JP2018136374A - Positively-charged toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positively-charged toner with which high-quality images can be continuously formed in continuous printing.SOLUTION: A positively-charged toner includes a plurality of toner particles including a toner base particle and an external additive. The toner base particle includes a toner core and a shell layer. The external additive includes silica particles. The work function Wof a surface layer part of the shell layer measured from a photoelectron spectrum of the toner before stress is applied thereto and the work function Wof a surface layer part of the silica particle satisfy the following formula (M1). The number of emitted photoelectrons Cat an excitation energy 7 eV measured from the photoelectron spectrum of the toner before stress is applied thereto and the number of emitted photoelectrons Cat an excitation energy 7 eV measured from a photoelectron spectrum of the toner after stress is applied thereto satisfy the following formula (M2). (M1) 0.00 eV≤W-W≤+0.10 eV; (M2) 0.95≤C/C≤1.05.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a positively chargeable toner.

  Patent Document 1 discloses a positively chargeable toner using two types of hydrophobic silica particles (hydrophobized silica) as external additives for toner particles.

JP 2001-13717 A

  However, when continuous printing is performed using the positively chargeable toner described in Patent Document 1, the quality of the formed image tends to decrease as the number of printed sheets increases. This is presumably because the toner particles are stressed during the image formation process, and the silica particles are detached from the toner base particles, or the silica particles are buried in the surface layer of the toner base particles.

  The present invention has been made in view of the above problems, and an object thereof is to provide a positively chargeable toner capable of continuously forming a high-quality image in continuous printing.

The positively chargeable toner according to the present invention includes a plurality of toner particles including toner base particles and an external additive attached to the surface of the toner base particles. The toner base particles include a toner core and a shell layer that covers a surface of the toner core. The external additive includes silica particles. The work function W ₁ of the surface layer portion of the shell layer and the work function W ₂ of the surface layer portion of the silica particles, which are measured from the photoelectron spectrum of the toner before being stressed, satisfy the following formula (M1). . Photoelectron emission number C ₁ at an excitation energy of 7 eV measured from the photoelectron spectrum of the toner before being stressed and photoelectron at an excitation energy of 7 eV measured from the photoelectron spectrum of the toner after being stressed The release number C ₂ satisfies the following formula (M2).
0.00eV ≦ W ₂ −W ₁ ≦ + 0.10 eV (M1)
0.95 ≦ C ₂ / C ₁ ≦ 1.05 (M2)
[After applying the stress, 100 parts by mass of zirconia beads having a number average primary particle diameter of 1 mm and 20 parts by mass of the toner are placed in a 500 mL capacity container so that the free capacity of the container is 30%. In this process, the contents of the container are stirred for 1 hour using a ball mill under the condition of a rotation speed of 200 rpm. ]

  According to the present invention, it is possible to provide a positively chargeable toner capable of continuously forming a high-quality image in continuous printing.

FIG. 3 is a diagram illustrating a cross-sectional structure of toner particles contained in a positively chargeable toner (first toner) according to an embodiment of the present invention. It is a graph which shows the photoelectron spectrum measured about the 1st toner. It is a graph which shows the photoelectron spectrum measured about the 2nd toner which concerns on a comparative example. FIG. 6 is a diagram illustrating a cross-sectional structure of toner particles contained in a positively chargeable toner (third toner) according to a comparative example. It is a graph which shows the photoelectron spectrum measured about the 3rd toner. It is a graph which shows the photoelectron spectrum measured about the 4th toner which concerns on a comparative example. FIG. 6 is a diagram illustrating a cross-sectional structure of toner particles contained in a positively chargeable toner (fifth toner) according to a comparative example. It is a graph which shows the photoelectron spectrum measured about the 5th toner.

  An embodiment of the present invention will be described. Note that the evaluation results (values indicating shape, physical properties, etc.) regarding the powder (more specifically, the toner core, toner base particles, external additive, toner, etc.) are a considerable number of particles unless otherwise specified. Is the number average of the values measured for.

Unless otherwise specified, the number average particle diameter of the powder is the number average of the equivalent-circle diameters of primary particles (Haywood diameter: the diameter of a circle having the same area as the projected area of the particles) measured using a microscope. Value. Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is measured using a laser diffraction / scattering particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value.

  The glass transition point (Tg) is a value measured according to “JIS (Japanese Industrial Standard) K7121-2012” using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) unless otherwise specified. It is. In an endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured with a differential scanning calorimeter, inflection points (baseline extrapolation line and falling line extrapolation line) The temperature (onset temperature) at (intersection point with) corresponds to Tg (glass transition point). Moreover, the softening point (Tm) is a value measured using a Koka type flow tester (“CFT-500D” manufactured by Shimadzu Corporation) unless otherwise specified. In the S curve (horizontal axis: temperature, vertical axis: stroke) measured with the Koka type flow tester, the temperature that becomes "(baseline stroke value + maximum stroke value) / 2" is Tm (softening point). Equivalent to.

  The chargeability means the chargeability in frictional charging unless otherwise specified. The strength of positive chargeability (or strength of negative chargeability) in frictional charging can be confirmed by a known charge train or the like.

  In the present specification, both untreated silica particles (hereinafter referred to as silica substrate) and silica particles obtained by subjecting a silica substrate to surface treatment (surface-treated silica particles) are described as “silica particles”. To do. In addition, silica particles hydrophobized with a surface treatment agent may be referred to as “hydrophobic silica particles”, and silica particles positively charged with a surface treatment agent may be referred to as “positive charge silica particles”, respectively.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. The crystalline polyester resin is described as “crystalline polyester resin”, and the non-crystalline polyester resin is simply described as “polyester resin”.

  The toner according to this exemplary embodiment is a positively chargeable toner and can be suitably used for developing an electrostatic latent image. The toner of the present exemplary embodiment is a powder that includes a plurality of toner particles (each having a configuration described later). The toner may be used as a one-component developer. Alternatively, a two-component developer may be prepared by mixing toner and carrier using a mixing device (for example, a ball mill). In order to form a high-quality image, it is preferable to use a ferrite carrier (ferrite particle powder) as a carrier. In order to form a high-quality image over a long period of time, it is preferable to use magnetic carrier particles including a carrier core and a resin layer covering the carrier core. In order to impart magnetism to the carrier particles, the carrier core may be formed of a magnetic material (for example, a ferromagnetic substance such as ferrite), or the carrier core may be formed of a resin in which magnetic particles are dispersed. Good. Further, magnetic particles may be dispersed in the resin layer covering the carrier core. In order to form a high-quality image, the amount of toner in the two-component developer is preferably 5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the carrier. The positively chargeable toner contained in the two-component developer is positively charged by friction with the carrier.

  The toner according to the exemplary embodiment can be used for image formation in, for example, an electrophotographic apparatus (image forming apparatus). Hereinafter, an example of an image forming method using an electrophotographic apparatus will be described.

  First, an image forming unit (charging device and exposure device) of an electrophotographic apparatus forms an electrostatic latent image on a photosensitive member (for example, a surface layer portion of a photosensitive drum) based on image data. Subsequently, a developing device of the electrophotographic apparatus (specifically, a developing device in which a developer containing toner is set) supplies the toner to the photoconductor to develop the electrostatic latent image formed on the photoconductor. The toner is charged by friction with the carrier, the developing sleeve, or the blade in the developing device before being supplied to the photoreceptor. The positively chargeable toner is positively charged. In the developing process, toner (specifically, charged toner) on a developing sleeve (for example, a surface layer portion of a developing roller in the developing device) disposed in the vicinity of the photosensitive member is supplied to the photosensitive member, and the supplied toner is By attaching to the electrostatic latent image on the photoconductor, a toner image is formed on the photoconductor. The consumed toner is replenished to the developing device from a toner container containing replenishment toner.

  In the subsequent transfer process, after the transfer device of the electrophotographic apparatus transfers the toner image on the photosensitive member to an intermediate transfer member (for example, a transfer belt), the toner image on the intermediate transfer member is further transferred to a recording medium (for example, paper). Transcript to. Thereafter, a fixing device (fixing method: nip fixing with a heating roller and a pressure roller) of the electrophotographic apparatus heats and pressurizes the toner to fix the toner on the recording medium. As a result, an image is formed on the recording medium. For example, a full color image can be formed by superposing four color toner images of black, yellow, magenta, and cyan. After the transfer step, the toner remaining on the photoreceptor is removed by a cleaning member (for example, a cleaning blade). The transfer method may be a direct transfer method in which the toner image on the photosensitive member is directly transferred to the recording medium without using the intermediate transfer member. The fixing method may be a belt fixing method.

  The toner particles include toner base particles and an external additive. The external additive is attached to the surface of the toner base particles. The toner base particles contain a binder resin. The toner base particles may contain an internal additive (for example, at least one of a release agent, a colorant, a charge control agent, and a magnetic powder) as necessary.

  In the toner according to the present exemplary embodiment, the toner base particles include a toner core and a shell layer that covers the surface of the toner core. The shell layer is substantially composed of a resin. Additives may be dispersed in the resin constituting the shell layer. Hereinafter, the material for forming the shell layer may be referred to as a shell material.

  The toner according to the exemplary embodiment is a positively chargeable toner having the following configuration (hereinafter referred to as a basic configuration).

[Basic toner configuration]
The positively chargeable toner includes a plurality of toner particles including toner base particles and an external additive attached to the surface of the toner base particles. The toner base particles include a toner core and a shell layer that covers the surface of the toner core. The external additive includes silica particles. The work function of the toner component (specifically, the shell layer and silica particles) and the photoelectron emission number (excitation energy: 7 eV) of the toner satisfy the following formulas (M1) and (M2). Regarding the number of photoelectrons emitted from the toner, the degree of change between before and after applying stress to the toner is defined. The method of applying stress is as follows. The toner before being stressed means an unused toner.

(Work function)
The work functions W ₁ and W ₂ satisfy the following formula (M1). The work function W ₁ is a work function of the surface layer portion of the shell layer measured from the photoelectron spectrum of the toner before being stressed. The work function W ₂ is a work function of the surface layer portion of the silica particles measured from the photoelectron spectrum of the toner before being stressed. The method for measuring the photoelectron spectrum of the toner is the same method as in Examples described later, or an alternative method thereof.
0.00eV ≦ W ₂ −W ₁ ≦ + 0.10 eV (M1)

In the photoelectron spectrum, the vertical axis represents the photoelectron count, and the horizontal axis represents the excitation energy. However, in the measurement of the work function, the “photoelectron count number” on the vertical axis corresponds to the nth power of the photoelectron yield per unit light quantity (hereinafter sometimes referred to as the normalized photoelectron yield). “N” is a power index. The unit of normalized photoelectron yield is (cps) ⁿ . By taking the normalized photoelectron yield (where 0 <n <1) on the vertical axis of the photoelectron spectrum, a graph having a certain slope (a graph including one to a plurality of linear portions) can be obtained (FIG. 2, FIG. 3, FIG. 5, FIG. 6, and FIG. 8). In the examples described later, n is set to “0.1”.

(Number of photoelectrons emitted at an excitation energy of 7 eV)
The photoelectron emission numbers C ₁ and C ₂ satisfy the following formula (M2). The photoelectron emission number C ₁ is a photoelectron emission number at an excitation energy of 7 eV, measured from the photoelectron spectrum of the toner before being stressed. The photoelectron emission number C ₂ is the photoelectron emission number at an excitation energy of 7 eV, measured from the photoelectron spectrum of the toner after being stressed. The method for measuring the photoelectron spectrum of the toner is the same method as in Examples described later, or an alternative method thereof.
0.95 ≦ C ₂ / C ₁ ≦ 1.05 (M2)

(Method of applying stress)
For the stress application, 100 parts by mass of zirconia beads having a number average primary particle diameter of 1 mm and 20 parts by mass of toner are placed in a 500 mL container so that the empty capacity of the container becomes 30%, and then a ball mill is used. In this process, the contents of the container are stirred for 1 hour under the condition of a rotation speed of 200 rpm.

Hereinafter, “not used” may be described before stress is applied, and “after use” may be described after stress is applied. Further, the ratio of the photoelectron emission number C ₂ to the photoelectron emission number C ₁ (= C ₂ / C ₁ ) may be referred to as “photoelectron retention rate Rc”. The photoelectron retention rate Rc may be expressed as a percentage. If the photoelectron retention rate Rc is 95% or more and 105% or less, the formula (M2) is satisfied. A photoelectron retention rate Rc of 100% means that the number of photoelectrons emitted did not change before and after the application of stress.

  In particles having a surface layer portion with a small work function, photoelectrons are emitted from the surface layer portion with weak energy. For this reason, particles having a smaller work function in the surface layer portion tend to be positively triboelectrically charged.

  By using silica particles as an external additive for toner particles, fluidity can be imparted to the toner. Further, the use of silica particles as an external additive for toner particles can enhance the chargeability of the toner. However, when an image is formed using such toner, the toner particles are stressed during the image formation process, and the silica particles are detached from the toner base particles, or the silica particles are buried in the surface layer portion of the toner base particles. Sometimes. Each of the separation and embedding of such silica particles (external additive) tends to weaken the chargeability of the toner.

In the toner having the basic configuration described above, the work functions W ₁ and W ₂ satisfy the formula (M1). That is, the work function W ₂ of the surface layer portion of the silica particles is the same as the work function W ₁ of the surface layer portion of the shell layer, or is slightly larger than the work function W ₁ of the surface layer portion of the shell layer. Specifically, the difference between the work function W ₁ of the surface layer portion of the shell layer and the work function W ₂ of the surface layer portion of the silica particles is within 0.10 eV. The strength of the positive charging property of the silica particles (external additive) is substantially the same as the strength of the positive charging property of the shell layer.

  As described above, in the toner having the above-described basic configuration, sufficient toner positive chargeability is ensured with only toner base particles, and fluidity is imparted to the toner with silica particles (external additive). By covering the toner core with a shell layer having a strong positive charging property (specifically, a shell layer having a positive charging property comparable to that of silica particles), sufficient toner positive charging property can be ensured with the toner mother particles alone.

In order to continuously form high-quality images in continuous printing, it is desirable that the toner has substantially the same photoelectron spectrum in the unused state and in the used state. When the work functions W ₁ and W ₂ satisfy the formula (M1), it is considered that the change in the photoelectron spectrum due to the detachment and burying of the silica particles (external additive) is reduced. However, it is also conceivable that the photoelectron spectrum of the toner changes due to other factors (deterioration of the surface layer portion of the toner base particles due to stress, etc.).

In the toner having the basic configuration described above, the photoelectron retention rate Rc (= C ₂ / C ₁ ) satisfies the formula (M2). That is, the number of photoelectrons emitted from the toner at an excitation energy of 7 eV is substantially the same before and after the application of stress. Specifically, the photoelectron retention rate Rc is 95% or more and 105% or less. The amount of change in the number of photoelectrons emitted before and after the application of stress is within ± 5% with respect to the number of photoelectrons emitted C ₁ (before the application of stress). The excitation energy of 7 eV generally corresponds to the strength of stress that the toner receives in the developing device. By establishing the formula (M2) in addition to the formula (M1), the photoelectron spectrum of the unused toner and the photoelectron spectrum of the used toner can be sufficiently approximated.

  The inventor of the present application has found that the toner having the above-described basic configuration tends to have substantially the same photoelectron spectrum in the unused state and the state after use. By performing continuous printing using such toner, it becomes possible to continuously form high-quality images.

  In the measurement of the photoelectron spectrum (vertical axis: photoelectron count, horizontal axis: excitation energy), the initial excitation energy is set to the lower limit of the measurement range (for example, 4.00 eV), and the excitation energy is increased for each excitation energy. The number of photoelectrons emitted is continuously counted. In the photoelectron spectrum, the excitation energy at the rising point (the point at which photoelectron emission starts) corresponds to the work function of the first component to be measured (hereinafter referred to as the first work function). The excitation energy at the rising point corresponds to the minimum energy necessary for emitting photoelectrons from the measurement target. After the photoelectron count rises, the photoelectron count number (specifically, the normalized photoelectron yield) increases linearly with a constant slope as the excitation energy increases. However, the slope of the straight line may change in an excitation energy region larger than the rising point. The excitation energy at this slope change point (hereinafter referred to as the first slope change point) corresponds to the work function of the second component to be measured (hereinafter referred to as the second work function). In addition, the slope of the straight line may further change in an excitation energy region larger than the first slope change point. The excitation energy at this slope change point (hereinafter referred to as the second slope change point) corresponds to the work function of the third component to be measured (hereinafter referred to as the third work function). Note that the slope of the straight line may further change in an excitation energy region larger than the second slope change point.

  FIG. 1 shows toner particles included in an example of the toner having the above basic configuration. Hereinafter, the toner particles shown in FIG. 1 are referred to as first toner particles 10. In addition, a toner (powder of the first toner particles 10) substantially composed of only the first toner particles 10 may be referred to as a first toner.

  The first toner particles 10 shown in FIG. 1 include toner base particles and a plurality of silica particles 13 (each external additive particle). The toner base particles include a toner core 11 containing a binder resin (specifically, a polyester resin) and a shell layer 12 formed on the surface of the toner core 11. The shell layer 12 is a resin film. The shell layer 12 covers the entire surface of the toner core 11. The toner core 11 does not contain a charge control agent. Each of the plurality of silica particles 13 is attached to the surface of the shell layer 12. The shell layer 12 contains a resin containing a repeating unit having an oxazoline group. By including such a resin in the shell layer 12, it becomes easy to ensure sufficient positive chargeability of the toner only with the toner base particles. Unopened oxazoline groups exhibit strong positive chargeability. In addition, the oxazoline group easily forms a chemical bond with the binder resin in the toner core 11. For this reason, detachment of the shell layer 12 from the toner core 11 is suppressed by the presence of the oxazoline group in the resin constituting the shell layer 12. By heating the shell material in the liquid at an appropriate temperature for an appropriate time, the reaction between the toner core 11 and the shell layer 12 can proceed and the resin constituting the shell layer 12 can be appropriately crosslinked. The shell layer 12 thus formed has a crosslinked structure.

  FIG. 2 shows photoelectron spectra measured for the first toner before and after applying stress. In FIG. 2, a line L11 indicates a photoelectron spectrum before applying stress, and a line L12 indicates a photoelectron spectrum after applying stress.

From the line L11 in FIG. 2, it can be seen that the first work function (excitation energy at the rising point) is 5.95 eV, and the second work function (excitation energy at the first inclination change point) is 5.97 eV. . In the photoelectron spectrum indicated by the line L11, there is no tilt change point in the excitation energy region (greater than 5.97 eV) larger than the first tilt change point. In the first toner (see FIG. 1), the first work function corresponds to the work function W ₁ of the surface layer portion (first component) of the shell layer 12, and the second work function corresponds to the surface layer portion (first surface) of the silica particles 13. This is considered to correspond to the work function W ₂ of (two components). Therefore, a value obtained by subtracting the work function W ₁ from the work function W ₂ (= W ₂ −W ₁ ) is +0.02 eV (= 5.97 eV−5.95 eV). In the photoelectron spectrum of the first toner shown in FIG. 2, the photoelectron retention rate Rc is 96%. In the first toner, both the above-described equations (M1) and (M2) are satisfied. As indicated by lines L11 and L12 in FIG. 2, the first toner has substantially the same photoelectron spectrum in the unused state and in the used state.

  FIG. 3 shows photoelectron spectra measured for the second toner before and after applying stress. In FIG. 3, a line L21 indicates a photoelectron spectrum before applying stress, and a line L22 indicates a photoelectron spectrum after applying stress.

  The second toner is a toner (a powder of the second toner particles) substantially composed only of the second toner particles. The crosslinking density of the shell layer of the second toner particles is higher than the crosslinking density of the shell layer of the first toner particles. Other configurations of the second toner particles are the same as those of the first toner particles 10 (see FIG. 1). By heating the shell material in the liquid for a long time, the crosslinking density of the resin constituting the shell layer can be increased. In the shell layer, the oxazoline group reacts with each other, or the oxazoline group reacts with another functional group (for example, carboxyl group), whereby the oxazoline group is ring-opened, and a crosslinked structure is formed in the shell layer. . An oxazoline group having a strong polarity loses its polarity upon ring opening. For this reason, the oxazoline group becomes weak in hydrophilicity by ring opening. By opening the oxazoline group in the shell layer, a shell layer in which charge attenuation due to moisture hardly occurs can be obtained. For this reason, the positive chargeability of the shell layer tends to increase as the crosslink density of the shell layer increases.

From the line L21 in FIG. 3, it can be seen that the first work function (excitation energy at the rising point) is 5.97 eV, and the second work function (excitation energy at the first inclination change point) is 5.86 eV. . In the second toner, the first work function corresponds to the work function W ₁ of the surface layer portion (first component) of the shell layer, and the second work function corresponds to the work function W of the surface layer portion (second component) of the silica particles. Equivalent to ₂ . Therefore, a value obtained by subtracting the work function W ₁ from the work function W ₂ (= W ₂ −W ₁ ) is +0.11 eV (= 5.86 eV−5.95 eV). In the photoelectron spectrum of the second toner shown in FIG. 3, the photoelectron retention rate Rc is 107%. In the second toner, neither the above-described formula (M1) nor formula (M2) is established. As indicated by lines L21 and L22 in FIG. 3, the photoelectron spectrum of the second toner is greatly different between the unused state and the used state.

  FIG. 4 shows the third toner particles 10a included in the third toner. The third toner is a toner (powder of the third toner particles 10a) substantially composed of only the third toner particles 10a. As shown in FIG. 4, the shell layer 12 of the third toner particle 10 a partially covers the surface of the toner core 11. Specifically, the coverage (area ratio) of the shell layer 12 is about 60%. That is, about 60% of the surface area of the toner core 11 is covered by the shell layer 12, and in the remaining area (area: about 40%), the toner core 11 is exposed from the shell layer 12. Each of the plurality of silica particles 13 is attached to the surface of the toner core 11 or the surface of the shell layer 12. Other configurations of the third toner particles 10a are the same as those of the first toner particles 10 (see FIG. 1).

  FIG. 5 shows photoelectron spectra of the third toner measured before and after applying stress. In FIG. 5, a line L31 indicates a photoelectron spectrum before applying stress, and a line L32 indicates a photoelectron spectrum after applying stress.

From the line L31 in FIG. 5, the first work function (excitation energy at the rising point) is 5.95 eV, the second work function (excitation energy at the first inclination change point) is 5.97 eV, It can be seen that the work function (excitation energy at the second slope change point) is 6.05 eV. In the third toner (see FIG. 4), the first work function corresponds to the work function W ₁ of the surface layer portion (first component) of the shell layer 12, and the second work function corresponds to the surface layer portion (first surface) of the silica particles 13. corresponds to the work function W ₂ of the two components), the third work function, is considered to correspond to the work function of the binder resin present in the surface layer of the toner core 11 (third component). Therefore, a value obtained by subtracting the work function W ₁ from the work function W ₂ (= W ₂ −W ₁ ) is +0.02 eV (= 5.97 eV−5.95 eV). In the photoelectron spectrum of the third toner shown in FIG. 5, the photoelectron retention rate Rc is 90%. In the third toner, the above-described expression (M1) is satisfied, but the above-described expression (M2) is not satisfied. As indicated by lines L31 and L32 in FIG. 5, the photoelectron spectrum of the unused third toner and the photoelectron spectrum of the third toner after use are not sufficiently approximate.

  FIG. 6 shows photoelectron spectra of the fourth toner measured before and after applying stress. In FIG. 6, a line L41 indicates a photoelectron spectrum before applying stress, and a line L42 indicates a photoelectron spectrum after applying stress.

  The fourth toner is a toner (powder of fourth toner particles) substantially composed of only the fourth toner particles. The shell layer of the fourth toner particles contains a resin not containing a repeating unit having an oxazoline group (specifically, an acrylic acid resin). The other configuration of the fourth toner particles is the same as that of the first toner particles 10 (see FIG. 1).

From the line L41 in FIG. 6, it can be seen that the first work function (excitation energy at the rising point) is 5.97 eV, and the second work function (excitation energy at the first inclination change point) is 6.01 eV. . In the fourth toner, the first work function corresponds to the work function W ₂ of the surface layer portion (first component) of the silica particles, and the second work function corresponds to the work function W of the surface layer portion (second component) of the shell layer. Equivalent to ₁ . Therefore, a value obtained by subtracting the work function W ₁ from the work function W ₂ (= W ₂ −W ₁ ) is −0.04 eV (= 5.97 eV−6.01 eV). In the photoelectron spectrum of the fourth toner shown in FIG. 6, the photoelectron retention rate Rc is 89%. In the fourth toner, neither the above-described formula (M1) nor formula (M2) is established. As indicated by lines L41 and L42 in FIG. 6, the photoelectron spectrum of the fourth toner is greatly different between the unused state and the used state.

  FIG. 7 shows the fifth toner particles 10b included in the fifth toner. The fifth toner is a toner (powder of the fifth toner particles 10b) substantially composed of only the fifth toner particles 10b. As shown in FIG. 7, the fifth toner particles 10b include toner base particles 11a containing a binder resin. The toner base particles 11a further contain a positively chargeable charge control agent 20 as an internal additive. Further, the toner base particles 11a do not include a shell layer. Each of the plurality of silica particles 13 is attached to the surface of the toner base particles 11a.

  FIG. 8 shows photoelectron spectra measured for the fifth toner before and after applying stress. In FIG. 8, a line L51 indicates a photoelectron spectrum before applying stress, and a line L52 indicates a photoelectron spectrum after applying stress.

  From the line L51 in FIG. 8, the first work function (excitation energy at the rising point) is 5.72 eV, the second work function (excitation energy at the first inclination change point) is 5.97 eV, It can be seen that the work function (excitation energy at the second slope change point) is 6.05 eV. In the fifth toner (see FIG. 7), the first work function corresponds to the work function of the charge control agent 20 (first component) present in the surface layer portion of the toner base particles 11a, and the second work function corresponds to the silica particles. It is considered that the work function of 13 surface layers (second component) corresponds to the work function of the binder resin (third component) present in the surface layer of the toner base particles 11a. In the photoelectron spectrum of the fifth toner shown in FIG. 8, the photoelectron retention rate Rc is 120%. In the fifth toner, neither the above-described formula (M1) nor formula (M2) is established. As indicated by lines L51 and L52 in FIG. 8, the photoelectron spectrum of the fifth toner is greatly different between the unused state and the used state.

  The first toner has the above-described basic configuration, and each of the second toner, the third toner, the fourth toner, and the fifth toner does not have the above-described basic configuration. The first toner is easier to form a high-quality image continuously in continuous printing than the other toners (second to fifth toners).

  In order to obtain a toner excellent in heat-resistant storage stability and positive chargeability, the shell layer preferably covers an area of 95% to 100% of the surface area of the toner core, and covers the entire surface of the toner core. It is particularly preferred. The covering ratio (area ratio) of the shell layer is obtained by, for example, analyzing an image of toner particles (previously dyed toner particles) photographed with a field emission scanning electron microscope (“JSM-7600F” manufactured by JEOL Ltd.). Can be measured. The covered area and the other area (non-covered area) on the surface of the toner core can be distinguished by, for example, a difference in luminance value. A covering rate of the shell layer of 100% means that the entire surface of the toner core is covered with the shell layer.

  By completely covering the toner core with a shell layer having strong positive chargeability (that is, covering the entire surface of the toner core), it is not necessary to use a charge control agent as an internal additive of the toner core. When the toner base particles having no shell layer contain a positively chargeable charge control agent (internal additive), a portion having a very strong positive chargeability in the toner base particles (hereinafter referred to as a charged patch). Will be present locally. The charged patch is also present on the surface layer portion of the toner base particles. If the external additive particles are attached to the charged patch existing on the surface layer of the toner base particles, the charged patches are exposed on the surface of the toner base particles when the external additive particles are detached from the toner base particles. As a result, the chargeability of the toner tends to vary greatly.

  In the toner having the basic configuration described above, the shell layer preferably contains a resin containing a repeating unit having an oxazoline group. By introducing an oxazoline group into the resin, it becomes easy to obtain a resin having an appropriate positive chargeability (specifically, a positive chargeability comparable to that of silica particles). Resins containing a repeating unit having an amino group (for example, melamine resin) tend not to have the same positive chargeability as silica particles (specifically, they have a stronger positive chargeability than silica particles).

  Examples of the resin containing a repeating unit having an oxazoline group include a polymer of a monomer (resin raw material) containing one or more vinyl compounds represented by the following formula (1) and one or more other vinyl compounds. preferable.

In Formula (1), R ¹ represents a hydrogen atom or an alkyl group (which may be linear, branched or cyclic) which may have a substituent. R ¹ is particularly preferably a hydrogen atom or a methyl group. For example, in 2-vinyl-2-oxazoline, R ¹ in formula (1) represents a hydrogen atom.

In the polymer of a vinyl compound, it is considered that the repeating unit derived from the vinyl compound is addition-polymerized (“C═C” → “—C—C—”) by a carbon double bond “C═C”. The vinyl compound is a compound having a vinyl group (CH ₂ ═CH—) or a group in which hydrogen in the vinyl group is substituted. Examples of the vinyl compound include ethylene, propylene, butadiene, vinyl chloride, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, or styrene in addition to the compound represented by the above formula (1). .

The vinyl compound represented by the above formula (1) forms a repeating unit represented by the following formula (1-1) by addition polymerization (hereinafter referred to as repeating unit (1-1)). R ¹ in formula (1-1) represents the same group as R ¹ in formula (1). The repeating unit (1-1) is a repeating unit derived from a vinyl compound having an oxazoline group (crosslinkable functional group). As a material for forming a resin containing a repeating unit having an oxazoline group, for example, an oxazoline group-containing polymer aqueous solution (“Epocross (registered trademark) WS series” manufactured by Nippon Shokubai Co., Ltd.) can be used. “Epocross WS-300” includes a copolymer of 2-vinyl-2-oxazoline and methyl methacrylate. “Epocross WS-700” includes a copolymer of 2-vinyl-2-oxazoline, methyl methacrylate, and butyl acrylate.

The repeating unit (1-1) has an unopened oxazoline group. The unopened oxazoline group has a cyclic structure and exhibits strong positive chargeability. Unopened oxazoline groups are likely to react with carboxyl groups, aromatic sulfanyl groups, and aromatic hydroxyl groups. For example, when the repeating unit (1-1) in the shell layer reacts with a carboxyl group of a polyester resin (represented as R ⁰ in the formula (1-2)) in the toner core, the following formula (1-2) is obtained. Thus, the oxazoline group is opened, and an amide ester bond is formed between the toner core and the shell layer. By forming such a bond, the bond between the toner core and the shell layer becomes strong, and the detachment of the shell layer from the toner base particles is suppressed.

  As the resin containing a repeating unit having an oxazoline group, contained in the shell layer, a monomer (resin containing one or more vinyl compounds represented by the formula (1) and one or more acrylic acid monomers The polymer of (raw material) is particularly preferred.

  In the toner having the basic structure described above, in order to enhance the bond between the toner core and the shell layer, the toner core preferably contains a polyester resin and does not contain an oxazoline group. The toner core is preferably a pulverized core (so-called pulverized toner). In general, the toner core is roughly classified into a pulverized core and a polymerized core (also called a chemical toner). The toner core obtained by the pulverization method belongs to the pulverization core, and the toner core obtained by the aggregation method belongs to the polymerization core. The pulverization method is a method of obtaining a powder (for example, a toner core) through a step of obtaining a kneaded product by melting and kneading a plurality of types of materials (resins and the like) and a step of pulverizing the obtained kneaded product. In the toner having the basic structure described above, the toner core is preferably a pulverized core containing a polyester resin. The pulverized core contains one or more polyester resins melt-kneaded.

  In order to obtain a toner having excellent heat-resistant storage stability, low-temperature fixability, and positive chargeability, the thickness of the shell layer is preferably 20 nm or more and 100 nm or less. If the thickness of the shell layer is too thin, the chargeability of the toner core can affect the chargeability of the surface layer portion of the shell layer. The thickness of the shell layer can be measured by analyzing a TEM (transmission electron microscope) image of the cross section of the toner particles using commercially available image analysis software (for example, “WinROOF” manufactured by Mitani Corporation). If the thickness of the shell layer is not uniform in one toner particle, four equally spaced locations (specifically, two straight lines that are perpendicular to each other at the approximate center of the cross section of the toner particle are drawn. The thickness of the shell layer is measured at each of the four points where the straight line intersects the shell layer, and the arithmetic average of the four measured values obtained is taken as the evaluation value of the toner particles (shell layer thickness). The boundary between the toner core and the shell layer can be confirmed, for example, by selectively dyeing only the shell layer of the toner core and the shell layer. When the boundary between the toner core and the shell layer is unclear in the TEM photographed image, a characteristic element contained in the shell layer in the TEM photographed image is formed by combining TEM and electron energy loss spectroscopy (EELS). By performing the mapping, the boundary between the toner core and the shell layer can be clarified.

  Furthermore, silica particles (external additive) having a number average primary particle diameter of 10 nm to 30 nm are added to a shell layer having a thickness of 20 nm to 100 nm in the surface layer of the toner base particles with respect to 100 parts by mass of the toner base particles. It is particularly preferable that the adhesive is attached in an amount corresponding to 0.5 to 3.0 parts by mass. The toner having such a configuration tends to have appropriate fluidity and positive chargeability. In addition, in order to suppress fluctuations in the chargeability of the toner in continuous printing, it is preferable that the toner particles have substantially only an external additive only for silica particles (powder).

In order to obtain a toner suitable for image formation, the volume median diameter (D ₅₀ ) of the toner core is preferably 4 μm or more and 9 μm or less.

  Next, the toner core (binder resin and internal additive), shell layer, and external additive will be described in order. Depending on the use of the toner, unnecessary components may be omitted.

[Toner core]
(Binder resin)
In the toner core, the binder resin generally occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the properties of the entire toner core. By using a combination of a plurality of types of resins as the binder resin, the properties of the binder resin (more specifically, the hydroxyl value, acid value, Tg, Tm, etc.) can be adjusted. When the binder resin has an ester group, a hydroxyl group, an ether group, an acid group, or a methyl group, the toner core tends to be anionic, and when the binder resin has an amino group, the toner core The tendency to become cationic becomes stronger.

  As the binder resin, a polyester resin is particularly preferable. The toner core may contain a crystalline polyester resin. By containing a crystalline polyester resin in the toner core, sharp melt properties can be imparted to the toner core.

  The polyester resin is composed of one or more polyhydric alcohols (more specifically, aliphatic diol, bisphenol, trihydric or higher alcohol as shown below) and one or more polyhydric carboxylic acids (more specifically). Specifically, it can be obtained by polycondensation with a divalent carboxylic acid or a trivalent or higher carboxylic acid as shown below. The polyester resin is a repeating unit derived from another monomer (a monomer that is neither a polyhydric alcohol nor a polyvalent carboxylic acid: more specifically, a styrene monomer or an acrylic acid monomer as shown below). May be included.

  Suitable examples of the aliphatic diol include diethylene glycol, triethylene glycol, neopentyl glycol, 1,2-propanediol, α, ω-alkanediol (more specifically, ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,12-dodecanediol, etc. ), 2-butene-1,4-diol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol.

  Preferable examples of bisphenol include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, or bisphenol A propylene oxide adduct.

  Preferable examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butane. Triol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5- Trihydroxymethylbenzene is mentioned.

  Preferable examples of the divalent carboxylic acid include aromatic dicarboxylic acid (more specifically, phthalic acid, terephthalic acid, or isophthalic acid), α, ω-alkanedicarboxylic acid (more specifically, malonic acid). , Succinic acid, adipic acid, suberic acid, azelaic acid, sebacic acid, or 1,10-decanedicarboxylic acid), α, ω-alkanedicarboxylic acid with a side chain added (more specifically, Alkyl succinic acid or alkenyl succinic acid), unsaturated dicarboxylic acid (more specifically, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, etc.), or cycloalkane dicarboxylic acid (more specifically, Are cyclohexanedicarboxylic acid and the like.

  Preferred examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) Examples include methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

  In order to achieve both heat-resistant storage stability and low-temperature fixability of the toner, the toner core preferably contains a plurality of types of polyester resins having different softening points (Tm), and a polyester resin having a softening point of 90 ° C. or lower; It is particularly preferable to contain a polyester resin having a softening point of 100 ° C. or higher and 120 ° C. or lower and a polyester resin having a softening point of 125 ° C. or higher.

  Suitable examples of polyester resins having a softening point of 90 ° C. or lower include bisphenol (for example, bisphenol A ethylene oxide adduct and / or bisphenol A propylene oxide adduct) as the alcohol component, and aromatic dicarboxylic acid as the acid component. Examples thereof include polyester resins containing (for example, terephthalic acid) and unsaturated dicarboxylic acids (for example, fumaric acid).

  As a suitable example of the polyester resin having a softening point of 100 ° C. or more and 120 ° C. or less, the alcohol component contains bisphenol (for example, bisphenol A ethylene oxide adduct and / or bisphenol A propylene oxide adduct), and the acid component contains a fragrance. And polyester resins containing an aliphatic dicarboxylic acid (for example, terephthalic acid) and no unsaturated dicarboxylic acid.

  Preferable examples of the polyester resin having a softening point of 125 ° C. or higher include bisphenol (for example, bisphenol A ethylene oxide adduct and / or bisphenol A propylene oxide adduct) as the alcohol component, and 10 or more carbon atoms as the acid component. Includes dicarboxylic acids having 20 or fewer alkyl groups (eg, dodecyl succinic acid having 12 alkyl groups), unsaturated dicarboxylic acids (eg, fumaric acid), and trivalent carboxylic acids (eg, trimellitic acid) A polyester resin is mentioned.

  If the shell layer covers the entire surface of the toner core, it becomes easy to ensure sufficient heat-resistant storage stability of the toner. For this reason, in the toner having such a configuration, the degree of freedom in selecting the binder resin is increased.

(Coloring agent)
The toner core may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. In order to obtain a toner suitable for image formation, the amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

  The toner core may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner core may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Vat yellow can be preferably used.

  The magenta colorant is, for example, selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. One or more compounds can be used. Examples of the magenta colorant include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254) can be preferably used.

  As the cyan colorant, for example, one or more compounds selected from the group consisting of a copper phthalocyanine compound, an anthraquinone compound, and a basic dye lake compound can be used. Examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue can be preferably used.

(Release agent)
The toner core may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or aliphatic hydrocarbon wax such as Fischer-Tropsch wax; oxidized polyethylene wax or a block thereof Oxides of aliphatic hydrocarbon waxes such as copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; animal properties such as beeswax, lanolin, or whale wax Waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanate ester wax or castor wax; fats such as deoxidized carnauba wax The wax portion of the ester or the whole was deoxygenated can be suitably used. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

(Charge control agent)
The toner core may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charge stability or charge rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  By adding a negatively chargeable charge control agent (more specifically, an organometallic complex or a chelate compound) to the toner core, the anionicity of the toner core can be enhanced. Further, by adding a positively chargeable charge control agent (more specifically, pyridine, nigrosine, quaternary ammonium salt, or the like) to the toner core, the toner core can be made more cationic. However, if sufficient chargeability is ensured in the toner, it is not necessary to include a charge control agent in the toner core.

(Magnetic powder)
The toner core may contain magnetic powder. Examples of magnetic powder materials include ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, Ferrite, magnetite, chromium dioxide, or the like) or a material subjected to ferromagnetization treatment (more specifically, a carbon material or the like imparted with ferromagnetism by heat treatment) can be suitably used. One type of magnetic powder may be used alone, or a plurality of types of magnetic powder may be used in combination.

[Shell layer]
In order to ensure sufficient positive chargeability of the toner, the shell layer preferably contains a resin containing a repeating unit having an oxazoline group. As a resin containing a repeating unit having an oxazoline group, a polymer of a monomer (resin raw material) containing at least one vinyl compound represented by the above formula (1) and at least one other vinyl compound is used. Is preferred. The other vinyl compound is selected from the group consisting of an alkyl acrylate that may have a substituent on the alkyl group, an alkyl methacrylate that may have a substituent on the alkyl group, and a styrene monomer. One or more vinyl compounds are preferred. Preferable examples of the styrenic monomer include styrene, alkyl styrene (more specifically, α-methyl styrene, p-ethyl styrene, 4-tert-butyl styrene, etc.), or halogenated styrene (more specifically, Are α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and the like.

  Other vinyl compounds are preferably alkyl acrylates which may have a substituent on the alkyl group. In order to improve the film quality of the shell layer, the resin constituting the shell layer (specifically, a resin containing a repeating unit having an oxazoline group) preferably contains a repeating unit represented by the following formula (2).

In formula (2), R ² represents an alkyl group (which may be linear, branched or cyclic) which may have a substituent. R ² is preferably an alkyl group having 1 to 8 carbon atoms, particularly preferably a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, or an iso-butyl group.

  As other vinyl compounds, methacrylic acid alkyl esters which may have a substituent in the alkyl group are preferred. In order to improve the film quality of the shell layer, the resin constituting the shell layer (specifically, a resin containing a repeating unit having an oxazoline group) preferably contains a repeating unit represented by the following formula (3).

In formula (3), R ³ represents an alkyl group (which may be linear, branched or cyclic) which may have a substituent. R ³ is preferably an alkyl group having 1 to 8 carbon atoms, particularly preferably a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, or an iso-butyl group.

[External additive]
In the toner having the above-described basic configuration, an external additive (specifically, a powder containing a plurality of external additive particles) adheres to the surface of the toner base particles. Unlike the internal additive, the external additive does not exist inside the toner base particles, but selectively exists only on the surface of the toner base particles (surface layer portion of the toner particles). For example, by stirring together the toner base particles (powder) and the external additive (powder), the external additive particles can be attached to the surface of the toner base particles. The toner base particles and the external additive particles do not chemically react with each other and are physically bonded instead of chemically. The strength of the bond between the toner base particles and the external additive particles depends on the stirring conditions (more specifically, the stirring time, the rotation speed of the stirring, etc.), the particle diameter of the external additive particles, and the shape of the external additive particles. And the surface condition of the external additive particles.

  In the toner having the basic configuration described above, the external additive contains silica particles. In addition to the silica particles, other external additive particles (external additive particles other than silica particles) may be adhered to the surface of the toner base particles. Preferable examples of the other external additive particles include particles of metal oxide (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, etc.). Further, particles of organic acid compounds such as fatty acid metal salts (more specifically, zinc stearate) or resin particles may be used as external additive particles. Moreover, you may use the composite particle which is a composite of a multiple types of material as external additive particle | grains.

  The external additive particles may be surface-treated. For example, when silica particles are used as the external additive particles, hydrophobicity and / or positive chargeability may be imparted to the surface of the silica particles by the surface treatment agent. Examples of the surface treatment agent include a coupling agent (more specifically, a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent), a silazane compound (for example, a chain silazane compound or a cyclic silazane compound). ) Or silicone oil (more specifically, dimethyl silicone oil or the like) can be preferably used. As the surface treatment agent, a silane coupling agent or a silazane compound is particularly preferable. Preferable examples of the silane coupling agent include silane compounds (more specifically, methyltrimethoxysilane or aminosilane). A preferred example of the silazane compound is HMDS (hexamethyldisilazane).

When the surface of the silica substrate (untreated silica particles) is treated with the surface treatment agent, a large number of hydroxyl groups (—OH) present on the surface of the silica substrate are partially or entirely derived from the surface treatment agent. Substituted with a functional group. As a result, silica particles having a functional group derived from the surface treating agent (specifically, a functional group that is more hydrophobic and / or positively charged than the hydroxyl group) on the surface can be obtained. For example, when the surface of a silica substrate is treated with a silane coupling agent having an amino group, a hydroxyl group of the silane coupling agent (for example, a hydroxyl group generated by hydrolysis of an alkoxy group of the silane coupling agent with moisture) A dehydration condensation reaction (“A (silica substrate) —OH” + “B (coupling agent) —OH” → “A—O—B” + H ₂ O) occurs with a hydroxyl group present on the surface of the silica substrate. By such a reaction, a silane coupling agent having an amino group and silica are chemically bonded to each other, so that an amino group is imparted to the surface of the silica particles, and positively charged silica particles are obtained. More specifically, the hydroxyl group present on the surface of the silica substrate is substituted with a functional group having an amino group at the end (more specifically, —O—Si— (CH ₂ ) ₃ —NH ₂ or the like). Silica particles provided with amino groups tend to have a positive chargeability stronger than that of a silica substrate. When a silane coupling agent having an alkyl group is used, hydrophobic silica particles are obtained. More specifically, the hydroxyl group present on the surface of the silica substrate may be replaced with a functional group having an alkyl group at the end (more specifically, —O—Si—CH ₃ or the like) by the dehydration condensation reaction. it can. Thus, silica particles to which a hydrophobic group (for example, an alkyl group having 1 to 3 carbon atoms) is added instead of a hydrophilic group (hydroxyl group) tend to have a stronger hydrophobicity than a silica substrate.

[Toner Production Method]
Hereinafter, an example of a method for producing a toner having the above-described basic configuration will be described. First, a toner core is prepared. Subsequently, a toner core and a shell material (for example, an oxazoline group-containing polymer aqueous solution) are added to the liquid. Subsequently, the shell material is reacted in the liquid to form a shell layer substantially composed of a resin on the surface of the toner core. In order to adjust the unopened oxazoline group content of the toner to a desired value, a basic substance (more specifically, ammonia, sodium hydroxide or the like) and / or a ring-opening agent (more specifically, The shell layer is preferably formed on the surface of the toner core in a liquid containing acetic acid or the like. By changing the amount of each of the basic substance and the ring-opening agent, the amount of unopened oxazoline groups contained in the toner can be adjusted. As the amount of the basic substance in the liquid increases, the amount of unopened oxazoline groups tends to increase. It is considered that the basic substance neutralizes (traps) the carboxylic acid, thereby suppressing the ring-opening reaction (nucleophilic addition reaction to the carbonyl group) of the oxazoline group. On the other hand, since the ring-opening agent promotes the ring-opening reaction of the oxazoline group, the amount of the unopened oxazoline group tends to decrease as the amount of the ring-opening agent in the liquid increases.

  In order to form a homogeneous shell layer, it is preferable to dissolve or disperse the shell material in the liquid by, for example, stirring the liquid containing the shell material. In order to suppress dissolution or elution of the toner core components (particularly, the binder resin and the release agent) when forming the shell layer, it is preferable to form the shell layer in an aqueous medium. The aqueous medium is a medium containing water as a main component (more specifically, pure water or a mixed liquid of water and a polar medium). The aqueous medium may function as a solvent. A solute may be dissolved in the aqueous medium. The aqueous medium may function as a dispersion medium. The dispersoid may be dispersed in the aqueous medium. As a polar medium in the aqueous medium, for example, alcohol (more specifically, methanol or ethanol) can be used. The boiling point of the aqueous medium is about 100 ° C.

  Hereinafter, the toner manufacturing method will be further described based on a more specific example.

(Preparation of toner core)
In order to easily obtain a good quality toner core, the toner core is preferably produced by an agglomeration method or a pulverization method, and more preferably produced by a pulverization method.

  Hereinafter, an example of the pulverization method will be described. First, a binder resin and an internal additive (for example, at least one of a colorant, a release agent, a charge control agent, and magnetic powder) are mixed. Subsequently, the obtained mixture is melt-kneaded. Subsequently, the obtained melt-kneaded product is pulverized, and the obtained pulverized product is classified. As a result, a toner core having a desired particle size can be obtained.

  Hereinafter, an example of the aggregation method will be described. First, the fine particles of the binder resin, the release agent, and the colorant are aggregated in an aqueous medium to obtain aggregated particles containing the binder resin, the release agent, and the colorant. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. As a result, a toner core dispersion is obtained. Thereafter, an unnecessary substance (such as a surfactant) is removed from the dispersion liquid of the toner core to obtain the toner core.

(Formation of shell layer)
Subsequently, a toner core and a shell material (for example, an oxazoline group-containing polymer aqueous solution) are added to an aqueous medium (for example, ion-exchanged water).

  Shell material (for example, an oxazoline group-containing polymer dissolved in an aqueous medium) adheres to the surface of the toner core in the liquid. In order to uniformly adhere the shell material to the surface of the toner core, it is preferable to highly disperse the toner core in a liquid containing the shell material. In order to highly disperse the toner core in the liquid, a surfactant may be included in the liquid, or the liquid is stirred using a powerful stirring device (for example, “Hibis Disper Mix” manufactured by Primics Co., Ltd.). May be.

  Subsequently, a basic substance (for example, an aqueous ammonia solution) is further added to the aqueous medium. By controlling the amount of basic substance added, the amount of unopened oxazoline groups contained in the toner can be adjusted.

  Subsequently, while stirring the liquid containing the shell material and the like, the temperature of the liquid is set at a predetermined holding temperature (for example, 50 ° C. at a speed selected from 0.1 ° C./min to 3 ° C./min). To a temperature selected from 70 ° C. to 70 ° C.). After completion of the temperature increase, the temperature of the liquid is maintained at the above holding temperature for a predetermined time (for example, a time selected from 30 minutes to 60 minutes) while stirring the liquid. It is considered that the reaction (immobilization of the shell layer) proceeds between the toner core and the shell material while the temperature of the liquid is kept high (or during the temperature rise). For example, the oxazoline group of the shell material is considered to open by reacting with a functional group present on the surface of the binder resin constituting the toner core and to form a crosslinked structure in the shell layer. The shell material is chemically bonded to the toner core to form a shell layer. By forming a shell layer on the surface of the toner core in the liquid, a dispersion of toner base particles can be obtained.

  After the shell layer is formed, the dispersion of the toner base particles is neutralized using a basic substance (for example, an aqueous ammonia solution). Subsequently, the toner mother particle dispersion is cooled to, for example, room temperature (about 25 ° C.). Subsequently, the dispersion of the toner base particles is filtered using, for example, a Buchner funnel. Thereby, the toner base particles are separated from the liquid (solid-liquid separation), and wet cake-like toner base particles are obtained. Subsequently, the toner base particles are washed. Subsequently, the washed toner base particles are dried.

(External addition process)
Using a mixer (for example, an FM mixer manufactured by Nippon Coke Kogyo Co., Ltd.), the toner base particles and the external additive (for example, silica particle powder) are not embedded in the toner base particles. By mixing under the condition, the external additive is adhered to the surface of the toner base particles. When a spray dryer is used in the drying step, the drying step and the external addition step can be performed simultaneously by spraying a dispersion of an external additive (for example, silica particle powder) onto the toner base particles. it can.

  Through the above process, a toner containing a large number of toner particles is produced. The contents and order of the toner manufacturing method can be arbitrarily changed according to the required configuration or characteristics of the toner. For example, the shell material may be added to the liquid at a time, or may be added to the liquid in a plurality of times. Further, the toner may be sieved after the external addition step. Further, unnecessary steps may be omitted. For example, when a commercially available product can be used as a material as it is, the step of preparing the material can be omitted by using a commercially available product. As a material for synthesizing the resin, a prepolymer may be used instead of the monomer, if necessary. In order to obtain a predetermined compound, a salt, ester, hydrate, or anhydride of the compound may be used as a raw material. In order to produce the toner efficiently, it is preferable to form a large number of toner particles simultaneously. The toner particles produced at the same time are considered to have substantially the same configuration.

  Examples of the present invention will be described. Table 1 shows toners TA-1 to TA-3 and TB-1 to TB-6 (each positively chargeable toner for developing an electrostatic latent image) according to Examples or Comparative Examples.

In Table 1, “S-1” to “S-3” mean the shell materials shown below.
Shell material S-1 is an oxazoline group-containing polymer aqueous solution (“Epocross WS-300” manufactured by Nippon Shokubai Co., Ltd., solid content concentration: 10 mass%).
Each of the shell materials S-2 and S-3 is a suspension of resin particles prepared by a method described later.

In Table 1, “EX-1” and “EX-2” mean the following external additives.
The external additive EX-1 is positively-charged silica particles (“AEROSIL (registered trademark) REA90” manufactured by Nippon Aerosil Co., Ltd.), content: dry-type silica particles imparted with positive charge by surface treatment, number average primary particle diameter : 20 nm).
The external additive EX-2 is hydrophobic silica particles (“AEROSIL (registered trademark) R972” manufactured by Nippon Aerosil Co., Ltd., hydrophobizing agent: dimethyldichlorosilane (DDS), number average primary particle size: about 16 nm). .

  Hereinafter, the production methods, evaluation methods, and evaluation results of the toners TA-1 to TA-3 and TB-1 to TB-6 will be described in order. In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

[Preparation of materials]
(Synthesis of polyester resin PES-1)
In a 10 L four-necked flask equipped with a thermometer (thermocouple), dehydration tube, nitrogen introduction tube, and stirrer, 370 g of bisphenol A propylene oxide adduct, 3059 g of bisphenol A ethylene oxide adduct, terephthalic acid 1194 g, 286 g of fumaric acid, 10 g of tin (II) 2-ethylhexanoate, and 2 g of gallic acid were added. Subsequently, the contents of the flask were reacted in a nitrogen atmosphere and at a temperature of 230 ° C. until the reaction rate reached 90% by mass or more. The reaction rate was calculated according to the formula “reaction rate = 100 × actual amount of reaction product water / theoretical product water amount”. Subsequently, the flask contents were reacted under a reduced pressure atmosphere (pressure 8.3 kPa) and a temperature of 230 ° C. until the Tm of the reaction product (resin) reached a predetermined temperature (89 ° C.). As a result, a polyester resin PES-1 having a Tm of 89 ° C. and a Tg of 50 ° C. was obtained.

(Synthesis of polyester resin PES-2)
The synthetic method of the polyester resin PES-2 is bisphenol A propylene oxide adduct 370 g, bisphenol A ethylene oxide adduct 3059 g, terephthalic acid 1194 g, and fumaric acid 286 g, bisphenol A propylene oxide adduct 1286 g, bisphenol A ethylene oxide Except for using 2218 g of adduct and 1603 g of terephthalic acid, it was the same as the synthesis method of polyester resin PES-1. Regarding obtained polyester resin PES-2, Tm was 111 degreeC and Tg was 69 degreeC.

(Synthesis of polyester resin PES-3)
In a 10 L four-necked flask equipped with a thermometer (thermocouple), dehydration tube, nitrogen introduction tube, and stirring device, 4907 g of bisphenol A propylene oxide adduct, 1942 g of bisphenol A ethylene oxide adduct, and fumaric acid 757 g, 2078 g of dodecyl succinic anhydride, 30 g of tin (II) 2-ethylhexanoate, and 2 g of gallic acid were added. Subsequently, the contents of the flask were reacted in a nitrogen atmosphere and at a temperature of 230 ° C. until the reaction rate represented by the above formula reached 90% by mass or more. Subsequently, the contents of the flask were reacted for 1 hour in a reduced pressure atmosphere (pressure 8.3 kPa) and a temperature of 230 ° C. Subsequently, 548 g of trimellitic anhydride is added to the flask, and Tm of the reaction product (resin) reaches a predetermined temperature (127 ° C.) under a reduced pressure atmosphere (pressure 8.3 kPa) and a temperature of 220 ° C. The flask contents were reacted. As a result, a polyester resin PES-3 having a Tm of 127 ° C. and a Tg of 51 ° C. was obtained.

(Preparation of shell material S-2)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was set in a water bath at a temperature of 30 ° C., and 875 mL of ion-exchanged water and an anionic surfactant (“Latemul® WX” manufactured by Kao Corporation) ”, Component: sodium polyoxyethylene alkyl ether sulfate, solid content concentration: 26% by mass), 75 mL. Thereafter, the temperature in the flask was raised to 80 ° C. using a water bath. Subsequently, two kinds of liquids (first liquid and second liquid) were dropped into the contents of the flask at 80 ° C. over 5 hours. The first liquid was a mixed liquid of 12 mL of styrene, 4 mL of 2-hydroxyethyl methacrylate (HEMA), 4 mL of n-butyl acrylate, and 0.5 mL of divinylbenzene. The second liquid was a solution in which 0.5 g of potassium persulfate was dissolved in 30 mL of ion exchange water. Subsequently, the temperature in the flask was kept at 80 ° C. for another 2 hours to polymerize the flask contents. As a result, shell material S-2 (specifically, suspension of hydrophobic resin particles) was obtained. The number average primary particle diameter of the resin particles contained in the obtained shell material S-2 was 39 nm.

(Preparation of shell material S-3)
In a 1 L three-necked flask equipped with a thermometer, a cooling pipe, a nitrogen introduction pipe, and a stirring blade, 90 g of isobutanol, 90 g of methyl methacrylate, 45 g of n-butyl acrylate, and 2- (methacryloyloxy) ) 30 g of ethyltrimethylammonium chloride (Alfa Aesar) and 2,2′-azobis (2-methyl-N- (2-hydroxyethyl) propionamide) (“VA-086” manufactured by Wako Pure Chemical Industries, Ltd.) 6 g was added. Subsequently, the contents of the flask were reacted for 3 hours under conditions of a nitrogen atmosphere and a temperature of 80 ° C. Thereafter, 3 g of 2,2′-azobis (2-methyl-N- (2-hydroxyethyl) propionamide) (“VA-086” manufactured by Wako Pure Chemical Industries, Ltd.) was added to the flask, and the nitrogen atmosphere and temperature were increased. The flask contents were further reacted for 3 hours under the condition of 80 ° C. to obtain a polymer solution. Subsequently, the obtained polymer solution was dried under a reduced pressure atmosphere and a temperature of 150 ° C. Subsequently, the dried polymer was crushed to obtain a positively chargeable resin.

  Subsequently, 200 g of the positively chargeable resin obtained as described above and ethyl acetate (Wako Pure Chemical Industries, Ltd.) were placed in a container of a mixing apparatus (“Hibismix (registered trademark) 2P-1 type” manufactured by PRIMIX Corporation). 184 mL of “Ethyl acetate special grade” manufactured by the company was added. Subsequently, using the mixing apparatus, the contents of the container were stirred for 1 hour at a rotation speed of 20 rpm to obtain a highly viscous solution. Thereafter, an aqueous solution such as ethyl acetate (specifically, 18 mL of 1N hydrochloric acid and a cationic surfactant (“Texonol (registered trademark) R5” manufactured by Nippon Emulsifier Co., Ltd., component: alkylbenzylammonium salt) was added to the resulting high-viscosity solution. ) 20 g and 20 mL of ethyl acetate (“ethyl acetate special grade” manufactured by Wako Pure Chemical Industries, Ltd.) 20 mL in ion-exchanged water 562 g) were added. As a result, shell material S-3 (specifically, a suspension of positively chargeable resin particles) was obtained. The number average particle diameter of the resin particles contained in the obtained shell material S-3 was 40 nm.

(Preparation of toner core C-1)
Using an FM mixer (Nippon Coke Kogyo Co., Ltd.), 300 g of the first polyester resin (polyester resin PES-1 synthesized by the procedure described above) and the second polyester resin (polyester resin PES-2 synthesized by the procedure described above) ) 100 g, 600 g of the third polyester resin (polyester resin PES-3 synthesized by the above procedure), 12 g of the first release agent (Carnauba wax: “Carnauba Wax No. 1” manufactured by Kato Yoko Co., Ltd.), 48g of two mold release agents (ester wax: "Nissan Electol (registered trademark) WEP-3" manufactured by NOF Corporation) and a colorant (phthalocyanine blue: "Colortex (registered trademark) blue B1021" manufactured by Sanyo Dye 144 g were mixed at a rotational speed of 2400 rpm.

Subsequently, the obtained mixture was subjected to conditions using a twin-screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.) at a material supply speed of 5 kg / hour, a shaft rotation speed of 160 rpm, and a set temperature (cylinder temperature) of 100 ° C. Was melt kneaded. Thereafter, the obtained kneaded material was cooled. Subsequently, the cooled kneaded material was coarsely pulverized using a pulverizer (“Rotoplex 16/8” manufactured by Toa Machinery Co., Ltd.). Subsequently, the obtained coarsely pulverized product was finely pulverized using a jet mill (“Ultrasonic Jet Mill Type I” manufactured by Nippon Pneumatic Industry Co., Ltd.). Subsequently, the obtained finely pulverized product was classified using a classifier (classifier using the Coanda effect: “Elbow Jet EJ-LABO type” manufactured by Nittetsu Mining Co., Ltd.). As a result, a toner core C-1 (powder) having a volume median diameter (D ₅₀ ) of 6.8 μm was obtained.

(Preparation of toner core C-2)
The toner core C-2 was prepared by using 1000 g of polyester resin PES-2 instead of the total amount of 1000 g of the first to third polyester resins (polyester resins PES-1 to PES-3) as an internal additive. The toner core C-1 was prepared in the same manner as the toner core C-1 except that 70 g of a charge control agent (“MA100” manufactured by Mitsubishi Chemical Corporation) was used in addition to the first and second mold release agents and the colorant. . The toner core C-2 (powder) obtained had a volume median diameter (D ₅₀ ) of 6.8 μm. The toner core C-2 is a toner core used in the toner TB-5 (see Table 1). In the toner TB-5, since the toner particles do not have a shell layer, it is difficult to ensure sufficient chargeability of the toner. Therefore, in the production of the toner core C-2, a charge control agent is added as a core component (internal additive).

[Toner Production Method]
In each of the toners TA-1 to TA-3, TB-1 to TB-4, and TB-6, a shell layer was formed on the toner core C-1. In the production of each of the toners TA-1 to TA-3 and TB-1 to TB-3, a shell layer was formed by the shell layer forming step A described below. In the production of the toner TB-4, a shell layer was formed by the following shell layer forming step B. In the production of the toner TB-6, a shell layer was formed by the following shell layer forming step C. In the production of the toner TB-5, the above-described toner core C-2 was used as toner base particles as it was without performing the following shell layer forming step, washing step, and drying step.

(Shell layer forming step A)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was set in a water bath, and 100 mL of ion-exchanged water was placed in the flask. Thereafter, the temperature in the flask was kept at 30 ° C. using a water bath. Subsequently, after a predetermined amount of shell material S-1 was added into the flask, the contents of the flask were sufficiently stirred. The amount of shell material was such that the shell layer coverage would be the values shown in Table 1. For example, in the production of toners TA-1 to TA-3 and TB-1 to TB-2, 90 g of shell material S-1 (containing oxazoline group) is formed so that a shell layer covering the entire surface of the toner core is formed. Polymer aqueous solution: Epocross WS-300) was added. In addition, in the production of the toner TB-3, 45 g of the shell material S-1 (high oxazoline group-containing high content) is formed so that a shell layer partially covering the surface of the toner core (specifically, at a coverage of about 60%) is formed. Molecular aqueous solution: Epocross WS-300) was added.

  Subsequently, 300 g of a toner core (toner core C-1 produced by the above-described procedure) was added to the flask, and the flask contents were stirred for 1 hour at a rotation speed of 200 rpm. Thereafter, 300 mL of ion exchange water was added to the flask.

  Subsequently, 6 mL of a 1% strength by weight aqueous ammonia solution was added into the flask. Subsequently, while stirring the contents of the flask at a rotational speed of 150 rpm, the temperature in the flask was raised to 60 ° C. at a rate of 0.5 ° C./min. Subsequently, while stirring the contents of the flask at a rotational speed of 100 rpm, the temperature (60 ° C.) was maintained for a predetermined time (specifically, the time shown in “Layer formation time” in Table 1). For example, in the production of toner TA-1, the holding time at a temperature of 60 ° C. was 60 minutes. Further, in the production of the toner TA-2, the holding time at a temperature of 60 ° C. was 30 minutes.

  Subsequently, a 1% by mass aqueous ammonia solution was added to the flask to adjust the pH of the flask contents to 7. Subsequently, the flask contents were cooled until the temperature reached room temperature (about 25 ° C.) to obtain a dispersion liquid containing toner mother particles.

(Shell layer forming step B)
A 1 L three-necked flask equipped with a thermometer and a stirring blade was set in a water bath, and 100 mL of ion-exchanged water was placed in the flask. Thereafter, the temperature in the flask was kept at 30 ° C. using a water bath. Subsequently, dilute hydrochloric acid was added to the flask to adjust the pH of the flask contents to 4.

  Subsequently, 20 mL of shell material S-2 (hydrophobic resin particle suspension) was added to the flask. Subsequently, 300 g of a toner core (toner core C-1 prepared by the above procedure) and 1 g of an anionic surfactant (“Emar (registered trademark) 0” manufactured by Kao Corporation, component: sodium lauryl sulfate) were added to the flask. . Subsequently, the flask contents were stirred for 1 hour at a rotation speed of 200 rpm. Thereafter, 300 mL of ion exchange water was added to the flask.

  Subsequently, sodium hydroxide was added to the flask to adjust the pH of the flask contents to 7.5. Subsequently, while stirring the contents of the flask at a rotational speed of 100 rpm, the temperature in the flask was raised to 60 ° C. at a rate of 1.0 ° C./min. Subsequently, the flask contents were kept at that temperature (60 ° C.) for 60 minutes while stirring the flask contents at a rotation speed of 100 rpm. Subsequently, the flask contents were cooled until the temperature reached room temperature (about 25 ° C.) to obtain a dispersion liquid containing toner mother particles.

(Shell layer forming step C)
Shell layer forming step C uses 20 mL of shell material S-2 (hydrophobic resin particle suspension) and 2 mL of shell material S-3 (positively charged resin particle suspension) instead of 20 mL of shell material S-2. Except for the above, it was the same as the shell layer forming step B.

(Washing process)
The dispersion of toner base particles obtained as described above was filtered (solid-liquid separation) using a Buchner funnel to obtain wet cake-like toner base particles. Thereafter, the obtained wet cake-like toner base particles were redispersed in ion-exchanged water. Further, dispersion and filtration were repeated 5 times to wash the toner base particles.

(Drying process)
Subsequently, the toner base particles were dried using a continuous surface modification device (“Coat Mizer (registered trademark)” manufactured by Freund Sangyo Co., Ltd.) under conditions of a hot air temperature of 45 ° C. and a blower air volume of 2 m ³ / min. . As a result, toner mother particle powder was obtained.

(External addition process)
Subsequently, the obtained toner base particles were externally added. Specifically, 100 parts by mass of toner base particles and 1 part by mass of an external additive (external additive EX-1 or EX-2 determined for each toner) shown in Table 1 are mixed with an FM mixer (Nippon Coke) having a capacity of 10 L. The external additive (silica particles) was adhered to the surface of the toner base particles by mixing for 5 minutes using Kogyo Co., Ltd. For example, in the production of toners TA-1 to TA-2, TB-1 to TB-4, and TB-6, an external additive (positively charged silica particles: AEROSIL REA90) is attached to the surface of the toner base particles. I let you. In the production of the toner TA-3, an external additive (hydrophobic silica particles: AEROSIL R972) was adhered to the surface of the toner base particles.

  Subsequently, the obtained powder was sieved using a sieve of 200 mesh (aperture 75 μm). As a result, toners containing many toner particles (toners TA-1 to TA-3 and TB-1 to TB-6 shown in Table 1) were obtained.

Regarding the toners TA-1 to TA-3 and TB-1 to TB-6 obtained as described above, the work function W ₁ of the surface layer portion of the shell layer and the work function W ₂ of the surface layer portion of the external additive Table 2 shows the measurement results of the toner and the photoelectron retention rate Rc (the photoelectron emission number measured under the condition of an excitation energy of 7 eV before and after applying the stress).

For example, for the toner TA-1, the work function W ₁ of the surface layer portion of the shell layer is 5.95 eV, the work function W ₂ of the surface layer portion of the external additive (silica particles) is 5.97 eV, The photoelectron retention rate Rc was 96%. The work functions W ₁ and W ₂ and the photoelectron retention rate Rc were obtained from photoelectron spectra (vertical axis: photoelectron count number, horizontal axis: excitation energy), respectively. Photoelectron spectra were measured for each of the toner before being stressed (unused toner) and the toner after being stressed (post-use toner). A method for applying stress to the toner and a method for measuring the photoelectron spectrum will be described below.

<Method of applying stress>
100 parts by mass of zirconia beads having a number average primary particle diameter of 1 mm (“YTZ (registered trademark) ball” manufactured by Nikkato Co., Ltd.) and toner (measuring objects: toners TA-1 to TA-3 and TB-1 to TB-6) 1) 20 parts by mass were placed in a 500 mL container (polyethylene wide-mouth bottle) so that the empty capacity of the container was 30%. In a container in which the mixture (zirconia beads and toner) is put at an empty capacity of 30% (volume ratio), 350 mL (= 0.7 × 500) out of the volume of 500 mL is occupied by the mixture (zirconia beads and toner). The remaining 150 mL (= 0.3 × 500) was free. Subsequently, the contents of the container were stirred for 1 hour under the condition of a rotation speed of 200 rpm using a ball mill (“desk type pot mill rotary table ANZ-51S” manufactured by Nippon Ceramic Science Co., Ltd.). As a result, mechanical stress was applied to the toner (measurement target), and the toner after the stress was applied (toner after use) was obtained.

<Measuring method of photoelectron spectrum>
A measurement object (powder: unused toner or used toner) was placed in a measurement cell. The object to be measured was pushed in from above using a slide glass, and the object to be measured (powder) was filled in the concave portion of the cell. The measurement object overflowing from the cell was removed by reciprocating the slide glass on the surface of the cell. Then, the measurement cell filled with the measurement object is set in the measurement device, and the photoelectron spectrum (vertical axis: photoelectron count number, horizontal axis: excitation energy) under the following conditions in an environment of temperature 22.5 ° C. and humidity 50% RH Was measured. The “photoelectron count” on the vertical axis was the photoelectron yield per unit light quantity to the power of 0.1.

(Measurement condition)
Measuring device: Atmospheric photoelectron spectrometer ("AC-3" manufactured by Riken Keiki Co., Ltd.)
Measuring principle: Low energy electronic counting method Light source: Ultraviolet lamp (deuterium lamp with lamp house)
Spectrometer: Nitrogen displacement type grating monochromator Measurement area (photoelectron measurement energy scanning range): 4.00 eV to 7.00 eV
Measurement interval: 0.01 eV
Excitation light intensity: 200 nW

In the above measuring apparatus, the light emitted from the ultraviolet lamp enters the chamber replaced with nitrogen, the light amount is adjusted by the light amount adjusting device in the chamber, and enters the spectroscope. Furthermore, the light whose wavelength is selected (energy selected) by the spectroscope is radiated into the atmosphere through the CaF ₂ window and collected on the surface of the measurement target. When light (excitation light) is irradiated onto the surface of the measurement target, photoelectrons are emitted from the surface layer portion (specifically, a region from the surface to a depth of about 200 mm) by the photoelectric effect. The photoelectrons are counted with an open counter.

The photoelectron spectrum was measured by scanning the excitation energy of ultraviolet light from low to high. The measurement result of the measuring apparatus was calculated by a computer, and the photoelectron spectrum was displayed on the display. Based on the measured photoelectron spectrum, the work functions W ₁ and W ₂ and the photoelectron retention rate Rc were determined. When the excitation energy was increased, photoemission began at a specific excitation energy. This excitation energy corresponds to the work function of the first component to be measured. That is, in the photoelectron spectrum, the excitation energy at the point where the photoelectron count rises corresponds to the work function of the first component to be measured. After the photoelectron count rose, the photoelectron count number (specifically, the normalized photoelectron yield) increased linearly with a constant slope as the excitation energy increased. Furthermore, as the excitation energy increased, the slope of the line changed at a specific excitation energy. The excitation energy at the tilt change point corresponds to the work function of the second to fourth components to be measured.

In the measurement of each of the toners TA-1 to TA-3, TB-1, and TB-2, two work functions (the work relating to each of the shell layer and the silica particles) are measured in the measurement range (4.0 eV to 7.0 eV). Function) was measured.
In the measurement of each of the toners TB-3 and TB-4, three work functions (work functions relating to each of the shell layer, the binder resin, and the silica particles) are measured in the measurement range (4.0 eV to 7.0 eV). It was done.
In the measurement of the toner TB-5, three work functions (a work function relating to each of the binder resin, the charge control agent, and the silica particles) were measured in the measurement range (4.0 eV to 7.0 eV).
In the measurement of the toner TB-6, in the measurement range (4.0 eV to 7.0 eV), four work functions (the work function relating to each of the binder resin, the two types of resins constituting the shell layer, and the silica particles). ) Was measured.

Even when the toner base particles and the external additive (silica particles) in each toner are separated and the photoelectron spectrum is measured for each of the separated toner base particles and the external additive, the measurement results shown in Table 2 ( The same results as the work functions W ₁ and W ₂ and the photoelectron retention ratio Rc) were obtained. When the measurement target is an external additive, the excitation energy at the point where the photoelectron count rises corresponds to the work function W ₂ of the surface layer portion of the external additive. The toner base particles and the external additive can be separated using an ultrasonic disperser (“Ultrasonic Miniwelder P128” manufactured by Ultrasonic Industrial Co., Ltd., output: 100 W, oscillation frequency: 28 kHz). The external additive separated from the toner base particles can be collected by centrifugation.

[Evaluation method]
The evaluation method of each sample (toners TA-1 to TA-3 and TB-1 to TB-6) is as follows.

<Method for preparing developer for evaluation>
100 parts by mass of developer carrier (carrier for “TASKalfa 5550ci” manufactured by Kyocera Document Solutions Co., Ltd.) and 10 mass of toner (evaluation target: any of toners TA-1 to TA-3 and TB-1 to TB-6) Were mixed for 30 minutes using a ball mill to obtain a developer for evaluation.

(Charge fluctuation)
The developer for evaluation prepared as described above was set in an evaluation machine, and a printing durability test was performed using the evaluation machine. As an evaluation machine, a multifunction machine (“TASKalfa 5550ci” manufactured by Kyocera Document Solutions Inc.) was used. The developer for evaluation was put into the developing device of the evaluation machine, and the toner for replenishment (evaluation object: any of toners TA-1 to TA-3 and TB-1 to TB-6) was put into the toner container of the evaluation machine. .

  A printing durability test was conducted in which continuous printing was performed on 10,000 sheets of paper (A4 size plain paper) at a printing rate of 2% using the above-described evaluation machine in an environment of temperature 22.5 ° C. and humidity 50% RH. . Nitrogen gas was sprayed onto the developing roller of the evaluator to collect the toner adhering to the surface of the developing sleeve of the evaluator at the start of the printing life test and every time 500 sheets were printed after the start of the press life test. The charge amount of 0.2 g of the collected toner was measured under the following conditions using a Q / m meter (“MODEL 210HS” manufactured by Trek).

<Measurement method of charge amount of toner in developer>
0.10 g of developer (carrier and toner) was charged into a Q / m meter measurement cell, and only the toner out of the charged developer was sucked through a sieve (metal mesh) for 10 seconds. Then, based on the formula “total electric amount of sucked toner (unit: μC) / mass of sucked toner (unit: g)”, the charge amount of toner in the developer (unit: μC / g) is calculated. Calculated.

The charge amount of the toner measured at the start of the printing durability test (specifically, immediately before printing the first sheet) corresponds to the initial toner charge amount Q _A. The largest charge amount of the toner charge amount measured during the printing durability test corresponds to the toner charge amount Q _B after printing durability. Based on the following equation, the fluctuation ratio (charge fluctuation ratio) of the post-printing toner charge quantity Q _B with respect to the initial toner charge quantity Q _A was determined.
Charge fluctuation rate = 100 × (Q _B −Q _A ) / Q _A

  When the charge fluctuation rate was more than −10% and less than + 10%, it was evaluated as “good”, and when it was −10% or less or + 10% or more, it was evaluated as “poor” (not good).

(Fogging resistance)
After the evaluation of the charging fluctuation, using the same evaluation machine (evaluation machine in which the developer for evaluation described above is set), 1000 sheets at a printing rate of 2% in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH. Continuous printing (A4 size plain paper). Then, continuous printing was performed on 100 sheets of paper (A4 size plain paper) at a printing rate of 80% using the above-described evaluation machine in an environment of a temperature of 32.5 ° C. and a humidity of 80% RH. During the continuous printing of 100 sheets, every time 10 sheets were printed, the reflection density of the blank portion in the printed paper was measured using a reflection densitometer (“SpectroEye (registered trademark)” manufactured by X-Rite). And the fog density (FD) was calculated | required based on the following formula.
Fog density = reflection density of blank area-reflection density of unprinted paper

  The highest fog density (maximum fog density) was determined among all the fog densities (FD) measured at each timing during the continuous printing of the 100 sheets (timing for every 10 sheets printed). When the measured maximum fog density was less than 0.010, it was evaluated as ◯ (good), and when it was 0.010 or more, it was evaluated as x (not good).

[Evaluation results]
Table 3 shows the evaluation results of toners TA-1 to TA-3 and TB-1 to TB-6. Table 3 shows measured values of charge fluctuation (charge fluctuation ratio) and fog resistance (maximum fog density).

The toners TA-1 to TA-3 (toners according to Examples 1 to 3) each had the above-described basic configuration. Each of the toners TA-1 to TA-3 includes a plurality of toner particles including toner base particles and an external additive (specifically, a plurality of silica particles). The toner base particles were provided with a toner core and a shell layer covering the surface of the toner core. The work function W ₁ of the surface layer portion of the shell layer and the work function W ₂ of the surface layer portion of the silica particles satisfy the following formula (M1), the photoelectron emission number C ₁ before stress application, and the photoelectron emission after stress application: The number C ₂ satisfied the following formula (M2) (see Table 2).
0.00eV ≦ W ₂ −W ₁ ≦ + 0.10 eV (M1)
0.95 ≦ C ₂ / C ₁ ≦ 1.05 (M2)

  When the cross section of the toner particles was confirmed using a TEM (transmission electron microscope), the thickness of the shell layer was 20 nm or more and 50 nm or less in any of the toners TA-1 to TA-3.

  As shown in Table 3, in toners TA-1 to TA-3 (toners according to Examples 1 to 3), the toner charge fluctuation was suppressed in continuous printing. By using such a toner, it was possible to continuously form high-quality images (specifically, images with low fog density) in continuous printing.

  The positively chargeable toner according to the present invention can be used for forming an image in, for example, a copying machine, a printer, or a multifunction machine.

DESCRIPTION OF SYMBOLS 10 1st toner particle 10a 3rd toner particle 10b 5th toner particle 11 Toner core 11a Toner mother particle 12 Shell layer 13 Silica particle 20 Charge control agent

Claims (7)

A positively chargeable toner comprising a plurality of toner particles comprising toner mother particles and an external additive attached to the surface of the toner mother particles,
The toner base particles include a toner core and a shell layer covering the surface of the toner core,
The external additive includes silica particles,
The work function W ₁ of the surface layer portion of the shell layer and the work function W ₂ of the surface layer portion of the silica particles measured from the photoelectron spectrum of the toner before being stressed satisfy the following formula (M1). ,
Photoelectron emission number C ₁ at an excitation energy of 7 eV measured from the photoelectron spectrum of the toner before being stressed and photoelectron at an excitation energy of 7 eV measured from the photoelectron spectrum of the toner after being stressed The discharge number C ₂ is a positively chargeable toner that satisfies the following formula (M2).
0.00eV ≦ W ₂ −W ₁ ≦ + 0.10 eV (M1)
0.95 ≦ C ₂ / C ₁ ≦ 1.05 (M2)
[After applying the stress, 100 parts by mass of zirconia beads having a number average primary particle diameter of 1 mm and 20 parts by mass of the toner are placed in a 500 mL capacity container so that the free capacity of the container is 30%. In this process, the contents of the container are stirred for 1 hour using a ball mill under the condition of a rotation speed of 200 rpm. ] The shell layer covers the entire surface of the toner core;
The positively chargeable toner according to claim 1, wherein the shell layer contains a resin including a repeating unit having an oxazoline group. The toner core does not contain a charge control agent,
The photoelectron spectrum of the toner before being stressed includes a rising point indicating a work function of the surface layer portion of the shell layer and an inclination changing point indicating a work function of the surface layer portion of the silica particles, and the inclination changing point. The positively chargeable toner according to claim 2, wherein the positively charged toner does not include an inclination change point in a larger excitation energy region. The resin containing a repeating unit having an oxazoline group is a polymer of a monomer containing at least one vinyl compound represented by the following formula (1) and at least one other vinyl compound. Item 4. The positively chargeable toner according to Item 2 or 3.

In formula (1), R ¹ represents a hydrogen atom or an alkyl group which may have a substituent. The toner core is a grinding core;
The positively chargeable toner according to claim 2, wherein the toner core contains a polyester resin and does not contain an oxazoline group.   The positively chargeable toner according to claim 2, wherein the shell layer has a thickness of 20 nm to 100 nm. The number average primary particle diameter of the silica particles contained in the external additive is 10 nm or more and 30 nm or less,
The positively chargeable toner according to claim 6, wherein the amount of the silica particles contained in the external additive is 0.5 parts by mass or more and 3.0 parts by mass or less with respect to 100 parts by mass of the toner base particles. .

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