JPH0647958U - Development device - Google Patents

Abstract

(57) [Summary] [Objective] To provide a developing device which can be miniaturized and manufactured at low cost and which can form a high-quality image. A developing roll is rotatably provided in a developer tank containing a magnetic developer so as to face an image carrier that carries an electrostatic charge image on the surface and moves. In a developing device configured to visualize an electrostatic charge image by approaching or contacting a carrier, a developing roll is formed of a permanent magnet material in a cylindrical shape, and a plurality of axially extending members are formed on the surface of the developing roll. The individual magnetic poles are provided at equal intervals so that different poles alternately appear in the circumferential direction, non-magnetized portions are provided at both ends of the developing roll, and the non-magnetized portions are provided so that the seal member contacts.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a developing device for visualizing an electrostatic charge image formed on the surface of an image carrier in electrophotography, electrostatic recording, etc., and particularly to a magnetic toner or a mixed powder of a toner and a magnetic carrier. The present invention relates to a developing device having a structure that can be manufactured at a low cost in the developing device using the magnetic developer described in 1.

[0002]

[Prior art]

 Conventionally, as a means for developing an electrostatic charge image formed on the surface of an image carrier, a two-component magnetic developer in which a magnetic carrier and a non-magnetic or weakly magnetic toner are mixed on the surface of a developing roll is used. A method of magnetically attracting and transporting and bringing the surface of the image carrier close to or in contact with it is often used. On the other hand, one-component magnetic toners are also used as magnetic developers.

When such a one-component magnetic developer is used, it is different from the two-component magnetic developer, and only the consumed amount needs to be replenished. Therefore, friction charging between the non-magnetic toner and the magnetic carrier is performed. There are advantages such as not requiring a mixing means for improving the toner quality, and a means for adjusting the concentration of the non-magnetic toner consumed in the developing process. For this reason, in recent years it has been used together with two-component developers in various types of recording devices such as electrophotographic copying machines, facsimiles, printers, and the like.

As a developing device using the above-mentioned one-component magnetic developer, for example, a developing device having a structure shown in FIG. 3 is known. In FIG. 3, reference numeral 1 denotes a developer tank, which holds and holds the magnetic toner 2. Reference numeral 3 denotes a sleeve, which has a hollow cylindrical cross section made of a non-magnetic material and is rotatably disposed so that a part thereof is immersed in the developer tank 1.

Next, in the sleeve 3, a transverse cross section is formed into a circular shape, and a plurality of magnetic poles extending in the axial direction are arranged at equal intervals so that different poles appear alternately in the circumferential direction. 4 is provided so as to be rotatable relative to the sleeve 3. Reference numeral 5 denotes a doctor member, which is arranged at a side edge portion of the developer tank 1 in a direction toward the axial center of the sleeve 3. An image carrier 6 is rotatably provided so as to face the sleeve 3 described above. Reference numeral 7 denotes a seal member, which is formed in a band shape from a material such as moltoplane or felt, and is in close contact with the sleeve 3 over at least a semicircle.

With the above structure, when the image carrier 6 and the permanent magnet member 4 are rotated clockwise and the sleeve 3 is rotated counterclockwise, the magnetic toner 2 is magnetically attracted onto the sleeve 3 and the doctor member Since the layer thickness on the sleeve 3 is regulated by 5 to form a magnetic brush of a certain height and the surface of the image carrier 6 is rubbed, the electrostatic charge image formed on the surface of the image carrier 6 is visualized. can do. In this case, the seal member 7 prevents the magnetic toner 2 from expanding outside the predetermined image forming area or leaking out of the developer tank 1.

[0007]

[Problems to be solved by the device]

 Since the developing roll having the above-mentioned configuration has a large number of constituent parts, it takes a lot of time and man-hours to manufacture, and there is a problem that the cost inevitably increases. Particularly in recent years, the advent of a low-priced and compact developing device is strongly desired, and the conventional structure cannot meet the above demand.

Further, in the case of using the developing roll having the above-mentioned conventional configuration, the permanent magnetic member 4 and the surface of the sleeve 3 are separated from each other, so that the surface magnetic flux density of the sleeve 3 is inevitably lowered. , The magnetic flux density in the magnetic poles provided in the permanent magnet member 4 must be increased. Therefore, in most cases, a magnetic field molding means (see, for example, JP-A-59-226367 and JP-A-60-10610) is adopted, and this also causes the manufacturing cost to rise.

In order to solve the above problems, a developing device having a structure as shown in FIG. 1 has been proposed (see, for example, Japanese Patent Publication No. 54-39139 and Japanese Patent Publication No. 60-113271). In FIG. 1, the same parts are designated by the same reference numerals as those in FIG. By omitting the sleeve as shown in Fig. 1, the developing device can be downsized and the manufacturing cost of the developing roll can be reduced.

However, in the configuration as shown in FIG. 1, inconvenience occurs if the sleeve 3 in FIG. 3 is simply omitted. That is, since the permanent magnet member 4 is generally provided with magnetic poles over the entire length in the axial direction, the end portion that comes into contact with the seal member 7 that is provided to prevent the magnetic toner 2 from leaking out of the developer tank 1. There is also a magnetic pole.

The contact surface between the permanent magnet member 4 and the seal member 7 is in close contact with each other without a gap to prevent the leakage of the magnetic toner 2, but the magnetic toner 2 is a fine particle and the magnetic toner 2 has a permanent magnet. The magnetic toner 2 penetrates between the permanent magnet member 4 and the seal member 7 due to the magnetic attraction of the member 4 and the fact that the seal member 7 is made of an elastic material.

The magnetic toner 2 that has entered as described above is crushed by the permanent magnet member 4 and the seal member 7 to form a granular body, a lump, or a plate-like body. When the magnetic toner 2 in such a solidified state is peeled off and mixed into the developer tank 1 and further adsorbed and conveyed by the permanent magnet member 4, it is caught between the doctor member 5 and the succeeding magnetic toner. As a result of blocking the passage of the second magnetic field, it becomes impossible to form a normal magnetic brush on the surface of the permanent magnet member 4 in the developing area facing the image carrier 6, resulting in a defect called a so-called blank area in the image. There is. Further, the magnetic toner 2 intrudes into the seal member 7 and is welded by frictional heat to generate a braking effect, which leads to an increase in driving torque of the permanent magnet member 4.

An object of the present invention is to solve the problems existing in the above-mentioned prior art, to provide a developing device that can be manufactured in a small size and at low cost and can obtain a high quality image.

[0014]

[Means for Solving the Problems]

 In order to achieve the above object, in the present invention, a developing roll is rotatably provided in a developer tank containing a magnetic developer so as to face a moving image carrier that carries an electrostatic charge image on the surface, In the developing device configured to visualize the electrostatic charge image by bringing the magnetic developer into contact with or in contact with the image carrier by the developing roll, the developing roll is formed into a cylindrical shape by a permanent magnet material. On the surface of the developing roll, a plurality of magnetic poles extending in the axial direction are arranged at equal intervals so that different poles appear alternately in the circumferential direction, and non-magnetized portions are provided at both ends of the developing roll. We adopted the technical means of providing the seal member in contact with this non-magnetized part.

In the present invention, the non-magnetized portion is formed by partially magnetizing a developing roll made of a permanent magnet material. In addition, it is desirable that the magnetization is an integral magnetization that forms all magnetic poles at the same time. Further, as a constituent material of the developing roll, a sintered magnet such as a ferrite magnet or a rare earth magnet, and a plastic magnet or a bond magnet in which a ferromagnetic powder material is dispersed in a resin binder can be used. The magnetic poles to be provided on the surface of the developing roll are preferably multi-pole, for example 32 poles or more, in order to prevent uneven development. Further, the surface magnetic flux density of the developing roll is preferably 300 to 500G.

[0016]

[Action]

 With the above configuration, it can be manufactured at a lower cost than the one using a conventional developing roller with a sleeve, and since the developing roller portion provided with a seal member is a non-magnetized portion, it can facilitate the intrusion of magnetic toner. Magnetic attraction does not work. Therefore, high quality images can be obtained without defects such as white spots that have been experienced in conventional developing devices.

[0017]

【Example】

FIG. 2 is a longitudinal sectional view of an essential part showing a developing roll in an embodiment of the present invention, and the same parts are designated by the same reference numerals as those in FIG. That is, the present invention is an improved device based on the configuration shown in FIG. In FIG. 2, in order to form the permanent magnet member 4 constituting the developing roll, a general formula of MO.nFe ₂ O ₃ (M is one or more of Ba, Sr, and Pb, n = 5 to 6) is used. A ferrite magnet material is used and is formed into a hollow cylinder with an outer diameter of 20 mm and an inner diameter of 6 mm, for example, by the rubber press method or extrusion molding method.

After sintering the molded body, the shaft 4a is fixed and the outer surface is ground, and 32 magnetic poles extending in the axial direction are provided so that different poles appear alternately at equal intervals in the circumferential direction. In this case, the non-magnetized portions 4b are formed at both ends of the permanent magnet member 4. In order to form such a non-magnetized portion 4b, the length of a magnetizing yoke (not shown) in the magnetizing device is formed in advance to a predetermined dimension, that is, a dimension corresponding to the width dimension W of the image forming area. Just keep it. The surface magnetic flux density of the permanent magnet member 4 is, eg, 300-500G.

A conductive layer may be provided on the surface of the permanent magnet member 4 constituting the developing roll by means such as plating or vapor deposition so that a bias voltage can be applied to prevent background fog or reverse development. desirable. Even if it has an insulating surface, the same effect can be obtained by applying a bias voltage to a conductive member that comes into contact with the developer, for example, the doctor member 5.

Next, 8 is a guide roll, which is formed in a disk shape, and is provided on both ends of the shaft 4 a via a bearing 9 so as to be relatively rotatable. The guide roll 8 rotates in contact with the surface of the image carrier 6 shown in FIG. 1 to secure a developing gap between the permanent magnet member 4 and the image carrier 6, for example, 0.45 mm. Form a diameter of 20.9 mm. The doctor gap between the doctor member 5 and the permanent magnet member 4 is, for example, 0.3 mm. Next, the seal member 7 is formed by felt or malt plane to have a thickness of 2 to 3 mm and a width of 8 to 10 mm, and is provided so as to contact the non-magnetized portions 4b formed at both ends of the permanent magnet member 4.

With the above structure, the image carrier drum made of OPC is rotated at a surface moving speed of 80 mm / sec, uniformly charged to −650 V and exposed, and the permanent magnet member 4 is rotated at 150 rpm, and − When a bias voltage of 550 V was applied and a magnetic toner with a charge amount of -15 μc / g (blow-off method) and a volume resistance of 10 ¹⁴ Ω · cm (measured in an electric field of DC 4 kV / cm) was used, reversal development was performed. Even after the continuous development of 50,000 sheets, a high quality image having an image density of 1.3 or more and a resolution of 8 lines / mm or more could be formed. No infiltration of magnetic toner was observed between the seal member 7 and the permanent magnet member 4.

In this embodiment, the permanent magnet member 4 is described as an example of a sintered magnet made of a ferrite magnet material, but other sintered magnets may be used, or plastic magnets may be used. In this case, in order to be able to apply a bias voltage to the developing roll, it is advisable to add a conductive substance in addition to the ferromagnetic powder and binder (plastic). Further, the shaft 4a may be integrated during molding. As the magnetic developer, not only a magnetic toner but also a mixture of a magnetic carrier and a magnetic toner may be used, or a two-component magnetic developer containing a non-magnetic toner and a magnetic carrier may be used.

[0023]

[Effect of device]

 Since the present invention has the configuration and operation as described above, the developing roll is formed of a permanent magnet member, and the magnetic developing agent can be directly adsorbed and conveyed on the surface thereof without passing through a sleeve. Cost reduction and miniaturization are possible. Moreover, since the seal member is provided so as to contact the non-magnetized portions formed on both ends of the permanent magnet member, it is possible to prevent the magnetic toner or the magnetic developer from entering between the two, There is an effect that it is possible to form a high-quality image without defects such as white spots caused by the mixture of crushed and solidified particles in the magnetic developer.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of essential parts showing an example of a developing device which is a premise of the present invention.

FIG. 2 is a vertical cross-sectional view of a main part showing a developing roll according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view of a main part showing an example of a conventional developing device.

[Explanation of symbols]

 4 Permanent magnet member 4b Non-magnetized part 7 Seal member

Claims (1)

[Scope of utility model registration request] 1. A developing roll is rotatably provided in a developer tank containing a magnetic developer so as to face an image carrier that carries an electrostatic charge image on the surface and moves, and the magnetic developer is held by the developing roll. In a developing device configured to visualize an electrostatic charge image by approaching or contacting the image carrier, a developing roll is formed into a cylindrical shape by a permanent magnet material, and the surface of the developing roll is formed in an axial direction. A plurality of extending magnetic poles are provided at equal intervals so that different poles appear alternately in the circumferential direction, and non-magnetized portions are provided at both ends of the developing roll, and the non-magnetized portions are provided so that the seal member makes contact. A developing device characterized in that