JP2011128495A - Gray toner for electrostatic charge image development and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide gray toner for electrostatic charge image development, capable of obtaining a color-balanced gray image, and to provide an image forming method capable of forming halftone images with high color reproducibility. <P>SOLUTION: For the gray toner for the electrostatic charge image development, lightness L<SP>*</SP>by the L<SP>*</SP>a<SP>*</SP>b<SP>*</SP>color system in a solid image of a toner attachment amount 4.0g/m<SP>2</SP>formed only of the gray toner for the electrostatic charge image development is 30-90 and saturation C<SP>*</SP>is ≤10. Three kinds of chromatic colorants are a yellow colorant comprising a color material selected from an azo yellow color material and an isoindoline yellow color material, a magenta colorant comprising a color material selected from a rhodamine magenta color material and a quinacridone magenta color material, and a cyan colorant comprising a phthalocyanine color material. The contents of the yellow colorant, the magenta colorant and the cyan colorant are all 25-40 mass% based on the total of 100 mass% of the three kinds of chromatic colorants. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrostatic image developing gray toner and an image forming method using the same.

  In an electrophotographic image forming method, it has recently been proposed to improve the gradation and graininess of a visible image using a gray toner (see, for example, Patent Documents 1 to 3).

As a colorant for such a gray toner, carbon black is widely used because of its excellent coloring power. However, a gray image having a well-balanced color balance is used for the gray toner using this carbon black as a colorant. Cannot be obtained. Specifically, there is a problem that the tone of the obtained gray image becomes reddish.
The reason why such a problem arises is that the toner for forming the inked image requires high developability and transferability, and in order to meet such demands, the gray toner has developability. In order to improve transferability, the colorant is finely dispersed in the toner particles. However, carbon black used as the colorant has a reddish color as it is finely divided and finely dispersed. This is because it has a characteristic of becoming felt.

On the other hand, in color photographic images and the like, vividness of colors is required, and development of color toners is progressing (see, for example, Patent Documents 4 and 5).
By using the new color toner developed in this way, it has become possible to obtain a visible image with improved saturation and lightness, while a soft tone (Soft Tone) image with low saturation and There is a problem in that it is difficult to reproduce a low tone lightness (Dull Tone) image. The use of gray toner is considered to be effective in solving such problems.
Here, “soft tone” is a color that brings out a gentle and gentle atmosphere with a slight dullness in a bright color, and “dull tone” is a gentle and slightly complex expression with a slight dullness in a bright color. It is a color that shows.

  However, even when gray toner is used to form a halftone image such as a soft tone image and a dull tone image, sufficient color reproduction can be achieved due to the gray image obtained by the gray toner becoming reddish. There is a problem that sex cannot be obtained.

Japanese Patent Laid-Open No. 11-84764 JP 2004-133247 A JP 2006-227308 A JP 2007-140478 A JP 2007-34264 A

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a gray toner for developing an electrostatic image capable of obtaining a gray image having a well-balanced color balance.
Another object of the present invention is to provide an image forming method capable of forming a halftone image with high color reproducibility.

The gray toner for developing an electrostatic charge image of the present invention is a gray toner for developing an electrostatic charge image containing at least a binder resin and three kinds of chromatic colorants,
Lightness L ^* of 30 to 90 according to the L ^* a ^* b ^* color system in the electrostatic image developing gray toner only formed solid image of the toner adhesion amount 4.0 g / m ^2, a chroma C ^* 10 And
The three kinds of chromatic colorants are a yellow colorant comprising a colorant selected from an azo yellow colorant and an isoindoline yellow colorant, and a colorant selected from a rhodamine magenta colorant and a quinacridone magenta colorant. A magenta colorant and a cyan colorant made of a phthalocyanine colorant,
The content of the yellow colorant, the content of the magenta colorant, and the content of the cyan colorant are all 25 to 40% by mass with respect to 100% by mass in total of the three kinds of chromatic colorants. It is characterized by that.

In the gray toner for developing an electrostatic charge image of the present invention, the color material constituting the yellow colorant is C.I. I. Pigment yellow 74 or C.I. I. Pigment yellow 139,
The color material constituting the magenta colorant is C.I. I. Pigment red 81: 4, C.I. I. Pigment Red 122 or a compound represented by the following general formula (1),
The color material constituting the cyan colorant is C.I. I. Pigment blue 15, C.I. I. Pigment Blue 16 or a compound represented by the following general formula (2) is preferable.

[Wherein, R ¹ represents a monovalent organic group, and R ² and R ³ each independently represents an alkyl group. ]

[Wherein, R ⁴ and R ⁵ each independently represent a monovalent organic group. ]

  In the gray toner for developing an electrostatic image of the present invention, the total content of the three kinds of chromatic colorants is preferably 0.5 to 3% by mass with respect to 100% by mass of the binder resin.

The image forming method of the present invention is an image forming method for forming a visible image using a plurality of electrostatic image developing toners having different colors.
The electrostatic charge image developing gray toner is used as the electrostatic charge image developing toner.

  According to the gray toner for developing an electrostatic charge image of the present invention, three specific chromatic colorants are contained as a colorant in a specific content ratio, and a color is obtained by combining these three chromatic colorants. Since the balance is adjusted, color development relating to gray can be obtained satisfactorily, so that a gray image with a well-balanced color can be obtained.

According to the image forming method of the present invention, a gray image with a well-balanced color balance can be obtained by using the gray toner for developing an electrostatic image of the present invention, so that a halftone image is formed with high color reproducibility. be able to.

(A) L ^* a ^* b ^* color L ^* a ^* b ^* coordinate diagram showing a color space according to system, in a ^* b ^* coordinate diagram showing a color space according to (b) L ^* a ^* b ^* color system is there. 1 is a cross-sectional view illustrating an example of a configuration of an image forming apparatus used in an image forming method using a gray toner for developing an electrostatic image according to the present invention.

  Hereinafter, the present invention will be described in detail.

  The gray toner for developing an electrostatic charge image (hereinafter also simply referred to as “gray toner”) of the present invention comprises toner particles (hereinafter also referred to as “gray toner particles”) containing at least a binder resin and a colorant. As the colorant, a yellow colorant composed of a color material selected from azo-based yellow color materials and isoindoline-based yellow color materials, and a color material selected from rhodamine-based magenta color materials and quinacridone-based magenta color materials. 3 types of chromatic colorants, that is, a magenta colorant and a cyan colorant made of a phthalocyanine colorant.

The gray toner of the present invention has a lightness L ^* of 30 to 90 according to the L ^* a ^* b ^* color system in a solid image having a toner adhesion amount of 4.0 g / m ² formed on the image support using only the gray toner. And the saturation C ^* is 10 or less.

Here, the “L ^* a ^* b ^* color system” is a means that is usefully used to represent colors numerically. The color space defined by the L ^* a ^* b ^* color system shown in FIG. In the L ^* a ^* b ^* coordinate diagram shown, the L ^* axis direction represents lightness, the a ^* axis direction represents the hue in the red-green direction, and the b ^* axis direction represents the hue in the yellow-blue direction. .
The “saturation C ^* ” is indicated by a ^* and b ^* in the L ^* a ^* b ^* color system. Specifically, for example, a ^* when a certain color takes the coordinate point P. A distance from the origin O of the coordinate point P ′ (a, b) in the axis-b ^* axis plane, which is represented by the following formula (C ^* ).
The lightness refers to the relative brightness of the color, the hue refers to a hue such as red, yellow, green, blue, and purple, and the saturation refers to the degree of vividness of the color.

Formula (C ^* ): Saturation C ^* = [(a ^* ) ² + (b ^* ) ² ] ^1/2
[In the above formula (C ^* ), a ^* and b ^* represent the values of a and b at the coordinate points (a and b), respectively. ]

Specifically, L ^* , a ^* and b ^* in the L ^* a ^* b ^* color system are spectrophotometers “Gretag Macbeth Spectrolino” (manufactured by Gretag Macbeth), D65 light source as a light source, and reflection measurement aperture The diameter is 4 mm, the measurement wavelength range is 380 to 730 nm at intervals of 10 nm, the viewing angle is 2 °, and the measurement is performed under the condition that a dedicated white tile is used for reference alignment.

[Yellow colorant]
The yellow colorant contained in the gray toner particles constituting the gray toner of the present invention is selected from azo yellow color materials and isoindoline yellow color materials. Preferred specific examples of yellow colorants include C . I. Pigment yellow 74, C.I. I. And CI Pigment Yellow 139.

[Magenta colorant]
The magenta colorant contained in the gray toner particles constituting the gray toner of the present invention is selected from rhodamine-based magenta colorants and quinacridone-based magenta colorants. Preferred specific examples of magenta colorants include C.I. I. Pigment red 81: 4, C.I. I. Pigment Red 122 and a pyrazolotriazole compound represented by the above general formula (1).

In the general formula (1) indicating the pyrazolotriazole compound relating to the magenta colorant, examples of the monovalent organic group representing R ¹ include a —C ₆ H ₄ —C ₂ H ₅ group.
As the alkyl group represented by R ² and R ^3, 3 to 10 carbon atoms, such as propyl group, butyl group, octyl group, decyl group and the like, preferably a propyl group. R ² and R ³ are preferably the same.
Preferred examples of the compound represented by the general formula (1) include those in which R ¹ is —C ₆ H ₄ —C ₂ H ₅ group, and R ² and R ³ are propyl groups (hereinafter referred to as “compound (1) ")").

[Cyan colorant]
The cyan colorant contained in the gray toner particles constituting the gray toner of the present invention is made of a phthalocyanine-based color material. Preferred examples of the cyan colorant include C.I. I. Pigment blue 15, C.I. I. Pigment Blue 16, a compound represented by the above general formula (2), and the like.

In the general formula (2) representing the compound relating to the cyan colorant, examples of the monovalent organic group representing R ⁴ and R ⁵ include an alkyl group having 1 to 8 carbon atoms such as a hexyl group and an octyl group, and —SiR. ⁶ ₃ groups (wherein R ⁶ represents an alkyl group having 1 to 5 carbon atoms) and the like, preferably a hexyl group. R ⁴ and R ⁵ are preferably the same.
Preferable specific examples of the compound represented by the general formula (2) include those in which R ⁴ and R ⁵ are hexyl groups (hereinafter also referred to as “compound (2)”).

  These three chromatic colorants include C.I. as a yellow colorant. I. Pigment Yellow 74, C.I. I. Pigment Red 81: 4 and C.I. I. Pigment Blue 15 is preferably used in combination.

  The content of the yellow colorant, magenta colorant and cyan colorant constituting the three chromatic colorants is 25 to 40% by mass with respect to 100% by mass in total of the three chromatic colorants. Preferably, it is 30 to 36% by mass.

  When the content of each of the three kinds of chromatic colorants is within the above range, the contents of the yellow colorant, the magenta colorant and the cyan colorant constituting the three kinds of chromatic colorants are equivalent, Since the color development relating to gray can be obtained satisfactorily, a gray image with a well-balanced color can be obtained.

  Here, the content of the yellow colorant, the magenta colorant, and the cyan colorant is preferably such that the difference between the maximum value and the minimum value thereof is in the range of 0 to 5% by mass.

  In the gray toner of the present invention, the total content of the three kinds of chromatic colorants is preferably 0.5 to 3% by mass with respect to 100 parts by mass of the binder resin. It is 5-2 mass%.

When the total content of the three kinds of chromatic colorants is in the above range, the color development relating to gray can be satisfactorily obtained, so that a gray image with a well-balanced color can be obtained.
If the total content of the three types of chromatic colorants is too small, sufficient coloring power may not be obtained, while the total content of the three types of chromatic colorants is excessive. In such a case, the gray image of the gray toner has a small difference in brightness from the black image of the black toner, and there is a possibility that a negative effect such as a poor granularity of the highlight portion may occur.

[Binder resin]
The binder resin contained in the gray toner particles constituting the gray toner of the present invention is not particularly limited, and a known resin can be used.
When the gray toner is manufactured by a pulverization method or the like, for example, a vinyl resin such as a styrene resin, a (meth) acrylic resin, a styrene- (meth) acrylic copolymer resin, an olefin resin, or a polyester resin. Polyamide resins, polycarbonate resins, polyether resins, polyvinyl acetate resins, polysulfone resins, epoxy resins, polyurethane resins, urea resins, and the like can be used. These can be used alone or in combination of two or more.
Further, when the gray toner is produced by a suspension polymerization method, a miniemulsion polymerization aggregation method, an emulsion polymerization aggregation method or the like, it is known as a polymerizable monomer for obtaining a binder resin constituting the gray toner particles. These polymerizable monomers can be used, and examples of the polymerizable monomer include vinyl monomers, and those having an ionic dissociation group are preferably used in combination. Moreover, by using a polyfunctional vinyl monomer as the polymerizable monomer, a binder resin having a crosslinked structure can be obtained.

  The gray toner particles constituting the gray toner of the present invention can contain internal additives such as magnetic powder, a charge control agent, and a release agent, if necessary.

[Magnetic powder]
As the magnetic powder, for example, magnetite, γ-hematite, or various ferrites can be used.
The content of the magnetic powder is preferably 10 to 500 parts by mass, more preferably 20 to 200 parts by mass with respect to 100 parts by mass of the binder resin.

[Charge control agent]
The charge control agent is not particularly limited as long as it can give positive or negative charge by frictional charging, and various known positive charge control agents and negative charge control agents can be used.
Specifically, examples of the positive charge control agent include quaternary ammonium salts such as “quaternary ammonium salt P-51” (manufactured by Orient Chemical Industries) and “copy charge PX VP435” (manufactured by Hoechst Japan). And imidazole compounds such as “PLZ1001” (manufactured by Shikoku Kasei Kogyo Co., Ltd.), and the like.
Examples of the negative charge control agent include “Bontron S-22” (manufactured by Orient Chemical Industries), “Bontron S-34” (manufactured by Orient Chemical Industries), and “Bontron E-81” (Orient Chemical Industries, Ltd.). ), “Bontron E-84” (Orient Chemical Co., Ltd.), “Spiron Black TRH” (Hodogaya Chemical Co., Ltd.) and other metal complexes, thioindigo pigments, “Copy Charge NX VP434” (Hoechst Japan) Quaternary ammonium salts such as “Bontron E-89” (manufactured by Orient Chemical Industries), boron compounds such as “LR147” (manufactured by Nippon Carlit), magnesium fluoride, fluorinated carbon Fluorine compounds such as In addition to the metal complexes used as negative charge control agents, oxycarboxylic acid metal complexes, dicarboxylic acid metal complexes, amino acid metal complexes, diketone metal complexes, diamine metal complexes, azo group-containing benzene-benzene derivatives Examples thereof include those having various structures such as skeletal metal bodies and azo group-containing benzene-naphthalene derivative skeleton metal complexes.
As described above, the gray toner particles are configured to contain the charge control agent, whereby the chargeability of the gray toner is improved.

  The content of the charge control agent is preferably 0.01 to 30 parts by mass, more preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

〔Release agent〕
Various known waxes can be used as the release agent.
As the wax, polyolefin waxes such as low molecular weight polypropylene, polyethylene, or oxidized polypropylene, polyethylene can be preferably used.

  It is preferable that content of a mold release agent is 0.1-30 mass parts with respect to 100 mass parts of binder resin, More preferably, it is 1-10 mass parts.

The gray toner particles constituting the gray toner of the present invention may have a core-shell structure composed of core particles and a shell layer made of a shell layer forming resin covering the outer peripheral surface thereof. Since the gray toner particles have a core-shell structure, high production stability and storage stability can be obtained.
Here, the “core-shell structure” may be not only a form in which the shell layer completely covers the core particles but also a part of the core particles. In addition, a part of the shell layer forming resin constituting the shell layer may form a domain or the like in the core particle. Further, the shell layer may have a multilayer structure of two or more layers made of resins having different compositions.

[Production method of gray toner]
The gray toner of the present invention includes a binder resin or a polymerizable monomer for obtaining a binder resin, three kinds of chromatic colorants, specifically, a yellow colorant, a magenta colorant, and a cyan colorant, If necessary, the amount of the yellow colorant, the magenta colorant, and the cyan colorant used as an internal additive is 25 to 40% by mass with respect to a total of 100% by mass of the three chromatic colorants. % To obtain gray toner particles, and if necessary, an external additive may be added to the gray toner particles.

Examples of the method for producing the gray toner of the present invention include a pulverization method, suspension polymerization method, emulsion polymerization aggregation method, miniemulsion polymerization aggregation method, and other known methods. It is preferable to use it. According to the emulsion polymerization aggregation method, the gray toner particles can be easily reduced in size from the viewpoint of production cost and production stability.
Here, the emulsion polymerization aggregation method refers to a dispersion of fine particles made of a binder resin produced by an emulsion polymerization method (hereinafter also referred to as “binder resin fine particles”) and fine particles made of a colorant (hereinafter, “ And agglomerating slowly while balancing the repulsive force on the surface of the fine particles by adjusting the pH and the cohesive force due to the addition of the aggregating agent made of an electrolyte. This is a method for producing toner particles by performing association while controlling the particle size distribution, and at the same time performing fusion control by heating and stirring to perform shape control.

  In the case of producing a gray toner by the emulsion polymerization aggregation method, the binder resin fine particles obtained by the emulsion polymerization method may have a multilayer structure of two or more layers made of binder resins having different compositions. For the binder resin fine particles having such a structure, for example, those having a two-layer structure, a dispersion of resin particles is prepared by emulsion polymerization treatment (first-stage polymerization) according to a conventional method, and a polymerization initiator is added to this dispersion. And a polymerizable monomer are added, and this system can be obtained by a polymerization treatment (second stage polymerization).

  Further, gray toner particles having a core-shell structure can be obtained by an emulsion polymerization aggregation method. Specifically, the gray toner particles having a core-shell structure are firstly divided into binder resin fine particles for core particles and three types. The core particles are prepared by agglomerating, associating and fusing the fine particles of the chromatic colorant, and then the binder resin fine particles for the shell layer are added to the core particle dispersion to form the shell layer on the surface of the core particles. It can be obtained by aggregating and fusing the binder resin fine particles for forming a shell layer covering the core particle surface.

[Gray toner particle size]
The particle size of the gray toner particles constituting the gray toner of the present invention is preferably 4 to 10 μm, and more preferably 5 to 9 μm, for example, on a volume basis median diameter.
When the volume-based median diameter is in the above range, the transfer efficiency is increased, the image quality of halftone is improved, and the image quality of fine lines and dots is improved.

The volume-based median diameter of the gray toner particles is measured using a measuring apparatus in which a computer system for data processing (Beckman Coulter) is connected to “Coulter Multisizer TA-III” (Beckman Coulter). Calculated.
Specifically, 0.02 g of gray toner is added to 20 mL of a surfactant solution (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water for the purpose of dispersing gray toner particles). After being added and blended in, ultrasonic dispersion treatment was performed for 1 minute to prepare a dispersion of gray toner particles, and this dispersion of gray toner particles was added to “ISOTONII” (Beckman Coulter, Inc.) in the sample stand. Pipette into a beaker containing) until the displayed concentration of the measuring device is 5% to 10%. Here, a reproducible measurement value can be obtained by setting the concentration range. In the measurement apparatus, the measurement particle count is 25000, the aperture diameter is 50 μm, the frequency value is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50 % Particle diameter is defined as a volume-based median diameter.

[Average circularity of gray toner particles]
From the viewpoint of improving transfer efficiency, the gray toner particles constituting the gray toner of the present invention preferably have an average circularity T represented by the following formula (T) of 0.930 to 1.000, more preferably 0.950 to 0.995.
Formula (T): Average circularity T = peripheral length of circle obtained from equivalent circle diameter / perimeter length of particle projection image

(External additive)
As the gray toner of the present invention, the gray toner particles can be used as they are. However, in order to improve the fluidity, charging property, cleaning property, etc. of the gray toner particles, a fluidizing agent and a cleaning aid are used. An external additive such as an agent can also be added and used.

Specific examples of the external additive include inorganic oxide fine particles such as silica fine particles, alumina fine particles, and titanium oxide fine particles, inorganic stearate compound fine particles such as aluminum stearate fine particles and zinc stearate fine particles, or strontium titanate and titanium. Examples include inorganic fine particles such as inorganic titanic acid compound fine particles such as zinc acid.
These inorganic fine particles are preferably those subjected to surface treatment with a silane coupling agent, a titanium coupling agent, a higher fatty acid, silicone oil, or the like from the viewpoint of heat-resistant storage stability and environmental stability.

  The addition amount of the external additive is 0.05 to 5 parts by mass, preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the gray toner. In addition, various external additives may be used in combination.

(Developer)
The gray toner of the present invention can be used as a magnetic or non-magnetic one-component developer, but may be mixed with a carrier and used as a two-component developer.
In the case where the gray toner of the present invention is used as a two-component developer, the carrier includes a ferromagnetic metal such as iron, an alloy such as a ferromagnetic metal and aluminum and lead, and a compound of a ferromagnetic metal such as ferrite and magnetite. Magnetic particles made of conventionally known materials can be used, and ferrite particles are particularly preferable. As the carrier, a coated carrier in which the surface of magnetic particles is coated with a coating agent such as a resin, a binder type carrier in which magnetic fine powder is dispersed in a binder resin, and the like can also be used. The coating resin constituting the coat carrier is not particularly limited, and examples thereof include olefin resins, styrene resins, styrene-acrylic resins, silicone resins, ester resins, and fluorine resins. Moreover, it does not specifically limit as resin which comprises a resin dispersion type carrier, A well-known thing can be used, For example, a styrene-acrylic-type resin, a polyester resin, a fluororesin, a phenol resin etc. can be used.

The volume-based median diameter of the carrier is preferably 20 to 100 μm, and more preferably 20 to 60 μm.
The volume-based median diameter of the carrier can be typically measured by a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by SYMPATEC) equipped with a wet disperser.

According to the gray toner of the present invention as described above, three kinds of specific chromatic colorants are contained as a colorant in a specific content ratio, and a color balance is obtained by combining these three kinds of chromatic colorants. Therefore, since the color development relating to gray can be obtained satisfactorily, a gray image with a well-balanced color can be obtained.
In the gray toner of the present invention, even when the colorant is finely dispersed in the gray toner particles for the purpose of obtaining high developability and transferability, the gray toner using carbon black as the colorant is used. The three kinds of chromatic colorants are evenly dispersed without causing any adverse effects such as the color tone of the gray image obtained due to the fine dispersion of the colorant. Therefore, a high-quality gray image with a well-balanced color can be obtained.
Therefore, according to the gray toner of the present invention, a gray image made of the gray toner of the present invention is superior by superimposing it on an image made of a toner different in color from the gray toner, such as a black image made of black toner. In addition, a visible image having high gradation and graininess can be obtained, and in particular, a halftone image can be formed with high color reproducibility by overlapping with a color image made of color toner.

(Image forming method)
The image forming method of the present invention is characterized by using the gray toner of the present invention, and using the gray toner of the present invention and a toner of a color different from the gray toner (toner for developing an electrostatic image). To obtain a visible image.

  Specific examples of the image forming method of the present invention include the following methods (1) and (2).

(1) A toner image forming process in which a toner image formed by developing an electrostatic latent image formed on an electrostatic latent image carrier directly with a toner is transferred to an image support using toners of different colors. Two or more times, one of which is carried out using the gray toner of the present invention to obtain an image support carrying a plurality of toner images of different colors, and fixing these toner images to the image support A so-called direct transfer type image forming method in which a visible image is formed by the above method.
(2) A toner image forming process in which a toner image formed by developing an electrostatic latent image formed on an electrostatic latent image carrier with a toner is transferred to an intermediate transfer body using toners of different colors. Two or more times, one of which is carried out using the gray toner of the present invention to obtain an intermediate transfer member carrying a plurality of toner images having different colors, and these toner images are transferred onto an image support, A so-called intermediate transfer type image forming method in which a visible image is formed by fixing.

Here, examples of the toner different in color from the gray toner for forming the toner image include black toner or color toners such as yellow toner, magenta toner, and cyan toner.
The color toner different from the gray toner is not particularly limited, and for example, a known toner containing at least a binder resin and a colorant can be used.

As the black toner, in a solid image having a toner adhesion amount of 4.0 g / m ² formed on the image support using only the black toner, the lightness L ^* by the L ^* a ^* b ^* color system is less than 30, In addition, it is preferable that the saturation C ^* is 5 or less.
In the black toner, the colorant content of the colorant is preferably 3 parts by mass or more, more preferably 7 to 12 parts by mass with respect to 100 parts by mass of the binder resin.

As the yellow toner, in a solid image having a toner adhesion amount of 4.0 g / m ² formed on the image support with the yellow toner alone, the hue angle H according to the L ^* a ^* b ^* color system is 60 to 100 °. A range is preferred.
In the yellow toner, the colorant content is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

Here, the “hue angle H” is a line segment OP ′ between the origin O and the coordinate point P ′ (a, b), for example, in the a ^* axis−b ^* axis plane, as shown in FIG. And the angle θ formed with the a ^* axis, specifically, calculated by the following equation (H).

Formula (H): Hue angle H = tan ⁻¹ (b ^* / a ^* )
[In the above formula (H), a ^* and b ^* represent the values of a and b at the coordinate points (a and b), respectively. ]

As the cyan toner, in a solid image having a toner adhesion amount of 4.0 g / m ² formed on the image support with the cyan toner alone, the hue angle H according to the L ^* a ^* b ^* color system is 200 to 280 °. A range is preferred.
In the cyan toner, the content of the colorant is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

As the magenta toner, in a solid image having a toner adhesion amount of 4.0 g / m ² formed on the image support using only the magenta toner, the hue angle H according to the L ^* a ^* b ^* color system is 300 to 360 ° and The thing of the range of 0-15 degrees is preferable.
In the magenta toner, the content of the colorant is preferably 1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  The image forming method of the present invention as described above can be executed in the following image forming apparatus.

[Image forming apparatus]
FIG. 2 is an explanatory sectional view showing an example of the configuration of an image forming apparatus used in the image forming method using the gray toner of the present invention.
This image forming apparatus is capable of forming a visible image using five color toners of yellow toner, magenta toner, cyan toner, gray toner and black toner. Five image forming units 18Y, 18M, This is a so-called direct transfer type full-color image forming apparatus in which 18C, 18G, and 18Bk are provided in this order along the conveying belt 15A and no intermediate transfer member is provided.
In FIG. 2, 15B is an AC static eliminator, 15C is a separation claw, 15D is a conveyance unit, and 16 is a fixing device.

Each of the image forming units 18Y, 18M, 18C, 18G, and 18Bk is obtained by forming a photoconductive layer made of a conductive layer and an organic photoconductor (OPC) on the outer peripheral surface of a cylindrical substrate, not shown. A photosensitive drum 10Y as an electrostatic latent image carrier that is rotated clockwise by power from a driving source or driven by a conveying belt 15A that conveys the image support P and the conductive layer is grounded; 10M, 10C, 10G, and 10Bk and the photosensitive drums 10Y, 10M, 10C, 10G, and 10Bk are disposed in a direction orthogonal to the moving direction of the photosensitive drums 10Y, 10M, 10C, 10G, and 10Bk, and corona discharge having the same polarity as the toner. Chargers 11Y, 11M, 11C, 11G, 1G, which are made of, for example, a scorotron charger or the like that apply a uniform potential to the surfaces of 10M, 10C, 10G, and 10Bk. Bk is scanned in parallel with the rotation axes of the photoconductive drums 10Y, 10M, 10C, 10G, and 10Bk, and image data is formed on the uniformly charged surfaces of the photoconductive drums 10Y, 10M, 10C, 10G, and 10Bk. An exposure device 12Y, 12M, 12C, 12G, and 12Bk, for example, formed of a polygon mirror, and a developing sleeve (not shown) that rotates to form an electrostatic latent image by performing image exposure based on the developing sleeve. Developing units 13Y, 13M, 13C, 13G, and 13Bk that convey the toner held on the surface of the photosensitive drums 10Y, 10M, 10C, 10G, and 10Bk are configured.
In FIG. 2, 19Y, 19M, 19C, 19G, and 19Bk are cleaning devices.

  In the image forming units 18Y, 18M, 18C, 18G, and 18Bk having such a configuration, a yellow toner image is formed by the image forming unit 18Y, and a magenta toner image is formed by the image forming unit 18M. A cyan toner image is formed by the forming unit 18C, a gray toner image is formed by the image forming unit 18G, and a black toner image is formed by the image forming unit 18Bk.

As the transport belt 15A, a polymer film such as polyimide, polycarbonate, PVdF, or a synthetic rubber such as silicone rubber or fluorine rubber added with a conductive filler such as carbon black to impart conductivity, and the like are used. Although it may be a drum shape or a belt shape, it is preferably a belt shape from the viewpoint of freedom in device design.
The surface of the conveyor belt 15A is preferably appropriately roughened, and for example, the ten-point surface roughness Rz is preferably 0.5 to 2 μm. By using the transport belt 15A having such a roughened surface, the adhesion between the image support P and the transport belt 15A becomes high, and the swinging of the image support P on the transport belt 15A is suppressed. As a result, the transferability of the toner image from the photosensitive drums 10Y, 10M, 10C, 10G, and 10Bk to the image support P can be improved.

  In the image forming apparatus having such a configuration, first, the toner images of the respective colors formed on the photosensitive drums 10Y, 10M, 10C, 10G, and 10Bk of the image forming units 18Y, 18M, 18C, 18G, and 18Bk, A color toner image is formed on the image support P by sequentially transferring and superimposing the image onto the image support P conveyed by the conveyance belt 15A by the transfer devices 14Y, 14M, 14C, 14G, and 14Bk. It is formed.

The image support P carrying the color toner image is subjected to a neutralizing action by the AC static eliminator 15B provided on the downstream side of the transfer region with the image forming unit 18Bk of the conveying belt 15A, and on the downstream side of the AC static eliminator 15B. Due to the separation action of the provided separation claw 15C, the separation claw 15C is separated from the conveyance belt 15A, conveyed to the conveyance unit 15D, and conveyed to the fixing device 16 via the conveyance unit 15D.
In the fixing device 16, the image support P is sandwiched in the nip portion N formed by the heating roll 16a and the pressure roll 16b, and heat and pressure are applied to the color toner image on the image support P. Is fixed to form a visible image, and the image support on which the visible image is thus formed is discharged out of the apparatus.

In the image forming method of the present invention, for example, when a monochrome image is formed using gray toner together with black toner, the toner image made of black toner overlaps the upper layer side of the toner image made of gray toner on the image support. It is preferable to be formed as follows.
Specifically, in the intermediate transfer type image forming method, it is preferable to perform the toner image forming step relating to black toner in advance and then performing the toner image forming step relating to gray toner, as shown in FIG. In the direct transfer type image forming method performed using such an image forming apparatus, it is preferable to perform the toner image forming step related to the gray toner in advance and then perform the toner image forming step related to the black toner.

  By performing the toner image forming process in the order as described above when forming a monochrome image, the gradation and graininess in the obtained visible image can be easily adjusted by the amount of gray toner attached, Even when a monochrome image is formed, the expressive power is increased, and a high-quality visible image can be formed.

For example, when a color image is formed using a yellow toner, a magenta toner, and a cyan toner together with a gray toner, a toner image made of a gray toner is changed to a toner image made of a color toner (a color other than gray) on the image support. The toner image is preferably overlapped on the upper layer side.
Specifically, in the intermediate transfer type image forming method, it is preferable to perform the toner image forming process for each toner in the order of gray toner, yellow toner, cyan toner, and magenta toner. In the direct transfer type image forming method performed using the forming apparatus, it is preferable to perform the toner image forming process for each toner in the order of yellow toner, cyan toner, magenta toner, and gray toner.

  When a color image is formed, the toner image forming process is performed in the order as described above, so that the degree of dullness in the obtained visible image, that is, an image with a color toner on the lower layer side (color toner image) ) Can be easily adjusted, so even when halftone images such as soft tone images and dull tone images are formed, the expressive power is increased and a high quality visible image can be formed. it can.

According to the image forming method of the present invention as described above, by using the gray toner of the present invention, a well-balanced color image can be obtained as a gray image, so that carbon black is contained as a colorant. Compared to the case where gray toner is used, a halftone image can be formed with high color reproducibility.
In addition, according to the image forming method of the present invention, a visible image having excellent gradation and graininess can be obtained.

(Image support)
As the image support used in the image forming method using the gray toner as described above, coated paper such as plain paper, fine paper, art paper or coated paper from thin paper to thick paper is commercially available. Various types of paper such as Japanese paper, postcard paper, OHP plastic film, and cloth can be used, but the invention is not limited to these.

  The embodiments of the gray toner and the image forming method using the same according to the present invention have been described above. However, the present invention is not limited to the above-described embodiments, and various modifications can be added.

  Specific examples of the present invention will be described below, but the present invention is not limited to these examples.

[Gray toner production example 1]
(1) Production of resin particles A (1-1) First stage polymerization 8 g of sodium dodecyl sulfate was dissolved in 3 L of ion-exchanged water in a 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introducing device. The internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. After the temperature increase, a polymerization initiator solution in which 10 g of potassium persulfate was dissolved in 200 g of ion-exchanged water was added, and the liquid temperature was again set to 80 ° C.
Styrene 480g
n-Butyl acrylate 250g
Methacrylic acid 68g
n-octyl-3-mercaptopropionate 16 g
After the dropwise addition of the polymerizable monomer mixed solution comprising 1 hour, polymerization was carried out by heating and stirring at 80 ° C. for 2 hours to prepare resin particles [1H].

(1-2) Second-stage polymerization 7 g of polyoxyethylene (2) sodium dodecyl ether sulfate was dissolved in 800 mL of ion-exchanged water in a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device. After charging the solution and heating the system to 98 ° C., 260 g of the resin particles [1H]
Styrene 245g
120g of n-butyl acrylate
n-octyl-3-mercaptopropionate 1.5 g
190 g of paraffin wax (melting point: 45 ° C.)
A solution obtained by dissolving a polymerizable monomer mixture comprising 90 ° C. was added, and mixed and dispersed for 1 hour using a mechanical disperser “CLEARMIX” (manufactured by M Technique Co., Ltd.) having a circulation path. By doing this, a dispersion containing emulsified particles (oil droplets) was prepared.
Next, a polymerization initiator solution in which 6 g of potassium persulfate is dissolved in 200 mL of ion-exchanged water is added to this dispersion, and the system is heated and stirred at 82 ° C. for 1 hour, thereby performing resin particles. [1HM] was obtained.

(1-3) Third-stage polymerization Further, a polymerization initiator solution prepared by dissolving 11 g of potassium persulfate in 400 mL of ion-exchanged water was added to the system in which the resin particles [1HM] were obtained, and the temperature condition was 82 ° C. Below,
Styrene 435g
n-Butyl acrylate 130g
Methacrylic acid 33g
n-octyl-3-mercaptopropionate 8 g
A polymerizable monomer mixed solution was added dropwise over 1 hour. After completion of the dropwise addition, polymerization was performed by heating and stirring for 2 hours, and then the reaction liquid was cooled to 28 ° C. to obtain a dispersion of resin particles [A].

(2) Production of resin particle B A 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introducing device was charged with a solution obtained by dissolving 2.3 g of sodium dodecyl sulfate in 3 L of ion-exchanged water, and a nitrogen stream The internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm. After the temperature increase, a polymerization initiator solution in which 10 g of potassium persulfate was dissolved in 200 g of ion-exchanged water was added, and the liquid temperature was again set to 80 ° C.
Styrene 520g
210g of n-butyl acrylate
Methacrylic acid 68g
n-octyl-3-mercaptopropionate 16 g
A polymerizable monomer mixture was added dropwise over 1 hour, and then polymerized by heating and stirring at 80 ° C. for 2 hours to prepare a dispersion of resin particles [B].

(3) Preparation of Colorant Dispersion Solution 90 g of sodium dodecyl sulfate was stirred and dissolved in 1400 g of ion-exchanged water, and C.I. I. 175 g of CI Pigment Yellow 74 and C.I. I. Pigment Red 81: 4 is 175 g, and C.I. I. After gradually adding 180 g of Pigment Blue 15 and dispersing the mixture using a stirring means “CLEARMIX” (manufactured by M Technique Co., Ltd.), a dispersion in which three kinds of chromatic colorants are dispersed A liquid (hereinafter referred to as “colorant dispersion [1]”) was prepared.
Here, the amount of each of the three kinds of chromatic colorants used in the preparation of the colorant dispersion [1] is such that the yellow colorant is 100% by mass of the total of these three kinds of chromatic colorants. Is 33% by weight, magenta colorant is 33% by weight and cyan colorant is 34% by weight.

(4) Production of gray toner particles In a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube and a nitrogen introducing device, 300 g of resin particles [A] (in terms of solid content), 1400 g of ion-exchanged water, A colorant dispersion [1] (82 g) and a solution of 3 g of polyoxyethylene (2) sodium dodecyl ether sulfate dissolved in 120 mL of ion-exchanged water were prepared, the liquid temperature was adjusted to 30 ° C., and 5N sodium hydroxide was added. The pH was adjusted to 10 by adding an aqueous solution. Next, an aqueous solution in which 35 g of magnesium chloride was dissolved in 35 mL of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After holding for 3 minutes, the temperature was raised and the system was heated to 90 ° C. over 60 minutes, and the particle growth reaction was continued while maintaining 90 ° C. In this state, the particle size of the associated particles was measured with “Coulter Multisizer III” (manufactured by Beckman Coulter, Inc.). When the volume-based median diameter reached 3.1 μm, 260 g of resin particles [B] (solid In addition, the particle growth reaction is continued, and when the desired particle size is reached, an aqueous solution in which 150 g of sodium chloride is dissolved in 600 mL of ion-exchanged water is added to stop the particle growth. By fusing and stirring at a liquid temperature of 98 ° C. as the fusing treatment, fusing was allowed to proceed until the circularity reached 0.965 as measured by “FPIA-2100” (manufactured by Sysmex). Thereafter, the solution was cooled to 30 ° C., hydrochloric acid was added to adjust the pH to 4.0, and stirring was stopped.

The particles thus produced were subjected to solid-liquid separation using a basket-type centrifuge “MARK III model number 60 × 40” (manufactured by Matsumoto Kikai Co., Ltd.) to form a wet cake. The wet cake was washed with ion exchange water at 45 ° C. until the electrical conductivity of the filtrate reached 5 μS / cm with the basket-type centrifuge, and then “flash jet dryer” (manufactured by Seishin Enterprise Co., Ltd.) was used. Gray toner particles [1] were produced by drying until the water content reached 0.5% by mass.
The obtained gray toner particles [1] contain a yellow colorant, a magenta colorant, and a cyan colorant as colorants, and the content of the yellow colorant is 33% by mass with respect to 100% by mass in total. The content of the magenta colorant is 33% by mass and the content of the cyan colorant is 34% by mass. The content of the colorant with respect to 100% by mass of the binder resin is 5% by mass.

(5) Addition of external additive To the obtained gray toner particles [1], 1% by mass of hydrophobic silica particles (number average primary particle size: 12 nm) and hydrophobic titania particles (number average primary particle size: 20 nm) 0 .3 mass% was added and mixed using a Henschel mixer to obtain a gray toner [1].
With respect to the obtained gray toner [1], a solid image having a toner adhesion amount of 4.0 g / m ² was formed on the image support “POD gloss coated paper” (manufactured by Oji Paper Co., Ltd.) using only the gray toner [1]. , the measured lightness and saturation by the method described above, lightness L ^* according to the L ^* a ^* b ^* color system in the solid image is 68, the chroma C ^* was 5.3.
In the gray toner [1], the shape and particle size of the gray toner particles did not change by the addition of the hydrophobic silica particles and the hydrophobic titania particles.

[Gray toner production examples 2 to 7]
In the step of (3) preparation of the colorant dispersion in Production Example 1 of gray toner, the colorant dispersion was prepared according to the formulation shown in Table 1, and (4) in the step of preparation of gray toner particles, shown in Table 1. Gray toners [2] to [7] were obtained in the same manner as in Production Example 1 of the gray toner except that the colorant dispersion was used according to the formulation.
Of the obtained gray toners [2] to [7], the gray toners [2] to [5] are those of the present invention, and the gray toners [6] and [7] are for comparison.
For each of the obtained gray toners [2] to [7], the brightness was determined in the same manner as in Production Example 1 for gray toner. And saturation was measured. The results are shown in Table 1 below.

  In Table 1, the content relating to the yellow colorant, magenta colorant, cyan colorant and black colorant indicates the ratio of the total colorant content to 100% by mass, and the colorant content is The ratio with respect to 100 mass% of binder resin is shown. “PY74” is C.I. I. Pigment Yellow 74, “PY139” is C.I. I. Pigment Yellow 139 and “PY83” are C.I. I. Pigment Yellow 83, “PR81: 4” is C.I. I. Pigment Red 81: 4, “PR122” is C.I. I. Pigment Red 122, “compound (1)” is a compound represented by the following structural formula (1), and “PR149” is C.I. I. Pigment Red 149, “PB15” is C.I. I. Pigment Blue 15, “PB16” is C.I. I. Pigment Blue 16, “compound (2)” is a compound represented by the following structural formula (2), and “PB1” is C.I. I. Pigment Blue 1 and “CB # 10” indicate carbon black.

[Developer Preparation Examples 1 to 7]
Using each of the obtained gray toners [1] to [7] and a ferrite carrier having a volume-based median diameter of 60 μm coated with a silicone resin, using a V-type mixer so that the toner concentration becomes 6% by mass. By mixing, gray developers [1] to [7] were produced.

<Examples 1 to 5, Comparative Examples 1 and 2>
As the image forming apparatus, a digital multi-function machine “bizhub PRO C6500” (manufactured by Konica Minolta Business Technologies Co., Ltd.) is used, and a gray toner image forming unit is provided. By using each developer of [1] to [7] and a black developer, a yellow developer, a magenta developer, and a cyan developer for the commercially available bizhub PRO C6500 related to the multifunction machine, the following (1) Evaluation of (4) was performed. The results are shown in Table 2.

(1) Gray color tone evaluation Test chart No. 7 (2008) is printed, and this printed matter is observed by 50 evaluators in the same environment (same lighting condition, same distance), paying particular attention to the background of the portrait and the gray gradient chart. The gray tone was evaluated according to the following evaluation criteria by the number of people who evaluated that the gray tone image portion was not reddish and did not deviate from the achromatic color.
-Evaluation criteria-
A: 45 or more B: 5-44 C: 4 or less

(2) Gray texture evaluation A halftone image having an image density of 0.4 is printed, and the halftone texture of the printed material is visually evaluated by 20 evaluators. The texture of gray was evaluated according to the following evaluation criteria.
Here, “texture” was evaluated from the viewpoint of the presence or absence of graininess and the degree of graininess. The graininess is not felt, and graininess is not felt at all, or it is faint by gazing. A case where a good graininess was felt but there was no problem in practical use was evaluated as having “excellent texture”.
-Evaluation criteria-
A: 15 people or more B: 10-14 people C: 9 people or less

(3) Color Reproducibility of Soft Tone Image Eight Soft Tone Color Codes: # cc6666, # cc9966, # cccc66, # 99cc66, # 66cc66, # 66cc99, # 66cccc and # 6699cc patch images as soft tone images In print mode, this printed matter and the color code sample of each soft tone displayed on the display are observed by 50 evaluators under the same environment (same lighting condition, same distance). The degree of redness perceived in comparison with the sample was evaluated according to the following evaluation criteria, and the most evaluation was made as the evaluation result of the color reproducibility of the soft tone image.
-Evaluation criteria-
A: Redness is not felt at all compared with the sample.
B: Redness is hardly felt unless compared with the sample.
C: A reddish color is felt compared to the sample.
D: Strong redness is felt without comparing with the sample.

(4) Color Reproducibility of Daltone Image Six-color dull tone color code: # 996666, # 9999966, # 669966, # 6669999, # 666699 and # 966699 are output in the printer mode as a dull tone image, and this printed matter The color code samples of each dull tone displayed on the display are observed by 50 evaluators under the same environment (same lighting conditions and the same distance), and how much redness is in print compared to the samples. Whether the image was felt was evaluated according to the following evaluation criteria, and the largest number of evaluations were evaluated as the color reproducibility evaluation results of the dull tone image.
-Evaluation criteria-
A: Redness is not felt at all compared with the sample.
B: Redness is hardly felt unless compared with the sample.
C: A reddish color is felt compared to the sample.
D: Strong redness is felt without comparing with the sample.

10Y, 10M, 10C, 10G, 10Bk Photoconductor drums 11Y, 11M, 11C, 11G, 11Bk Chargers 12Y, 12M, 12C, 12G, 12Bk Exposure units 13Y, 13M, 13C, 13G, 13Bk Developers 14Y, 14M, 14C , 14G, 14Bk Transfer device 15A Conveyor belt 15B AC neutralizer 15C Separation claw 15D Conveyor 16 Fixing device 16a Heating roll 16b Pressing roll 18Y, 18M, 18C, 18G, 18Bk Image forming unit 19Y, 19M, 19C, 19G, 19Bk Cleaning device N Nip part P Image support

Claims (4)

A gray toner for developing an electrostatic image containing at least a binder resin and three kinds of chromatic colorants,
Lightness L ^* of 30 to 90 according to the L ^* a ^* b ^* color system in the electrostatic image developing gray toner only formed solid image of the toner adhesion amount 4.0 g / m ^2, a chroma C ^* 10 And
The three kinds of chromatic colorants are a yellow colorant comprising a colorant selected from an azo yellow colorant and an isoindoline yellow colorant, and a colorant selected from a rhodamine magenta colorant and a quinacridone magenta colorant. A magenta colorant and a cyan colorant made of a phthalocyanine colorant,
The content of the yellow colorant, the content of the magenta colorant, and the content of the cyan colorant are all 25 to 40% by mass with respect to 100% by mass in total of the three kinds of chromatic colorants. A gray toner for developing electrostatic images. The color material constituting the yellow colorant is C.I. I. Pigment yellow 74 or C.I. I. Pigment yellow 139,
The color material constituting the magenta colorant is C.I. I. Pigment red 81: 4, C.I. I. Pigment Red 122 or a compound represented by the following general formula (1),
The color material constituting the cyan colorant is C.I. I. Pigment blue 15, C.I. I. The gray toner for developing electrostatic images according to claim 1, which is CI Pigment Blue 16 or a compound represented by the following general formula (2).
[Wherein, R ¹ represents a monovalent organic group, and R ² and R ³ each independently represents an alkyl group. ]
[Wherein, R ⁴ and R ⁵ each independently represent a monovalent organic group. ]   3. The electrostatic charge according to claim 1, wherein the total content of the three kinds of chromatic colorants is 0.5 to 3% by mass with respect to 100% by mass of the binder resin. Gray toner for image development. In an image forming method for forming a visible image using a plurality of electrostatic image developing toners having different colors,
4. An image forming method, wherein the electrostatic image developing gray toner according to claim 1 is used as the electrostatic image developing toner.