JP2683623B2 - Carrier for two-component developer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic carrier used in a magnetic brush developing method for forming a magnetic brush in an electrophotographic method or the like for development, and more specifically, to a magnetic carrier of a photosensitive layer. The present invention relates to a magnetic carrier used in a magnetic brush developing method in which a moving direction and a moving direction of a sleeve are rubbed in opposite directions.

(Prior Art) In the electrophotographic method using a two-component developer, a toner which is colored resin particles in which a colorant is dispersed in a binder resin is mixed with a magnetic carrier, and the two-component developer is internally contained. It is supplied onto a developing sleeve equipped with a magnet to form a magnetic brush made of this composition, and the magnetic brush is rubbed against a photosensitive layer made of a photoconductive substance having an electrostatic latent image, thereby forming a toner image. Are formed on the photosensitive layer. The toner obtains a desired triboelectric charge by friction with the magnetic carrier, and the toner particles on the magnetic brush are transferred to and adhere to the electrostatic latent image on the photosensitive layer by Coulomb force or the like to develop the electrostatic latent image. Done.

On the other hand, the magnetic carrier is attracted to the inside of the sleeve by the magnet, and the charged electric charge has the same polarity as the electric charge of the electrostatic latent image. Therefore, the magnetic carrier remains on the sleeve.

There are two methods of rubbing the photosensitive layer and the magnetic brush at the rubbing position, in which the moving directions of both are the same direction, and in which the moving directions of both are opposite, but both have advantages and disadvantages. There is. In the former same-direction moving method, the magnetic brush and the surface of the photoconductor contact in a soft state, so it is excellent in reproducing halftones, but there is a problem that it is difficult to obtain image density, and in order to obtain image density, the sleeve is used. It is necessary to increase the rotation speed of the toner to increase the toner supply ability, and particularly during high-speed copying, the rotation speed of the sleeve with respect to the photosensitive layer needs to be extremely high, which easily causes toner scattering and image fog. There is a point. On the other hand, in the latter reverse movement method, since the magnetic brush comes into contact with the surface of the photoconductor in a compressed state, a high image density is obtained, and it is not necessary to remarkably increase the rotation speed of the sleeve even in high-speed copying. However, there is an advantage that toner scattering and image fog are less likely to occur. However, on the other hand, there are many cases where a brush mark, that is, a thin and short white line extending in the rubbing direction of the brush is included in the image, and a defect such as tailing is generated in the image.

In general, the developing method is not limited to the same direction or the opposite direction, but when the developer on the sleeve passes through the sliding position (developing area), the resistance may appropriately change depending on the strength of the electric field between the sleeve and the photosensitive layer. It can be said that the one is preferable.

That is, it is preferable that the developer acts as a developing electrode in a solid portion where the latent image potential is high and a high electric field acts between the sleeve and the photosensitive layer, and the resistance is low, and the latent image potential of characters and line images is low and narrow range. At a position where a low electric field is applied, it is preferable that high electric resistance is exerted and an edge effect is exerted to develop with high resolution.

In view of this, JP-A-56-125751 discloses a carrier in which the specific resistance value when a DC electric field of 10 V / cm is applied is 5 to 15 times the specific resistance value when a DC electric field of 100 V / cm is applied. ,Ten
When a DC electric field of V / cm is applied, the specific resistance value is 10 ⁸ to 10 ^11.
A developer carrier having a specific resistance value of 10 ⁷ to 10 ¹⁰ Ω · cm when a DC electric field of 100 V / cm at Ω · cm is applied has been proposed.

(Problems to be Solved by the Invention) However, the specific resistance value having the above resistance value when a 10V DC electric field is applied is 5 to 15 times the specific resistance value when a 100V DC electric field is applied. When the developer composed of a carrier is applied to a developing system in which the moving directions of the photosensitive layer and the magnetic brush are opposite to each other, the magnetic brush contacts the photosensitive layer in a compressed state at the sliding position, and Since the relative speed of the sleeve to the photosensitive layer is generally lower than that in the developing method in the same direction, when the above carrier is used, the magnetic brush, which is in close contact with the photosensitive layer due to the low specific resistance value, charges the electrostatic latent image. It leaks and creates brush marks in the image.

Also, between the sleeve and the photosensitive layer, the electric field strength changes from several tens of volts to several hundreds of volts between the non-image area, the character line drawing area, and the solid area, and the resistance value between the electric field of 10 V and 100 V increases. Carriers that change to the above range have a larger change in resistance value at the rubbing position where the electric field strength changes by several hundreds of volts, and in the rubbing part, the latent image part of the low image non-image part to the solid part of the high electric field. When the magnetic brush penetrates into the latent image area of the magnetic field, it is more susceptible to electrostatic induction due to a sudden change in the electric field, and a charge of the opposite polarity to the charge on the photosensitive layer is injected into the carrier of the tip through the brush. . Further, the toner at the tip of the brush is attracted to the latent image charge in the solid portion before the brush enters the solid portion, and is separated from the brush and adheres to the latent image portion in the solid portion. Therefore, when the magnetic brush invades from the latent image portion of the non-image portion of the low electric field to the latent image portion of the solid portion of the high electric field, the relative speed of the sleeve to the photosensitive layer of the magnetic brush is generally small. The electric charge may be first attached and neutralized by the toner, and the carrier may be attached to the non-image portion at the tip of the solid portion, resulting in black spots or streaky stains on the copied image due to the carrier.

Therefore, the present invention has been made in view of the above-mentioned problems, and an object of the present invention is to develop a solid portion with a high density and a character and a line drawing portion with a high resolution without causing carrier adhesion. Image quality is good and stable,
Another object of the present invention is to provide a carrier for a developer applicable to a reverse-moving type developing method that does not cause tailing, brush marks, or image fog.

(Means and Actions for Solving Problems) According to the present invention, the specific resistance value when a DC electric field of 1000 V / cm is applied is 5 × 10 ^{8 to} 2 × 10 ⁹ Ω · cm, and a DC electric field of 100 V / cm is applied. Carrier whose specific resistance value is in the range of 2 × 10 ^{9 to} 1 × 10 ¹⁰ Ω · cm, and whose specific resistance value at 100 V / cm is 2 to 10 times that of 100 V / cm By using the above, the above-mentioned conventional method acts very favorably in the developing method in which the photosensitive layer and the sleeve are rubbed so that the moving directions of the photosensitive layer and the sleeve at the sliding position of the magnetic brush on the sleeve are opposite to each other. The technical problems are solved and the object of the present invention is achieved.

 Hereinafter, the present invention will be described in detail.

First, a reverse movement type developing method applied to the present invention will be described with reference to the drawings.

In FIG. 2, for example, an electrophotographic photosensitive layer 2 such as a selenium-based photoconductive layer is provided on the surface of the driving drum 1, and on the surface thereof, although not shown, uniform charging and image exposure are performed. An electrostatic latent image is formed by such means.

A developing device, generally designated by 3, is provided along the path of movement of the photosensitive layer 2. This apparatus has a magnet 4 having a plurality of magnetic poles, and a sleeve 5 made of a non-magnetic material such as aluminum is provided around the magnet 4. The sleeve 5 is rotatably provided in the direction of arrow A, and the magnet 4 is fixedly provided in the sleeve 5. A stirring mechanism 7 is provided to stir the two-component developer 6, and the stirring mechanism 7 mixes the magnetic carrier and the toner particles.
A mixture that is triboelectrically charged with each other and electrostatically coupled with each other is formed, and is supplied onto the sleeve 5.

The two-component developer forms a magnetic brush 8 on the sleeve 5, and the magnetic brush is cut into a suitable length by the cutting mechanism 9 and supplied to the developing area 10. In the developing area 10, the photosensitive layer 2 and the sleeve 5 move in mutually opposite directions, and the magnetic brush 8 and the photosensitive layer 2 rub against each other. The charged toner particles on the magnetic carrier are attracted to the electrostatic latent image on the photosensitive layer 2 by the rubbing, and the electrostatic latent image is developed. The magnetic brush 8 after development is separated from the sleeve 5 by the scraping plate 11, and the separated two-component developer is agitated by the agitation mechanism 7 and then supplied again onto the sleeve 5. In order to supply the toner 12 consumed in the development, a toner storage unit 13 and a toner replenishing roller 1 are provided, and the toner 12 is continuously or intermittently supplied into the developing mechanism 3. And
In the developing area 10, the developing-like main pole 15 and the photosensitive layer 2 are in a positional relationship such that they are substantially opposed to each other, and rubbing with the photosensitive layer of the magnetic brush is performed to perform development. The carrier of the present invention has a specific resistance value of 5 × 10 ^{8 to} 2 × 10 ⁹ Ω when 1000 V / cm is applied.
・ Cm, the specific resistance value when applying 100V / cm is 3 × 10 ^{9 to} 1
It is in the range of × 10 ¹⁰ Ω · cm, and it is an important feature that the specific resistance value when a DC electric field of 100 V / cm is applied fluctuates by a factor of 2 to 10 when a DC electric field of 1000 V / cm is applied. .

The resistance value of the above carrier is 200 mg of carrier and the distance between electrodes is 2
The magnet is slowly moved closer to both poles, and the magnets are moved multiple times to homogenize the developer, and then a DC electric field of 1000 V and 100 V is applied at a temperature of 23 ° C. and a relative humidity of 60 ± 5%. It is the resistance value when applied, and the resistance value of the carrier is measured at the applied voltage of 100 V and 1000 V so as to correspond to the change in the electric field strength (several hundred volts) that acts between the photosensitive layer and the sleeve during actual development. did.

When the resistance value of the carrier at the time of applying 100 V is larger than the above range, the characters and line images are likely to be faint, and when the resistance value is smaller, the resolution is likely to be deteriorated. Further, if the resistance value of the carrier at the time of applying 1000 V is larger than the above range, the image density is likely to decrease, and if the resistance value is small, tailing or brush marks are likely to occur. Furthermore, the fluctuation of the specific resistance value at 100V and the fluctuation value of the specific resistance value at 1000V change between 2 to 10 times, which effectively prevents the carrier from adhering to the non-image part at the tip of the solid part of the carrier. Therefore, it is possible to form an excellent image, and it is possible to form a clear image with good density and resolution.

In addition, the specific resistance value of the above carrier at 100 V applied and 1000
If the ratio of the specific resistance value at V exceeds the above range, image sticking may occur due to carrier adhesion.If the ratio is less than the above range, the density may be insufficient in the solid part or the image may be crushed in the characters or fine line parts. Or

Examples of the carrier used in the present invention include iron oxide, reduced iron, copper, ferrite, nickel, cobalt and the like, and alloys with these zinc, aluminum and the like. Ferrite particles that can form ears are preferred. For example, Zn-based ferrite, Ni-based ferrite, Cu-based ferrite, Mn-based ferrite, Ni-Zn-based ferrite, Mn-Mg-based ferrite, Cu-Mg
System ferrite, Mn-Zn system ferrite, Mn-Cu-Zn system ferrite, etc. are mentioned. In particular, Mn-Cu-Zn ferrite is preferable. These carrier particles may be coated with a resin, for example, silicone resin, fluorine resin, acrylic resin, styrene resin, styrene-acrylic resin, olefin resin, ketone resin, phenol resin, xylene resin, diallyl resin. One kind or a mixture of two or more kinds such as a phthalate resin is used.

The applied voltage dependency of the carrier can be changed not only by the composition but also by the sintering temperature, the sintering time and the like.

The carrier has a particle size of generally 20 to 300 μm, especially 30.
To 150 μm are preferably used. The saturation magnetization of the carrier is preferably 45 to 60 emu / g, particularly preferably 48 to 58 emu / g, and the residual magnetization is preferably adjusted to about 0.3 emu / g.

The toner has a particle size of 5 to 20 μm in which a colorant, a charge control agent and, if necessary, a magnetic material are dispersed in a binder resin, which is selected in consideration of the charging property and fixing property with a carrier. Resin fine powder of is used.

As the binder resin, general thermoplastic resin or thermosetting resin such as vinyl aromatic resin such as polystyrene, acrylic resin, polyvinyl acetal resin, polyester resin, epoxy resin, phenol resin, petroleum resin or olefin resin is used. To be done.

As the colorant, conventionally known colorants generally used in this field can be used, and particularly carbon black, lamp black, chrome yellow, Hansa yellow, benzidine yellow, slen yellow G, quinoline yellow, permanent orange GTR. , Pyrazolone Orange, Vulcan Orange, Wo Chang Red, Permanent Red, Brilliant Carmine 3B, Brilliant Carmine 6B, DuPont Oil Red, Pyrazolone Red, Resole Red, Rhodamine B Lake, Lake Red C, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco oil blue, methylene blue chloride, phthalocyanine blue, phthalocyanine green, malachite green oxalate, etc., or CISo
lvent Yellow60, CISolvent Red27, CISolvent Blu
Examples include oil-soluble dyes such as e35. These colorants may be used alone or in combination of two or more. Further, as the charge control agent, conventionally known charge control agents used in this field can also be used, for example, nigrosine base, oil black, oil-soluble dyes such as spirone black, metal salts of naphthenic acid, and fatty acid metal. Examples thereof include soap and resin acid soap.

Various means are used to adjust the electric resistance of the developer including the magnetic carrier and the toner. However, by increasing the concentration of the toner particles or reducing the particle size of the toner particles, It is also possible to increase the resistance, increase the diameter of the magnetic carrier to increase the resistance, and vice versa, to decrease the resistance. Further, it is natural that the electric resistance is changed depending on the material of the carrier particles themselves, the material of the coating resin, the material of the resin of the toner particles, and the like. For example, as described in JP-A-58-145621, during firing, the resistance of carrier particles is continuously changed by continuously changing the oxygen partial pressure of the firing atmosphere from the air to the nitrogen atmosphere. If the equilibrium oxygen partial pressure during firing is reduced, the resistance value will decrease,
The resistance value rises if it is increased. In addition, JP-A-61-2005
As described in JP-A No. 51 and JP-A No. 61-270769, a carrier having an arbitrary resistance value is obtained by changing the resistance according to the composition of the carrier or adjusting the resin coating on the carrier surface. It is possible.

The specific resistance value of the developer composed of the carrier and toner is 6 × 10 ^{9 to} 2 × 10 ¹⁰ Ω · cm, 1 at 100V.
It is preferably 1 × 10 ^{9 to} 6 × 10 ⁹ Ω · cm at 000V. Since the electric field acting on the rubbing portion acts on the entire developer layer, the electric resistance of the carrier constituting the developer satisfies the above-mentioned conditions, and the electric resistance of the developer when used as a toner and the developer is within the above range. It is more preferable to select a toner such that the following can be obtained in order to obtain the effects of the present invention.

In the present invention, a bias voltage is applied between the photoconductor drum and the developing sleeve, and the bias voltage is determined so that troubles such as discharge breakdown do not occur in the photoconductor and the magnetic brush. This voltage is generally suitable in the range 100 to 350 volts, especially 150 to 300 volts.

In developing the magnetic brush of the present invention, the distance between the photosensitive drum and the sleeve is generally 1.0 to 2.0 mm,
Particularly, 1.5 to 1.8 mm is suitable for using the carrier of the present invention. Further, the bristle cutting of the magnetic brush is 1.1 to 3.0, particularly 1.2 to the distance between the photosensitive drum and the sleeve.
It is preferable to carry out the cutting so that the pan length becomes 2.0 times.

 The present invention will be described in more detail below with reference to Examples.

(Experimental example) Toner Styrene-acrylic resin XPA-3421 (Mitsui Toatsu Co., Ltd.)
Made, product name) 100 parts by weight Carbon Black R-330R (made by Cablack Co., Ltd., product name) 10 parts by weight Charge control agent Spinro Black (made by Hodogaya Chemical Co., Ltd., product name) 3 parts by weight Offset prevention Agent Biscol 550P (manufactured by Sanyo Kasei Co., Ltd.,
Product name) 1.5 parts by weight The above mixture is heated and mixed with a two-roll to knead,
The kneaded product was pulverized and classified to obtain a toner having an average particle size of 12 μm.

Saturation magnetization of 50emu / g and residual magnetization of 0.3 were obtained by sintering carrier Fe ₂ O ₃ , CuO, ZnO, and MgO by changing the temperature and time.
Carriers having emu / g, coercive force of 3 Oe, and average particle size of 40 μm, which are substantially equal to each other and have different electric resistance characteristics, were prepared. Then, each specific resistance value at the time of applying a DC voltage of 100 V and 1000 V by the method of the present invention described above is measured, and the toner is mixed with various carriers to adjust the toner concentration to 10% to obtain a developer, The same copying test was performed for each developer under the following developing conditions.

Drum-sleeve distance 1.7mm Photosensitive surface potential 850V Development bias potential 250V The results are shown in Table-1 and Table-2.

In the table, the evaluation of brush mark and carrier development is ◯: no generation, ×: generation, solid area density and fog density were measured by a reflection densitometer, and resolution was obtained by a resolution test chart. In the copied image, it was judged how many fine lines with the same width were developed with good reproducibility within the interval of 1 mm. Then, a comprehensive judgment was made from all items.

Furthermore, using the log-log graphs of the results in Tables 1 and 2, the horizontal axis represents the resistance value of the carrier when a DC voltage of 1000 V is applied, and the vertical axis represents the resistance value of the carrier when a DC voltage of 100 V is applied. , And the results of the comprehensive judgment of the electrical characteristics and images of each carrier were plotted.

From the figure, the resistance value of the carrier when 1000V is applied is 5 × 10 ⁸ ~
Within the range of 2 × 10 ⁹ without causing tailing or fog,
It can be seen that a high density image can be obtained. Further, it is understood that the resolution is high when the carrier resistance when 100 V is applied is in the range of 2 × 10 ^{9 to} 9 × 10 ⁹ , and development can be performed without causing blur. The straight line L ₁ is a straight line that shows the fluctuation amount of the carrier resistance value at 1000 V and 100 V applied, and the straight line L ₂ is the fluctuation amount of the carrier resistance value at 1000 V and 100 V applied. It is a straight line showing double, and it is easy to generate a brush mark or carrier development on the boundary of these straight lines, and it is understood that a carrier whose resistance value fluctuates within this range is preferable.

(Effect of the Invention) According to the present invention, a carrier suitable for a developing method in which a photosensitive layer and a developing sleeve move in opposite directions at a rubbing position, such as fogging, brush marks, tailing, and carrier development. It is possible to obtain a carrier for a two-component developer in which a solid portion and a thin portion of a character portion can be well reproduced without causing the occurrence of, and a copy image with high density and high resolution can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between changes in resistance value and image evaluation with respect to applied voltages of various carriers shown in Table-1 and Table-2. FIG. 2 is a diagram showing an example of a developing device in which the carrier of the present invention is preferably used, in which the photosensitive layer and the sleeve move in opposite directions at the sliding position.

Claims (1)

(57) [Claims] 1. The specific resistance value when a DC electric field of 1000 V / cm is applied is 5
× 10 ^{8 to} 2 × 10 ⁹ Ω · cm, the specific resistance value when a 100 V / cm DC electric field is applied is in the range of 9 × 10 ^{9 to} 2 × 10 ⁹ Ω · cm,
The specific resistance value when 0 V / cm is applied varies from 2 to 10 times the specific resistance value when 1000 V / cm is applied, and the photosensitive layer and the sleeve at the sliding position between the photosensitive layer and the magnetic brush on the sleeve. A carrier for a two-component developer used in a developing method in which rubbing is performed so that the moving directions of and are opposite to each other.