JPS61196257A - Electrostatic developing method - Google Patents

Abstract

PURPOSE:To hold the carrier density in a developer container constant even when a developer which contains at most 10% of carriers is supplied at any time by providing an automatic removing and recovering function for excessive carriers detected by a developer density sensor. CONSTITUTION:The conventional carrier density (about 90wt% in case of iron powder) of a two-component developer is suppressed to at most 10% and toner supply is carried out completely with said two-component developer which contains a small amount of carriers. The content of carriers in the developer container increases as developing operation is repeated. For the purpose, a proper detecting means for a toner-carrier ratio is proviced so as to the specific content of carriers and excessive carriers are removed. Namely, a developer density sensor 12 which varies in magnetic characteristics with th mixing ratio of toner and carriers, but outputs the variation as variation in the inductance of a coil is added to the upper part of an agitatot blade 11.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a developing method for electrostatic copying machines and the like.

In particular, in a developing method using a two-component developer consisting of toner and carrier, a static static filter is used to compensate for the decrease in toner due to repeated development and eliminate the excessive increase in carrier when replenishing the developer with the same mixing ratio as the developer described above. Regarding electrophotographic development.

(Prior Art) In general, there are two general methods of magnetic brush development using a cylindrical developer holding member containing a magnetism generating means in an electrostatic recording device. One of them is a two-component development method that uses a developer containing carrier and toner mixed in a predetermined ratio. In this two-component development method, the magnetic carrier is used as a toner spike-forming agent, or to prevent toner agglomeration by utilizing the difference in fluidity with the toner particles, and also to triboelectrically charge the toner particles. It is also added as an adjuvant. However, as toner is consumed during development, unless a toner density control device is used to automatically replenish the amount of toner that is commensurate with the amount of toner that is decreasing,
The mixing ratio of toner and carrier changes significantly. Further, even if the above-described control mechanism is provided, after the developer is used for a long period of time, toner adheres to the surface of the carrier, resulting in deterioration of carrier performance. Therefore, since the conventional two-component developing method does not have a means for automatic carrier replacement, the two-component developer is necessarily used for a certain period of time in order to guarantee a certain level of developed image quality. Therefore, maintenance of a copying machine using a two-component developer becomes extremely complicated.

Conventionally, excess or damaged carrier has been replaced by a skilled person during maintenance by measuring the weight of a certain amount of developer to determine changes in the amount of carrier and the lifespan of the developer.

Therefore, in recent years, as a second developing method, a one-component developing method that excludes carrier and uses only toner as a developer has become popular. According to this method, a toner concentration control mechanism is not required and the carrier deterioration described above does not occur, so that maintenance can be significantly reduced.

One-component developers include conductive toners and magnetic toners that are electrically insulating and contain magnetic powder in toner particles.

The former uses induction charging between a latent image holding member such as a photoreceptor and the sleeve by grounding a developer holding member (hereinafter referred to as the sleeve), while the latter uses toner between toners, toner and sleeve, or toner ears. This applies electrification caused by friction with a blade attached near the sleeve to restrict standing. However, various problems also exist in the one-component development method.

First, in comparison with the two-component development method, since the developer lacks carrier, it is inferior in toner conveying force and charging stability, and there are also problems such as the appearance of toner of opposite polarity. Further, under the influence of van der Waals forces and humidity, toner particles coagulate, and when the coagulated particles cause clogging between the sleeve and the blade, a blocking phenomenon, so-called white spots, occurs. In order to avoid this, a method was proposed in Japanese Patent Application Laid-Open No. 5-11201 to solve the problems of the one-component development by adding a small amount of ferromagnetic powder to the one-component developer to act as a carrier for the two-component developer.
No. 8-144865 or Japanese Patent Application Laid-open No. 172664/1983.

(Problems to be Solved by the Invention) However, in the above method, ferromagnetic particles are added to the one-component developer to serve as a substitute for the carrier in the two-component developer. However, the desired effect is completely lost and the drawbacks of the original one-component developer are exposed.6 The present invention eliminates the above drawbacks.

(Means for Solving the Problems) The present invention suppresses the conventional carrier content of two-component developers (approximately 90% by weight in the case of iron powder) to at most 10%, and replenishes toner. All of these steps are carried out using the two-component developer containing a small amount of carrier. The content of carrier in the developer container increases with repeated development operations. Therefore, in order to maintain the carrier content at a predetermined level, the above-mentioned problems can be solved by performing development with means for detecting an appropriate toner to carrier ratio and means for removing excess carrier.

That is, one aspect of the present invention uses a developer containing a small amount of carrier for toner replenishment, and has a means for detecting fluctuations in the ratio of toner to carrier, and when the carrier ratio exceeds a specified value by this means, detects the change in the ratio of the photoreceptor member. A means for erasing the latent image and making the surface potential the residual potential of the photoreceptor member, and adjusting a bias voltage between the sleeve and the photoreceptor member to cause the carrier to adhere to the residual potential of the photoreceptor member. means.

The present invention is characterized by a configuration including a cleaning means for removing carrier attached to the surface of the photoreceptor member.

(Function) According to the present invention, with the above-described configuration, new carrier is always replenished at the same time as toner, and while the toner to carrier ratio in the developer container is detected, if the carrier concentration becomes higher than a set value, The surface potential is lowered to the residual potential on the photoreceptor, the bias voltage applied to the sleeve is adjusted, and an electric field opposite to that for toner development is applied between the photoreceptor surface and the sleeve, causing the carrier to move onto the photoreceptor. It is deposited on the surface and collected and removed by ordinary photoreceptor surface cleaning means. As a result, carriers are constantly replenished and removed, so carrier replacement is automatically performed and carrier deterioration is avoided. Therefore, while taking advantage of the advantages of the two-component development method, the complicated maintenance of replacing carriers, like the one-component development method, is not required.

The intended purpose is achieved.

(Example) An example of the present invention will be described below with reference to the drawings. The figure shows the main parts of a copying machine as an example. Reference numeral 1 denotes a photoreceptor member that holds a latent image, and is formed as a photoreceptor drum made of a 5e-Te alloy with a diameter of 901 mm. It rotates at a circumferential speed of (220 m/5 ec), and its surface is uniformly charged to a positive polarity with a surface potential of 750 V by a corona charger 2. Next, this photoreceptor member 1 is exposed to light according to the original to be copied through the optical system 3, and a latent image of the original is formed on the surface by electric charge.

On the other hand, in the developing section, a magnetic flux density of 850 Gauss is applied to the surface of a so-called sleeve 5, a cylindrical developer holding member with a diameter of 31 mm, which contains an 8-pole magnetic roll 4 serving as a magnetism generating means. Due to the suction force, the developer 6 containing 8 wt % carrier and the remainder toner forms brush-like spikes.

The sleeve 5 is rotated counterclockwise at 15 Orpm, and the magnetic roll 4 is rotated clockwise at 1100 Orpm.

The above toner is made by kneading acrylic styrene resin, iron oxide powder, other powders, charge control agents, etc., and crushing and classifying it. The amount of charge was -10.5 pc/g (according to Toshiba blow-off charge amount meter (TB-200)).

On the other hand, the carrier is mainly composed of iron oxide powder, which is kneaded with an acrylic resin and classified, and has an average particle size of 20 μm and a charge amount of +3.3 μc/g as measured by the above-mentioned measurement method. The height of the spikes of the developer 6 is regulated by the gap between the blade 7 and the sleeve 5, and the gap is 0.4 mm. The developer 6 rubs against the surface of the photoreceptor member 1 as the sleeve 5 rotates, and the toner in the developer is attracted to and adheres to the latent image, resulting in visualization, that is, development. Mixed developer 6 with carrier containing toner that did not contribute to development
The developer is collected into the developer container 8 by the rotation of the sleeve 5, and once scraped from the surface of the sleeve 5 by the scraper 9, and mixed with newly supplied developer introduced from the hopper mouth 10 by the stirring blade 11. Stirred. Then, it is again attracted to the surface of the sleeve 5 by the magnetic field of the magnetic roll 4 and transported for development. Stirring blade 11
At the top of the , there is a developer concentration sensor 1 that focuses on the fact that the magnetic properties change depending on the mixing ratio of toner and carrier, and uses this change as a change in coil inductance.
2 is attached. The coil included in this developer concentration sensor 12 forms a resonant circuit of an LC oscillator (not shown), and changes in the mixture ratio of toner and carrier are replaced by changes in the oscillation frequency, which is detected by FM detection. , obtain the signal voltage corresponding to the mixing ratio. This signal voltage is applied to a comparator circuit (not shown) and compared with a reference (comparison) voltage that lowers the mixing ratio to 10 ut%, and if the carrier ratio exceeds the 10 wt% mixing ratio, carrier overflow is detected. generates a signal.

The visualized latent image, that is, the toner image, moves to the transfer step as the photoreceptor member 1 rotates, and is transferred onto the paper 13 to be copied by the action of the transfer charger 14. Since some toner remains on the surface of the member 1 without being transferred, this is scraped off with a cleaning blade 15 made of rubber elastic material and placed in the waste toner reservoir 1.
Collect at 6. As the cleaned photoreceptor member 1 rotates, the remaining latent image and the like are erased by optical static electricity removal from the static elimination lamp 17, and the surface potential of the photoreceptor member 1 is usually 50V or less. Potentially smoothed to potential. Note that the copied paper 13 on which the toner image has been transferred
The toner image is fixed by a fixing device (not shown),
It is ejected outside the copying machine.

Here, in general, in order to prevent toner from adhering to the residual potential on the surface of the photoreceptor member 1 (commonly called fogging), a power source 18 is provided between the photoreceptor member 1 and the sleeve 5 on the sleeve side. A bias potential of 100V with positive polarity is applied.

The above operation completes one process of copying, but according to the developing method of the present invention, when the carrier over signal described above is generated, the application of high voltage to the corona charger 2 and the transfer charger 14 is stopped. , stops its operation, turns on the static elimination lamp 17, and turns the power supply 18 on to 40
Increase the voltage to 0v. As a result, the surface of the photoreceptor member 1 is held at a residual potential, and the voltage on the sleeve 5 increases, so an electric field is formed in the opposite direction to the electric field during normal development, and the toner is charged in the opposite direction. The carrier attached thereto adheres to the surface of the photoreceptor member 1, and is scraped off by the cleaning blade 15 to be collected and removed, thereby maintaining a constant mixing ratio of toner and carrier. In addition.

This operation continues until the carrier mixing ratio drops to 8%, which is 2% from this normal setting lO% to 8%.
The width of is set for the hysteresis of the comparison circuit.

Next, specific data regarding this example will be shown.

The copying machine used has the main parts arranged as shown in FIG. Initially, 200 g of the developer 6 was put into the developer container, and thereafter, a fixed amount of 40 B was replenished from the hopper opening 10 every time an A4 size original with a blackening rate of 7% was copied. When A4 paper was continuously copied at a rate of 25 sheets per minute at a room temperature of 25° C., the carrier removal mechanism, which is the main part of the present invention, was activated after approximately 2000 sheets had been copied. Maximum reproduced image density was measured with a Macbeth 914 reflectometer and showed a range of 1.40 to 1.45;
As a result of continuing to copy up to 1 sheet, the concentration above the fire path was maintained.

As is clear from the above description, according to the present invention.

Since at most 10% of the carrier is constantly exchanged, stable copied images can be obtained over a long period of time.

In the above-mentioned embodiment, when the developer becomes overloaded with carrier, the carrier removal mechanism operates, but if copying is being performed continuously for a long time, copying will be interrupted if this mechanism is activated, causing problems. may occur. To avoid this, when the carrier ratio is around 10%, when warming up the copier (turn on the power to the copier,
The time it takes for the fuser to reach a certain temperature; Normal process to 3
It is effective to adjust the carrier ratio to a specified value using

(Effects of the Invention) As described above in detail, the present invention is a developing method having a function of automatically removing and collecting excess carrier detected by a developer concentration sensor. Due to these functions, the carrier concentration in the developer container can be maintained constant even if the developer containing at most 10% carrier is replenished as needed. In this way, even though it is a two-component developer, there is no need to consider measures against carrier deterioration, and the complexity of maintenance, which is a drawback of a two-component developer, can be greatly reduced.
It is possible to solve all of the problems of conveying force, charging stability, and aggregation of component-based developers.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a main part of a copying machine according to an embodiment of the present invention. 1... Photoreceptor member, 2... Corona charger, 3...
・Optical system, 4... Magnetic roll, 5... Sleeve,
6...Developer, 7...Blade. 8...Developer container, 9...Scraper, 10...
・Hopper mouth, 11... Stirring blade, 12... Developer concentration sensor, 13... Paper, 14... Transfer charger, 1
5... Cleaning blade, 16... Waste toner reservoir, 17... Static elimination lamp, 18... Power supply.

Claims (1)

[Claims] In the electrostatic development method using a magnetic brush, which uses a cylindrical sleeve that holds a developer with a built-in magnetism generating means and uses a two-component developer consisting of toner and carrier to develop a latent image on a photoreceptor member. , the above developer is composed of at most 10% by weight of carrier and the remainder is toner, and the decrease in toner in the developer due to repeated development operations is compensated for by using a developer in which the composition ratio of toner and carrier is the same as above. Excessive increase in the amount of carrier exceeding the set value due to repeated replenishment is detected using means for detecting the toner to carrier ratio in the developer, and the detection output is used to detect the latent value of the photoreceptor member. erasing the image and lowering its surface potential to a residual potential; further adjusting a bias voltage between the photosensitive member and the sleeve to cause carrier to adhere to the photosensitive member maintained at the residual potential; An electrostatic development method characterized by removing and recovering this adhered carrier.