5, a transfer roller on a peripheral surface of an electrophotographic photosensitive member 1.
A liner 6, a cleaner 7, and a pre-exposure means 8 are provided. In the image forming method, first, a voltage is applied to a charging member 2 which is arranged in contact with the photoreceptor 1, the surface of the photoreceptor 1 is charged, and an image corresponding to a document is formed on the photoreceptor 1 by the image exposure means 3. Image exposure is performed to form an electrostatic latent image. Next, the developing device 4
The toner in the photoreceptor 1 is adhered to the photoreceptor 1.
The upper electrostatic latent image is developed (visualized). Further, the toner image formed on the photoreceptor 1 is transferred by a transfer roller 6 onto a transfer material such as paper supplied through a paper supply roller and a paper supply guide 5, and is transferred to a cleaner-7. Thus, the remaining toner remaining on the photoreceptor 1 without being transferred to the transfer material is recovered. In the case where residual charges remain inside the photoconductor, it is preferable that the pre-exposure unit 8 irradiates the photoconductor 1 with light to eliminate the charge. On the other hand, the transfer material on which the toner image has been formed is sent to a fixing unit (not shown) by the transport unit 9 to fix the toner image.

In this image forming apparatus, the image exposing means 3
As the light source, a halogen light, a fluorescent light, a laser light or the like can be used. Other auxiliary processes may be added as needed.

FIG. 2 is a block diagram showing an example in which the image forming apparatus is used as a facsimile printer.

The controller 11 controls the image reading section 10 and the printer 19. The whole controller 11 is controlled by the CPU 17. The read data from the image reading unit 10 is transmitted to the partner station through the transmission circuit 13. Data received from the partner station is sent to the printer 19 through the receiving circuit 12. The image memory 16 stores predetermined image data. Print controller-18
Controls the printer-19. 14 is a telephone.

Image information received from the line 15 (image information from a remote tanmatsu connected via the line)
Are demodulated by the receiving circuit 12 and then subjected to decoding processing by the CPU 17 and are sequentially stored in the image memory 16. When the image information of at least one page is stored in the memory 16, the image of the page is recorded. The CPU 17HA <reads out one page of image information from the memory 16 and sends out the combined one-page image information to the printer controller 18. When receiving the image information of one page from the CPU 17, the printer controller 18 controls the printer 19 to record the image information of the page.

The CPU 17 is receiving the next page during recording by the printer 19.

As described above, image reception and recording are performed.

FIG. 3 shows an example of the operation sequence of the apparatus shown in FIG. This example shows a case of continuous printing of two sheets.

[0044] On the basis of the print (copy) start signal, the rotation drive of the photosensitive member 1 of the apparatus in the standby state is started and the pre-rotation period is started. Simultaneously with the start of the rotation of the photoconductor 1, the neutralization exposure 15 is turned on, and in the section A1, one or more peripheral surfaces of the photoconductor 1 are neutralized.

[0045] Next, a DC bias which is a primary charging bias for the charging roller-2 which is a contact charging member is set to O.
N.

[0046] Starting with the primary charging bias, section B
In step 1, the DC voltage is detected, and a DC current is detected. The photoconductor thickness is calculated from a predetermined relationship between the photoconductor thickness and the DC current value. , The DC voltage value and the image exposure amount are determined (primary voltage correction, image exposure amount correction).

[0047] When the charging roller DC constant voltage control is started with the primary correction voltage, the first image is formed by image exposure (exposure of a slit to a document image). The charging roller 2 corresponds to the surface of the image forming area of the photoreceptor 1, and charges the surface of the photoreceptor 1 in a DC constant voltage control state.

[0048] The so-called photoreceptor surface between the sheets between the time when the image formation for the first print is completed and the time when the image formation for the next second print is started is a non-image forming area surface. The constant voltage control of the charging roller 2, the DC current detection, and the DC constant voltage control are executed again even between the sheets.

That is, when the first printing is completed, the primary charging bias is applied again in the section B2 between the sheets.
Lar DC constant voltage control, no DC current detection,
Next, the charging roller constant voltage control according to the detected DC current is executed to execute image formation for the second print.

During the continuous printing of three or more sheets, the sequence of charging roller DC constant voltage control, DC current detection, and DC constant voltage control is similarly performed between each sheet.

[0051] When the image formation of the last print has been completed, the photoconductor 1 enters a post-rotation period, and in the section A2 of the post-rotation period, the charge-removal exposure 15 on one or more peripheral surfaces of the photoconductor 1
Is performed and the charge is removed.
At F, the apparatus enters a standby state until the next print start signal is input.

In the above configuration, when the surface of the photoreceptor is shaved due to durability and the thickness of the photoreceptor is reduced, the charging roller is charged.
When DC-2 corresponds to the non-image forming area surface of the photoconductor 1, the detected DC current in the DC constant voltage control periods B1 and B2 increases, and the DC voltage is reduced by the correction voltage corresponding to the detected DC current. The charging process for the image forming area of the photosensitive member 1 is performed under the charging roller DC constant voltage control.
And the image formation is executed.

In a low-humidity environment, particularly, the resistance of the charging roller-2 decreases, and the charging roller DC in the periods B1 and B2 is reduced.
The detected DC current of the constant voltage control decreases. Under the charging roller DC constant voltage control with the increasing correction voltage according to the detected DC current, the charging roller-2 performs a charging process on the surface of the image forming area of the photosensitive member 1 to form an image. Therefore, the charging potential of the photoreceptor 1 is kept constant irrespective of the resistance fluctuation in the environment of the charging roller-2.

[0054]

【Example】

Example 1 100 parts by weight of urethane rubber was melt-kneaded with 4 parts by weight of conductive carbon, and a roller-shaped charging member was formed to have a diameter of 16 mm x 320 mm around a stainless steel core of 16 mm in length and 350 mm in length. did.

Next, an electrophotographic photosensitive member was prepared as follows. An aluminum cylinder of φ30 mm × 357.5 mm was used as a support, and a 5% methanol solution of a polyamide resin (trade name: Amilan CM8000, manufactured by Toray Industries, Inc.) was applied to the support by an immersion method. A pull layer was formed.

Next, 5 parts by weight of a disazo pigment represented by the following structural formula

Embedded image 2 parts by weight of a resin represented by the following structural formula

Embedded image And 150 parts by weight of tetrahydrofuran were dispersed in a sand mill using a φ1 mm glass bead for 20 hours. A coating solution prepared by adding 200 parts of cyclohexanone to the dispersion was dip-coated on the undercoat layer to form a charge generation layer.

Next, 6.7 parts by weight of a triphenylamine compound represented by the following structural formula

Embedded image And 2.8 parts of a styryl compound represented by the following structural formula

Embedded image And a polycarbonate having a number average molecular weight of 40,000 represented by the following structural formula.
10 parts by weight of bone resin

Embedded image With 30 parts by weight of chlorobenzene and 20 parts of dichloromethane
It was dissolved in parts by weight to prepare a coating solution. This coating solution was applied onto the charge generation layer by dip coating to form a charge transport layer having a thickness of 25 μm, thereby producing an electrophotographic photoreceptor.

Examples 2 and 3 In Example 1, a polycarbonate resin of the same structural formula of Mn = 60,000 and Mn = 80,000 was used in place of the polycarbonate resin of Mn = 40,000. Other than that, an electrophotographic photosensitive member was prepared in the same manner as in Example 1. Example 2 (Mn
= 60,000) and Example 3 (Mn = 80,000).

Examples 4 to 6 In the above Examples, a hydrazone compound represented by the following structural formula was used instead of the triphenylamine compound and styryl compound.

Embedded image Was used in the same manner as in Example 1, except that 9.5 parts by weight was used.
The electrophotographic photosensitive member of Example 6 was produced in the same manner as in Example 3.

Examples 7 to 9 In Example 1, the polycarbonate resin was replaced with a polycarbonate resin represented by the following structural formula.

Embedded image An electrophotographic photoreceptor was prepared in the same manner as in Example 1, except that Mn = 40,000 of the polycarbonate resin was used in Example 7, and Example 8 was used in the case of Mn = 60,000. Example 9 is the case where Mn = 80,000.

Comparative Example 1 In the same manner as in Example 1, except that Mn = 40,000 of the polycarbonate resin was replaced with a polycarbonate resin of Mn = 20,000 having the same structure. An electrophotographic photoreceptor was prepared.

The electrophotographic photosensitive members prepared in Examples 1 to 9 and Comparative Example 1 were mounted on the image forming apparatus shown in FIG.
The potential control according to the present invention was carried out according to the operation sequence shown in FIG. Using another unused photoreceptor prepared in each example, copying was repeated up to 10,000 sheets without performing potential control according to the present invention, and evaluation was performed. Table 1 shows the results.

[0063]

[Table 1] As shown in Table 1, the photoconductors of Examples 1 to 9 correspond to Comparative Example 1
The amount of abrasion of the photoreceptor is smaller than that of the photoreceptor, and by controlling the potential, the potential is stable even after 10,000 sheets of durability, and there is no problem on the image.

[0064]

According to the image forming apparatus of the present invention, in the contact charging method, the amount of wear of the photosensitive member is suppressed, the thickness of the photosensitive member changes due to durability, the durability of the charging member changes, and the environmental change of the resistance layer of the charging member. Irrespective of this, a remarkable effect of maintaining a sufficient image density and image quality without difference in charge SRU without charge failure is exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus of the present invention.

FIG. 2 is a block diagram of a facsimile using the image forming apparatus as a printer.

FIG. 3 is an operation sequence diagram of an example of the image forming apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic photosensitive member 2 Charging roller 3 Image exposure means 4 Developing device 5 Paper feed roller and paper feed guide 6 Transfer roller 7 Cleaner 8 Pre-exposure means 9 Conveying section 10 Image reading Unit 11 Controller 12 Receiving Circuit 13 Transmitting Circuit 14 Telephone 15 Line 16 Image Memory 17 CPU 18 Printer Controller 19 Printer

Claims (3)

[Claims] In an image forming apparatus for forming an image by applying an image forming process including a step of charging a surface of a charged body to a charged body, the charged body has a number average molecular weight on a conductive support. An electrophotographic photoreceptor having a surface layer containing 30,000 or more polycarbonate resins, wherein a charging means for charging the charged body contacts a charged member to which a voltage is applied to contact the charged body. A contact-type charging device for charging a surface of a charged body, wherein when the charging member corresponds to an image forming area of the charged body, the charging member is controlled by a DC constant voltage, and the thickness of the charged body layer at that time is controlled. Is detected, and when the charging member corresponds to the image forming area of the member to be charged, the DC voltage of the charging member is controlled with a DC voltage corresponding to the detected DC current amount. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein an exposure amount of light irradiation performed during image formation is controlled according to the detected amount of direct current. 3. The image forming apparatus according to claim 1, wherein the charging member is a conductive charging member having a high resistance layer on a surface layer.