JPH0432881A - Electrophotographic developing device - Google Patents

Abstract

PURPOSE:To make a developer supplied to a supporting body into a thin layer having a uniform density and to obtain an excellent image without having irregularities in an image, etc., when development is carried out by providing an electret layer and a magnet on a doctor blade. CONSTITUTION:A developer quantity regulating member 20 has the magnet 41 and the electret dielectric layer 40, the magnet 41 of the developer quantity regulating member 20 has the polarity reverse to that of the magnet part of a carrying member 16 facing each other, and the electret layer 40 has the polarity reverse to the electrifying polarity of a electrifying developer. The potential of the electret 40 of the blade 20 has the polarity reverse to the electrifying polarity of the developer 18, so that the developer 18 is electrically attracted to the surface of the electret 40, the developer layer 18 on the sleeve 16 in an extending state passes through a gap for cutting nap. Therefore, the precision of the gap for cutting nap has room, the density of the developer 18 is uniformized, and the electrifiability of the developer 18 is uniformized, as well. Thus, the excellent image without having density irregularities, fogging, etc., can be formed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electrophotographic developing device.

More specifically, by forming the developer magnetic brush formed on the surface of the developer transporting member into an even and sufficiently thin layer, image area blurring during development can be eliminated, and density unevenness and fogging can be prevented. The present invention relates to a developing device that can form excellent images.

(Prior art) In the early development devices, there were those that sprayed developer directly onto the electrostatic image support, that is, the photoreceptor, etc., but in the current commercial electrophotographic development devices, The developer is supplied to the latent image portion of the photoreceptor through a developer conveying member, ie, a sleeve or the like. In such a developing device, the surface of the sleeve etc. is magnetized, the developer is made of a magnetic material, and a magnetic brush, a magnetic brush, etc. are attached to the sleeve surface.
That is, a developer layer is formed. Such a developer layer may be a two-component developer consisting of a mixture of a magnetic carrier and electrostatic toner, or a one-component magnetic developer itself containing magnetic powder, which is applied in an electrically charged state by a sleeve. It is moved to the surface of the photoreceptor and is transferred to the latent image area by rubbing against the surface at a bias potential.

In addition, a developer amount regulating member (doctor blade) is provided close to the sleeve surface, and the doctor blade scrapes off the magnetic brush tip of the flowing developer to control the amount of developer supplied to the photoreceptor surface. It is regulated. The purpose of the doctor blade is to form a magnetic brush in a thin and uniform layer to prevent fogging or density unevenness caused by supplying too much developer.

(Problems to be Solved by the Invention) In the conventional one-component developing method, an aluminum blade is used as a doctor blade, and the cutting gap (distance between the sleeve and the blade) is about 100 μm. However, such a conventional developer amount regulating member has the following problems.

j[1] The conventional doctor blade only physically restricts the developer, and there is no margin for precision (tolerance) of the cutting gap. I have no choice but to tighten the installation. Therefore, if the blade is not properly adjusted, fogging and the like are likely to occur.

The second problem is that the developer is sent to the blade after being stirred, but the developer is sent to the blade with uneven density or concentration depending on the stirring state, and the blade ends up merely physically processing the developer.

A uniform developer layer or magnetic brush may not be formed on the sleeve. In such a case, the image quality becomes non-uniform during development. The third problem is that the developer sent to the blade may have an uneven charge state, and since the developer is not electrically processed by the blade, uncharged particles are carried to the photoreceptor. It contains a large proportion of developer. Therefore, the image becomes non-uniform during development.

The fourth problem is that a developer of opposite polarity (
(same polarity as the photoreceptor), and if such developer is passed through a conventional blade to the photoreceptor, it will cause image quality degradation and artifacts during development.

In addition, in view of this, there are conventional blades in which the blade is made of a magnet, and it has been proposed that the magnet magnetically attracts the magnetic developer. however,
When such a magnet is used in a blade, it can be expected to have some effect, but it is not easy to provide a sufficient margin for the cutting gap and form a sufficiently thin developer layer on the sleeve.

Therefore, an object of the present invention is to provide a developing device capable of accurately feeding a powder developer to a support supporting an electrostatic image and forming an excellent image without image disturbance, density unevenness, fog, etc. during development. Our goal is to provide the following.

Another object of the present invention is to provide a developing device that can form a sufficiently thin layer of developer by providing a sufficient margin in the cutting gap between the developer amount regulating member and the developer transporting member. be.

It is a further object of the present invention to make the density of the developer layer on the sleeve uniform, to reduce the proportion of uncharged developer supplied to the photoreceptor, and to reduce the proportion of developer supplied to the photoreceptor of opposite polarity. Therefore, it is an object of the present invention to provide an electrophotographic developing device that can form excellent images during development.

(Means for Solving the Problems) According to the present invention, there is provided a support for supporting an electrostatic image, a mechanism for charging a powder developer, and a surface of the charged magnetic powder developer by a magnetic attraction force. a developer transporting member that holds and transports the developer and applies the developer to the electrostatic image area of the support; and a developer amount regulating member that is close to the transporting member and adjusts the amount of developer supplied. The regulating member has a magnet and an electret dielectric layer, and the magnet of the developer amount regulating member has a polarity opposite to that of the magnet portion of the opposing conveying member, and the electret layer has a magnet of the charged developer. A developing device is provided which is characterized by having a polarity opposite to that of a charging electrode.

Further, the present invention may be characterized in that the elect-left layer is made of a fluorine resin.

As the developer, a two-component developer consisting of a magnetic carrier and an electrostatic toner can be used, or a one-component toner containing WL powder can also be used.

(Function) In the present invention, a developer conveying member (hereinafter referred to as a sleeve) has a magnet inside and an electret layer on the surface.
A developer layer or this magnetic brush is formed on the sleeve, and a developer amount regulating member provided close to the sleeve thins the developer layer and makes its density uniform. After making the amount of charge uniform, it is sent to an electrostatic latent image support (hereinafter referred to as a photoreceptor). A magnet within the sleeve is necessary to transport the developer material in the form of a magnetic brush and into contact with the photoreceptor. Electret is a dielectric material that exhibits permanent electric polarization, and in the present invention, the electret layer is provided so as to have a polarity opposite to that of the developer particles. Further, the magnetic pole of the magnet is opposite to that of the magnet of the conveying member.

The developer after stirring is charged and held on the sleeve surface while being attracted by the magnet of the sleeve, and passes through the gap between the developer amount regulating member and the sleeve, that is, the ear cutting gap. Since the regulating member is provided with an electret layer, a potential is generated there due to charge polarization.
Its potential is opposite to that of the charged developer. In addition, the magnetic pole on the sleeve surface facing the regulating member (N
.

SI! exist alternately. ), for example, if it is the si plane,
The magnet of the regulating member has a north pole, and the opposing surface is a north pole.
If it is at the pole, it is S-Tochi.

When the developer passes between the regulating member and the sleeve, the amount of the developer is physically limited by the regulating member and is also subjected to magnetic and electrical effects. In addition to being attracted to the sleeve surface, the developer is also attracted to the blade, and since the developer is of opposite polarity, it stands up along the lines of magnetic force. Further, a potential is generated in the electret layer of the blade, and since this potential is opposite to the charging electrode of the developer, the developer is electrically attracted to the surface of the electret layer. Therefore, the developer layer on the sleeve passes through in a fully stretched state, which gives margin for the precision of the cutting gap, makes the density of the developer uniform, and makes the charging property of the developer uniform. be.

In Figure 12 for explaining this principle, the sleeve is 16, the magnet inside the sleeve is 30, 31, and the photoreceptor is 2.
2. Stirring developer is 18. The developer amount regulating member is 20. and the electret layer is 40°, and the magnet of the regulating member is 41°.
It is. The magnetic developer particles 18 are, for example, negatively charged and are conveyed to the photoreceptor 22 by forming a magnetic brush with the sleeve 16 . The outer surface of the electret layer 40 has a charge opposite to that of the developer particles 18 . Further, the magnet 3o of the sleeve 16 faces the regulating member 20, and the magnet 30 and the magnet 41 have opposite polarities.

The developer 18 is regulated to some extent by the blade 2o,
The spiked developer that is passing through is stretched between the sleeve 20 and the electret 40. This is due to the electrical attractive force of the electret 40 and the magnetic attractive force of the magnets of the sleeve 16 and the blade. Therefore, the developer layer under tension tends to be divided into parts based on the balance point of these suction forces, and the part near the blade remains without being conveyed, while the part near the unleaved part is on the sleeve side. It remains as a substantial developer layer. Therefore, the thickness of the developer can be formed into a thin layer that is approximately half or more of the ear cutting gap. This means that the ear cutting gap can be made larger than in the past, and it is understood that the accuracy requirements are more relaxed, and gap clogging is less likely to occur. Further, the ears of the developer magnetic brush located between the electret 40 and the sleeve 16 are in a fully extended state, and the density or concentration thereof becomes uniform, and the value of the density itself also depends on the density unevenness of the developer during stirring. Alternatively, it remains almost constant without being affected by density unevenness. The fact that the density becomes uniform is the same effect as described above, but it is understood that the fact that the density itself is not affected during stirring means that the accuracy error between the ear cutting gaps is eliminated and there is more margin for tolerance. Ru.

Also, the developer passing through the doctor blade.

It is electrostatically affected by the electret layer,
The non-uniform charging state that occurs in the stirring developer is made uniform by the electric action of the electret, and the proportion of uncharged developer and opposite polarity developer tends to be reduced.

(Embodiments) Hereinafter, preferred embodiments of the developing device according to the present invention will be described in detail with reference to the accompanying drawings.

I! FIG. 1 is an explanatory diagram of the principal parts of the developing device used in the present invention, and the developing device of the present invention is not limited to such a structure.

As shown in FIG. 1, a normal developing device 2 is provided with a box-shaped developer supply mechanism 4, into which developer 6 is introduced from above. The developer 6 is supplied into the lower developing device 10 through a supply port 8 with a feeder, and is stirred by an agitator 12, 12 in the developing device 10 (in the case of a two-component developer, it is mixed with a carrier). charged.

There are many s8 in the developer lo! Developing sleeve 1 equipped with
A magnet 17 is provided in the sleeve 16 to apply a magnetic field to the sleeve surface.

The developer 14 that has been triboelectrically charged is supplied to the developing sleeve 16, and a magnetic brush 18 of the developer is formed on the sleeve surface by magnetic force. The length of the magnetic brush is adjusted by a doctor blade 2°, and the magnetic brush is conveyed to the nip position of photosensitive #24 on the electrophotographic photosensitive drum 22. The distance of the tk light drum 22 from the developing sleeve 16!
The developing sleeve 16 and the photoreceptor drum 22 are rotatably supported by a machine frame (not shown) so that the moving directions (arrows) at the nip position are the same (or opposite). ).

In such a configuration, the developer 14 is transferred to the developing sleeve 1.
A magnetic brush 18 is formed on the doctor blade 2.
After being regulated by 0, a visible image of the developer is formed on the photosensitive layer 24 by reacting with the electrostatic latent image of the photosensitive layer 24 at the nip position.

FIG. 2 is an explanatory view of the main parts of the developing device according to the present invention, in which the electric left layer is at the same polarity as the developer.
! As shown in FIG. 2, an electret dielectric layer 40 is formed on the outer surface layer of the doctor blade 20. Also,
The electret layer 40 includes a blade base body 41 formed of a magnet. For example, when the magnetic developer particles 18 are negatively charged, the outer surface of the electret layer 40 is negatively charged so that the outer surface of the electret layer 40 has a charge opposite to that of the developer particles. Further, the magnetic pole of the blade base 41 is opposite to that of the magnet inside the opposing sleeve, and in this case, if the sleeve surface is the T-pole, the blade base 41 is the S-pole.

Any organic or inorganic material can be used as the material for electret as long as it is a film-forming material that can be permanently electrically polarized. In this respect, various polymeric materials are suitable. Suitable examples thereof include, but are not limited to, polyethylene.

Olefin resins such as polypropylene, ethylene-butene copolymer, ionically crosslinked olefin copolymer, ethylene-acrylic copolymer; vinyl fluoride, polyvinylidene fluoride, vinyl fluoride/vinylidene fluoride copolymer, tetrafluoride Ethylene #l resin (PTFE), tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin (
PFA resin), fluororesins such as tetrafluorinated ethylene-hexafluorinated propylene copolymer resin (FEP resin); polyvinyl chloride.

Chlorinated resins such as chlorinated polyolefin; polyethylene terephthalate, polyethylene naphthalate.

Thermoplastic polyesters such as polybutylene terephthalate; polyamides such as nylon 6, nylon 12, nylon 66, and nylon 6.10; various acrylic resins, etc. are used alone or in combination of two or more. Among these, fluororesins such as P-FE resin, PFA resin, and FEP resin are preferred because they have good critical surface tension, good charge retention, and good durability.

Electrets can be produced by applying any method known per se, such as a thermal electretization method, an electroelectretization method, a radiation electretization method, or a photoelectretization method, depending on the type of polymer used. be exposed. Thermal electretization method and electroelectretization method are advantageously applied to the above-mentioned polymers, especially fluororesins.

Further, in order to provide an electret layer on the surface of the developing blade, a layer of a non-electret polymer film may be provided on the blade surface, and then this polymer film layer may be converted to an electret layer by the above-mentioned method. The chemical film may be attached to the blade surface via an adhesive layer. The former method is generally advantageous.

The electret layer 40 has a thickness of O1O○5 to 2
．． 0 am, especially 0.01 to 0.1+n+n, charge density σ is 5 X 10-"' to 2 X 10-'c/cr
rf, especially 1X10-' to 1.5X10-7c/cm
It is desirable that it be within the range of . When the thickness is within the above range, workability is good. Also, the thickness has a large effect on the charge density,
The charge density improves as the electret layer becomes thinner. If the charge density is within the above range, the developer passing through the blade will form a thin layer with good precision and its density will be uniform. Moreover, it can sufficiently influence the charge of the developer and make the charge of the developer uniform. Moreover, the surface potential ES of the electret layer is 200 to 100
0V, special 1. : The magnetic pole of the blade base 41 is preferably in the range of 300 to 900 V. The magnetic pole of the blade base 41 is the same as the magnetic pole of the opposing sleeve surface, and it may be a permanent magnet or an electromagnet. Good too.

The magnetic force of the base body also depends on the thickness of the electret layer, but when the magnetic flux density on the surface of the electret layer is 10 to 50
0 Gauss, especially 20 to 300 Gauss is desirable.

The gap D between the developing sleeve and the doctor blade, that is, the cutting gap D is 0.05 to 2. Omn, especially 0.1 to 1
．． 5. It is desirable to set the range to satisfy the following range.

With such a set width, the developer layer D' formed on the sleeve becomes thinner than D. In addition, within this range, the uniform layer thickness of the developer on the sleeve can be adjusted to a maximum of 05m+n, and the density becomes high. The developer layer D' of the magnetic brush depends on the type of developer, but in the case of a two-component magnetic developer, the developer layer D' is 0. 5 to 3
．． In the case of Ol, -component type developer, 0. 1 to 1. 0
It is preferable that it be within the range of mm.

In the present invention, the magnetic pole in the developing sleeve (developer conveying member) preferably has a relatively small magnetic flux density within a range that does not cause carrier attraction, and is generally 4oo to 1200 gauss, particularly 50o to 1000 gauss. . The rotational speed of the developing sleeve is preferably within a relatively large range that does not cause developer scattering, and generally the peripheral speed is 5.
to 100 cm/sec, especially 10 to 80 CII
/SeC is preferable. Further, the distance dD-5 between the developing sleeve and the photosensitive layer is 0.5 to 3.0 in the case of a two-component developer. 5+nm, 0.0 for -component developer. A range of 1 to 1.0 mm is appropriate.

In the present invention, the photoreceptor includes photoreceptors conventionally used in electrophotography, such as selenium photoreceptors, amorphous silicon photoreceptors, zinc oxide photoreceptors, cadmium selenide photoreceptors, cadmium sulfide photoreceptors, and various other photoreceptors. All organic photoreceptors etc. are used.

As the two-component magnetic developer, a mixture of a magnetic carrier and electrostatic toner is used, and the magnetic carrier used here is a ferrite carrier or an iron powder carrier. Examples of ferrite carriers include iron zinc oxide (Z
nFe20−), iron indolium oxide (Y3FesO
+ 2), iron cadmium oxide (CdFe204),
Iron gadolinium oxide (Gd3Fes O+ 2 ), iron oxide steel (CuFe20.), iron oxide complex (PbFe+20.
+h), iron nickel oxide (NiFe20n), iron neodymium oxide (NdFeO3), iron oxide barium (Ba
Fe+20+9), magnesium iron oxide (AgFe20
t), H pig iron manganese (MnFe20a),
Sintered ferrite particles having a composition consisting of one or more types of lanthanum iron oxide (LaFeO3) etc. are used, and in particular at least one of the metal components selected from the group consisting of Cu, Zn, Kg, Mn and N1. Soft ferrite containing two or more seeds, preferably copper-zinc-magnesium ferrite, or particles thereof coated with resin etc. are used, and the particle size is 30 to 12
At 0 μm, especially from 40 to 100 μm, those having a saturation magnetization in the range from 40 to 70 e+++u/g, especially from 45 to 65 emu/g are advantageously used. Its volume resistivity is preferably in the range of 10 6 to 10 12 Ωl.

The toner used in the present invention is a fixing resin medium containing a colorant, a charge control agent, or a toner compound known per se.
It is preferable that the dielectric skewer has a volume resistivity of X 10” to 3
It is desirable that the value be in the range of 4.0 to 4.0.

The fixing resin medium, colorant, charge control agent, and other toner compounding agents for the toner are preferably selected and combined so as to obtain the above characteristics. First, as the fixing resin medium, a styrene resin, an acrylic resin, or a styrene-acrylic copolymer resin is generally used.

The styrene monomer used in these resins has the following formula (2), where R1 is a hydrogen atom, a low Ii & alkyl group (having 4 or less carbon atoms), or a halogen atom, and R2 is a lower alkyl group. monomers such as styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene, vinylxylene, etc., where n is an integer of 2 or less including zero. Examples include vinyl naphthatone. Among these, styrene is preferred.

On the other hand, as an acrylic monomer, CH2=C... (3) C-0-R4 In the formula, R3 is a hydrogen atom or a lower alkyl group, and R
4 is a hydrogen atom or an alkyl group having up to 18 carbon atoms, Monomer 9 represented by 9 For example, ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylic acids, methacrylic acid, etc. In addition to the above-mentioned acrylic monomers, other ethylenically unsaturated carboxylic acids or their anhydrides,
For example, maleic anhydride, fumaric acid, maleic acid, crotonic acid.

Itaconic acid and the like can also be used.

Styrene-acrylic copolymer resin is one of the suitable resin media, and the styrene monomer (A) and acrylic monomer (B) have a ratio of A:B=50:50 to 90. : 10, preferably in the range of 60:40 to 85:15. In addition, the resin used is generally O to 25
It is preferable to have an acid value of . Further, from the viewpoint of fixing properties, it is preferable to have a glass transition temperature (Tz) of 50 to 65°C.

As the coloring agent to be contained in the resin, the following inorganic or organic pigments, dyes, etc. may be used alone or in combination of two or more. Carbon black such as furnace blank and channel black; Iron black such as triiron tetroxide; Titanium dioxide such as rutile type or anatase type; Phthalocyanine blue; Phthalocyanine green; Cadmium yellow; Molybdenum orange; Pyrazolone red;
Fast Bio Left B etc.

As the charge control agent for electric fi'a4J, any known charge control agent may be used, such as nigrosine hace (C1504]5
), Oil Black (CI26i50), Subiron Blank, etc., 1:1 type or 2:1 type metal complex dyes, naphthenic acid metal salts, fatty acids, soaps, resin acid soaps, etc. are used.

The particle size of the toner particles is 8 to 14 μm on a volume basis, especially when measured with a Coulter counter.
The size of the particles is preferably in the range of 0 to 12 μm, and the particle shape may be amorphous ones produced by the melting W&mixture/pulverization method, or spherical ones produced by the dispersion or suspension polymerization method.

The mixing ratio of toner and magnetic carrier varies depending on the physical properties of the toner and magnetic carrier, but the weight ratio is generally 1:99 to 10:90, particularly 2:98 to 5.
: Desirably within the range of 95. In addition, the electrical resistance of the developer as a whole is 5×1o9 to 5×101”
Ω”cm, especially lXl0I” to 4X10”Ω・Cl1
1 is preferred for the purposes of the present invention.

The one-component magnetic developer used in the present invention includes:

The electrostatic toner composition containing magnetic powder in an amount of 30 to 70% by weight, particularly 40 to 60% by weight, is used. The magnetic powder has a particle size of 0.1 to 3
Triiron tetroxide (magnetite) and ferrite in the μm range, especially those having the chemical compositions mentioned above, are used. Other components may be the same as the above-mentioned components in the two-component toner.

According to the present invention configured as described above, the charged developer 18 of the -component system or the two-component system is regulated to some extent by the blade 2o, and the developer 18 passing through is affected by the electrical attraction force. and receives magnetic attraction. elect left layer 4
o is given a surface potential ES, and since the tiL developer silver agent is charged to the opposite polarity to this potential, it receives an attractive force. Furthermore, since the magnetic poles of the blade and the magnetic poles of the sleeve surface are opposite in polarity, the ears are extended along the lines of magnetic force between the sleeve 20 and the electret 140, as shown in FIG.

Therefore, the developer layer located between the electret/W40 and the sleeve 16 is fully extended and its density or concentration becomes uniform. Further, the developer layer is separated near the sleeve surface of the cutting gap, and as a result, the developer layer supplied is a thin layer that is considerably thinner than the gear tooth width. This makes the above-mentioned requirement for gap accuracy less strict and prevents gap clogging.

Also, because the spikes of developer are always in an extended state,
The concentration or density of the developer passing through the sleeve 20 and the electret 40 takes a predetermined value. Since the concentration or density does not vary as in the conventional case, the width of the ear cutting gap can be adjusted in a sensitive manner, and there is a margin for the tolerance. In addition, the developer passing through the doctor blade is electrostatically affected by the electret layer, and the non-uniform charging state that occurs in the agitated developer is made uniform by the electric action of the electret, and the uncharged developer and reversely charged state are made uniform. The proportion of polar developer tends to be reduced.

The invention will be further illustrated by the following experimental examples.

Experimental Example 1 The thickness of the electret layer of the blade is 0. ○25■, charge density is 2.2 x 10-'c/c, surface tension is 17
dyne/am, the surface potential ES was 300 V, and the polarity was opposite to that of the developer.

The magnetic flux density of the magnetofte of the blade base was set to 100 Gauss, and the magnetic pole of the opposing sleeve surface was set to be opposite.

Further, the ear cutting gap was set to 0.4 μm.

Such a blade was attached to an improved electrophotographic copying machine DC-112C manufactured by Sanda Kogyo Co., Ltd., which uses an amorphous selenium photoreceptor, and transfer and fixing were performed under the following conditions.

Photosensitive layer peripheral speed: 13.5 cm/
sec developing sleeve circumferential speed: 270 ro/sec
e Photosensitive layer/sleeve rotation method: Forward magnetic pole in sleeve = 800 Gauss Distance between photosensitive layer sleeves DD-5: 0.2+un developer 2-component developer evaluation (1) The image density of the obtained copy is 1 .35, and the fog density was O1○02.

(2) The developer layer (length of the panicle) was 0.2.

(3) Image S degree unevenness was 0.1 or less.

(Effects of the Invention) As explained above, according to the present invention, since the doctor blade is provided with the electric left layer and the magnet,
The charged developer layer is located between the blade and the sleeve and has a uniform density at a predetermined value due to the effects of electrical attraction and magnetic attraction. Therefore, the developer supplied to the support forms a thin layer with uniform density, and an excellent image without image unevenness can be provided during development. Also, in this case,
Since there is a margin in the accuracy of the cutting gap, the adjustment of the blade becomes easy, and there is no possibility of excessive supply of developer causing fogging or the like.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the principle of a developing device according to the present invention, and FIG. 2 is a sectional view of a main part of FIG. 1.

Claims (2)

[Claims] (1) A support for supporting an electrostatic image; a mechanism for charging a magnetic powder developer; It consists of a developer conveying member applied to the electrostatic image area of the support, and a developer amount regulating member disposed close to the conveying member to adjust the amount of developer supplied, and the regulating member includes a magnet and an electret dielectric layer. The magnet of the developer amount regulating member has a polarity opposite to that of the magnet portion of the opposing conveying member, and the electret layer has a polarity opposite to the charging electrode of the charged developer. Electrophotographic developing device. (2) The developing device according to claim 1 or 2, wherein the electret layer is made of a fluororesin.