JPH038542B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing method for developing an electrostatic latent image.

The present applicant previously disclosed a novel developing method in Japanese Patent Application Laid-Open Nos. 18656-18659. this is,
Insulating magnetic toner is uniformly applied onto a cylindrical developer support member having a magnet inside, and the toner is placed facing the latent image holding member without coming into contact with it for development. At this time, a low frequency alternating voltage is applied between the developer support member and the base conductor of the latent image holding member to cause the toner to reciprocate between the developer support member and the latent image holding member, thereby eliminating background fog. It has excellent gradation reproduction and can perform good development without thinning at the edges of the image. In this developing method, since the toner is an insulator, transfer is easy. or,
The developing device is extremely simple and inexpensive.

However, this developing method has the following drawbacks because it requires the use of magnetic toner. Since magnetic toner generally contains black magnetic powder, it is difficult to produce toner of colors other than black. Furthermore, by containing magnetic powder, when a toner image is fixed using a heat fixing device, a pressure fixing device, etc., the fixing performance is poor and the image becomes rough.

2. Description of the Related Art A method has long been known in which a non-magnetic toner is applied to a developer supporting member, and the toner is developed by facing an electrostatic image holding member. However, this is because it is difficult to uniformly apply toner to the developer support member, it is difficult to develop the electrostatic image unless it has an extremely high potential, and the image quality of the developed image is poor. Due to these drawbacks, it has not been put to practical use.

Due to these drawbacks of the one-component development method, conventional
Especially when developing using color toner,
A common method is to use a two-component developer containing a mixture of toner and carrier. However, the two-component development method has drawbacks such as deterioration of the carrier, the need to maintain a constant ratio of toner and carrier, which is difficult to control, and a large and complicated developing device. have.

The purpose of the present invention is to eliminate the above-mentioned drawbacks of conventional developing methods. It is possible to use the same developing device as that used, or one having almost the same configuration. The developer contains a small amount of carrier, but this is hardly consumed and does not deteriorate. Also, there is a wide permissible range for the mixing ratio of toner and carrier.

The present invention uses a developer in which an insulating toner and a powder having conductivity and magnetism are mixed in a weight ratio of 1:4 to 1:1, the size ratio of which is within 1:3. The developer is supplied to the developer carrier, and the developer is applied onto the developer carrier by a developer regulating means in a layer thinner than the distance between the developer carrier and the image carrier at the development position. The layer is transported to a development position where the magnetic poles of a magnet disposed within the developer carrier face the image carrier, and an alternating electric field is formed between the developer carrier and the image carrier at the development position. This developing method is characterized in that insulating edge toner is attached to and detached from the image carrier, and conductive magnetic powder is attached to and detached from the image carrier to perform development.

As the conductive and magnetic powder, iron oxide powder etc. can be used, but it is also possible to use a powder similar to the known conductive magnetic toner, which is made by melting and mixing a magnetic material and resin, pulverizing it, and treating it with conductive material such as carbon. , is more suitable.

As a method of applying the developer to the developer support member, for example, as described in Japanese Patent Application Laid-Open No. 54-43037,
It is possible to arrange a blade of a magnetic material opposite to the magnetic pole of a magnetic field generating means built into the developer support member, and form a toner layer thinner than the gap between the blade and the support member by magnetic cutting. Generally, it is difficult to apply non-magnetic toner uniformly to a developer support member, but in the method of the present invention, since the toner is mixed with a magnetic carrier, it can be applied thinly and uniformly together with the carrier. .

The applied developer layer is extremely thin, and there are many opportunities for the toner to come into direct contact with the developer support member, blade, etc. Therefore, the triboelectric charging properties of the carrier powder are not very important, and good images can be obtained as long as the toner itself has excellent triboelectric charging properties. Therefore, there is almost no deterioration in image quality due to deterioration of the carrier as seen in ordinary two-component development systems.

The developer is opposed to a latent image holding member supported by a magnet installed in the developer support member while the toner and carrier are still mixed. Here, the developer jumps to the latent image holding member due to the electrostatic force of the latent image and the low frequency alternating voltage applied between the developer supporting member and the latent image holding member, and moves back and forth in response to the alternating voltage.

The principle of this reciprocating movement of the developer will be explained below using FIGS. 1 and 2 as examples. In the figure, the voltage waveform applied to the toner carrier is shown in the lower part, and although it is a rectangular wave here, it is not limited to this as will be described later. During time interval t ₁ a negative polarity bias voltage of magnitude Vmin is applied, and during time interval t ₂ a positive polarity bias voltage of magnitude Vmax is applied. The magnitude of Vmin and Vmax is determined by assuming that the image area charge formed on the image surface is positive and that this is to be developed with negatively charged toner, the image area potential is V _D and the non-image area potential is V _L. When, Vmin < V _L < V _D < Vmax (1) is selected. If chosen in this way, during the time interval t ₁ the bias voltage Vmin acts to provide a bias electric field that tends to promote the adhesion of toner to the image and non-image areas of the electrostatic latent image carrier, so that the toner transfer stage It is called. In the time interval t ₂ , the bias voltage Vmax acts to provide a bias electric field that tends to return the toner transferred to the latent image holding surface in the time interval t ₁ to the toner carrier, which is called a toner reverse transfer stage.

Vth・f and Vth・r in FIG. 1 are potential thresholds for toner transfer from the toner carrier to the latent image surface and from the latent image surface to the toner carrier, respectively, and the curves shown in the figure It is considered that the potential value is extrapolated by a straight line from the point where the slope of the rise is the largest.
In the upper part of FIG. 1, the amount of toner transfer at t ₁ and the degree of toner reverse transfer at t ₂ are plotted as a model against the latent image potential.

In the toner transfer stage, the amount of toner transferred from the toner carrier to the electrostatic image holder is as shown by curve 1 shown by a broken line in FIG. The slope of this curve is approximately equal to the slope of the curve when no alternating bias voltage is applied. This slope is large, and the amount of toner transfer tends to be saturated at an intermediate value between V _L and V _D , resulting in poor halftone image reproduction and poor gradation. The second broken line curve 2 shown in FIG. 1 represents the probability of the degree of toner reversal.

In the developing method according to the present invention, an alternating electric field is applied so that the toner transfer stage and the toner reverse transfer stage are alternately repeated, and in the bias phase t ₁ of the toner transfer stage of the alternating electric field,
The toner from the toner support is intentionally made to reach the non-image area of the electrostatic latent image holding member (of course, it also reaches the image area), and the potential of the midtone has a low potential close to the bright area potential (V _L ). The toner is sufficiently attached to the area to improve the gradation, and then, in the bias phase t ₂ of the toner reverse transfer stage, a bias is applied in the opposite direction to the toner transfer direction as described above. The toner that has reached the non-image area is returned to the original toner support side. In this toner reverse transfer stage, as will be described later, since the non-image area originally has no image potential, when a bias electric field of opposite polarity is applied, the toner reaches the non-image area as described above. tends to immediately leave the non-image area and return to the toner carrier.
On the other hand, since the toner once attached to the image area including the halftone area is attracted by the charge of the image area, even if a reverse bias is applied in the opposite direction to this attraction force as described above, the toner will not actually leave the image area. The amount that returns to the toner support is small. By alternating the bias electric fields having mutually different polarities at a preferable amplitude and frequency, the above-mentioned toner transfer and reverse transfer are repeated many times at the development position. In this way, the amount of toner transferred to the latent image surface can be made faithful to the potential of the electrostatic image. That is, as shown in Figure 1 as curve 3, the toner transfer flow has a small slope and V _L
We were able to obtain a phenomenon in which the amount of toner transfer changes almost uniformly from VD to _VD . Therefore, in the non-image area, there is almost no toner adhesion in practical terms, while toner adhesion to the halftone image area results in an excellent visible image with extremely high gradation in accordance with the surface potential. is obtained. This tendency can be overcome by setting the gap between the electrostatic latent image holding member and the toner carrying member to become larger towards the end of the developing process.
This is even more pronounced by reducing and converging the strength of the above-mentioned electric field in the development gap.

An example of such a developing process according to the present invention is shown in the second example.
As shown in the figure. As shown in FIGS. 2A and 2B, the electrostatic image holder 4 moves in the direction of the arrow, during which it passes through a development area and reaches . 5 is a toner carrier. Therefore, the gap between the electrostatic image holding surface and the toner carrier gradually widens starting from the closest position in the developing section. A in the same figure shows the image area of the electrostatic image holder;
B shows the electric field of the transfer and countertransference from the toner carrier in the non-image area. Further, C in the same figure shows the waveform of the alternating voltage applied to the toner carrier, and when the electrostatic image charge is positive, |Vmax−V _L |>|V _L −Vmin|, |Vmax−V _D | <|V _D −Vmin| ...(2) is set.

A first process in development is occurring in the area, and a second process is occurring in the area. In the case of the image area shown in FIG. 2A, both toner transfer and countertransference occur alternately in the area depending on the phase of the alternating electric field. As the development gap becomes larger, both the transition and reverse transition electric fields become weaker, and although toner transfer is possible, the reverse transition electric field is no longer strong enough to cause reverse transition (below the threshold). Now, neither transfer nor countertransference occurs, and development is completed.

In the case of the non-image area shown in FIG. 2B, both toner transfer and reverse transfer occur in the area. Therefore, ground fog occurs in this area. In this case, both the transfer and counter-transition electric fields become weak, and although toner counter-transition is possible, the transfer electric field (below the threshold value) sufficient to cause the transition disappears. Therefore, ground fog does not substantially occur in this area, and any ground fog that has occurred is also removed. In this case, neither transfer nor countertransference occurs anymore, and development is completed. For halftone image areas, the final amount of toner transferred to the latent image surface is determined by the magnitude of the toner transfer amount and the reverse transfer amount according to the potential, and the slope is as shown in curve 3 in Figure 1. Small. Therefore, a microscopic image with high gradation can be obtained.

In this way, in order to cause the toner to fly through the development gap and once reach the non-image area to improve the gradation, and then to mainly strip off the adhered toner from the non-image area, the alternating bias voltage to be applied is necessary. It is necessary to appropriately select the amplitude of the signal and the frequency of the alternation.

In this way, the developer is reciprocated between the toner carrier and the electrostatic image holder, but the details of this process have not yet been fully elucidated. In the present invention, it is presumed that both the carrier and the toner in the developer jump and move back and forth. However, during this process, the toner and carrier are separated, and only the toner remains on the latent image holding member. This is presumed to be because the carrier particles are electrically conductive. Toner, which is an insulator and has a charge, does not easily separate when it adheres to the image area of an electrostatic image. However, during the process of conductive particles jumping from the developer support member to the latent image holding member, charge is injected from the developer support member, but when they come into contact with the image area of the electrostatic image, the charge of the electrostatic image is injected into the conductive particles. The developer is easily neutralized by the developer, and in some cases, the polarity is reversed, causing the developer to jump to the developer support member. As described above, since the conductive particles do not exhibit strong adhesion, they are ultimately held on the developer support member by magnetic force. Therefore, a visible image is ultimately formed on the electrostatic image holding member only by the insulating toner.

In the developing method of the present invention, the carrier particles are mainly necessary for thinly coating the toner on the developer support member, supporting it with magnetic force, and loosening it with magnetic force, and the electrostatic properties are not so important. . Therefore, the mixing ratio of toner and carrier is relatively free. Furthermore, if there is a predetermined amount of carrier particles on the developer support member, the carrier particles will be
Since the toner does not separate from the developer support member, only toner needs to be replenished.

〔Example〕

Experiments were conducted using the developing device shown in FIG. In the apparatus shown in the figure, 4 is an electrostatic image carrier having an electrostatic latent image obtained by a known electrophotographic method.
Reference numeral 5 designates a developing sleeve as a non-magnetic developer carrier having a fixed magnet roll 6 therein. The developing section has a magnetic pole (for example, the S pole shown in the figure, approximately 650 mm) inside the developing sleeve 5, facing the electrostatic image holding section 4.
Gauss), and the distance between the developing sleeve 5 and the electrostatic image holder 4 is maintained at 300 μm by spacer rollers arranged at both ends of the sleeve. Alternatively, it is a blade made of a magnetic material, and regulates the developer 9 of the present invention in the hopper 8 to a desired thickness. The toner is mainly triboelectrically charged between it and the developing sleeve 5. Opposing this blade 7 made of a magnetic material or magnet, one magnetic pole of a magnetic roll 6 (for example, _N1 pole 850 Gauss in the illustrated example) is arranged inside the developing sleeve 5. In this case, the developing sleeve 5
The distance between the blade 7 made of magnetic material and
The thickness of the layer of the developer 9 of the present invention on the developing sleeve 5 is regulated by a magnetic field between the blade 7 made of a magnetic material and the developing sleeve 5. The direction of rotation of the developing sleeve 5 is the same as the direction of rotation of the photoreceptor, as shown in the figure. In the figure, 10 is a scraper blade for scraping off residual developer on the sleeve 5, and 11 is a power source for forming an alternating electric field between the sleeve 5 and the photosensitive drum 4, which is a pulse wave, alternating current, Generates a voltage that is a combination of alternating current and direct current. In this example, a power supply in which +200V DC bias was superimposed on 1000V _PP AC was used. Incidentally, the latent image potential on the photosensitive drum 4 was +500V in the image area and OV in the non-image area.

The toner used was as follows.

Polyester resin (melting point 106°C) 100 parts by weight Rhodamine lake pigment 4 parts by weight Anthraquinone dye classified as C/I Sonorevent Red 52 2 parts by weight or more were mixed and ground in a ball mill, then melted and kneaded in a roll mill. After cooling, it is coarsely pulverized using a hammer mill, and then finely pulverized using an air jet type pulverizer. The obtained finely pulverized product was classified to select 5 to 20 microns, which was used as a toner. This is a magenta color toner.

The carrier particles used were: (1) Minolta Co., Ltd. EG101 copier toner (2) Sharp Co., Ltd. SF730 copier toner (3) Magnetite 100 parts Epoxy resin 100 parts Same as the above toner. 4% by weight of carbon black was added to the resulting powder and treated in hot air.

Although the above three types were used, no significant difference was observed between them. In the following description of the experiment, these three types of developer will not be particularly distinguished.

Of these three types, developer (2) has relatively high resistance;
When the resistance value was measured by sandwiching the powder between electrodes without applying pressure, it was 10 ¹² Ωcm under an electric field of 1000V/cm,
Under an electric field of 10,000 V/cm, the resistance value was 10 ⁹ Ωcm. However, it is not highly resistive enough to hold a static charge and is considered conductive.

The developer (3) has a relatively low resistance of 10 ⁶ Ωcm or less under an electric field of 1000 V/cm. The above-mentioned toner has a resistance of 10 ¹³ Ω under an electric field of 10000 V/cm using the same measurement method.
The resistance value exceeded cm and was impossible to measure.

When the above toner and carrier were mixed and used as a developer, the mixing ratio of toner and carrier was as follows.
When the weight ratio was 1:4 to 1:1, almost good images were obtained, but some unevenness was observed in the developer layer on the developer support member, resulting in slight unevenness in the images. did.

Therefore, the scraper 10 was removed and the developer support member was replaced with a
As described in the specification of No. 16453, the support member was replaced with one whose surface was roughened. As a result, a good image without unevenness was obtained.

At this time, approximately the same amount of toner as the developer in the developing device was added to the hopper, but good images were similarly obtained. This is because the carrier particles on the developer support member are attracted to the developer support member by magnetic force, and are not mixed with the newly added toner in the hopper. This is because it adheres to. In any of these cases, no carrier particles were observed to adhere to the latent image holding member.

In addition, turn off the bias voltage applied to the developing device,
When the developing device was grounded, development was possible. However, the image quality was inferior to that with bias added.

Further, in addition to the above-mentioned examples as carrier particles, they are used in ordinary two-component magnetic brush development. Although we used iron powder (particle size: approximately 50 to 100 μm) whose surface was nitrided, a satisfactory image could not be obtained. This is believed to be because carrier particles have a large particle size and tend to be insufficiently mixed with toner particles. Furthermore, when magnetite powder (particle size is about 0.2 μm) was used, the developed image contained a large amount of carrier particles. This is believed to be because the particle size is too small compared to the toner particles, and the toner particles and carrier particles are not sufficiently separated during the development process. It is desirable that the toner particles and carrier particles are relatively similar in size. According to experiments, it is good when the ratio of both sizes is within about 1:3. In this case, either the toner particles or the carrier particles may be large.

As described in detail above, in the present invention, an insulating toner is mixed with conductive and magnetic fine powder, and this is uniformly applied onto a developer support member having a magnet on the back surface, and this is coated in a latent manner. Because the image is developed by facing the image holding member without contacting it,
The toner fixability is also good, and color toners can also be used.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an example of the characteristics of the toner transfer amount and toner reverse transfer degree with respect to the latent image potential, and the applied voltage waveform. FIG. 3 is a process explanatory diagram schematically showing applied voltage waveforms, and FIG. 3 is a sectional view of a developing device showing an embodiment of the present invention. In the figure, 4...electrostatic image holder, 5...developing sleeve, 6...fixed magnet roll, 7...
...Magnetic blade, 8...Hopper, 9...Developer, 10...Scraper, 11...Bias power supply.

Claims (1)

[Claims] 1 If one is larger, the size ratio is 1:3
A developer prepared by mixing an insulating toner with conductive and magnetic powder at a weight ratio of 1:4 to 1:1 is supplied to the developer carrier, and this developer is placed on the developer carrier. The developer regulating means applies the developer layer in a layer thinner than the gap between the developer carrier and the image carrier at the development position, and the magnetic pole of a magnet placed inside the developer carrier applies this developer layer to the image carrier. At the developing position, an alternating electric field is formed between the developer carrier and the image carrier to cause the insulating toner to adhere to and detach from the image carrier, and the conductive toner A developing method characterized by developing by adhering powder to and detaching from an image carrier.