JP2005338776A - Toner for electrophotographic apparatus and electrophotographic apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce scattering of a toner and to obtain high image quality in electrostatic transfer of an electrophotographic process. <P>SOLUTION: The toner used for an electrophotographic apparatus is so prepared that the number N (piece) of a charge controlling agent existing on the surface of one piece of the toner satisfies formula (1) and formula (2) when the average radius of the toner is defined as r (μm) and the electrostatic charge quantity per unit weight of the toner as q/m (μC/g). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a toner for an electrophotographic apparatus and an electrophotographic apparatus using the same.

  Hereinafter, a conventional developing method and developing apparatus will be described. A recording apparatus using an electrophotographic method forms an electrostatic latent image on a photosensitive member by charging and exposure, develops the colored particles, and visualizes them as an image, and then transfers the colored particles to the surface of the recording member. The fixing step. As the colored particles, a powder called toner exclusively for electrophotography is used.

  The entire surface of the photosensitive member is once charged, and then a partial charge discharge is performed by irradiating light. Here, a potential contrast between the charged area and the exposed area is formed on the surface of the photoreceptor, which is called an electrostatic latent image.

  In the development step, first, toner particles, which are colored particles, are charged using a developer. The developer includes a two-component system composed of a mixed powder of toner and carrier beads, which are magnetic particles, and a one-component system composed of only toner. The developer is contained in a developing device and stirred there. At that time, in the case of a two-component developer, the toner is charged by friction with the carrier beads. In the case of a one-component developer, the toner is charged by friction with a member or the like.

  Hereinafter, the case of a two-component developer will be described.

  The toner is a fine particle having an average particle size of about 6 to 10 μm, and 90% or more of the component is a resin, and further contains a colorant (carbon black or pigment), a charge control agent, an external additive, wax and the like. The toner is triboelectrically charged when contacting with the carrier beads by mixing and stirring with the carrier beads having a particle size of about 30 to 100 μm, and after repeated contact several times, finally the electrostatic charge is applied to any of the carrier beads. Adheres. Since the toner is charged only by contact with the carrier beads, the surface of the toner is not completely uniformly charged, and local charging regions are scattered.

  Since resin is generally easily negatively charged by friction, a positively charged charge control agent plays a role in positively charging the toner. The charge control agent is a highly conductive substance such as a metal complex, and has a property of being easily charged, and various substances for positive charge and negative charge are used.

  That is, the charge control agent present on the toner surface and the carrier beads come into contact with each other to be charged, and the local charge exists in the charge control agent portion on the toner surface. In the case of negative charging, the charge amount of toner is controlled by using a charge control agent having a property of being more negatively charged than resin.

  In the case of the crushed toner, the charge control agent is kneaded with the resin in advance and solidified, and then the toner is produced by crushing. In the case of a polymerized toner, there are various production methods. However, it is considered that the charge control agent present on the toner surface is almost uniformly distributed because it is a material responsible for charging the toner as described above.

  In the case of a two-component developer, the toner is developed by rubbing the electrostatic latent image on the surface of the photoreceptor with a “magnetic brush”. The magnetic brush is formed by brushing carrier beads, which are magnetic particles, by the force of a magnet and formed in a brush shape, and the above-mentioned charged toner adheres to each carrier bead. The magnetic brush is conveyed to a developing position facing the electrostatic latent image by a rotating roller using a magnet called a developing roller. Such a development method is called magnetic brush development.

  Also, a method called bias development is often used as means for promoting visualization of an electrostatic latent image. In bias development, a bias voltage is applied to the developing roller to separate charged toner particles from carrier beads on the developing roller by the action of an electric field generated between the latent image potential formed on the surface of the photoreceptor and the developing roller. Then, development is performed by moving it to the surface of the photoreceptor. As the latent image potential (that is, the potential of the image forming portion of the photoconductor), the above-described charging potential or the exposure potential may be used.

  In general, a method using a charging potential as a latent image potential is called a normal development method, and a method using an exposure potential is called a reversal development method. Of the charging potential and the exposure potential, the potential that is not used as the latent image potential is called the background potential. The bias voltage of the developing roller is set between the charging potential and the exposure potential, and the difference between the latent image potential is called a developing potential difference. Similarly, the difference from the background potential is called the background potential difference. Usually, the developing potential difference that determines the developing performance itself is set larger than the background potential difference. If the development potential difference is large, the electric field formed (referred to as the development electric field) becomes strong, and it goes without saying that the development performance (toner development amount) increases, and the toner development amount varies depending on the bias voltage. A method of increasing the developing roller rotation speed between the developing roller and the photosensitive member, a method of reducing the distance, and a method of reducing the electric resistance of the developer have the same effect as increasing the developing electric field, and increase the amount of toner development. can do.

  Next, the transfer process will be described. The toner developed on the photoreceptor is stacked in two to three layers. The toner is electrostatically attached to the photoconductor, and the toners are aggregated with the same electrostatic force. Therefore, even after the development process, the toner is aggregated in layers on the photoconductor even if the development bias voltage is removed. As a method of transferring the toner image to a recording medium such as paper, the paper is brought close to the photoconductor and the toner layer is sandwiched between the photoconductor and the electrostatic attraction force from the back side of the paper to the toner on the paper side. An electrostatic transfer method in which a transfer electric field is applied and transferred onto a sheet is generally used. Specific methods include applying a reverse polarity charge to the toner using a corona charger (corona transfer), or applying a reverse voltage to the roller by pressing the roller from the back of the paper with a roller (roller). Transcription).

  The toner image transferred onto the paper is preferably a mirror image that faithfully reproduces the toner image on the photoreceptor. Further, since it is not possible to transfer all the multilayer toners with a weak transfer electric field, it is necessary to apply a strong transfer electric field. However, when a strong transfer electric field is applied, Paschen discharge occurs in the gap between the paper and the photoconductor in both corona transfer and roller transfer, and the toner is reversely charged, causing toner scattering during transfer. As a result, the toner image transferred onto the paper causes image quality degradation such as toner scattering on both sides of the line drawing and around the dots of halftone dots, compared to the toner image on the photoreceptor. Non-patent document 1 shows the scattering of toner at the time of transfer.

Takahashi Iwai Iino Kosugi Japan Hardcopy 2003 Lecture Collection The Imaging Society of Japan (2003) P53

Takeuchi The Journal of Electrophotographic Society Vol. 36 No. 3 (1997) P175

Takeshi Otani Journal of the Imaging Society of Japan Vol. 40 No. 1 (2001) P24

Hase Murata Journal of the Electrostatic Society of Japan, Vol. No. 22 1 (1998) P23

Murata Journal of the Imaging Society of Japan Vol. 39 no. 3 (2000) P248

JP 2003-91100 A

  As described above, in electrostatic transfer, it is an object to obtain high image quality by reducing toner scattering, and the present invention provides a means for this.

In the present invention, conditions are set for the size of the charge control agent on the toner surface in order to reduce toner scattering in electrostatic transfer. In an electrophotographic apparatus, the charge amount q / m per unit weight of toner is mostly 10 to 25 μC / g. The reason is that the upper limit of the surface potential of the photoreceptor is about 1000 V (1.0 × 10 ^{−3 to} 2.0 × 10 ⁻³ C / m ² in terms of surface charge density), and the toner particle size is It is about 6-10 micrometers. To develop 2 to 3 layers of toner having a size of about 6 to 10 μm on the photoreceptor, the surface charge density is about 1.0 × 10 ^{−3 to} 2.0 × 10 ⁻³ C / m ^2. Must be about 10-25 μC / g.

Therefore, the adhesion force is considered for a spherical toner having a charge amount of q / m and a radius r. According to the experimental results according to Non-Patent Document 2, the adhesion force of one toner to the photoreceptor is about 1.0 × 10 ⁻⁷ N. When the toner is spherical and the density is p, one toner charge amount Q is expressed by Equation 3.
(Formula 3)

In Equation 3, when q / m = 17.5 μC / g, r = 5 μm, and p = 1.1 × 10 ³ kg / m ³ , Q = 1.0 × 10 ⁻¹⁴ C.

Next, assuming that the toner surface is uniformly charged, the mirror image force with respect to the surface of the photoreceptor is expressed by Expression 4.
(Formula 4)

In Equation 4, if εr = 3, Q = 1.0 × 10 ⁻¹⁴ C, and r = 5 μm, F = 4.5 × 10 ⁻⁹ N and 1.0 × 10 ⁻⁷ N Obviously different. As described above, assuming that the toner surface is locally charged in the charge control agent portion and assuming N local charges on the toner surface, the mirror image force acting on one local charge is expressed by Equation 5.
(Formula 5)

In Equation 5, when ε _r = 3, d = 0.1 μm, and N = 11, F = 0.93 × 10 ⁻⁷ N, which is substantially equal to 1.0 × 10 ⁻⁷ N.

  According to the experimental results by Non-Patent Document 3, it is considered that the average particle diameter of the charge control agent contained in the toner is about 0.2 μm, and there are about 15 particles on the surface, which is almost in agreement with the above results. That is, an adhesive force acts between the photoreceptor and other toners due to such local charges. The adhesion force between the toners is a mirror image force between the local charge localized on the charge control agent and the toner resin surface. When the toner surface is uniformly charged, no electrostatic attractive force acts between the toners.

  It is conceivable that the toner scattering against the adhesion force acting between the toners during electrostatic transfer is affected by the reverse charging of the toner due to discharge. The reverse polarity charge adheres to the toner surface due to the gap discharge, and the repulsive force between the opposite polarity charges is the main cause of toner scattering. However, it is also conceivable that the toner layer scatters due to the fact that the discharge is not involved in contact between the toner layer and the paper.

  This scattering can be prevented by increasing the adhesion between the toners. In order for the adhesion force between toners to overcome this repulsive force and not scatter, it is desirable that the charge amount of one charge control agent is as large as possible. Obviously, if the charge amount Q of one toner is constant, the smaller the number of charge control agents, the larger the local charge amount and the greater the image power thereof, and thus the less the scattering. For example, when there are four local charges on the toner surface, the image power is about 7.5 times larger than when there are 11 local charges.

However, if the adhesion force is increased too much, the adhesion force between the photosensitive member and the toner also increases, and the toner cannot be transferred with a normal transfer electric field strength (0.5 × 10 ^{7 to} 5.0 × 107 V / m).

  From the above, in order to prevent toner scattering during transfer, it is necessary to reduce the number of charge control agents present on the toner surface as much as possible under conditions that allow transfer with normal transfer electric field strength. desirable.

Therefore, the relationship between the number of charge control agents present on the toner surface and the adhesion between the toner and the photoreceptor is estimated. When the charge control agent is present almost uniformly on the toner surface and the charge amount Q of the toner is 1.0 × 10 ⁻¹⁴ C, the electric field strength E in the gap is 20 μm when the paper and the toner are in contact with each other. Assuming that the potential difference is 1000 V, the force from the gap electric field applied to one toner is calculated by Equation 6 because it is approximately 5.0 × 10 ⁷ V / m.
(Formula 6)

  In order for the toner to be electrostatically transferred, the mirror image force between the charge control agent on the toner surface and the surface of the photoreceptor must be smaller than the value of Equation 5, but when N = 5 in Equation 5, Match the value. That is, it is necessary that five or more charge control agents exist on the toner surface. Accordingly, in the above example, the presence of five charge control agents on the toner surface is the most difficult condition for scattering.

The above is a concrete result when the charge amount of the toner is 17.5 μC / g and the particle diameter is 10 μm. In general, the force from the gap electric field and the charge control are obtained by using Equation 6> Equation 5. The relationship between the charge amount Q of one toner and the number N of charge control agents when the image force of the agent and the surface of the photosensitive member becomes equal can be obtained. That is, it is expressed as Expression 7 and Expression 8.
(Formula 7)

(Formula 8)

When the relationship between the charge amount per unit weight (q / m) of toner and N is obtained from Expression 7 and Expression 8, it is expressed as Expression 9.
(Formula 9)

The condition of the toner with less scattering in electrostatic transfer is when the number N of charge control agents on the toner surface is in the range represented by Equation 9 and is the minimum value. That is, it is expressed by Expression 10 and Expression 11.
(Formula 10)

(Formula 11)

Here, since the right side of Expression 10 is generally not an integer, it is expressed by Expression 12.
(Formula 12)

Therefore, the maximum value of the number N of charge control agents is the condition with the least scattering.

Next, let's assign a specific value. Assuming that ε _r = 3, E = 5.0 × 10 ⁷ V / m, p = 1.1 × 10 ³ kg / m ³ , and d = 0.1 μm, it is expressed by Equation 13.
(Formula 13)

For example, if q / m = 15 μC / g and r = 4 μm are substituted in Equation 13, N ₀ = 3.16, so N = 4 is most desirable.

Now, the value of N ₀ represented by Equation 10 varies depending on the relative dielectric constant ε _r and the transfer electric field strength E of the photoreceptor. That is, k in Equation 11 changes. The density p1 μm of the resin used for various toners is fixed, and the relative dielectric constant ε _r = 3 to 11 of a commonly used photoreceptor, and the normal transfer electric field strength E = 0.5 × 10 ^{7 to} 5.0 × 10 ⁷ When the minimum value and the maximum value of the coefficient k in Expression 11 are obtained in the range of V / m, they are 0.0104 and 0.173, respectively. Therefore, the conditions represented by Equation 10 to Equation 12 are
It represents with Formula 14-Formula 16.
(Formula 14)

(Formula 15)

(Formula 16)

In actual machine development, it is necessary to change the transfer electric field strength E in various ways to set conditions for less scattering in electrostatic transfer. Therefore, N in the equation 14 includes the case where the maximum value k = 0.173. This condition is necessary. That is, it is desirable to use a toner represented by Formula 17 and Formula 18.
(Formula 17)

(Formula 18)

FIG. 1 shows the relationship between N ₀ and q / m obtained by Equation 17 when the toner radius r = 3 μm, 4 μm, and 5 μm. q / m was shown in the range of 10-25 μC / g.

  The spherical toner has been described above. However, even in the case of a crushed toner, the mirror image force acting on one charge control agent on the toner surface is expressed by Equation 5 as in the case of the spherical toner. 18 is the condition with the least scattering.

  Here, the charge amount q / m per toner unit weight can be measured using, for example, a toner charge amount measuring device Model-210HS-2A manufactured by Trek Japan. Further, the toner average radius r can be measured using, for example, a Coulter counter manufactured by Coulter USA. The number N of charge control agents present on the surface of one toner is measured using a scanning microscope for observing the charged state as described in Non-Patent Document 4 and Non-Patent Document 5, for example. Can do.

  Incidentally, as a toner for realizing high transfer efficiency, an invention characterized in that the specific surface area of the charge control agent on the surface of the toner particles is within a certain value range is described in Patent Document 1, but the present invention Defines the number of charge control agents on the toner particle surface.

  According to the present invention, electrostatic transfer that hardly causes toner scattering can be realized, and a high-quality image can be provided.

Assuming that the charge amount per unit weight of the toner is q / m and the average number of charge control agents present on the surface of one toner is N, electrostatic charge can be obtained by using the toner represented by the following relational expression. Toner scattering during transfer can be reduced.
(Formula 19)

(Formula 20)

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 2 is a sectional side view of an electrophotographic apparatus using the toner of this embodiment. Reference numeral 1 denotes a photosensitive drum, 2 denotes a charger, 3 denotes toner, 4 denotes a developing machine, 5 denotes paper, 6 denotes a transfer device, 7 denotes a fixing device, 8 denotes a cleaner, and 9 denotes an exposure device. An electrostatic latent image is formed on the surface of the photosensitive drum 1 uniformly charged by the charger 2 by a semiconductor laser whose light emission is controlled by an exposure control means such as a laser driver and an exposure device 9 consisting of an optical system. .

  Thereafter, the developing device 4 develops the electrostatic latent image with the toner 3. The toner 3 is transferred to the paper 5 by the transfer device 6. Thereafter, the transferred toner image is heated and melted by the fixing device 7 and fixed on the paper 5. Further, the toner 3 remaining on the surface of the photosensitive drum 1 without being transferred is collected by the cleaner 8 and the series of processes is completed.

  FIG. 3 is a sectional side view showing details of a transfer device (corona transfer) using the toner of the present invention. Reference numeral 11 denotes a toner developed on the photosensitive member, 12 denotes a photosensitive member, 13 denotes a sheet or transfer belt, 14 denotes a substrate of the photosensitive drum, 15 denotes a corona wire, and 16 denotes a shield of the corona transfer unit.

The sheet or transfer belt 13 is in contact with the toner 11 so as to be sandwiched between the photosensitive member and the back surface of the sheet or transfer belt 13 is charged with a reverse polarity to the toner by a corona transfer device. The image is transferred by generating a transfer electric field for attracting the toner. In the case of corona transfer, the transfer electric field strength E is large and is usually in the range of 1.0 × 10 ^{7 to} 5.0 × 10 ⁷ V / m. In FIG. 3, the toner 11 has negative polarity. Toner 11 has a charge amount q / m per unit weight of toner in the range of 10 to 25 μC / g and a toner radius r in the range of 3 to 5 μm, and is a charge control agent present on the surface of one toner. The number N (pieces) satisfies the conditions given by Equation 17 and Equation 18.

FIG. 4 is a sectional side view showing details of another type of transfer device (roller transfer) using the toner of the present invention. Reference numeral 11 denotes a toner developed on the photosensitive member, 12 denotes a photosensitive member, 13 denotes a sheet or transfer belt, 14 denotes a substrate of the photosensitive drum, 17 denotes a core of a transfer roller, and 18 denotes a dielectric such as rubber. The sheet or transfer belt 13 is pressed against the transfer roller and comes into contact with the toner 11 so as to be sandwiched between the photosensitive member and the transfer roller is applied with a voltage having a polarity opposite to that of the toner. Transfer is performed by generating a transfer electric field for attracting toner. In the case of roller transfer, E is usually in the range of 0.5 × 10 ^{7 to} 1.0 × 107 V / m. In FIG. 4, the toner 11 has negative polarity. Toner 11 has a charge amount q / m per unit weight of toner in the range of 10 to 25 μC / g and a toner radius r in the range of 3 to 5 μm, and is a charge control agent present on the surface of one toner. The number N (pieces) satisfies the conditions given by Equation 17 and Equation 18.

FIG. 6 is an explanatory diagram showing conditions for defining the toner of the present invention. FIG. 3 is a cross-sectional view of an electrophotographic apparatus using the toner of the present invention. FIG. 3 is an explanatory diagram of a transfer device portion of an electrophotographic apparatus using the toner of the present invention (Example 1). FIG. 4 is an explanatory diagram of a transfer device portion of an electrophotographic apparatus using the toner of the present invention (Example 2).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Toner 4 Developing machine 5 Paper 6 Transfer device 7 Fixing device 8 Cleaner 9 Exposure device 11 Toner developed on the photosensitive member,
12 Photoconductor 13 Paper or transfer belt 14 Photoconductor drum substrate 15 Corona wire 16 Shield of corona transfer device 17 Core of transfer roller 18 Dielectric material such as rubber of transfer roller

Claims (2)

In the toner used in the electrophotographic apparatus, when the toner average radius is r (μm) and the charge amount per unit weight of the toner is q / m (μC / g), the charge control agent present on the surface of one toner A toner for an electrophotographic apparatus, wherein the number N satisfies the formulas 1 and 2.
(Formula 1)

(Formula 2)

An electrophotographic apparatus using the toner for an electrophotographic apparatus according to claim 1.

Images