JPH0284679A - Developing device - Google Patents

Abstract

PURPOSE:To prevent 'tailing' and 'scattering' from occurring on an image by allowing the absolute value of the rate of change concerning a developer supporting cylinder rotating direction of the component of the magnetic field of magnetic pole in a normal line direction on the surface of a developer supporting cylinder to have a maximum value >=30 gauss/degree. CONSTITUTION:With the component of the magnetic field in the normal line direction formed by the magnetic pole 31, napping is realized in a developed area D on the surface of a sleeve 2. The maximum value is added to the absolute value of the rate of change of the component of the magnetic field in the normal line direction corresponding to the magnetic pole 31 and set >=30 gauss/degree. Therefore, the developer is napped suddenly or falls suddenly on the sleeve 2 in the vicinity of a position where the maximum value exists. Thus, the image without 'tailing' and 'scattering' can be obtained.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an apparatus for developing an electrostatic latent image, particularly in a developing area where the thickness of the developer layer is greater than the gap between the image carrier and the developer support. The present invention also relates to a developing device that develops a replacement image by placing a thin developer layer facing an image carrier.

[Prior Art and Problems] Conventionally, this type of developing device has a non-magnetic rotating body that is disposed with its outer circumferential surface facing an image carrier and supports a magnetic developer on its outer circumferential surface. . In a developing area including the closest portion between the image carrier and the rotating body, the developer is transferred by flying from the rotating body to the image carrier, thereby developing the electrostatic latent image.

In this case, a magnet having a plurality of magnetic poles is fixedly installed inside the rotary body as a means for magnetically attracting the developer to the surface of the rotary body. One of the plurality of magnetic poles is located within the range of the development area and near a position corresponding to the proximity of the image carrier and the rotating body, and is located approximately at the center of the development area and has a normal line. The magnetization is set to have the maximum density point of the directional magnetic field component (magnetic field component in the normal direction to the surface of the rotating body). This normal magnetic field component magnetically restrains the developer on the outer circumferential surface of the rotating body within the range of the development area to form a so-called "stiffness" and transfer the developer to the image carrier. .

However, as one moves toward both ends of the developing area, the density of the normal magnetic field component gradually decreases, and conversely, the density of the tangential magnetic field component (the magnetic field component in the tangential direction to the outer peripheral surface of the rotating body) gradually decreases. increase to

The closer the developer is to both ends of the image area, the more the developer tip is inclined toward the rotating body, causing various problems in the image developed in that area. For example, Fig. 9 (A
), this is called "tailing" and is a condition in which the developer appears to be trailing in a linear manner from the image in the opposite direction to the direction of movement of the image carrier, or "splatter". The above-mentioned "tailing" is further worsened, and this adversely affects image formation, such as a state in which developer particles are scattered even near the periphery of the copied image.

FIG. 8(A) shows an enlarged view of the developing area at this time, showing the appearance of spikes of developer. In the figure, a developer 10 is supported on a developing sleeve 2 serving as a developer carrier. Further, an electrostatic latent image (represented by reference numeral 11 of negative polarity in FIG. 8) is carried on the photosensitive drum i as an image carrier. Then, at the closest part between the photosensitive drum 1 and the developing sleeve 2 (in the case shown, the central part of the developing area), the developer lO that has stood up on the developing sleeve 2 is moved toward the photosensitive drum 1 by the electric attraction force. do. However, from the center of the developing area toward the non-developing areas at both ends, the ears gradually become inclined due to the influence of the horizontal magnetic field component. This trend can be seen with reference numeral 1
As shown in 2, it is quite noticeable at both ends of the development area. For example, in the left side portion of the developing area shown in FIG. Even though it tends to increase in size, it is electrically attracted to the photosensitive drum 1 in the direction of the arrow W, so the developer 10 is drawn onto the rotating photosensitive drum 1 in a direction opposite to the photosensitive drum rotation direction B. A misalignment will occur. This deviation of the developer 10 is the above-mentioned "tail" that extends linearly backward on the copied image. Furthermore, when a portion of the ears breaks apart during flight or due to the impact of collision with a drum, the above-mentioned "floating off" phenomenon occurs.

[1.Object and Overview of the Invention] An object of the present invention is to provide a developing device that can prevent the above-mentioned "tailing" and "flying dust" from occurring.

In the present invention, a fixed magnet having 11 poles is provided in the development region to make the ears of developer stand up on the developer support member, and the magnetic poles are arranged in the normal direction on the surface of the developer support cylinder. A magnetic field is formed in which the absolute value of the rate of change of the magnetic field component with respect to the rotational direction of the supporting cylinder has a maximum value of 30 Gauss/degree or more.

[Example] In FIG. 3, the electrophotographic photosensitive drum 1 is rotated in the direction of the arrow B, and the electrostatic latent image formed on the drum 1 is attached to the drum 1 and a cylindrical non-magnetic material such as aluminum or stainless steel silk. The sleeve 2 arrives at the developing area opposite to each other with a minute distance +41 in between. The sleeve 2 rotates in six directions indicated by arrows. That is, the drum 1 and the sleeve 2 rotate in the same direction in the developing area. The sleeve 2 supports and conveys the developer to the development area O. A developer is supplied to the photosensitive tram 1 in the development area.

A one-component magnetic developer (magnetic toner) 10 is contained in a container 8 in which the sleeve 2 is rotatably provided. The stirring rod 6 rotates in the direction of arrow P to convey the developer 10 toward the developing sleeve 2 . The auxiliary stirring rod 7 rotates in the direction of arrow Q to convey the developer in the direction of the stirring rod 6.

The developer supplied to the sleeve 2 is attracted onto the outer peripheral surface of the sleeve 2 by the magnetic force of the magnet 3 fixedly disposed within the sleeve 2 . The magnet 3 has four magnet parts a and b in the figure.
, c, d are provided, and each one magnetic pole (
(indicated by N and S in the figure) are present at the outer periphery of the magnet. The magnetic pole 31 is a developer 1ifl 44 disposed facing the developing area, and the 6A1 pole 32 is a magnetic material such as iron that regulates the developer layer J7. These are layer thickness regulation magnetic poles, and the 6th poles 33 and 34 are developer transporting magnetic poles.

The magnetic field from the magnetic pole 32 concentrates on the magnetic plate 4, thereby forming a thin layer of °C magnetic developer 10 on the sleeve 2. (Refer to Japanese Patent Publication No. 59-8831) The developer layer formed on the sleeve 2 has a thickness smaller than the minimum gap between the tram l and the sleeve 2 in the developing area. As a means for forming the thin layer of developer on the sleeve 2, an elastic plate that is in contact with the sleeve 2 can also be used, as described in Japanese Patent Publication No. 16736/1983. Moreover, a non-IIu blade may be used instead of the magnetic blade 4.

In the developing area, the developer is caused to stand up on the surface of the sleeve by the normal component of the magnetic field formed by the magnet 8i31. That is, a magnetic brush is formed. Then, in the developing area, the developer flies from the sleeve 2, adheres to the drum 1, and develops the electrostatic latent image. In order to facilitate this flight, DC bias voltage (preferably the potential of the latent image area exposed to light, i.e. bright area potential) and the potential of the latent image area not exposed to light, i.e. It is preferable to apply a voltage with a value between the dark potential. Alternatively, in order to further improve the image quality, an alternating bias voltage may be applied to the sleeve 2 by the source 5 to form a photographing electric field in the developing area. A high-quality image is finally obtained through a process in which the developer repeatedly adheres to and leaves the drum 1 in this oscillating electric field. (Refer to Japanese Patent Publication No. 58-32377.) It is preferable that the alternating bias voltage includes a DC voltage component having a value between the bright area potential and the dark area potential.

In FIG. 4, a line connecting the rotation center 2a of the developing sleeve 2 and the rotation center 1a of the photosensitive drum 1 is defined as a reference line, and a point on the developing sleeve 2 is defined as X. This standard Pj! Let the intersections of L and the outer circumferential surface of the developing sleeve 2 and the outer circumferential surface of the photosensitive drum 1 be Xo and Yo, respectively. The distance 11fXoYo is the shortest distance between the developing sleeve 2 and the photosensitive drum 1,
The XO is located approximately in the middle of the development area.

The maximum distance between the developing sleeve and the photosensitive drum, which is the limit at which the electrostatic latent image on the photosensitive drum l can be developed by the developer on the developing sleeve 2, is 11 may.

A line segment X with a length equal to this It max. The line segment parallel to YO that connects the developing sleeve 2 and the surface of the photoreceptor l is X,
Let's say Y. This line segment XIY is x as shown in FIG. The distance between the opposing developing sleeve 2 and the photosensitive drum 1 is the longest within the developing range. In other words, these two line segments! Yl-XIYI
It can be said that the circumferential range sandwiched between is the range that can be set as the development area. Here, since the value of It raax changes depending on design conditions such as magnetic field strength, the maximum range (range in the circumferential direction) that can be set as the development area also changes accordingly. According to the results, usually 1
1 wax≦2000 μm. Arbitrary position X in the circumferential direction on the developing sleeve 2 shown in FIG. 4 and the developing sleeve 2
The angle between the line segment connecting the center of rotation 2a and the base IV line is α. Further, the angle of the position X from the reference line at this time is αI+lax. Here, the development area is
If expressed by angle α, it is within the range of lαmax l.

FIG. 5 shows the 6R field strength on the outer peripheral surface of the sleeve 2, that is, the division D of the magnetic flux density in polar coordinates. That is, at each angular position of a polar coordinate graph centered on the rotation center 2a of the sleeve 2, the magnetic flux density at that position is plotted in the radial direction. However, the circle Z indicates the 0 Gauss line. Therefore, curve 3a
, 3b, 3c, and 3d are magnetic poles 31, 32, 33, and 34, respectively.
The intensity distribution of the normal magnetic field component corresponding to is shown.

As shown in FIG. 5, the position where the normal magnetic field component due to the magnetic pole 31 has a maximum value, that is, the center of the magnetic pole 31, is located on or near a straight line. Then, the strength of the normal direction magnetic field component gradually becomes weaker from the position at the maximum value toward the upstream side and the downstream side in the sleeve rotation direction.

Needless to say, the position where the normal direction 671 field component corresponding to the 6A1 pole 31 has a maximum weight of 1°l exists within the development area.

For reference, Fig. 6 shows the sleeve outer circumference as position coordinate fq.
b, and the intensity component i1 of the l different component in the normal direction corresponding to the magnetic pole 31 is schematically shown when the straight line is taken as the magnetic field intensity coordinate 11ilI+.

Now, as mentioned above, the occurrence of "one tail trailing" and "flying failure" is caused by the developer spike slowly tilting on the sleeve or slowly rising up. I found out. When the ears of developer tilt, the degree to which they stand up corresponds to the rate of change in the intensity of the normal magnetic field component. This is because the normal magnetic field component contributes to causing the spikes of developer to stand up on the sleeve.

As a result of various experiments conducted by the inventor, the following was discovered. That is, as shown in Fig. 7, the amount of change in the strength (magnetic flux density) of the normal direction magnetic field component on the sleeve surface per unit center angle as seen from the sleeve rotation center is 30 Gauss/
If it is smaller than 1 degree, there will be a lot of "r1 bowing" and "splashing".
Image quality often deteriorated.

Therefore, by giving a maximum value λ to the absolute value of the rate of change of the normal direction magnetic field component corresponding to 6n8i31, and making this maximum value 30 Gauss/degree or more, development can be performed near the position where this maximum value exists. The agent suddenly stood up or fell down on the sleeve, and an image as shown in FIG. 9(B) was obtained without the above-mentioned "tailing" or "splatter".

Below, in more detail, the development 6B pole 31 of the Honjishika example device will be described.
The magnetic flux density distribution state of the normal direction magnetic field component formed by will be specifically explained using diagrams. FIG. 2 is a diagram in which the magnetic flux density distribution of the normal direction magnetic field component is shown by a solid line 3a for the developing magnetic pole of the apparatus according to the embodiment of the present invention, and by a two-dot chain line e for the developing pole of the conventional apparatus. The horizontal axis is located at an intermediate position between the magnetic pole 31 shown in FIG. 3 and the magnetic pole 32 located on the upstream side in the rotation direction A of the developing sleeve 2.
The position where the density of the magnetic field component in the normal direction of the developing pole 1 is 0 Gauss is defined as the (mold position θ0), and the position where the density of the magnetic field component in the normal direction of the developing pole 1 becomes 0 Gauss is expressed as f, (+ degrees θ) toward the downstream side with respect to the rotation center 2a of the developing sleeve 2. The vertical axis represents the normal direction magnetic field component magnetic flux density G (Gauss) on the surface of the developing sleeve 2. In the figure, when comparing both the present embodiment and the conventional device, the present embodiment (solid line) In 3a), the rate of change in density is relatively stable near the maximum magnetic flux density point S at the center position of the magnetic pole (near angle θ = 50 degrees) than in the conventional device (F1 line e); The rate of change becomes large at positions where there is a predetermined distance sequence on both sides from the value Is. - To clarify the above relationship, the magnetic flux density (G (Gauss)) of the vertical magnetic field component of the Mi1 sleeve in Fig. 2 is Figure 1 shows the differentiation with respect to the angle θ and the rate of change with respect to the angle θ is plotted on the vertical axis. 3a' is the rate of change of curve 3a, and eo is the rate of change of curve e. Comparing these two, , at positions a predetermined distance from the center position S to both sides, the rate of change is large, and the local maximum value N and local minimum value N2 (the local maximum value when viewed in absolute value) are clear.Then, the local maximum value N
1. and the absolute value lN21 of the minimum value N2 are both greater than 30 Gauss/degree. Therefore, as shown in FIG. 8(B), near the positions N, N2, the spikes of developer suddenly rise on the sleeve 2, in other words, the spikes of developer rise outside the rising area. suddenly falls onto sleeve 2. In this way, the boundary between the area where the ears stand up on the sleeve 2L and the area where the ears lie down along the sleeve 2 becomes relatively clear due to the magnetic field component in the tangential direction to the outer peripheral surface of the sleeve. Since the developer in the area where the spikes lie along the sleeve 2 is suppressed from flying toward the photosensitive drum, in the state shown in FIG. , the developer downstream of the N2 point is unlikely to fly to the photosensitive drum. On the other hand, in the region between points N1 and N2, the ears of developer are large relative to the sleeve, or stand up at a near angle perpendicular to the sleeve, and the individual particles of developer are arranged in an orderly manner. In this area, the developer tends to fly toward the drum 1 and adhere to it, causing "tailing" and "
Flying and adhering methods that result in "splatter" are suppressed.

Therefore, the point N is near the inlet side end E of the developing area, that is, near the upstream end of the developing area in the sleeve rotation direction.
It is preferable that point N2 be placed near the outlet side end F of the developing area, that is, near the end of the developing area on the downstream side in the rotational direction of the sleeve. Point N3 is located within 1 mm on the upstream and downstream sides of the sleeve rotation direction, centering on the entrance end E of the developing area, and point N2 is located around the exit end F of the developing area. If the sleeve is located within II on the upstream and downstream sides in the rotational direction of the sleeve, good results can be obtained in preventing "tailing" and "splashing".

Further, it is preferable that the points N3 and N7 are provided within 30 degrees on the upstream side and the downstream side, respectively, from the center S of the magnetic pole 31 with respect to the rotational direction of the sleeve. In addition, in order for the developer to fly and adhere to the photosensitive drum, it is generally preferable that the gap between the drum and the sleeve is 2000 μm or less, so for the N3 point s, the gap between the drum and the sleeve is 20 μm or less.
It is preferable to locate it in a region where the thickness is 00 μm or less.

Incidentally, the developer near the entrance side of the developing area is less likely to fly toward the photosensitive drum than the developer near the exit side. Therefore, even if the developer is in the state shown in FIG. 8(A) near the entrance, "tailing" and "flying away" caused by this are relatively minor. Therefore, the magnet is magnetized so that the absolute value of the rate of change in the intensity of the normal direction magnetic field component has a maximum value (30 Gauss/degree or more) only in the vicinity of the exit side end F of the developing area. It's okay. In this case, near the entrance of the developing area, the developer will be in a spiked state as shown in FIG. 2(A), and near the exit, the developer will be in a spiked state as shown in FIG. 8(B).

Next, as another embodiment of the present invention, an apparatus in which a separating plate is provided between the developing sleeve 2 and the photosensitive drum 1 will be described. However, since the device of this embodiment has many of the same features as the device of the first embodiment described above, the isolation plate 14, which is a feature of this embodiment, is shown in FIG. The explanation will be omitted. In this embodiment, the device has a partition plate 1 to prevent the inclined developer at both ends of the development area from participating in the development.
4 was established. This isolation plate 14 is arranged so that the developing sleeve 2 is located within the range of at least X,
and the photoreceptor 1 in the longitudinal direction of the sleeve 2 . The material can be selected from non-magnetic, magnetic, insulating, conductive, etc., depending on the properties of the developer used and surrounding materials. Also, regarding its shape, the tip may be pointed or 1/-r as shown in FIG. 4, or it may be rectangular. As shown in FIG.
, = 2000 μm, the thickness at the base is 5 to 1500 μm
Polyethylene terephthalate and stainless steel plates can be used. In FIG. 4, the isolation plate 14 is provided only at the exit end F of the developing area, but it is also possible to provide it only at the entrance end E, or it is also possible to provide it at both. According to the apparatus of this embodiment as described above, it is possible to roughly and reliably prevent development due to spikes of developer having a large slope at the end of the development area.

The magnets used in the above-described apparatus of the present invention may be of a bonded type, an embedded type, a ferrite sintered type, an integrally molded type made of resin containing magnetic powder, etc. In particular, the diameter of integrally molded resin magnets can be reduced,
It is useful because it is inexpensive and lightweight.

In addition, the development magnetic pole magnetization setting is such that the intensity distribution of the normal direction magnetic field component does not have to be symmetrical with the maximum magnetic flux density point at the center, but may be asymmetrical or have a distorted shape. Good too.

Furthermore, the present invention can be applied not only to a one-component magnetic developer but also to an apparatus using a two-component developer having a magnetic carrier and a toner.

[Effect] According to the present invention, by rapidly laying down the spikes of developer, it is possible to prevent the occurrence of "tails" and "splatters" on the image.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the rate of change of the normal direction magnetic field component, FIG. 2 is an explanatory diagram of the normal direction magnetic field component distribution on the surface of the developing sleeve, and FIG. 3 is an explanatory diagram of an embodiment of the present invention. Fig. 4 is an explanatory diagram of the development area, Fig. 5 is an explanatory diagram of the intensity distribution of the magnetic field component in the normal direction, Fig. 6 is another explanatory diagram of the intensity distribution of the field component at 6 points in the normal direction, and Fig. 7 8(A) is an explanatory diagram of the effect, FIG. 8(A) is an explanatory diagram of the state of the developer in the conventional example, FIG. 8(B) is an explanatory diagram of the state of the developer in the present invention, and FIG. 9(A) is an explanatory diagram of a developed image according to a conventional example, and FIG. 9(B) is an explanatory diagram of a developed image according to the present invention. 1 is an electrophotographic photosensitive drum, 2 is a developing sleeve, 3 is a magnet, 31, 32, 33, 34 are magnetic poles, and N2 is a minimum value. (θ, ノP120 l good θ 10 go 30 ω ta 1t11dku 1 Kotetsu'
7 AL, the tribe's sword, τ Gai, and the black 5fE.
l (A) Figure 6 (已)

Claims (9)

[Claims] (1) A rotatable developer support member that faces the image carrier in the development area, supports a magnetic developer, and transports it to the development area; and the thickness of the developer layer on the developer support member. , a layer thickness regulating member that regulates the layer thickness to be thinner than the minimum gap between the image carrier and the developer supporting member in the developing area; and a layer thickness regulating member fixedly arranged inside the developer supporting member, the developing area a magnet for causing ears of developer to stand up on a developer support member; A magnetic field is formed such that the position where the absolute value of
A developing device characterized in that the temperature is higher than 100%. (2) A rotatable developer support member that faces the image carrier in the development area and supports a magnetic developer and transports it to the development area, and a thickness of the developer layer on the developer support member. , a layer thickness regulating member that regulates the layer thickness to be thinner than the minimum gap between the image carrier and the developer supporting member in the developing area; and a layer thickness regulating member fixedly arranged inside the developer supporting member, the developing area a magnet for causing ears of developer to stand up on a developer support member; A magnetic field is formed in which the absolute value of the developing area takes a first maximum value near the entrance end of the development area and a second maximum value near the exit end of the development area, and the first and second The maximum value of each is 30 Gauss/
A developing device characterized in that the temperature is higher than 100%. (3) A rotatable developer support cylinder that faces the image carrier in the development area and supports a magnetic developer and transports it to the development area; and the thickness of the developer layer on the developer support cylinder. , a layer thickness regulating member that regulates the layer thickness to be thinner than the minimum gap between the image carrier and the developer supporting member in the developing area; and a layer thickness regulating member fixedly arranged inside the developer supporting cylinder, the developing area a magnet having a magnetic pole that causes ears of developer to stand up on the developer supporting cylinder; The absolute value of the rate is 30
A developing device characterized by forming a magnetic field having a maximum value of Gauss per degree or more. (4) The developing device according to claim 3, wherein the position where the maximum value exists is a position downstream of the center of the magnetic pole in the rotational direction of the developer support cylinder. (5) The developing device according to claim 4, wherein the strength of the normal component of the magnetic field formed by the magnetic pole decreases from the center of the magnetic pole toward the downstream side in the rotational direction of the developer support cylinder. (6) The magnetic pole has a second maximum value of 30 Gauss/degree or more in which the absolute value of the rate of change of the normal direction magnetic field component in the direction of rotation of the developer support cylinder is set to a second maximum value of 30 Gauss/degree or more. The developing device according to claim 4, wherein the developing device forms a magnetic field at an upstream position in the rotation direction. (7) The strength of the magnetic field formed by the magnetic pole in the normal direction decreases from the center of the magnetic pole toward the upstream side and the downstream side in the rotational direction of the developer supporting cylinder.
The developing device described in . (8) The developing device according to any one of claims (3) to (7), further comprising means for applying an alternating bias voltage to the developer supporting cylinder. (9) The developing device according to any one of claims (3) to (7), further comprising means for applying a DC bias voltage to the developer supporting cylinder.