JPH02120773A - Developing device - Google Patents

Abstract

PURPOSE:To form a satisfactory developing layer by determining magnet force by a built-in magnet of the upstream side of a cylindrical member for carrying a developer and press-contacting force of an elastic member for controlling a developer error so as to satisfy a prescribed condition. CONSTITUTION:In a sleeve 2 of a cylindrical member for carrying a developer which turns in the direction as indicated with an arrow B, a magnet roll of a fixed magnet is contained. In the periphery of this roll 3, four magnetic poles 3a-3d whose polarity is changed alternately to the S pole and the N pole are placed, a magnetic field for preventing fog is formed by the magnetic pole opposed to a developing area is formed, a developer 7 is sucked to the sleeve 2 and by an elastic blade 5 of an elastic control member, thickness of a developer layer carried by the sleeve 2 is controlled. Also, when F gauss of magnetic force of the upstream side magnetic pole 3c in the magnetic poles 3d, 3c for inserting the blade 5 and abutting force pg/cm of the blade 5 are selected so as to satisfy a condition of an expression I, a developing layer having uniform thickness and a satisfactory frictional electrification electric field is formed and a developed image of a good quality is obtained.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an apparatus for developing electrostatic latent images.

[Prior Art] A fixed magnetic field generating means is disposed inside a cylindrical developer carrier made of a rotating non-magnetic material, and while being held on the developer carrier by the magnetic force of the magnetic field generating means. The developer conveyed toward the developing section is regulated to a predetermined layer thickness by the contact pressure of a regulating member such as a thin rubber plate, and then transferred to the latent image carrier in the developing section. A developing device for developing an image is known.

In this type of apparatus, the quality of the developed image tends to depend on the force with which the regulating member contacts the developer carrier. That is, if the contact force is too high, the toner, which is the developer, will not be sufficiently applied onto the developer carrier, causing problems such as image unevenness and insufficient C degree of solid black. Furthermore, if the contact force is too low, it will not be possible to impart sufficient triboelectric charge to the toner, and the coating layer of the developer carrier will become thick, resulting in ghost images and foggy images. The disadvantage is that it gets stored away.

US Pat. No. 4,579,081 discloses means for adjusting the contact force of a regulating member against a developer carrier. However, if there is a magnetic pole for conveying the developer toward the regulating section, this magnetic force also affects the formation of the developer layer, but this known publication does not suggest the magnetic force of such a magnetic pole.

[Objective] An object of the present invention is to provide a developing device in which the thickness of a developer layer is regulated by an elastic regulating member, and which allows formation of a good developer layer.

[Summary of the Invention] In the present invention, a developer layer is formed by bringing an elastic member into contact with a cylindrical member of a developer carrier. The magnetic force F of the magnetic pole on the upstream side in the direction of rotation of the cylindrical member among the adjacent magnetic poles is set to (0,71p+385) Gauss or more (-1,
43p+1630) Gauss or less (p is the force of contact of the elastic member against the cylindrical member expressed in g/cm) to form a good developer layer.

[Example] In FIG. 1, reference numeral 1 denotes an electrophotographic photosensitive drum that rotates in the direction of arrow A. OP installed on the surface of this tram
An electrostatic latent image is formed on an electrophotographic photoreceptor such as C by the well-known Carlson electrophotography method, and this latent image is developed in a developing section. Charging means, exposure means, transfer means, cleaning means, etc. disposed around the drum 1 are well known, so they are omitted from the drawing for the sake of simplicity.

The developing device has a developer container 4 having an opening 4a on the front surface and containing a one-component magnetic developer (magnetic toner) 7 therein, and is arranged so as to face the photoreceptor drum l with a gap in the developing section. The developing sleeve 2 (non-magnetic cylindrical body) is a rotatable developer-carrying member that is arranged to partially protrude from the developer container 4 and faces the opening, and is made of a non-magnetic elastic thin plate made of, for example, urethane rubber. It has a regulating member 5 that is elastically in contact with the developing sleeve 2 at a contact portion 8, and furthermore, inside the developing sleeve 2, there are four magnetic poles 3a, 3b, 3 around the periphery.
A magnet roll 3 as a magnetic field generating means having magnetic field generating means 3c and 3d is fixedly arranged. In the present embodiment shown in FIG. 1, the number of magnetic poles of the magnet roll 3 is four, but it may be two or more.

The regulating member 5 is fixed to the container 4 via a holder 6. As the regulating member 5, other than the urethane rubber described above, nitrile rubber, fluororubber, silicone rubber, ethylene propylene rubber, etc. can be used. In any case, the regulating member 5 is preferably made of a material that charges the toner to a polarity for developing a latent image upon contact with the toner.

The developing sleeve 2 as described above rotates in the direction of arrow B (counterclockwise), and the developer adheres to the surface of the developing sleeve 2 by the magnetic force of the magnet roll 3, and is directed toward the outside of the developing device, i.e. It is designed to be carried out to a developing area. In this embodiment, a predetermined gap is set between the developing sleeve and the photoreceptor drum. However, if the two are in contact with each other, when a so-called elastic developing sleeve is used, is also applicable.

A developing bias power source 9 is connected to the developing sleeve 2 . That is, by forming an alternating electric field in which a DC component is superimposed by the power source 9 between the developing sleeve 2 and at least the image portion of the latent image carrier in the developing section.

The developer is caused to vibrate and adhere to the image area of the electrostatic latent image formed on the drum 1 for development.

Next, the magnet roll 3 has four magnetic poles 3a, 3b, 3c, 3d around the magnet roll 3 as described above.
A magnetic pole 3a (S pole) is arranged as a developing pole that faces the developing area and forms a magnetic field that contributes to fog prevention in the developing area. 3b, 3c, and 3d are arranged in this order.

The magnetic pole 3c magnetically attracts the developer 7 in the container 4 onto the sleeve 2, and contributes to the formation of a magnetic field for conveying the developer to the layer thickness regulating section by the elastic regulating member 5. The magnetic field formed by the magnetic pole 3c is applied to the contact portion 8 between the elastic regulating member 5 and the sleeve 2.
It also extends to The magnetic pole 3b contributes to the formation of a magnetic field for conveying the developer that has passed through the developing section into the container 4. The magnetic pole 3d also contributes to the formation of a magnetic field for transporting the developer layer whose thickness is regulated by the elastic developing member 5 to the developing section. In the embodiment shown in FIG. 1, the magnetic poles 3a and 3c are located on the diameter line of the magnet roll 3, but this is not essential; it is sufficient that the magnetic pole 3c faces the inside of the container 4.

Moreover, each of the above-mentioned magnets may be a permanent magnet or an electromagnet.

In the above-described particular apparatus shown in FIG. 1, the developer 7 in the developer container 4 is held on the surface of the developing sleeve 2 by the magnetic force of the magnetic pole 3c of the magnet roll 3. Along with this, the developer is conveyed to the contact portion 8 where the regulating member 5 and the developing sleeve 2 stop, and at this contact portion 8, the amount of conveyance (coating layer thickness) of the developer is regulated M1, and at the same time, the developer is prevented from friction with the sleeve 2 and the member. Sufficient electric charge is imparted during development due to the friction between the developing sleeve 2 and the developing sleeve 2, and the developing sleeve 2 is rotated while being held on the surface of the developing sleeve 2 by the magnetic force of the magnet 3d. The developing sleeve 1 and the developing sleeve 2 are conveyed to the opposing portion, and developed by a known method. The developer 7 that contributed to the development is transferred to the developing sleeve 2
Due to the rotation of the developer, the developer is collected into the developer container 4 while being held on the surface of the sleeve 2 by the magnetic force of the magnetic pole 3b.

FIG. 2 shows the developer 7 near the contact portion 8 in FIG.
FIG. 3 is an enlarged view of the part to show the behavior of the part.

As is clear from FIG. 2, the elastic regulating member 5 is in contact with the sleeve 2 at a position between two adjacent magnetic poles 3c and 3d. In other words, the maximum magnetic flux density position of the magnetic pole 3C on the sleeve surface is at a position on the upstream side of the contact portion 8 with respect to the rotational direction of the sleeve 2, and the maximum magnetic flux density position of the magnetic pole 3d on the sleeve surface is It is located downstream of the vi section 8 with respect to the rotational direction of the sleeve 2.

In FIG. 2, the developer 7 is held on the surface of the developing sleeve 2 by the magnetic force F of the magnetic pole 3c, and as the developing sleeve 2 rotates as indicated by the arrow B, the developer 7 moves from the arrow C'? ' , 75 and reaches the contact portion 8, but since pressure is applied to the contact portion 8 due to the elastic force of the regulating member 5, some of the developer is returned in the direction indicated by the arrow. In order to contribute to the development, the remaining developer passes through the contact portion 8 and is held on the surface of the developing sleeve 2 by the magnetic force of the magnetic pole 3d, and is conveyed to the developing section by the rotation of the developing sleeve 2.

At this time, the developer passing through the contact portion 8 is provided with a triboelectric charge necessary and sufficient for development due to the above-mentioned pressure. It is known that the higher the pressure is, the greater this imparting ability is, and the lower the pressure is, the smaller it is.

It is also known that the higher the pressure, the less the amount of developer applied on the sleeve, and the lower the pressure, the more the amount of developer applied on the sleeve.

Furthermore, the stronger the magnetic force of the magnetic pole 3C, the more the developer 7 is retained on the surface of the developing sleeve 2, and the thicker the developer layer is formed. Furthermore, the weaker the magnetic force of the magnetic pole 3c, the thinner the developer layer becomes. Experiments have shown that if this magnetic force is less than 400 Gauss, the amount of developer retained on the surface of the developing sleeve 2 is too small, making it impossible to obtain sufficient density when copying a solid black image. The result is clear.

FIG. 3 shows the device shown in FIG. 1 in which the contact force p of the elastic member 5 against the sleeve 2 (contact load per 1 cm in the longitudinal direction of the sleeve, that is, in the direction parallel to the axis, g/cm) is 50 When the magnetic force F (Gauss) of the magnetic pole 3C is changed while maintaining a constant value of g/cm, the amount of triboelectric charge per unit weight of developer Q/G (gcoul
/g) and developer application Q on the developing sleeve 2 G/S
(B/cm2) shows how it changes.

As can be seen from Figure 3, when the magnetic force F is 400 Gauss or more, the charging flQ/G does not change much, but the stronger the magnetic force F, the less the amount of developer applied on the developing sleeve G/S. are doing. Therefore, the magnetic force F
It has been found that if the contact force p is extremely strong, it is impossible to obtain sufficient density when copying a 1-peta black image unless the contact force p is weakened.

In view of the above, FIG. 4 shows the results of a study on the range in which a stable state of developer application on the developing sleeve and a stable amount of triboelectric charge can be obtained in the relationship between the magnetic force F and the contact force p. It was found that the upper limit of the straight line I is approximated by F=-1,43p+1630, and the lower limit of the straight line I is approximated by F=0.71p+385. Above the straight line (■), the amount of developer applied was too small, causing image unevenness and making it impossible to obtain an image with sufficient density. Further, below the straight line H, it is difficult to stably apply sufficient triboelectric charge to the developer during development, and a ghost image of the previously developed image may appear in the magnetic field developed image, or the image may It was found that fogging occurred. Note that the O mark and the X mark in the figure indicate whether the image is good or bad.

Furthermore, even in the region below the straight line ■ and above the straight line H, the contact force p is p<:2o (g/cm)
It has also been found that, similar to the phenomenon that occurs in the area below the straight line (3), the amount of triboelectric charging of the developer is insufficient, resulting in ghosting or fogging on the image.

Furthermore, even if the area is below the straight line I and above the straight line H, if the contact force p is >300 (g/cm), the same phenomenon as that occurring in the area above the straight line I will occur. However, the amount of developer coated on the development sleeve was insufficient, resulting in uneven images and failure to obtain images with sufficient density.

From the above experimental study results, by configuring the developing device within the shaded area shown in FIG. 4, stable triboelectric charging of the developer and coating state on the developing sleeve can be obtained.
We have reached the conclusion that even better image quality can be obtained.

In addition, if the distance between the magnetic pole 3c and the contact portion 8 on the sleeve circumferential surface is expressed as expression 1, and the distance between the abutment portion 8 and the magnetic pole 3d on the sleeve circumferential surface is expressed as expression 2, the following can be said. (The distance between the abutting part and the magnetic pole on the sleeve circumferential surface is the distance between the abutting part and the maximum magnetic flux density position of the magnetic pole on the sleeve circumferential surface in the circumferential direction of the sleeve circumferential surface. First, if the magnetic pole 3d is directly under the contact portion 8, the developer will magnetically stand up in the contact portion 8, making it impossible to obtain a stable developer coating layer.

Therefore, it is preferable that the distance sentence is 5 ms or more.

Further, even if the magnetic pole 3c is located directly under the contact portion 8, a stable developer coating layer cannot be obtained for the same reason as above. However, since the upstream position of the contact portion 8 is filled with developer, the magnetic pole 3c may be placed closer to the contact portion 8 than the magnetic pole 3d. Therefore, it is preferable that the distance *i is 2 or more.

However, if the poles 3c and 3d are too far away from the contact portion 8, it will be difficult to carry the developer into the space between the sleeve 2 and the regulating member 5, so the sum of the distance #9.1 and the distance #2 (u++u2 ) is preferably 20 m1 or less.

Furthermore, if the magnetic force of the magnetic pole 3d is less than 400 Gauss, the developer conveying force is reduced, so that the developer is not carried into the space and the developer layer thickness becomes too thin. Furthermore, if the magnetic force of the magnetic pole 3d is greater than 1200 Gauss, the developer conveyance force will be too strong, and the developer with insufficient amount of friction band will also be transferred to the contact portion 8.
Too much is being drawn out. Come closer, magnetic pole 3
The magnetic force d is preferably 400 Gauss or more and 1200 Gauss or less.

In the present invention, the magnetic force of the magnetic pole refers to the maximum magnetic flux density of the magnetic pole on the surface of the sleeve.

FIG. 5 shows another embodiment of the present invention, which is characterized in that the magnet roll has only two different poles 3a', 3c' around it. In the illustrated example, poles 3a' 3c
' is located on one diameter line of the roll 3, but is not limited to this. (A developing device using a two-pole magnetic roll is described in Japanese Patent Application Laid-Open No. 11139/1973.) With this arrangement, the magnetic poles 3a', 3c
' is the magnetic pole 3a in FIG.

Although it can exhibit the same effect as 3c.

At this time, the magnetic force of the magnetic pole 3c' at the contact portion 8 becomes relatively weak, and the developer is more actively stirred in the force direction of the arrow D' in FIG. 5 due to the structure of the device. can be effective.

Furthermore, even if a two-pole magnet is used, the outer diameter of the sleeve is
In the case of 25 liters, the developer can be sufficiently transported.

Further, in the above embodiment, the plate-like regulating member 5 is brought into contact with the sleeve 2 in the forward direction with respect to the rotational direction of the sleeve 2. Even when the developing sleeve 2 is in contact with the counter in the opposite direction to the rotating direction, it can be effectively applied.

The present invention is applicable not only to electrophotographic copying machines but also to developing devices such as laser beam printers and LED printers. Further, the present invention can be applied not only to a developing device that attaches toner to a dark potential area of a latent image, but also to a so-called reversal developing device that attaches toner to a bright potential area of a latent image.

[Effects] According to the present invention, a developer layer having a uniform thickness and good triboelectric charge can be formed, and a developed image of good quality can be obtained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of one embodiment of the present invention, Fig. 2 is an enlarged view of the main part of the apparatus shown in Fig. 1, Fig. 3 is an explanatory diagram of the developer triboelectric charge amount and coating layer with respect to magnetic force, and Fig. 4 is an explanatory diagram of the coating layer. FIG. 5 is an explanatory diagram of another embodiment of the present invention; FIG. 6 is an explanatory diagram of yet another embodiment of the present invention; 2 is an explanatory diagram of another embodiment of the present invention; In the developing sleeve, 3 is a magnet, 3a to 3d are magnetic poles, and 5 is an elastic blade.

Claims (1)

[Scope of Claims] (1) A rotatable cylindrical member that carries and conveys a developer, a fixed magnet disposed inside the cylindrical member, a means for supplying the developer to the cylindrical member, and an adjacent portion of the magnet. an elastic member that contacts the cylindrical member at a position between the two adjacent magnetic poles and regulates the layer thickness of the supplied developer; When the magnetic force of the magnetic pole located upstream in the rotating direction of the rotating member from the position of contact with the member is F (Gauss), and the contact force of the elastic member with the cylindrical member is p (g/cm),
Magnetic force F is 0.71p+385≦F≦-1.43p+1
A developing device within the range indicated by 630. (2) The contact force p of the elastic member to the cylindrical member is 20 g/c
2. The developing device according to claim 1, wherein the developing device has a particle size of not less than m and not more than 300 g/cm. (3) Claim (1) wherein the magnetic force F is 400 Gauss or more.
) or the developing device according to (2). (4) The developing device according to claim 3, wherein the magnetic force of the magnetic pole located downstream of the contact position with respect to the rotational direction of the rotating member is 400 Gauss or more and 1200 Gauss or less. (5) The distance on the circumferential surface of the cylindrical member between the magnetic pole on the upstream side of the abutting part and the abutting part is l_1 (mm), and the circumferential surface of the cylindrical member between the magnetic pole on the downstream side of the abutting part and the abutting part. The distance above is l_2 (mm
), then l_1≧2, l_2≧5, l_1+l_2≦
20. The developing device according to claim 4, wherein the developing device is 20. (6) The developing device according to any one of claims (1) to (5), wherein the magnet has only two magnetic poles around the circumference. (7) The developing device according to any one of claims (1) to (6), wherein the cylindrical member has an outer diameter of 5 mm or more and 25 mm or less. (8) Claims (1) to (7), wherein the cylindrical member has means for forming an oscillating electric field in the developing section facing the latent image carrier.
The developing device according to any one of the above.