JPH08314190A - Developing method - Google Patents

Abstract

PURPOSE: To provide a developing method by which toner scattering and white stripe do not occur, and which can develop a high-quality image. CONSTITUTION: As to this developing method in which a developing roll 9 obtained by making at least the external peripheral surface formed to be a cylindrical surface by a non-magnetic elastic material is rotatably arranged to face oppositely to an image carrier 1 moving while carrying an electrostatic charge image, magnetic toner is supplied on the surface of the roll 9, and also a controlling member slidably abuts on the surface so as to form a toner layer, and the electrostatic charge image is visualized by bringing the image carrier 1 into contact with the roll 9 through the toner layer; the magnetic toner including welding resin whose molecular weight distribution is 10 to 70 and magnetic powder having 10 to 40 pts.wt. as main components is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic method, an electrostatic recording method, a magnetic recording method, etc., in which an electrostatic charge image formed on the surface of an image carrier which carries and moves an electrostatic charge image is formed into a cylindrical shape. The present invention relates to a developing method of developing using a magnetic toner held on the surface of a developing roller formed in a sheet shape.

[0002]

2. Description of the Related Art Conventionally, in an image forming method utilizing electrophotography or electrostatic recording, an electrostatic charge image formed by various means on the surface of an image carrier made of a photoconductor or a dielectric is used, for example. By using a developing means including a sleeve having a built-in permanent magnet member and being inserted into the permanent magnet member so as to be rotatable relative to the permanent magnet member, the magnetic developer is attracted and conveyed by the developing means to form a so-called magnetic brush. Rubbing is performed to develop as a toner image.

Then, the toner image is directly fixed, or the toner image is transferred onto a transfer sheet such as plain paper and then fixed to obtain a final image. In the case of the method of transferring a toner image, it is usual to provide a cleaning means for removing the excess toner remaining on the surface of the image carrier after the transfer.

[0004]

In the case of the system in which the magnetic developer is used as described above and the magnetic developer is attracted and conveyed by the developing means, the permanent magnet member and the sleeve are coaxially combined. Since it constitutes the developing means, there are problems that the processing and assembling are complicated and the manufacturing cost increases.

Therefore, a non-magnetic one-component type developer is used,
There has been proposed a system in which this developer is attracted and conveyed by a developing means composed of a rubber roller via electrostatic force. This type has the advantage that the developing unit has a simple structure and can be downsized, but on the other hand, since the holding force of the developer to the developing unit is small, so-called toner scattering does not occur. Many. Further, as a means for removing the surplus toner remaining on the surface of the image carrier, there is no choice but to use a mechanical means such as a fur brush or a blade,
There is a problem that the surface of the image carrier is easily damaged.

In order to solve the above problems, a one-component magnetic toner is used, and this magnetic toner is charged by a developing means in which a doctor blade is brought into contact with the surface of a non-magnetic rubber roller, and electrostatic force is applied. A method of adsorbing and transporting it is being studied. In this type, the surplus magnetic toner remaining on the surface of the image carrier after transfer can be removed by the magnetic cleaning means in the non-contact state, so that there is an advantage that the surface of the image carrier is not damaged. is there. However, the triboelectric charge amount of the magnetic toner is low and the image quality is low.

On the other hand, if the contact force or pressing force of the doctor blade with respect to the non-magnetic rubber roller is increased in order to improve the triboelectric charge amount, the magnetic toner may adhere firmly to the doctor blade, and the magnetic toner may subsequently pass. Will be disturbed. For this reason, there are problems that the image density is lowered, and inconveniences such as occurrence of white stripes on the image occur. Further, the magnetic toner passes between the non-magnetic rubber roller and the doctor blade, but the magnetic toner needs toughness in order to cope with the large pressing force of both, and the magnetic toner of normal toughness is required. When used, there is a problem that durability is insufficient.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems existing in the prior art and to provide a developing method capable of stably developing a high quality image without causing toner scattering and white streaks.

[0009]

In order to achieve the above object, in the present invention, a cylinder made of a non-magnetic elastic material is provided at least on the outer peripheral surface of the cylinder facing an image carrier that carries and moves an electrostatic charge image. The developing roll formed on the surface is rotatably arranged, magnetic toner is supplied to the surface of the developing roll, and a regulating member is slidably abutted to form a toner layer. In the developing method of bringing the electrostatic charge image into a visible image by bringing the image carrier and the developing roll into contact, the magnetic toner has a molecular weight distribution of 10 to 10.
The technical means of using a resin containing 70 as a main component and 10 to 40 parts by weight of magnetic powder was adopted.

In the present invention, if the molecular weight distribution of the binder resin is less than 10, white streaks are generated, sufficient fixing-offset resistance cannot be obtained, and the image density is lowered, which is not preferable. On the other hand, if the molecular weight distribution exceeds 70, in the binder resin having two or more molecular weight distribution peaks, the peaks are located apart from each other, the toner becomes brittle, and white streaks and the like are generated, which is inconvenient.

Next, in the present invention, when the content of the magnetic powder in the magnetic toner is less than 10 parts by weight, the cleaning action of the magnetic toner remaining on the surface of the image carrier after transfer becomes insufficient, resulting in background fog. It is not preferable because it causes On the other hand, if the content of the magnetic powder exceeds 40 parts by weight, background fog will occur and the image density and fixability will decrease, which is inconvenient.

Further, in the present invention, the molecular weight of the binder resin can be set to number average molecular weight Mn = 2 × 10 ³ to 8 × 10 ³ and weight average molecular weight Mw = 8 × 10 ^{4 to} 20 × 10 ⁴ .

Furthermore, in the present invention, the binder resin GP
The chromatogram measured by C (gel permeation chromatography) has at least one local maximum and at least one local minimum, and the ratio between the minimum local maximum and the maximum local maximum is 1 / 20 or more, preferably 1
It is possible to use one having a value of / 5 or more. The above ratio is 1/20
If it is less than the above range, the proportion of intermediate molecular weight compounds in the binder resin becomes small, and the binder resin becomes brittle, which is inconvenient.

The magnetic toner is preferably an insulating one having a volume resistivity of 10 ¹⁴ Ω · cm or more from the viewpoint of improving transferability, and one which is easily charged by friction with a doctor blade (friction). Absolute amount of charge is 10μ
(c / g or more) is preferable. The average particle size of the toner is preferably 5 to 10 μm in order to obtain a high-definition image.

The composition of the magnetic toner is the same as that used normally, and the binder resin (styrene-acrylic copolymer, polyester resin, etc.) and magnetic powder (magnetite, soft ferrite, etc.) are essential components, and optional components. As the charge control agent (nigrosine, metal-containing azo dye, etc.), a release agent (polyolefin, etc.), and a fluidizing agent (hydrophobic silica) (internal and / or external addition) can be used.

The average particle diameter (volume) was measured using a particle size analyzer (Coulter Counter Model TA-II manufactured by Coulter Electronics Co.). In addition, the value of the above-mentioned volume resistivity is obtained by weighing an appropriate amount of sample (10 mg or more),
It was filled in a Teflon (trade name) cylinder with an inner diameter of 3.05 mm with an improved dial gauge and was loaded with 0.1 kg load. C. An electric field of 4000 V / cm was applied and measured, and the resistance value was calculated. A Yokogawa Hewlett-Packard Model 4329 Insulation Resistance Tester was used to measure the resistance. Regarding the triboelectric charge amount, first, a magnetic developer prepared to have a toner concentration of 5% by weight was mixed well, the toner was blown at a blow pressure of 1.0 kgf / cm ² , and the blow-off powder charge amount measuring device (manufactured by Toshiba Chemical Co., Ltd. TB-200 type).

In the present invention, the non-magnetic elastic material constituting the developing roll is 100 parts by weight of a rubber material such as urethane, silicone, butyl, ethylene propylene terpolymer (EPDM), and 1 to 10 parts by weight of a cross-linking agent. , 10 to 100 parts by weight of a conductive agent such as carbon black, and a mixture of a small amount of a plasticizer, an antioxidant, a lubricant and the like as an optional component can be used. Further, as the doctor blade as the restricting member, an elastically deformable material such as urethane, stainless steel, phosphor bronze or the like can be used.

[0018]

With the above construction, the magnetic toner is triboelectrically charged between the developing roll and the regulating member, the layer thickness is regulated, and the magnetic toner is adsorbed on the surface of the developing roll by electrostatic force and conveyed, and the surface of the image carrier is conveyed. Development is carried out by adhering to the electrostatic charge image formed on. The surplus magnetic toner remaining on the surface of the image carrier after the toner image transfer can be easily removed by the magnetic cleaning means, so that the surface of the image carrier is cleaned.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional explanatory view of essential parts showing an example of an image forming apparatus in an embodiment of the present invention. In FIG. 1, 1
Is a photoconductor drum, is provided rotatably in the direction of the arrow, and is provided with a charging unit 2, an exposing unit 3, a developing unit 4,
The transfer unit 5 and the cleaning unit 6 are arranged in this order so as to face the photosensitive drum 1.

The developing means 4 has a toner tank 8 for containing the magnetic toner 7, a developing roller 9 rotatably provided below the toner tank 8, and a doctor blade 10 provided in contact with the surface of the developing roller 9. Composed by.

The developing roll 9 is made of, for example, free cutting steel (SU).
The rubber layer 12 (diameter 20) composed of 100 parts by weight of urethane rubber and 30 parts by weight of carbon black is provided on the outer periphery of the shaft 11 formed by M) to have a diameter of 6 mm and a length of 280 mm.
mm, length 227 mm, volume resistivity 10 ³ Ω · cm)
It is formed by fixing. Doctor blade 10
Was formed with a thickness of 0.5 mm, for example, using SUS304.

Next, the cleaning means 6 is a rotatable cleaning roll 14 formed in the housing 13 in a cylindrical shape by, for example, a ferrite magnet, and having a plurality of NS magnetic poles alternately provided on the outer periphery thereof, such as stainless steel ( SU
S304) is formed in a hollow cylindrical shape by a non-magnetic material, and is provided on the outside of the cleaning roll 14 coaxially and relatively rotatably, and by the scraper 16 slidingly contacting the outer peripheral surface of the sleeve 15. Composed.

With the above structure, the photosensitive drum 1
After the surface of 1 is uniformly charged by the charging means 2, an electrostatic charge image is formed by the exposing means 3. In the developing means 4, the magnetic toner 7 is guided between the developing roll 9 and the doctor blade 10 by the rotation of the developing roll 9, is triboelectrically charged, and is regulated to have a predetermined layer thickness. To be done.

In the developing area where the developing roll 9 and the photosensitive drum 1 are opposed to each other and contact with each other via the magnetic toner 7, the magnetic toner 7 adheres to the electrostatic charge image formed on the surface of the photosensitive drum 1, A toner image 17 is formed. The toner image 17 is transferred (17a) onto the transfer sheet 18 moving in the direction of the arrow by the transfer means 5, and then fixed by the fixing means (not shown).

On the other hand, the excess magnetic toner 17b remaining on the surface of the photosensitive drum 1 is adsorbed and removed by the cleaning means 6. That is, it is adsorbed on the sleeve 15 by the magnetic attraction force of the cleaning roll 14, and is further collected in the housing 13 by the scraper 16. Therefore, the surface of the photosensitive drum 1 is cleaned and the next development is started.

The result of forming an image by using the magnetic toner with the image forming apparatus having the above-mentioned structure will be described. The magnetic toner is composed of 67 parts of resin having a molecular weight shown in Table 1 by weight ratio, magnetic powder (EPT500 manufactured by Toda Kogyo,
30 parts of an average particle size of 8 to 9 μm, 2 parts of polypropylene (TP32 manufactured by Sanyo Kasei), and 1 part of a charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.) were mixed, and the mixture was heated and kneaded, cooled and solidified, pulverized and classified to obtain an average particle size. 9 μm and hydrophobic silica on the surface (Aerosil R97 manufactured by Nippon Aerosil Co., Ltd.)
2) 0.5 part was externally added. Volume resistivity is 5 × 10 ¹⁴ Ω
-Cm, the triboelectric charge amount was -22 μc / g.

The photosensitive drum 1 is formed to have a diameter of 30 mm by negatively charging OPC, and the peripheral speed is 60 mm / sec.
The surface potential was set to -650V. Further, in order to perform reversal development, a DC bias voltage of -500V is applied to the developing roll 9, and the developing gap and the doctor gap are each 0 mm.
After roller transfer, heat roll fixing was performed at 180 ° C. and 1 kg / cm.

[0028]

[Table 1]

(Minimum value) of resin molecular weight in Table 1 /
The (maximum value) is calculated as follows. FIG. 2 is a diagram showing a chromatogram of the resin measured by gel permeation chromatography (GPC), in which (a), (b), and (c) are Nos. In Table 1, respectively.
It corresponds to 2, 3, and 5. It should be noted that those with a large resin molecular weight have a short elution time, while those with a small resin molecular weight have a long elution time.

The one shown in FIG. 2 has two peaks in the chromatogram, and there are two maximum values. The (minimum value) / (maximum value) in Table 1 is Mmin./M in FIG.
It is calculated by max. Note that N in Table 1
o. No. 1 and No. 4 have no local minimum value, and are one peak in the chromatogram.

As is apparent from Table 1, N which is a comparative example.
o. In No. 4, since the weight average molecular weight Mw is small and the value of the ratio Mw / Mn with the number average molecular weight Mn is small, the initial image is good, but 3000
After printing one sheet, the image density becomes low and white streaks are observed. In addition, No. 5 is G
The chromatogram measured by PC shows two peaks, but since the ratio of the minimum value and the maximum value is small, it is good in the evaluation of the image density and white streaks in the initial stage, but the background fog Occurrence is recognized. After printing 3000 sheets, the image density is lowered, and the occurrence of background fog and white streaks is recognized.

On the other hand, No. 1 is the embodiment of the present invention.
In 1 to 3, of course, in the initial stage, 300
It can be seen that even after printing 0 sheets, a high-quality image having a high image density and free from background fog and white streaks is obtained.

Next, as shown in Table 1, No. Table 2 shows the image evaluation results of the magnetic toner using the resin of No. 2 in which the content of the magnetic powder was changed.

[0034]

[Table 2]

In Table 2, first, No. In No. 26, since the content of magnetic powder in the magnetic toner is large, the image density is low and the occurrence of background fog is recognized. On the other hand, No. In No. 21, the content of magnetic powder in the magnetic toner is small and the image density is good, but background fog occurs and the residual toner after transfer is not sufficiently cleaned. On the other hand, No. 22-25 (N
o. No. 24 in Table 1 is No. (Same as 2),
The image density is high, and there is no background fog or cleaning failure, and a high quality image is obtained.

[0036]

EFFECT OF THE INVENTION Since the present invention has the structure and operation as described above, it does not cause toner scattering and white stripes.
There is an effect that a high-quality image can be stably developed for a long period of time.

[Brief description of drawings]

FIG. 1 is an explanatory cross-sectional view of essential parts showing an example of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a chromatogram of a resin measured by gel permeation chromatography.

[Explanation of symbols]

 1 image carrier 9 developing roll 10 doctor blade

Claims (3)

[Claims] 1. A developing roll having a cylindrical surface, at least the outer peripheral surface of which is formed of a non-magnetic elastic material, is rotatably arranged so as to face an image carrier that carries and moves an electrostatic charge image.
While supplying magnetic toner to the surface of this developing roll,
A developing method in which a regulating member is slidably abutted to form a toner layer, and the electrostatic latent image is visualized by bringing the image bearing member and the developing roll into contact with each other via the toner layer, A developing method characterized in that a magnetic toner containing a binder resin having a molecular weight distribution of 10 to 70 and 10 to 40 parts by weight of magnetic powder as main components is used. 2. The molecular weight of the binder resin is the number average molecular weight Mn.
= 2 × 10 ³ to 8 × 10 ³ , weight average molecular weight Mw = 8 ×
10. It is 10 ^{4 to} 20 × 10 ⁴ , and it is characterized by the above-mentioned.
The developing method described. 3. The chromatogram of the binder resin measured by GPC (gel permeation chromatography) has at least one local maximum value and at least one local minimum value, and the minimum local minimum value. The developing method according to claim 2, wherein the ratio to the maximum value is 1/20 or more.