JPS59172660A - Magnetic brush developing method using ferrite carrier - Google Patents

Abstract

PURPOSE:To obtain a magnetic brush developing method using ferrite carriers which form a toner image with high density and gradations without any defect such as white absence by performing development on specific condition. CONSTITUTION:A two constituent developer 3 which consists of ferrite carriers and developing toner particles at a 4:1-20:1, specially, 5:1-12:1 weight ratio is used; while a nonmagnetic sleeve 2 is rotated at the rubbing position of a developer magnetic brush in the direction opposite to the moving direction of a drum 7, an in-sleeve magnet 1 is fixed for development. Further, the development is carried out on the condition satisfying expressions (1), (2), and (3), wherein theta (degree) is the set angle of a magnetic pole N or S closest to a line M connecting the center of the drum 7 and the center of a sleeve 2 in the drum rotation downstream direction on the basis of said line M, V is the peripheral speed of the drum 7, and (v) is the peripheral speed of the sleeve 2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic brush developing method, and more particularly to a toner image with excellent image characteristics using a two-component developer containing a ferrite carrier and electrostatic toner particles. The present invention relates to a magnetic brush development method for forming a film.

In electrophotography using a two-component magnetic developer, an electrostatic toner and a magnetic carrier are mixed, and this two-component composition is supplied onto a developing sleeve equipped with a magnet inside. By forming a magnetic brush made of material and rubbing this magnetic brush against an electrophotographic photosensitive plate having an electrostatic latent image, an electrostatic toner image is formed on the photosensitive plate. Due to friction with the magnetic carrier, the electrostatic toner is charged to a charge of opposite polarity to that of the electrostatic latent image on the photosensitive plate, and electrostatic latent particles on the magnetic brush are transferred to the electrostatic latent image by Coulomb force. It is deposited on the image and development of the electrostatic latent image takes place. On the other hand, the magnetic carriers are attracted by the magnet in the sleeve, and the charge thereon has the same polarity as the charge on the electrostatic latent image, so that the magnetic carriers remain on the sleeve. In order to form a clear and high-density image, it is necessary to provide a sufficient relative speed difference between the photosensitive plate and the magnetic brush so that the photosensitive plate is sufficiently rubbed by the magnetic brush. is important.

Although iron powder carriers are generally widely used as magnetic carriers, many drawbacks are still recognized in these iron powder carriers. In other words, in a two-component developer using this iron powder carrier, the development sensitivity curve (curve of potential difference between the electrostatic image and the developing sleeve versus image density) rises steeply, the gradation is poor, and the midtones are poor. It has the disadvantage of poor reproducibility. Also,
Developers containing this iron powder carrier may form hard magnetic brushes, which may damage the photosensitive layer, and when copying solid black areas, brush marks, that is, brush scratches, may appear on the formed image. The disadvantage is that there are many rows of thin and short white lines extending in the direction. Furthermore, the iron powder carrier is sensitive to humidity and has a tendency to change its development characteristics or to rust itself due to the influence of humidity, and there is also the problem that a large torque is required to drive the magnetic brush. be.

In recent years, it has been proposed to use ferrite, especially soft ferrite, as a magnetic carrier for two-component developers. However, ferrite carriers have higher electrical resistance than iron powder carriers, which causes problems such as carrier pull during development, that is, carrier migration to the photosensitive layer side, and edge effects in the formed images. Easy to cause problems.

Despite the fact that magnetic brush development using a ferrite carrier produces phenomena that are quite different from those in development using an iron powder carrier, much is still unknown about the development conditions.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a magnetic brush development method using a ferrite carrier which eliminates the various drawbacks mentioned above.

Another object of the present invention is to eliminate the disadvantages of white background removal due to brush marks, carrier drag, edge effects, etc.
It is an object of the present invention to provide a magnetic brush development method using a ferrite carrier capable of forming a toner image with high density and gradation.

According to the present invention, a two-component developer consisting of a mixture of magnetic carrier particles and toner particles that can be charged by friction with the magnetic carrier is supplied onto a developing sleeve provided with a magnet within a non-magnetic sleeve. forming a magnetic brush of developer;
A toner image corresponding to the electrostatic latent image is formed by rubbing the surface of the photoreceptor having the electrostatic latent image with the magnetic brush while a bias voltage is applied between the photoreceptor and the sleeve. In the magnetic brush development method, the two-component developer is a two-component developer containing a ferrite carrier and chargeable toner particles in a weight ratio of 4:1 to 20:1, and a non-magnetic sleeve is used. At the developer sliding position, the drum is moved in the opposite direction to the moving direction of the drum, and the magnet inside the sleeve is fixed to perform development. A magnetic brush characterized by performing development under conditions that satisfy the following formula %, where the set angle in the downstream direction is θ (button, the circumferential speed of the drum is V, and the circumferential speed of the sleeve is U) A development method is provided.

The present invention will be explained in detail below.

In FIG. 1 for explaining the magnetic brush development method, a magnet roll 1 having a large number of magnetic poles N, S is housed in a sleeve 2 made of a non-magnetic material such as aluminum.
The magnet roll 1 and sleeve 2 are provided in a relationship that will be described in detail below.

A two-component developer 6 is supplied from a developer tank 4 to the outer peripheral surface of this sleeve 2 to form a magnetic brush 5. This magnetic brush 5 is adjusted in the standing length of the grain by a panicle cutting mechanism 6, and is conveyed to a position where it rubs against the electrophotographic photosensitive layer 7 on the drum base, and the electrostatic latent image on the photosensitive layer 7 is made electrostatic. Develop with toner 8,
Form a visible image.

A feature of the present invention is that, as the two-component developer 6, the ratio of ferrite carrier and electrostatic toner particles is 4:1 to 20:1.
1. In particular, using a two-component developer containing a weight ratio of 5:1 to 12:1, the non-magnetic sleeve 2 is moved in the opposite direction to the moving direction of the drum 7 at the sliding position of the developer magnetic brush. At the same time, development is performed with the magnet 1 in the sleeve fixed, and with the line M connecting the center of the drum 7 and the center of the sleeve 2 as a reference, the pole magnet N or S closest to the ridge is moved in the downstream direction of the drum rotation. When the set angle is θ (degrees) and L, the circumferential speed of the drum 7 is V, and the circumferential speed of the sleeve 2 is υ, develop under conditions that satisfy the following formula % formula % (1) (2) (3) The goal is to do the following.

Generally, the electrical characteristics of a two-component developer are such that an electrode drum of the same size as the electrophotographic photoreceptor drum is installed in place of the photoreceptor drum, and the developer is supplied onto the developing sleeve to form a magnetic brush. Evaluation can be made by rubbing this magnetic brush against the electrode drum, applying a voltage between the sleeve and the drum, and measuring the current flowing between them.

Figure 2 shows developer A in which an iron powder carrier and electrostatic toner are mixed in a weight ratio of 10:1, and developer B in which a ferrite carrier and the same electrostatic toner are mixed in a weight ratio of 10:1. The current value (μA) measured by the method described above for
and the operating time (hr) of the drum and sleeve. According to the measurement results, the developer using a ferrite carrier shows significantly higher electrical resistance than the developer using an iron powder carrier, and the developer using a ferrite carrier has a lower electrical resistance even during long-term operation. In contrast, it is clear that the electrical resistance changes rapidly in the developer using the iron powder carrier, resulting in a significant increase in electrical resistance.

In this way, when an iron powder carrier is used, the reason why the electrical resistance of the developer increases over time is that the toner particles are pulverized by the carrier and their particle size becomes finer, and that the carrier contains the resin that makes up the toner particles. This is thought to be caused by the formation of a film-like coating. The results shown in Figure 2 show that the combination of ferrite carrier and electrostatic toner has stable electrical characteristics even during long-term operation, and that the combination of toner particles is fine, as is the case with iron powder carriers. This proves that defects such as pulverization and resin coating on the carrier surface do not occur.

In the present invention, sintered ferrite particles, in particular spherical sintered ferrite particles, are advantageously used as ferrite carriers. The particle size of the sintered ferrite particles is generally in the range of 20 to 100 microns.

If the particle size of the sintered ferrite particles is smaller than 20 microns, it tends to be difficult to make the magnetic brush stand up well.On the other hand, if the particle size is as large as 100 microns, , there is a tendency for the aforementioned brush marks, ie, scratches, to appear in the toner image formed.

The sintered ferrite particles used in the present invention are known per se, and include, for example, zinc iron oxide (ZnFetO4), yttrium iron oxide (YsFeaolx), cadmium iron oxide (CdFel04), gadolinium iron oxide (Gd, Pg, O, , oxidized steel (CaFexO4),
Iron oxide complex (P hFg120.), iron nickel oxide (N z Fex O4), iron neodymium oxide (NdF
t 0s) - barium iron oxide < Ba””lt0++1
), iron oxide magnesila A (MqFe20.), iron oxide mangaf (MrLFg2 O4), iron lanthanum oxide (LaFeO, ), etc., or sintered ferrite particles having a composition of two or more are used. Particularly suitable for the purposes of the present invention are sintered ferrite particles consisting of iron manganese zinc oxide.

Any colored toner having electrostatic properties and fixing properties can be used as the toner, and a granular composition with a particle size of 5 to 60 microns in which a colored pigment, a charge control agent, etc. are dispersed in a binder resin is used. used. As the resin, a thermoplastic resin or an uncured or initial condensate thermosetting resin is used. Suitable examples thereof, in order of importance, are vinyl aromatic resins such as polystyrene, acrylic resins, polyvinyl acetal resins, polyester resins, epoxy resins, phenolic resins, petroleum olefin resins, etc.

Examples of pigments include one or two of carbon black, cadmium yellow, molybdenum orange, pyrazolone red, fast violet B1 phthalocyanine blue, etc.
As the charge control agent, for example, nigrosine base (CI50415), oil black<c
26150), oil-soluble dyes such as Subiron Black, metal salts of nanthenate, fatty acid metal soaps, resin acid soaps, etc. are used as necessary.

In the present invention, it is also important to use the ferrite carrier and the electrostatic toner in the weight ratio described above; if the amount of the ferrite carrier is greater than the above range, the image density tends to decrease; If it is less than , there will be more capri (background coloring) in non-image areas.

In the present invention, in connection with using a two-component developer consisting of a ferrite carrier and electrostatic toner, the moving directions of the drum and sleeve at the magnetic brush rubbing position are opposite to each other, and the reference line It is also important to deviate the magnetic pole closest to M by an angle θ in the downstream direction of drum rotation.

The hardness of the ferrite carrier is lower than that of the iron powder carrier, and its particle shape is almost spherical.As a result, the developer magnetic brush formed on the sleeve is different from the magnetic brush using the iron powder carrier. It has the characteristic of being softer than. In the present invention, at the rubbing position,
Setting the moving directions of the drum and sleeve in opposite directions means that the photosensitive layer is rubbed by the magnetic brush evenly and many times.
Shifting the magnetic poles toward the downstream direction of the drum rotation means that the development area or development time of the IJ-spray is expanded because the peaks of the spikes correspond to the magnetic poles. A developer using an iron powder carrier increases the rubbing frequency of the magnetic brush,
Furthermore, when the rubbing area is enlarged, there is a tendency for noticeable brush marks to occur in the image, but in the present invention,
By using a ferrite carrier, it is possible to prevent the occurrence of brush marks, and by increasing the rubbing frequency and expanding the rubbing area, it is possible to form a high-density, uneven image.

The development conditions used in the present invention are represented by the area surrounded by four lines 1-a, 1-h, 2 and 6 in FIG. Here, line 1-α is IV1=1.5, line 1-b is l'l=2.4, line 2 is 1. l=-0,12θ+1.
8, line 6 corresponds to θ=5, respectively.

That is, in the region below the straight line 1-α, the frequency of rubbing decreases, resulting in a significant decrease in density, and edge effects are likely to occur in the formed image. In the region above the straight line 1-b, the frequency of rubbing is too high, resulting in poor gradation of the formed image and further causing defects such as trailing. Furthermore, in the area to the left of the straight line 2, the contact time with the magnetic brush is short, so toner is not sufficiently applied, resulting in a decrease in image density and a tendency for brush marks and edge effects to occur in the image. Furthermore, since the contact time with the magnetic brush is long on the right side of the straight line, too much toner is deposited on the area, which also tends to reduce the gradation.

In this way, the development area surrounded by the four lines in Figure 6 is
The fact that the quality of the formed image is extremely critical will become clear from the fact in the example described below, in which the image quality is significantly degraded under conditions just a little away from this region.

As for the development conditions in the present invention, it is clear from FIG. 6 that in the range where the value of -1 is small, the allowable range of the magnetic pole setting angle θ is small, and on the other hand, as the value of 1p1 becomes sharper, the allowable range of θ becomes wider. be.

It is most preferable that IVl and θ are in a range that satisfies the following formula % (1 (2) (3)), that is, in the shaded area in FIG.

In the present invention, a bias voltage is applied between the photoreceptor drum and the developer sleeve, and although this bias voltage sufficiently injects charge into the toner during development, it causes discharge damage to the photoreceptor and magnetic brush. Establishments shall be established to prevent such troubles from occurring. This voltage is generally between 100 and 6
00 volts, particularly a range of 150 to 250 volts is suitable.

The polarity of the bias voltage is of course selected so that it becomes positive when the charge on the photoreceptor is positive, that is, the polarity is the same. According to the present invention, by employing the development conditions described above, development can be performed by applying a relatively low bias voltage, and as a result, the printing durability of the photoreceptor can be improved.

In the magnetic brush development of the present invention, the tip of the magnetic brush is determined so that the magnetic brush can sufficiently rub the surface of the photoreceptor at a clearance d between the photoreceptor drum and the developing sleeve. Generally, for development clearance d, 1
．． It is desirable to cut the ears so that the length of the ears is 1 to 60 times, particularly 1.2 to 2.0 times. In the present invention, since a ferrite carrier with low residual magnetization is used,
Another advantage is that ears can be cut at small intervals.

The photoreceptor may be a known electrophotographic photoreceptor such as a selenium vapor-deposited photoreceptor, an amorphous silicon photoreceptor, or a CdS photoreceptor.
Any photoreceptor, organic photoconductor photoreceptor, etc. may be employed, and the electrostatic latent image can be easily formed by a method known per se, such as a combination of charging and image exposure.

The invention is illustrated by the following example.

Example The weight ratio of the ferrite carrier and toner shown below is 9:
Mix and stir well at a ratio of 1:1 and the electrical resistance between the electrode drum and the developing sleeve is 2.0 x 108Ω.
Adjust the developer.

(a) Ferrite carrier electrical resistance: 2.6X10QΩ~2.5X10”Ω,
Maximum magnetization: 49.8 emuA, residual magnetization: 0.25
gm, +no/9, coercion crab 3.380e, center grain size: 4
0μ (b) Toner Hymer SBM-76 (styrene resin: manufactured by Sanyo Chemical Industries, Ltd.) 87 parts by weight Viscoel 550P (low molecular weight polypropylene: manufactured by Sanyo Chemical Industries, Ltd. KK) ... 5 parts by weight Special Black 4 (carbon plaque: manufactured by Degussa)
・・・・・・・・・・・・・・・5.5
Part by weight Bontron S-32 (dye: manufactured by Orient Chemical Co., Ltd.) ・・・・・・・・・・・・・・・
A mixture consisting of 1.5 parts by weight of the above composition was thoroughly melted and mixed in a hot three-roll mill, taken out, cooled, and coarsely pulverized to about 2wn in a coarse pulverizer (Rotoplex cutting mill: manufactured by Alpine). Sonic jet mill (NIPPON pNEUMATIC MFCCo.

(manufactured by LTD) into a particle size of approximately 10 to 20μ.

Next, using this developer, the radius of the photoreceptor drum: R=
45.0, surface potential of photoreceptor near 50 volts, radius of developing sleeve: γ=19. Own, bias voltage: 250 volts, developer cutting gap: δ=1.0m+
Under each condition, while the photoconductor drum and developing sleeve rotate in opposite directions, various combinations of drum and sleeve rotation speeds as shown in Table 1, and the drum with the magnetic pole closest to the photoconductor drum were performed. When we conducted a copying test by changing the set angle in the downstream direction of rotation, we found that the developing clearance d was 1
．． Copy image evaluations as shown in Tables 2 to 9 were obtained in the range of 5 wM to 1.9 wM. In each table,
The X marks represent defects such as poor gradation, white spots due to fogging, edge effects, etc., low-density images, brush marks, and trailing. Tables 2 to 9 show image evaluations based on changes in the set angle of the magnetic poles in Experimental Examples A to H in Table 1, respectively.

The overall evaluation of the image is shown in Figure 6 with an O mark: Excellent and a Δ mark: Good.

× mark: Indicates as defective.

[Brief explanation of the drawing]

Fig. 1 is a principle diagram explaining the magnetic brush development method according to the present invention, Fig. 2 is a diagram showing changes in the electrical characteristics of the developer over time, and Fig. 6 is a diagram showing the circumferential speed ratio of the developing sleeve and photoreceptor drum and the developing roll. FIG. 3 is a diagram showing the relationship between the set angles of the magnetic poles. 1... Magnet roll, 2... Developing sleeve, 6... Developer, 5... Magnetic brush, 7... Photosensitive layer. Patent applicant Sanda Kogyo Co., Ltd. Continued from page 10 Inventor Akira Funakoda 1-2-28 Tamatsukuri, Higashi-ku, Osaka-shi Sanda Kogyo Co., Ltd. Inventor Hideo Fukuda 1-2-28 Tamatsukuri, Higashi-ku, Osaka Inside Sanda Kogyo Co., Ltd.

Claims (1)

[Scope of Claims] (1,) A two-component developer consisting of a mixture of magnetic carrier particles and toner particles that can be charged by friction between the magnetic carrier and the non-magnetic sleeve is placed on a developing sleeve having a magnet inside the non-magnetic sleeve. to form a magnetic brush of the developer, and slide the developer between the surface of the drum-shaped photoreceptor having the electrostatic latent image and the magnetic brush while a bias voltage is applied between the photoreceptor and the sleeve. In a magnetic brush development process comprising rubbing to form a toner image corresponding to an electrostatic latent image, the two-component developer comprises a ferrite carrier and chargeable toner particles in a ratio of 4:1 to 20:1 by weight. This is a two-component developer containing a ratio of When the line connecting the center is the standard pressure, the set angle of the nearest pole magnet in the downstream direction of the drum rotation is θ (degrees), the circumferential speed of the drum is V, and the circumferential speed of the sleeve is υ, then the following % formula is used. A magnetic brush development method characterized by performing development under conditions that satisfy %