JPH0443899Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a roller used as a magnetic developing roller or the like of an electrophotographic copying machine.

[Conventional technology]

One-component developing devices using magnetic toner are widely used as electrophotographic copying machines. As shown in FIG. 6, this device includes a photosensitive drum 1, a developing roller 2 that is disposed opposite to the photosensitive drum 1 at a constant distance, and a developing roller 2 that is fixed to the base of the device and that is attached to the surface of the developing roller 2. and a layer forming member 3 that is pressed into contact with each other. As shown in the figure, the developing roller 2 has a hollow cylindrical sleeve 6 (see FIG. 7 showing the cross section A-A' in FIG. 6) coaxially attached to the outer peripheral surface of the bar magnet 5 while maintaining a certain space. Note that the rod-shaped magnet 5 is fixed to the base of the device and does not rotate.

In this configuration, the cylindrical sleeve 6 is rotated, and in this state, the toner 4 is supplied from the toner box 7 onto the surface of the sleeve 6. Then, the toner 4 is charged by the sliding friction generated between the fixed layer forming member 3 and the rotating sleeve 6 and is conveyed to a position facing the photosensitive drum 1. At this position, the toner 4 is electrically repelled by the magnetic poles of the magnet 5, and is caused to fly toward the electrostatic latent image to be copied formed on the outer peripheral surface of the photosensitive drum 1. As a result, the toner 4 adheres to the electrostatic latent image on the outer peripheral surface of the photosensitive drum 1, forming a toner image. This toner image is then transferred to copy paper (not shown) to become a duplicate image and a copy is completed. Note that 8 is a high voltage bias power supply for making the toner 4 fly.

[Problem that the invention attempts to solve]

In the developing device as described above, the developing roller 2
Conventionally, metal sleeves such as stainless steel (SUS304) and aluminum have been used as the cylindrical sleeve 6, but in order to improve image quality and extend the life of the developing roller, semiconductive thermosetting resin has recently been used Sleeves made of synthetic fibers are increasingly being used. However, such a resin sleeve has low rigidity and is easily bent, so as shown in FIG.
In a developing device of the type that is installed at a position biased towards the photosensitive drum 1 side and presses against the sleeve 6 in that state, the sleeve 6 receives an evenly distributed load in the axial direction due to the pressing force of the layer forming member 3. It bends in the direction away from the photosensitive drum 1. However, since both ends of the sleeve 6 are supported by bearings (not shown), the center of the sleeve 6 flexes more (the position of the center of the sleeve in the flexed state is shown by the chain line in FIG. 8). . As a result, the distance between the photosensitive drum 1 and the surface of the sleeve 6, that is, the flight distance of the toner 4 becomes non-uniform in the axial direction of the sleeve 6, and the portion of the copied image corresponding to the center of the sleeve 6 becomes short of toner 4. Therefore, the colors become lighter toward the center of the image, causing a so-called "color dropout phenomenon."

This invention was developed in view of the above circumstances, and its purpose is to provide a roller that allows toner to fly over a uniform distance at all times.

[Means for solving problems]

In order to achieve the above object, the roller of this invention is a magnetic developing roller that is installed at a constant distance from the photosensitive drum and has a layer forming member pressed against it at a position on the outer peripheral surface that is biased towards the photosensitive drum. It comprises a bar-shaped magnet and a resin sleeve that is coaxially provided on the outer periphery of the bar-shaped magnet with a certain space maintained therebetween and is rotatably driven in the circumferential direction of the bar-shaped magnet, and the resin sleeve is rotated from both ends. It has a drum-shaped structure that gradually becomes larger in diameter toward the center.

[Effect]

In other words, in the roller of this invention, when the layer forming member is pressed against the photosensitive drum at a position biased toward the photosensitive drum, the deformation of the sleeve due to the pressure contact force of the layer forming member reduces the distance between the roller surface and the photosensitive drum in the axial direction of the roller. The sleeve is deformed into a drum shape by the amount of pressure deformation in advance so as not to cause any change in the shape. Therefore, even if the roller of this invention is deformed by pressure contact load from the layer forming member during use, the sleeve surface after deformation remains straight with respect to the photosensitive drum, and the distance between the roller surface and the photosensitive drum, that is, the toner flight distance remains constant. Therefore, it is possible to obtain a clear copy image without toner shortage.

Next, the configuration of this invention will be explained.

As shown in FIG. 1, the roller of this invention consists of a bar-shaped magnet 5 and a resin sleeve that is coaxially provided around the outer periphery of the bar-shaped magnet 5 with a constant space therebetween and is driven to rotate in the circumferential direction of the bar-shaped magnet. 10, and the resin sleeve 10 is formed into a drum shape whose diameter gradually increases from both ends toward the center.

The rod-shaped magnet 5 is similar to that used in a normal developing roller, etc., as shown in FIGS. 6 and 7, and does not need to be anything special.

Moreover, any resin may be used as the resin constituting the resin sleeve 10 provided on the outer periphery of the rod-shaped magnet 5, but thermosetting resins such as phenol resin and epoxy resin are particularly suitable. The thickness is preferably set in the range of 0.5 to 3.0 mm, and the Young's modulus of the resin formed is set in the range of 5.0 × 10 ⁴ to 5.0 × 10 ⁵ Kg/cm ^2. It is preferable to do so.

The amount of expansion of the drum-shaped sleeve 10 is appropriately set depending on the degree to which the layer forming member 3 (see FIG. 6) is biased toward the photosensitive drum 1 in the developing device in which this roller is used. That is,
The degree of swelling of the sleeve 10 is determined by this sleeve 10.
is set according to the load (pressure contact load) received from the layer forming member 3 during use. In making this setting, the present inventors conducted experiments in advance to determine what kind of pressure load the various sleeves 10 receive and how they deform depending on the degree of deviation of the layer forming member 3. Adapting the following general formula derived from the data yields good results. That is, if the diameter of both ends of the sleeve 10 is A ₁ and the diameter of the center part is A ₂ (see Fig. 1), the above A ₁ and A ₂
Sleeve 10 such that satisfies the following relational expression
If the central portion of the photosensitive drum 1 is made to have a bulging shape, even if the layer forming member 3 is pressed against the angle θ as shown in FIG.
On the other hand, it was found that they are directly facing each other in the longitudinal direction.

A ₂ −A ₁ = 2・sinθ・5/384・P×L ⁴ /E×I θ: The straight line connecting the axis of the photosensitive drum and the roller axis and the tangent line passing through the contact point of the layer forming member and the roller Angle P: Load per unit (g/cm ² ) E: Young's modulus of resin sleeve (Kg/cm ² ) I: Section modulus L: Length of layer forming member (mm) The above formula It is applicable to all cases in which the forming member 3 is in pressure contact with the outer peripheral surface of the sleeve 10 on the left side of the chain line in FIG. Therefore, in this invention, the fact that the layer forming member is biased towards the photosensitive drum means that the layer forming member is located at any position to the left of the dashed line.

Next, examples will be described.

〔Example〕

Both ends diameter 20mm, center diameter 20.2mm, thickness 1mm, length
A 300mm drum-shaped sleeve is made from phenolic resin and combined with a regular bar magnet.
A developing roller as shown in Figure 1 was made. However, the sleeve shape was designed based on the above formula. Then, this developing roller was used in the developing device shown in FIG. 2 (θ=20°), and the deviation of the roller surface (that is, the sleeve surface) from the direction of the photosensitive drum was measured. The results are shown in FIG.
In the above-mentioned developing device, the load of the layer forming member 3 is 150 g/cm, and the length is 300 mm.

[Comparative example]

A cylindrical sleeve with an outer diameter of 20 mm, a thickness of 1 mm, and a length of 300 mm was made from phenolic resin, and a developing roller similar to the conventional one was made. Then, it was used in a developing device similar to that described above, and the deviation of the sleeve surface from the direction of the photosensitive drum was measured. The result is the fourth
As shown in the figure.

From these results, the example product is layer forming member 3
It can be seen that the bulge becomes substantially straight with respect to the photosensitive drum 1 in a state in which the bulge is deformed by the pressing load. On the other hand, it can be seen that in the comparative example product, the originally straight portion is deformed into a concave shape by the pressing load of the layer forming member 3, so that the center part is further away from the photosensitive drum 1.

Further, when a copy image was obtained using a developing device using the above example product, a clear image quality with no shading was obtained. On the other hand, when a copy image was obtained using a developing device using the comparative product, a "white spot" (insufficient toner flying) was formed in the center.

In addition, the above-mentioned comparative example product is as shown in Fig. 5.
When used in a device in which the layer forming member 3 contacts directly above the developing roller 2 (θ = 0°), pressure deformation by the layer forming member 3 occurs in the vertical direction. Surface and photosensitive drum 1
There was no effect on the positional relationship with the outer circumferential surface, and a good copy image was obtained.

[Effect of idea]

As described above, the roller of this invention is designed to be deformed in advance so that the deformation in pressure contact when the layer forming member is pressed at a position biased toward the photosensitive drum does not cause a change in the distance between the roller surface and the photosensitive drum. Because the sleeve is transformed into a drum shape,
Even if the sleeve is deformed by receiving a pressure load from the layer forming member during use, the deformed sleeve surface remains straight with respect to the photosensitive drum, and the toner does not fly unevenly. Therefore, it becomes possible to form a high-quality image without image unevenness.

[Brief explanation of the drawing]

Figure 1 is a longitudinal sectional view of one embodiment of this invention;
The figure is a configuration diagram showing the positional relationship of the layer forming members when using the above example product, Figure 3 is a diagram showing the deviation of the sleeve surface of the example product, and Figure 4 is a diagram showing the sleeve surface of the comparative example product. A diagram showing the deviation, FIG. 5 is a configuration diagram showing another developing device using a comparative example product, FIG. 6 is an explanatory diagram illustrating a normal developing device, and FIG. 7 is a sectional view taken along line A-A'. , FIG. 8 is an explanatory diagram showing a state in which the sleeve is deformed by pressure contact of the layer forming member. 1...Photosensitive drum, 2...Developing roller, 3...
Layer forming member, 4... Toner, 5... Bar-shaped magnet, 1
0...Resin sleeve.

Claims (1)

[Scope of utility model registration request] A magnetic developing roller that is installed alongside the photosensitive drum at a constant distance, and has a layer forming member pressed against it at a position on its outer peripheral surface that is biased toward the photosensitive drum,
It is equipped with a bar-shaped magnet and a resin sleeve that is provided coaxially around the outer periphery of the bar-shaped magnet while maintaining a certain space and is rotationally driven in the circumferential direction of the bar-shaped magnet. A roller characterized by being formed into a drum shape that gradually became larger in diameter.