JPH07122764B2 - Development device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a developing device for developing an electrostatic latent image with a non-magnetic developer.

(Prior Art and Problems) Various devices have been proposed and put into practical use as dry one-component developing devices. However, it is extremely difficult to form a thin layer of a dry one-component developer by any of the developing methods. However, at present, it is essential to develop a method for forming a thin layer of a dry type one-component developer and an apparatus therefor, which is required to improve the sharpness of the developed image, the resolution, and the like.
In response, some measures have been proposed.

On the other hand, in order to form a thin layer of a two-component developer using a non-magnetic developer and magnetic particles, for example, a magnetic particle restraining member is provided facing the developer carrier, and the surface of the developer carrier is moved. Regarding the direction, a magnetic brush of magnetic particles is formed by the magnetic force of the magnetic field generating means upstream of the magnetic particle restraining member, and the magnetic particles are retained in the developer container by restraining the magnetic brush with the magnetic particle restraining member. An apparatus for forming a thin layer containing only a non-magnetic developer on a developer carrier has already been proposed. This made it possible to develop only with a non-magnetic developer, and it became possible to colorize. However, in the developing device in which the magnetic particles and the toner particles are mixed only in the developer container as described above, there is a problem that the magnetic particles leak if fine magnetic particles are used for improving the image quality. Further, in response to the demand for high image quality, there is also a demand that tribo is imparted to the toner sufficiently and uniformly by stirring in the developer container.

(Means for Solving the Problems) The present invention solves the problems of the conventional developing device using the above-described two-component developer, and provides good magnetic particle restraint and stability with a simple structure. It is an object of the present invention to provide a developing device which guarantees a stable formation of a thin layer of a non-magnetic developer on the surface of a developer bearing member for a long period of time and obtains a good image.

For this purpose, the present invention provides a developer carrier which is provided in an opening of a developer container containing a non-magnetic developer and magnetic particles and is capable of endless movement inside and outside the developer container, The magnetic field generating means provided inside the developer carrying member is in contact with the developer carrying member to prevent the passage of magnetic particles and allow the non-magnetic developer to pass therethrough so that the surface of the developer carrying member is non-magnetically developed. In a developing device including magnetic particle restraining means for forming a developer layer, the magnetic particle restraining means forms a gap between the free end and the developer carrier, the gap being smaller than the average particle diameter of the magnetic particles. In this way, the antinode surface near the free end is the non-magnetic elastic plate abutting on the developer carrier, and the antinode surface from the abutting part to the fixed end and the surface of the developer carrier. Non-magnetic elastic plate arranged so that the interval between the two increases in the moving direction of the developer carrier. Provided on the surface of at least the free end of the elastic plate opposite to the antinode surface, and is located upstream of the elastic plate free end of the magnetic field generating means in the moving direction of the developer carrier. And a magnetic member that forms a magnetic field that restrains magnetic particles between the magnetic pole and the magnetic pole.

Embodiment An embodiment of the present invention will be described below with reference to the accompanying drawings. In the developing device as one embodiment shown in FIG. 1, reference numeral 21 is a developer container for containing a two-component developer, and 22 is a developing sleeve as a developer carrying member. The developing sleeve
22 is a non-magnetic sleeve such as aluminum,
In the figure, a right approximately half-circumferential surface is projected into the developer container 21 in a laterally long opening formed in the lower part of the left side wall of the developer container 21 in the longitudinal direction of the container (a direction perpendicular to the paper surface), and a left approximately half peripheral surface is outside the container. It is exposed to and is rotatably supported and laid laterally, and is rotationally driven in the counterclockwise direction b indicated by the arrow. The developer carrying member 22 is not limited to the above cylindrical body (sleeve), and may be in the form of an endless belt that is rotationally driven. Alternatively, a conductive rubber roller may be used. The exposed surface of the developing sleeve 22 to the outside of the container is a latent image holding member 3 such as a photoconductor that is rotationally driven in the direction of arrow a.
Is in contact with or facing each other with a small gap.

The inside of the developing sleeve 22 is a permanent magnet (magnet) as a magnetic field generating means that is positioned and held in the position and orientation shown in the figure.
23 is inserted in the fixed position. The magnet 23 has two magnetic poles, an N pole 23a and an S pole 23b, as shown in the figure, but it may be an electromagnet instead of a permanent magnet.

An elastic blade 50, which is a non-magnetic elastic member as a magnetic particle restraining member, is provided on the upper surface of the developing sleeve 22 so as to come into contact with the developing sleeve 22 in the longitudinal direction. The elastic blade 50 is fixed at one end and is in contact with the free end, which is the other end, at a distance 1 in the longitudinal direction in the figure (hereinafter, this contact is referred to as a "nip"). A gap is formed between the free end and the developing sleeve 22, and a magnetic member 51 is formed on the upper surface of at least the portion near the free end.
Is installed. For example, the elastic blade 50,
A preferred form is a urethane rubber plate having a thickness of 0.5 to 3.0 mm and a hardness of 30 ° to 90 ° (JIS-A), and a contact pressure of 20 to 200 g / cm (at a pressure per unit distance in the direction perpendicular to the paper surface). They are in contact with each other at the indicated line pressure. The thickness of the magnetic member 51 is
0.5-2 mm steel plate is used. Further, with respect to the nip width l, as shown in FIG. 2, the magnetic attraction action based on the magnetic field between the magnetic pole 23a of the magnet 23 and the magnetic member 51 works properly and effectively so as to restrain the magnetic particles. It is desirable to set it to 5 mm or less, preferably 3 mm or less. If this l is larger than 5 mm, the magnetic field acts in a direction that facilitates the passage of magnetic particles at the free end of the elastic blade, which increases the burden of mechanical restraint by the elastic blade 50. Therefore, the setting condition of the elastic blade 50 becomes narrow.

The gap d between the free end of the elastic blade and the developing sleeve is preferably r> d in relation to the average particle size r of the magnetic particles. That is, the contact condition of the non-magnetic elastic blade 50 with the sleeve can be obtained by causing the contact surface of the non-magnetic elastic blade 50 with the elastic blade 50 to have a so-called abdomen contact at the free end.

As described above, when the elastic blade 51 having a magnetic member is brought into contact with or pressed against the sleeve 22, it is possible to prevent leakage of magnetic particles almost completely. This is because not only the binding force of the magnetic field between the magnetic member 51 and the magnetic pole 23a but also the mechanical binding force of the non-magnetic elastic blade 50 acts. However, in this case, it is necessary to set the blade contact pressure and tip shape so that the developer coating layer to be coated on the sleeve 22 after passing through the elastic blade is not scraped off by the elastic blade. The contact pressure and the gap d are generally set only by the non-magnetic elastic blade 50, but according to the present invention, the magnetic force generated between the magnetic member 51 and the magnetic pole 23a causes the non-magnetic elastic blade 50 to develop. Since the surface of 22 is uniformly attracted in the longitudinal direction, the mechanical setting conditions for the non-magnetic elastic blade 50 are relaxed.

Next, in the developer container 21, the magnetic particles 27 and the non-magnetic developer are
A two-component developer consisting of 28 is contained. Magnetic particles 27
Has an average particle size of 30 to 200 μm, preferably 40 to 70 μm.

The finer the particle size of the magnetic particles, the better the imageability, and especially the good against the background fog and the sleeve ghost. This is because the smaller the particle size is, the more the specific surface area is increased and the degree of contact with the contacted object is also increased. Therefore, tribo is sufficiently applied to the developer between the developing sleeve 22 and the magnetic particles. Is. On the contrary, if the magnetic particles are made coarse, background fog and sleeve ghost will occur.

However, if the particle size is made small, the magnetic restraining force due to the magnetic field becomes small, and the magnetic particles easily leak out of the developing container. Therefore, the particle size distribution of the magnetic particles should be as fine as possible within the range where the magnetic particles do not leak out of the container, and accurate classification is required.

For example, by a known method, a ferrite-based magnetic particle coated with a silicon-based resin is formed on the surface and classified using a standard sieve defined by JIS-Z8801, and a particle size distribution test method according to JIS-H2601 is used. The distribution was measured, and the magnetic particles were classified into 5 stages between 145 and 400 mesh and appropriately mixed, and the quality of image formation was compared. As a result, the following was confirmed.

In order to deal with leakage of magnetic particles, it is preferable that the particle size component of 400 mesh or less is 10% by weight or less.

For the sleeve ghost of the image, it is preferable to remove the particle size component of 145 mesh or more as much as possible so as to have a peak of the average particle size of 250 to 350 mesh.

The ground fog did not occur even when about 50% of magnetic particles having a relatively large size of 145 to 250 mesh were included. This is because the non-magnetic developer on the developing sleeve is rubbed by the elastic blade, so that the ground fog is less likely to occur even in the insufficient tribo-applied state where the ground fog is generated only by the rubbing with the magnetic particles. .

Each magnetic particle may be composed of only a magnetic material, a combination of a magnetic material and a non-magnetic material, or a mixture of two or more kinds of magnetic particles. When the magnetic particles and the non-magnetic developer are mixed, the magnetic field formed between the magnet 23 and the magnetic member 51 attached to the elastic blade 50 causes the first magnetic field relative to the sleeve 22 in the developer container. A large amount of it is stored outside the magnetic particle layer as a layer and exists as a second layer. Then, a magnetic brush 27a of magnetic particles is formed in the magnetic particle layer portion near the surface of the sleeve corresponding to the position of the magnetic pole 23a of the magnet 23 by the strong magnetic field of the magnetic pole 23a.

Further, the developing sleeve 22 is shown by the arrow b in the magnetic particle layer portion near the tip of the non-magnetic elastic blade 50 which is a magnetic particle restraining member.
Direction, the gravitational force, magnetic force, and magnetic member 51
Of the developing sleeve 22 and the carrying force in the moving direction of the developing sleeve 22 are balanced by the restraining force due to the presence of
A stationary layer that is constrained in position and can move slightly, but is almost immobile 27
form b.

Further, when the developing sleeve 22 is rotated in the direction of arrow b, the magnetic brush 27a is moved in the direction of arrow c near the magnetic pole 23a by appropriately selecting the arrangement position of the magnetic pole 23a and the fluidity and magnetic characteristics of the magnetic particles 27. It circulates to form a circulation layer 27c (see FIG. 1). In the circulation layer 27c, the magnetic particles relatively close to the developing sleeve 22 swell from the vicinity of the magnetic pole 23a to the downstream side of the developing sleeve by the rotation of the developing sleeve 22. That is, it receives the force of pushing it up. The magnetic particles pushed up fall by gravity, and the magnetic pole 23
a Return to the vicinity. That is, in the circulation layer 27c, the magnetic brush 27a of magnetic particles is circulated as indicated by an arrow c due to the magnetic force and frictional force due to gravity and magnetic poles and the fluidity (viscosity) of the magnetic particles. The non-magnetic developer 28 is successively taken from the developer layer above the particle layer and returned to the lower part inside the developer container 21, and this circulation is repeated as the developing sleeve 22 is rotationally driven. At this time, due to the influence of the magnetic member 51, compared with the case where the magnetic member 51 does not exist, the magnetic pole 23
Since the magnetic field of a tends to concentrate on the tip of the elastic blade 50, the holding force of the magnetic particles is increased at the tip position and the tribo imparting ability to the non-magnetic developer 28 is increased, and the tip of the elastic blade 50 having a magnetic member is provided. Therefore, the non-magnetic developer 28 is not directly taken in, and a good image without fog or sleeve ghost can be obtained. In addition, due to the influence of the magnetic field, the developing sleeve 22 is magnetically constrained at the tip of the elastic blade.
Since it is uniformly held in the longitudinal direction, the surface of the developing sleeve 22 can be coated with the nonmagnetic developer 28 evenly.

Furthermore, the end of the magnetic member 51 is connected to the non-magnetic elastic blade.
It is also possible to improve this circulation by projecting the sleeve 50 upstream of the free end in the rotational direction of the sleeve. Further, by disposing the magnetic member in this manner, the non-magnetic developer 28 is also attached to the tip 25 of the elastic blade.
Is not directly taken in from above, and a good image without fog or sleeve ghost can be provided. Further, according to the experiment, the protruding length l ₁ of the magnetic member is not more than 1 cm, preferably not more than 8 mm, rather, the circulation becomes worse, the packing of the magnetic particles near the point 25 becomes too strong, and the non-magnetic blade. The mechanical restraining force of 50 must be increased, and the setting conditions of the non-magnetic elastic blade 50 become strict, which is not preferable.

The non-magnetic developer that is sequentially taken into and mixed in the magnetic particle layer on the surface of the developing sleeve 22 is charged by friction with the magnetic particles due to the flow of the magnetic particles, friction with the developing sleeve surface, and the like. in this case,
Preferably, the surface of the magnetic particles is subjected to an insulation treatment such as an oxide film or a resin that is electrostatically in the same level as the non-magnetic developer to reduce tribo application from the magnetic particles and receive necessary charging from the developing sleeve 22. By doing so, it is possible to prevent the influence of the deterioration of the magnetic particles and stabilize the application of the developer to the developing sleeve 22. Since this charged developer is non-magnetic, it is not restricted by the magnetic field of the magnetic pole 23a, and the developing sleeve surface is free from the non-magnetic elastic blade 50 from the magnetic member 31 at the lower edge of the container opening where the developing sleeve 22 is arranged. While rotating and moving to the end, the surface of the developing sleeve is uniformly and thinly coated by the mirror force.

The magnetic particles in the magnetic particle stationary layer 27b near the free end of the non-magnetic elastic blade 50 are constrained by the effect of gravity and the magnetic force and the presence of the magnetic blade 51 as described above even when the developing sleeve 22 is rotating. Is constrained by the balance between the force and the conveying force in the moving direction of the developing sleeve 22, and does not pass through the gap d between the free end of the non-magnetic elastic blade 50 and the developing sleeve 22, and is formed on the surface of the developing sleeve 22. Only the coating thin layer of the above-mentioned non-magnetic developer is applied to the developing sleeve.
Between the elastic blade and the developing sleeve with the rotation of 22 d
After passing through, the toner is rotatably conveyed to the latent image carrier 3 side, approaches the developing unit 32 of the latent image carrier (see FIG. 1), and development is performed here.

Thus, in the developing device, each portion of the non-magnetic developer has a sufficient charge amount with respect to the surface of the developer carrying member,
It is possible to form a uniform thin layer and form a stable coating over a long period of time. Therefore, this thin developer layer makes it possible to develop the latent image on the latent image bearing surface clearly and with good resolution.

Further, since a non-magnetic developer having a vivid color can be obtained, it is possible to obtain a high-quality color copy (single color, multi-color, natural color) having excellent color reproducibility.

Next, a specific example of the developing device shown in FIG. 1 will be described.
In FIG. 1, as the developer carrying member 22, an aluminum sleeve having a diameter of 20 mm, the surface of which has been irregularly sandblasted with alundum abrasive grains, is used.
Two poles are magnetized, and the N pole is about 750 gauss and the angle α with the vertical line m passing through the center O of the sleeve is 95 as shown in FIG.
It was placed at a position where It should be noted that when the above magnet was set to 1000 gauss, the circulation in the direction c in FIG. 1 doubled.

The non-magnetic elastic blade 50 is made of urethane rubber having a thickness of 2 mm and a hardness of 65 °. Further, the magnetic member 51 is a 1 mm thick iron plate plated with chemical nickel, and an SPC steel plate, a silicon steel plate, a permalloy or the like which is industrially commonly used as a material of the iron plate is preferable. Further, these magnetic bodies may be magnetized so as to strengthen the magnetic field in the tangential direction. This magnetic member 51
Is set at a distance of 2 mm from the free end of the non-magnetic elastic blade 50 as shown in FIG. In the device of FIG. 1, θ =
It was set at 30 ° (see Fig. 2).

As magnetic particles, ferrite particles (maximum magnetization 65 emu / g) of 63 to 44 μm (250/350 mesh) coated with a mixed resin of acrylic and fluorine on the surface were used. Butadiene Copolymer Resin 100
Average particle diameter of 12μ consisting of 5 parts of copper phthalocyanine pigment
m toner powder with 0.6% colloidal silica added externally, the coating thickness on the sleeve was about 30-50 μm, and the tribo charge on the sleeve measured by the blow-off method was +15 μCoul / g. A good coating was obtained.

The developing device of this embodiment is shown in FIG.
As a result, it was used in a copying machine in which a DC voltage of -300V was superimposed on an AC voltage of frequency 1600Hz and a peak-to-peak value of 1300V, and development was performed by setting the distance between the developing sleeve 22 and the OPC photoconductor 3 to 300µm. I got a nice blue image.

The present invention can be effectively exhibited even when a magnetic field generating means is used for the magnetic member.

FIG. 3 shows an example thereof. In FIG. 3, reference numeral 52 is a magnetic member as a magnetic field generating means, and in this embodiment, a bipolar permanent magnet is used. As shown in Figure 3,
By arranging the S pole side of the magnetic pole 52a, which is different from the N pole of the magnetic pole 23a, on the free end side of the non-magnetic elastic blade 50, the magnetic field between the magnetic pole 23a and the magnetic pole 52a is further strengthened. Therefore, the holding force and the binding force of the magnetic particles 28 near the point 25 are increased. Therefore, the ability to apply tribo to the non-magnetic developer 27 is enhanced, and the mechanical setting conditions of the non-magnetic elastic blade 50 are alleviated.

Alternatively, a thin metal plate may be used as the elastic member.

Further, when a metal elastic member is used, it is preferable to use a soft elastic member on the surface of the metal elastic member that comes into pressure contact with the sleeve, because the abrasion due to the sliding friction between the metal elastic member and the sleeve becomes severe.

Although a non-magnetic developer was used in the above-mentioned examples, a magnetic developer can be used as long as the magnetic property is extremely weak as compared with the magnetic particles and tribo charging is possible.

Also, an example of supplying the developer was described using a single-use type developing device in which the developer container is integrated with the developer container, but this point is also a separate body from the developer container and can be replaced. The present invention can be applied to various replenishment cartridges. Further, as the developing method, a non-contact developing method utilizing an alternating bias electric field is preferable, but other known developing methods may be used.

The developing bias may be a DC electric field regardless of the periodic displacement electric field. For the non-magnetic elastic blade, it is preferable to select a material having a frictional charge line away from the developer so as to give a predetermined charge polarity to the developer. Further, the surface of the non-magnetic elastic blade facing the developing sleeve may be roughened to provide irregularities on the surface to further improve tribo imparting to the toner. Further, a magnet 23 arranged in the developing sleeve 22
Is not limited to the two-pole arrangement shown in the embodiment. A plurality of magnetic poles may be provided on the upstream side of the magnetic pole 23b in the rotation direction of the developing sleeve within a range that does not significantly affect the restraint of the magnetic particles according to the present invention. Thus, even if a small amount of magnetic particles leak from the elastic blade portion, the magnetic particles can be collected in the developing container.

(Effects of the Invention) As described above, according to the present invention, in a developing device using magnetic particles by using a magnetic elastic blade having a simple structure, the magnetic particles can be restrained and stably and uniformly circulated. Further, by providing at least the elastic blade free end and the magnetic member, the binding force to the magnetic particles is increased due to the influence of the magnetic field generated between the magnetic member and the magnetic pole in the developing sleeve. A large amount can be held near the elastic blade contact part,
The effect of imparting tribo to the developer is enhanced, and as a result, a small amount of magnetic particles is used, and a thin developer layer having a uniform layer thickness and a sufficient charge amount can be stably obtained over a long period of time. Bring At that time, since the magnetic member forms a magnetic field for restraining the magnetic particles between the magnetic field generating means and the magnetic pole on the upstream side of the free end of the elastic plate in the moving direction of the developer carrier, the magnetic particles are As described above, the gap between the free end of the elastic plate and the developer carrying member is prevented from being clogged, and the nonmagnetic developer can be uniformly formed over a long period of time to form a thin layer. In particular, the same effect can be obtained with a non-magnetic toner of fine particles (particle diameter of 10 μm or less). Further, when the thin developer layer is subjected to the developing action, it becomes possible to obtain a stable developed image for a long period of time. In particular, even if vibration or the like is applied, the magnetic particles can be restrained in the developing container without leaking.

Furthermore, since the non-magnetic developer on the developing sleeve is sufficiently rubbed by the non-magnetic elastic member to impart a uniform and stable tribo, a good image can be obtained even if a developing sleeve having an outer diameter of 6 to 20 mm is used. Obtainable.

Based on such an effect, it becomes possible to form a clear color image using a non-magnetic developer.

Further, since the toner on the developing sleeve is rubbed by the elastic body, the tribo is imparted to the toner by the elastic body, and the tribo imparting effect to the toner by the magnetic particles can be reduced accordingly. Therefore, the amount of magnetic particles charged into the developing device can be reduced to a small amount, and a substantially good image can be obtained even if it is reduced to 1/5 of that in the embodiment.

[Brief description of drawings]

1 is a sectional view of a developing device of the present invention, FIG. 2 is an enlarged sectional view of a developing sleeve and a magnetic elastic blade portion of the device of FIG. 1, and FIG. 3 is an elasticity of another embodiment of the developing device of the present invention. It is sectional drawing at the time of using a magnet as a magnetic member for a blade. 21 …… Developer container 22 …… Developer holding member (developing sleeve) 23 …… Magnetic field generating means (magnet) 50 …… Developer restraining member (elastic blade) 51 …… Magnetic member

 ─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP 62-96979 (JP, A) JP 61-175664 (JP, A) JP 62-234175 (JP, A) JP 57- 78064 (JP, A) JP 61-86772 (JP, A) JP 62-59049 (JP, A)

Claims (1)

[Claims] 1. A developer carrier provided in an opening of a developer container containing a non-magnetic developer and magnetic particles and capable of endless movement between the inside and the outside of the developer container, and the developer carrier. The magnetic field generating means provided inside is in contact with the developer carrying member, which blocks the passage of magnetic particles and allows the nonmagnetic developer to pass therethrough to form a nonmagnetic developer layer on the surface of the developer carrying member. In the developing device, the magnetic particle restraining means is configured such that a gap smaller than the average particle diameter of the magnetic particles is formed between the free end and the developer carrier. The non-magnetic elastic plate whose abdominal surface near the free end is in contact with the developer carrier, and the gap between the abdominal surface from this abutting part to the fixed end and the surface of the developer carrier is A non-magnetic elastic plate arranged so as to increase in the moving direction of the agent carrier, and a small number of these elastic plates. At least the free end portion, which is provided on the surface opposite to the surface with the antinode surface, of the magnetic field generating means,
A developing device comprising: a magnetic member that forms a magnetic field that restrains magnetic particles between a magnetic pole located upstream of the free end of the elastic plate in the moving direction of the developer carrier.