JPS60229037A - Method for developing electrostatic latent image - Google Patents

Abstract

PURPOSE:To form soft magnetic brush bristles, and to obtain a fine sharp image high in density by using the mixture of ferromagnetic particles of a ferromagnetic material, and binder type magnetic particles obtained by dispersing a fine magnetic powder into a binder resin. CONSTITUTION:The ferromagnetic particles and the binder type magnetic particles are mixed in advance, and this mixture is placed in an empty chamber 7, and after a developing device is preliminarily runned, an insulating magnetic toner is supplied to a toner replenishing vessel 6. Said toner is carried in the arrow (a) direction along the outer circumference of a developing sleeve 2 by rotation of a magnetic roller 3 in the direction of arrow (b) and rotation of the sleeve 2 in the direction of arrow (a), and when the toner passes through the empty chamber 7, it is mixed and stirred with the magnetic particles, triboelectrifying each other separately. As a result of mixing and stirring, the insulating magnetic toner and the magnetic particles, both being the components of the magnetic developer, are united continuously in a constant mixing ratio, and a magnetic brush made of the magnetic developer is formed with certainty in a developing zone A.

Description

Detailed Description of the Invention Technical Field The present invention relates to electrostatic latent image development M-L, which is a step of electrophotography.
: Pressure 1-PIB1 Deluxe-No Prior Art As a developing method of this type that has already been put into practical use, there is a one-component developing method using a powder developer consisting only of magnetic toner. This component development method has a difficult problem in that the toner requires contradictory conditions such as conductivity during development and insulation during transfer.Currently, the copying process requires less than one step. A magnetic toner with high resistance that does not impose a burden and has good transfer characteristics is used, and various measures are taken to improve the development characteristics.

As one of these types of measures, the applicant has already
By supplying insulating magnetic toner to the magnetic particles adsorbed onto the outer circumferential surface of the developing sleeve, magnetic particles consisting of a mixture of the magnetic particles and insulating magnetic toner are formed on the outer circumferential surface of the developing sleeve. An electrostatic latent image developing method has been proposed in which a developer is prepared and the prepared magnetic developer is used to develop an electrostatic latent image carried on the surface of an electrostatic latent image carrier.

According to this development method, the mixing of magnetic particles ensures triboelectric charging of the magnetic toner, increases the conveyance force by improving magnetic permeability, prevents toner agglomeration caused by this, and improves the effective magnetic field and electric field strength in the development area. As a result, a significant improvement in development characteristics can be expected.

However, on the other hand, the present inventors have confirmed that various drawbacks occur depending on the type of magnetic particles used.

For example, in the case of magnetic particles made of iron powder with an average particle diameter of about 100 to 200 μm, toner adheres to the surface of the magnetic particles and deteriorates after long-term use, and fog is likely to occur in developed images, resulting in low image resolution.

Ikegata: With magnetic particles made of ferromagnetic ferrite, when the particle size of the magnetic particles themselves is reduced in order to improve image quality, the magnetic attraction force generated between the magnetic particles during magnetic brush formation is too strong, resulting in hard magnetic brush ears. , each magnetic particle aggregates in a chain or fin shape on the magnetic brush carrier, which hinders the transport of the developer and causes problems such as white smudges in the solid developed image. 109Ω
・Because it is as low as elf, there are problems such as charge on the surface of the electrostatic latent image carrier escaping, causing disturbance of the latent image, resulting in image defects, and magnetic particles adhering to the image area of the electrostatic latent image carrier. In addition, there are drawbacks in that the edge effect cannot be obtained much and the reproduction of fine lines is not sharp.

Moreover, when magnetic particles adhere to the surface of the electrostatic latent image carrier,
Since ferrite is extremely hard, it has the disadvantage that the surface of the electrostatic latent image carrier is scratched when toner remaining on the surface of the electrostatic latent image carrier is removed using a blade cleaner.

Note that the problem caused by low resistance can be solved by covering the ferrite single particles with an insulating material.
The problem of the hard ears of the magnetic brush, which causes white streaks on developed images, remains. Moreover, contrary to the case where the resistance is low, when the amount of charge of the magnetic particles increases too much and the development bias is high, the magnetic particles may adhere to the non-image area on the surface of the electrostatic latent image carrier. This causes a problem of damaging the electrostatic latent image carrier.

Purpose of the Invention The present invention is an improvement of the electrostatic latent image developing method proposed by the present applicant, which is expected to improve the development characteristics described above, in view of the above-mentioned drawbacks. It is possible to form a brush without causing agglomeration of magnetic particles.
Another object of the present invention is to provide an electrostatic latent image developing method that does not cause adhesion of magnetic particles to the surface of an electrostatic latent image carrier.

In order to achieve the above objects, the electrostatic latent image developing method according to the present invention supplies insulating magnetic toner to magnetic particles magnetically attracted on the outer peripheral surface of a developing sleeve. A magnetic developer made of a mixture of the magnetic particles and an insulating magnetic toner is prepared on the outer peripheral surface of the developing sleeve, and the prepared magnetic developer is used to reduce the electrostatic charge carried on the surface of the electrostatic latent image carrier. An electrostatic latent image developing method for developing a latent image, wherein the magnetic particles include ferromagnetic particles;
It is characterized by the use of a mixture with binder-type magnetic particles made by dispersing magnetic fine powder in a binder resin.

In the present invention, the insulating magnetic toner in the magnetic developer prepared on the outer peripheral surface of the developing sleeve is a thermoplastic resin containing magnetic fine powder and an arbitrary colorant dispersed therein, or, if necessary, further Those in which a charge control agent etc. are dispersed can be used, and the average particle size is 9 to 20μI, 1012
It is desirable to use one having a volume resistivity (if) (resistance value measured under an electric field of V/cm) of Ω·Cl11 or more.

As the thermoplastic resin, polystyrene, styrene, etc.
Acrylic copolymer resin, acrylic resin, epoxy resin, fluororesin, polyester, etc. may be used. As the magnetic fine powder, iron powder, magnetic iron oxide, ferrite, etc. having an average particle diameter of 3 μI11 or less may be used.

As the ferromagnetic particles, those consisting of a single ferromagnetic particle may be used, and if necessary, the surface of the single ferromagnetic particle may be thinly coated with an insulating material such as resin. . The ferromagnetic particles preferably have an average particle size of 35 to 9 μm. This is because if the average particle size of the ferromagnetic particles is less than 35μI11, the developer transportability deteriorates and the image density tends to decrease, and if it exceeds 90μ[fi, the magnetic brush ears become hard and the image deteriorates. This is because white streaks may occur and it may be difficult to obtain a fine-grained image. As the ferromagnetic material, for example, soft type ferrite made of oxides of metals such as nickel, manganese, magnesium, zinc, and iron oxide may be used. This type of ferromagnetic material typically has 10
'~10"□Ω・ctn volume resistivity (5X11'E
\'/cill (resistance value measured under an electric field), and preferably has a specific product resistivity within the above range.

Binder-type magnetic particles are obtained by dispersing magnetic fine powder in a binder + 31 fat, if necessary together with a conductivity control agent, a charge control agent, etc., and pulverizing and classifying the particles, and the average particle size thereof is 2( A range of 55 μm1 is preferred.

This is because if the average particle size of the binder type magnetic particles is less than 20 μm, they tend to adhere to the surface of the electrostatic latent image carrier, and if it exceeds 55 μm, it becomes difficult to obtain a fine-grained image. As the magnetic fine powder, iron powder, magnetic iron oxide, ferrite, etc. with an average particle size of 3 μω or less can be used, or the type and type are usually selected so as to obtain binder-type magnetic particles having a coercive force of 60 krusted or more. It is preferable to select the mixing ratio with the binder resin. Further, as the binder resin, in addition to the resin similar to the resin of the insulating magnetic toner, a thermosetting resin can also be used.

Further, it is preferable to use binder type magnetic particles having a volume resistivity (resistance value measured under an electric field of sxl 0''V/cm) of 1012 Ω·eta or more.

This is because when the volume resistivity is less than 01''Ω·0111, the resistance of the entire particle decreases in balance with the volume resistivity of the ferromagnetic particles, which exhibit a relatively low resistance value, and the surface resistance of the electrostatic latent image carrier decreases. This is because charge leakage or deterioration of thin line reproducibility due to the bottom edge effect may occur.As mentioned above, the average particle size of the binder type magnetic particles is 2.
It is preferable that the average particle size is in the range of 0 to 55 It +n, or that the average particle size is smaller than the average particle size of the ferromagnetic particles in order to obtain good magnetic developer transportability.

The mixing ratio of ferromagnetic particles and binder-type magnetic particles is determined by the content of ferromagnetic particles in the total magnetic particles (ferromagnetic particles and binder-type magnetic particles) (~70% by weight) (Il
t%). This is because if the content of ferromagnetic particles is less than 01%, the developer transportability will deteriorate, or the binder-type magnetic particles will adhere to the surface of the electrostatic latent image carrier, and if the content is more than 7fiu+L%, the entire magnetic particle This is because the volume resistivity of the magnetic particles decreases too much or agglomeration of magnetic particles occurs, resulting in white spots appearing on the image.

[Developing device 1] Is the electrostatic latent image developing method according to the present invention carried out by preparing the above-mentioned magnetic developer on the outer peripheral surface of the developing sleeve? It is effective to use a developing device having a structure in which a magnetic roller whose peripheral surface is magnetized with sequentially different polarities is covered with a developing sleeve made of a non-magnetic material. In this case, there are two methods: a method in which the internal magnetic roller is fixed and the developing sleeve is rotated, a method in which the developing sleeve is fixed and the magnetic roller is rotated, and a method in which both are rotated in the same direction or in mutually opposite directions. method can also be adopted. Examples of this type of developing device include those having the structure shown in the accompanying drawings.

The developing device shown in the accompanying drawings is characterized in that magnetic particles are present only on the outer peripheral surface of the developing sleeve 7 (2). Specifically, a magnetic roller (3) whose outer periphery is sequentially magnetized with S and N poles is housed coaxially within a developing sleeve (2) formed in a cylindrical shape from a conductive non-magnetic material, and a height regulating plate is installed. (
4), the magnetic developer is rotated in the direction of the arrow (1) of the magnetic roller (3) and/or the developing sleeve (2).
Based on the rotation in the direction of arrow (a), the developing sleeve (2
) is circulated and transported in the direction of arrow (a). Furthermore, a magnetic developer front regulation plate (5) is installed upstream of the height regulation plate (4). This front regulating plate (5) is formed integrally with the housing member of the toner supply 1 (, 6) for storing insulating magnetic toner, and its tip faces the outer peripheral surface of the developing sleeve (2). . A cavity (7) for storing magnetic particles (a mixture of ferromagnetic particles and binder-type magnetic particles) is formed between the head height regulation plate (4) and the front regulation plate (5). The upper part of this empty space (7) is covered with a cover (8) that can be opened and closed, and the developing sleeve (
2) is open only toward the outer peripheral surface.

On the other hand, the lower part of the toner replenishing tank (6) is a toner replenishing part (9) that opens upstream of the front regulation plate (5), and the lower part of this toner replenishing part (9) is a replenishing tank bottom forming plate (10). ) is installed, and a perforated scraper (11) is installed so as to press against the outer peripheral surface of the developing sleeve (2) in a so-called forward direction. Further, below the developing area (A) at the lower end of the toner supply tank (6) and facing the surface of the developing sleeve (2) or the main photosensitive drum (1), there is a developer spill prevention plate (12). 13) is installed.

[Developing method 1 When developing the electrostatic latent image carried on the surface of the photoreceptor drum (1) using a magnetic developer using the developing device configured as described above, first, the cover (8) is After opening and loading the empty chamber (7) with magnetic particles in which ferromagnetic particles and binder-type magnetic particles are mixed in advance, and the developing device is pre-operated, insulating magnetic toner is placed in the toner replenishing tank (6). loaded. At this time, a small amount of insulating magnetic toner may be mixed into the magnetic particles loaded into the empty chamber (7). In this state, the electrostatic latent image can be developed by the present developing device.

Here, the insulating magnetic toner is attached to the magnetic roller (3) by the arrow (
1])) and rotate the developing sleeve (2) in the direction of the arrow (,
) is conveyed on the outer circumferential surface of the developing sleeve (2) in the direction of arrow (a), and as it passes through the empty chamber (7), it is mixed and stirred with magnetic particles, and the toner and magnetic particles are each Frictionally charged. As a result of this mixing and agitation, the insulating magnetic toner and magnetic particles, which are each component of the magnetic developer, are constantly integrated at a constant mixing ratio at this point, and in the development area (A), the magnetic developer A magnetic brush consisting of is reliably formed. The magnetic brush formed here rubs the surface of the photoreceptor drum (1), and develops the electrostatic latent image on the surface into a visible image. After being subjected to development, the developing sleeve (2)
Remove the magnetic developer remaining on the outer surface of the
It reaches the toner replenishing section (9) through the hole 11), where it is replenished with insulating magnetic toner and then used again for development.

As the developing bias, a DC voltage is applied to the developing sleeve (2) based on the usual method, but an AC voltage may be superimposed on this, or the developing sleeve (2) may be grounded. .

By the way, the amount of magnetic developer conveyed to the development area (A) is regulated by the height regulation plate (1), but the front regulation plate (5)
The pre-regulating gap formed by the developing sleeve (2) and the developing sleeve (2) is set to be larger than the brush height regulating gear and b, which are formed by the brush height regulating plate (4) and the developing sleeve 7 (2).
All magnetic particles pass through the pre-regulation camp and reach the empty chamber (7). Here, the magnetic particles regulated by the height regulating plate (4) and the insulating magnetic toner accumulate in the empty chamber (7) and are also mixed and stirred in the axial direction of the developing sleeve (2). In particular, the magnetic particles are stirred only within the empty chamber (7) and are not diffused into the toner supply tank (6) from the toner supply section (9). The toner concentration of the magnetic developer forming the magnetic brush in the development area (A) is determined by the amount of magnetic particles accumulated in the empty chamber (7). Therefore, the development area (A)
The toner concentration is always maintained at a constant value, and this toner concentration can be adjusted depending on the amount of magnetic particles loaded in advance into the empty chamber (7).

In the above development method, it is necessary that the pre-regulating gap allows a large amount of the magnetic developer to pass through the head height regulating camp. In other words, the front regulation cap must be large enough to allow all of the insulating magnetic toner containing magnetic particles to pass through, and the front regulation plate (5) must be large enough to pass through the empty chamber (7) and the toner supply tank (6).
A replenishment tank (
6) Prevent internal spread. If the front regulation gap is narrower than the height regulation gap, the magnetic flux (!
Magnetic particles accumulate in the pre-regulating plate (5), making it impossible to achieve good development. Furthermore, allowing the magnetic particles to accumulate in the empty chamber (7) not only ensures sufficient frictional electrification between the insulating magnetic toner and the magnetic particles when the magnetic developer passes through the empty chamber (7), but also prevents the axial Toner density unevenness in the direction is effectively eliminated.

Note that, in order to increase the developer conveying force of the developing sleeve (2), minute irregularities may be formed on the outer circumferential surface of the developing sleeve (2) by blasting or the like.

[Experimental Example 1] Using the above-described developing device, the present inventors changed the type of insulating magnetic toner and magnetic particles (ferromagnetic particles, binder-type magnetic particles), or changed the gap in the developing area (A), Various experiments were conducted by changing the developing conditions such as the height regulating gear knob and the height regulating gap, and good results were obtained for each. Here, some experimental examples will be described.

Experimental example-1 Ferromagnetic particles: 63.3 ut% of ferric oxide with an average particle size of 0 and 5 μm, 25.9 wL% of zinc oxide with an average particle size of Mixture 3 (10) containing 10.8 wt% of nickel and 1195 g of water were mixed to form a slurry, and 25 u+t of polymethacrylic acid sodium salt, Durban'7 (Product 8 manufactured by 2R T Pandelbilt) was added to the slurry. After adding and mixing 98g of % aqueous solution,
Spray dry with an atomizer and then heat to 1190'C in air.
After firing for 2 hours, ferrite [composition: (NiO)
,,=(ZnO),,,(Fe=03). , 85] was obtained by classification.

The average particle size is 50 μm, the coercive force is about O Oe, and the volume resistivity (measured under an electric field of 5X 102V/c111; all magnetic particles shown below are measured under this condition) is 1.
．． The true specific gravity is 4.8 at 1×10°Ω・C wire.

Binder-type magnetic particles: Styrene-acrylic copolymer resin, Hymer SBM73 (
(Product name: Sanyo Chemical) 100 parts by weight, magnetic iron oxide, R
B-BL (Product name: Titanium Kogyo Co., Ltd., average particle size 0.5-0
．． 6μ+n) 200 parts by weight and 4 parts by weight of carbon black were mixed in a ball mill for 20 hours, thoroughly mixed with three rolls, allowed to cool, and mixed in a feather mill for 5+++ m
After coarsely pulverizing and further finely pulverizing in a Gen) mill,
What I got from the classification.

The average grain size is 37 μm, the coercive force is 200 oersted, the volume resistivity is 1014 Ω·eIa, and the true specific gravity is 2°4.

Insulating magnetic toner (negatively chargeable): Styrene/acrylic copolymer resin, Braolite ACL (
100 parts by weight of magnetic iron oxide, KBC-1 (IOL (trade name: manufactured by Goodyear, product name: manufactured by Goodyear, average particle size 0.5-0.6.1/m), 81'1 part by weight, This product was obtained by kneading 4 parts by weight of a negatively chargeable charge control agent, TRH (trade name: manufactured by Hodogaya Chemical Co., Ltd.) and 2 parts by weight of carbon black, followed by pulverization and classification.

The average particle diameter is 13μω, the volume resistivity (measured under an electric field of 10″ to 7cm, all toners shown below are measured under these conditions) is 1×1015Ω・Cl3, and the true specific gravity is 1.65.
It is.

Preparation of magnetic developer: Using the thus obtained ferromagnetic particles, binder-type magnetic particles, and insulating magnetic toner, in a powder image transfer type electrophotographic copying machine equipped with the above-mentioned developing device, empty chamber (7) 60g of magnetic particles (ferromagnetic particles, binder type magnetic particles weight ratio 1)
: At the same time, the toner supply tank (mixture 6) is loaded.
) was loaded with insulating magnetic toner. In this case, the magnetic developer present in the development area (A) has a ratio of ferromagnetic particles: binder type magnetic particles: insulating magnetic toner in a ratio of 1:100:60 (weight ratio).

Development conditions Photoconductive layer: Se-based developing sleeve: Diameter 24+111n, aluminum rotation speed 80 rpm Magnetic roller: 8 poles, magnetic flux density 800 Gauss rotation speed?
OOrp+.

Front regulation cap: 1.0 basket 1111 Height regulation gap: 0.35aui Development gap: 0.45m Photosensitive ram circumferential speed: 11cm/see Electrostatic latent image maximum potential: 6oov Development bias: DC 200V More than experimental results When we conducted a copying experiment using the same magnetic developer under the developing conditions, there were no white streaks or toner fog in the developed image.
A copy image with sufficient image density was obtained. In addition, the reproducibility of fine lines is sharp, there is no adhesion of ferromagnetic particles or binder-type magnetic particles to the photoconductor, and even when 60,000 A4 size copies are made, images are as good as the initial one. It was done.

On the other hand, the mixing ratio of ferromagnetic particles and binder-type magnetic particles in the magnetic particles loaded into the empty chamber (7) is N)
:190 to 190:1 (I experimented under the above-mentioned development conditions by varying the content of ferromagnetic particles in the range of 0 to 70%, but
If the amount was less than 10 u+t%, the conveyance of the magnetic particles decreased, resulting in insufficient image density. Moreover, when it exceeded 70 wt%, agglomeration of the magnetic developer and generation of self-streaks on images were observed.

In this case, the amount of magnetic particles loaded into the empty chamber (7) is such that the mixing ratio of magnetic particles and insulating magnetic toner in the magnetic developer present in the development area (A) is 20 in terms of weight ratio.
The experiment was conducted with the amount adjusted appropriately to ensure that it was within the range of 0:60±20. Specifically, it was adjusted within the range of 40 to 100 g.

Experimental Example-2 Ferromagnetic particles: Same as in Experimental Example-1 Binder-type magnetic particles: Same as in Experimental Example-1 Insulating magnetic toner (positively chargeable): Styrene-acrylic copolymer resin, Hymer SBM73 (
(Product name: Sanyo Chemical) 100 parts by weight, magnetic iron oxide, R
B-BL (Product name: Titanium Kogyo, average particle size 0.5-
(1,6μ+o) 60 parts by weight, a positively chargeable charge control agent,
Nigrosine Base EX (product name: Orient Chemical) 5
parts by weight and 3 parts by weight of carbon black were kneaded, crushed,
What I got from the classification.

The average particle size is 14μm, and the volume resistivity is 2×1015Ω・
am, and the true specific gravity is 1.5.

Preparation of magnetic developer Same as in Experimental Example-1 above, and the magnetic developer present in the development area (A) has the following ratio: Ferromagnetic particles: Binder-type magnetic particles: Insulating magnetic toner 100:100:50 (weight ratio) is in a state of

Development conditions: Highest potential of electrostatic latent image: -600V Development bias: DC -25 (l) V pond conditions were the same as in Experimental Example 1. Experimental Results: Similar to Experimental Example 1, a good image was obtained.

Comparative Example-1 Experiment was carried out under the same conditions as Experimental Example-1 except that the ferromagnetic particles 10 (lFi obtained in Experimental Example-1 were changed to be loaded into the empty chamber (7) of the developing device described above). did.

In this case, the magnetic developer present in the development area (A) has a ratio of ferromagnetic particles to insulating magnetic toner of 100:20 (weight ratio).
It was in a state of ``.

As a result of the experiment, the magnetization of the magnetic developer as a whole was strong, and many white streaks were observed in the image. Furthermore, fine line reproduction was insufficient.

Comparative Example-2 An experiment was conducted under the same conditions as Experimental Example-1, except that 40 g of the binder-type magnetic particles obtained in Experimental Example-1 were loaded into the empty chamber (7) of the developing device described above. . In this case, the magnetic developer present in the development area (A>) was in a state of ``binder-type magnetic particles:insulating magnetic toner'' (weight ratio) of 100:413.

The results of the experiment showed that the image density was insufficient and adhesion of binder-type magnetic particles to non-image areas was observed.

Effects of the Invention As is clear from the above explanation, the present invention includes ferromagnetic particles made of a ferromagnetic material as magnetic particles loaded on the outer peripheral surface of the developing sleeve during development with an insulating magnetic toner.
Because it is characterized by using a mixture with binder-type magnetic particles made by dispersing magnetic fine powder in a binder resin,
It is possible to form soft magnetic brush ears, and at the same time, the aggregation of ferromagnetic particles is prevented, which further improves the conveyance of the magnetic developer, resulting in high-density, fine-grained, sharp images. This provides an excellent effect in that there is no adhesion of the magnetic particles to the surface of the electrostatic latent image carrier or the occurrence of white streaks due to aggregation of the magnetic particles.

[Brief explanation of the drawing]

The drawing is a sectional view showing a developing device for carrying out the electrostatic latent image developing method according to the present invention. (A)...Development area, (1)...Photosensitive drum, (
2)...Developing sleeve, (3)...Magnetic roller, (
4)...Hot height regulation plate, (5)...Front regulation plate, (6)
...Toner supply tank, (7)...vacant. Patent applicant Minolta Camera Co., Ltd.

Claims (1)

[Claims] (1) Supplying an insulating magnetic Y agent to the magnetic particles attached to the outer circumferential surface of the developing sleeve. An electrostatic latent image developing method in which a magnetic developer consisting of a mixture with a magnetic toner is prepared, and the prepared magnetic developer is used to develop an electrostatic latent image carried on the surface of an electrostatic latent image carrier. An electrostatic latent image developing method, characterized in that, as the magnetic particles, a mixture of ferromagnetic particles and baying type magnetic particles formed by dispersing magnetic fine powder in an inder resin is used.