JP2008116927A - Image forming method, image forming apparatus and developer - Google Patents

Abstract

ε'：像担持体の比誘電率、q：トナー１粒子あたりの帯電量、r：トナー粒子の体積平均半径としたとき求められるa/rが、0.2≦a/r≦0.7とする。
【選択図】なしEven if the toner charge amount fluctuates over time or depending on the environment, it is possible to suppress fluctuations in an appropriate transfer bias electric field, to obtain a high-quality image having high-efficiency and stable transfer characteristics. An image forming method, an image forming apparatus, and a developer are provided.
An image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium, the toner particles including a colorant and a resin, And the average value F _e of the electrostatic adhesion force with the image carrier,
[Expression 15]

ε ′: relative permittivity of the image carrier, q: charge amount per toner particle, r: a / r obtained when the volume average radius of toner particles is 0.2 ≦ a / r ≦ 0.7.
[Selection figure] None

Description

  The present invention relates to an image forming method, an image forming apparatus, and a developer used for forming an image by an electrophotographic method such as a copying machine or a printer.

  In general, in an image forming apparatus using an electrophotographic method, toner is conveyed via a conveyance medium such as an electrostatic latent image carrier such as a photosensitive member, or an intermediate transfer medium such as a transfer belt, and desired on a transfer medium such as paper. It is attached to the position. An image is formed on the transfer medium by pressing with a heat roller or the like to fix the toner on the transfer medium.

  At this time, the toner adheres to these transport media by electrostatic force, van der Waals force, and liquid crosslinking force based on the charge amount of the toner particles. The adhered toner is peeled off from the medium mainly by an external electric field and adheres to the next transport medium. The toner thus adhered and peeled off and conveyed on the conveyance medium is finally fixed on the transfer medium. Therefore, by electrostatically controlling the adhesion force of the toner to the medium, the toner can be efficiently conveyed to finally form a high quality image, that is, transfer characteristics can be improved.

  In recent years, application of a cleanerless process has been advanced in image forming apparatuses. In the cleaner-less process, the toner on the photoconductor is recovered simultaneously with development by electrostatically controlling the adhesive force without using a cleaner. In the cleanerless process, there is a problem that exposure is hindered due to the influence of residual transfer toner due to poor adhesion force control, or retransfer is performed in time for recovery to the developing device, causing image defects.

  In addition, when such a cleanerless process is applied to a color image forming apparatus having a tandem configuration, the toner transferred from the photoreceptor to the (intermediate) transfer medium due to poor adhesion control is transferred from the subsequent photoreceptor. There is a possibility that reverse transfer is performed by receiving a transfer electric field in the transfer region and pressing it. When the reversely transferred toner is collected in the developing device by a cleaner-less process, the toner of the previous color is mixed and color management becomes difficult. Generally, reverse transfer tends to occur when the transfer electric field is increased to increase transfer efficiency. Therefore, there is a problem that a condition for preventing reverse transfer must be adopted even if the transfer efficiency is sacrificed to some extent.

  In order to peel the toner from the transport medium by an external electric field and transport it, an electric field (necessary transfer electric field) that increases the toner charge amount × the electric field strength with respect to the adhesive force between the toner and the transport medium. It is necessary to apply. Accordingly, the required transfer electric field E also varies as the toner charge amount varies with time or varies depending on the environment. In recent years, in order to improve image quality, it has been promoted to reduce the particle size of toner. Since the surface area is increased by reducing the particle size, even a slight change in the surface charge density causes a large variation in the charge amount Q / M per weight. Therefore, it is desirable that the required transfer electric field does not fluctuate much and can be controlled stably even if the toner charge amount fluctuates to some extent.

Until now, various methods for improving the transfer characteristics by paying attention to the adhesive force have been proposed. For example, Patent Document 1 specifies that the adhesion force F / volume average particle diameter D of an uncharged toner to an image carrier is 4.5 nN / μm or less, and weakens the adhesion force of the uncharged toner. Thus, a method has been proposed in which the adhesion of uncharged toner to the image carrier is reduced to reduce the transfer residue. However, no mention is made of the electrostatic control of the adhesive force and the influence of fluctuations in the toner charge amount.
JP 2004-212540 A

  The present invention suppresses fluctuations in the appropriate transfer bias electric field even when the toner charge amount fluctuates over time or depending on the environment, and has a high-efficiency and stable transfer characteristic to obtain a high-quality image. An object of the present invention is to provide an image forming method, an image forming apparatus, and a developer.

としたとき求められるa/rが、
0.2≦a/r≦0.7
である画像形成方法が提供される。 According to one aspect of the present invention, there is provided an image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium, wherein the toner particles include a colorant and a resin. The average value F _e of electrostatic adhesion between the toner particles and the image carrier,

A / r required when
0.2 ≦ a / r ≦ 0.7
An image forming method is provided.

としたとき求められるa/rが、
0.2≦a/r≦0.7
である画像形成方法が提供される。 According to another aspect of the present invention, there is provided an image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium via a conveyance medium, the toner forming method comprising: particles comprise a colorant and a resin, and the toner particles, an average value F _e of the electrostatic adhesion between the conveying medium,

A / r required when
0.2 ≦ a / r ≦ 0.7
An image forming method is provided.

  With the image forming method, the image forming apparatus, or the developer according to one embodiment of the present invention, even if the toner charge amount fluctuates with time or depending on the environment, the fluctuation of the appropriate transfer bias electric field is suppressed, and high efficiency and stability are achieved. It is possible to obtain a high-quality image having excellent transfer characteristics.

としたとき求められるa/rが、
0.2≦a/r≦0.7
である。 According to one aspect of the present invention, there is provided an image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium, wherein the toner particles include a colorant and a resin. The average value F _e of electrostatic adhesion between the toner particles and the image carrier,

A / r required when
0.2 ≦ a / r ≦ 0.7
It is.

としたとき求められるa/rが、
0.2≦a/r≦0.7
である。 The image forming method of one embodiment of the present invention is an image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium via a conveyance medium. the toner particles comprise a colorant and a resin, and the toner particles, an average value F _e of the electrostatic adhesion between the conveying medium,

A / r required when
0.2 ≦ a / r ≦ 0.7
It is.

  Here, the toner particles are carbon black, condensed polycyclic pigments, azo pigments, phthalocyanine pigments, known pigments such as inorganic pigments, colorants such as dyes, polyester resins, styrene-acrylic resins, cyclic olefins. Binder resin such as resin is included. Furthermore, if necessary, fixing aids such as waxes such as polyethylene, polypropylene, carnauba, rice, paraffin, charge control agents (CCA), silica, alumina, titanium oxide, etc. for the purpose of improving fluidity It is a known composition to which inorganic fine particles, organic fine particles and the like are externally added, and is formed by a chemical manufacturing method such as a pulverization method or a polymerization method.

  As the image carrier (electrostatic latent image carrier), a known photoreceptor such as positively charged or negatively charged OPC (Organic Photoconductor) or amorphous silicon is used. In these photoreceptors, a charge generation layer, a charge transport layer, and a protective layer may be laminated, or a layer having a plurality of functions among these layers may be formed. The conveyance medium is either a transfer belt, an intermediate transfer belt, or a roller. The transfer medium is a medium on which an image is finally formed, such as paper.

  The toner particles are used as a one-component developer. Further, by adding a magnetic carrier, it can be used as a two-component developer. Magnetic carriers include magnetic particles such as ferrite, magnetite and iron oxide, resin particles mixed with those magnetic powders, and fluorine resin, silicone resin, acrylic resin on at least a part of the surface of magnetic powder, etc. The particles are coated with a resin coat.

  The volume average particle size of the magnetic carrier particles is desirably 20 to 100 μm. If it is smaller than 20 μm, the magnetic force of one grain is small, so it will be detached from the developer carrier and easily adhere to the photoconductor. If it is larger than 100 μm, the magnetic brush will be hard and the brush marks may appear in the image. This makes it impossible to supply a precise toner. Preferably it is 30-60 micrometers.

Mean value F _e of the electrostatic adhesion between the transport medium of the toner particles is determined from the non-electrostatic adhesion force F ₀ for the average adhesive force F (N) and the toner particles to the carrier medium of the toner particles.

  The average adhesion force F (N) of toner particles to the carrier medium is measured using Hitachi Koki's ultracentrifuge for separation (CP100MX), angle rotor (Angle Roter: P100AT2), and cells manufactured for powder adhesion measurement. Measured as follows.

(Measurement method of average adhesive force F (N))
(1) A sheet having a surface protective layer equivalent to the conveyance medium to be measured for adhesion is formed on the surface. For example, if the adhesion force to the photosensitive member, a photosensitive sheet is produced, and if the adhesion force to the intermediate transfer belt, a sheet equivalent to the belt material is produced.
In order to measure the adhesive force, it is desirable that the surface protective layer is equivalent. As in actual use, a charge generation layer (CGL layer) and a charge transport layer (CTL layer) may be laminated. The adhesion force is more dependent on the shape (surface roughness, etc.), the charge amount of the toner particles, the environmental temperature and humidity, etc. than the substance of the object to be adhered, so it is not necessary to be exactly the same substance.
This sheet is wound around an aluminum tube, and the photosensitive layer is set to the GND potential and set at the position of the photosensitive drum. The toner is developed / attached to the surface in the same manner as normal image formation. In measuring the toner adhesion force to the intermediate transfer belt, the toner is transferred onto a sheet equivalent to the intermediate transfer belt material.
(2) Place the sheet with toner on the sample set. As shown in FIG. 1, the sample set 1 includes a plate A2, a plate B3, and a cylindrical spacer 4. The outer diameters of the plate A2, the plate B3, and the spacer 4 are 7 mm, the thickness of the spacer 4 is 1 mm, and the height is 3 mm. The sheet with the toner attached is cut to the size of plate A, and attached to the side of plate A2 in contact with the spacer with double-sided tape.
(3) As shown in FIG. 2, a sample set is set in the cell 5. Then, this cell 5 is set in the angle rotor 6 shown in FIG. 3 so that the back side of the plate A2 sample attached is directed to the center of rotation, and the angle rotor 6 is placed in an ultracentrifuge (not shown). Attach to.
(4) After rotating the ultracentrifuge at 10000 rpm, A and B are taken out, and the toner particles adhering to each are peeled off with a mending tape and pasted on a white paper. Then, the reflection density of the mending tape to which the toner has adhered is measured with a Macbeth densitometer.
(5) Separately, a calibration formula for the reflection density with respect to the toner amount is prepared, and the amount of toner separated and the amount of toner not separated are calculated in light of it.
(6) The sheet to which the toner is attached is cut and pasted on the plate A in the same manner as in (2), and set in the ultracentrifuge as in (3). Then, the ultracentrifuge is rotated at 20000 rpm and taken out as in (4), and the amount of toner adhering to the plates A and B is measured. Similarly, repeat up to 100,000 rpm every 10,000 rpm. The minimum number of rotations and the set interval for separation can be appropriately changed depending on the magnitude of the adhesive force or the distribution of the adhesive force.
(7) The centrifugal acceleration RCF that the sample set in the cell receives by the rotation of the rotor is
RCF = 1.118 × 10 ^-5 × r × N ² × g (2)
r: Distance from the rotation center of the sample set position
N: Rotational speed (rpm)
g: Gravitational acceleration, and the centrifugal force F received by the toner particles is when the weight of one toner particle is m.
F = RCF × m
m = (4/3) π × r ³ × ρ ・ ・ ・ (3)
r: True sphere equivalent radius
ρ: Since the specific gravity of the toner, at each rotation speed, the sum of the centrifugal force F applied to the toner and the ratio of the separated toner at each rotation speed is the sum of the toner and the photoreceptor in the developer. The average adhesion force is F (N).

  In such a method for measuring the average adhesion force F (N), the charge amount of the toner greatly affects the average adhesion force F (N). Therefore, in order to measure with high accuracy, it is desirable to prepare a measurement sample to which toner is adhered in accordance with an actual process.

Thus the average adhesion is measured F (N) is expressed by the sum of the non-electrostatic adhesion force F ₀ and the electrostatic adhesion force F _e. Further, the electrostatic adhesion force F _e is proportional to the square of the charge amount q per toner 1 particles.
F = F _e + F ₀ = K · q ² + F ₀ (4)
K: slope (proportional constant)

The non-electrostatic adhesion force F ₀ can be obtained, for example, by varying the toner / carrier mixture ratio, plotting q ^{2 on} the x-axis and the average adhesion force F on the y-axis, and obtaining a y-intercept by linear approximation. it can. The value of the non-electrostatic adhesive force F ₀ is desirably 1.5 × 10 ⁻⁸ <F ₀ <1 × 10 ⁻⁷ (N). If F ₀ is 1.5 × 10 ⁻⁸ (N) or less, the adhesion force of uncharged toner to the photoreceptor is reduced, which causes scattering of toner particles that cannot be controlled by the electric field. On the other hand, if F ₀ is 1 × 10 ⁻⁷ (N) or more, problems such as a necessary transfer electric field becoming too large and being difficult to develop occur.

From non-electrostatic adhesion force F ₀ for the average adhesive force F (N) and the toner particles against this way the medium of the toner particles obtained, the mean value F _e of the electrostatic adhesion between the transport medium of the toner particles is determined It is done.

In order to move the toner particles by the electric field E, an electric field force qE larger than the adhesion force F is required. That is, the required transfer electric field E is
E> F / q = K ・ q + F ₀ / q (5)
It becomes. Therefore, even if F ₀ is increased to suppress the movement of toner particles to which an electric field force is not applied, the required transfer electric field can be suppressed even for highly charged toner particles by decreasing the slope K.

  As described above, the required transfer electric field E also varies as the charge amount varies with time or varies depending on the environment. Furthermore, as the particle size is reduced, the charge amount Q / M per weight varies greatly. Then, transfer residue and reverse transfer occur due to toner particles that cannot be controlled by the electric field.

  In general, the particle size distribution and charge amount distribution of toner particles need to be narrowed to some extent. This is because the adhesion force, particle size, and charge amount are usually controlled by average values, so if there are particles that are significantly different from those average values, it causes transfer residue and reverse transfer.

  By reducing the slope K, the toner charge amount fluctuates, and even if there is a distribution in the adhesion force, particle size, and charge amount, there is no need to greatly change the transfer electric field. In addition, transfer residue and reverse transfer can be suppressed, and control can be performed stably and stably even in a cleaner-less process.

  Therefore, by suppressing the value of the slope K, it is possible to achieve both high transfer efficiency and stability of transfer characteristics, and maintenance of high image quality.

It is known that the actual measurement value of electrostatic adhesion force of toner particles is 10 times or more than the theoretical value of electrostatic adhesion force of generally used spherical particles. For example, according to Journal of Imaging Science and Technology vol.48, No.5 2004, the theoretical value Fi of electrostatic adhesion is
Fi = α ・ q ² / 4πε ₀ D ² (6)
ε ₀ : Dielectric constant of vacuum
α: Correction coefficient resulting from the difference in dielectric constant between the photoreceptor and toner particles
q: Charge amount of one toner particle
D: Expressed as the particle size of the toner particles, and the difference between the measured value and the theoretical value is considered. Similarly, in Japan Hardcopy 2005 B-13, consideration is given to theorizing the actual measured values. However, no theory has yet been established to clearly explain the mechanism by which the difference between the measured value and the theoretical value occurs.

で与えられる。 Assuming that the toner particles are true spheres and the charge is located at the center of the sphere, the formula for the image force is

Given in.

  However, the toner particles are atypical when formed using conventional grinding processes. In addition, when a chemical manufacturing method is used, it may be intentionally non-spherical in order to improve the normal cleaning performance. Further, the toner particles (bulk) are not homogeneous because the wax for assisting the fixing performance, the charge control agent (CCA) for controlling the chargeability, and the colorant are dispersed in the binder resin. In addition, one or more types of organic or inorganic fine particles (external additives) are attached to the toner particle surface for the purpose of ensuring fluidity, assisting in cleaning performance, and controlling chargeability.

  As described above, the toner particles have a complicated structure in both the bulk and the surface, and the formula of the image force when the charge is assumed to be a true sphere and located at the center of the sphere is rarely applied. The measured value of the adhesive force is also one or two orders of magnitude larger than the theoretical value obtained by the above formula.

とすることにより、実際の付着力特性をよく表すことができることを見出した。 Therefore, the inventors do not have the position of the electric charge at the center of the true sphere with the radius r, but are unevenly distributed at a position shifted by a from the center in the contact direction with the adherend such as the image carrier or the conveyance medium. As a formula that introduces into the above formula (7) of the mirror image force;

As a result, it was found that the actual adhesive force characteristics can be expressed well.

  When the toner is charged, the charge is present at the charging sites on the surface of the toner particles (bulk), external additives, etc., and is not necessarily uniformly present on the surface. A / r can be taken as a guideline representing the non-uniformity. That is, as the charge distribution on the toner particle surface is more uniform, a / r approaches 0 and approaches the theoretical value when it is assumed that the position of the charge is at the center of the true sphere. And the more uneven the charge distribution, the more the surface portion where the charge exists is considered to contact the adherend and generate a strong image force, and this state can be expressed as an increase in a / r. .

a / r is obtained from the electrostatic adhesion force obtained from the average adhesion force actually measured as described above. The range is
0.2 ≦ a / r ≦ 0.7
It needs to be.

  When a / r approaches 0, it is considered that the toner particles are almost spherical, the surface material is homogeneous, and the external additive almost completely covers the surface. Since the external additive has the purpose of assisting fluidity as well as controlling the chargeability, the a / r is less than 0.2, and the external additive adheres in a form that almost completely covers the surface. And the function as a fluidizer will be impaired. Therefore, a / r needs to be 0.2 or more.

となるため、大きくなる方向にシフトする。a/rが0.7を超え、傾きKが大きくなると、非静電付着力が小さい時に低い必要転写電界を示すトナーの最適帯電量qのマージンは小さくなる。また、帯電量qが変動した場合、必要転写電界Eがドラスティックに変動し、高転写効率を維持することが困難となる。従って、a/rを0.7以下とすることにより、最適トナー帯電量qの十分なマージンが得られ、帯電量が変動しても、初期設定した転写条件を変動させることなく、高転写効率および転写特性の安定性と、高画質の維持を両立することができる。 On the other hand, when a / r exceeds 0.7 and approaches 1, the slope K described above becomes

Therefore, it shifts in the direction of increasing. When a / r exceeds 0.7 and the slope K increases, the margin of the optimum charge amount q of the toner that exhibits a low required transfer electric field when the non-electrostatic adhesive force is small decreases. Further, when the charge amount q varies, the required transfer electric field E varies drastically, making it difficult to maintain high transfer efficiency. Therefore, by setting a / r to 0.7 or less, a sufficient margin of the optimum toner charge amount q can be obtained, and even if the charge amount fluctuates, high transfer efficiency and transfer can be performed without changing the initial transfer conditions. It is possible to achieve both stability of characteristics and high image quality.

Here, the charge amount q per toner particle is calculated from the charge amount Q per weight (μC / g).
q = (4/3) πr ³ × d × Q (9)
r: Volume average radius of toner particles
d: It can be determined as the specific gravity of the toner particles. The pre-transfer charge amount Q (μC / g) of the toner is preferably −20 to −80 μC / g. If the charge amount is smaller than -20 μC / g, it is difficult to control by an electric field particularly in a small particle size toner, so that it is scattered outside the developing device by the centrifugal force due to the rotation of the developer carrying member, or is not on the photosensitive member. Problems such as contamination of the image area arise. On the other hand, if it exceeds -80 μC / g, it becomes difficult to supply a sufficient amount of toner to the electrostatic latent image in the development region, and there arises a problem that a high density image cannot be obtained.

  In addition, it is necessary to control the charge amount to a narrower range when more precise control of the adhesive force is required, such as when applying a cleanerless process to the 4-drum tandem process used in a full-color image forming apparatus, -25 to -50 (μC / g) is desirable.

  The volume average radius r of the toner particles is preferably 1.5 to 4 μm. If it is smaller than 1.5 μm, if each toner particle is provided with a charge amount that can be controlled by an electric field, the charge amount per weight becomes too large, and it is difficult to obtain a desired development amount. On the other hand, if it is larger than 4 μm, the reproducibility and granularity of the fine image deteriorate. More preferably, it is 2 to 3 μm.

  Using such an image forming method, an image forming apparatus, or a developer, an image is formed by, for example, the following electrophotographic process.

(Two-component development process)
FIG. 4 shows an image forming apparatus using a two-component development process. As shown in the figure, a photoreceptor 41, a charging device 42 for charging the photosensitive member 41, an exposure device 43 for forming an electrostatic latent image, a developing device 44 for supplying toner particles to the electrostatic latent image, Cleaner 45 for removing transfer residual toner, static elimination lamp 46 for removing electrostatic latent image, paper feeding device 47 for supplying paper as a final transfer medium, fixing device for fixing toner image on paper 48, a transfer device 50 for transferring the toner image on the photoreceptor 41 onto the transfer medium 49 is disposed. Then, using such an image forming apparatus, an image is formed on the transfer medium 49 by the following process.

  The photoreceptor 41 such as a belt or a roller is uniformly desired by a known charging device 42 such as a charger wire, a comb-shaped charger, a corona charger such as a scorotron, a contact charging roller, a non-contact charging roller, a solid charger, or a contact charging brush. Charge to the potential of.

  As the photoreceptor 41, a known photoreceptor such as a positively charged or negatively charged OPC (Organic Photoconductor) or amorphous silicon is used. In these photoreceptors, a charge generation layer, a charge transport layer, and a protective layer may be laminated, or a layer having a plurality of functions among these layers may be formed.

  An electrostatic latent image is formed on the photoreceptor 41 by exposure with an exposure device 43 using a known means such as a laser or LED.

  In the developing device 44, for example, 100 g to 700 g of a two-component developer composed of a carrier and toner particles is stored in a hopper. The developer is conveyed to a developing roller containing a mag roller by a stirring auger, and is visualized by supplying and adhering charged toner particles to the electrostatic latent image on the photoreceptor 41 by a magnetic brush phenomenon. Is done. At this time, a developing bias in which AC is superimposed on DC or DC is applied to the developing roller in order to form an electric field that causes toner particles to adhere uniformly and stably.

  The undeveloped toner particles are separated from the developing roller at the peeling pole position of the mag roller, and are collected in the developer storage by the stirring auger. A known toner density sensor is attached to the developer storage. When the density sensor detects a decrease in the toner amount, a signal is sent to the toner supply hopper to supply new toner. At this time, the toner consumption may be estimated from the integration of the print data or / and the development toner amount on the photoconductor, and new toner may be replenished based on the estimated toner consumption. Also, both means for sensor output and consumption estimation may be used.

  The formed toner image is placed in contact with the photosensitive member 41, and a belt, a transfer roller, a transfer blade, a corona charger and the like that transfer the toner image by a transfer voltage applied thereto are used. It is transferred to a transfer medium 49 such as paper through an intermediate transfer medium such as a roller or directly.

  The transfer medium 49 onto which the toner image has been transferred is peeled off from the intermediate transfer medium or the photoconductor 41, conveyed to the fixing unit 48, fixed by a known heating / pressure fixing means such as a heat roller, and discharged outside the machine. .

  After the toner image is transferred, the untransferred toner remaining without being transferred onto the photoconductor 41 is removed by the cleaner 45, and the electrostatic latent image on the photoconductor 41 is erased by the charge eliminating lamp.

  The transfer residual toner removed by the cleaner 45 is discharged after being stored in a waste toner box via a conveyance path by a stirring auger or the like. In the recycling method, the developer is collected from the conveyance path to the developer storage of the developing device 44 and reused.

(Single component development process)
In the one-component development process, an image is formed in the same manner by the same image forming apparatus as in the two-component development process, but the developing unit is different. The developing device contains only toner particles and is developed without using a carrier.

  The toner particle is a developer carrier such as an elastic roller having a conductive rubber layer on its surface or a metal roller such as SUS having a surface roughened by sandblasting or the like with a known structure such as a transport auger or intermediate transport sponge roller. Supplied on the surface. The toner particles supplied to the surface of the developer carrying member are triboelectrically charged by a toner charging member such as silicon rubber, fluorine rubber, or a metal blade pressed onto the surface of the developer carrying member. At this time, toner charged in advance by friction with the magnetic particles may be supplied to the developer carrier itself. The photoreceptor is in contact with the developer carrying member or in a non-contact manner with a specified gap, and the toner particles are developed by rotating with a speed difference. At this time, a developing bias in which AC is superimposed on DC or DC is applied to the developing roller in order to form an electric field that causes toner particles to adhere uniformly and stably.

(Cleanerless process)
In the cleaner-less process, an image is formed in the same manner by an image forming apparatus similar to the two-component development process, but differs in that there is no cleaner as shown in FIG. Transfer residual toner is collected at the same time as development without using a cleaner.
Similar to the two-component development process, the photoconductor 51 is charged, exposed, developed by adhering toner particles, and the toner image is transferred to the transfer medium 59 via an intermediate transfer medium or directly. In FIG. 5, the direct transfer method is adopted, and transfer is performed by the transfer roller 57. The untransferred toner remaining in the non-image portion is conveyed again to the development region through the next static elimination, charging by the charging device 52, and exposure process by the exposure device 53 while remaining on the photoreceptor 51. Then, the untransferred toner is collected by the developing device 54 by the magnetic brush which is a developer carrying member and is newly developed.

  At this time, a memory disturbing member 55 such as a fixed brush, a felt, a rotating brush, or a lateral sliding brush may be disposed before or after the static eliminating step. Alternatively, a temporary collection member may be arranged so that the untransferred toner is once collected, discharged onto the photoreceptor 51 again, and collected by the developing device 54. Further, a toner charging device may be disposed on the photoreceptor 51 in order to make the charge amount of the untransferred toner equal to a desired value. In addition, the toner charging device, the memory disturbing member, the temporary recovery member, and the charging device may have a part or all of the roles as one member. These members may be applied with positive or negative DC and / or AC voltages in order to efficiently perform their functions.

  For example, the tips of two side-sliding brushes that play all three roles are placed between the transfer region and the charging member of the photosensitive member 51 so as to contact the photosensitive member 51. A voltage having the same polarity as the developing toner charge is applied to the upstream brush, and a different polarity from the developing toner charge is applied to the downstream brush.

  The transfer residual toner includes a mixture of a different polarity toner and a toner having the same polarity and a very high charge, and the different polarity toner coming into contact with the same polarity brush reverses the charge or passes through the brush once. Collected. The transfer residual toner that reaches the downstream opposite polarity brush is all aligned with the same polarity as the developing toner.By contacting with the different polarity brush, the strong same polarity charge is alleviated or slipped through the brush once. Collected.

  The untransferred toner, which is aligned with a weak charge amount and loses the image structure due to the mechanical contact of the brush, is charged non-contactingly with the photosensitive member 51 by the charging member of the photosensitive member 51, and is charged just as much as the developing toner. To be aligned. As a result, the non-image portion transfer residual toner in the new latent image is collected in the developing device 54 in the development area, and the image portion transfer residual toner is transferred as it is together with the toner particles newly supplied from the development device 54. Transferred to the medium.

(4 tandem process)
Fig. 6 shows an image forming apparatus using a 4-drum tandem process. As shown in the figure, image forming units 60a, 60b, 60c, and 60d each having toner, each containing toner particles of yellow, magenta, cyan, and black are provided with four colors. Are arranged in parallel along the transport path of the transfer medium 69a. As in FIG. 4, a fixing device 68 for fixing the toner image on the paper is disposed. Then, using such an image forming apparatus, an image is formed by the following process. Here, a case where the colors are arranged in the order of yellow, magenta, cyan, and black will be described as an example.

In the yellow image forming unit, a yellow toner image is formed on the photoreceptor 61a and transferred to the transfer medium 69a. In the case of direct transfer, paper or the like, which is the final transfer medium, is conveyed by a conveying member such as a transfer belt or a roller, and is supplied to the transfer area of the yellow image unit. FIG. 6 shows a configuration in which transfer is performed by a transfer roller 65 onto a sheet conveyed by a transfer belt 64 as a conveying member. At this time, the volume resistance of the transfer belt is preferably 10 ⁷ Ωcm to 10 ¹² Ωcm. For the transfer belt, rubber materials such as ethylene propylene rubber (EPDM) and chlorobrene (CR) rubber, and resin materials such as polyimide, polycarbonate, polyvinylidene difluoride (PVDF), and Ethylene Tetrafluoro Ethylene (ETFE) are used. In addition, various configurations such as a resin sheet, a rubber elastic layer, a protective layer, etc., which are laminated by laminating one layer or two or more layers are possible. As a transfer method, a transfer method using a known transfer means such as a transfer roller, a transfer blade, or a corona charger can be used.

  At the transfer position, from a transfer roller 65 provided so as to press the transfer belt 64 in contact with the photoreceptor 61a against the photoreceptor 61a side, a transfer medium 69a positioned between the transfer belt 64 and the photoreceptor 61a. A transfer bias voltage having a predetermined magnitude and polarity is supplied from the transfer bias power supply device. By supplying this transfer bias voltage, the toner image (toner) electrostatically attached to the outer peripheral surface of the photoreceptor 61a is attracted to the transfer medium 69a and transferred to the transfer medium 69a.

  As shown in FIG. 7, an intermediate transfer belt 69b may be provided as an intermediate transfer medium. The intermediate transfer belt 69b is made of semi-conductive resin, rubber having a thickness of 50 to 3000 μm, or a laminated member thereof. The transfer roller 65 (transfer roller 65) is formed on the back side of the belt facing the photoreceptor 61a. Means) are in contact. A predetermined transfer bias voltage is applied to the transfer roller 65 by a transfer bias voltage application unit, and a transfer electric field is generated at or around the transfer nip where the photoreceptor 61a and the intermediate transfer belt 69b are in contact with each other. It has become such a thing.

In the present embodiment, the transfer roller 65 using a semiconductive sponge having a volume resistivity of 10 ⁵ Ωcm to 10 ⁹ Ωcm is brought into contact with the back surface of the belt, and DC 300 V to 3000 V is applied, so that the intermediate transfer belt 69 b Then, the toner image on the photosensitive member of each process unit is transferred. Four such process units are superimposed and transferred to form a full-color image, which is then transferred to a transfer medium 69a 'such as paper at the secondary transfer position, and the image is heated and fixed by a fixing device 68. To be the final image.

In the intermediate transfer belt, the same material and configuration as those of the transfer belt 64 described above are used. The surface resistance is preferably 10 ⁷ Ωcm to 10 ¹² Ωcm, for example, 10 ⁹ Ωcm.

  Similarly, in the magenta image forming unit 60b, a magenta toner image is formed on the photoreceptor 61b, and the transfer medium 69a on which the yellow toner image has already been transferred is supplied to the transfer area of the magenta image forming unit 60b, and the yellow toner The magenta toner image is transferred from the top of the image by aligning the positions. At this time, the yellow toner on the transport medium may be reversely transferred to the magenta photosensitive member 61b depending on the toner charge amount and the strength of the transfer electric field by contacting the magenta photosensitive member 61b.

  Similarly, in the cyan and black image forming units 60c and 60d, toner images are formed and sequentially transferred onto the transfer medium 69a. Similarly, the toner on the preceding stage may be reversely transferred to the cyan and black photoreceptors 61c and 61d, respectively.

  The transfer medium 69a formed by overlapping the toner images of four colors is peeled off from the conveying member, conveyed to the fixing device 68, and fixed by a known heating / pressure fixing method using a heat roller, etc. Released. When the intermediate transfer medium 69b is used, the toner images for four colors are collectively transferred to the final transfer medium 69a ′ such as paper supplied by the supply member to the secondary transfer unit, and then transferred to the fixing device 68. It is conveyed, fixed in the same way, and discharged out of the machine.

  In each image forming unit, as in the two-component development process, the photoreceptors 61a, 61b, 61c, 61d are neutralized, and after the transfer residual toner and the reverse transfer toner are removed by the cleaning process, the process returns to the image forming process again. . In the developing device, the toner specific density is adjusted in the same manner as the above-described two-component development process. Here, an example in which the image forming units are arranged in the order of colors of yellow, magenta, cyan, and black has been described. However, the order of colors is not particularly limited.

(4 tandem cleanerless process)
In the four-tandem tandem cleanerless process, an image is formed in the same manner by the same image forming apparatus as in the four-tandem tandem process, but, unlike the cleanerless process described above, there is no cleaner.

  Similar to the cleaner-less process, the untransferred toner and the reverse transfer toner are collected with the charge amount adjusted at the same time as the development without using a cleaner.

  In these development processes described above, by using a contact-type charging device, it is possible to prevent ozone degradation of the photoconductive layer of the photoconductor and extend the life of the photoconductor.

  Until now, a corona charger, which is a non-contact charging device, has been widely used to charge a photoreceptor. However, since a large amount of ozone is generated in the corona charger, a bad odor or deterioration of the surface of the photoreceptor occurs. On the other hand, it is possible to suppress the influence of ozone by filtering out malodors and removing the deteriorated layer little by little with a cleaning blade or the like. However, if the amount of wear exceeds a certain amount, the photoconductivity will be impaired, and the life of the photoreceptor will be shortened. On the other hand, the contact charging device has an advantage that ozone is not generated.

For example, as the charging device, a charging roller having at least an elastic layer such as an ion conductive rubber or a carbon dispersion rubber and having a volume resistance of about 10 ⁴ to 10 ⁸ Ωcm is used. The charging roller is brought into contact with the photosensitive member at a constant pressure, and is rotated around the photosensitive member, at the same speed as the photosensitive member, or with a slight speed difference. At this time, by applying a DC voltage of 400 to 1000 V to the charging roller mandrel, charges are injected into the surface of the photoreceptor, and the surface of the photoreceptor can be charged to a predetermined potential.

  When applied to a cleaner-less process, residual transfer toner may remain on the photoreceptor during charging. In addition, when applied to the cleanerless tandem process, reverse transfer toner may remain on the photosensitive member in addition to the residual transfer toner during charging. For this reason, it is preferable that a web, a brush, a blade, etc. for cleaning the charging roller are always or appropriately brought into contact with each other.

  Hereinafter, the present invention will be described specifically by way of examples.

  In this example and comparative example, a particle size distribution measuring device (BECKMAN COULTER COUNTER MULTISIZER 3) was used to measure the volume average particle size of the toner particles.

  In addition, for measuring the circularity of the toner particles, a flow type particle image analyzer FPIA-3000 manufactured by Sysmex Corporation was used, and the perimeter calculated from the diameter of a perfect circle equivalent to the projected area of the particle was D1, the projected particle Where D2 is the perimeter of the circle, the degree of circularity = D1 / D2 (1 for a perfect circle (= true sphere)).

Furthermore, the transfer efficiency measurements, using an image forming apparatus according to the two-component development process as shown in FIG. 4, with respect to the toner on the photosensitive member development amount T1 (e.g. 300 [mu] g / cm ^2), un the posttranscriptional photoreceptor to a transfer medium Measure the transfer toner amount T2,
Transfer efficiency = (T1-T2) / T1
Was used to determine the transfer efficiency. At this time, the amount of toner on the photoreceptor is determined by sucking a certain area of toner, measuring its weight, measuring the reflection density of the tape peeled off and pasted on white paper with a Macbeth densitometer, The amount of toner is calculated by applying a calibration formula between the amount of toner and the amount of toner.

(Example 1)
(Preparation of toner particles)
Toner particles were formed as follows.

  First, a polyester batch: 28 wt% as a resin, carmine 6B: 7 wt% as a colorant, rice wax: 5 wt%, and carnauba wax: 1 wt% as a release agent were kneaded with a YPK kneedex to prepare a master batch. After coarsely pulverizing this, polyester resin: 59 wt% and CCA (TN105): 1 wt% were added and kneaded. Then, after coarsely and finely pulverizing this, 7 μm or more and 3 μm or less were cut by elbow jet classification to form fine particles having a volume average particle diameter of 5.0 μm.

  Acrylic / methacrylic resin fine particles having a particle diameter of 1 μm or less were mixed with 100 wt% of the fine particles in such an amount that the coverage was about 100%. At this time, when the particle size of the resin fine particles is 0.1 μm, it becomes about 8 wt%. This mixture was mechanochemically treated (Nara Machinery, Hybridization System) to form encapsulated particles (toner base particles) in which resin fine particles were fused on the surface of the fine particles.

  Next, silica with an average particle size of 12 nm (R974, Nippon Aerosil Co., Ltd.): 1.5 wt%, silica with an average particle size of 100 nm (X-24, Shin-Etsu Chemical Co., Ltd.): Toner particles were formed by adhering 1.5 wt% of titanium oxide (NKT90 manufactured by Titanium Industry Co., Ltd.) of 0.3 wt% to the surface using a Henschel mixer.

  The corners produced by the pulverization were slightly spheroidized due to impact and friction during mechanochemical treatment, and the finally obtained toner particles had a volume average particle size of 6.3 μm and a circularity of 0.94.

The toner particles thus obtained were mixed with a carrier in which spherical ferrite particles having a volume average particle diameter of 40 μm were coated with a silicone resin to prepare a two-component developer. By changing the mixing ratio, the charge amount of the toner particles is changed, and the average of the toner particle transport medium (photosensitive sheet: dielectric constant ε ′ = 3.3) at each charge amount developed with about 300 μg / cm ^2. The adhesion force F (N) was measured.

より、r=6.3μm/2=3.15μmとして、得られたトナー粒子のa/rは0.54となった。 Plot the average adhesive force F on the vertical axis and q ² on the horizontal axis,
F = F _e + F ₀ = K · q ² + F ₀ (4)
Thus, F ₀ = 4 × 10 ⁻⁸ (N) and K = 9.64 × 10 ²⁰ (N / C ² ) were obtained. further,

As a result, when r = 6.3 μm / 2 = 3.15 μm, a / r of the obtained toner particles was 0.54.

  FIG. 8 shows the charge amount dependency of the required transfer electric field E in the toner particles thus obtained. As shown in the figure, it can be seen that, at −20 to 80 μC / g, the fluctuation of the required transfer electric field E is small and good characteristics are obtained.

  This is because the toner base particles are spheroidized by impact or friction during mechanochemical treatment, and by adding an external additive, non-electrostatic adhesion is reduced, and the toner base particles are encapsulated with a binder resin. This is considered to be because the uniformity of the charge distribution could be improved by homogenizing the surface.

(Evaluation of transfer efficiency and charge amount)
The toner particles thus obtained were mixed with a carrier in which the above-mentioned spherical ferrite particles having a volume average particle size of 40 μm were coated with a silicone resin at a toner particle ratio: 7 wt%, and were put into an electrophotographic process. Accelerated evaluation was made of changes over time in transfer efficiency and charge amount.

When the volume resistance of the intermediate transfer belt in the printing device is 10 ⁹ Ωcm and the initial environmental conditions are normal temperature and humidity, the toner charge is -45μC / g and the optimal transfer bias is 98% at 600V. It was in good condition.

  When the printing device was put in an environment with a printing rate of 6%, printing 60K sheets, temperature: 32 ° C, humidity: 80%, the toner charge amount fluctuated to -30μC / g, but the transfer efficiency was 98%. It was.

  This is considered to be because the required transfer electric field hardly fluctuates even when the toner charge amount fluctuates from −45 μC / g to −30 μC / g, as shown in FIG. Since the transfer efficiency is not deteriorated due to the environmental change over time, the initial image quality can be kept good.

  In addition, it was possible to maintain high transfer efficiency and high image quality without controlling transfer bias conditions, so there was no need to change the transfer bias, and for that purpose, toner charge amount, environmental temperature and humidity for controlling the transfer electric field. This eliminates the need for a control sequence such as changing the transfer condition based on the sensor and the sensor output.

  Furthermore, when it is put into a cleanerless image forming apparatus, the transfer efficiency does not change due to changes in the environment over time, and the remaining transfer amount can be kept low. It was possible to maintain high image quality without causing image defects.

(Example 2)
(Preparation of toner particles)
Toner particles were formed as follows.

  First, a polyester-based prepolymer is dissolved in an organic solvent, and carbon black: 7 wt% as a colorant, stearic acid: 2 wt% as a release agent, and benzoyl peroxide: 0.1 wt% as a polymerization initiator are dispersed, The solvent was put into an aqueous solvent and emulsified. By heating this while stirring, fine particles having a uniform particle size distribution including a resin, a colorant, and a release agent were formed.

  Further, a prepolymer is further added to the solvent to polymerize so as to wrap the fine particles, and then the solvent is removed and dried to form encapsulated particles (toner mother particles) having a volume average particle size of 5.2 μm. It was. The circularity at this time was 0.95.

  Next, silica with an average particle size of 12 nm (R974, Nippon Aerosil Co., Ltd.): 2 wt%, silica with an average particle size of 100 nm (X-24, Shin-Etsu Chemical Co., Ltd.): 1.8 wt. wt%, titanium oxide (NKT90 manufactured by Titanium Industry Co., Ltd.) 0.3 wt% was adhered to the surface using a Henschel mixer to form toner particles having a volume average particle size of 5.2 μm.

  In the same manner as in Example 1, the toner particles thus obtained were mixed with a carrier in which spherical ferrite particles having a volume average particle diameter of 40 μm were coated with a silicone resin to prepare a two-component developer. By changing the mixing ratio, the charge amount of the toner particles was changed, and the average adhesion force F (N) with the toner particle transport medium (photoreceptor: dielectric constant ε ′ = 3.3) at each charge amount was measured.

In the same manner as in Example 1, by plotting the average adhesive force F on the vertical axis and q ² on the horizontal axis, and performing linear approximation, F ₀ = 2.5 × 10 ⁻⁸ (N), K = 2.03 × 10 ²¹ ( N / C ² ) was obtained. Further, as in Example 1, from the K value, r = 5.2 μm / 2 = 2.6 μm, and the a / r of the obtained toner particles was 0.64.

  FIG. 9 shows the charge amount dependency of the required transfer electric field E in the toner particles thus obtained. As shown in the figure, it can be seen that, at −20 to 80 μC / g, the fluctuation of the required transfer electric field E is small and good characteristics are obtained.

  This is because toner base particles are spheroidized by emulsion polymerization, and by adding an external additive, non-electrostatic adhesion is reduced, and the toner base particles are encapsulated with a binder resin to homogenize the surface. This is considered to be because the uniformity of the charge distribution could be improved.

(Evaluation of transfer efficiency and charge amount)
The toner particles thus obtained were mixed with a carrier in which the above-mentioned spherical ferrite particles having a toner particle ratio: 6 wt% and a volume average particle size of 40 μm were coated with a silicone-based resin, and were put into an electrophotographic process. Accelerated evaluation was made of changes over time in transfer efficiency and charge amount.

When the volume resistance of the intermediate transfer belt in the printer is 10 ⁹ Ωcm and the initial environmental conditions are normal temperature and humidity, the toner charge amount is -53μC / g and the optimal transfer bias is 700% at 700V. It was in good condition.

  As in Example 1, 60K sheets were printed at a printing rate of 6%, and when the printing device was put in an environment of temperature: 32 ° C. and humidity: 80%, the toner charge amount fluctuated to -35 μC / g. The transfer efficiency was 98%.

  This is considered to be because the required transfer electric field hardly fluctuates even when the toner charge amount fluctuates from −53 μC / g to −35 μC / g, as shown in FIG. Since the transfer efficiency hardly deteriorates due to environmental changes over time, the image quality can be kept in a good state in the initial stage.

  Further, as in the first embodiment, high transfer efficiency and high image quality can be maintained without controlling the transfer bias condition, so there is no need to change the transfer bias, and a control sequence for that is unnecessary.

  Furthermore, as in Example 1, when it was put into a cleanerless image forming apparatus, the transfer efficiency did not change due to changes in the environment over time, and the remaining transfer amount could be kept low. High image quality could be maintained without image defects such as negative memory and positive memory.

(Example 3)
(Preparation of toner particles)
Toner particles were formed as follows.

  First, a polyester resin: 28 wt% as a resin, carbon black: 6 wt% as a colorant, and rice wax: 6 wt% as a mold release agent were kneaded with a YPK kneedex to prepare a master batch. After coarsely pulverizing this, polyester resin: 60 wt% and CCA (TN105): 1 wt% were added and kneaded. Then, this was coarsely pulverized and finely pulverized, and then 8 μm or more and 3 μm or less were cut by elbow jet classification to form fine particles having a volume average particle diameter of 6.0 μm.

The fine particles are spheroidized by heat treatment, and further 100% by weight of the spheroidized fine particles, silica having a particle size of 16 nm (R972 made by Nippon Aerosil Co., Ltd.): 1.5 wt%, silica having an average particle size of 100 nm (X- 24 manufactured by Shin-Etsu Chemical Co., Ltd.): 1.3 wt% and aluminum oxide (Al ₂ O ₃ : manufactured by NanoTek) 0.5 wt% were adhered to the surface using a Henschel mixer to form toner particles.

  The corners produced by the pulverization were spheroidized by the heat treatment, and the finally obtained toner particles had a volume average particle size of 6.0 μm and a circularity of 0.96.

  In the same manner as in Example 1, the toner particles thus obtained were mixed with a carrier in which spherical ferrite particles having a volume average particle diameter of 40 μm were coated with a silicone resin to prepare a two-component developer. By changing the mixing ratio, the charge amount of the toner particles was changed, and the average adhesion force F (N) with the toner particle transport medium (photoreceptor: dielectric constant ε ′ = 3.3) at each charge amount was measured.

In the same manner as in Example 1, by plotting the average adhesive force F on the vertical axis and q ² on the horizontal axis and performing linear approximation, F ₀ = 2.5 × 10 ⁻⁸ (N), K = 2.11 × 10 ²¹ ( N / C ² ) was obtained. Further, as in Example 1, from the K value, r = 6.0 μm / 2 = 3.0 μm, and the a / r of the obtained toner particles was 0.70.

  In the toner particles obtained in this way, the charge amount dependency of the required transfer electric field E was good. This is because non-electrostatic adhesion force can be reduced by spheroidizing toner base particles by heat treatment and adding an external additive, and electrostatic adhesion force can be reduced by the spacer effect of the external additive. It is thought that.

(Evaluation of transfer efficiency and charge amount)
The toner particles thus obtained were mixed with a carrier in which the above-mentioned spherical ferrite particles having a toner particle ratio: 6 wt% and a volume average particle size of 40 μm were coated with a silicone-based resin, and were put into an electrophotographic process. Accelerated evaluation was made of changes over time in transfer efficiency and charge amount.

When the volume resistance of the intermediate transfer belt in the printer is 10 ⁹ Ωcm and the initial environmental conditions are normal temperature and humidity, the toner charge amount is -40μC / g, the optimal transfer bias is 965V, and the transfer efficiency is 96%. Slightly good condition.

  As in Example 1, 60K sheets were printed at a printing rate of 6%, and when the printing device was put in an environment of temperature: 32 ° C. and humidity: 80%, the toner charge amount fluctuated to -23 μC / g. The transfer efficiency was 96%.

  This is presumably because the required transfer electric field hardly fluctuates even when the toner charge amount fluctuates from -40 μC / g to -23 μC / g. Since the transfer efficiency does not deteriorate due to environmental changes over time, the image quality can be maintained in a slightly good state in the initial stage.

Example 4
(Preparation of toner particles)
Toner particles were formed as follows.

  First, 20 wt% of styrene monomer and n-butyl methacrylate monomer mixed at a ratio of 6: 4, nonionic surfactant (polyethylene oxide): 1% as an emulsifier, potassium persulfate: 0.5% as a polymerization initiator An aqueous dispersion of emulsion-polymerized fine particles having a particle size of 1 μm or less was formed by throwing into wt% dispersed water and stirring while heating. Also, an aqueous dispersion was prepared in which carbon black as a colorant and rice wax as a release agent were finely dispersed in water. Then, each aqueous dispersion is mixed so that the resin content is 69 wt%, the colorant is 8 wt%, and the release agent is 3 wt%, and the particle size is about 3 to 4 μm using a metal salt as an aggregating agent. To form particles in which a resin, a colorant, and a release agent are associated. The particles were agitated while heating above the glass transition point of the resin to fuse the associated particles.

  Further, in the dispersion of the coalesced aggregated particles, CCA (TN105): an aqueous dispersion of resin fine particles dispersed in an amount equivalent to 1 wt% with respect to the total solid content is added, and the coalesced association with these resin fine particles Aggregation was performed so as to cover the periphery of the particles. Then, the resin fine particles were fused by heating and stirring. This was washed and dried to form encapsulated particles (toner base particles) having a volume average particle size of 5.8 μm. The circularity at this time was 0.97.

  Next, silica having an average particle diameter of 16 nm (R972 manufactured by Nippon Aerosil Co., Ltd.): 1.5 wt% silica having an average particle diameter of 100 nm (X-24 manufactured by Shin-Etsu Chemical Co., Ltd.) with respect to 100 wt% of the encapsulated particles: 1.5wt%, Titanium oxide (NKT90 manufactured by Titanium Industry Co., Ltd.) 0.6wt% is put into Henschel mixer one component at a time and attached to the surface of encapsulated particles in order, volume average particle size: 5.8μm, circular Toner particles having a degree of 0.97 were formed.

  In the same manner as in Example 1, the toner particles thus obtained were mixed with a carrier in which spherical ferrite particles having a volume average particle diameter of 40 μm were coated with a silicone resin to prepare a two-component developer. By changing the mixing ratio, the charge amount of the toner particles was changed, and the average adhesion force F (N) with the toner particle transport medium (photoreceptor: dielectric constant ε ′ = 3.3) at each charge amount was measured.

As in Example 1, by plotting the average adhesive force F on the vertical axis and q ² on the horizontal axis, and by linear approximation, F ₀ = 3.2 × 10 ⁻⁸ (N), K = 7.95 × 10 ²⁰ ( N / C ² ) was obtained. Further, as in Example 1, from the K value, r = 5.8 μm / 2 = 2.9 μm, and the a / r of the obtained toner particles was 0.39.

  In the toner particles obtained in this way, the charge amount dependency of the required transfer electric field E was good. The reason for this is that the toner base particles have a uniform and nearly spherical shape and are encapsulated so that the surface material becomes uniform. It is considered that the charge distribution on the surface of the toner particles can be made more uniform because of the uniform adhesion. In addition, silica with a large particle size plays the role of a spacer, and styrene-acrylic resin is more easily charged than polyester resin, and even if there is no charge control agent (CCA), friction with the carrier is sufficient. It is conceivable that there is a characteristic that the charge distribution tends to become more uniform because of its ability to be charged.

(Evaluation of transfer efficiency and charge amount)
The toner particles thus obtained were mixed with a carrier in which the above-mentioned spherical ferrite particles having a toner particle ratio: 6 wt% and a volume average particle size of 40 μm were coated with a silicone-based resin, and were put into an electrophotographic process. Accelerated evaluation was made of changes over time in transfer efficiency and charge amount.

When the volume resistance of the intermediate transfer belt in the printing device is 10 ⁹ Ωcm and the initial environmental conditions are normal temperature and humidity, the toner charge amount is -48μC / g, the optimal transfer bias is 600% at 600V, It was in good condition.

  As in Example 1, 60K sheets were printed at a printing rate of 6%, and when the printing device was put in an environment of temperature: 32 ° C. and humidity: 80%, the toner charge amount fluctuated to -40 μC / g. The transfer efficiency was 98%.

  This is presumably because the required transfer electric field hardly fluctuates even when the toner charge amount fluctuates from −48 μC / g to −40 μC / g. Since the transfer efficiency does not deteriorate due to environmental changes over time, the image quality can be maintained in a slightly good state in the initial stage.

(Comparative Example 1)
(Preparation of toner particles)
Toner particles were formed as follows.

  First, a polyester resin: 28 wt% as a resin, carmine 6B: 7 wt% as a colorant, and rice wax: 5 wt% as a mold release agent were kneaded with a YPK kneedex to prepare a master batch. After coarsely pulverizing this, polyester resin: 59 wt% and CCA (TN105): 1 wt% were added and kneaded. After coarsely and finely pulverizing this, elbow jet classification was used to cut 8 μm or more and 4 μm or less to form toner base particles having a volume average particle diameter of 6.0 μm.

  Silica with a particle size of 12 nm (R974 manufactured by Nippon Aerosil Co., Ltd.): 1.5 wt%, silica with an average particle size of 100 nm (X-24 manufactured by Shin-Etsu Chemical Co., Ltd.): 1.5 wt% with respect to 100 wt% of the toner base particles Then, 0.3 wt% of titanium oxide (NKT90 manufactured by Titanium Industry Co., Ltd.) was adhered to the surface using a Henschel mixer to form toner particles. The circularity was 0.94.

  In the same manner as in Example 1, the toner particles thus obtained were mixed with a carrier in which spherical ferrite particles having a volume average particle diameter of 40 μm were coated with a silicone resin to prepare a two-component developer. By changing the mixing ratio, the charge amount of the toner particles was changed, and the average adhesion force F (N) with the toner particle transport medium (photoreceptor: dielectric constant ε ′ = 3.3) at each charge amount was measured.

As in Example 1, by plotting the average adhesion force F on the vertical axis and q ² on the horizontal axis, and by linear approximation, F ₀ = 6.5 × 10 ⁻⁸ (N), K = 2.20 × 10 ²¹ ( N / C ² ) was obtained. Further, as in Example 1, from the K value, r = 6.0 μm / 2 = 3.0 μm, and the a / r of the obtained toner particles was 0.73.

  FIG. 10 shows the charge amount dependency of the required transfer electric field E in the toner particles thus obtained. As shown in the figure, it can be seen that the fluctuation of the required transfer electric field E is large at −20 to 80 μC / g.

  This is presumably because sufficient uniformity of the charge distribution could not be obtained because the spheroidizing treatment was not performed.

(Evaluation of transfer efficiency and charge amount)
The toner particles thus obtained were mixed with a carrier in which the above-mentioned spherical ferrite particles having a volume average particle size of 40 μm were coated with a silicone resin at a toner particle ratio: 7 wt%, and were put into an electrophotographic process. Accelerated evaluation was made of changes over time in transfer efficiency and charge amount.

When the volume resistance of the intermediate transfer belt in the printing device is 10 ⁹ Ωcm and the initial environmental conditions are normal temperature and humidity, the toner charge amount is -40μC / g, and the optimal transfer bias is 1200% at 1200V. Slightly good condition.

  As in Example 1, 60K sheets were printed at a printing rate of 6%, and when the printing apparatus was put in an environment of temperature: 32 ° C. and humidity: 80%, the toner charge amount varied to -25 μC / g. As a result, the transfer efficiency decreased to 88% at the same transfer bias of 1200 V as in the initial stage.

  This is presumably because the required transfer electric field greatly fluctuated as the toner charge amount fluctuated from -40 μC / g to -25 μC / g, as shown in FIG. As the remaining transfer amount increased, the image density decreased and the image quality deteriorated greatly.

  Further, the necessary transfer bias at this time is 1500 V, but at this voltage, the electric field in the transfer region becomes too strong, the charge is injected into the toner, the polarity of the charge is reversed, and the transfer efficiency is further deteriorated. Therefore, the required transfer electric field cannot be set, transfer efficiency is lowered, toner consumption is increased, and image quality is also deteriorated.

(Comparative Example 2)
(Preparation of toner particles)
Toner particles were formed as follows.

  First, a polyester-based prepolymer is dissolved in an organic solvent, and carbon black: 7 wt% as a colorant, stearic acid: 2 wt% as a release agent, and benzoyl peroxide: 0.1 wt% as a polymerization initiator are dispersed, The solvent was put into an aqueous solvent and emulsified. By heating this while stirring, fine particles having a uniform particle size distribution including a resin, a colorant, and a release agent were formed.

  Further, a prepolymer is further added to the solvent to polymerize so as to wrap the fine particles, and then the solvent is removed and dried to form encapsulated particles (toner mother particles) having a volume average particle size of 5.2 μm. It was. The circularity at this time was 0.95.

  Next, silica (R974 Nippon Aerosil Co., Ltd.): 3.5 wt% and titanium oxide (NKT90 Titanium Industry Co., Ltd.) 1.2 wt% with respect to 100 wt% of the encapsulated particles were added to a Henschel mixer. To form toner particles having a volume average particle size of 5.2 μm.

  In the same manner as in Example 1, the toner particles thus obtained were mixed with a carrier in which spherical ferrite particles having a volume average particle diameter of 40 μm were coated with a silicone resin to prepare a two-component developer. By changing the mixing ratio, the charge amount of the toner particles was changed, and the average adhesion force F (N) with the toner particle transport medium (photoreceptor: dielectric constant ε ′ = 3.3) at each charge amount was measured.

As in Example 1, the average adhesion force F is plotted on the vertical axis and q ² is plotted on the horizontal axis, and F ₀ = 3.3 × 10 ⁻⁸ (N), K = 3.03 × 10 ²¹ (N N / C ² ) was obtained. Further, as in Example 1, from the K value, r = 5.2 μm / 2 = 2.6 μm, and the a / r of the obtained toner particles was 0.72.

  FIG. 11 shows the charge amount dependency of the required transfer electric field E in the toner particles thus obtained. As shown in the figure, it can be seen that the fluctuation of the required transfer electric field E is large at −20 to 80 μC / g.

  This is presumably because the spacer effect of the external additive was not obtained because the large particle external additive was not added.

(Evaluation of transfer efficiency and charge amount)
The toner particles thus obtained were mixed with a carrier in which the above-mentioned spherical ferrite particles having a volume average particle size of 40 μm were coated with a silicone resin at a toner particle ratio: 7 wt%, and were put into an electrophotographic process. Accelerated evaluation was made of changes over time in transfer efficiency and charge amount.

When the volume resistance of the intermediate transfer belt in the printing device is 10 ⁹ Ωcm and the initial environmental conditions are normal temperature and humidity, the toner charge amount is -38μC / g, the optimal transfer bias is 98% at 1000V, and the transfer efficiency is 98%. It was in good condition.

  As in Example 1, 60K sheets were printed at a printing rate of 6%, and when the printing device was put in an environment of temperature: 32 ° C. and humidity: 80%, the toner charge amount varied to -23 μC / g. Along with this, the transfer efficiency decreased to 90% at the same transfer bias of 1000 V as in the initial stage.

  This is presumably because the required transfer electric field greatly fluctuated as the toner charge amount fluctuated from −38 μC / g to −23 μC / g as shown in FIG. As the remaining transfer amount increased, the image density decreased and the image quality deteriorated greatly.

  Further, since the required transfer electric field increases, it is necessary to change the transfer bias voltage in order to maintain high transfer efficiency. Therefore, it is necessary to add a control sequence for that purpose.

  In addition, this invention is not limited to embodiment mentioned above. Various other modifications can be made without departing from the scope of the invention.

FIG. 3 is a perspective view showing a sample set for measuring an average adhesion amount of toner particles in one embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a cell for measuring an average adhesion amount of toner particles in one embodiment of the present invention. FIG. 3 is a perspective view showing an angle rotor for measuring an average adhesion amount of toner particles in one embodiment of the present invention. FIG. 3 is a cross-sectional view showing an angle rotor for measuring an average adhesion amount of toner particles in one embodiment of the present invention. 1 is a conceptual diagram illustrating an image forming apparatus using a two-component development process in one embodiment of the present invention. 1 is a conceptual diagram illustrating an image forming apparatus using a cleaner-less process according to one embodiment of the present invention. 1 is a conceptual diagram illustrating an image forming apparatus using a quadruple tandem process in one embodiment of the present invention. 1 is a conceptual diagram illustrating an image forming apparatus using a four-tandem tandem process provided with an intermediate transfer medium according to an embodiment of the present invention. FIG. 6 is a graph showing a relationship between a charge amount of toner particles and a necessary transfer electric field in one embodiment of the present invention. FIG. 6 is a graph showing a relationship between a charge amount of toner particles and a necessary transfer electric field in one embodiment of the present invention. FIG. 6 is a graph showing a relationship between a charge amount of toner particles and a necessary transfer electric field in one embodiment of the present invention. FIG. 6 is a graph showing a relationship between a charge amount of toner particles and a necessary transfer electric field in one embodiment of the present invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Sample set, 2 ... Plate A, 3 ... Plate B, 4 ... Spacer, 5 ... Cell, 6 ... Angle rotor, 41, 51, 61a, 61b, 61c, 61d ... Photoconductor, 42, 52 ... Charging device, 43, 53 ... exposure device, 44, 54 ... developing device, 45 ... cleaner, 46 ... static discharge lamp, 47 ... feed device, 48, 68 ... fixing device, 49, 59, 69a, 69a '... transfer medium, 50 ... Transfer device 55. Memory disturbing member 57 57 Transfer roller 60a, 60b, 60c, 60d Image forming unit 64 Transfer belt 65 Transfer roller 69b Intermediate transfer belt

Claims (8)

An image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium,
The toner particles include a colorant and a resin,
And the toner particles, an average value F _e of the electrostatic adhesion between the image bearing member,

A / r required when
0.2 ≦ a / r ≦ 0.7
An image forming method characterized by that.   The image forming method according to claim 1, wherein the toner image is transferred to the transfer medium via a conveyance medium. An image forming method for forming an image by transferring a toner image formed of toner particles on an image carrier onto a transfer medium via a conveyance medium,
The toner particles include a colorant and a resin,
And the toner particles, an average value F _e of the electrostatic adhesion between the conveying medium,

A / r required when
0.2 ≦ a / r ≦ 0.7
An image forming method characterized by that. An image carrier for forming a toner image with toner particles, and an image forming apparatus for forming an image by transferring a toner image formed with the toner particles on the image carrier to a transfer medium,
The toner particles include a colorant and a resin,
An average value F _e of the electrostatic adhesion between the image carrier and the toner particles,

A / r required when
0.2 ≦ a / r ≦ 0.7
An image forming apparatus.   The image forming apparatus according to claim 4, further comprising a conveyance medium for conveying the toner image to the transfer medium. An image forming apparatus that includes an image carrier for forming a toner image with toner particles and a transport medium for transporting the toner image, and forms the image by transferring the transported toner image to a transfer medium. There,
The toner particles include a colorant and a resin,
An average value F _e of electrostatic adhesion force between the toner particles and the transport medium,

A / r required when
0.2 ≦ a / r ≦ 0.7
An image forming apparatus. A developer having toner particles containing a colorant and a resin, and forming an image by transferring a toner image formed of the toner particles on an image carrier onto a transfer medium,
An average value F _e of the electrostatic adhesion between the image carrying body of the toner particles,

A / r required as
0.2 ≦ a / r ≦ 0.7
A developer characterized by being A developer having toner particles containing a colorant and a resin, and forming a toner image on a transfer medium via a conveyance medium,
The average value F _e of electrostatic adhesion force with the carrier medium of toner particles,

A / r required as
0.2 ≦ a / r ≦ 0.7
A developer characterized by being

Images