JP4476191B2 - Image forming apparatus and image forming method - Google Patents

Description

The present invention relates to an image forming apparatus and an image forming method . More specifically, the present invention relates to an image forming apparatus and an image forming method that enable stable toner density control.

  An electrophotographic image forming apparatus such as a copying machine, a printer, or a facsimile forms an electrostatic latent image on a photosensitive member by various image forming processes, and then uses the toner supplied from the developing machine to generate the electrostatic latent image. Is developed into a toner image, the toner image is transferred to a recording material, and then fixed by a heat and pressure roller to obtain an image. As a photoconductor, an organic photoconductor drum having a photoconductive layer containing an organic polymer compound and a conductive material is widely used because it is highly safe in the manufacturing process and environmentally safe and has a low material cost. Is done.

  An electrophotographic image forming apparatus is easy to operate and maintain, and can form an image having a good image quality at a relatively high speed. Therefore, it has become an indispensable apparatus in various situations. For the purpose of saving space, further downsizing is being promoted. Along with this, further downsizing of constituent devices inside the image forming apparatus, for example, a photosensitive member and a plurality of devices arranged around the photosensitive member, a toner container, etc. is required.

  In addition to downsizing, the image forming apparatus is required to increase the image forming speed and increase the number of images that can be formed per toner filling. Although an increase in the number of images that can be formed can be achieved by increasing the capacity of the toner container, on the other hand, there is a conflicting demand for downsizing the apparatus, and therefore it is not possible to simply increase the capacity. Accordingly, it is required to store a larger amount of toner than in the conventional case or to reduce the amount of toner consumed per image formation. For this purpose, for example, it is conceivable to reduce the diameter of the toner particles and increase the hiding power of the toner on the recording material. However, when the diameter of the toner particles is reduced, the triboelectric charge amount of each toner is reduced, and when the electrostatic latent image is developed, the toner is scattered from the developing device and contaminates the image forming apparatus. In addition, when the triboelectric charge amount of the toner is decreased, the van der Waals force between the toner particles is increased and the toner is agglomerated, so that a uniform toner image cannot be formed on the electrostatic latent image, causing image defects. become. In addition, the occurrence of background fogging that causes toner to adhere to portions other than the electrostatic latent image and remarkably increase the amount of toner consumption becomes significant. Furthermore, when transferring the toner image on the photoconductor, the character image is blurred (a phenomenon in which the toner is scattered around the character image), tailing (a phenomenon in which the toner adheres to the trailing edge of the character image). Will occur.

  When an image is formed using toner, an oxide for improving the fluidity of the toner, such as silicon dioxide, titanium oxide, and aluminum oxide, is added to the toner. When used as a magnetic toner, an inorganic magnetic material is used in combination. Such oxides and inorganic magnetic materials have the property of polishing the photoconductive layer of the organic photoreceptor drum. Therefore, in the process of overlapping image formation, the photoconductive layer is gradually polished and thinned. As a result, the residual potential in the photoconductive layer is increased, image quality defects such as background fogging and widening of the line width of the fine line image occur frequently, and the life of the organic photosensitive drum is shortened. In view of such a current situation, instead of the oxides as described above, a weight average particle diameter of 0.6 to 5 μm, a number average particle diameter of 0.5 to 4 μm, and a weight average particle diameter / number average particle diameter of 1.0 to It has been proposed to use 2.4 metal oxide powder as a fluidizing agent for toner (see, for example, Patent Document 1). Although this metal oxide powder is effective in securing the fluidity of the toner, it has the same drawbacks as conventional oxides or inorganic magnetic materials that exhibit high abrasiveness and shorten the life of the organic photosensitive drum. Have.

  On the other hand, a polyester resin is generally used as a binder resin that serves as a matrix for holding the colorant in the toner. By using the polyester resin, the toner can be fixed to the recording material at a relatively low temperature. Further, since the polyester resin has the frictional charging property required for the toner, there is an advantage that it is possible to prevent filming where the toner adheres not to the recording material but to the photosensitive member. However, a toner using a polyester resin as a binder resin has a drawback that a so-called offset phenomenon occurs in which the toner adheres to the heat and pressure roll when the toner image is fixed on the recording material by the heat and pressure roll. . Therefore, waxes are added as an anti-offset agent. Examples of the wax include nonpolar low molecular weight polyolefin resin, Teflon (registered trademark) resin, and paraffin. However, since these offset inhibitors have low compatibility with the polyester resin, the occurrence of the offset phenomenon cannot be sufficiently prevented. In addition, the offset preventive agent is present in the toner as fine particles, and a part of the anti-offset agent is fused to the photosensitive member or adheres to a carrier used in combination with the toner to make the charging property of the toner non-uniform. Causes a similar phenomenon.

  In order to increase the hiding power of the toner, it is extremely important to control the particle diameter and the amount of the wax adhering to the toner particle surface. When a large number of wax particles are present on the surface of the toner particles, it becomes difficult to impart triboelectric charge to the toner, it is difficult to obtain a desired toner triboelectric charge amount, toner particles with a small amount of charge increase, and consequently toner scattering, background fogging, Problems are likely to occur. Further, if the amount of wax particles adhering to the surface of the toner particles is too small, it is a matter of course that an offset phenomenon is likely to occur and the fixing property of the toner to the recording material is impaired.

  In electrostatic latent image developing toner containing a polyester resin as a binder resin, it has been proposed to use an oxidized polyolefin having an acid value of 1 or more obtained by graft polymerization of an unsaturated carboxylic acid to a polyolefin resin as an anti-offset agent. (For example, see Patent Document 2). In the invention of Patent Document 2, since the oxidized polyolefin having polarity is added to the polyester resin having polarity originally, the compatibility of both is improved, and the fusion of the oxidized polyolefin to the photoreceptor and the adhesion to the carrier are prevented. It can be avoided reliably. Furthermore, the oxidized polyolefin is effective in preventing the offset phenomenon. However, the combination of a general polyester resin and an oxidized polyolefin is too compatible, and the oxidized polyolefin excessively disperses fine particles, so that the high lubricity inherent to the oxidized polyolefin is not sufficiently exhibited. . Therefore, the releasability between the heat and pressure roller and the paper as the recording material becomes insufficient. In particular, when there is a solid black image at the leading edge of the image, there is a problem that a paper jam occurs inside the image forming apparatus. In addition, since this toner is inferior in slidability on the surface of a black solid image after fixing, so-called rubbing fixability, when recording a plurality of image-formed recording materials and viewing them by turning, the recording materials rub against each other. In addition, there is a problem that the toner adheres to the surface opposite to the image forming surface of the recording material, and the back-off or back-stain.

  When a two-component developer containing toner for electrostatic latent image development and a carrier is used and an image is formed on a recording material by an electrophotographic image forming apparatus, the magnetic permeability of the developer is detected by a magnetic permeability sensor. Thus, the toner density is measured, and the image density is stabilized by controlling the toner density to a constant density. However, there is a “waviness” in which the detection output of the magnetic permeability sensor deviates from the allowable range, and the toner density deviates from the allowable range due to the waviness phenomenon. The inventors of the present invention have recognized that when the toner density is too low, the formed image becomes thin, and the inventors of the present invention have recognized such problems and solutions. Absent. Although the cause of the waviness phenomenon has not yet been fully elucidated, there is a difference in the timing of toner replenishment with respect to the output of the magnetic permeability sensor, and the time required for the replenished toner to be uniformly dispersed in the developer. And so on.

JP-A-6-3854 JP 59-129863 A

One of the main objects of the present invention is to provide an image forming apparatus and an image forming method capable of stably controlling the toner density during image formation.

The inventors of the present invention have conducted extensive research to elucidate the undulation phenomenon of the permeability sensor that detects the permeability of the two-component developer. As a result, the physical property parameters relating to the toner and the carrier, particularly the relative permeability of the developer. By setting the magnetic susceptibility to a specific range, it has been found that toner density control can be stabilized during image formation, and the present invention has been completed.
Thus, according to the present invention, the developer for developing an electrostatic latent image, and a magnetic permeability sensor for detecting the magnetic permeability of the developer, the developer includes a binder resin containing a polyester resin and a pigment. An electrostatic latent image developing toner including coloring resin particles having a hydrophobic fluidizing agent particle adhering to the surface of the coloring resin particles, and a carrier, and the development by the magnetic permeability sensor. The magnetic permeability of the developer is detected, and an image is recorded on the recording material by an electrophotographic method while controlling the toner concentration of the developer so that the relative permeability of the developer becomes 1.65 to 2 based on the detected data. An image forming apparatus configured to be possible is provided.
Further, according to another aspect of the present invention, a coloring resin particle having a binder resin containing a polyester resin and a pigment, and a hydrophobic fluidizing agent particle attached to the surface of the coloring resin particle The magnetic permeability of the electrostatic latent image developing developer containing the toner and the carrier containing the carrier is detected by a magnetic permeability sensor, and the relative permeability of the developer is 1.65 based on the detected data. There is provided an image forming method in which toner is supplied to a developer so as to be ˜2 and an image is recorded on a recording material by an electrophotographic method while controlling the toner density .

  According to the present invention, by setting the relative permeability of the two-component developer having the electrostatic latent image developing toner and the carrier to 1.65 to 2, the magnetic permeability sensor of the image forming apparatus can be used at the time of image formation. Swelling phenomenon of output can be suppressed and toner density control can be stabilized. As a result, it is possible to improve image density, fogging, abrasion resistance and the like.

The image forming apparatus of the present invention includes a developer for developing an electrostatic latent image, and a magnetic permeability sensor for detecting the magnetic permeability of the developer,
The developer includes an electrostatic latent image development including a coloring resin particle having a binder resin containing a polyester resin and a pigment, and a hydrophobic fluidizing agent particle adhering to the surface of the coloring resin particle. Toner and a carrier, and the magnetic permeability sensor detects the magnetic permeability of the developer, and the developer has a relative magnetic permeability of 1.65 to 2 based on the detected data. An image can be recorded on a recording material by an electrophotographic method while controlling the toner density .
That is, in the present invention, in order to stabilize the toner density control, the relative magnetic permeability of the two-component developer having the electrostatic latent image developing toner and the carrier is set to 1.65 to 2 to form an image. When the image is formed by the apparatus, the swell phenomenon of the output of the magnetic permeability sensor can be suppressed, and the image density (image quality), fogging, rubbing resistance (fixing rate) and the like can be improved. If the relative permeability is less than 1.65, carrier adhesion (pulling) is likely to occur, and dielectric polarization with the photoconductor in the image forming apparatus tends to occur. As a result, the surface of the photoconductor is scraped by the carrier and scratches are generated. The amount of the developer is reduced due to the occurrence or the consumption of the carrier, and the toner density is unstable. On the other hand, when the relative dielectric constant exceeds 2, the resistance increases, the image density (ID) decreases, and the fog increases.

In the present invention, the relative permeability refers to a value obtained by measuring the relative permeability of the two-component developer by the following method, and the quantity symbol is expressed in μs.
While holding the measurement beaker containing the two-component developer as the sample with the measurement jig, the tip of the magnetic permeability probe attached to the measurement jig is brought close to the sample from below the beaker, and the magnetic permeability probe is The relative permeability was measured using a relative permeability measuring apparatus connected to a portable magnetometer MB140 manufactured by Shimadzu Corporation (the last two significant digits). At this time, the amount of the sample is 80 cc, and the distance from the tip of the magnetic permeability probe to the sample (developer) is 4.5 mm.

In the present invention, the main parameter for stabilizing the toner density control is the relative permeability μs of the developer for developing an electrostatic latent image, and the following formula (I)
Relative permeability μs = (6.63 × 10 ⁻⁴ ) σs + (− 6.80 × 10 ⁻³ ) D ₅₀ + (2.97 × 10 ⁻⁴ ) I + (− 7.10 × 10 ⁻² ) T / D + 2.51 (I)
Can be expressed as
In the formula (I), s is the saturation magnetization of the carrier (unit: Am ² / kg), D ₅₀ is the carrier volume average particle size (unit: μm), I is the carrier current (unit: μA), and T / D is the toner. Concentration (unit: weight%) (T: toner weight, D: developer weight).
The above formula (I) representing the relative magnetic permeability μs is tested to suppress the undulation phenomenon of the output of the magnetic permeability sensor, and the multiple regression analysis based on the above-described parameters in the developer in which the suppression of the undulation phenomenon is confirmed. It is derived by. According to this formula (I), the saturation magnetization σs of carriers
, Parameters relating such carrier volume average particle diameter D ₅₀ and the toner concentration T / D to the fluidity of the toner is contained as primarily affect the controllability of the relative permeability μs of the developer (undulation phenomenon). In the developer of the present invention, the toner concentration T / D has the strongest correlation with the controllability of the relative magnetic permeability μs from the formula (I), then the carrier volume average particle diameter D ₅₀ , and then the carrier It can be seen that the saturation magnetization σs and the carrier current I has the weakest correlation.

In the present invention, the saturation magnetization σs of the carrier means the maximum magnetization in the hysteresis curve of the carrier that is a magnetic substance, and is a value measured by the following known method.
As a measuring device, a vibration data type magnetometer VSMP-1S manufactured by Toei Kogyo Co., Ltd. was used, an external magnetic field 1.1 (MA / m) was applied, and saturation magnetization (maximum magnetization) was determined.

In the present invention, the carrier volume average particle diameter D ₅₀ was measured by the following known method.
The carrier volume average particle diameter D ₅₀ (μm) was determined from each sieve classification according to a particle size test method (JISZ2510) by metal powder-dry sieving.

  In the present invention, the carrier current I was measured using a carrier current measuring device manufactured by Powdertech Co., Ltd. having the circuit shown in FIG. In measurement, a single carrier as a sample is put into a magnetic brush on a developing sleeve containing a magnet, 500 V is applied at 5 μA, and after 30 seconds, a current value measuring machine and a recorder (not shown) are used for 30 seconds. The current value was measured (converted from a voltage drop at a fixed resistance of 10 KΩ). The sample used weighed 800 g and was exposed to an environment with an indoor temperature of 20 to 26 ° C. and a humidity of 50 to 60% RH for 15 minutes or more. The aluminum drum in FIG. 3 does not have a photoreceptor on the surface, and the gap between the aluminum drum and the developing sleeve is 0.6 mm.

  Furthermore, in the developer for developing an electrostatic latent image of the present invention, the binder resin further includes a polyalkylene resin, a polyolefin-based dispersant, and a non-oxidized polyethylene resin, and the polyolefin-based dispersant is added to the polyolefin resin with a styrene-based polymer. A polyolefin-based dispersant selected from a graft polymer obtained by graft polymerization of a chain or a styrene (meth) acrylic polymer chain and a styrene (meth) acrylic polymer, and a toner time constant of 100 to 350 msec. Is another feature.

By comprising in this way, a non-oxidized polyethylene resin can be uniformly disperse | distributed as a moderately sized particle | grain of 1 micrometer or less in binder resin. As a result, the low compatibility between the polyester resin and the polyalkylene resin, which could not be solved simply by adding a polyolefin-based dispersant, the particles of the polyalkylene resin were appropriately dispersed in the polyester resin, Since the toner particle surface also adheres to the toner particles with a sufficient amount of triboelectric charge and does not impair offset resistance, transferability, fixability, etc., a desired toner for developing an electrostatic latent image can be obtained. Can do.
As described above, the electrostatic latent image developing toner in the present invention is based on the fact that the polyalkylene resin particles are appropriately and uniformly dispersed in the polyester resin, which is the main component of the binder resin, as described in the following (1). It has an effect like (4).

(1) It has excellent storage stability and does not cause fusing (blocking), aggregation, deformation, etc. even in a miniaturized toner container, and it has excellent fluidity. Can be uniformly and smoothly performed over a long period of time.
(2) Transferability to a recording material and fixability are good, and filming on a photoconductor and offset to a heat and pressure roller (fixing roller) hardly occur.
(3) The polishing action of the organic photoreceptor on the photoconductive layer is small, and the lifetime of the organic photoreceptor is not shortened. In addition, since the amount of consumption per image formation is very small, even if the toner container is reduced in size, a larger amount of images can be formed than in the past by filling the image forming apparatus once.
(4) The toner in the present invention can be adjusted to a particle size of preferably 3 to 15 μm, more preferably 5 to 8 μm, but the diameter can be reduced to about 3 to 5 μm without deteriorating various performances required for the toner. Is also possible.

  Further, by adopting the above-described configuration, the electrostatic latent image developing toner in the present invention becomes a toner having a time constant τ in the range of 100 to 350 msec and a reasonably fast charge rise time. For this reason, even if the diameter of the toner is reduced, the toner has sufficient frictional charging properties, so that it does not scatter in the image forming apparatus, does not cause blurring of characters, tailing, background fogging, etc., and is jammed. Can also be prevented. Therefore, the use of the electrostatic latent image developing toner according to the present invention can efficiently form an image having a sufficient image density and high image quality, in combination with excellent transferability and fixability. it can. The toner time constant τ will be described in detail later.

  Furthermore, according to the present invention, among the above-mentioned polyester resins, those having an acid value of 15 to 30 mgKOH / g and a hydroxyl value of 4 to 17 mgKOH / g are preferable. By adjusting the acid value of the polyester resin within the above range, the offset resistance and negative charge stability of the toner of the present invention are further improved. Further, by adjusting the hydroxyl value of the polyester resin within the above range, the toner of the present invention exhibits stable charging performance even in a high temperature and high humidity environment.

  Furthermore, according to the present invention, among the above-mentioned polyester resins, those having a glass transition temperature of 55 to 65 ° C are preferable. By using the polyester resin, the blocking resistance, offset resistance, filming resistance and the like of the toner of the present invention are further improved.

Furthermore, according to the present invention, among the aforementioned polyester resins, those having a melt index of 0.1 to 6.0 g / 10 min are preferred. By using the polyester resin, the compatibility with the polyalkylene resin which is a wax component is further improved, and the polyalkylene resin is uniformly dispersed in the polyester resin, so that various properties of the toner of the present invention are further improved.
Further, according to the present invention, the time constant of the present invention is adjusted to a desired range by using carbon black as a pigment and using 5 to 20 parts by weight with respect to 100 parts by weight of the polyester resin. Will be very easy.

Furthermore, according to this invention, the addition effect of a polyalkylene resin is based on presence of a polyalkylene resin by making the usage-amount of the above-mentioned polyalkylene resin into 0.2-20 weight part with respect to 100 weight part of polyester resins. It is exhibited most efficiently without various harmful effects.
Furthermore, according to this invention, the addition effect is exhibited most efficiently by making the usage-amount of the above-mentioned non-oxidized polyethylene 0.5-5.0 weight part with respect to 100 weight part of polyester resins.

Furthermore, according to the present invention, among the above-mentioned hydrophobic fluidizing agent particles, hydrophobic silica having a specific surface area of 90 to 240 m ² / g is preferable. By using this hydrophobic silica, good fluidity can be secured even when the toner of the present invention is reduced in diameter.
Furthermore, according to the present invention, by using 0.1 to 3.0 parts by weight of the above-described hydrophobic fluidizing agent particles with respect to 100 parts by weight of the colored resin particles, the effect of imparting fluidity to the toner is further improved. Prominently demonstrated.

(Explanation of toner time constant)
In the present invention, the electrostatic latent image developing toner preferably has a time constant τ of 100 to 350 msec as described above. The time constant τ is a physical property that serves as an index indicating the time required for the toner to be charged (power storage). When the toner has a time constant in the above-described range, the toner charge (power storage) time, that is, the so-called charge rise time is reasonably fast. Thus, it is possible to sufficiently prevent toner scattering from the developing unit and occurrence of background fogging in the non-image area. When the time constant τ is less than 100 msec, the rising of the charge is quick, but there is a possibility that the uniform dispersion of the pigment in the toner is insufficient and fixing stains and fixability are deteriorated. On the other hand, if it exceeds 350 msec, the rise of charging is delayed, and there is a risk of toner scattering, background fogging, and the like.

Since toner is a dielectric, it has both a resistance component and a capacitance (capacitor) component. Here, assuming that the resistance of the toner is R (Ω) and the electrostatic capacity of the toner is C (F), the state in which a voltage is applied to the toner is expressed by the resistance of R (Ω) and the electrostatic capacity of C (F). Can be compared to a series-connected circuit. A DC voltage E (V) is applied to this series circuit, the moment when the voltage E is applied is time 0, the current flowing through the circuit at time t is i (t) (A), and the amount of electricity stored in the capacitor is q (t ) (C, Coulomb). At this time, the equation of the circuit is as follows.
E = R · i (t) + q (t) / C (1)
Here, since the current is the flow of electrons, that is, the magnitude of the time change of the charge amount, it is expressed as i (t) = dq (t) / dt, and the equation (1) is expressed by the following charge amount q ( Rewritten as a differential equation for t).
E = [(R · dq (t) / dt) + q (t)] / C (2)
Solving equation (2) reveals that q (t) is represented by the following exponential function with respect to t.
q (t) = CE (1-exp (−t / RC)) (3)
Furthermore, if the voltage across the capacitor is ec (t), then q (t) = C · ec (t).
ec (t) = E (1-exp (−t / τ)) (4)
[Where τ = RC. ]
Is obtained.

Here, the product of R and C is the time constant τ of the circuit. Therefore, when the resistance of the toner is R and the electrostatic capacity of the toner is C, the product RC is defined as the toner time constant τ. According to equation (4), the longer it takes for ec (t) to reach its maximum value E, the greater τ. Since the time constant τ is proportional to the resistance value R of the toner and the electrostatic capacity (charge amount) C, the larger the amount of charge induced by the toner resistance or the toner capacity component, the longer the time required for the toner to be stored. That is, the rise of frictional charging of the toner is delayed.
To obtain the time constant τ, an AC rectangular wave is applied to the circuit instead of turning on / off the DC power supply. Actually, using a dielectric loss measuring apparatus (trade name: TRS-10T type, manufactured by Ando Electric Co., Ltd.), the resistance (R) and the capacity (C) of the toner were measured, and the time constant τ was obtained. .
Hereinafter, each component of the developer for developing an electrostatic latent image of the present invention will be specifically described.

(Career description)
In the present invention, the carrier refers to a magnetic carrier. Although it does not restrict | limit especially as a carrier, Although what is normally used in this field | area can be used, 1 type or 2 types or more mainly consisting of iron, copper, magnesium, zinc, nickel, cobalt, manganese, chromium, lithium elements, etc. are mainly used. The composite ferrite, carrier core particles whose surface is coated with a coating substance, and the like are used. The coating material is appropriately selected according to the components contained in the toner. For example, polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, ditertiary butyl salicylic acid metal Compound, Styrenic resin, Acrylic resin, Polyacid, Polyvinyllar, Nigrosine, Aminoacrylate resin, Resin composition such as basic dye and its lake, or Silica fine powder, Alumina fine powder, Titanium oxide fine powder Although powder, a fluorine-type fine powder, etc. are mentioned, it does not need to be specifically limited to these coating substances. A coating substance can be used individually by 1 type, or can use 2 or more types together. The average particle size of the carrier is 10 to 100 μm, preferably 20 to 50 μm.

(Description of binder resin)
The binder resin of the electrostatic latent image developing toner in the present invention contains (a) a polyester resin, (b) a polyalkylene resin, (c) a polyolefin-based dispersant, and (d) a non-oxidized polyethylene resin.

(A) Polyester resin The polyester resin used in the present invention is a polycondensate of a basic acid and a polyhydric alcohol. As the basic acid, those commonly used in the production of polyester resins can be used. For example, maleic acid, maleic anhydride, fumaric acid, citraconic acid, itaconic acid, mesaconic acid, phthalic anhydride, isophthalic acid, terephthalic anhydride, anhydrous Succinic acid, Adipic acid, Azelaic acid, Sebacic acid, Tetrahydrophthalic anhydride, Hexahydrophthalic anhydride, Tetrabromophthalic anhydride, Tetrachlorophthalic anhydride, Het anhydride, Endomethylenetetrahydrophthalic anhydride, Trimellitic acid, Examples include trimellitic anhydride, pyromellitic acid, pyromellitic anhydride, and the like. Among these, aromatic dicarboxylic acids are preferable from the viewpoint of further improving the blocking resistance of the toner. A polybasic acid can be used individually by 1 type, or can use 2 or more types together. As the polyhydric alcohol, those commonly used in the production of polyester resins can be used. For example, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,3-butylene glycol, 1, 6-hexanediol, 1,5-pentanediol, 1,6-pentanediol, diethylene glycol, dipropylene glycol, neopentyl glycol, triethylene glycol, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A, bisphenol dihydroxypropyl ether, glycol, glycerin and the like. Among these, diols are preferable from the viewpoint of further improving the blocking resistance of the toner. A polyhydric alcohol can be used individually by 1 type, or can use 2 or more types together.

  The polyester resin can be synthesized, for example, by performing a dehydration condensation reaction or an ester conversion reaction in an organic solvent containing a polybasic acid and a polyhydric alcohol in the presence of a catalyst. As the organic solvent, an organic solvent that can dissolve or disperse the polybasic acid and the polyhydric alcohol and is inactive in the dehydration condensation reaction and the ester conversion reaction may be appropriately selected and used. As the catalyst, an esterification catalyst and an ester conversion catalyst commonly used in the synthesis of polyester resins can be used, and examples thereof include magnesium acetate, zinc acetate, lead acetate, and antimony trioxide. A catalyst can be used individually by 1 type or can use 2 or more types together. The reaction temperature is not particularly limited but is preferably 150 to 300 ° C.

The polyester resin may be either a saturated polyester resin or an unsaturated polyester resin, but is preferably an unsaturated polyester resin.
The polyester resin preferably has an acid value based on JIS K0070-1966 of 15 to 30 mgKOH / g and a hydroxyl value based on JIS K0070-1916 of 4 to 17 mgKOH / g. Here, the acid value means the number of carboxyl residues at the end of the polyester resin, and the hydroxyl value means the number of hydroxyl residues at the end of the polyester resin. By adjusting the acid value within the above range, the offset resistance and negative chargeability of the toner of the present invention can be further improved. The acid value can be adjusted by using a polybasic acid (maleic anhydride, trimellitic anhydride, etc.) in combination with a dibasic acid as a basic acid. Specifically, for example, maleic anhydride and trimellitic anhydride may be used in an amount of about 1 to 5 mol% of the total amount of monomer compounds. Further, since the hygroscopicity of the toner of the present invention is lowered by using a polyester resin having a hydroxyl value adjusted to the above range, the toner of the present invention exhibits excellent charging stability even in a high temperature and high humidity environment. The adjustment of the hydroxyl value can be carried out, for example, by reducing the number of hydroxyl groups according to a general method.

The polyester resin preferably has a glass transition temperature (Tg) based on ASTM D 3418-82 of 55-65 ° C. By using a polyester resin having a glass transition temperature in this range, the blocking resistance and offset resistance of the toner of the present invention can be further improved.
The polyester resin preferably has a melt index (MI) of 0.1 to 6.0 g / 10 min. By using the polyester resin, the compatibility with the polyolefin resin, which is a wax component, is further improved, and the polyolefin resin is uniformly dispersed in the polyester resin, so that various properties of the toner of the present invention are further improved.

  The polyester resin preferably has a number average molecular weight (Mn) of 5200 to 7000, more preferably 5700 to 6400 as measured by GPC. By adjusting the number average molecular weight within the above range, an excellent image with excellent image reproducibility, particularly when a low density image (for example, an image with a 1% character area ratio) is recorded or copied over a long period of time. Can be formed. Here, the case of recording or copying a low density image over a long period of time is, for example, recording or copying in a facsimile mode of a facsimile or a multi-function printer. In the present invention, since the toner diameter can be reduced and the amount of consumption per image formation is small, once the toner container in the developing device in the image forming apparatus is filled with toner, the toner replacement is reduced. Overstirred toner increases. As a result, the hydrophobic fluidizing agent particles on the toner surface are buried in the toner, the fluidity of the toner is lowered, and the supply of toner to the electrostatic latent image becomes insufficient, causing image defects such as rustiness in the image. May occur. Note that the roughness is an image defect in which a halftone image becomes rough due to fine shading. If the number average molecular weight is less than 5200, the embedding of the hydrophobic fluidizing agent particles in the toner cannot be sufficiently prevented, and there is a possibility of causing roughness. On the other hand, if the number average molecular weight exceeds 7000, the toner fixing property is lowered.

The polyester resin preferably has a temperature drop of 4 mm by a flow tester isothermal heating method (6 ° C./min, load 20 kg, die 1 mm × 0.5 mmφ, apparatus: trade name CFT500, manufactured by Shimadzu Corporation) of 160 to 175 ° C. By adjusting to this range, it is possible to further improve the toner fixing property, offset resistance, and the like.
Various physical properties of the polyester resin are set within a desired range by appropriately selecting, for example, the types of the basic acid and polyhydric alcohol that are monomer compounds, the mixing ratio, the reaction temperature, the reaction time, and the type of the catalyst. be able to.

The content of the polyester resin in the toner can be appropriately selected according to the type of the polyester resin itself and the types of other components, but is preferably 67 to 95% by weight, more preferably 85 to 90% by weight of the total amount of the toner.
In the present invention, as a main component of the binder resin, a polyester resin, a polyolefin resin such as alkyd resin, polyethylene terephthalate, polybutylene terephthalate, and polyarylate, as long as the preferable characteristics of the electrostatic latent image developing toner are not impaired. 1 type, or 2 or more types, such as these, can be used.

(B) Polyalkylene Resin The polyalkylene resin is used, for example, to improve the offset resistance of the toner for developing an electrostatic latent image in the present invention.
As the polyalkylene resin, those conventionally used for improving the physical properties of polyester resins, which are binder resins for toners, can be used. For example, polyethylene wax, polypropylene wax, polybutene wax, ethylene-propylene copolymer wax, ethylene- Examples include butene copolymer wax. Among these, polyethylene wax is preferable from the viewpoint of improving fixability at a low temperature, and polypropylene wax is preferable from the viewpoint of further improving the offset resistance. A polyalkylene resin can be used individually by 1 type, or can use 2 or more types together as needed.

  The amount of the polyalkylene resin used can be appropriately selected according to the type of the polyester resin, the type of the polyalkylene resin itself, the type of other components and the amount of use thereof, and preferably 0.2% with respect to 100 parts by weight of the polyester resin. -20 parts by weight, more preferably 1-8 parts by weight. If it is less than 0.2 part by weight, the effect of improving the offset resistance may be insufficient. On the other hand, when the amount exceeds 20 parts by weight, the offset resistance is not sufficiently improved, and adhesion to a photoconductor and / or adhesion to a carrier used in combination with toner may occur, resulting in image defects. There is.

(C) Polyolefin-based dispersant The polyolefin-based dispersant contributes to, for example, dispersion of a polyalkylene resin in a polyester resin.
Examples of the polyolefin dispersant include a graft polymer obtained by graft polymerization of a styrene polymer chain and / or a styrene- (meth) acrylic polymer chain to a polyolefin resin, and a styrene- (meth) acrylic polymer. .
Here, examples of the polyolefin resin include polyethylene, polypropylene, polyethylene terephthalate, and polybutylene terephthalate. Among these, polyethylene, polypropylene and the like are preferable. Non-oxidized polyethylene, non-oxidized polypropylene, and the like can also be used. Polyolefin resin can be used individually by 1 type, or can use 2 or more types together.

  Examples of the styrenic polymer include polystyrene homopolymer, hydrogenated styrene resin, styrene-isobutylene copolymer, styrene-butadiene copolymer, acrylonitrile-butadiene-styrene terpolymer, acrylonitrile-styrene-acrylic acid ester terpolymer. Terpolymer, styrene-acrylonitrile copolymer, acrylonitrile-acrylic rubber-styrene terpolymer, acrylonitrile-chlorinated polystyrene-styrene terpolymer, acrylonitrile-EVA-styrene terpolymer, styrene- Examples include p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene rubber, styrene-maleic acid ester copolymer, styrene-isobutylene copolymer, styrene-maleic anhydride copolymer. That. A styrenic polymer can be used individually by 1 type, or can use 2 or more types together.

  Examples of the styrene-acrylic polymer include styrene-acrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-methyl acrylate copolymer, Examples thereof include styrene-ethyl acrylate copolymer and styrene-acrylic acid-maleic anhydride copolymer. Further, in the present invention, polyvinyl chloride, polyvinyl acetate and the like are also included in the styrene-acrylic polymer. Styrene-acrylic polymers can be used alone or in combination of two or more.

  The graft polymer may be prepared by, for example, dissolving or dispersing a polyolefin resin in an aromatic hydrocarbon such as toluene or xylene or other appropriate solvent, and then heating the polyolefin resin to 100 to 200 ° C. under heating to 100 to 200 ° C. It can be obtained by dropping a monomer compound constituting the acrylic polymer and a polymerization initiator. A well-known thing can be used as a polymerization initiator, For example, benzoyl peroxide, di tert- butyl peroxide, tert- butyl peroxybenzoate etc. are mentioned. Although the amount of the polymerization initiator used is not particularly limited, it is preferably 0.2 to 10% by weight based on the total amount of the monomer compounds.

A polyolefin-type dispersing agent can be used individually by 1 type, or can use 2 or more types together.
The amount of the polyolefin-based dispersant used can be appropriately selected depending on other components, particularly the type and amount of polyalkylene resin used, but preferably 0.2 to 5.0 parts by weight with respect to 100 parts by weight of the polyester resin, More preferably, it is 0.5-3.0 weight part. If it is less than 0.2 parts by weight, the polyalkylene resin may not be sufficiently dispersed in the polyester resin. On the other hand, if the amount exceeds 5.0 parts by weight, the dispersion is too good and the effect of blending the polyalkylene resin is reduced, and fixing offset may occur.

(D) Non-oxidized polyethylene In this invention, non-oxidized polyethylene means the nonpolar polyethylene wax which belongs to polyethylene wax. In contrast to this nonpolar polyethylene wax, there is an oxidized polyethylene wax.
The amount of non-oxidized polyethylene used can be appropriately selected according to the type and amount of other components, but is preferably 0.5 to 5.0 parts by weight, more preferably 0.8 to 100 parts by weight of polyethylene resin. -3.0 parts by weight. If the amount is less than 0.5 part by weight, the effect of adding non-oxidized polyethylene becomes insufficient, and dispersion of the polyalkylene resin in the polyester resin may become non-uniform. If the amount exceeds 5.0 parts by weight, the dispersibility of the non-oxidized polyethylene itself is lowered, and the effect of the addition may not be sufficiently exhibited.

(Description of pigment)
As the pigment contained in the colored resin particles in the present invention, both an organic pigment and an inorganic pigment can be used, and the color is not particularly limited. Among them, the conductive inorganic pigment is preferable because it has a role as a colorant, enhances the hiding power of the toner on the recording material, and can adjust the time constant of the toner by appropriately selecting the amount used. .

  The reason why the time constant of the toner can be adjusted by the amount of the inorganic pigment used is not yet clear, but when the inorganic pigment is dispersed in the toner, the inorganic pigment is a carbonaceous material such as a metal oxide or carbon black, and is conductive. Thus, the inorganic pigment becomes an electrode, the characteristics of the capacitor are manifested between adjacent inorganic pigments, and a hall electrical circuit is formed where the inorganic pigment is continuously in contact with the toner, and the time constant τ (= RC) is considered to change. In addition to selecting the amount of inorganic pigment used, one method for adjusting the time constant is to increase the acid value of the polyester resin. However, if the acid value is increased, the molecular chain of the polyester resin is increased. A large amount of hydroxyl groups (COOH, OH) are present, the toner charge amount in a high humidity environment is remarkably reduced, toner scattering occurs in the image forming apparatus, and background fogging occurs. Therefore, as described above, the inorganic pigment has an advantage of increasing the toner hiding power in addition to the adjustment of the time constant. Therefore, it is preferable to adjust the time constant according to the amount of the inorganic pigment used.

As the inorganic pigment, those commonly used in this field can be used. For example, various carbon blacks produced by the thermal black method, acetylene black method, channel black method, furnace black method, lamp black method, aniline black, Examples thereof include copper oxide, triiron tetroxide, and activated carbon. Among these, carbon black is preferable because it has high conductivity and it is easy to adjust the time constant within a predetermined range. An inorganic pigment can be used individually by 1 type, or can use 2 or more types together.
Although the usage-amount of an inorganic pigment can be suitably selected according to the kind etc. of inorganic pigment itself, Preferably it is 5-20 weight part with respect to 100 weight part of polyester resins, More preferably, it is 7-15 weight part. If it is less than 5 parts by weight, the time constant exceeds 350 msec, the toner storage speed (charging rise) becomes slow, and there is a possibility that toner scattering, background fogging, etc. occur in the image forming apparatus. Further, the image density of the image obtained by the toner of the present invention may be lowered. If the amount exceeds 20 parts by weight, the toner charge rises quickly and exhibits good chargeability, but the toner fixability may be impaired.

  As colorants other than inorganic pigments, those commonly used in this field can be used. For example, nitro, stilbeneazo, diphenylmethane, triphenylmethane, methine, thiazole, anthraquinone, imidazoline, azine Organic dyes or organic pigments, for example, oxaazine, thiazine, sulfur dye, indigoid, and phthalocyanine. The colorant can be used alone or in combination of two or more.

(Description of hydrophobic fluidizing agent particles)
As the hydrophobic fluidizing agent particles to be attached to the surface of the colored resin particles, those commonly used in this field can be used, for example, metal oxides such as silica, alumina, titania, zirconia, tin oxide, and fluorine resins. Examples thereof include resin powders such as powder, fatty acid metal salts such as zinc stearate, aluminum stearate, calcium stearate, and fluidizing agent particles such as carbon black that have been subjected to a hydrophobization treatment. The water-repellent treatment can be carried out according to a known method. For example, fluidizing agent particles are mixed with silane coupling agents such as silicone oil, modified silicone oil, silicone varnish, tetramethyldisilazane, organoalkoxysilanes, and organochlorosilanes. Then, a silane coupling agent may be attached to the surface of the fluidizing agent particles.

Among these, those having a specific surface area of 90 to 240 m ² / g are preferable, and silica (hydrophobic silica) having a specific surface area of 90 to 240 m ² / g is more preferable. By using hydrophobic fluidizing agent particles having a specific surface area of 90 to 240 m ² / g, sufficient fluidity is imparted even with a small diameter toner. The imparting of fluidity to the toner is based on the function of the fluidizing agent particles as a spacer. Due to the presence of the fluidizing agent particles, air is interposed between the toner particles, and the fluidity of the toner is improved. When the specific surface area is significantly less than 90 m ² / g, the spacer effect becomes insufficient, the amount of air intervening between the toner particles is reduced, and the fluidity may be lowered. On the other hand, if it significantly exceeds 240 m ² / g, aggregation of the fluidizing agent particles occurs, the fluidizing agent particles are released from the coloring resin particles, and the free fluidizing agent particles cause the image. May cause image defects such as vitiligo. Hydrophobic fluidizer particles can be used alone or in combination of two or more.

The specific surface area of the hydrophobic fluidizing agent particles was measured by the BET specific surface area using a model “automatic specific surface area meter” manufactured by Nikkiso Co., Ltd.
The particle size of the hydrophobic fluidizing agent particles is preferably 7 to 30 μm.
The amount of the hydrophobic fluidizing agent particles used is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the colored resin particles depending on the type of the hydrophobic fluidizing agent particles and the like. If it is less than 0.1 part by weight, the spacer effect may be insufficient. If it exceeds 3.0 parts by weight, floating silica may be generated and white spots may be generated in the image.

(Description of other ingredients)
In addition to the above-described components, the coloring resin particles may be a negative charge control agent, a positive charge control agent, a wax other than a polyalkylene resin, an inorganic material, as long as the preferable characteristics of the toner for developing an electrostatic latent image in the present invention are not impaired. One or more selected from colorants other than pigments, magnetic powder, and the like can be included.

〔式中、ＸはＣｌ^-、Ｂｒ^-、−ＳＯ₂ＮＨ₂、−ＳＯ₂ＣＨ₃または−ＳＯ₂Ｃ₂Ｈ₅を示す。Ａ⁺は炭素数８〜１６の直鎖状アルキルアンモニウム基または炭素炭素結合の間に１個のヘテロ原子が介在してもよい炭素数８〜１６の分岐鎖状アルキルアンモニウム基を示す。〕 As the negative charge control agent, those commonly used in this field can be used, and among them, a chromium complex compound is preferable. As the chromium complex compound having a negative charge control effect, a known compound, for example, a chemical structural formula (1) can be used.

[Wherein X represents Cl ⁻ , Br ⁻ , —SO ₂ NH ₂ , —SO ₂ CH ₃ or —SO ₂ C ₂ H ₅ . A ⁺ represents a linear alkylammonium group having 8 to 16 carbon atoms or a branched alkylammonium group having 8 to 16 carbon atoms in which one hetero atom may intervene between carbon-carbon bonds. ]

In the chemical structural formula (1), examples of the linear alkylammonium group having 8 to 16 carbon atoms represented by the symbol A ⁺ include NH ₃ ⁺ C ₁₂ H ₂₅ , NH ₃ ⁺ C ₁₄ H _{29 and the} like. It is done.
In the above chemical structural formula (1), in the branched alkylammonium group having 8 to 16 carbon atoms in which one heteroatom may be interposed between carbon-carbon bonds represented by the symbol A ⁺ , Examples thereof include atoms capable of forming multivalent ions such as nitrogen atoms, oxygen atoms, and sulfur atoms. Among these, an oxygen atom is preferable. Specific examples of the branched alkylammonium group include, for example, NH ₃ ⁺ C ₃ H ₆ OC (C ₂ H ₅ ) HC ₄ H ₉ , NH ₃ ⁺ C ₃ H ₆ OCH ₂ C (C ₂ H ₅ ) HC ₄ H _{9 and the} like can be mentioned.
A negative charge control agent can be used individually by 1 type, or can use 2 or more types together.
The amount of the negative charge control agent is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.5 to 5.0 parts by weight, more preferably 1 to 3% by weight with respect to 100 parts by weight of the polyester resin. It is.

  As the positive charge control agent, those commonly used in this field can be used, and examples thereof include nigrosine dyes, pyridinium salts, ammonium salts, and chelate compounds thereof. A positive charge control agent can be used individually by 1 type, or can use 2 or more types together. The amount of the positive charge control agent is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.05 to 5 parts by weight, more preferably 0.1 to 0.3 parts by weight with respect to 100 parts by weight of the polyester resin. Part.

  Waxes other than the polyalkylene resin are used, for example, to further improve the fixability of the toner of the present invention. As the wax, those commonly used in this field can be used, and examples thereof include natural waxes such as montanic acid ester wax and carnauba wax, silicone wax, and fluorine wax. The wax can be used alone or in combination of two or more.

(Description of manufacturing method of toner for developing electrostatic latent image)
The toner for developing an electrostatic latent image in the present invention can be produced according to a known method. For example, polyester resins, polyalkylene resins, polyolefin-based dispersants and non-oxidized polyethylene, and other internal additives as necessary (additives that can be added to the colored resin particles) are added to a Henschel mixer, a super mixer, a mechanomill, Q Mixed with an air flow mixer such as a type mixer, melted and kneaded at a temperature of about 70 to 180 ° C. with a kneader such as a twin-screw kneader or a single-screw kneader, and the obtained kneaded material is cooled and solidified, and then solidified Is then pulverized by an air-type pulverizer such as a jet mill, and the particle size is adjusted as necessary to produce colored resin particles having a particle size of preferably 3 to 15 μm, more preferably 5 to 8 μm. The toner for developing an electrostatic latent image in the present invention is prepared by mixing particles and an external additive (hydrophobic fluidizing agent particles) and attaching the external additive to the surface of the colored resin particles. Can be manufactured.

(Description of image forming method)
The image forming method of the present invention detects the magnetic permeability of the developer for developing an electrostatic latent image, and records an image on a recording material by electrophotography while controlling the toner concentration of the developer based on the detected data. It is characterized by doing. In this case, it is preferable to detect the magnetic permeability of the developer for developing an electrostatic latent image using a differential transformer type magnetic permeability sensor from the viewpoint of the simplest and high accuracy in toner density control. Further, the magnetic permeability sensor may be a magnetic bridge type magnetic permeability sensor.
When forming an image, for example, based on the image information, the exposure means exposes the electrophotographic photosensitive member to form an electrostatic latent image on the electrophotographic photosensitive member, and the electrostatic latent image is charged. The toner for developing an electrostatic latent image of the present invention is supplied and developed as a toner image. The toner image is transferred to a recording material such as paper or an OHP film by a method such as pressurization, and further transferred to the recording material. An image is formed on the recording material by fixing the image on the recording material by a method such as heating and pressing.
As the electrophotographic photoreceptor used here, an organic photoreceptor drum having a photoconductive layer can be preferably used.

(Description of image forming apparatus)
The image forming apparatus of the present invention includes the developer for developing an electrostatic latent image described above and a magnetic permeability sensor for detecting the magnetic permeability of the developer, detects the magnetic permeability of the developer, and detects the detected magnetic permeability. The present invention is characterized in that an image can be recorded on a recording material by electrophotography while controlling the toner density of the developer based on the data. In this case, the magnetic permeability sensor is preferably a differential transformer type magnetic permeability sensor for the same reason as described above. Further, the magnetic permeability sensor may be a magnetic bridge type magnetic permeability sensor.

Next, the image forming apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a side sectional view schematically showing a configuration of a main part of the image forming apparatus of the present invention.
The image forming apparatus 100 records and outputs an image read by the image reading apparatus and data (image information) from an external device (for example, an image processing apparatus such as a personal computer) connected to the image forming apparatus 100 as an image. To do.

The image forming apparatus 100 includes an image forming unit 1, a recording material supply unit 2, an image fixing unit 3, and a control unit 4.
The image forming unit 1 includes a photosensitive drum 5, a charging unit 6, an exposure unit 7, a developing unit 8, a transfer unit 9, a cleaning unit 10, and a charge removing unit 11 provided so as to face the circumferential surface of the photosensitive drum 5. including.
The photosensitive drum 5 includes a cylindrical or columnar conductive substrate (not shown) and a photoconductive layer formed on the surface of the conductive substrate.

The charging unit 6 includes a contact type or non-contact type charger such as a charging roller or a charging charger, and charges the peripheral surface of the photosensitive drum 5 to a predetermined polarity and potential.
The exposure unit 7 is constituted by a laser unit such as a semiconductor laser, and exposes the peripheral surface of the photosensitive drum 5 in a charged state by the charging unit 6 based on image information transmitted from the control unit 4. Write an electrostatic latent image on

The developing unit 8 supplies a developer containing toner supplied from the developer supply container 13 to the electrostatic latent image written on the peripheral surface of the photosensitive drum 5 to visualize the electrostatic latent image. As a result, a toner image is formed on the circumferential surface of the photosensitive drum 5. Further, the developing unit is provided with the differential transformer type magnetic permeability sensor (not shown) in the vicinity of the developer accommodating portion, detects the magnetic permeability of the developer, and transmits the detected data to the control portion 4. The control unit 4 supplies toner of a toner amount (weight) based on the detection data from the developer supply container 13 to the developer storage unit as needed, and controls the toner concentration in the developer to a predetermined concentration range.
The transfer unit 9 includes, for example, a transfer roller 12 and a voltage application unit (not shown). The transfer unit 9 charges the recording material by applying a voltage from the transfer roller 12 side of the recording material. By pressing, the toner image on the circumferential surface of the photosensitive drum 5 is transferred to the recording material. The recording material is supplied to the transfer means 9 by the recording material supply means 2 described later in synchronization with the exposure by the exposure unit 7.

The cleaning unit 10 includes a cleaning blade made of an elastic material, and removes toner remaining on the peripheral surface of the photosensitive drum 5 after transferring the toner image to the recording material.
The neutralization unit 11 is configured by a neutralization lamp or the like, and removes the electric charge on the peripheral surface of the photosensitive drum 5 after cleaning.
In the image forming unit 1, the peripheral surface of the photosensitive drum 5 is uniformly charged by the charging unit 6, and exposure is performed from the exposure unit 7 to write an electrostatic latent image. This electrostatic latent image is visualized by the developer supplied from the developing unit 8, and a toner image is formed on the circumferential surface of the photosensitive drum 5. This toner image is transferred to the recording material by the transfer means 9. After the transfer, the photosensitive drum 5 is cleaned by being subjected to removal of residual toner by the cleaning unit 10 and charge removal by the charge removing means 11. By repeating this series of operations, a plurality of images can be formed.

The recording material supply unit 2 includes a recording material storage tray 20, a pickup roller 21, and a registration roller 22. The recording material storage tray 20 is a tray for storing recording materials such as plain paper, color copy paper, and OHP film. The recording material supply to the recording material storage tray 20 is performed by pulling out the recording material storage tray 20 to the front side (operation side) of the image forming apparatus 100. The pickup roller 21 separates the recording materials in the recording material storage tray 20 one by one and feeds them to the registration rollers 22. The registration roller 22 sequentially feeds the recording material between the photosensitive drum 5 and the transfer unit 9 in synchronization with the exposure of the exposure unit 7 on the circumferential surface of the photosensitive drum 5 in the image forming unit 1.
According to the recording material supply unit 2, the recording material stored in the recording material storage tray 20 is supplied to the image forming unit 1 via the pickup roller 21 and the registration roller 22.

The image fixing unit 3 includes a fixing device 30, a conveyance roller 31, a switching gate 32, a reverse roller 33, and a stacking tray 34. The fixing device 30 includes a fixing roller 35 and a pressure roller 36. In the fixing device 30, the recording material on which the toner image is transferred by the transfer unit 9 of the image forming unit 1 is passed between the fixing roller 35 and the pressure roller 36, and the toner image is applied to the recording material by heat and pressure. Let it settle. As a result, an image is formed (recorded) on the recording material. The conveyance roller 31 feeds the recording material on which the image is formed by the fixing device 30 to the switching gate 32. The switching gate 32 switches the feeding path of the image-recorded recording material. Through the switching gate 32, the image-recorded recording material is conveyed to the reversing roller 33, or a relay conveyance device (not shown) or a recording material resupply / conveyance device. The relay conveyance device and the recording material re-feed conveyance device will be described later. The reversing roller 33 discharges the image-recorded recording material to the stacking tray 34 when the recording material discharge tray is set to the stacking tray 34. On the other hand, when double-sided image formation or post-processing is designated, the reversing roller 33 rotates reversely after discharging a part of the recording material toward the stacking tray 34 with the image-recorded recording material sandwiched therebetween. The recording material is transported from the switching gate 32 to a relay transport device (not shown). At this time, the switching gate 32 is switched from the solid line state to the broken line state. The stacking tray 34 is a tray that is provided outside the image forming apparatus 100 and discharges and stores the image-recorded recording material outside the image forming apparatus 100.
According to the image fixing unit 3, the toner image is fixed by the fixing device 30, and the recording material on which the image is recorded is conveyed to the reversing roller 33 via the conveying roller 31 and the switching gate 32, and is loaded according to the setting. 34, or is reversely conveyed to a relay conveyance device or a recording material resupply conveyance device (not shown) via the switching gate 32 again.

  The control unit 4 is provided in the upper and lower space portions of the exposure unit 7 inside the image forming apparatus 100, and includes a circuit board that controls the image forming process, an interface board that receives image data from an external device, and a power supply unit (not shown). Consists of. The power supply device supplies power not only to the circuit board and the interface board but also to each device in the image forming unit 1, the recording material supply unit 2, and the image fixing unit 3.

Note that conveyance paths 37, 38, and 39 are provided on the lower and side surfaces of the image forming apparatus 100. The conveyance paths 37, 38, and 39 are used for conveying a recording material to the inside or the outside of the image forming apparatus 100 when an external apparatus is connected to the image forming apparatus 100.
According to the image forming apparatus 100, an electrostatic latent image is written on the peripheral surface of the photosensitive drum 5 based on image information input to the control unit 4, and the electrostatic latent image is developed and transferred to a recording material. Then, the toner is further fixed and discharged to the stacking tray 34 or used for another image forming process.

  FIG. 2 is a side sectional view schematically showing the overall configuration of the image forming apparatus of the present invention. The image forming apparatus according to the present embodiment includes a recording material supply device 50, a recording material supply device 51, a recording material resupply / conveyance device 52, a relay conveyance device 53, a post-processing device 54, and an image reading device outside the image forming device 100. A device 55 is arranged. Description of the image forming apparatus 100 will be omitted.

  The recording material supply device 50 includes recording material accommodation trays 56 a, 56 b, 56 c and a feeding path 57. The recording material storage trays 56a, 56b, and 56c store recording materials of the same size or different sizes. When replenishing or replacing the recording material in the recording material storage trays 56a, 56b, and 56c, the recording material storage trays 56a, 56b, and 56c are pulled out toward the front side of the recording material supply device 52 main body. In this figure, the recording material supply device 50 is constituted by three recording material accommodation trays 56a, 56b, and 56c, but may be constituted by one, two, or four or more recording material accommodation trays. The recording material feeding path 58 is connected to the conveyance path 37 on the lower surface of the image forming apparatus 100 on the upper surface of the recording material supply apparatus 50, and the recording material fed from the recording material accommodation trays 56a, 56b, and 56c is supplied to the image forming apparatus. 100. The recording material supply device 50 selectively operates any of the recording material storage trays 56a, 56b, and 56c that store the recording material specified by the user, and stores them in the recording material storage trays 56a, 56b, and 56c. The transferred transfer material is fed to the image forming apparatus 100 via the feeding path 57. The recording material supply device 50 is also a unit having a desk function on which the image forming apparatus 100 is placed, and is configured to be detachable from the image forming apparatus 100. According to the recording material supply device 50, the recording material is transferred to the conveyance path 37 of the image forming apparatus 100 via the feeding path 57 and reaches the image forming unit 1.

  The recording material supply device 51 includes a recording material storage tray 58, a recording material supply means 59 provided inside the recording material storage tray 58, and a feeding path 60 provided on the upper side of the recording material supply tray. The recording material accommodation tray 58 can accommodate a larger amount of recording material than the recording material accommodation tray 20 in the image forming apparatus 100 and the recording material accommodation trays 56 a, 56 b, 56 c in the recording material supply apparatus 50. The recording material is placed on the recording material supply means 59. The recording material supply means 59 adjusts so that the uppermost part of the recording material placed thereon comes to the position of the conveyance path 60 by a driving means and a sensor (not shown). The feeding path 60 is connected to a feeding path 63 provided at a lower side surface of a recording material refeeding and conveying apparatus 52 to be described later, and the feeding path 63 is further connected to a conveying path 38 provided at a lower side surface of the image forming apparatus 100. Connected. According to the recording material supply device 51, the recording material accommodated in the recording material accommodation tray 58 is separated and fed to the image forming unit 1 via the feeding path 60, the feeding path 63 and the transport path 38.

The recording material refeeding / conveying device 52 includes feeding paths 61, 62, and 63.
One of the feeding paths 61 is connected to a conveyance path 39 on the side surface of the image forming apparatus 100 at the upper part of the side surface facing the image forming apparatus 100, and the other is a feeding path 64 provided on a side surface of the relay conveyance apparatus 53 described later. Connected to.
The feeding path 62 is branched from the feeding path 61, and after joining the feeding path 63, is connected to the conveyance path 38 on the side surface of the image forming apparatus 100 at the lower side surface facing the image forming apparatus 100. Is done.
The feeding path 63 is connected to a feeding path 60 provided at the upper part of the side surface of the recording material supply apparatus 51 at the lower part of the side surface facing the recording material supply apparatus 51.
According to the recording material resupply / conveyance device 52, the recording material that is reversely conveyed by the reversing roller 33 in the image fixing unit 3 of the image forming apparatus 100 is fed via a feeding path 61 to a relay conveyance device 53 described later. Or is fed again to the image forming apparatus 100 via the feeding paths 61 and 62. The feeding to the relay conveyance device 53 is a case where post-processing is performed. The re-feeding to the image forming apparatus 100 is when double-sided image formation is performed. Further, the recording material accommodated in the recording material supply device 51 is supplied to the image forming apparatus 100 via the supply paths 62 and 63.

One end of the relay conveyance device 53 is mounted on the recording material refeeding conveyance device 52, and the other end is mounted on a receiving conveyance portion 65 of the post-processing device 54 described later, and a rotation fulcrum 66 provided on the conveyance portion 65 is the center. It is rotatably supported. In addition, a feeding path 64 is provided therein, and one end of the feeding path 64 is connected to the feeding path 61 of the recording material refeeding device 52, and the other end is fed inside the post-processing device 54. Connected to path 68.
The relay conveyance device 53 is a device that feeds the image-formed recording material supplied from the image forming apparatus 100 via the recording material re-supply conveyance device 52 to the post-processing device 54.
The relay conveyance device 53 does not need to be rotatably provided, and can be a connecting member (first positioning member) that connects the image forming apparatus 100 and the post-processing device 54.

The post-processing device 54 is connected to the image forming apparatus 100 via the recording material re-feeding and conveying device 52 and the relay conveying device 53, and receives and conveys a receiving portion 65, a rotation fulcrum 66 provided in the receiving and conveying portion 65, and post-processing A section 67, a feeding path 68 provided so as to penetrate the receiving conveyance section 65 and the post-processing section 67, a first recording material discharge section 69, and a second recording material discharge section 70. The
The receiving and conveying unit 65 feeds the image-recorded recording material supplied from the relay conveying device 53 to the post-processing unit 67 via the feeding path 68.
Although not shown, the post-processing unit 67 is a post-processing unit having a function (stapling function) for applying a predetermined number of recording materials, such as staple, and a function for folding the recording material into a predetermined size (A4, B4, etc.). Processing means, post-processing means having a function for punching holes for filing (punch function), post-processing having a function (sorter function) capable of changing the discharge position within a range of several bins to several tens bins for sorting or sorting One or more means such as means can be provided.

In the first recording material discharge unit 69, the image-recorded recording material is sorted into a plurality of units and discharged by the sorter function of the post-processing unit 67. Of course, it may be discharged without using the sorter function and without sorting. The recording material on which the image has been recorded is discharged to the second recording material discharge section 70 after being subjected to processing such as stapling (stapling) and punching (file hole making). Which is discharged is selected by the user.
According to the post-processing device 54, desired post-processing is performed on the image-recorded recording material.
The image reading device 55 includes a document table (not shown), an optical scanning unit 71 provided at the lower part of the document table, an image sensor 72, an automatic document feeder 73, an image reading device support table 74, and a memory (not shown). Consists of including.
The document table is made of a transparent material such as glass and is provided for placing a document on which an image has been recorded.

  The optical scanning unit 71 is provided so as to be able to scan and move the lower surface of the document table, exposes and scans an image of the document set on the document table, and transmits the optical image to the image sensor 72. The optical scanning unit 71 scans and reads a document image from below the document in the process of conveying the document along the automatic document transport path. The optical scanning unit 71 guides an optical image to the image sensor 72 and reads a document image. When both sides of the document are read simultaneously, the light source that exposes the document, an optical lens that guides the optical image to the image sensor, an imaging element that converts the optical image into image data, and the like are attached to the upper surface of the document. An image sensor (CIS) can be mounted on the automatic document feeder 73. In such a configuration, when the double-sided original reading mode is set, the originals set in a supply unit (not shown) of the automatic original conveying apparatus 73 are sequentially conveyed and images on both sides of the original are read almost simultaneously.

The imaging device 72 is configured by a charge coupled device (CCD) or the like, and converts the optical image guided from the optical scanning unit 71 into image data.
The automatic document feeder 73 is a device that sequentially feeds documents placed on a supply unit (not shown) one by one to the document table. The automatic document feeder 73 operates when the image reading device 55 is set to the automatic reading mode. On the other hand, the image reading device 55 is provided with a manual reading mode in addition to the automatic reading mode. In the manual reading mode, an original in which a plurality of originals are bound together such as a book or a magazine, or a sheet original that cannot be automatically supplied by the automatic original conveying device 73 is manually set on an original table and the original is placed. This is a method of reading an image.
According to the image reading device 55, an image of a document set on the transparent mounting table is exposed and scanned by the exposure unit 71 to form an image on the image sensor 72, and the image of the document is converted into an electrical signal. After being stored in the memory, it is output to the control unit 4 as image data.

Synthesis Examples, Examples, Comparative Examples and Test Examples are given below to specifically explain the present invention. Hereinafter, “parts” and “%” mean “parts by weight” and “% by weight”, respectively, unless otherwise specified.
(Synthesis Example 1) (Synthesis of polyalkylene resin dispersant)
40 parts of xylene and 20 parts of non-oxidized polypropylene (softening point: 152 ° C., trade name: Viscol 550P, manufactured by Sanyo Chemical Industries, Ltd.) are put into a stainless steel pressure reactor, and the pressure reactor is sufficiently filled with nitrogen. After the replacement, the temperature was raised to 170 ° C. in a sealed state. While maintaining this temperature, a mixed solution of 80 parts of styrene, 12 parts of n-butyl acrylate, 8 parts of methyl methacrylate and 1 part of di-butyl peroxide was added dropwise over 4 hours, and further maintained at 170 ° C. for 1 hour. A xylene solution containing a graft polymer and a styrene (meth) acrylate resin was obtained. By distilling off xylene from the solution, a polyalkylene resin dispersant (a) was obtained.

(Manufacture of toner A)
Polyester resin (acid value 25, hydroxyl value 11, Sanyo Chemical Industries Co., Ltd.) 100 parts Polyalkylene resin dispersant 3 parts Negative charge control agent (trade name: Aizen Spiron Black TRH, Hodogaya Chemical Co., Ltd.) 1 .5 parts carbon black (trade name: MA77, manufactured by Mitsubishi Chemical Co., Ltd.) 10 parts non-oxidized polypropylene (Biscol 550P) 3 parts non-oxidized polyethylene (PE-130) 3 parts After melt-kneading with a shaft extruder, the mixture was cooled and crushed to obtain toner particles (coloring resin particles) having an average particle diameter (D ₅₀ ) of 6.7 μm. The average particle diameter D ₅₀ of the toner particles is a value measured with a commercially available Coulter Counter TAII type manufactured by Coulter USA.
To 100 parts of the toner particles, 2.8 parts by weight of hydrophobic silica (trade name: R976S, specific surface area 110 m ² / g, manufactured by Nippon Aerosil Co., Ltd.) was added and mixed to obtain toner A.

(Manufacture of toner B)
Toner A having toner particles having an average particle diameter (D ₅₀ ) of 8.7 μm in the same manner as toner A, except that polyester resin, carbon black and hydrophobic fluidized particles are changed to the following in the production of toner A B was obtained.
Polyester resin (acid value 20, hydroxyl value 3, Sanyo Chemical Industries, Ltd.) 100 parts Carbon black (MA-77) 3 parts Hydrophobic silica (trade name: R812, specific surface area 260 m ² / g, Nippon Aerosil Co., Ltd. ) Made) 0.3 parts

(Manufacture of toner C)
In the production of the toner A, the average value was changed in the same manner as in the toner A1, except that the polyester resin and the hydrophobic fluidized particles were changed to the following and the amount of carbon black (MA-77) was changed to 4 parts. Toner C having toner particles with a particle size (D ₅₀ ) of 7.0 μm was obtained.
Polyester resin (acid value 32, hydroxyl value 18, manufactured by Sanyo Chemical Industries) 100 parts Hydrophobic silica (trade name: RX50, specific surface area 50 m ² / g, manufactured by Nippon Aerosil Co., Ltd.)
4.0 parts

(Manufacture of toner D)
Toner D was obtained in the same manner as Toner A except that the average particle size (D ₅₀ ) of the toner particles was changed to 8.7 μm in the production of Toner A.

Table 1 shows the acid value, hydroxyl value and glass transition temperature (Tg, ° C) of the polyester resin in toners A to D, the amount and specific surface area of the hydrophobic fluidizing agent particles, and the average particle diameter (D ₅₀ ) of the toner particles. And the time constant.

Developers A to Q were prepared by mixing toners A to D and carriers A to H shown in Table 2 in the following combinations and toner concentrations (toner weight / developer weight). Among these developers A to Q, developers A to O correspond to Examples 1 to 15 of the present invention, and developers P and Q correspond to Comparative Examples 1 and 2.
Developer A (Example 1): Toner A + Carrier A, Toner concentration%: 3.5%
Developer B (Example 2): Toner B + Carrier A, toner concentration%: 5.0%
Developer C (Example 3): Toner A + Carrier B, toner concentration%: 3.5%
Developer D (Example 4): Toner B + Carrier B, Toner concentration%: 4.0%
Developer E (Example 5): toner C + carrier C, toner concentration%: 5.0%
Developer F (Example 6): Toner A + Carrier D, Toner concentration%: 3.5%
Developer G (Example 7): Toner A + Carrier A, Toner concentration%: 4.8%
Developer H (Example 8): Toner A + Carrier B, Toner concentration%: 3.2%
Developer I (Example 9): Toner A + Carrier C, Toner concentration%: 6.0%
Developer J (Example 10): Toner A + Carrier D, Toner concentration%: 2.9%
Developer K (Example 11): Toner A + Carrier E, Toner concentration%: 4.8%
Developer L (Example 12): Toner A + Carrier F, Toner concentration%: 5.3%
Developer M (Example 13): Toner A + Carrier G, Toner concentration%: 2.5%
Developer N (Example 14): toner A + carrier H, toner concentration%: 2.2%
Developer O (Example 15): Toner D + Carrier A, Toner concentration%: 4.5%
Developer P (Comparative Example 1): Toner D + Carrier B, Toner concentration%: 6.0%
Developer Q (Comparative Example 2): Toner A + Carrier F, Toner concentration%: 2.0%

(Test Example 1)
Using toners of Developers A to Q, the number of histories shown in Table 3 is displayed at room temperature (20 ° C., 65%) in a digital copying machine (trade name: AR-705, manufactured by Sharp Corporation) under a normal temperature environment. The actual evaluation test (using a 6% manuscript) was performed and the following evaluation was performed. The results are shown in Table 3. In addition, domestic paper was used for the paper.

[Image density]
The image density of the image formed using an image density measuring machine (trade name: PROCESS MEASUREMENTS RD914 type, Macbeth (manufactured by Macbeth)) was measured, and 1.30 or more was evaluated as ◯, and less than 1.30 was evaluated as ×.

[Cover]
Measuring instrument: Commercially available NIPPON DENSHOKU Color Meter ZE2000 type Evaluation method: 1.5 or less was evaluated as ◯, and more than 1.5 was evaluated as ×.

[Abrasion resistance (rubbing fixation rate)]
The rubbing resistance of the black solid image was examined. If the rubbing resistance is good, it means that a paper jam due to poor fixation of a black solid image hardly occurs. Evaluation was carried out as follows (A) to (C).
(A) Using a digital copying machine (AR-705), a black solid image of 30 mm square was recorded on 8.5 inch × 11 inch cat paper, and the image density was measured (image density A). In addition, domestic paper was used for the paper.
(B) A cat paper is pasted on the bottom of a circular weight (400 g) having a diameter of 50 mm, and the 30 mm square black solid image is rubbed 5 times so that the surface of the weight of the cat paper touches the 30 mm square black solid image. The image density of the image was measured (image density B).
(C) The rubbing and fixing rate of the black solid image was calculated based on the following equation.
Friction fixing rate (%) = (Image density B / Image density A) × 100
The rubbing and fixing rate was evaluated as ◯ for 90% or more and x for less than 90%.

[Swelling phenomenon]
The output of a magnetic permeability sensor that detects a change in the magnetic permeability of the developer was recorded on a recorder, and the swell phenomenon was determined based on the recorded output line of the magnetic permeability sensor. The waviness phenomenon refers to a phenomenon in which peaks and troughs occur continuously in the output line of the magnetic permeability sensor. When the value δ obtained by subtracting the central value of the valley from the central value of the peak of the output line is 0.05 (V) or less, it is evaluated as ◯, and when it exceeds 0.05 (V), it is evaluated as x.

As shown in Table 3, in Examples 1 to 12, since the relative magnetic permeability of the developer is within the range of 1.65 to 2 which is preferable in the present invention, no swell phenomenon was observed.
Further, among Examples 1 to 12 of the present invention, except for Examples 2, 4 and 5, other various performances required for image formation (image density, fogging and scratch resistance) are satisfied at a high level. I found out that
In Examples 2 and 4 (Developers B and D), only the image density was poor. As a cause of this, the toner B of Examples 2 and 4 has a time constant of 540 msec, which can be considered to largely exceed the preferable range of 100 to 350 msec in the present invention.
Further, Example 5 (Developer E) was poor only in abrasion resistance. This is because the time constant of the toner C of Example 5 is as large as 425 msec, and the specific surface area of the hydrophobic fluidizing agent particles is 50 cm ² / g, which is preferably 90 to 240 m ² / g in the present invention. It is mainly thought that it is smaller than.
On the other hand, since Comparative Example 1 (Developer P) caused carrier adhesion, an image could not be formed. This is because the developer has a low relative magnetic permeability, so the resistance of the developer is high, and the counter charge remaining on the carrier surface after developing the toner moves slowly. It is inferred that it adhered.
In Comparative Example 5 (Developer Q), the developer concentration is low and the amount of toner contributing to development is insufficient, and the relative permeability is high, so the resistance of the developer is low. It is presumed that the electric field strength necessary for development between the photoconductor and the developer has decreased due to so-called charge injection, where the development bias neutralizes the photoconductor surface charge through the developer that rubs the photoconductor. Is done.

1 is a side sectional view schematically showing a configuration of a main part of an image forming apparatus of the present invention. 1 is a side sectional view schematically showing an overall configuration of an image forming apparatus of the present invention. It is a circuit diagram of the carrier current measuring device used in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image formation part 2 Recording material supply part 3 Image fixing part 4 Control part 5 Photosensitive drum 6 Charging means 7 Exposure unit 8 Development unit 9 Transfer means 10 Cleaning unit 11 Static elimination means 12 Transfer roller 20 Recording material accommodation tray 21 Pickup roller 22 Registration roller 30 Fixing device 31 Conveying roller 32 Switching gate 33 Reversing roller 34 Stacking tray 35 Fixing roller 36 Pressure roller 37, 38, 39 Conveying path 50, 51 Recording material supply device 52 Recording material re-feeding conveying device 53 Relay conveying device 54 Post-processing device 55 Image reading device 56a, 56b, 56c, 58 Recording material storage tray 57, 60, 61, 62, 63, 64, 68 Feeding path 59 Recording material supply means 65 Receiving and conveying unit 66 Rotating fulcrum 67 Post-processing unit 69 First recording material discharge unit 70 Second recording Discharge portion 71 the optical scanning unit 72 photoelectric conversion element 73 automatic document feeder 74 image reading apparatus support base 100 an image forming apparatus

Claims (12)

A developer for developing an electrostatic latent image, and a magnetic permeability sensor for detecting the magnetic permeability of the developer;
The developer includes an electrostatic latent image development including a coloring resin particle having a binder resin containing a polyester resin and a pigment, and a hydrophobic fluidizing agent particle adhering to the surface of the coloring resin particle. Toner and carrier,
An electrophotographic method while detecting the magnetic permeability of the developer by the magnetic permeability sensor and controlling the toner concentration of the developer so that the relative magnetic permeability of the developer becomes 1.65 to 2 based on the detected data. An image forming apparatus configured to be capable of recording an image on a recording material . The relative permeability of the developer is determined by the carrier saturation magnetization σs (unit: Am ² / kg), carrier volume average particle diameter D ₅₀ (unit: μm), carrier current value I (unit: μA), and toner concentration (unit). : Weight%)
The carrier has a saturation magnetization σs of 55 to 93 Am ² / kg, the carrier volume average particle diameter D _{50 of 50} to 85 μm , the carrier current value I of 0.1 to 140 μA , and the toner concentration of 2.2 to. The image forming apparatus according to claim 1, wherein the image forming apparatus is set to 6.0% by weight. The image forming apparatus according to claim 1, wherein the carrier contains one or more of manganese, magnesium, copper, zinc, and lithium. The image forming apparatus according to any one of claims 1 to 3 acid value of the polyester resin is 15~30mgKOH / g and a hydroxyl value of 4~17mgKOH / g. The image forming apparatus according to any one of claims 1 to 4 , wherein the polyester resin has a glass transition temperature of 55 to 65 ° C. The image forming apparatus of any one of claims 1 to 5 melt index of the polyester resin is 0.1~6.0g / 10 min. Wherein the pigment is a carbon black, the image forming according to any one of claims 1-6 contained in the colored resin particles in a proportion of 5 to 20 parts by weight based on the polyester resin 100 parts by weight Equipment . The hydrophobic fluidizing particles are hydrophobic silica having a specific surface area 90~240m ² / g image forming apparatus according to any one of claims 1-7. The hydrophobic fluidizing particles, the image forming apparatus according to any one of claims 1-8 is mixed from 0.1 to 3.0 parts by weight based on the colored resin particles 100 parts by weight. The magnetic permeability sensor, the image forming apparatus according to any one of claims 1 to 9 is a differential transformer type magnetic permeability sensor. Toner for electrostatic latent image development comprising coloring resin particles comprising a binder resin containing a polyester resin and a pigment, and hydrophobic fluidizer particles adhering to the surface of the coloring resin particles, and a carrier supply toner to the developer as detected by the permeability sensor permeability of the electrostatic latent image developing developer relative permeability of the developer based on the detected data is from 1.65 to 2, including bets And forming an image on a recording material by electrophotography while controlling the toner density. The image forming method according to claim 11, wherein a magnetic permeability of the developer for developing an electrostatic latent image is detected using a differential transformer type magnetic permeability sensor as the magnetic permeability sensor.

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