JPS62168162A - Electrophotographic method - Google Patents

Abstract

PURPOSE:To obtain excellent development characteristics free from ground fogging and inversion fogging by sticking a negatively charged particle group positively on an image carrier when no image is formed. CONSTITUTION:A latent image is erased on the surface of a drum 1 and the entire surface is held almost at 0V. A DC potential difference of about +400V based upon a sleeve 6 is generated on the surface of the drum and a particle group having the opposite polarity sticks on the drum 1 and is removed from the sleeve 6. When no image is formed while the particle group with the opposite polarity is removed by a cleaning member 15, a control means 11 turns off a transfer charger 14 and the particle group with the opposite polarity is guided on the drum surface to the member 15.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an electrophotographic method, and particularly to an electrophotographic method using a one-component magnetic toner as a developer.

[Description of prior art]

As the electrophotographic method, US Pat.
Various methods are described in Japanese Patent No. 24748, etc., but all of these methods apply electrostatic charges to the surface of a photoreceptor having a photoconductive layer by means such as corona discharge, and remove the charged photoconductive layer. An electrostatic latent image is formed by irradiating a light image corresponding to the original, and then colored fine powder called toner having the opposite polarity is deposited on the electrostatic latent image to remove the electrostatic latent image. After developing the image and transferring the toner image to a transfer material such as paper as necessary, it is fixed by heat, pressure, solvent vapor, etc. to obtain a copy.

The process of developing the electrostatic latent image involves attracting toner particles charged with a polarity opposite to that of the latent image by electrostatic attraction and making them adhere to the electrostatic latent image. Methods for developing images using toner can be roughly divided into:
There is a method using a so-called two-component developer in which a small amount of toner is dispersed in a medium called a carrier, and a method using a so-called one-component developer in which the toner is used alone without using a carrier.

The method using a two-component developer is to charge the toner and carrier to different polarities by stirring and rubbing the toner and carrier, and there are two methods: a cascade method using glass beads as a carrier, and a magnetic brush method using iron powder as a carrier. There are laws etc. In either case, the toner in the developer maintains its charged state during the development process and is gradually consumed during image formation, so if the toner content falls below the optimum content, the image density will decrease and the image will become faint and faded. but also
The carrier may adhere to the photoreceptor or paper surface, causing various defects. In addition, if an excessive amount of toner is contained, the amount of toner adhering to the image will increase, which will increase the image density, but it will also cause "graininess", "capri" in non-image areas, "poor cleaning", etc. Electrostatic repulsion between toner particles tends to cause scattering and contamination inside the device. Therefore, during development, it is necessary to replenish toner and maintain the content in the developer always within a certain range.

In order to eliminate these problems with two-component developers, development methods using various one-component developers have been proposed and put into practical use. Among these methods, there are many excellent methods that use magnetic toner as a developer, but in particular, a method in which a thin layer of insulating magnetic toner is applied onto a developing sleeve, triboelectrically charged, and then subjected to the action of a magnetic field. A method of developing an electrostatic latent image by making it face extremely close to the electrostatic latent image and causing toner to fly has been put to practical use as a method for obtaining excellent images.

However, the method using -component magnetic ratio toner has the disadvantage that the tribocharge amount of the toner particles coated on the sleeve is significantly smaller than the tribocharge amount of the toner particles in a two-component developer. are doing. That is, the charging of toner in a two-component developer involves, firstly, frictional mixing with carrier particles, and other contact opportunities such as frictional contact with the developing sleeve and friction with the side wall of the developing device. Therefore, it can have a fairly high amount of charge. On the other hand, since the dominant factor in triboelectric charging in -component magnetic toner is only the contact between the toner and the developing sleeve and the contact between toners, the amount of charge of -component magnetic toner is different from that of toner in two-component developer. Compared to/"
・It becomes thinner. When a magnetic toner that retains only a weak amount of charge as described above is used, image defects are likely to occur.

Further, the magnetic toner on the developing sleeve is affected by the magnetic force between the toner and the magnet disposed inside the sleeve,
held on the sleeve. Therefore, since the magnetic toner near the surface of the developing sleeve can directly rub against the sleeve, it can have a relatively high amount of charge.
As the contact with the sleeve is reduced, the magnetic toner in the upper layer, which is also separated from the developer sleeve and is only charged by friction between the toners, can only obtain a weak charge.

When a magnetic toner having such variations in the amount of charge is used, image deterioration such as blurring and density unevenness is likely to occur. (Here, "ground strength blur" refers to the bright area potential (VL) of the part of the latent image carrier that is hit by light during the development process.
A phenomenon in which excess toner adheres to the surface and causes fogging. ) In order to eliminate the drawbacks of the developing method using -component magnetic toner, attempts have been made to use additives with a polarity opposite to that of the toner in order to improve the charging ability of the magnetic toner, but due to durability There is a problem in that additives of opposite polarity accumulate and cause image deterioration such as reverse fog.

(Here, "inversion fog" refers to L
EDl This is a phenomenon in which when a stronger light is emitted onto the latent image carrier using a fuse run or the like to give a potential (VSL) lower than V2, excess toner adheres to this area and causes it to become covered. ) Also, as a method for fixing developed toner images, the hot roll fixing method has recently been widely used.
For the purpose of improving offset resistance, attempts have been made to add low molecular weight polyolefins internally and externally. However, when a low molecular weight polyolefin is externally added to a positively charged magnetic toner, although the offset resistance is certainly improved, since the low molecular weight polyolefin has negative chargeability, the increase in reversal fog due to durability is reduced. There are problems such as sleeve contamination and image quality deterioration due to accumulation of molecular weight polyolefin.

[Purpose of the invention]

The present invention aims to solve the above-mentioned problems in electrophotography using a one-component magnetic toner as a developer.

That is, the main object of the present invention is to provide an electrophotographic method with excellent development characteristics free of background blur and reversal fog.

Another object of the present invention is to provide an electrophotographic method that can obtain excellent images with high density from the initial stage.

Another object of the present invention is to provide an electrophotographic method that does not cause an increase in reverse fog, sleeve contamination, or image quality deterioration due to durability.

[Structure of the invention]

The inventor of the present invention has obtained the above-mentioned knowledge as a result of intensive research to overcome the above-mentioned problems in electrophotography using conventional one-component magnetic toner and achieve the above-mentioned purpose. Based on this, the present invention was completed.

That is, the present invention is an electrophotographic method using a one-component developer consisting of at least a positively charged magnetic toner and a negatively charged low molecular weight I lyolefin as an additive, which does not form an image on a latent image carrier. The present invention sometimes relates to an electrophotographic method characterized by actively attaching negatively charged particle groups to the latent image carrier.

The findings obtained as a result of extensive research by the present inventors are summarized as follows.

When a negatively charged low molecular weight polyolefin is added to a positively charged magnetic toner as a developer, when the magnetic toner is placed on a developing sleeve, friction between the magnetic toner and the developing sleeve and the magnetic toner In addition to mutual friction, the friction between the magnetic toner and the negatively charged low molecular weight polyolefin is an important factor that can ensure that the magnetic toner has a sufficient amount of charge.
The occurrence of soil burrs due to variations in the amount of charge is prevented.

Additionally, in general, when a large amount of fine magnetic toner particles are present,
It is known that the negative charge, low molecular weight polyolefin, causes the above-mentioned soil retention, and the positively charged magnetic toner, which is the cause of the soil retention, is selected by Coulomb force because the fine particles have a large amount of charge. Attach it to
Prevents blurring and improves image quality.

However, if particles of opposite polarity are present in the developer used for image formation, they will adhere to the bright areas of the latent image, causing blurring. Further, in order to erase images in specific areas for the purpose of multiple copying, multicolor copying, etc., a potential (vsL) lower than the bright area potential (VL) is applied, but when the developing bias is set to VDC, l Voc
The degree of reverse fog that occurs varies depending on the magnitude of Vst and l. The higher the proportion of particles of opposite polarity existing alone, the more l VDC-V
From the point when the value of SL l is /'', reverse fogging tends to occur. However, if negatively charged particles are actively adhered to the latent image carrier when no image is being formed, the negatively charged particles cause the ground force blur and reversal force blur. is removed from the sleeve to prevent negatively charged particles from adhering to the image area.

The negatively charged low molecular weight polyolefin to be added to the positively charged magnetic toner used in the electrophotographic method of the present invention includes:
Polyethylene, polypropylene, chlorinated polyethylene, copolymers thereof, or mixtures thereof can be used.

When the negatively charged low molecular weight polyolefin is placed on the developing sleeve, it is charged in the same polarity as the electrostatic latent image, so it receives a repulsive force due to Coulomb force, and also receives a charge of the opposite polarity to that of the positively charged toner. Because of this, it is subjected to attractive force due to Coulomb force. Therefore, the amount of charge, particle size, surface properties, etc. of the low molecular weight polyolefin have a large influence.

For these reasons, the low molecular weight polyolefin used in the present invention has a polarity opposite to that of the positively charged magnetic toner and is well dispersed in the magnetic toner when measuring the amount of charge by the two-component mesh method. something desirable. That is, the charging R(q/M) by the two-component mesh method
is IQ/M I≦50, preferably −1≧
It is desirable that Q/M≧−30. In the case of <−50, the low molecular weight polyolefin itself will be charged up, and it is likely to become permanently stuck to the developing sleeve. Incidentally, the amount of charge is measured by the two-component mesh method in the present invention as follows. That is,
The test substance is thoroughly mixed with an iron powder carrier having a particle size of 200/300 in a ratio of 1=10. The mixture 0.
5~1.5!1! - is accurately weighed and aspirated with a pressure of 25 cr ILH20 on a 400 mesh metal screen connected to an electrometer. At this time, the amount of toner separated and attracted, the amount of charge indicated by the electrometer, and the amount of charge per unit weight are determined.

Further, the volume average particle diameter dv of the low molecular weight polyolefin used in the present invention is usually 1 to 30μ, preferably 2 to 20μ.
μ is preferable. When dv exceeds 30, the surface area becomes large, and a large amount of positively charged magnetic toner adheres to the toner, resulting in an increase in ground force blur. On the other hand, if dv is less than 1, the fluidity will be very poor and image deterioration such as a decrease in density will occur. In addition, the volume average particle diameter dv in the present invention is Coulter Kakuntar TA type 11 (aperture diameter 10
0μ).

As mentioned above, in the present invention, when an image is not formed, negatively charged particles are actively attached to the latent image carrier, so these negatively charged particles are present in the image area during development. It's getting harder to do. Therefore, the additive 7In of the low molecular weight polyolefin to the positively charged magnetic toner
Although the permissible range of fU is considerably wider than conventional ones, it is usually desirable to set it to 0.1 to 10% by weight, preferably 0.2 to 5% by weight.

If the amount of low molecular weight polyolefin added exceeds 10% by weight based on the positively charged magnetic toner, the offset resistance will decrease.
The image density may be clearly improved, or the image density may be significantly reduced, and image quality deterioration such as fogging during formation of a latent image is likely to occur.

On the other hand, if it is less than 0.1% by weight, it will be difficult to uniformly disperse it in the magnetic toner, and it will not only have no anti-offset effect, but will also tend to cause a decrease in density, especially in the initial stage. .

The positively charged magnetic toner used in the present invention contains a magnetic material in a binder resin.

As a binder resin for the magnetic toner used in the present invention, c. a monopolymer of styrene and its substituted products such as polystyrene, polyp-chlorostyrene, and polyvinyltoluene: styrene-
p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer,
Styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer,
Styrene-butyl methacrylate copolymer, styrene-acrylic-aminoacrylic copolymer, styrene-aminoacrylic copolymer, styrene-alpha chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl Methyl ether copolymer, styrene-vinylethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer,
Styrenic copolymers such as styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer: polymethyl methacrylate, polybutyl methacrylate, polychloride Vinyl, polyvinyl acetate, polyethylene, polyglopylene, polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin,
Terpene resins, phenolic resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffins, paraffin waxes, etc. can be used alone or in combination.

In addition, the magnetic substances contained in the binder resin include ferromagnetic elements, alloys containing these, and compounds such as magnetite, hematite, and ferrite, such as iron, cobalt, nickel,
Alloys and compounds of manganese and other ferromagnetic alloys can be used as appropriate.

The particle size is 100 to 800 mμ, preferably 300 mμ.
~ soo mμ, 30-70 for polymer particles
% by weight preferably 40-65% by weight preferably 50% by weight
The content is preferably 60% by weight.

In addition, this magnetic toner contains a charge control agent, a flow modifier,
The present invention is not hindered in any way even if a coloring agent, a lubricant, etc. are added and contained as necessary.

When the binder resin is made to contain a magnetic substance and formed into particles, the particle size is preferably 5 to 20 microns, which is the general toner particle size.

In the production of the positively charged magnetic toner used in the present invention, the constituent materials are thoroughly kneaded using a heat kneader such as a heated roll or a kneader-1 extruder, and then mechanically pulverized and classified. A method is obtained by dispersing a material such as magnetic powder in a binder resin solution and then spray-drying it, or a method in which a prescribed material is mixed with the monomers that should constitute the binder resin, and then this emulsified suspension is polymerized. Various methods such as polymerization toner manufacturing methods for obtaining magnetic toner can be applied.

The electrophotographic method of the present invention provides particularly remarkable effects when using a magnetic toner obtained by suspension polymerization or a microcapsule toner having a core material and a wall material. That is, in a magnetic toner or a microcapsule toner obtained by a suspension polymerization method, the magnetic powder ratio inevitably becomes small on the fine powder side due to problems with the dispersibility of the magnetic powder. Therefore, it is also having a negative impact on shi and yellowtail, which have been charged up due to the influence of fine powder. If the manufacturing process includes heat kneading, pulverization and classification, it is possible to cut out the fine powder that causes image quality deterioration in the classification process and reuse the cut classified fine powder, but magnetic toner obtained by suspension polymerization Moreover, it is quite difficult to reuse microcapsule toner.

However, according to the electrophotographic method of the present invention, even in the case of toners or microcapsule toners obtained by suspension polymerization that tend to contain fine powders, it is possible to efficiently prevent the occurrence of burrs caused by fine powder toners. The developer used in the present invention is obtained by adding and mixing a negatively charged low molecular weight polyolefin to the above-mentioned positively charged magnetic toner. , a V-type mixer, a tarpaulin mixer, or a fixed container mixer such as a pump type, a scree type, a rotary blade type, or the like can be used as appropriate.

In the electrophotographic method of the present invention, methods for cleaning the latent image carrier from the particles of opposite polarity attached to the latent image carrier or the developer remaining after transfer include blade cleaning, fur brush cleaning, magnetic brush cleaning, etc. However, the blade cleaning method is particularly preferable because the lubricant of negative polarity is actively deposited on the latent image carrier, and when no latent image is formed, the lubricant is uniformly deposited on the photoreceptor surface, so the latent image carrier is Body filming is prevented.

Hereinafter, typical examples of the electrophotographic method of the present invention will be described in more detail with reference to the drawings, but the present invention is not limited thereto.

FIG. 1 is a sectional view schematically showing a copying apparatus to which an example of the electrophotographic method of the present invention is applied.

In the figure, 1 is a photosensitive drum (hereinafter simply referred to as "drum") which is a latent image carrier.After being uniformly charged over the entire surface by a corona discharger 2 via a voltage applying means 10, The optical information that has passed through the lens array 3 is irradiated onto the surface of the drum 1, forming an electrostatic latent image.

Reference numeral 4 denotes a developing container, which includes a developer 5 and a developing sleeve 6 (hereinafter simply referred to as "sleeve") that supports the developer 5. Sleeve 6 is approximately 30 mm from drum 1.
They are arranged with a narrow interval of 0 μm, and the drum 1 is placed in the developing section 8.
A Fugnet roller 4 having a developing magnetic pole is disposed inside the sleeve 6, which rotates in the same direction as the roller.

A magnetic blade 7 is disposed above the sleeve 6, and the developer 5 is regulated by the magnetic blade 7, and the toner is carried on the sleeve 6 in a single layer having a thickness of about 70 μm. In the developing section 8, a voltage is applied between the drum 1 and the sleeve 6 via the voltage rigidity means 9.
The magnetic toner carried on the drum 1 adheres to the latent image on the drum 1 and is developed. The voltage application timing of the voltage application means 9 and the above-mentioned voltage application means 10 to the corona discharger 2 is controlled by a control means 11 which takes timing using a clock pulse.

A recording paper 13 is fed by a registration roller 12 in synchronization with the rotation of the drum 1, and a developed image is transferred onto the recording paper 13 by a transfer charger 14. The transferred image is then fixed by a fixing member (not shown).

After the transfer, the magnetic toner remaining on the drum 1 is removed by the cleaning member 15.

The above is an outline of a copying apparatus to which the electrophotographic method of the present invention can be applied.Next, the developing step in the electrophotographic method of the present invention will be described in more detail.

In the developing section 8 of the embodiment shown in FIG. 1, an alternating voltage with a frequency of 1800 Hz and a peak open voltage of 1400 V and a developing bias DC voltage are applied between the drum 1 and the sleeve 6. That is, during image formation, a dark area voltage of about -700V and a light area voltage of about -200V are applied to the surface of the latent image carrier.
A latent image is formed, and the latent image is developed by alternating voltage and direct current voltage applied on the sleeve.

The DC voltage during image formation is approximately -200% of the bright area voltage of the latent image.
-250V to -300V is applied, which generates a potential difference of 50V to 100V with the opposite polarity to V. Here, if the magnetic toner has sufficient triboelectricity, the magnetic toner will not adhere and no ground force blur will occur due to the potential difference having the opposite polarity to the bright portion of the latent image, that is, the same polarity as the magnetic toner.

However, if particles of opposite polarity are present in the developer used for development, they will adhere to the bright areas of the latent image and cause blurring.

That is, it is necessary to remove the opposite polarity particle group by the following means.

FIG. 3 shows the relationship between the DC potential difference between the drum 1 and the sleeve 6 and the image density of the developer attached to the drum 1 when the alternating voltage is applied. The central part of the graph shown in Figure 3 Ov
indicates that drum 1 and sleeve 6 have the same voltage,
The ease with which the latent image is developed is shown on the right side of the OV, and the ease with which the reversal toner adheres to the four parts of the image is shown on the left side of the OV.

As is clear from Figure 3, drum 1
It can be seen that the amount of reversed toner adhering to the image begins to increase.

That is, in the embodiment of the present invention, by applying a developing bias of 350 V or more DC when no image is being formed, negatively charged particle groups can be actively deposited on the latent image carrier. can.

Next, the developing method of the present invention will be explained in more detail.

FIG. 2 shows an example of the developing bias DC voltage applied to the sleeve and the timing of application.

When an image is not formed, a developing bias with a frequency of 1800 Hz, a peak open voltage of 1400 V, and a DC component of -400 V is applied. Control of switching between the image area and the non-image area of the DC voltage is performed by the control means 11.

The latent image on the surface of the drum 1 has been erased and the surface is approximately QV. Approximately +4 on the drum surface based on sleeve 6
A DC potential difference of 0.00 V exists, and as can be seen from FIG. 3, +400 V (> +350 V) tends to adhere to the drum 1 from the sleeve 6. Therefore, the opposite polarity particles adhere to the drum 1 and are removed from the sleeve 6.

Here, the opposite polarity particles adhering to the drum are removed by the cleaning member 15. Since this is the time when no image is to be formed, the control means 11 controls the transfer charging device 4 to be turned off, and the fine particles of opposite polarity are guided to the cleaning member 15 while remaining attached to the surface of the drum 1. Let it happen.

According to this method, since the reverse polarity particles are actively removed from the sleeve 6 when an image is not formed, it is possible to remove the reverse polarity particles caused by the negatively charged low molecular weight polyolefin, and the reverse polarity particles are firmly attached to the reverse polarity particles. The particulate toner particles adhering to the drum can be removed while performing normal copying operations, and since the latent image has been erased, the particles of opposite polarity are evenly deposited on the drum, which is advantageous in terms of cleaning performance such as preventing filming. be.

Incidentally, the developing method in the present invention is not limited to the above example, and any developing method may be used as long as it uses magnetic force or the like to actively adhere particles of opposite polarity to the drum when no image is formed. It is something.

〔Example〕

The electrophotographic method of the present invention will be explained in more detail below using Examples 1 to 4 and Comparative Examples 1 to 4, but the present invention is not limited thereto.

Example 1 The above mixture was kneaded at 150° C. using a roll mill, cooled, and then coarsely ground using a speed mill. Thereafter, the powder was finely pulverized with a jet mill and classified into powders with a size of 5 to 20 μm using an air classifier to obtain a positively charged magnetic toner. The charge amount of the toner is 16
, 3 μC/0 The above positively charged magnetic toner was coated with a substantially colorless polyethylene resin (volume average particle size 8.3 μC, charge amount -15.6 μC/
y) 0.6% and colloidal silica 0.5% were mixed to prepare a developer.

When images were formed using this developer by a combination of the above-mentioned developing method and a fixing method using a hot roll fixer for a Canon copier NP 150Z, there was some ground blurring from the initial to the 20th sheet. However, after that, neither ground force blur nor reverse fog was observed up to 50,000 sheets, including when replenishing the developer. Also,
From the initial stage up to 50,000 sheets, the image density was good at 1.3 to 1.4, including when replenishing the developer. In the middle,
When the latent image carrier was observed under an optical microscope in a state where no image was formed, it was found that 2 to 5 black fine particles were attached to the transparent particles, which were recognized to be polyethylene particles. , were observed in random proportions.

Comparative Example 1 An image was formed in the same manner as in Example 1 except that only the positively charged magnetic toner used in Example 1 was used as a developer.
Significant yellowtail was observed from the height of the fish. When the bright area (non-image area) on the latent image carrier was observed with an optical microscope while an image was being formed, a large number of black fine particles were observed.

Comparative Example 2 Volume average particle size 3.2μ, charge 151-51.5μc/,
Example 1 except that colorless polyethylene resin powder of
When I printed the image in the same way as above, the image density started to decrease after about 200 sheets. When the developing sleeve was inspected after 500 sheets had been produced, white powder, which appeared to be polyethylene resin, had adhered to it.

Comparative Example 3 When image formation was carried out in the same manner as in Example 1 except that 0.09% of a polyethylene resin with a volume average particle size of 8.3μ and a charge amount of -15.6μCh was used, the initial density was as low as 1.05. Ta. When about 200 more sheets were printed, the offset was severe and a large amount of toner adhered to the fixing roller.

Comparative Example 4 When image printing was carried out in the same manner as in Example 1 except that 11% of the polyethylene resin used in Example 1 was used, reverse fog and ground force blur were noticeable from the beginning and did not disappear until about 500 sheets. . A decrease in concentration was also observed, with an extremely large amount of white powder.

Example 2 1.2 for the polyethylene resin glue used in Example 1
% polypropylene resin (volume average particle size 10.5 μm, charging ffl -25.2 μC) was carried out in the same manner as in Example 1, and good results were obtained as in Example 1.

Example 3 The above mixture was kneaded at 150° C. for about 30 minutes using a roll mill, and 30 parts by weight were dispersed with 50 parts by weight of THP in a ball mill pot to obtain a THP suspension having a particle size of 5 to 15 μm. This suspension is Suspension A
And so. Separately, suspension B was prepared by ball milling 100 parts by weight of THF and 20 parts by weight of styrene-diethylaminomethacrylate copolymer.

Susbenjin Al00ju FF Part 1 Tosusbanjen B
While stirring 50 parts by weight of THF and 100 parts by weight of THF in a stirring tank, ion-exchanged water was added dropwise to precipitate an outer wall around the particles made of polyethylene and magnetic material to form a microcapsule toner (DV=10.8μ, 6.35 in number distribution
30% below μ and 4.3% above 20.2 μ in volume distribution. The amount of charge of this toner was 19.8μ.

To 100 parts by weight of the above magnetic microcapsule toner, 0.7% of polypropylene fine particles (volume average particle size: 8.9μ, charge amount: -14.3μC, /p) and 0.5% of colloidal silica were mixed to prepare a developer. . When this developer was used to produce an image as in Example 1, good results were obtained as in Example 1.

Example 4 was kneaded and mixed for about 30 minutes in a container equipped with a high shear mixing device such as a TK Homomixer (manufactured by Tokushu Kogyo Co., Ltd.). During this time, the temperature rose to about 55°C. During this time, the magnetic powder was uniformly dispersed in the styrene monomer. Separately, 2,000 ml of P water and polyvinyl alcohol as a dispersion stabilizer were put into a TK homo mixer, and the above slurry was put into a system maintained at 70°C while stirring with the TK homo mixer.
Stirred for 30 minutes at 4000 rpm. Thereafter, this reaction mixture system was stirred with paddle blade stirring to complete the polymerization. After washing with water, filtering and drying, the volume average diameter is 11.0μ, the number distribution is 6.35μ or less 21%, and the volume distribution is 20.2μ or more 5%.
I got the toner. The amount of charge of this toner is +11.6μc
/,Met.

Polyethylene resin (volume average particle diameter 8.3μ, charge amount -15.6μC/y) per 100 parts by weight of the above magnetic toner.
) 0.6% and colloidal silica 0.5% were mixed to prepare a developer. Using this developer, image formation was carried out as in Example I, and as in Example 1, good results were obtained.

[Summary of effects of the invention]

When an image is formed using the electrophotographic method of the present invention, a high-density image can be maintained from the initial stage, and a high-quality image without reversal fog can be obtained.
It is also possible to prevent the occurrence of soil strain due to durability.

[Brief explanation of drawings]

FIG. 1 shows one of the copying apparatuses to which the electrophotographic method of the present invention is applied.
FIG. 2 is an explanatory diagram showing the timing of application of DC voltage to the sleeve and charging by a corona discharger in the embodiment of the present invention; FIG. The figure is an explanatory diagram showing the relationship between the DC potential difference between the drum and the sleeve and the toner concentration. Regarding Figure 1,

Claims (6)

[Claims] (1) An electrophotographic method using a one-component developer consisting of at least a positively charged magnetic toner and a negatively charged low molecular weight polyolefin as an additive. An electrophotographic method characterized by actively attaching negatively charged particles to an image carrier. (2) A one-component developer in which a magnetic toner has a volume average particle size of 5 to 20 μm and a low molecular weight polyolefin having negative chargeability has a volume average particle size of 1 to 30 μm is used. Electrophotography according to scope item (1). (3) The electrophotographic method according to claim (1), wherein the magnetic toner is manufactured by a manufacturing process including thermal kneading, pulverization, and classification. (4) The electrophotographic method according to claim (1), wherein the magnetic toner is produced by a suspension polymerization method. (5) The electrophotographic method according to claim (1), wherein the magnetic toner is a microcapsule toner consisting of a core material and a wall material. (6) The electrophotographic method according to claim (1), which comprises the step of fixing the developed and transferred magnetic toner image by a thermal heat roll fixing method.