JPS61160764A - Developing method - Google Patents

Abstract

PURPOSE:To obtain high image quality applicable to pictorial colors as well with the less edge effect and with substantial flat black density by specifying the contents of magnetic powder and the intensity of the magnetic field of a developer in the tangential direction on the surface of a developer carrying body. CONSTITUTION:The image having good quality is obtd. if the intensity of the horizontal magnetic field component is set preferably at >=300 gauss. The reason is: If the intensity is >=200 gauss, the sticking of the magnetic particles to the drum arises hardly. The good quality image is obtainable if the content of the magnetic powder is made >=40wt% up to 80-100mum number average grain size of the magnetic particles but if said size exceeds 100mum, the preferable content of the magnetic particles in the developer approaches 10wt% and there is not much difference from the mixing ratio at which the conventional two- component developer is used, then the strict control of the mixing ratio is necessary and there are no advantages. The number average grain size of the magnetic particles is therefore preferably >=40mum, more preferably <=80mum and the content of the magnetic powder in the magnetic particles is preferably >=40wt%.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a non-contact developing method which can also be applied to Victorian color for developing electrostatic latent images.

[Prior art]

Conventionally, as one of the non-contact development methods, an insulating magnetic toner or a non-magnetic toner is thinly applied on the surface of a developer carrier, and in a developing section, the surface of this thin layer of developer and the surface of the latent image carrier are separated. A method of developing an electrostatic latent image on a latent image carrier by forming a gap between the two and applying an alternating electric field to the developing section to cause the toner to fly onto the developer carrier is disclosed in Japanese Patent Application Laid-Open No. 1983-1999. 186
It is disclosed in Publication No. 56.

However, such a developing method has the following problems. In short, if you try to reliably charge each toner particle on the developer carrier surface to the desired polarity, the thickness of the toner layer on the developer carrier surface will inevitably become thinner, and the developed density of the solid black area will decrease. cannot obtain a sufficiently high value. More specifically, when a character-shaped latent image is developed, not only the toner on the surface of the developer carrier facing the latent image is concentrated, but also the toner in the surrounding area is also affected by the alternating electric field. Because they gather together, a sufficiently high concentration of current
I-wei is obtained.

On the other hand, when an electrostatic latent image with solid black areas or thick lines is developed, the thin layer of toner on the surface of the developer carrier tends to be insufficient to obtain a high density, and the edges of the latent image tend to be insufficient. Toner gathered in the black areas, resulting in image quality that lacked toner in the black areas.

This lack of toner concentration in solid black areas is more pronounced when developing with non-magnetic toner made mainly of resin than when developing with magnetic toner made of resin and magnetic material. ) is remarkable. Therefore, the problem became more serious when performing color development than black and white development.

In particular, for high-quality image development aiming at Victorian colors, edge effects and lack of density in solid black areas become serious problems.

Therefore, if the thickness of each layer of toner on the surface of the developer carrier is increased, each toner becomes difficult to be charged to the desired polarity and charge amount. For this reason, not only excess toner adhered to non-image areas, but also the resulting image quality was poor and the toner density was poor.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing method that eliminates all of the above-mentioned drawbacks and provides high image quality that can be applied to Victorian colors with little edge effect and sufficient peta black density.

[Summary of the invention]

The present invention provides a developer in which magnetic particles containing 4Qwt% or more of magnetic powder and non-magnetic particles mainly made of resin are mixed on the surface of a latent image carrier and a developer carrier having a magnetic field generating means on the back surface. In the developing section, the magnetic poles of the magnetic field generating means on the back surface of the developer carrier are made to face the latent image carrier, and the strength of the magnetic field in the tangential direction on the surface of the developer carrier is set to 200 Gauss or more. In addition, the thickness of the developer layer maintains a large development gap, and an alternating electric field is formed in the development gap to restrain the magnetic particles on the surface of the developer carrier. Development is carried out by alternately repeating the process of making non-magnetic particles fly from the developer layer to the latent image carrier in both image areas and non-image areas, and the process of returning excess non-magnetic particles to the developer carrier. This is a developing method that performs

Therefore, according to the present invention, it is possible to obtain a high-quality developing section that has little edge effect, sufficient peta black density, and is applicable to uniform Victorian color development. Further, even if an alternating electric field is applied to the developing section, the electric field does not transfer to the carrier, which is the magnetic particle holder, and there is an advantage that stable and clear color image quality can always be obtained.

〔Example〕

The present invention will be explained in detail below using examples.

FIG. 1 is a schematic diagram of a developing device to which the developing method of the present invention is applied. In the figure, 1 is an electrostatic latent image holding member, 11 is a back electrode, and 12 is an electrostatic latent image holding layer thereon, which may be an insulating layer or an electrophotographic photoreceptor layer. Here, it is shown as a photosensitive drum 1. A developer carrier 2 is a conductive sleeve made of a non-magnetic material and rotates in the direction of arrow A. Reference numeral 3 denotes a magnetic field generating means fixedly provided inside the sleeve, which in this example is a magnet roller having four magnetic poles. 4 is a developing agent in which magnetic particles containing magnetic powder in a resin are mixed with non-magnetic particles (toner) having a smaller average particle diameter and mainly made of resin. Between the back electrode 11 of the photosensitive drum l rotating in the direction of arrow B and the sleeve 2, a current voltage is applied by a DC power source 5 and an AC power source 6. 7 is an elastic member, 8
9 is a toner supply roller, and 9 is a developer layer thickness regulating member, which is a doctor blade here.

Opposing the photosensitive drum 1 which has an electrostatic latent image on its surface and rotates in the direction of arrow B, the sleeve 2 is 200 to 800 μm thick.
Preferably, they are installed with a gap of 300 to 600 μm.

The toner supply roller 8, which has a plurality of recesses on its surface, rotates slowly as the drive gear of the sleeve 2 meshes with the drive gear of the photosensitive drum 1.

The non-magnetic particles (toner) T in the hopper part 9 are dropped little by little into the developing chamber below by the elastic member 7, and the toner T is supplied.

The toner T supplied to the developing chamber is mixed with magnetic particles M (particles containing magnetic powder in resin) present near the surface of a sleeve 20 having a magnet roller 3 inside.

When the sleeve 2 rotates in the direction of arrow A, the developer 4 on the sleeve surface moves in the direction of arrow C, and the toner supplied by this movement gradually enters the developer 4 and is mixed. Ru.

The mixed developer 4 is transferred to a doctor blade formed of a non-magnetic material and fixed at a distance of about 100 to 55Q, 4m, preferably 150 to 450μm from the surface of the sleeve 2, facing between the magnetic poles Nl and 83. 10 to an appropriate thickness, for example 100 to 600 μm, preferably 150 to 600 μm.
It is regulated to 500 μmk and applied to the surface of the sleeve 2. The thickness of this developer layer is smaller than the drum-sleeve gap in the development area, and therefore the developer layer and the drum surface are in a stationary state and are not in contact with each other.

The non-magnetic particles (toner) T in the applied toilet preparation 4 are triboelectrically charged by friction with the magnetic particles M and friction with the sleeve 2,
In this state, due to the electrostatic force between the sleeve 2 rotating in the direction of the arrow and the electrostatic force between the magnetic particles and the magnetic particles, they remain attached to the sleeve 2 as the sleeve rotates 20 times. It is carried to the development area.

In the developing area, the magnetic poles N1 and S1 of the magnet roller 3 inside the sleeve 2 are arranged to face each other with respect to the photosensitive drum IK. Therefore, the developer on the surface of the sleeve 2 does not form spikes in the development area and has a uniform layer thickness.

Therefore, the distance between the photosensitive drum surface 2 and the sleeve 2 is t''&, which keeps the developer layer and the drum surface non-contact, and there is no need for a distance of about 1 mm or more, for example.

Therefore, since the sleeve and the drum can be placed close to each other in the developing area, clear image quality with the effective development electrode effect can be obtained. It has been confirmed that if the development gap distance is set at a distance of about 1 mm or more, the image becomes blurred and unclear.

During development, alternating voltages are applied between the sleeve 2 and the back electrode 11 of the photosensitive drum 1 to form an alternating electric field in the developing area. At this time, the DC voltage from the DC power supply 5 and the AC voltage from the AC power supply 6 are superimposed to perform development. Also, it is optimal to use a bias voltage. Alternatively, only an alternating current voltage may be used as a bias.

The AC R voltage does not necessarily have to be a sine wave.

It may be a rectangular wave. Peak vs. heat/value of AC used Vp-p=200~4KV, Itl tl number 1d
f=Zoo~4KHz is good.

Example 1 Reservoir part [position VD power + 600 V, background 11th place VL power 0
When (3), the peak-to-peak value is 18 as the developing bias voltage.
00Vpp 1 cycle, +15 to AC voltage with wave number 1.6KHz
Development was carried out by superimposing a DC voltage of 0V.

The non-magnetic particles used are toner particles having a number average particle diameter of about 8 μm and mainly composed of thermoplastic resin (polystyrene), and are particles that are negatively charged with respect to magnetic particles. Reversal development can also be performed by using positive polarity toner and selecting an appropriate DC voltage. The magnetic particles contain magnetite (Fe
Particles having a number average particle diameter of 50 μm were used by mixing the magnetic powder of A.ast) to 75 weight and pulverizing the mixture.

In addition, there are 2 components in this two-component mixed developer from the viewpoint of charging series.
Better image quality can be obtained by mixing silica particles located between the two particles in the charge series of 1 weight X or less.

When the above-mentioned developing bias voltage is applied, when the potential of sp+7- exceeds the threshold value in the negative voltage phase, the negatively charged non-magnetic particles are removed from at least drum 1 and sleeve 2.
The developer flies from the developer layer on the sleeve 2 to the photosensitive drum 1, both in the image area and in the non-image area (background area).

However, in a phase of opposite polarity to the above, at least the excess non-magnetic particles undergo a reverse transition and return to the sleeve. After repeating this process several times, the gap between the drum and the sleeve widens, the alternating electric field weakens, the flying particles disappear, and development ends.

In order to weaken the alternating electric field, the applied voltage may be weakened.

What is important here is to prevent the magnetic particles from flying and transferring from the developer layer on the sleeve 2 to the photosensitive drum 1. This is because when the magnetic particles are transferred, the magnetic particles in the developing device gradually disappear, and the ratio between the number of magnetic particles and the number of non-magnetic particles in the developer becomes significantly different. If this ratio (toner/magnetic number) is significantly disrupted, it will cause background capri. Therefore, it is important to restrain the magnetic particles on the sleeve surface by magnetic force.

What is more important is that the distance between the photosensitive drum 1 and the sleeve 2 is not too large, resulting in blurred image quality. If the magnetic poles are opposed to the drum in the boundary region, the brushes will stand up, making it difficult to reduce the distance between the drum and the sleeve.

For this reason, the distance between the drum and sleeve should be set between 200 and 800.
It is important to make the magnetic poles of the magnet row 23 (between Nl and 81) face the drum in the boundary area so that μm1 can be set to preferably 300 to 600 μm.

FIG. 2 is a magnetic field distribution diagram of the magnet roll 3, which represents the perpendicular magnetic field component (magnetic pole strength), which is generally used to represent the strength of the magnetic field on the sleeve surface.

In the figure, the horizontal axis connecting the centers of the drum and the sleeve is taken as the horizontal axis, and the drum facing portion is designated as 00. This vertical component refers to a magnetic field component in a direction perpendicular to the surface of the sleeve 20, and the second
The figure shows this distribution around the circumference of the sleeve. From this figure, it can be seen that there is a θ Gauss angle between the magnetic poles N1 and 81. According to experiments, the magnetic particles were magnetically restrained on the sleeve even between the magnetic poles, and were not substantially transferred to the drum 1. This result is difficult to understand from FIG.

This can be easily understood from the following Figure 3. FIG. 3 is a magnetic field distribution diagram showing horizontal magnetic field components on the surface of the sleeve, which is the developer carrier 2, with the angular coordinate axes in FIG. 2 being fixed. In the embodiment of FIG. 3, magnetic pole N1. The horizontal magnetic field component between the magnetic poles of S was 600 Gauss. According to many experiments, it has been confirmed that high quality images can be obtained by setting the strength of this horizontal magnetic field component to at least 200 Gauss or more, preferably 300 Gauss or more. This is because when the pressure is 200 Gauss or more, almost no magnetic particles adhere to the drum. On the other hand, if it is less than this, adhesion of magnetic particles tends to occur, so the particle size of the magnetic particles must be increased, and the concentration of toner/magnetic particles decreases, making it difficult to control the concentration. Additionally, the developer layer becomes thicker and the distance between the drum and sleeve becomes wider, causing blur in the image.

By arranging the magnetic poles to face the drum in this manner, it is possible to prevent the magnetic particles from being substantially transferred to the drum IK, and the photosensitive drum and the sleeve must be separated to avoid spikes of developer. As a result, blurred images can be prevented. Therefore, in the present invention, the above conditions are important.

Furthermore, as a condition for stably obtaining image quality without fog,
The necessary conditions for magnetic particles are summarized in Table 1.

Table 1 The number average particle size of the magnetic particles is shown in Table 1, and the content of magnetic powder contained in the magnetic particles is shown in weight in the table. In the table, the X mark indicates a combination that is unacceptable, the ○ mark indicates a combination that resulted in a practically usable result, and the ◎ mark indicates a combination that yielded a more favorable result. If the number average particle diameter is less than 30 μm, the magnetic particles will be transferred to the photosensitive drum 1, which is not practical. In addition, it is possible to achieve a number average particle size of 80 to 100 μm by increasing the magnetic powder content to 40% by weight or more, but
When the particle size exceeds 00 μm, the preferred content of non-magnetic particles in the developer approaches 10 weight XK, which is not much different from the mixing ratio using a conventional two-component boundary agent, and strict control of the mixing ratio is required. The advantage is lost.

Therefore, the number average particle diameter of the magnetic particles is 30 μm or more,
The thickness is preferably 40 μm or more and 100 μm or less, more preferably 40 μm or more and 80 μm or less. Further, the magnetic powder content of the magnetic particles is preferably 4 OititX or more.

It is also possible to use magnetic particles whose entirety is made of a magnetic material. Further, particles having a magnetic material as a core and a resin coating around the core can easily be formed into spherical particles, and triboelectric charges can be applied uniformly. In addition, by mixing a charge control agent such as a pigment or dye into the resin that makes up the magnetic particles so that the non-magnetic particles (toner) can be charged to the desired polarity and charge amount, better high-quality image development can be achieved. becomes possible.

Furthermore, the mixing ratio of toner and magnetic particles is 15 wt% to 45 w.
It was possible to obtain images with high developed density and no blur over a very wide range of t%. Therefore, there is an advantage that the toner concentration can be easily controlled. When the mixing ratio is less than 15 wt
If the temperature exceeds that level, soil pre-loading occurs and favorable results cannot be obtained.

In the explanation of FIG. 1, the sleeve 2 was rotated in the direction indicated by the arrow, but good image quality was obtained even when the sleeve 2 was rotated in the opposite direction to the direction indicated by the arrow. Rather, rotating the sleeve in the direction opposite to A had the effect of increasing the development density at the high speed boundary.

The magnitude of the horizontal magnetic field component on the surface of the sleeve 2 between the magnetic poles in the developing section, which is related to the magnetic restraint of the magnetic particles;
The relationship between the magnitude of the vertical magnetic field component on the sleeve surface at the position of the two magnetic poles (N1°81) sandwiching this is as follows: If the magnitude of the vertical magnetic field component on the sleeve surface of the two magnetic poles is large,
The magnitude of the horizontal magnetic field component between the sandwiched magnetic poles is not necessarily large. If the two magnetic poles that sandwich the developing section are too far apart, the magnitude of the horizontal magnetic field component on the sleeve surface between the magnetic poles will also become small. On the other hand, if the two magnetic poles are brought too close together, not only will the distance between the magnetic poles become narrower and the appropriate boundary area will also become narrower, but the magnitude of the horizontal magnetic field component on the sleeve surface will not be increased as much.

Therefore, the central angle eu between the magnetic poles N1 and 81 as seen from the center 0 of the magnet roller 3 (the center of the sleeve 2) is 45
It is preferable to set the angle to °≦6≦135°.

In addition, in order to stably obtain high-quality images, the number-average particle size DT of one non-magnetic particle (toner) is set as DT≦DC≦ with respect to the number-average particle size Dc of magnetic particles. It is best to choose from the range of 15DT. If the particle size of the non-magnetic particles is larger than the ratio of the particle size of the magnetic particles, tribocharging of the non-magnetic particles will be insufficient, and conversely, if the ratio is too small, the image quality will be poor.

Further examples of the present invention are shown below along with comparative examples.

] 1. The distance between the photosensitive drum l and the sleeve 2 is 500μm1lc.
The thickness of the developer layer was regulated with a doctor blade to be 400 μm at the position closest to the photosensitive drum. The developer used was a mixture of non-magnetic particles and magnetic particles with an average particle size of 8 μm, and the concentration ratio of the non-magnetic particles was 30 wtXK. Incidentally, the content of magnetic powder in the magnetic particles was set to Fi70wt, and particles with an average particle size of 50 μm were used. Furthermore, the arrangement of one magnetic pole was such that the magnetic poles faced the drum as shown in FIG. 1, and the strength of the magnetic field at 8° with respect to the magnetic pole N1 was set so that the vertical magnetic field component was 700 Gauss.

The strength of the horizontal magnetic field between the magnetic poles at this time was 610 Gauss.

Under such conditions, the latent potential VD of the image area has negative polarity.
00V, when the background potential VL is OvO, positively charged non-magnetic particles (toner) are used, the developing bias voltage is Vp-1) = 1soov, f = 1, 6 KHz AC voltage and DC voltage - When developing with a superimposed voltage of 150V, only non-magnetic particles flew and transferred to the image area (VD), and neither non-magnetic particles nor magnetic particles adhered to the non-image area, resulting in good both sides with no ground force blur. was gotten.

Comparative Example: Average particle size is 40 μm when the magnetic powder content is 30 wtX.
When development was carried out in the same manner as in Example 2 using the magnetic particles, the magnetic particles adhered to the non-image area, and favorable results were not obtained.

Example 3 Under the same conditions as in Example 2, reversal development was carried out to develop the bright area (L) of the reservoir. In this example, when the dark part vD of the reservoir potential is 1600 V and the bright part vL is 150 V, negatively charged particles are used as non-magnetic particles, and the developing bias voltage is 1800 Vp-p and 1.6 KHzO AC. Direct fi to voltage! When developing is carried out by superimposing a pressure of -450V,
Only non-magnetic particles are transferred by flight to the bright area of the drum, which is the image area, and neither magnetic particles nor non-magnetic particles are attached to the dark area, which is the non-image area. Good development was achieved.

Note that even when the reservoir potential was positive, the same results as above were obtained by setting the charged polarity of the nonmagnetic particles to positive polarity and setting the DC voltage to +450V.

〔Effect of the invention〕

As explained above, in the present invention, magnetic particles containing 40% by weight or more of magnetic powder and non-magnetic particles mainly made of resin are mixed on the surface of a developer carrier having a magnetic field generating means on the back surface. A developer layer is supported, and in the developing section, the magnetic poles of the magnetic field generating means on the back surface of the developer carrier are opposed to the reservoir holder, and the strength of the magnetic field in the tangential direction on the surface of the developer carrier is 2.
00 Gauss or more, preferably 300 Gauss or more, and maintain a development gap larger than the thickness of the developer layer, and form an alternating electric field in the development gap to restrain the magnetic particles on the surface of the developer carrier. a step of causing non-magnetic particles to fly from the developer layer on the developer carrier to the reservoir holder in both the region and the non-region, and returning excess non-magnetic particles to the developer carrier. By repeating the steps alternately and developing, many effects such as those described below were obtained.

(1) A developed area with sufficient peta black density was obtained without edge effects, which could not be obtained with conventional non-contact development methods.

C2) Clear (sharp) image quality without blurring was obtained.

(3) Since the magnetic particles do not substantially fly and transfer to the latent holder, the magnetic particles are not mixed into the image area with the non-magnetic particles during development, making it possible to develop vivid colors.

(4) It was also possible to prevent the magnetic particles from being consumed.

(5) Do not use the standing part of the brush in the developing section.

By arranging the magnetic poles to face the developing section, a region with a uniform thickness of the developer layer can be used, so a uniform counter electrode (developing electrode) effect can be obtained, and development with uniform image quality is possible.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a developing device to which the present invention is applied, and FIG. 2 is a vertical magnetic field distribution diagram of a magnet roller. FIG. 3 is a horizontal magnetic field distribution diagram of the magnet roller. In the figure, 1 is a photosensitive drum and 2 is a sleeve. 3 magnet rollers, 4 a developer, 5.6 a developing bias power supply, and 10 a doctor blade.

Claims (1)

[Claims] A developer layer containing a mixture of magnetic particles containing 40 wt% or more of magnetic powder and non-magnetic particles mainly made of resin is carried on the surface of a latent image carrier and a developer carrier having a magnetic field generating means on the back side. In the developing section, the magnetic poles of the magnetic field generating means on the back surface of the developer carrier are opposed to the latent image carrier, and the strength of the magnetic field in the tangential direction on the developer carrier surface is set to 200 Gauss or more, and A development gap larger than the thickness of the developer layer is maintained, and an alternating electric field is formed in the development gap to restrain the magnetic particles on the surface of the developer carrier while allowing the magnetic particles to be removed from the developer layer on the developer carrier. Development is performed by alternately repeating the process of flying non-magnetic particles onto the latent image carrier in both the image and non-image areas, and the process of returning excess non-magnetic particles to the developer carrier. A developing method.