JPH0990766A - Developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing method in which a developing device can be miniaturized, and an image of high quality can be provided by use of a magnetic toner of one component system. SOLUTION: In a developing method for carrying a static charge image on an image carrying means 7 moved with carrying the static charge image to a developing area by a developer support means 4 provided opposite to the image carrying means 7 while attracting a magnetic developer 2 to the surface to develop it, the developer support means is formed of a permanent magnet member 4 having 8-32 magnetic poles on the surface, formed to have a surface magnetic flux density of 850G or more, and integrally molded into a cylinder 10-20mm in diameter, and the magnetic developer 2 is formed of a magnetic toner of one component system containing 20-70wt.% of magnetic powder and a binder resin as essential components and having an average particle size of 5-10μm, a volume natural resistance of 10<14> Ω.cm or more and an absolute value of frictional charge quantity of 10μc/g or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface of a developer supporting means composed of a permanent magnet member integrally formed in a cylindrical shape with an electrostatic charge image formed on the surface of an image carrying means carrying an electrostatic charge image. The present invention relates to a developing method for developing using a one-component magnetic toner that is adsorbed and held on a magnetic recording medium.

[0002]

2. Description of the Related Art Conventionally, in an image forming method using electrophotography or electrostatic recording, an electrostatic charge image formed on a surface of an image carrier made of a photoconductor or a dielectric is incorporated into, for example, a permanent magnet member. At the same time, a developing means comprising a sleeve which is rotatably fitted to the permanent magnet member is used, and is rubbed with a so-called magnetic brush made of a magnetic developer to develop a toner image. Next, the toner image is directly fixed, or the toner image is transferred onto a transfer sheet such as plain paper and then fixed to obtain a final image. However, in the magnetic brush method, the magnetic brush made of a magnetic developer contacts not only the image portion forming the electrostatic charge image but also the non-image portion, so that the background fog is likely to occur. Therefore, a means for applying an electric field in which an AC bias is superimposed on a DC bias is used between the image carrier and the sleeve.

FIG. 2 is a lateral cross-sectional view of a main part showing an example of a conventional developing method. In FIG. 2, reference numeral 1 denotes a developer tank, which contains a magnetic developer 2 and is provided with a plurality of permanent magnets 3 below it to form a columnar permanent magnet member 4 and a non-magnetic metal material (for example, SUS304). A developing roller 6 is provided that is coaxially and relatively rotatable with the sleeve 5 formed in a hollow cylindrical shape.

Reference numeral 7 denotes a photosensitive drum, which is rotatable in the direction of the arrow, and faces the developing roll 6 with a gap g therebetween. Reference numeral 8 denotes a doctor blade, which is provided in the developer tank 1 and faces the developing roll 6 with a gap t therebetween to regulate the layer thickness of the magnetic developer adsorbed on the sleeve 5 constituting the developing roll 6. Is. Reference numeral 9 is an AC power source, 10 is a DC power source, and the photosensitive drum 7 and the doctor blade 8 are provided.
It is for connecting between and applying a superimposed bias of direct current and alternating current. The gap g is formed slightly larger than the gap t.

With the above construction, when the permanent magnet member 4 is fixed and the sleeve 5 is rotated in the direction of the arrow, the magnetic developer 2 is adsorbed onto the sleeve 5 and conveyed, and the developing area facing the photosensitive drum 7 is formed. Then, due to the electric field of the electrostatic charge image formed on the photosensitive drum 7, the magnetic developer 2 overcomes the attraction force of the permanent magnet member 4 to the sleeve 5 and is transferred. Thereby, the electrostatic charge image can be developed.

[0006]

In the above-described developing method, the outer peripheral surface of the sleeve 5 attracts the magnetic developer 2 by the magnetic attraction force of the permanent magnet member 4 and conveys it by the frictional force. In order to improve the transportability, the surface roughness is usually increased by, for example, blasting. However, there is a problem that the wear proceeds, the coefficient of friction changes, or a local change occurs during use, so that the layer thickness of the magnetic developer 2 adsorbed changes and the developability decreases.

Since the developing roll 6 which adsorbs and supports the magnetic developer and conveys it is constituted by coaxially combining the permanent magnet member 4 and the sleeve 5, the processing and assembly are complicated and the production is complicated. There is a problem that the cost increases.

In order to reduce the size of a printer or the like, a developing method of omitting the sleeve 5 constituting the developing roll 6, using only the permanent magnet member 4 in a rotating state, and developing an electrostatic charge image by a magnetic brush method is proposed. (See, for example, JP-A-62-201463). In such a developing method, about half the height of the magnetic brush made of a magnetic developer comes into contact with the surface of the photosensitive drum 7.

However, in the magnetic brush developing method in which the sleeve 5 as described above is omitted, there is a difference in height and developability of the magnetic brush between the magnetic poles of the permanent magnet member 4 and between the magnetic poles. Change, and particularly when developing a halftone image, there is a problem in that the image quality deteriorates. On the other hand, if the number of revolutions of the permanent magnet member 4 is increased to eliminate the above-described density unevenness, the drive torque is increased and noise is generated, which is not preferable.

Therefore, the peripheral speed Vm of the permanent magnet member 4 is about 1.5 times Vp of the peripheral speed Vp of the photosensitive drum 7.
Usually, it is set to be twice or more. However, since the magnetic developer adsorbed and supported on the surface of the permanent magnet member 4 constantly rubs the surface of the photosensitive drum 7, the image becomes a state in which the magnetic developer is swept in the rotation direction of the permanent magnet member 4. However, there is a disadvantage that a high quality image cannot be obtained.

In order to solve the above-mentioned drawbacks, it has been proposed to make the relative speed between the moving speed of the magnetic developer and the photosensitive drum 7 approximately zero to less than 1.9 times (Japanese Patent Publication No. 63-3).
9910 and Japanese Patent Laid-Open No. 6-274025). However, each of these proposals has a configuration in which a permanent magnet member and a sleeve are coaxially combined, and there is a problem that the processing and assembling are complicated as described above. Particularly, in the former, since both the magnet and the non-magnetic cylinder are configured to rotate, there is a disadvantage that the configuration of the drive system is further complicated and it is difficult to reduce the size.

Next, in the magnetic brush developing method in which the sleeve 5 is omitted as described above, the use of a two-component developer composed of a non-magnetic toner or a mixture of a magnetic toner and a magnetic carrier is relatively expensive. Although there is an advantage that the image density can be obtained, the management of the developer is complicated and the toner density is restricted. For example, when a non-magnetic toner is used, the toner density is restricted to 10 to 40% by weight. Therefore, there is a case where the toner density control means by the toner density detection means is required, and there is a drawback that the developing device becomes complicated. On the other hand, when the one-component magnetic toner is used, there is an advantage that the toner density control means is unnecessary, but on the other hand, in the magnetic brush developing method in which the sleeve 5 is omitted as described above, the image density is lowered. At the same time, there is a problem that uneven density occurs.

The present invention solves the above-mentioned problems existing in the prior art, enables downsizing of a developing device, and can form a high-quality image even when a one-component magnetic toner is used. The challenge is to provide.

[0014]

In order to solve the above-mentioned problems, in the present invention, an electrostatic charge image on an image carrying means for carrying and moving an electrostatic charge image is provided facing the image carrying means. In the developing method in which the magnetic developer is adsorbed on the surface of the developer by the developer supporting means thus obtained, and the magnetic developer is conveyed to the developing area for development, the developer supporting means has magnetic poles of 8 to 32 poles on the surface to reduce the surface magnetic flux density. Formed over 850G and diameter 10-2
It is composed of a permanent magnet member integrally formed in a cylindrical shape of 0 mm, contains 20 to 70% by weight of magnetic powder of a magnetic developer and a binder resin as an essential component, has an average particle diameter of 5 to 10 μm and a volume resistivity of 10 ¹⁴ Ω · cm or more, absolute value of triboelectric charge 10
composed of a one-component magnetic toner of μc / g or more,
I adopted the technical means.

In the present invention, the moving directions of the developer supporting means and the image carrying means in the developing area can be formed in opposite directions. Further, in the present invention, it is possible to form the developer supporting means and the image carrying means in the developing region in the same moving direction and at substantially the same moving speed, and at the same time, the developing gap and the doctor gap can be formed substantially the same. That is, the doctor gap t, which is the gap between the surface of the permanent magnet member and the tip of the doctor blade, is the developing gap g, which is the gap between the permanent magnet member and the image carrying means, from the viewpoint of image quality.
And the same size as t.gtoreq.g. In this case g−t ≦
It should be 0.1 mm.

The permanent magnet member in the present invention is not limited to a sintered magnet, but may be a resin magnet containing magnetic powder and a resin material as main components. The permanent magnet member may be formed by integrally forming the magnet in a roll shape on the outer circumference of the shaft, or may be formed entirely of a magnetic material including the shaft. However, in order to prevent development unevenness, the permanent magnet member preferably has no joint in the circumferential direction and the axial direction, and is preferably integrally formed as a whole.

On the surface of the permanent magnet member, magnetic poles having different polarities are alternately arranged in the circumferential direction with a minute interval, so that the surface magnetic flux density decreases as the number of magnetic poles increases. On the other hand, from the viewpoint of preventing the magnetic developer from scattering, the surface magnetic flux density of the permanent magnet member is 850 G or more, preferably 1000 to 240.
It should be 0G. Further, the number of magnetic poles is preferably 8 to 32 poles corresponding to the surface magnetic flux density, and the diameter is preferably 10 to 20 mm from the viewpoint of miniaturization.

Next, since the permanent magnet member in the present invention is a semiconductive or insulating material, it is preferable to apply a bias voltage from a doctor blade when applying a bias voltage. In this case, the doctor blade is made of metal or the like. It may be formed of a conductive material.

As the bias voltage, when a DC voltage alone or a DC voltage and an AC voltage are superimposed and applied, the AC voltage to be superimposed on the DC voltage is more than that of 500 to 1 kHz which is usually used. A low frequency one is preferable, and the number of magnetic poles of the permanent magnet member is M and the peripheral speed is Vm (mm /
Second), f = M · Vm / π · determined by the diameter D (mm)
D (Hz), and the peak-to-peak voltage _Vpp is 1
It is good to be 00-800V.

It is important that the superimposed voltage is applied in synchronization with the magnetic pole of the permanent magnet member. That is, when the magnetic poles of the permanent magnet member are closest to the surface of the image carrying means, the valley value Vmin of the voltage waveform is applied, while when the magnetic poles of the permanent magnet member are closest to the surface of the image carrying means. The output value of the AC power supply is controlled so that the peak value Vmax is applied. As an example of this synchronizing means, a magnetic sensor for detecting the magnetic field of the permanent magnet member may be attached to serve as a frequency trigger of the AC power source, or a synchronizing signal of the AC power source may be taken out from the rotating shaft of the permanent magnet member.

Next, the magnetic toner of the present invention preferably has an average particle diameter of 5 to 10 μm, and has an insulating property with a volume resistivity of 10 ¹⁴ Ω · cm or more from the viewpoint of improving transferability, and the carrier and the doctor. Those that are easily charged by friction with the blade are preferable.

The composition of the toner is the same as that of a commonly used toner, such as a binder resin (styrene-acrylic copolymer, polyester resin, etc.), a coloring agent (carbon black, etc., but when magnetite is used as the magnetic powder). Does not have to be added) and magnetic powder (magnetite, soft ferrite, etc.) as essential components, and charge control agents (nigrosine, metal-containing azo dyes, etc.), release agents (polyolefin, etc.), fluidization as optional components. Those containing an agent (hydrophobic silica) (internal addition and / or external addition) can be used. It should be noted that if the amount of magnetic powder is small, the amount of toner scattering increases, while if the amount of magnetic powder is large, the fixability deteriorates. By appropriately selecting a coloring agent, a color toner can be produced.

The average particle size (volume) was measured using a particle size analyzer (Coulter Counter Model TA-II manufactured by Coulter Electronics Co.). The volume resistivity is DC4KV / cm, and 10 dozen mg of the sample is filled in a Teflon (trade name) cylinder with an inner diameter of 3.05mm and
It is a value measured by an insulation resistance meter (Yokogawa Hewlett Packard model 4329A) with a load of 00 gf applied. Further, the triboelectric charge amount is a value measured by a commercially available blow-off triboelectric charge amount measuring device (TB-200 manufactured by Toshiba Chemical) with a toner concentration of 5% (using a ferrite carrier (KBN-100 manufactured by Hitachi Metals as a standard carrier)). Is.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a transverse cross-sectional view of an essential part showing an example of a developing means in an embodiment of the present invention. In FIG. 1, the permanent magnet member 4 is an isotropic ferrite magnet (YBM-3 made by Hitachi Metals), Mn.
-Al-C magnets and Nd bond magnets (Nd _12.5 Fe
₇₉ B _6.5 90 parts by weight of magnetic powder (crushed powder of 30 mesh or less) made of Al ₂ and 10 parts by weight of ethylene-ethyl acrylate copolymer were kneaded at 100 ° C., and then formed by extrusion molding. A plurality of magnetic poles extending in the axial direction are provided to form a columnar shape and are rotatably provided below the developer tank 1. The AC power source 9 and the DC power source 10 are connected between the doctor blade 8 and the photosensitive drum 7, and between the magnetic developer 2 and the photosensitive drum 7 that are attracted and conveyed to the surface of the permanent magnet member 4, An alternating electric field in which an AC bias is superimposed on a DC bias is formed so that an alternating electric field can be applied. The AC power supply 9 may be omitted.

A description will be given of the result of image formation using the magnetic developer 2 made of magnetic toner by the developing means having the above-mentioned structure. First, the magnetic toner is a styrene-acryl n-butyl methacrylate copolymer (M
w = 210,000, Mn = 16,000) 57 parts, magnetic powder (Toda Kogyo EPT500) 40 parts, polypropylene (Sanyo Kasei TP32) 2 parts, charge control agent (Orient Chemical Co. Bontron E81) 1 part And heat kneading, cooling and solidifying, pulverizing and classifying to form an average particle size of 10 μm,
0.5 part of a fluidizing agent (R972 manufactured by Nippon Aerosil) was externally added to the surface. The volume resistivity was 5 × 10 ¹⁴ Ω · cm, and the triboelectric charge amount was −22 μc / g.

On the other hand, the photosensitive drum 7 was formed by OPC and had a surface potential of -600 V and a peripheral speed of 25 mm / sec. Further, the developing gap (g) was set to 0.3 mm and 0.4 mm, the doctor gap (t) was set to 0.3 mm, and a DC bias voltage of -500 V was applied from a doctor blade 8 made of brass. Table 1 is a table showing image evaluation results when the developed image was corona-transferred and heat roll-fixed at 180 ° C. and 1 kg / cm. The environment for development and fixing was 20 ° C. and 60% R.F. H. Met.

[0027]

[Table 1]

As is clear from Table 1, in Nos. 1 and 2, since the surface magnetic flux density of the permanent magnet member 4 as the developing roll is small, the spikes of the magnetic brush are weak, and the image density is low. Occurrence of uneven density is observed. On the other hand, in Nos. 3 and 4, since the surface magnetic flux density was large, the magnetic brush had strong ears, and a good image without fog and density unevenness was obtained. In this case, since the developing gap g and the doctor gap t have the same size, it is recognized that the density unevenness is eliminated as a result of the accumulation of the magnetic toner in the developing area.

Next, in Nos. 5 to 8, since the surface magnetic flux density of the permanent magnet member 4 constituting the developing roller is large, the ears of the magnetic brush are strong, and the permanent magnet member 4 and the photosensitive member in the developing area are strong. Since the rotating direction of the drum 7, that is, the moving direction, is the opposite direction, regardless of the dimensional relationship between the developing gap g and the doctor gap t, a pool of magnetic toner is formed in the developing area, and there is no fog or uneven density. Image is formed. If the peripheral speed ratio between the permanent magnet member 4 and the photoconductor drum 7 is made too large, the driving torque of the permanent magnet member 4 becomes large. Therefore, it is preferably 6 or less.

[0030]

Since the present invention has the configuration and operation as described above, the following effects can be obtained.

(1) Since only the permanent magnet member is used as the constituent member of the developing roll, the developing device can be downsized and the image forming apparatus as a whole can be downsized. (2) Since the surface magnetic flux density of the developing roll is large, the ears of the magnetic brush are strong and a good image without density unevenness can be obtained.

(3) Since the permanent magnet member, which is a means for supporting the magnetic developer, is hard, it is possible to improve the durability with little wear of the surface and little change over time. (4) A stable and high-quality image can be obtained even if the development gap is large.

(5) Since the one-component magnetic toner is used as the magnetic developer, it is not necessary to use the toner concentration control means, and the entire apparatus can be made compact.

[Brief description of drawings]

FIG. 1 is a lateral cross-sectional view of an essential part showing an example of a developing unit in an embodiment of the present invention.

FIG. 2 is a cross-sectional view of essential parts showing an example of a conventional developing method.

[Explanation of symbols]

 4 Permanent magnet member 7 Photoreceptor drum 9 AC power supply 10 DC power supply

Claims (3)

[Claims] 1. A magnetic developer is adsorbed on the surface of an electrostatic charge image on an image carrying means, which carries and moves an electrostatic charge image, by a developer supporting means provided facing the image carrying means. In the developing method in which the developer is conveyed to the developing area and is developed, the developer supporting means has 8 to 32 magnetic poles on the surface and has a surface magnetic flux density of 850 G or more and is integrally molded into a cylindrical shape having a diameter of 10 to 20 mm. And a magnetic developer containing 20 to 70% by weight of magnetic powder and a binder resin as essential components, an average particle size of 5 to 10 μm, a volume resistivity of 10 ¹⁴ Ω · cm or more, and friction charging. Absolute value of amount 10μc
/ G or more of a one-component magnetic toner. 2. The developing method according to claim 1, wherein the moving directions of the developer supporting means and the image carrying means in the developing area are opposite to each other. 3. The developer supporting means and the image carrying means in the developing area are formed to have the same moving direction and substantially the same moving speed, and the developing gap and the doctor gap are formed to be substantially the same. The developing method according to claim 1.