JPH02256075A - Developing method - Google Patents

Abstract

PURPOSE:To obtain good development performance by respectively specifying the content of the magnetic powder in magnetic toner particles and the transporting speed of a developer by the rotation of a sleeve and impressing alternating voltages of a low frequency to the sleeve at the time of forming visual images. CONSTITUTION:The content of the magnetic powder in the particles of the magnetic toner 5 which contains a binder resin and the magnetic powder and has a charge capacity in unidirectional polarization is specified to <50wt.% and the transporting speed of the developer by the rotation of the sleeve 3 is specified to 0.8 to 2.5 times the moving speed of an electrostatic image carrier 1. The alternating voltages of the low frequency are impressed to the sleeve 3 at the time of the formation of the visual images. The high developability is obtd. by impressing the alternating voltages to the sleeve 3 even if the developer is transported at a relatively low speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing method in electrophotography in which an electrostatic charge image formed on the surface of an image carrier is visualized using an insulating magnetic toner.

[Prior Art] In electrophotography, an electrostatic charge image is formed on the surface of a photoreceptor, this electrostatic charge image is visualized using colored particles called toner, and the visualized toner image is transferred onto a transfer member. A typical example is one that is fixed by post-thermal means or the like to obtain a hard copy.

Various developing methods for electrophotography have been proposed so far.

The mainstream is a method using a magnetic brush method using a two-component developer which is a mixed powder of a non-CN toner and a magnetic carrier as a developer, or a method using only magnetic toner. Conventionally, when using these powder developers, a non-magnetic metal sleeve and a magnet roll placed inside the non-magnetic metal sleeve are rotated relative to each other, and the developer adsorbed on the surface of the non-magnetic metal sleeve is transferred to the inside of the developing machine. A method is adopted in which the liquid is transported to the developing section and then collected back into the developing machine.

Generally, the conveyance speed of these developers is set to a relatively high speed in both the -component method and the two-component method in order to improve image quality or increase image density. A typical known example is a developing method using an insulating magnetic toner described in US Pat. No. 4,121,931.

[Problem to be solved by the invention]

However, in the above method, since the developer is conveyed at high speed, there are problems such as toner scattering outside the developing machine, and in the -component method, the force applied to the toner becomes large, causing toner aggregation. The two-component method promotes the adhesion of the resin components that make up the toner on the carrier surface,
There are problems that shorten the life of the developer. Therefore, it is ideal to set the developer transport speed as low as possible, but in order to obtain sufficient image density, that is, sufficient developability, it is necessary to transport one developer at a relatively high speed. There is.

Next, a method described in US Pat. No. 4,120,305 is known as a method for improving developability in a system using a one-component magnetic toner. In this specification, conductivity at high electric fields.

Then, a method is described in which a magnetic toner that exhibits insulating properties is used in a low electric field, and a low frequency, high voltage alternating electric field is applied to the magnetic toner in the development area during development, but the peak-to-peak value of the alternating electric field applied in this case is is 20 to 100 V/μ
- It is considered to be about. However, when such a high voltage is applied, a neutralizing current tends to flow from the conductive magnetic toner to the electrostatic image.

There may be cases where a predetermined electrostatic charge image cannot be maintained.

Furthermore, in the above-mentioned developing method, since the development gap is set large, the developer conveyance speed must be set relatively fast.

Another example of applying an alternating electric field in a system using magnetic toner is typified by the proposal described in Japanese Patent Publication No. 5B-32377. The above publication describes a method in which insulating magnetic toner is conveyed onto the surface of a metal sleeve in a state that is thinner than the development gap, and development is performed by causing the magnetic toner to fly onto an electrostatically charged image using an alternating voltage applied to the metal sleeve. ing. The above publication states that the circumferential speed of the metal sleeve that conveys the magnetic toner is approximately the same as the circumferential speed of the photoreceptor.

However, in the single-bokuto method, although the developer conveyance speed is set low, the development gap setting is very narrow, which requires high precision in the dimensions of the metal sleeve, and there are problems in that it is susceptible to the effects of dust, etc. be. On the other hand, the Tokuko Showa 6
3-25350 proposes a method of applying an alternating electric field in a two-component method. The above publication states that the circumferential speed of the metal sleeve that conveys the developer is almost the same as the speed of the object to be developed, but the process speed in this case is 500 m5+/sec, which is extremely high. It has become. If the process speed is reduced, the two-component method will not work unless an insulating carrier is used.

It is obvious to those skilled in the art that charge injection from the conductive carrier to the image carrier (photoreceptor) is accelerated and the developed toner visible image is far from the desired image.

Also, in recent years, 5 Japanese Patent Publication Nos. 59-162563 and 59-21
As described in No. 6149 and No. 62-184474, it has also been proposed to use a mixture of a magnetic carrier and a magnetic toner as a developer, which shares the advantages of the two-component system and the one-component magnetic toner system described above. It is assumed that In this method of using a mixture of magnetic carrier and magnetic toner as a developer, a relatively conductive magnetic carrier is used.1 The toner concentration is not particularly controlled, so the toner concentration in the developing area is determined by weight ratio. So 15
% to over 80%. therefore.

Because the electrical resistance of the developer itself is extremely high,
In order to efficiently develop an electrostatic image, the developer transport speed must be set high, and as a result, the metal sleeve or magnetic roll, which is the developer transport means, is rotated at high speed. In such a situation, the damage to the developer is significant.

There are many problems such as increased noise in the device drive system.

The present invention solves the problems existing in the prior art, and provides a developing method for electrophotography using a developer made of a mixture of a magnetic carrier and a magnetic toner, which causes less damage to the developer.

It is an object of the present invention to provide a developing method that has extremely high stability even though the transport speed of developer is low.

[Means for Solving the Problems] In order to achieve the above object, the present invention uses magnetic toner particles containing a binder resin and magnetic powder and having a unidirectional polarity charging ability, and a relatively conductive toner particle. A developer mixed with magnetic carrier particles is adsorbed onto the surface of a non-magnetic and conductive sleeve by magnetic means, and the developer is brought into contact with an electrostatic image carrier by at least rotating the sleeve. In a developing method in which the electrostatic charge image on the surface of the electrostatic charge image carrier is visualized by the magnetic toner particles, the magnetic powder contained in the magnetic toner particles is
%, the conveying speed of the developer by rotation of the sleeve is 0.8 to 2.5 times the moving speed of the electrostatic image carrier, and a low-frequency alternating voltage is applied to the sleeve at least during visualization. The configuration is configured to apply . A technical method was adopted.

In the present invention, an insulating magnetic toner having a unidirectional polarity charging property is used, and its typical characteristics are confirmed by an apparatus as shown in FIG.

In FIG. 1, l is a metal drum, and a sleeve 3 containing a zero-order multipolar magnet 2 that is electrically grounded and rotatable in the direction of the arrow (x) is made of a non-magnetic metal material and has a hollow cylindrical shape. They are arranged relatively close to the surface of the metal drum 1 and at approximately equal intervals in the longitudinal direction, as shown by the arrows (
It is rotatable in the y) direction. The regulating member 4 is provided with its tip close to the surface of the sleeve 3, and the interval is set so that the magnetic toner 5, which is attracted to the surface of the sleeve 3 and is conveyed as it rotates, can contact the metal drum 1 in an appropriate state. Set to . Note that a voltage 'tX6 is connected between the metal drum l and the sleeve 3.

Formed so that a bias voltage can be applied.

With the above configuration, when the bias voltage applied to the sleeve 3 by the voltage source 6 is changed, the amount of magnetic toner 5 adhering to the metal drum 1 is changed.

FIG. 2 shows how the amount of magnetic toner 5 adhering to the surface of the metal drum 1 changes when a DC voltage is applied to the sleeve 3 and changed in the apparatus shown in FIG. FIG. 2 shows a case where the magnetic toner 5 (see FIG. 1) has negative charge polarity.

When a negative bias voltage is applied to sleeve 3.

More magnetic toner 5 adheres to the surface of the metal drum 1. Conversely, if the polarity of the bias voltage applied to the sleeve 3 is positive, although a current is observed, the amount of magnetic toner 5 attached to the surface of the metal drum 1 is small.

It is observed that this is extremely small compared to the case where a bias voltage of opposite polarity is applied. Generally, the adhesion force of the particles forming the magnetic toner 5 to the metal surface is considered to be due to the interaction between the electric charge of the magnetic toner 5 and a mirror image formed on the metal surface, that is, electrostatic mirror image force. On the other hand, the electric field formed between the particles forming the magnetic toner 5 that are charged and attached to the metal surface and their mirror images is
It is in the direction of recombining with the charge of and neutralizing the charge, but 3
The electric charge of the magnetic toner 5 overcomes this force and is retained.

On the other hand, charges of opposite polarity are easily recombined by the electric field formed between the mirror image and the magnetic toner 5.
It is considered that the adhesion to the sleeve 3 disappears.

In other words, this phenomenon means that the charge retention ability of the magnetic toner 5 is significantly different between the positive polarity side and the negative polarity side, or that the potential barrier to the counter-conductive surface is significantly different depending on the polarity of the charge. This is an important characteristic when applied to devices. Therefore, in the present invention,
It was decided to use magnetic toner particles that have the ability to charge in one direction. Such a magnetic toner is obtained by adding a charge control agent such as a nigrosine dye or a metal-containing ab dye to particles whose main components are a binder resin and a magnetic powder.

Next, the above characteristics are largely influenced by the amount of magnetic powder in the magnetic toner 5, and as the amount of magnetic powder increases, the amount of adhesion to the metal drum 1 decreases. This is considered to be because the charge retention ability of the magnetic toner 5 decreases as the amount of magnetic powder increases, or because the magnetic force in the direction of the multipolar magnet 2 increases as the amount of magnetic powder increases. In order to have sufficient unidirectional charge retention power, the amount of magnetic powder in the magnetic toner 5 is desirably less than 50% by weight.

From the above, in general, when performing development, the improvement in developing performance by alternating voltage applied to a sleeve made of a metal material is most pronounced in magnetic toner containing a small amount of magnetic powder. It is thought that the magnetic force acting on the magnetic toner changes depending on the amount of magnetic powder, which affects the developability, but the magnetic powder content in the magnetic toner is necessary to obtain a sufficient improvement in developability by applying an alternating voltage to the sleeve. It is less than 50 weight (more preferably 45 weight or less). In addition, the amount of magnetic powder is 2
When the amount is less than 0% by weight, background fogging tends to occur in images when the toner concentration is high, so it is desirable to use a toner with a magnetic powder amount of 20% by weight or more, especially when the toner concentration is not controlled. In the present invention, a magnetic toner having an average particle size of 5 to 20 .mu.m can be used like a normal magnetic toner.

Next, as mentioned above, when used in electrophotography, insulating magnetic toner that has the ability to charge in a unidirectional manner shows good development performance, but when used alone, the magnetic toner itself does not charge. Since it is difficult to remove the toner, there are disadvantages in that toner tends to adhere to the sleeve surface or cause charged agglomeration. When using such magnetic toner, it is known that by using a mixture with a magnetic carrier as a developer, agglomeration of the magnetic toner can be eliminated and long-term reliability can be obtained. In order to fully demonstrate the development characteristics of magnetic toner with such charging performance, prevent toner aggregation, and ensure long-term use,
It is desirable that the weight ratio of magnetic toner, that is, the toner concentration, in the developer conveyed in the developing section or on the surface of a sleeve made of a non-magnetic metal material is 85% by weight or less. Further, the toner concentration is desirably above a certain level in order to reduce the electrical resistance of the developer and prevent an electrical short circuit between the surface of the image carrier and the sleeve when an alternating voltage is applied. Furthermore, when a magnetic carrier that electrically breaks down under high voltage is used in the present invention, consideration must be given to maintaining the toner concentration at a high level and ensuring that the electrical resistance of the developer is sufficiently high. Must be. It is preferable to use a carrier made of soft ferrite manufactured by a sintering method that has high bulk electrical resistance and does not break down even under high voltage application conditions.

Such a ferrite carrier (not coated with resin) usually has a volume resistivity of 10' to 1010 Ω·cm (measuring electric field: DC200V/c+a). The particle size of the ferrite carrier is of course larger than that of the 5 magnetic toner, but preferably has an average particle size of 50 to 100 μm. If it is smaller than 50 μm, it tends to adhere to the surface of the photoreceptor, while if it is larger than 100 μm, the surface of the photoreceptor is easily damaged, which is disadvantageous. The preferred volume resistivity of the developer used is 10'3Ω・C11 or more under an electric field of 10 kV/a*, but even when using a low-resistance magnetic carrier, it is satisfactory if the toner concentration is about 15% by weight or more. can. Note that the electrical resistance of the developer is 3I
After charging the developer between the two electrodes installed at a distance of 100 mm, the developer is sufficiently filled by vibration.

A DC voltage of 3000 V is applied between the electrodes, the current value is measured after 60 seconds, and the volume resistivity value is determined from this.

Furthermore, if the conveyance speed of the developer is sufficiently fast compared to the movement speed of the image carrier, the speed of the developer itself will have a large effect on developing performance, so even if an alternating voltage is applied to the sleeve, it will not be affected by it. The effect of improving developability is small. However, the conveyance speed of the developer or the circumferential speed of the sleeve becomes about 2.5 times or less than the moving speed of the image carrier, and the deterioration of developability due to the decrease in the conveyance speed of the developer appears prI.
In this range, depending on the type of magnetic toner used, the effect of applying the 5 alternating voltage to the sleeve can be significant, and the developing performance can be greatly improved. In this case, the multipolar magnet roll constituting the magnetic means does not need to be rotated at high speed, and even if it is fixed, a sufficient effect of improving the developability can be obtained. Note that in order to obtain sufficient developing performance by applying an alternating voltage, the developer conveying speed should be approximately 0.8 times or more the speed of the image carrier, and the frequency of the alternating current component applied to the sleeve should be low. If it becomes too much, shading will occur in the image corresponding to the alternating cycle of the voltage. It should be noted that as the frequency becomes higher, ground blurring is reduced, but if the frequency is too high, there is no effect on improving image density. Therefore, the frequency is approximately 200, depending on the speed of the image carrier.
~3000) tz, preferably 1000-2000
It is best to set it to Hz. Also, AC PE voltage (VPp)
+;t 300-1600 V NiItltrunoka is effective.

[Function] With the above configuration, even if the developer is transported at a relatively low speed,
High developability can be obtained by applying an alternating voltage to the sleeve, and the mechanism is presumed to be as follows. In order for the magnetic toner particles to form an adhesion force according to the electrostatic charge image in the development area, it is necessary for the magnetic toner to be charged. Charges of opposite polarity to those of the magnetic toner existing in the developer near the development area must be quickly eliminated from the development area. When charges of opposite polarity are present in the development area.

Potential conditions near the development area work in a direction that reduces developability. If the developer speed is fast enough.

Charges of opposite polarity to those of the magnetic toner that contribute to development quickly disappear from the development area as the developer is transported.
Since a sufficient developing electric field is formed, developing performance is improved.

On the other hand, when the developer transport speed is slow, the disappearance of the charge opposite to the toner polarity from the development area is delayed, and the electric field that promotes development is inhibited by a self-bias phenomenon, resulting in a decrease in developability and It is thought that toner scattering occurs around the image area. On the other hand, if the developer transport speed is slow relative to the image carrier, this means that the developer area on the sleeve surface, which is in contact with the image carrier, will be in contact with the developing section for a longer period of time. Therefore, when an alternating electric field is applied in such a state, the number of alternations between a relatively large electric field that promotes development and an electric field that inhibits development that alternately act on the developer in the development area is substantially reduced. will increase. In this case, when an electric field that promotes development is applied to the development area, it is thought that charges are injected from the sleeve side via the conductive carrier particles into the magnetic toner particles involved in development that are in contact with the carrier particles. . Needless to say, this electric charge has an electric polarity in a direction in which the magnetic toner has a charge retention ability, and it is thought that the magnetic toner comes to have a larger electric charge in addition to being triboelectrically charged with the carrier. On the other hand, when an electric field that inhibits development is applied to the development area, the charge of the magnetic toner is not neutralized due to its retention ability, and a considerable portion of the charge is considered to be retained. Therefore, if such an alternating phenomenon is repeated several times in one area of the developer, it is considered that the charging of the magnetic toner is further accelerated. In addition, when charged magnetic toner is developed on the surface of the image carrier, charges of opposite polarity remaining on the magnetic carrier, etc. quickly move from the vicinity of the development area to the sleeve due to the action of the alternating electric field, and disappear from the development area. It is assumed that the formation of a self-biased electric field is prevented and the development performance is improved as a result.Under the assumption of 0 or more, the most effective state under the influence of the alternating electric field in the development area This can be said to be the case when the developer conveying speed and the image carrier moving speed are the same, but this state may not necessarily match the desired image characteristics. Image characteristics change not only depending on the magnitude and frequency of the alternating voltage applied to the sleeve, but also on the developer transport speed and other development conditions, so the conditions related to each development should be set according to the desired image characteristics. Should.

[Embodiment] FIG. 3 is a diagram explaining the main structure of an example of a developing device according to an embodiment of the present invention. In FIG. 3, reference numeral 7 denotes an image carrier, which carries an electrostatic charge image on one surface, is formed to be rotatable in the direction of arrow (x), and is electrically grounded. The sleeve 9 containing the multipolar magnet 8 is formed of a non-magnetic metal material into a hollow cylindrical shape, and is arranged relatively close to the surface of the image carrier 7 and at approximately equal intervals in the longitudinal direction.

It is rotatable in the direction of arrow (y). IO is a developer tank that stores a developer that is a mixture of magnetic toner 11 and magnetic carrier 12 or replenishment magnetic toner. The regulating member 13 magnetically attracts the surface of the sleeve 9 and controls the amount of the developer 14 carried by the rotation of the sleeve 9 on the image carrier 7.
The distance between the sleeve 9 and the sleeve 9 is set so that the sleeve 9 contacts the surface of the sleeve 9 in an appropriate state. Furthermore, a voltage source 15 is connected to the sleeve 9, so that at least a low frequency alternating voltage is applied during development.

Next, magnetic toner A should be stored in the developing device.

B was prepared in the following manner.

Magnetic toner A Styrene acrylic resin 56% by weight (38M600 manufactured by Sanyo Chemical) Magnephyte 40% by weight (BCloo manufactured by Kanto Denka ■) Metal-containing ab dye 3% by weight (Bontron E81 manufactured by Orient Chemical) Carbon blank
1-ply ■% (Mitsubishi Kasei ■ MA600
) Magnetic toner B Styrene acrylic resin (same as above) 38% by weight Magnetite (same as above) 58% by weight Metal-containing azo dye (same as above) 3% by weight Carbon black (same as above) 1% by weight The above raw materials are melt-kneaded and cooled. The powder was then crushed to obtain magnetic toners A and B having an average particle size of 12 μm. These magnetic toners A and B and ferrite carrier (K B N 10'O4 manufactured by Hitachi Metals)
(particle size: 35 to 105 μI) was mixed to prepare a developer, and a development test was conducted. During development, a negative polarity OPC photoreceptor is used as the image carrier 7 shown in FIG.
Sleeve 9 (
The developer I4 is adsorbed onto a sleeve (made of aluminum alloy with an outer diameter of 24 m), and the developer 14 is absorbed by rotating only the sleeve 9.
This was carried out with the distance between the regulating member 13 and the sleeve 9, that is, a doctor gap of 0.35 mm, and the development gap of 0.4 M. Also, the OP of the charged area
The C surface potential was set at -550V, and the OPC surface potential of the exposed area was set at -90V. Under the above conditions, a DC bias voltage of -400 cm was applied to the sleeve 9 to perform reversal development. As a result, when the conveyance speed of the developer 14 is approximately 2.5 times or more for both magnetic toners A and B, the density of one image is 1.35.
A sufficient image density was obtained. Further, when the conveying speed of the developer 14 was reduced below this, the co-developing performance of both magnetic toners significantly decreased. The conveyance speed of the developer 14 is o
The image densities of magnetic toners A and B were approximately 0.6 and 0.4, respectively, when the peripheral speed was approximately the same as the peripheral speed of the PC2 light body. In this state, when an AC component of 800 V and frequency of 800 Hz was superimposed on a developing bias of -400 cm, the image density was as low as 0.9 for magnetic toner B, but the image density for magnetic toner A was 1.38. It rose above that. The toner density on the surface of the sleeve 9 immediately before and after replenishing the magnetic toner 11 into the developer tank 10 was 18 weight percent and 75 weight percent, respectively.

Furthermore, the frequency of the AC component is set to 40 (1-2000fiz,
When the voltage was varied within the range of 300 to 1600 V, the same phenomenon as described above was observed.

FIG. 4 is a diagram showing the relationship between the peripheral speed ratio of the sleeve to the image carrier and the image density. In this case, the peripheral speed of the image carrier 7 shown in FIG. 3 is 100 mm/see, and the developing gap is 0.
3an, doctor gap is 0.25 mm,
Development was performed with the magnetic powder content in the magnetic toner 11 being 40% by weight and the toner concentration being 50% by weight.

Note that curve a indicates DC bias voltage of -430■ to sleeve 9.
The -force curve also shows the case where only Vpp is applied.
1600 V, frequency 1600 Hz (7) This shows the case where AC components are superimposed.

As is clear from FIG. 4, the image density improves when the peripheral speed ratio of the sleeve to the image carrier is increased, but the image density is saturated when the peripheral speed ratio is approximately 2.5.

Further, by superimposing an alternating current component on the direct current bias voltage, a remarkable improvement in image density is observed, as shown by curve 9.

However, even in this case, the peripheral speed ratio is 0.8
If it is less than this, the image density will decrease and a clear image that can be put to practical use will not be obtained, which is not preferable.

FIG. 5 is a diagram showing the relationship between AC voltage and image density,
The development conditions correspond to those in FIG. 4 above. In FIG. 5, Vs and Vp indicate the peripheral speeds of the sleeve 9 and image carrier 7 shown in FIG. 3, respectively.

As is clear from FIG. 5, it is recognized that the density of one image is improved by increasing the AC voltage in each case. However, around 2000 V, the image 4 degrees is approximately saturated, and even if the AC voltage is increased further, there is hardly any improvement in image density. As mentioned above, conventionally only a DC bias voltage was applied to the sleeve 9, but by superimposing an AC voltage, it is recognized that image density is improved and fogging is prevented. However, from the viewpoint of safety, the AC voltage is preferably 2000 V or less, preferably 1600 V or less.

[Effects of the Invention] As described above, according to the developing method of the present invention, a mixed powder of a magnetic toner having a unidirectional charging ability and a magnetic carrier is used as a developer, and at least a low frequency alternating voltage is applied during development. By applying this to the developing section, good development performance can be obtained even if the developer transport speed is set relatively low. Therefore, when applied to an electrophotographic apparatus, there is no need for high-speed rotation for conveying the developer, so the load on the drive system can be reduced and noise is less likely to occur. Furthermore, since the force acting on the developer can be reduced, damage to the magnetic toner is reduced, resulting in long-term reliability.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the main part of a device for confirming the characteristics of magnetic toner that has the ability to be charged with unidirectional polarity, and Figure 2 is a unidirectional polarity charging that can be obtained using the device shown in Figure 1. Figure 3 showing typical characteristics of magnetic toner having the ability to
FIG. 4 is a diagram showing the relationship between the peripheral speed ratio of the sleeve to the image carrier and the image density, and FIG. 5 is a diagram showing the relationship between the AC voltage and the image density. FIG. 3 is a diagram showing the relationship with concentration. 7: Image carrier, 9 sleeves. Figure 1

Claims (1)

[Scope of Claims] (1) A developer formed by mixing magnetic toner particles containing a binder resin and magnetic powder and having the ability to charge with unidirectional polarity, and magnetic carrier particles having relatively electrical conductivity. The developer is attracted to the surface of a non-magnetic and conductive sleeve by magnetic means, and by rotating at least the sleeve, the developer is conveyed to the contact area with the electrostatic image carrier, and the electrostatic image is formed by the magnetic toner particles. In a developing method for visualizing an electrostatic charge image on the surface of a carrier, the content of magnetic powder in the magnetic toner particles is set to less than 50% by weight, and the conveying speed of the developer due to rotation of the sleeve is set to the same level as that of the electrostatic charge image carrier. A developing method characterized in that the speed is 0.8 to 2.5 times the moving speed and a low frequency alternating voltage is applied to the sleeve at least during visualization. (2) The content of magnetic toner in the developer adsorbed on the sleeve surface is 1
The developing method according to claim 1, wherein the content is 5 to 85% by weight. (3) The developing method according to claim (1), wherein the developer is configured to exhibit electrical insulation.