JP2003345136A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device with which stable image density can be obtained by preventing a selection phenomenon (a phenomenon in which a toner of smaller particle diameter is preferentially developed) which tends to occur when a jumping development is continuously used, and to realize steady development even in the case where the developing device is used for, in particular, an image forming apparatus designed to ensure longer operating life. <P>SOLUTION: The developing device has a magnet roll provided within a cylindrical sleeve. In the magnet roll, if the magnetic flux density peak of a developing magnetic pole facing a latent image carrier is taken as reference value, a circumferential angle with 80% of the reference value is set in the range of 30% to 45% of the circumferential angle with 50% of the reference value. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a printer, a fax machine or a copying machine using an electrophotographic system, and more specifically, a magnetic one-component jumping developing system is adopted. The present invention relates to a developing device.

[0002]

2. Description of the Related Art Conventionally, exposure on the outer peripheral surface of a photosensitive drum,
Development, transfer, cleaning (remove residual toner), static elimination,
An electrophotographic apparatus based on a so-called Carlson process, in which each process means for charging and charging are arranged and an image is formed by a predetermined electrophotographic process, is widely used.

In this type of electrophotographic apparatus, a non-magnetic sleeve having a fixed magnet assembly inserted therein is opposed to a photosensitive drum, and the magnetic toner conveyed to the facing position (developing gap) through the non-magnetic sleeve. A developing method is adopted in which the latent image is selectively attached to the exposed image.

In the developing method using this kind of magnetic toner, only one-component magnetic toner is used, for example, the developing bias applied on the developing gap is used to selectively fly the toner to the photosensitive drum side. Flying developing method, or by using a magnetic toner and one or a plurality of carriers, the magnetic toner charged with electric charges in a developing container by rubbing against the carrier is carried on a non-magnetic sleeve, and the magnetic toner is applied to the photosensitive drum. There is a multi-component developing method in which a toner image is formed while being rubbed to the side.

Among these developing methods, the so-called jumping developing method, which is a flying developing method using a one-component magnetic toner having a simple structure and easily obtaining high image quality, is widely put into practical use. In this jumping development, a magnetic toner having a predetermined charge is held on a non-magnetic toner carrier (developing sleeve), and an AC electric field is applied between the developing sleeve and a photoconductor having an electrostatic latent image. By applying
The toner is selectively blown to a portion corresponding to an image to be developed. Therefore, the magnetic toner does not fly to the non-image area, and as a result, high image quality without fog is obtained.

However, in the case of this jumping development, since the alternating electric field flies between the triboelectric charge of the toner and the electrostatic latent image formed on the photoconductor, the amount of charge of the toner is large for the development. To contribute. Therefore, if the charge amount of the toner is large, the toner will fly easily, and conversely, if the charge amount is small, it will be difficult to fly.

In general, since toner has a predetermined particle size distribution, a toner having a large particle size has a smaller specific surface area than a toner having a small particle size, so that the amount of charge generally held tends to be small. On the other hand, a toner having a large particle size has a large magnetic attraction to the surface of the sleeve, and a toner having a small particle size has a small magnetic attraction.

Therefore, when the developing device adopting the jumping developing system described above is used, toner having a large amount of electric charge and a small magnetic attraction force (toner having a small particle diameter) is preferentially developed and used. Accordingly, the toner having a large particle size tends to remain on the sleeve.
Then, a problem of so-called "selective development" occurs in which the amount of toner to be developed gradually decreases, resulting in a decrease in image density. As the life of the image forming apparatus is extended in recent years and the life of the developing apparatus is also extended, this tendency becomes a more remarkable problem.

[0009]

As a means for preventing the phenomenon of the decrease in the developing density caused by the use of the developing device, the timing of not forming an image is utilized depending on the use condition of the developing device. Therefore, it is also proposed to perform so-called refresh development in which the toner on the sleeve is forcibly transferred to the photoconductor (Japanese Patent Laid-Open No. 2000-31090).
9, JP-A-2000-330379).

By carrying out such refresh development, the toner remaining on the sleeve can be forcibly removed, so that stable development can be obtained for a long period of time, but on the other hand, it is drastic without depending on such processing. Measures are also desired. The present invention efficiently develops even if the amount of charge held by the toner is uneven, without performing such refresh development, and makes a large change in the average particle size of the toner held on the sleeve surface even when the developing device is used for a long period of time. It is an object of the present invention to provide a developing device that does not cause
It is another object of the present invention to provide a developing device that suppresses selective development of the toner held on the surface of the sleeve and does not cause a decrease in image density even after long-term use.

[0011]

In order to achieve the above object, the invention (developing device) described in the claims is a developing device including a magnet roll provided in a cylindrical sleeve. Is the peak value of the magnetic flux density of the developing magnetic pole facing the latent image carrier,
The circumferential angle at 80% of the reference value is in the range of 30% to 45% of the circumferential angle at 50% of the reference value.

According to the invention of this claim, the flying force of the toner can be enhanced by concentrating the magnetic flux density peak value portion that most contributes to the development in a specific narrow range, and the toner can be held as described above. It is possible to effectively prevent selective development caused by the difference in charge amount.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be exemplarily described in detail below with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the constituent parts described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Only.

FIG. 1 is a diagram showing the overall construction of a developing device using a one-component magnetic developer according to an embodiment of the present invention.
In the figure, A is a photosensitive drum, and B is a developing device. The developing device B includes a developing container 20 that stores one-component toner,
From a rotating non-magnetic sleeve 11 containing a pair of agitating mixers 21 and 22 arranged in the developing container 20 and a fixed magnet roller 10 having a plurality of magnetic poles arranged on the drum opening side of the developing container 20. A developing roller 12 (toner carrying roller), a magnetic blade 13 hanging from above the developing roller 12 toward the upper surface of the developing roller 12, a side wall surface of the container 20 of the magnetic blade 13, and a lower end of which is S.
It is composed of a polar magnet body 14 and a developing bias 16 applied between the developing roller 12 and the photosensitive drum A.

A toner replenishing hole 25 is formed in the upper surface of the developing container 20 above the pair of mixers 21 and 22 so that toner from a toner cartridge (not shown) can be introduced. The toner is sufficiently stirred by the pair of mixers 21 and 22 and is guided to the rotary sleeve 11. The relationship between the peripheral surface of the rotary sleeve 11 and the developing container 20 is such that the peripheral surface of the rotary sleeve 11 below the peripheral surface of the rotary sleeve 11 is opened in a range of about 90 ° facing the mixer 22, and the peripheral surface of the rotary sleeve 11 is concealed via a predetermined gap. The bottom surface 20a of the developing container extends. The magnetic blade 13 is arranged with respect to the rotary sleeve 11 with a gap of 0.3 mm, for example. The developing bias 16 is a low electric field developing bias in which DC and AC are superimposed (for example, VDC 160V, VPP 1.8kV).
Is applied, and the image density is adjusted by controlling the oscillation frequency of this AC. On the other hand, at the time of non-development, DC is turned off and only AC is applied to remove the opposite polarity toner. As the photoconductor drum A, for example, an organic photoconductor thin film silicon drum having a photoconductive layer thickness of 25 to 40 μm is used. The diameter of the photosensitive drum A is set to 30 mmφ and the diameter of the rotary sleeve 11 is set to 20 mmφ. Of course, other than the organic photoconductor, the film thickness is 4 to 2
It is possible to use a 5 μm silicon photoreceptor.

The developer used in the present invention is a so-called magnetic one-component toner, and has an average particle size of 5 to which a property improving agent is added to a binder resin, a charge control agent, and magnetic material particles for convenience and convenience. The particles are about 12 μm.

As the binder resin, polystyrene resin, polyester resin, epoxy resin, polyamide, polymethylmethacrylate, polyvinyl butyral, etc. are used. These can be used alone, copolymerized or mixed. The toner binder resin is preferably contained in the toner in an amount of 30 to 80% by weight, more preferably 30 to 70% by weight. Magnetic powders are ferrous, magnetite and other iron, cobalt, nickel and other ferromagnets, or alloys, or compounds containing these elements, or they do not contain ferromagnetic elements, but are appropriately heat-treated. Examples thereof include alloys which exhibit ferromagnetism, chromium dioxide, and the like. These magnetic powders have an average particle size of 0.1 to 1 μm, preferably 0.1 to 0.5.
It is evenly dispersed in the toner binder in the form of a fine powder in the range of μm. The magnetic powder may be a single substance or may be surface-treated with a surface treatment agent such as a titanium coupling agent or a silane coupling agent. The magnetic powder is preferably contained in the toner in an amount of 35 to 60% by weight,
Preferably, it is 40 to 60% by weight.

For the purpose of further improving the offset resistance, a material having releasability, for example, a low molecular weight polyolefin wax such as polyethylene wax or polypropylene wax can be used. In the toner of the present invention, the surface of the toner particles can be treated with colloidal silica, hydrophobic silica or the like for the purpose of maintaining the fluidity and storage stability of the toner. The toner of the present invention preferably has an average particle size of about 5 to 12 μm.

Next, the features of the present invention will be described with reference to FIG.
The state of the magnetic pole arrangement of the fixed magnet roller 10 and the magnetic flux density of the magnetic pole will be described. This FIG. 2 illustrates the magnetic characteristics of the magnet used for the developing roller. To measure the normal magnetic force pattern of the magnet roll used, GAUSS METER (HGM
-8300L) Gauss meter is used, and as a probe for detection, a vertical probe (WS-) also manufactured by ADS
10) was used.

Referring to FIG. 2, each magnetic pole is located at a position facing the N-pole developing pole N1 disposed near the developing position and the developing container bottom 20a downstream of the developing pole N1 in the rotation direction of the rotating sleeve 11. An S-pole recovery pole S1 and an S-pole blade pole S2 are arranged at positions facing the doctor blade on the upstream side of the developing pole N1 in the rotation direction of the rotary sleeve 11, respectively.
The blade position is expressed as a reference position (0 degree).
Specifically, when expressed in addition to the reference position, the developing pole (N1) is approximately 95 degrees and the recovery pole (S1) is approximately 250 degrees.
And the blade pole (S2) is located at about 350 degrees.

It is described that each magnetic pole is represented by a magnetic intensity circle graph, and the innermost circle of the circular scale in the graph is 0 gauss, and the outermost circle is a unit of 200 gauss and is 1000 gauss.

Here, the developing pole (N
The peak intensity of 1) (about 800 gauss in Fig. 2) is 100.
%, The spread angle having a strength of 80% is θ
(80) and the spread angle with 50% strength is θ
(50).

In the present invention, 80% defined in the above definition is used.
By narrowing the angle θ (80) having the strength of 1 so as not to spread as much as possible, the developing area in which jumping development is performed is controlled and used in an extremely small range. Therefore, the angle θ (80) is selected and used in the range of 30% to 45% with respect to the angle θ (50) similarly defined.

In this way, the peak intensity of the developing electrode is 8
By controlling the width of 0% intensity to be narrow, the flying range can be limited to an extremely narrow range, so that the flying range of the toner itself having a high toner charge amount can be made to substantially coincide with the flying range of the toner having a low toner charge amount. This makes it possible to prevent the toner having a high toner charge amount from being preferentially developed.

As can be seen from the examples to be described later, this good developing range can make the developing area extremely concentrated by making the range of the angle θ (80) itself 25 degrees or less. It is possible and more effective. Furthermore, by making the range of the angle θ (50) itself 75 degrees or less, the developing area can be made extremely concentrated, which is more effective.

[0026]

EXAMPLES In the developing device having the above-described structure, the degree of influence of the developing characteristics was examined by using a plurality of magnet rolls in which the distribution state of the magnetic flux density of the developing pole was changed. The results are shown in Table 1. The developing conditions at this time were as follows. Machine configuration Drum φ30 Positive charging Single layer type OPC charging Scorotron charging Exposure Laser scanner Development Magnetic jumping development Transfer roller transfer Cleaning Counter blade method Static elimination LED light static elimination Developer configuration Drum / Development sleeve linear velocity ratio 1.4 Drum / Development gap 0. 32 mm blade / developing sleeve gap 0.3 mm developing sleeve / mixer 1 linear velocity ratio 0.48 mixer 1 / mixer 2 linear velocity ratio 1.0 Mag roll configuration Roller diameter φ20 mm Number of magnetic poles 3 poles Development pole (N1) magnetic force 90 mT recovery pole ( S1) Magnetic force 70 mT Blade pole (S2) Magnetic force 75 mT NI pole position 110 ° (blade reference) S1 pole position 210 ° (blade reference) S2 pole position 350 ° (blade reference) Blasting condition Bead blasting (# 200) Sleeve surface roughness 8 μm toner structure Composition Internal additive Magnetic powder 40% Wax 2% External additive Silica 1.0% Titanium oxide 1.5% Toner particle size 25% value 6.3 μm 50% value 7.5 μm 75% value 8.5 μm Setting value Drum charging Potential 460V Laser Laser wavelength 780nm Laser exposure 0.9μJ / cm2 Development bias DC + AC Rectangular wave DC voltage 350V AC frequency 2.4kHz AC amplitude 1.6kV, DUTY ratio 50% Transfer bias 10μA Constant current control Cleaning Wire thickness 15g / cm Static neutralization LED wavelength 630 nm LED exposure amount 4.0 μJ / cm 2 Under the above conditions, Kyocera printer FS-1800
Comparison of image density and particle size change amount using a modified machine of the present invention, and carrying out a predetermined durability test using the current mag roll (reference product) and the half value and 80% value of the present invention setting (countermeasure product). I went. The results of the comparison are shown in Table 1 below.

[0027]

[Table 1]

As is clear from the above table, the angular ratios of Examples 1 to 3 are within the range of the present invention, 30 to 45%.
In this case, the image density was high and stable development was performed. The amount of change in particle size at this time was also suppressed to a very small range of 0.3 or less, which confirmed that good development was performed.

On the other hand, when the angle ratio exceeds the range of the present invention as in Comparative Example 1, the image density is largely reduced, and when the angle ratio is smaller than the range of the present invention as in Comparative Example 2. However, it was revealed that the image density was greatly reduced. Moreover, in these two comparative examples, the amount of change in particle size after printing was large, which proves that the selective development was performed.

Also in the embodiment, the range of θ (80) is 25 degrees or less as in the first and second embodiments, and θ
It was found that when the range of (50) was 75 degrees or less, the change in particle size after the printing durability test was even smaller. As described above, according to the present invention, it was clarified that stable development without so-called selective development can be performed by controlling the magnetic flux density peak value of the developing magnetic pole within a specific range.

[0031]

As described above, according to the present invention, by setting the magnetic pole strength of the developing roll within a predetermined range, it is possible to improve the performance of separating toner from the developing sleeve, and the toner can be used on the sleeve for a long period of time. The toner particle size distribution did not change. Further, no reduction in image density due to development was observed. As a result, it is possible to provide a durable one-component developing device.

[Brief description of drawings]

FIG. 1 is a cross-sectional configuration diagram of a developing device using a one-component magnetic developer according to an embodiment of the invention.

FIG. 2 shows a main configuration of a developing roller portion of FIG. 1 including a fixed magnet roller having magnetic poles arranged in three poles.

[Explanation of symbols]

A photoconductor drum B developing device 20 developer container 21,22 mixer 10 Fixed magnet roller 11 rotating sleeve 12 developing roller 13 Magnetic blade 14 Magnet body 16 Development bias N1 development pole S2 blade pole S1 shield pole

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Claims (4)

[Claims] 1. A developing device comprising a magnet roll provided in a cylindrical sleeve, wherein the magnet roll has a magnetic flux density peak value of a developing magnetic pole facing a latent image carrier as a reference value, The circumferential angle at 80% of the reference value is 30% of the circumferential angle at 50% of the reference value.
% To 45% of the developing device. 2. The developing device develops an electrostatic latent image formed on the surface of a latent image bearing member, so that a latent image larger than the magnetic one-component toner layer thickness at the developing magnetic pole position formed on the sleeve surface is developed. The developing device according to claim 1, wherein the image carrier and the sleeve are arranged with a distance therebetween. 3. The developing device according to claim 1, wherein the angle in the circumferential direction at 80% of the reference value is 25 degrees or less. 4. The developing device according to claim 1, wherein the angle in the circumferential direction at 50% of the reference value is 75 degrees or less.