JPS59229568A - Two-component type dry developer - Google Patents

Abstract

PURPOSE:To attain stable image density for a long term by preparing a developer by mixing a toner with a carrier which increases the resistance of the resulting developer with the lapse of time when the developer is stirred and a carrier which decreases the resistance of the resulting developer with the lapse of time. CONSTITUTION:A two-component type dry developer consisting of a carrier mixture and a toner is prepd. The carrier mixture consists of 40-20wt% ferrite carrier which increases the resistance of the developer with the lapse of time when the developer is stirred and 60-80wt% powdered iron carrier which decreases the resistance of the developer with the lapse of time. A reduction in image density due to an increase in the resistance of the developer is prevented, and stable image density at the beginning of use of the developer is maintained for a long term.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry two-component developer used for developing an electrostatic latent image formed on a charge retention member in an electrophotographic copying machine or the like.

For example, in a magnetic brush developing device used in an electrophotographic copying machine, a dry two-component developer consisting of toner and a magnetic carrier is used, and the toner and magnetic carrier are mixed and stirred to develop the toner by mutual frictional electrification. The electrostatic latent image is developed with toner by being charged to a polarity opposite to that of the electrostatic latent image and acting on the charge retention member.

Conventionally, iron powder carriers have been used as magnetic carriers for dry two-component developers used in such magnetic brush developing devices, but recently attempts have been made to use ferrite carriers. Ferrite carriers have a small specific gravity, and therefore the stirring torque applied to the developer can be reduced, which can effectively prevent toner filming on the carrier surface, and can also be easily miniaturized, allowing for a large specific surface area. It has the advantage of being able to increase its charging capacity, and is said to have a longer lifespan than iron powder carriers.

The present inventor has also attempted to develop a dry two-component developer using a ferrite carrier, and has conducted various experiments using an electrophotographic copying machine equipped with a magnetic brush developing device. In the developer used, there is a phenomenon in which the image density decreases in the relatively early number of copies made, which is a few dozen sheets.When an iron powder carrier is used, this decrease in image density is due to a decrease in the charging ability of the carrier. Although it is said that the cause is a decrease in the toner charge amount, when a ferrite carrier is used, there is almost no such decrease in the toner charge amount, so it is thought that there is another cause.

Therefore, as a result of various studies on the causes of this decrease in image density, the inventors of the present invention found that, in general, the lower the developer resistance, the higher the image density. Since it is desired that the resistance be constant, we measured the resistance depending on the stirring time for various developers using this developer folding method and various developers using a ferrite carrier. As a result, with iron powder carriers, developer resistance both decreases over time and increases with time, but with ferrite carriers, developer resistance increases over time, and this change also occurs in iron powder carriers. I realized that it was relatively large. Therefore, the above-mentioned initial decrease in image density when using a ferrite carrier is considered to be mainly due to the increase in developer resistance over time. It has been confirmed that in both iron powder carriers and ferrite carriers, when the stirring time is about 20 hours, there is almost no change in developer resistance and y remains constant.

In view of the above-mentioned points, an object of the present invention is to provide a dry two-component developing system which is appropriately configured to effectively prevent changes in initial image density and to stably obtain a constant image density over a long period of time. The aim is to provide a drug.

The present invention provides a dry two-component developer in which toner and carriers located at different positions on a triboelectrification array are mixed and stirred so that the toner is charged by mutual triboelectrification, in which the carrier is mixed with the toner. The developer is characterized by being composed of a mixed carrier consisting of at least the same type of carrier exhibiting the characteristic that the developer resistance increases over time when agitated and at least the same type of carrier exhibiting the characteristic that the developer resistance decreases over time. It is something to do.

The present inventor has discovered that by using a carrier that is a mixture of a ferrite carrier whose developer resistance increases over time and an iron powder carrier whose developer resistance decreases over time, a developer with small changes in developer resistance can be obtained. Based on the idea that "C" may be used as a carrier, various experiments were conducted, and it was found that a developer using a mixed carrier with the above configuration has a lower i'+ than a developer using only an iron powder carrier and a ferrite carrier as carriers The developer resistance is intermediate to y, and if an appropriate ratio is selected, a developer with a small change in 'fA developer resistance can be obtained, and when actually used in an electrophotographic copying machine, there was no initial decrease in image density. The present invention was developed after confirming that stable images can be obtained over a long period of time.As for developer resistance, in addition to toner concentration, material and shape of carrier and toner, Since it is affected by various factors such as the stirring conditions in the developing device and the arrangement of magnetic poles, it is better to measure developer resistance changes using a configuration similar to that of the equipment actually used for better reproducibility during actual use.

The present invention will be described in detail below based on experimental examples.

FIG. 1 shows the configuration of the main parts of an electrophotographic copying machine used in the experiments described below. This copying machine forms an electrostatic latent image on a photosensitive drum rotating in the direction of arrow A, develops this electrostatic latent image with toner using a magnetic brush developing device 2, and then transfers this toner image onto recording paper to obtain a copy. It is something. The magnetic brush developing device 2 fixes a magnetic roller 8 having a main developing pole and a plurality of conveying magnetic poles, and rotates a non-magnetic sleeve 4 in the direction of the arrow by approaching the outer peripheral surface of the magnetic roller 8. The magnetic carrier is stored in a developer storage section 5, and the toner is stored in a toner hopper 6, and the rotation of a toner replenishment roller 7 keeps the toner concentration in the developer 8 almost at a predetermined level at all times. The developer storage unit 5 is replenished so that the developer storage unit 5
The toner inside and the magnetic carrier are mixed and stirred by the stirring blade 9, and the toner is charged with the opposite polarity to the polarity of the electrostatic fa image formed on the photosensitive drum 1 by mutual frictional charging. A doctor blade 1O regulates the transport of toner and magnetic carrier due to the rotation of the non-magnetic sleeve, and a scraper 11 scrapes off the developer on the non-magnetic sleeve 4 after the developing action.

Figure 2 shows the same configuration of the developer resistance measuring device used in the experiment.
It is constructed by modifying a copying machine of the same type as the electrophotographic copying machine shown in the figure, and an aluminum drum 21 of the same diameter is fixedly arranged in place of the photosensitive drum shown in Fig. A DC power source 22 and an ammeter 28 are connected between the developing device 2 and the non-magnetic sleeve 4, and the developer resistance is calculated from the voltage value of the DC power source 22 and the current value measured by the ammeter 28. be. The magnetic brush developing device 2 shown in FIG. 2 has an old toner hopper and a toner replenishing roller removed.

Example Ferrite carrier with average particle size of 48 μm (100 parts)
Developer resistance, toner charge amount, and image density were measured for a developer prepared by mixing a black toner (9 parts) in which pigments and dyes such as carbon black were dispersed in styrene resin.

Developer resistance is 'toug's ferrite carrier and 68
g of toner in 16 polyethylene bottles.
1 0 r. p. The mixture mixed by rotation at m for 80 minutes was placed as a starting developer in the magnetic development device B of the developer resistance measuring device shown in FIG. Calculations were made at appropriate time intervals during continuous rotation for 20 hours at the normal operating speed of a photocopying machine. As a result, "C" was 59MΩ at the start, and 515MΩ after 20 hours.
Ω, and changed as shown in FIG. 8 during that time.

The toner charge amount was measured by sampling the above-mentioned starting developer and the developer continuously stirred and mixed for 20 hours using a blow-off powder charge amount measuring device (manufactured by Toshiba Chemical Corporation).
The toner and carrier were forcibly separated from each other by spraying N2 gas, and then the charge amount of the carrier was equivalently determined. As a result, at the start, 10
．． At 9 μ'i, the concentration was 11.8 parts % after 20 hours.

Image density was determined by continuous copying using an electrophotographic copying machine shown in FIG. In this case, the developer containing portion 5 of the magnetic brush developing device 2 uses an initial developer that has been stirred and mixed in the same manner as in the developer resistance measurement, and the toner hopper 6 contains toner. By rotating the toner replenishment row 27, the toner is supplied to the developer storage portion 5 such that the amount of toner in the developer is always r9 parts per 100 parts of ferrite x rear. As a result, i
The image density of the first copy of l.1 was 1.55, and the image density of the copy obtained after 20 hours was 0.9, so from the start! A rapid decrease in image density was observed until 1"aooo sheets were copied.

Example average particle size: 85 pm (150 to 250 mesh) f) Iron oxide powder carrier (100 parts); DSF-
158: Manufactured by Dowa Iron Powder Industry Co., Ltd.; and experimental example! For a developer prepared by mixing the same black toner (8.5 parts) used in Example I, developer resistance, toner charge amount, and image density were measured in the same manner as in Experimental Example I.

However, in the developer resistance measurement, the iron powder carrier was
00g, toner was 59.5g, and in the measurement of image density, the amount of toner in the developer was 10g.
It is always y8.5 parts for 0 copies.5K, the toner stored in the toner hopper 6 is transferred to the toner supply roller? The developer is replenished into the developer storage section by the rotation of the developer.

As a result, the developer resistance was 216 at the start.
After 20 hours of MΩ, there were 49 faces, and the number changed as shown in FIG. 4 during that time. In addition, the toner charge amount was 18.6μ% at the start and 1 after 20 hours.
1.5μ%, and the image density is 1 at the start.
．． 85. After 20 hours, it becomes 1.61 and Capri occurs, and from the start,! An increase in image density was observed up to 10,000 copies of 1".

Ferrite carrier used in Experimental Example I and Experimental Example ■
The weight ratio of the iron powder carrier used in 50150゜80/7
0, 100 parts each of carrier mixed 20/80,
Experimental example 1 above. Black toner 9, same as used in TI
The developer resistance, toner charge amount, and image density were similarly measured for each developer prepared by mixing the above.

In addition, in the developer resistance measurement, 10 is the mixed carrier of 700 g and the toner is 68 g, and in the image density measurement, the toner amount in the developer is always W9 parts with respect to the mixed carrier ioo part. The toner stored in the toner hopper 6 is replenished into the developer accommodating portion 5 by rotation of the toner replenishment roller so that the toner is stored in the toner hopper 6.

As a result, the developer resistance at the start and after 20 hours was 219 M for the mixed carrier with a ratio of 50,750.
Ω to 400 MΩ, with ratio 80/70 218 MΩ
to 195 MΩ, with a ratio of 2o/8o to 2o.

The resistance changed from MΩ to 86Ω, and changed as shown in Figure 5. In addition, the toner charge amount is at a ratio of 501
50 from 14.8μ to 12.4μ3, ratio 8
0/70 (7) from 16.4 p”/g to 12.
At 0 μgin, the ratio of 210/80 is 17.2 μ% to 11.8 μ%, and the image density is 1.48 to 1.09 K for the ratio of 50150, 80/7 (1).
1.45 K, 1.48 K, ratio 20/80
1.40 to 1.51 K, especially when the ratio is 80
/70 and 20/80, there was almost no decrease in image density until 80,000 copies were made, and good quality images could be obtained.

The above experimental results are shown in the table below and FIGS. 6A-C.

As is clear from the developer resistance characteristics, toner charge amount characteristics, and image density characteristics against the carrier shown in the table above and FIGS. 6A to 6C, the stability of image density is independent of the stability of toner charge amount regardless of the tube. is correlated with the stability of developer resistance, and in the ferrite carrier and iron powder carrier used in the above experiments, the mixed carrier had a ratio of 40 to 20% by weight of ferrite carrier and 60 to 80% by weight of iron powder carrier. It can be seen that by configuring , it is possible to effectively prevent initial image density changes and to stably obtain a constant image density over a long period of time. In addition, Figure 6 A-C
The characteristics shown in (1) were confirmed through similar experiments using a developer using a mixed carrier having a ratio other than the above.

The present invention is not limited to the above-mentioned examples, but can be modified or modified in many ways. For example, the mixed carrier is not limited to two types of carriers, but can also be composed of three or more types of carriers. In addition, in products using iron powder carriers, developer resistance may increase or decrease over time as described above, so it is recommended to combine multiple types of these iron powder carriers to form a mixed carrier. You can also do it. Furthermore, the developer using the mixed carrier according to the present invention does not necessarily have to have a constant resistance over time, but may increase or decrease somewhat to compensate for changes over time in other factors such as the amount of toner charge. The lens can also be constructed so that a constant image density can be obtained.

As described above, in the present invention, the carrier constituting the dry two-component developer is a mixed carrier consisting of a carrier whose developer resistance increases over time when mixed with toner and a carrier whose developer resistance decreases over time. By appropriately setting the mixing ratio of the multiple types of carriers that make up this mixed carrier, initial changes in image density can be effectively prevented, and it is possible to maintain a constant image density. can be obtained stably. In addition, in the past, one type of toner and carrier was selected from among several types of toners and carriers to find a stable developer combination, which resulted in a huge number of combinations and long-term problems. Although it took several days, according to the present invention, it is only necessary to find at least two types of carriers that have different changes in developer resistance over time, and then adjust the mixing ratio appropriately, so that a stable developer can be obtained. can be obtained easily and in a short period of time.

[Brief explanation of the drawing]

Figure 1 is a line diagram showing the configuration of an example of the main parts of an electrophotographic copying machine using a dry two-component developer used in the experiment, and Figure 2 is a line diagram showing the configuration of a developer resistance measuring device also used in the experiment. Figure 8, Figure 4 and Figure 5 are graphs showing developer resistance characteristics with respect to stirring time determined experimentally, and Figures 6A, B and C are diagrams showing developer resistance characteristics with respect to carrier ratio determined experimentally. , are diagrams showing toner charge amount characteristics and image density characteristics, respectively. 1... Photosensitive drum 2... Magnetic brush developing device 8... Magnet row 24... Non-magnetic sleeve 5
...Developer storage section 6...Toner hopper 7...
・Toner supply roller 8...Developer 9...Agitating blade lO...Doctor blade 11...Scraper 21...Aluminum tram 22...
・DC power supply 28...Ammeter. Waiting fl'F exit 1 side 1 person Olympus Optical Industry Co., Ltd. (MQ) Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] L A dry two-component developer in which toner and carriers located at different positions on a triboelectrification array are mixed and stirred so that the toner is charged by mutual triboelectrification,
A mixed carrier of at least one type of carrier exhibiting a characteristic that developer resistance increases over time when the carrier is mixed and stirred with toner and at least one type of carrier exhibiting a characteristic that developer resistance decreases over time. A dry two-component developer characterized by comprising: A ferrite carrier is used as a carrier whose developer resistance increases over time, and an iron powder carrier is used as a carrier whose developer resistance decreases over time. %
2. The dry two-component developer according to claim 1, wherein the mixed carrier has a ratio of: