JPS6329741B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrophotographic method in which an electrostatic latent image formed on the surface of an electrostatic latent image carrier is developed using a relatively high resistance magnetic toner, and then fixed after transfer. The present invention relates to an electrostatic latent image developing method suitable for development in which the surface movement speed is relatively fast. Electrophotography involves forming an electrostatic latent image on the photoconductive surface of a photoreceptor, developing the electrostatic latent image to form a toner image, and then fixing the toner image directly or transferring the toner image to a transfer member. A copy is obtained by transferring the image onto the surface and then fixing it. In this electrophotographic method, development has conventionally been carried out by a magnetic brush method using a two-component developer which is a mixed powder such as a non-magnetic toner and an iron powder carrier. The magnetic brush development method using this two-component developer charges the toner to a predetermined polarity by frictional charging with a carrier and causes only the toner to adhere to the electrostatic latent image carrier surface, which has advantages such as easy transfer. There is. However, since a mixing means is required to frictionally charge the toner and the carrier, and since only the toner is consumed during development, a toner replenishing means is required to maintain a uniform toner concentration, making the developing device larger and less structured. This method is complicated, and furthermore, the carrier becomes fatigued after being used for a predetermined period of time, so it is necessary to replace the carrier. Therefore, in recent years, one-component magnetic toners containing resin and magnetic powder as main components have been used as developers. As a developing method using this magnetic toner, the method described in US Pat. No. 3,909,258 is known. This development method uses conductive magnetic toner,
This is held on a conductive sleeve, and the back surface of the electrostatic latent image carrier and the conductive sleeve are electrically coupled, and a conductive magnetic toner layer is interposed between the surface of the electrostatic latent image carrier and the conductive sleeve. In this method, a conductive path is formed in the film and development is performed by induction. However, in this developing method, since the toner is conductive, when the developed toner image is transferred onto the transfer member, the transferred image may be lost due to the loss of charge in the toner or the injection of charge from the transfer electrode. This causes problems such as turbulence and is not suitable for the so-called PPC method, which involves a post-development transfer process and then fixing to obtain a copy. Therefore, in order to apply magnetic toner to the PPC method, a developing method using an insulating toner with increased electrical resistance of the toner has been proposed. For example, U.S. Patent No.
No. 4121931 discloses that in order to improve the developability of insulating magnetic toner, the toner is forcibly charged by bringing it into electrical contact with an electrode, and then the charged toner is conveyed at high speed to the latent image surface to increase the developing current. It is described that the developability can be improved by doubling the . However, in this method, it is necessary to rotate the non-magnetic cylindrical sleeve at a relatively high speed in order to increase the moving speed of the toner. A large force acts on the spaced portion, causing phenomena such as magnetic toner agglomerating or even sticking to the sleeve surface. Further, a method for improving both developability and transferability in the PPC method is described in US Pat. No. 4,120,305. This development method uses toner particles that are conductive in a high electric field and insulative in a low electric field.A high electric field is applied to the toner particles in a development area to make them conductive, and development is performed.Then, the toner particles are transferred to a transfer area. The transfer is performed in the absence of a high electric field. In this publication, as a specific example, in order to form an alternating current electric field between a photoconductive surface and a non-magnetic cylinder, an AC power source is connected to the cylinder and the peak-to-peak value is 20 to 100 V/μ (20000 to 1000000 V). It is described that a voltage of about 500 to 5000 Hz is applied at a frequency of about 500 to 5000 Hz. However, when such a high alternating current voltage is applied, if the developing cap is narrow, there is a great risk of creating pinholes in the electrostatic latent image carrier used due to discharge. In addition, in order to make the magnetic toner used conductive near the peak value of the AC electric field, charges are injected from the magnetic toner that has become conductive onto the surface of the electrostatic latent image carrier.
There may be cases in which development does not occur in accordance with a predetermined electrostatic latent image. Furthermore, in the embodiments in the above specification, the developing cap is quite wide at approximately 1.65 mm, but such a wide cap may cause toner scattering, or in the case of PPC toner, which has relatively poor fluidity, near the cylindrical surface of the magnetic brush. The formation of a passive layer or toner aggregation caused by this tends to occur, and there is a great risk of developing defects, and it cannot be applied to electrophotographic devices that require long-term reliability. In view of the problems of the prior art as described above, the present invention
The present invention provides a developing method that can ensure long-term reliability by considering the long-term stability of the magnetic brush due to the relative rotation of the magnet and the cylindrical sleeve containing the magnet, and the electrically auxiliary stage. That is, an object of the present invention is to provide an electrostatic latent image developing method that can provide good developability even in relatively high-speed development and can also provide good transferability at the same time. In the electrostatic latent image developing method according to the present invention, the surface of a non-magnetic cylindrical sleeve containing a magnet having a plurality of magnetic poles has a volume resistivity in the range of 10 ¹² to 10 ¹⁶ Ω·cm in a DC electric field of 10000 V/cm. A certain magnetic toner is attracted, and the magnet and the non-magnetic cylindrical sleeve are both rotated in the same direction so that the ratio of the number of rotations between the magnet and the non-magnetic cylindrical sleeve is approximately 20 or more. A magnetic brush formed by conveying the magnetic toner adsorbed on the surface of the cylindrical sleeve along the surface of the non-magnetic cylindrical sleeve is brought into contact with the surface of the electrostatic latent image carrier, and the surface of the electrostatic latent image carrier is When the electrostatic latent image is visualized, an alternating current voltage having a specific frequency and peak-to-peak value is applied to the contact portion between the magnetic brush and the electrostatic latent image carrier. The details of the present invention will be explained below with reference to the drawings. 1st
The figure is a schematic sectional view of a transfer type dry type electronic copying machine for explaining the electrostatic latent image developing method of the present invention. 1st
In the figure, the surface of a photoreceptor drum 1 is uniformly charged by a corona charger 2 and then exposed to light by an exposure device 3 to form an electrostatic latent image. Next, the electrostatic latent image is developed by the developing device 4 to form a toner image on the surface of the photoreceptor drum 1, and the toner image is electrostatically transferred to the transfer paper 6 by the corona discharger 5.
Then, the pressure fixing device 7 performs fixing to obtain a copy. The developing device 4 includes a hopper 41 that accommodates the magnetic toner 8 and a non-magnetic cylindrical sleeve 42 facing the lower opening of the hopper 41. Inside the non-magnetic sleeve 42, a permanent magnet 43 having a plurality of magnetic poles rotates. The non-magnetic sleeve 42 is connected to ground or AC via a switch 45.
Connected to power. FIG. 2 shows an enlarged sectional view of the developing device 4 in FIG. 1. Conventionally, the development method generally used is the so-called sleeve fixing method in which the non-magnetic cylindrical sleeve 42 is fixed and the magnet 43 is rotated in the direction of the arrow x shown in the figure, or the magnet 43 is fixed and the non-magnetic cylindrical sleeve 42 is rotated in the direction shown by the arrow This is a so-called magnet fixing method that rotates in the x direction or the y direction. In the case of the sleeve fixation method, the magnetic toner 81 on the surface of the non-magnetic cylindrical sleeve 42 is transported while rotating in the direction of the arrow y in the figure.
A pool of magnetic toner 81 is formed between the cylindrical sleeve 42 and the non-magnetic cylindrical sleeve 42, that is, in the developing section 44, and as this pool grows, the movement of the magnetic brush in the developing section 44 cannot follow the rotating magnetic field generated by the magnet 43, resulting in poor development. will occur. In addition, in the case of the magnet fixing method, in many cases the photoreceptor 1 and the non-magnetic cylindrical sleeve 42 are
The interval between the developing caps, so-called development caps, cannot be narrowed, making it unsuitable for systems using high-resistance magnetic toner. Furthermore, even if the developing cap is narrowed, dust or aggregated magnetic toner may be deposited between the flow rate regulating plate (not shown) of the magnetic toner 8 to the surface of the non-magnetic cylindrical sleeve 42 and the non-magnetic cylindrical sleeve 42. etc. are easily clogged and lack reliability. Therefore, the present invention employs a developing method that can eliminate the drawbacks of the sleeve-fixed type or magnet-fixed type. This developing method was previously proposed by the present inventors (Japanese Unexamined Patent Publication No. 116233/1983). That is, the non-magnetic cylindrical sleeve 42 and the magnet 43 are both rotated in the direction of the arrow x shown in the figure, but the magnetic toner 83 that has passed through the developing section 44 is rotated by the non-magnetic cylindrical sleeve 42 so that it is transported in the direction of the arrow y shown in the figure. The rotation speed of the magnet 43 is set to a relatively low rotation speed, and the rotation speed of the magnet 43 is set to a relatively high rotation speed. Under these rotational speed setting conditions, the magnetic toner 8 that could not pass through the developing section 44 begins to move in the direction of the arrow x shown as the non-magnetic cylindrical sleeve 42 rotates, and moves from the developing section to the non-magnetic cylindrical sleeve. 42, a layer (not explicitly shown) of a certain thickness of magnetic toner is formed in the direction of the arrow x shown in the figure. The thickness of this layer is mainly determined by the rotational speed of the non-magnetic cylindrical sleeve 42, but it can always maintain a nearly constant contact width with the photoreceptor 1, and the developing cap in the developing section 44 becomes extremely narrow. Also, since the motion of the magnetic brush can follow the rotating magnetic field generated by the magnet 43, it has the excellent feature that stable development and good developability can always be obtained. Therefore, in the experiment using the electronic copying machine shown in FIG.
The number of rotations of magnet 2 is 1/30 or less of that of magnet 43 (25~
80rpm) range. The outer diameter of the non-magnetic cylindrical sleeve 42 is 31.4 mm, and the outer diameter of the magnet 43 is 29.3 mm.
The magnetic force on the surface of the non-magnetic cylindrical sleeve 42 is 700
A Gaussian cylinder was used. As a result of a copy test using the above-mentioned copying machine, we found that the number of times N and S poles alternately appear in the developing section 44 (hereinafter referred to as NS alternation number) and the moving speed of the surface of the photoreceptor 1 (hereinafter referred to as developing speed) It was found that there was a significant correlation between NS as shown in Figure 3
It has been found that when the number of alternations is x and the development speed is y, each straight line is approximately expressed by the relationship y=kx in order to perform good development. For example, when the volume resistivity of magnetic toner in an electric field of D.C10000V/cm is about 10 ⁸ to 10 ^{11 Ω.cm} , the relationship between the development speed and the number of NS alternations is about 1.0 or less for good development. However, 10 ¹⁴ Ω. When using a magnetic toner having a volume resistivity of cm or more, k must be set to 0.5 or less, preferably 0.3 or less. The smaller the value of k, the more the rotation speed of the magnet 43 must be increased.
The value of the NS alternation number of 200 corresponds to 1000 rpm when a magnet with 12 magnetic poles is used.
For example, the straight line shown in Figure 3 has a development speed of 60 mm/sec.
In the case of , the volume resistance is 10 ¹⁴ Ω. In order to perform good development using magnetic toner of cm or larger, NS
Since the number of alternations is 200, this means that if a 12-pole magnet is used, a rotation speed of at least 1000 rpm is required. By the way, when the development speed becomes faster, it is clear from the relationship y=kx shown in FIG. 3 that the number of rotations of the magnet needs to be increased in proportion to the development speed. However, increasing the number of rotations of the magnet is not preferable from the viewpoint of speed reduction mechanisms such as gears and pulleys. The critical rotation speed is around 2000rpm. That is, this is not preferable from the viewpoint of preventing toner scattering. Therefore, the volume resistivity is 10 ¹³ Ω. When using magnetic toner with a diameter of cm or more, the moving speed of the photoreceptor surface is approximately
When developing at a high speed of 120 mm/sec or higher, it is necessary to take measures to compensate for developing performance. Therefore, in order to cope with the above-mentioned high-speed development, the present inventors connected the non-magnetic cylindrical sleeve 42 of the developing device to an AC voltage source and applied an AC bias to the developing section as shown in FIG. A copy test was conducted with the purpose of actively injecting charge into the toner to improve its developability in a pulsating electric field. First, as a result of examining the frequency of the applied bias, we found that it is necessary to set a frequency that has a value that is at least approximately equal to the number of NS alternations, where k is equivalent to 0.3 as shown in Figure 2. .
For example, if the development speed is 240 mm/sec, at least 800
It is necessary to apply a bias with a frequency of about Hz. By setting such a frequency, it is possible to perform good development even when the magnet rotation speed is lowered to 1/2 or less of that when no bias is applied. Next, the present inventors conducted a study on the peak-to-peak value of the applied voltage. The result was 10 ¹³ Ω. cm
Using the above insulating magnetic toner, it has been found that the image density with respect to the change in peak-to-peak value has a tendency as shown in FIG. In other words, up to about 800Vpp, the image density was around 1.2.
The concentration increases by applying a voltage of about 1200Vpp to 2200Vpp.
The concentration increases to about 1.35, and when a voltage of 3200 Vpp or more is applied, the concentration decreases rapidly. However, the frequency of the AC voltage is 800Hz, the development speed is 200mm/sec, the dark potential is 800V using a selenium photoreceptor, and the development cap is 0.35.
mm. Furthermore, although the image quality of detailed areas was not good up to around 800 Vpp, it became clearer by applying 1300 Vp-p or more. The reason for this is that the electric charge in the magnetic brush on the sleeve moves efficiently near the peak of the electric field against the electrostatic latent image surface, so that the magnetic toner particles that come into contact with the electrostatic latent image This is thought to be because the charge follows the surface well. In addition, the phenomenon that image density decreases when the peak value is increased too much is because the magnetic toner, which should have been insulating, has become conductive, so charges are rapidly injected into the magnetic brush, and the electrostatic latent image is retained. This is thought to be because the high electric field formed between the body and the sleeve causes charges to be injected even into the electrostatic latent image surface. Therefore, there is no need to increase the AC bias voltage to make the insulating magnetic toner conductive. Therefore, the peak-to-peak value of the AC voltage applied to the sleeve is
Vp−p ₁ If the dark potential of the electrostatic latent image is Vs, then Vpp
If the range satisfies the relationship 1.5VsVp-p4Vs, it can be said that the necessary and sufficient conditions are satisfied. The magnetic toner used in the present invention has a resistance of 10 ¹² to 10 ¹⁶ Ω in a DC electric field of 10,000 V/cm in consideration of developability and transferability. Preference is given to those having a volume resistivity in the cm range. Examples of the present invention will be shown below. A copy test was conducted under various conditions using the electronic copying machine shown in FIG. 2, and the results shown in the table below were obtained. Note that a Se drum with an outer diameter of 120 mm was used as the photoreceptor.

[Table] In the above table, Nos. 1 to 4 show the experimental results according to the present invention, and it is clear that they have excellent developability and transferability. That is 10 ¹⁵ Ω.
Since a good developed image can be obtained even when using a magnetic toner with a high resistance of about cm, a high quality image can be obtained even when plain paper is used as the transfer paper.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional view showing an example of a transfer type dry type electronic copying machine used in the present invention, Fig. 2 is an enlarged sectional view of the developing device in Fig. 1, and Fig. 3 is a diagram showing the development speed and the number of NS alternations. FIG. 4 is a diagram showing the relationship between applied voltage and image density. 1: Photosensitive drum, 4: Developing device, 41: Hopper, 42: Non-magnetic sleeve, 43: Permanent magnet,
44: developing section, 8: magnetic toner.

Claims (1)

[Claims] 1. Magnetic toner having a volume resistivity in the range of 10 ¹² to 10 ¹⁶ Ω·cm in a DC electric field of 10000 V/cm is adsorbed onto the surface of a non-magnetic cylindrical sleeve having a plurality of magnetic poles, and the magnet and the non-magnetic cylinder are The magnet and the non-magnetic cylindrical sleeve are both rotated in the same direction so that the rotation speed ratio with the non-magnetic cylindrical sleeve is approximately 20 or more, and the magnetic toner adsorbed on the surface of the non-magnetic cylindrical sleeve is removed from the non-magnetic cylindrical sleeve. In the method of visualizing an electrostatic latent image on the surface of an electrostatic latent image carrier by bringing a magnetic brush formed by conveying it along the surface of a magnetic cylindrical sleeve into contact with the surface of the electrostatic latent image carrier, the method includes: An alternating current voltage is applied to the contact portion between the magnetic brush and the electrostatic latent image carrier, and the frequency of the alternating voltage is F (Hz), the peak-to-peak value is _Vpp , and the surface of the electrostatic latent image carrier is The moving speed is υ (mm/sec), and the dark potential of the electrostatic latent image is V _s
When F≧υ/0.3 and 1.5V _s V _pp
An electrostatic latent image developing method characterized by setting the voltage to 4V _s .