JP2014145943A - Image forming method, and toner for electrostatic latent image development - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method capable of appropriately fixing a toner image on a recording medium irrespective of the line velocity of the recording medium when image formation is performed using an image forming apparatus capable of changing the line velocity of a recording medium passing through between a heating roller and a pressure roller; and to provide a toner for electrostatic latent image development that is appropriately used in the image forming method and has excellent heat-resistant storage stability.SOLUTION: In an image forming apparatus capable of changing the line velocity of a recording medium passing through between a heating roller and a pressure roller, images are formed by using a toner for electrostatic latent image development that is formed of toner core particles containing a binder resin and a shell layer coating the surface of each of the toner core particles, and in which the glass transition point of the binder resin (Tg) and the glass transition point of a material forming the shell layer (Tg) satisfy a predetermined relationship, and are within a predetermined range.

Description

  The present invention relates to an image forming method and an electrostatic latent image developing toner.

  With regard to the toner, in recent years, from the viewpoint of energy saving and downsizing of the apparatus, a toner excellent in low temperature fixability that can be fixed satisfactorily without heating the fixing roller as much as possible is desired. However, toners excellent in low-temperature fixability often use a binder resin having a low melting point or glass transition point or a release agent having a low melting point, and generally easily aggregate. When the toner aggregates, there is a problem that an image defect due to adhesion of the toner to the developing sleeve or the photosensitive drum occurs in the formed image when the image is formed.

  In order to solve such problems, toner core particles using a binder resin having a low melting point are used for the purpose of improving storage stability at high temperatures and improving blocking resistance. A capsule toner coated with a resin having a Tg higher than the glass transition point (Tg) of the resin is used.

  As such a capsule toner, a vinyl resin fine particle dispersion liquid in which vinyl resin fine particles are dispersed in an aqueous medium is dispersed in a dispersion liquid in which core particles (toner core particles) containing at least a binder resin and a colorant are dispersed. A colored resin particle (capsule toner) manufactured using a manufacturing method (see Patent Document 1) characterized in that it includes a step of introducing and attaching fine particles onto core particles (toner core particles) has been proposed. .

JP 2011-046865 A

  However, the capsule toner manufactured by using the manufacturing method described in Patent Document 1 has a high temperature depending on the combination of the binder resin used for the toner core particles and the material (vinyl resin) that covers the toner core particles. In some cases, it is difficult to obtain a toner that can achieve both storage stability (heat-resistant storage stability) and fixability.

  In addition, excellent gloss is often required for an image formed using toner. As a method for forming an image having excellent gloss on a recording medium, an image forming apparatus including a heating roller that heats the recording medium on which the toner image is transferred, and a pressure roller that is disposed to face the heating roller and pressurizes the recording medium. A method of forming an image by reducing the linear velocity of a recording medium passing between a heating roller and a pressure roller using an apparatus can be mentioned. In such a method, by reducing the linear velocity, the thermal energy given to the toner image when fixing the toner image is increased, and an image with high glossiness is fixed on the recording medium.

  However, when an image is formed by such a method, if the image is formed using a capsule toner manufactured by using the manufacturing method described in Patent Document 1, recording is performed with a reduced linear velocity in the image forming apparatus. As the amount of heat applied to the toner image is increased when the medium is moved, there is a case where the toner image is hardly fixed on the recording medium due to the occurrence of the offset.

  The present invention has been made in view of such circumstances, and in the case of forming an image using an image forming apparatus capable of changing the linear velocity of a recording medium passing between a heating roller and a pressure roller. An object of the present invention is to provide an image forming method capable of satisfactorily fixing a toner image on a recording medium regardless of the linear velocity of the recording medium. Another object of the present invention is to provide a toner for developing an electrostatic latent image that is suitably used in the above-described image forming method and has excellent heat-resistant storage stability.

The present inventors have disclosed an image forming apparatus capable of changing a linear velocity of a recording medium passing between a heating roller and a pressure roller, and a toner core particle containing a binder resin and a shell covering the surface of the toner core particle. The glass transition point (Tg ₁ ) of the binder resin and the glass transition point (Tg ₂ ) of the material constituting the shell layer satisfy a predetermined relationship and are within a predetermined range. The present inventors have found that the above problems can be solved by forming an image using toner for developing an electrostatic latent image, and have completed the present invention. Specifically, the present invention provides the following.

The first aspect of the present invention is:
A heating roller that heats a recording medium to which a toner image formed using a toner for developing an electrostatic latent image is transferred, and a pressure roller that is disposed opposite to the heating roller and pressurizes the recording medium,
An image forming method using an image forming apparatus capable of changing a linear velocity of the recording medium passing between the heating roller and the pressure roller,
The electrostatic latent image developing toner comprises toner core particles containing a binder resin and a shell layer covering the surface of the toner core particles,
The glass transition point (Tg ₁ ) of the binder resin is 25 ° C. or more and 51 ° C. or less,
The glass transition point of the material constituting the shell layer (Tg _2), and at temperatures above 55 ℃, and, ^{_{[- 0.007 (Tg 1) 2 +0.182}} (Tg 1) +79.735 ] ° C. or less The present invention relates to an image forming method.

The second aspect of the present invention is:
Consists of a toner core particle containing a binder resin and a shell layer covering the surface of the toner core particle,
The glass transition point (Tg ₁ ) of the binder resin is 25 ° C. or more and 51 ° C. or less,
The glass transition point of the material constituting the shell layer (Tg _2), and at temperatures above 55 ℃, and, ^{_{[- 0.007 (Tg 1) 2 +0.182}} (Tg 1) +79.735 ] ° C. or less The present invention relates to a toner for developing an electrostatic latent image.

  According to the present invention, when forming an image using an image forming apparatus capable of changing the linear velocity of the recording medium passing between the heating roller and the pressure roller, regardless of the linear velocity of the recording medium, An image forming method capable of satisfactorily fixing a toner image on a recording medium can be provided. In addition, according to the present invention, it is possible to provide an electrostatic latent image developing toner that is used in the above-described image forming method and has excellent heat-resistant storage stability.

1 is a diagram illustrating an example of an image forming apparatus. Is a graph showing the relationship between Tg ₁ and Tg ₂ of the toner used in Examples 1-10. Is a graph showing the relationship between Tg ₁ and Tg ₂ of the toner used in Examples 1-15 and Comparative Examples 1-9.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. . In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the summary of invention is not limited.

An image forming method of the present invention includes a heating roller that heats a recording medium onto which a toner image has been transferred, and a pressure roller that is disposed opposite to the heating roller and pressurizes the recording medium. An image forming apparatus capable of changing the linear velocity of the recording medium passing between the two is used. The electrostatic latent image developing toner (also simply referred to as toner in the specification of the present application) includes toner core particles containing a binder resin and a shell layer covering the surface of the toner core particles. A toner is used in which the glass transition point (Tg ₁ ) and the glass transition point (Tg ₂ ) of the material constituting the shell layer satisfy a predetermined relationship and are within a predetermined range. Hereinafter, the image forming apparatus used in the image forming method of the present invention and the electrostatic latent image developing toner will be described in order.

[Image forming apparatus]
An image forming apparatus used in the image forming method of the present invention includes a heating roller that heats a recording medium to which a toner image is transferred, and a pressure roller that is disposed opposite to the heating roller and presses the recording medium. The image forming apparatus can change the linear velocity of the recording medium passing between the heating roller and the pressure roller. In the image forming method of the present invention, by using such an image forming apparatus in combination with a toner described later, the toner can be satisfactorily fixed on the recording medium regardless of the linear velocity of the recording medium. Here, a tandem color image forming apparatus having a fixing unit including such a heating roller and a pressure roller will be described as a suitable image forming apparatus.

  In the tandem color image forming apparatus described below, a plurality of latent images arranged in parallel in a predetermined direction to form toner images made of different color toners on the surface of each latent image carrier. A carrying unit and a roller (developing sleeve) that is disposed opposite to each latent image carrying unit, carries the toner on the surface and conveys the toner, and supplies the conveyed toner to the surface of each latent image carrying unit. A plurality of developing units, and an electrostatic latent image developing toner described later is supplied to the latent image carrying unit by the developing unit.

  FIG. 1 is a diagram illustrating a configuration of a preferred image forming apparatus. Here, the color printer 1 will be described as an example of the image forming apparatus.

  As shown in FIG. 1, the color printer 1 has a box-shaped device body 1a. In the apparatus main body 1a, a paper feeding unit 2 that feeds a paper P as a recording medium, and a toner image based on image data on the paper P while conveying the paper P fed from the paper feeding unit 2. And a fixing unit 4 for performing a fixing process for fixing the unfixed toner image transferred onto the paper P by the image forming unit 3 to the paper P. Further, on the upper surface of the apparatus main body 1a, a paper discharge unit 5 for discharging the paper P subjected to the fixing process by the fixing unit 4 is provided.

  The paper feed unit 2 includes a paper feed cassette 121, a pickup roller 122, paper feed rollers 123, 124, 125, and a registration roller pair 126. The paper feed cassette 121 is provided so as to be detachable from the apparatus main body 1a and stores the paper P. The pickup roller 122 is provided at the upper left position of the paper feed cassette 121 shown in FIG. 1 and takes out the paper P stored in the paper feed cassette 121 one by one. The paper feed rollers 123, 124, and 125 send out the paper P taken out by the pickup roller 122 operating to the paper transport path. The registration roller pair 126 temporarily waits for the paper P sent to the paper transport path by operating the paper feed rollers 123, 124, 125, and then supplies the paper P to the image forming unit 3 at a predetermined timing.

  The paper feeding unit 2 further includes a manual feed tray (not shown) and a pickup roller 127 that are attached to the left side surface of the device main body 1a shown in FIG. The pickup roller 127 takes out the paper P placed on the manual feed tray. The paper P taken out by the pickup roller 127 is sent out to the paper conveyance path when the paper feed rollers 123 and 125 are operated, and is supplied to the image forming unit 3 at a predetermined timing when the registration roller pair 126 is operated. .

  The image forming unit 3 performs primary transfer of an image forming unit 7 and a toner image based on image data transmitted from a device such as a computer to the surface (contact surface) of the image forming unit 7 by operating the image forming unit 7. An intermediate transfer belt 31 and a secondary transfer roller 32 for secondarily transferring the toner image on the intermediate transfer belt 31 onto the paper P fed from the paper feed cassette 121 are provided.

  The image forming unit 7 includes a black unit 7K, a yellow unit 7Y, and a cyan unit 7C that are sequentially arranged from the upstream side (right side in FIG. 1) to the downstream side in the moving direction of the intermediate transfer belt 31. And a magenta unit 7M. In each of the units 7K, 7Y, 7C, and 7M, a drum-type latent image carrier 37, which is an image carrier, is disposed at the center position so as to be rotatable in the arrow (clockwise) direction. Around each latent image carrier 37, members such as a charging unit 39, an exposure unit 38, a developing unit 71, a cleaning unit (not shown), and a static eliminator (not shown) are arranged. Are arranged in order from the upstream side in the rotation direction.

  The charging unit 39 uniformly charges the peripheral surface of the latent image carrying unit 37 rotated in the direction of the arrow. The charging unit 39 is not particularly limited as long as the peripheral surface of the latent image carrying unit 37 can be uniformly charged, and may be a non-contact type or a contact type. Specific examples of the charging unit include members such as a corona charging device, a charging roller, and a charging brush.

  The surface potential (charging potential) of the latent image carrying part 37 is preferably +200 V or more and +500 V or less, preferably +200 V or more and +300 V or less, considering the balance between developability and the charging ability of the latent image carrying part 37. More preferred.

  As the latent image carrier 37, an inorganic photosensitive member such as amorphous silicon; a single-layer or multi-layered photosensitive layer containing components such as a charge generator, a charge transport agent, and a binder resin is formed on a conductive substrate. And an organic photoreceptor prepared.

  The exposure unit 38 is a so-called laser scanning unit, and laser light based on image data input from a personal computer (PC), which is a host device, on the peripheral surface of the latent image carrier 37 uniformly charged by the charging unit 39. To form an electrostatic latent image based on the image data on the latent image carrier 37. The developing unit 71 supplies the toner of the present invention to the peripheral surface of the latent image carrying unit 37 on which the electrostatic latent image is formed, and forms a toner image based on the image data. In the image forming method of the present invention, this image forming apparatus and a toner described later are used in combination, so that the paper P can be used regardless of the linear speed of the paper P passing between the heating roller 41 and the pressure roller 42. The toner image transferred above can be fixed satisfactorily. The configuration of the developing unit 71 is appropriately changed according to the type of developer and the development method. The toner image formed on the peripheral surface of the latent image carrier 37 using the developing unit 71 is primarily transferred to the intermediate transfer belt 31.

  After the primary transfer of the toner image to the intermediate transfer belt 31 is completed, the toner remaining on the peripheral surface of the latent image carrier 37 is cleaned by operating a cleaning unit (not shown) as necessary. .

  The static eliminator neutralizes the peripheral surface of the latent image carrier 37 after the primary transfer is completed. The peripheral surface of the latent image carrier 37 cleaned by the operation of the cleaning unit and the static eliminator is directed to the charging unit 39 for a new charging process, and a new charging process is performed.

  The intermediate transfer belt 31 is an endless belt-like rotating body, and includes a driving roller 33, a driven roller 34, a backup roller 35, and a front surface (contact surface) side in contact with the peripheral surface of each latent image carrier 37. And a plurality of rollers such as the primary transfer roller 36. The intermediate transfer belt 31 is rotated endlessly by a plurality of rollers operating in a state where the primary transfer roller 36 disposed opposite to each latent image carrier 37 is operated and pressed against the latent image carrier 37. It is configured. A drive source such as a stepping motor (not shown) drives the drive roller 33 to rotate, and gives the intermediate transfer belt 31 a drive force for endless rotation. The driven roller 34, the backup roller 35, and the primary transfer roller 36 are rotatably provided, and are driven to rotate with the endless rotation of the intermediate transfer belt 31 that is generated when the driving roller 33 is driven. These rollers 34, 35, 36 are driven to rotate via the intermediate transfer belt 31 according to the main rotation of the drive roller 33 and support the intermediate transfer belt 31.

  The primary transfer roller 36 applies a primary transfer bias to the intermediate transfer belt 31. By doing so, the toner image formed on each latent image carrier 37 is driven by the drive roller 33 between each latent image carrier 37 and the primary transfer roller 36, and an arrow (counterclockwise). The image is sequentially transferred (primary transfer) in an overcoated state to the intermediate transfer belt 31 that circulates in the rotation direction.

  The secondary transfer roller 32 applies a secondary transfer bias to the paper P. By doing so, the toner image primarily transferred onto the intermediate transfer belt 31 is secondarily transferred to the paper P between the secondary transfer roller 32 and the backup roller 35, and a color transfer image (undecided) is transferred to the paper P. A toner image) is transferred.

The fixing unit 4 performs a fixing process on the transfer image transferred to the paper P by the image forming unit 3. The fixing unit 4 is disposed opposite to the heating roller 41 that is heated using an energization heating element, A pressure roller 42 having a peripheral surface pressed against and in contact with the peripheral surface of the heating roller 41.
The unfixed toner image formed on the paper P is softened by the operation of the heating roller 41, and the softened toner image is pressed against the surface of the paper P according to the operation of the pressure roller 42. To be established.

  Then, when the paper P passes between the secondary transfer roller 32 and the backup roller 35 in the image forming unit 3, the toner image on the intermediate transfer belt 31 is transferred to the paper P, and a transfer image is formed on the paper P. The The transferred image on the paper P is fixed on the paper P by a fixing process including heating and pressure when the paper P passes between the heating roller 41 and the pressure roller 42. Then, the paper P subjected to the fixing process is discharged to the paper discharge unit 5. Further, in the color printer 1 of the present embodiment, a plurality of conveyance roller pairs 6 are disposed at appropriate positions between the fixing unit 4 and the paper discharge unit 5.

  In addition, the image forming apparatus used in the image forming method of the present invention controls the number of rotations of a motor for rotating a fixing roller, so that the paper P passing between the heating roller 41 and the pressure roller 42 is used. The linear velocity of the (recording medium) can be changed. In the image forming apparatus used in the image forming method of the present invention, the linear velocity before the change is preferably 150 mm / second or more and 300 mm / second or less.

  When the linear velocity of the paper P is lowered, the amount of heat energy applied to the formed image (toner image) increases, and the glossiness of the formed image increases. When lowering the linear velocity, a speed that is at least half the normal linear velocity is preferable.

  In the image forming apparatus capable of changing the linear velocity of the paper P passing between the heating roller and the pressure roller, when the linear velocity is lowered, the toner image is favorably applied to the paper P due to the occurrence of the offset. It may be difficult to fix. However, in the image forming method of the present invention, such an image forming apparatus and a toner described later are used in combination, so that the toner image can be satisfactorily fixed on the paper P regardless of the linear velocity of the paper P. Can do.

  The paper discharge unit 5 is formed by recessing the top of the device main body 1a of the color printer 1, and a paper discharge tray 51 for receiving the discharged paper P is formed at the bottom of the concave portion. .

  The color printer 1 forms an image on the paper P according to the image forming operation as described above. In the image forming apparatus capable of changing the linear velocity of the paper P passing between the heating roller 41 and the pressure roller 42, the toner image is applied to the paper P due to the occurrence of offset when the linear velocity is decreased. It may be difficult to fix well. However, by using the color printer 1 having such a configuration in combination with the toner described later, the toner image can be satisfactorily fixed on the paper P regardless of the linear speed of the paper P.

[Electrostatic latent image developing toner]

In the image forming method of the present invention, an electrostatic latent image developing toner comprising toner core particles containing a binder resin and a shell layer covering the surface of the toner core particles is used. The glass transition point (Tg ₁ ) of the binder resin and the glass transition point (Tg ₂ ) of the resin constituting the shell layer satisfy a predetermined relationship and are within a predetermined range.

Further, the storage elastic modulus (G ′ _c ) at 110 ° C. of the toner core particles is 2.0 × 10 ² Pa or more, and the storage elastic modulus (G ′ _t ) of the toner at 100 ° C. is 5.0 × 10 ^2. It is preferable that it is Pa or more. When a toner having G ′ _c and G ′ _t within such a range is used in the above-described image forming method, the toner image is particularly easily fixed on the recording medium. The storage elastic modulus can be measured using a measuring device such as MCR301 (Anton Pearl Japan Co., Ltd.).

  The toner may have an external additive attached to the surface as necessary. In addition, the toner can be mixed with a desired carrier and used as a two-component developer. Hereinafter, the toner core particle and shell layer constituting the toner, the external additive, the carrier used when the toner is used as the two-component developer, and the method for producing the electrostatic latent image developing toner will be described in order.

[Toner core particles]
The toner core particles constituting the toner contain a binder resin having a glass transition point (Tg ₁ ) of 25 ° C. or more and 51 ° C. or less. The toner core particles may contain components such as a colorant, a release agent, a charge control agent, and magnetic powder, if necessary, in addition to the binder resin. Hereinafter, the binder resin, the colorant, the release agent, the charge control agent, and the magnetic powder, which are essential or optional components of the toner core particles, will be described in order.

(Binder resin)
The binder resin contained in the toner core particles is not particularly limited as long as the glass transition point (Tg ₁ ) is 25 ° C. or higher and 51 ° C. or lower.

  Specific examples of the binder resin include styrene resin, acrylic resin, styrene acrylic resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyester resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether. And thermoplastic resins such as styrene resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, a styrene acrylic resin and a polyester resin are preferable, and a polyester resin is more preferable in terms of dispersibility of the colorant in the toner, toner chargeability, and toner fixing property to the paper. Hereinafter, the styrene acrylic resin and the polyester resin used in this embodiment will be described.

  The styrene acrylic resin is a copolymer of a styrene monomer and an acrylic monomer. Specific examples of the styrene monomer include styrene, α-methylstyrene, vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-ethylstyrene. Specific examples of the acrylic monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, meta Examples include (meth) acrylic acid alkyl esters such as methyl acrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate.

  When a polyester resin is used as the binder resin, it is easy to prepare a toner that can be satisfactorily fixed over a wide temperature range and has excellent color developability. As the polyester resin, those obtained by condensation polymerization or co-condensation polymerization of a divalent or trivalent or higher alcohol component and a divalent or trivalent or higher carboxylic acid component can be used. The components used when synthesizing the polyester resin include the following alcohol components and carboxylic acid components.

  Specific examples of the divalent or trivalent or higher alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A Bisphenols such as hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sol Tan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2, Examples include trivalent or higher alcohols such as 4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

  Specific examples of the divalent or trivalent or higher carboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, Sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid Divalent carboxylic acids such as acids, isododecyl succinic acid, alkyl such as isododecenyl succinic acid or alkenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5- Benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4- Phthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid Examples thereof include trivalent or higher carboxylic acids such as acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empole trimer acid. As these divalent or trivalent or higher carboxylic acid components, acid halides, acid anhydrides, and ester-forming derivatives of lower alkyl esters may be used. Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

The glass transition point (Tg ₁ ) of the binder resin contained in the toner core particles of the toner used in the image forming method of the present invention is 25 ° C. or more and 51 ° C. or less. When Tg ₁ is too high, the toner is difficult to fix on the recording medium at a low temperature. If Tg ₁ is too low, the toner may aggregate during storage at high temperature, and the heat-resistant storage stability of the toner tends to be impaired.

  The glass transition point of the binder resin can be obtained from the change point of specific heat using a differential scanning calorimeter (DSC). More specifically, it can be determined by measuring the endothermic curve of the binder resin using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device. Place 10 mg of measurement sample in an aluminum pan, use an empty aluminum pan as a reference, and measure under the conditions of a measurement temperature range of 25 ° C to 200 ° C, a heating rate of 10 ° C / min, and the ambient environment at normal temperature and humidity. The glass transition point can be determined from the endothermic curve of the binder resin obtained.

  The number average molecular weight (Mn) of the binder resin is preferably from 1,300 to 3,500, more preferably from 1,500 to 2,000. The weight average molecular weight (Mw) of the binder resin is preferably 3,000 or more and 100,000 or less, and more preferably 4,500 or more and 50,000 or less. The molecular weight distribution (Mw / Mn) represented by the ratio of the number average molecular weight (Mn) and the mass average molecular weight (Mw) is preferably from 3.0 to 50.0. By setting the molecular weight distribution of the binder resin in such a range, it is easy to obtain a toner having excellent low-temperature fixability. The number average molecular weight (Mn) and the mass average molecular weight (Mw) of the binder resin can be measured using gel permeation chromatography.

(Coloring agent)
The toner core particles may contain a colorant as necessary. As the colorant, a known pigment or dye can be used in accordance with the color of the toner particles. Specific examples of suitable colorants that can be added to the toner include the following colorants.

  Examples of the black colorant include carbon black. Specifically, Raven 1060, 1080, 1170, 1200, 1250, 1255, 1500, 2000, 3500, 5250, 5750, 7000, 5000, ULTRAII, 1190 ULTRAII, manufactured by Columbian Carbon; Black PearlsL, Moguul, manufactured by Cabot -L, Regal 400R, 660R, 330R, Monarch 800, 880, 900, 1000, 1300, 1400; Color Black FW1, FW2, FW200, 18, S160, S170, Special Black 4, 4A, 6, Printex35, U manufactured by Degussa 140U, V, 140V; No. manufactured by Mitsubishi Chemical Corporation. 25, 33, 40, 47, 52, 900, 2300, MCF-88, MA600, 7, 8, 100. Further, as the black colorant, a colorant that is toned to black using a colorant such as a yellow colorant, a magenta colorant, and a cyan colorant, which will be described later, can also be used. Examples of the color toner colorant include a yellow colorant, a magenta colorant, and a cyan colorant.

  Examples of yellow colorants include condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and allylamide compounds. Specifically, C.I. I. Pigment Yellow 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 and 194.

  Examples of the magenta colorant include condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. Specifically, 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 and 254.

  Examples of cyan colorants include copper phthalocyanine compounds, copper phthalocyanine derivatives, anthraquinone compounds, and basic dye lake compounds. Specifically, C.I. I. Pigment blue 1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, 66.

  These colorants can be used alone or in combination. The amount of the colorant used is preferably 3% by mass or more and 15% by mass or less based on the mass of the toner.

(Release agent)
The toner core particles may contain a release agent for the purpose of improving the toner fixing property and offset resistance. The type of release agent is not particularly limited as long as it is conventionally used as a release agent for toner.

  Suitable mold release agents include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymers, polyolefin waxes, microcrystalline waxes, paraffin waxes, and aliphatic hydrocarbon waxes such as Fischer-Tropsch wax; oxidized polyethylene waxes, and Oxides of aliphatic hydrocarbon waxes such as block copolymers of oxidized polyethylene waxes; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, and rice wax; beeswax, lanolin, and whale Animal waxes such as waxes; mineral waxes such as ozokerite, ceresin, and vetrolactam; waxes based on fatty acid esters such as montanate ester wax and castor wax; Some fatty acid esters such as acid carnauba wax, or wax deoxidizing the like all.

  Specifically, the amount of the release agent used is preferably 8% by mass or more and 20% by mass or less, and more preferably 10% by mass or more and 15% by mass or less with respect to the mass of the toner. When the amount of the release agent used is too small, a desired effect may not be obtained with respect to the suppression of the occurrence of offset and image smearing regarding the formed image. When the amount of the release agent used is excessive, the heat resistant storage stability of the toner may be deteriorated due to fusion between the toners.

(Charge control agent)
The toner core particles may contain a charge control agent as required. The charge control agent improves the stability of the charge level of the toner and the charge rise characteristic that is an indicator of whether the toner can be charged to a predetermined charge level in a short time. Used for gaining purposes. When developing with positively charged toner, a positively chargeable charge control agent is used. When developing with negatively charged toner, a negatively chargeable charge control agent is used.

  The type of charge control agent can be appropriately selected from charge control agents conventionally used in toners. Specific examples of the positively chargeable charge control agent include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1, 2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, Azine compounds such as phthalazine, quinazoline and quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azine Violet BO, Azine Direct dyes composed of azine compounds such as N-Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, and Azin Deep Black 3RL; Nigrosine such as Nigrosine, Nigrosine Salt, Nigrosine Derivative Compounds; Acid dyes consisting of nigrosine compounds such as nigrosine BK, nigrosine NB, nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; 4 such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride A class ammonium salt is mentioned. Among these positively chargeable charge control agents, a nigrosine compound is particularly preferable in that a quicker charge rising property can be obtained. These positively chargeable charge control agents can be used in combination of two or more.

  A resin having a quaternary ammonium salt, carboxylate, or carboxyl group as a functional group can also be used as a positively chargeable charge control agent. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, and a carboxylate Styrene resin having carboxylate, acrylic resin having carboxylate, styrene acrylic resin having carboxylate, polyester resin having carboxylate, styrene resin having carboxyl group, acrylic resin having carboxyl group, carboxyl group Styrene acrylic resin having a carboxyl group and polyester resin having a carboxyl group. The molecular weight of these resins is not particularly limited as long as the object of the present invention is not impaired, and may be an oligomer or a polymer.

  Specific examples of the negatively chargeable charge control agent include organometallic complexes and chelate compounds. Examples of organometallic complexes and chelate compounds include acetylacetone metal complexes such as aluminum acetylacetonate and iron (II) acetylacetonate, and salicylic acid metal complexes such as chromium 3,5-di-tert-butylsalicylate. A salicylic acid metal salt is preferable, and a salicylic acid metal complex or a salicylic acid metal salt is more preferable. These negatively chargeable charge control agents can be used in combination of two or more.

  The use amount of the positively or negatively chargeable charge control agent is typically 1.5 parts by mass or more and 15 parts by mass or less, preferably 2.0 parts by mass when the total amount of the toner is 100 parts by mass. The amount is more preferably 8.0 parts by mass or less, and particularly preferably 3.0 parts by mass or more and 7.0 parts by mass or less.

(Magnetic powder)
The toner core particles may contain magnetic powder as necessary. Examples of suitable magnetic powders include irons such as ferrite and magnetite; ferromagnetic metals such as cobalt and nickel; alloys containing iron and / or ferromagnetic metals; compounds containing iron and / or ferromagnetic metals A ferromagnetic alloy subjected to a ferromagnetization treatment such as heat treatment; chromium dioxide.

  The particle size of the magnetic powder is preferably 0.1 μm or more and 1.0 μm, and more preferably 0.1 μm or more and 0.5 μm or less. When magnetic powder having a particle diameter in such a range is used, it is easy to uniformly disperse the magnetic powder in the binder resin.

  When the toner is used as a one-component developer, the magnetic powder is preferably used in an amount of 35 to 60 parts by weight, more preferably 40 to 60 parts by weight, based on 100 parts by weight of the toner. When toner is used as a two-component developer, the amount of magnetic powder used is preferably 20% by mass or less and more preferably 15% by mass or less with respect to 100 parts by mass of the toner.

[Shell layer]
Shell layer constituting the toner has a glass transition point (Tg ₂₎ is, and at temperatures above 55 ℃, and, ^{_{[- 0.007 (Tg 1) 2 +0.182}} (Tg 1) +79.735 ] ° C. or less Made of material.

The material of the shell layer is not particularly limited as long as Tg ₂ is in such a range. As the material for the shell layer, a resin is preferable because Tg ₂ can be easily adjusted, and one or more selected from the group consisting of (meth) acrylic resins, styrene- (meth) acrylic resins, and polyester resins. It is more preferable to use a resin. Then, the Tg ₂ since easily adjusted to a value within a predetermined range, as the resin constituting the shell layer (meth) acrylic resin, and styrene - (meth) acrylic resin is more preferable. As the polyester resin suitably used as the resin constituting the shell layer, the same kind of resin as the binder resin can be used. Hereinafter, a (meth) acrylic resin and a styrene- (meth) acrylic resin used as a resin that can constitute the shell layer will be described.

((Meth) acrylic resin)
When a (meth) acrylic resin is used as the resin constituting the shell layer, the (meth) acrylic resin is a resin obtained by polymerizing a monomer containing at least a (meth) acrylic monomer. (Meth) acrylic monomers used for the preparation of (meth) acrylic resins include (meth) acrylic acid; alkyls such as methyl (meth) acrylate, ethyl (meth) acrylate, and propyl (meth) acrylate ( (Meth) acrylates; such as (meth) acrylamide, N-alkyl (meth) acrylamide, N-aryl (meth) acrylamide, N, N-dialkyl (meth) acrylamide, and N, N-diaryl (meth) acrylamide (meta) ) Acrylamide compounds.

  The (meth) acrylic resin preferably contains a carboxyl group contained in a unit derived from (meth) acrylic acid as an acidic group. In this case, the acid value of the (meth) acrylic resin can be adjusted by increasing or decreasing the amount of (meth) acrylic acid used when preparing the (meth) acrylic resin.

  When the (meth) acrylic resin is a resin obtained by copolymerizing other monomers other than the (meth) acrylic monomer, the other monomers include ethylene, propylene, butene-1, pentene-1, hexene-1, Olefins such as heptene-1 and octene-1; allyl esters such as allyl acetate, allyl benzoate, allyl acetoacetate, and allyl lactate; hexyl vinyl ether, octyl vinyl ether, ethylhexyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl Vinyl ether, chloroethyl vinyl ether, 2-ethylbutyl vinyl ether, dimethylaminoethyl vinyl ether, diethylaminoethyl vinyl ether, benzyl vinyl ether, vinyl phenyl ether, vinyl tolyl ether, vinyl Vinyl ethers such as rolphenyl ether, vinyl-2,4-dichlorophenyl ether, and vinyl naphthyl ether; vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl diethyl acetate, vinyl chloroacetate, vinyl Examples include vinyl esters such as methoxyacetate, vinylbutoxyacetate, vinylphenylacetate, vinylacetoacetate, vinyl lactate, vinyl benzoate, vinyl salicylate, vinyl chlorobenzoate, and vinyl naphthoate.

  The (meth) acrylic resin may be one in which a chargeable functional group such as a quaternary ammonium salt is introduced, as in the case of the resin that can be used as the charge control agent.

  The total content of the units derived from the (meth) acrylic monomer contained in the (meth) acrylic resin is not particularly limited as long as the object of the present invention is not impaired, but is preferably 80% by mass or more, and 90% by mass. % Or more is more preferable, and 100 mass% is particularly preferable.

(Styrene- (meth) acrylic resin)
When a styrene- (meth) acrylic resin is used as the resin constituting the shell layer, the styrene- (meth) acrylic resin is a copolymer of at least a monomer containing a styrene monomer and a (meth) acrylic monomer. It is resin obtained.

  Styrene monomers used for the preparation of styrene- (meth) acrylic resins include styrene, α-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-ethylstyrene, 2, 4-dimethylstyrene, pn-butylstyrene, p-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, and p-chlorostyrene.

  The (meth) acrylic monomer used for the preparation of the styrene- (meth) acrylic resin is the same as the (meth) acrylic monomer used for the preparation of the (meth) acrylic resin. Moreover, it is preferable that styrene- (meth) acrylic-type resin contains the carboxyl group contained in the unit derived from (meth) acrylic acid as an acidic group.

  In the case where the styrene- (meth) acrylic resin is a resin obtained by copolymerizing a styrene monomer and another monomer other than the (meth) acrylic monomer, examples of the other monomer are those in the (meth) acrylic resin. The same as other monomers other than the (meth) acrylic monomer.

  The total content of the units derived from the styrene monomer and the unit derived from the (meth) acrylic monomer contained in the styrene- (meth) acrylic resin is not particularly limited as long as the object of the present invention is not impaired. However, 80 mass% or more is preferable, 90 mass% or more is more preferable, and 100 mass or more is especially preferable.

  In addition, the styrene- (meth) acrylic resin may be one in which a chargeable functional group such as a quaternary ammonium salt is introduced, as in the case of the resin that can be used as the charge control agent.

As described above, the glass transition point of the material constituting the shell layer (Tg ₂₎ is at temperatures above 55 ℃, and, ^{_{[- 0.007 (Tg 1) 2 +0.182}} (Tg 1) +79.735 ] ° C. It is as follows.

Is the upper limit of Tg _2, wherein: ^{_{[- 0.007 (Tg 1) 2 +0.182}} (Tg 1) +79.735 ] is empirically derived as described below. Specifically, it is derived by the following method.

First, toner core particles including a plurality of binder resins having different Tg ₁ are prepared. Each of the obtained plural types of toner core particles is combined with a plurality of shell layers having different glass transition temperatures (Tg ₂ ) by about 1 ° C. to prepare a toner. The width for changing the Tg for the plurality of shell layers is not limited to about 1 ° C. For a large number of toners obtained in this manner, Tg ₁ and Tg ₂ that can fix the toner image satisfactorily even when the linear velocity for moving the recording medium in the image forming apparatus is reduced from the normal linear velocity. Check the combination with. For each Tg ₁ , the highest temperature (Tg ₂ ^max ) of Tg ₂ of the shell layer provided in the toner having a good toner image fixing result is obtained. Using software such as Microsoft (registered trademark) Excel (registered trademark), a plurality of coordinates (Tg) corresponding to the type of the binder resin on a plane having Tg ₁ as the horizontal axis and Tg ₂ as the vertical axis. ₁ , Tg ₂ ^max ) and approximating the plotted coordinates to a quadratic curve, the above-described equation regarding the upper limit of Tg ₂ is derived.

FIG. 2 shows the toner used in the image forming methods of Examples 1 to 10 using Microsoft (registered trademark) Excel (registered trademark) on a plane with Tg ₁ as the horizontal axis and Tg ₂ as the vertical axis. 4 is a graph plotting Tg ₁ and Tg ₂ for each toner. The graph of FIG. 2 shows an approximate curve obtained by approximating a plurality of plotted coordinates to a quadratic curve. Each toner of Examples 1 to 10, a toner core of each toner, a toner Tg ₂ is obtained by combining a plurality of shell layers differ by about 0.5 to 1.0 ° C., image Even when the linear velocity for moving the recording medium in the forming apparatus is decreased from the normal linear velocity, the toner having the highest Tg ₂ among the toners that can fix the toner image satisfactorily. From the graph shown in FIG. 2, a quadratic approximate expression related to the approximate curve was obtained using Microsoft (registered trademark) Excel (registered trademark), and the following equation (1) was obtained.
Tg ₂ = −0.007 (Tg ₁ ) ² +0.182 (Tg ₁ ) +79.735 (1)
Regarding the obtained quadratic approximate expression, the R2 value was 0.99 or more, and Tg ₁ and Tg ₂ related to the toners of Examples 1 to 10 were in good agreement with the approximate expression.

FIG. 3 shows the toner used in the image forming methods of Examples 1 to 15 and Comparative Examples 1 to 9, using Microsoft (registered trademark) Excel (registered trademark), Tg ₁ as the horizontal axis, and Tg. ₂ is a graph in which Tg ₁ and Tg ₂ for each toner are plotted on a plane with ₂ as the vertical axis. As shown in FIG. 3, the image forming methods of Examples 3, 13 and Comparative Example 7, the image forming methods of Examples 6, 14, and Comparative Example 8, and Examples 9, 15 and Comparative Example 9 For the toners having the same Tg ₁ used in the image forming method, the toner having a Tg ₂ higher than the above approximate curve (the toner used in the comparative example) does not have a desired fixing property. I understand that.

As described above, the upper limit of the glass transition point (Tg ₂ ) of the material constituting the shell layer is defined as [−0.007 (Tg ₁ ) ² +0.182 (Tg ₁ ) +79.735] ° C. or less. The When a toner having a shell layer made of a material whose Tg ₂ is a temperature within the above range is used, an image forming apparatus capable of changing the linear velocity of the recording medium passing between the heating roller and the pressure roller is used. Thus, when forming an image, the toner image can be satisfactorily fixed on the recording medium regardless of the linear velocity of the recording medium. If Tg ₂ is too low, toner particles may aggregate in a high temperature environment. If Tg ₂ is too high, it may be difficult to fix the toner satisfactorily at a low temperature. Tg ₂ can be measured using a method similar to the method for measuring the glass transition point of the binder resin.

  The number average molecular weight (Mn) of the resin constituting the shell layer is preferably from 2,000 to 3,500, and more preferably from 2,500 to 3,000. The mass average molecular weight (Mw) of the resin constituting the shell layer is preferably 10,000 or more and 300,000 or less, and more preferably 50,000 or more and 200,000 or less. The molecular weight distribution (Mw / Mn) represented by the ratio between the number average molecular weight (Mn) and the mass average molecular weight (Mw) is preferably from 5 to 85. The number average molecular weight (Mn) and the mass average molecular weight (Mw) of the resin constituting the shell layer can be measured using gel permeation chromatography.

  The mass of the shell layer with respect to the total mass of the toner particles is preferably 5% by mass or more and 35% by mass or less. When the mass of the shell layer is too small, it is difficult to obtain a toner having excellent heat resistant storage stability. When the mass of the shell layer is excessive, it is difficult to satisfactorily fix the toner image on the recording medium at a low temperature.

(External additive)
The surface of the toner may be treated with an external additive as necessary. In the specification of the present application, particles treated with an external additive are referred to as “toner mother particles”. The type of external additive can be appropriately selected from external additives conventionally used for toners. Specific examples of suitable external additives include silica and metal oxides such as alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. These external additives can be used in combination of two or more.

  The particle diameter of the external additive is preferably 0.01 μm or more and 1.0 μm or less.

  Typically, the amount of the external additive used is preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.2 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the toner base particles.

[Carrier]
In the image forming method of the present invention, a two-component developer in which a toner and a desired carrier are mixed can also be used. When preparing a two-component developer, it is preferable to use a magnetic carrier.

  Suitable carriers include those in which a carrier core material is coated with a resin. Specific examples of the carrier core material include particles such as iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, and cobalt, and particles of alloys of these materials with manganese, zinc, and aluminum. , Particles like iron-nickel alloy, iron-cobalt alloy, titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, titanate Ceramic particles such as lead, lead zirconate and lithium niobate, particles of high dielectric constant materials such as ammonium dihydrogen phosphate, potassium dihydrogen phosphate and Rochelle salt, and the above magnetic particles dispersed in resin A resin carrier is mentioned.

  Specific examples of the resin covering the carrier core material include (meth) acrylic polymer, styrene polymer, styrene- (meth) acrylic copolymer, olefin polymer (polyethylene, chlorinated polyethylene, polypropylene). , Polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, polyester resin, unsaturated polyester resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, fluororesin (polytetrafluoroethylene, polychlorotrifluoroethylene, polyfluoride) Vinylidene), phenol resin, xylene resin, diallyl phthalate resin, polyacetal resin, and amino resin. These resins can be used in combination of two or more.

  The particle diameter of the carrier is a particle diameter measured using an electron microscope, preferably 20 μm or more and 120 μm or less, and more preferably 25 μm or more and 80 μm or less.

  The content of the toner in the two-component developer is preferably 3% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less with respect to the mass of the two-component developer.

[Method for producing toner for developing electrostatic latent image]
The method for producing the toner used in the image forming method of the present invention is not particularly limited. Hereinafter, a method for producing toner used in the image forming method of the present invention will be described, but the method for producing toner is not limited to the following method.

  As a method for producing the toner, an aggregation method is preferable because it is easy to obtain toner particles having a uniform shape and a shell layer having a uniform thickness is easily formed on the surface of the toner core particles. Hereinafter, a method for producing a toner for developing an electrostatic latent image using the aggregation method will be described.

The specific method of the aggregation method is not particularly limited, and various methods conventionally used as a toner production method can be applied. A suitable method for producing a toner for developing an electrostatic latent image using the aggregation method will be described in order by dividing it into the following steps (I) to (VI).
Step (I): A step of obtaining an aqueous medium dispersion (B) containing toner core particles by aggregating fine particles in the presence of an aggregating agent after obtaining an aqueous medium dispersion (A) containing fine particles containing a binder resin. ,
Step (II): The aqueous medium dispersion liquid (B) and the fine aqueous medium dispersion liquid (C) containing the resin constituting the shell layer are mixed to form the toner core particles and the fine particles containing the resin constituting the shell layer. Obtaining an aqueous medium dispersion (D) comprising:
Step (III): A step of heating the aqueous medium dispersion (D) to obtain an aqueous medium dispersion (E) containing toner core particles provided with coating layers made of fine particles containing a resin constituting the shell layer on the surface thereof, And step (IV): a step of heating the aqueous medium dispersion (E) to form a shell layer on the surface of the toner core particles.

The method for producing a toner for developing an electrostatic latent image may include the following steps (V) to (VII) as necessary, in addition to the steps (I) to (IV).
(V): A cleaning step of cleaning toner particles or toner base particles.
(VI): A drying step of drying the toner particles or toner base particles.
(VII): an external addition step of attaching an external additive to the surface of the toner base particles.

  Hereinafter, steps (I) to (VII) will be described in order.

  The method for preparing the fine particle aqueous medium dispersion (A) containing the binder resin used in the step (I) is not particularly limited, and a well-known method can be adopted. After roughly pulverizing the composition containing the binder resin, the coarsely pulverized product is heated to a temperature higher by 10 ° C. or more than the softening point of the binder resin in an aqueous medium. A dispersion in an aqueous medium containing fine particles containing a binder resin can be obtained by applying a strong shearing force using a machine made by Kikai Kogyo Co., Ltd.) or a pressure discharge type dispersing machine.

  A surfactant can be contained in the aqueous medium dispersion of fine particles containing the binder resin. When the surfactant is contained in the aqueous medium dispersion of fine particles containing the binder resin, the fine particles containing the binder resin can be stably dispersed in the aqueous medium. The surfactant that can be contained in the aqueous medium dispersion of fine particles containing the binder resin can be appropriately selected from the group consisting of an anionic surfactant, a cationic surfactant, and a nonionic surfactant.

  In step (I), an aqueous medium dispersion (A) containing fine particles containing a binder resin, and an aqueous medium dispersion containing fine particles of a release agent, and an aqueous medium dispersion containing fine particles of a colorant, if necessary. After mixing with the liquid, fine particles in the aqueous medium are aggregated with an aggregating agent to form toner core particles. A method for preparing an aqueous medium dispersion containing fine particles of a release agent and an aqueous medium dispersion containing fine particles of a colorant is not particularly limited, and a known method can be adopted.

  Examples of the flocculant include inorganic metal salts, inorganic ammonium salts, and divalent or higher metal complexes. Inorganic metal salts include metal salts such as sodium sulfate, sodium chloride, calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; inorganics such as polyaluminum chloride and polyaluminum hydroxide A metal salt polymer is mentioned. Examples of inorganic ammonium salts include ammonium sulfate, ammonium chloride, and ammonium nitrate. Further, a quaternary ammonium salt type cationic surfactant, polyethyleneimine can also be used as a flocculant.

  As the flocculant, a divalent metal salt and a monovalent metal salt are preferably used. A divalent metal salt and a monovalent metal salt are preferably used in combination. Since the divalent metal salt and the monovalent metal salt have different aggregation speeds of the fine particles, when used together, the particle diameter of the obtained toner core particles is controlled and the particle size distribution is easily sharpened.

  The addition amount of the flocculant is preferably 0.1 mmol / g or more and 10 mmol / g or less with respect to the solid content of the aqueous medium dispersion containing fine particles. Moreover, it is preferable to adjust suitably the addition amount of a flocculant according to the kind and quantity of surfactant which are contained in the aqueous medium dispersion liquid containing microparticles | fine-particles.

  The conditions for adding the aggregating agent are not particularly limited as long as the aggregation of the fine particles proceeds well. The flocculant is preferably added at a temperature not higher than the glass transition point of the binder resin after adjusting the pH of the aqueous medium dispersion containing fine particles. When the polyester resin is included as the binder resin, it is preferable to add the flocculant after adjusting the pH of the aqueous medium dispersion containing fine particles to the alkali side, preferably pH 10 or more.

  After aggregation has progressed until the toner core particles, which are fine particle aggregates, have a desired particle size, it is preferable to add an aggregation terminator. Examples of the aggregation terminator include sodium chloride and sodium hydroxide. In this way, an aqueous medium dispersion (B) containing toner core particles can be obtained.

  In the step (II), the aqueous medium dispersion (B) obtained in the step (I) and the aqueous medium dispersion (C) containing fine particles containing a resin constituting the shell layer are mixed to obtain toner core particles. Then, an aqueous medium dispersion (D) containing fine particles containing a resin constituting the shell layer is obtained. The method for mixing the aqueous medium dispersion (B) and the aqueous medium dispersion (C) is not particularly limited. The method for preparing the aqueous dispersion (C) of fine particles containing a resin constituting the shell layer is not particularly limited, and a known method can be adopted.

  Before mixing the aqueous medium dispersion (B) and the aqueous medium dispersion (C), a basic substance is added to the aqueous medium dispersion (C) in advance in order to stabilize the dispersion state of the fine particles in the dispersion. Thus, it is preferable to adjust the pH of the aqueous medium dispersion (C) to about 8.

  In the step (III), the aqueous medium dispersion (D) obtained in the step (II) is heated to disperse the aqueous medium containing toner core particles having a coating layer made of fine particles containing a resin constituting the shell layer on the surface thereof. A liquid (E) is obtained. The temperature for heating the aqueous medium dispersion (D) is preferably 50 ° C. or higher and 65 ° C. or lower. By heating the aqueous medium dispersion (D) at a temperature within such a range, a coating layer composed of fine particles containing a resin constituting the shell layer can be uniformly formed on the surface of the toner core particles.

  In step (IV), the aqueous medium dispersion (E) obtained in step (III) is heated to form a shell layer on the surface of the toner core particles to obtain an aqueous medium dispersion of toner particles or toner base particles. Before the aqueous medium dispersion (E) is heated, it is preferable to add the above-mentioned aggregation terminator to the aqueous medium dispersion (E) after the formation of the coating layer has progressed to a desired degree. Examples of the aggregation terminator include sodium chloride and sodium hydroxide.

The temperature at which the aqueous medium dispersion (E) is heated is preferably from the glass transition point (Tg ₂ ) to 90 ° C. of the resin constituting the shell layer. By heating the aqueous medium dispersion (G) at a temperature within such a range, the coating layer can be favorably formed, and the toner core particles can be satisfactorily covered with the shell layer.

  The toner particles or toner base particles obtained in the step (IV) are washed with water in the (V) washing step as necessary. The washing method is not particularly limited, and the toner particles or toner base particles are recovered as a wet cake by solid-liquid separation from the aqueous medium dispersion containing toner particles or toner base particles, and the obtained wet cake is used with water. And a method of precipitating particles in an aqueous medium dispersion containing toner particles or toner base particles, replacing the supernatant with water, and redispersing the toner particles or toner base particles in water after the replacement. It is done.

  The toner particles or toner base particles obtained in the step (IV) are dried through a (VI) drying step as necessary. The method for drying the toner particles or toner base particles is not particularly limited. Suitable drying methods include methods using a dryer such as a spray dryer, fluidized bed dryer, vacuum freeze dryer, and vacuum dryer. Among these methods, a method using a spray dryer is more preferable because aggregation of toner particles during drying is easily suppressed. When the particles recovered in the step (IV) are used as toner mother particles, a dispersion of an external additive such as silica is added to the toner mother particles together with an aqueous medium dispersion containing the toner mother particles using a spray dryer. By spraying, the external additive can be attached to the surface of the toner base particles.

  The toner may be one having an external additive attached to the surface as necessary. In step (VII), particles collected through the above step are used as toner base particles, and an external additive is attached to the surface of the toner base particles. A method for attaching the external additive to the surface of the toner base particles is not particularly limited. As a suitable method, there is a method of mixing by using a mixer such as a Henschel mixer or a Nauter mixer, adjusting the conditions so that the external additive is not buried in the surface of the toner base particles.

  In the image forming method of the present invention described above, since the electrostatic latent image developing toner is used, an image forming apparatus capable of changing the linear velocity of the recording medium passing between the heating roller and the pressure roller is provided. When an image is formed using the toner image, the toner image can be satisfactorily fixed on the recording medium regardless of the linear velocity of the recording medium. Further, the toner described above used in the image forming method of the present invention is excellent in heat resistant storage stability.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to the scope of the examples.

[Preparation Example 1]
(Preparation of polyester resin fine particle dispersion)
Polyester resin fine particle dispersions A to L were prepared according to the following method.
As the polyester resin used for the preparation of the polyester resin fine particle dispersion, a polyester resin having physical property values described in Tables 1 and 2 prepared by appropriately changing the blending ratio of the following monomers a to d was used.
Monomer a: Polyoxypropylene (2,2) -2,2-bis (4-hydroxyphenyl) propane monomer b: Polyoxyethylene (2,0) -2,2-bis (4-hydroxyphenyl) ) Propane monomer c: fumaric acid monomer d: trimellitic acid

  10 parts by mass of coarsely pulverized polyester resin having an average particle size of about 400 μm obtained by coarsely pulverizing a polyester resin using a turbo mill (manufactured by Turbo Kogyo Co., Ltd.) and 2 parts by mass of an anionic surfactant (sodium dodecylbenzenesulfonate) Then, 4 parts by mass of triethylamine and 84 parts by mass of ion-exchanged water were mixed using a stirring apparatus with a blade (RW20 digital (manufactured by IKA)) to prepare a slurry. Using the nanomizer (NV-200 (manufactured by Yoshida Kikai Kogyo Co., Ltd., added heating system)), the obtained slurry was repeatedly treated three times under the conditions of a heating system temperature of 160 ° C. and a processing pressure of 100 MPa. The polyester resin fine particle dispersion having a solid content concentration of 20% by mass was obtained.

[Preparation Example 2]
(Preparation of colorant fine particle dispersion)
15 parts by weight of a cyan colorant (copper phthalocyanine, CI Pigment Blue 15: 3), 2 parts by weight of an anionic surfactant (sodium dodecylbenzenesulfonate), 83 parts by weight of ion-exchanged water, Using a stirrer (RW20 digital (manufactured by IKA)), a dispersion treatment was carried out at 500 rpm for 30 minutes to prepare a colorant fine particle dispersion having a solid content concentration of 15% by mass.

[Preparation Example 3]
(Preparation of release agent fine particle dispersion)
The release agent (WEP-7 (manufactured by NOF Corporation)) was coarsely pulverized using a turbo mill (manufactured by Turbo Industry Co., Ltd.) to obtain a coarsely pulverized product having an average particle diameter of about 400 μm. 10 parts by mass of the coarsely pulverized release agent obtained, 2 parts by mass of an anionic surfactant (sodium dodecylbenzenesulfonate), and 88 parts by mass of ion-exchanged water were mixed with a bladed stirrer (RW20 digital (IKA). To prepare a slurry. Using the nanomizer (NV-200 (manufactured by Yoshida Kikai Kogyo Co., Ltd., added heating system)), the obtained slurry was repeatedly treated three times under the conditions of a heating system temperature of 160 ° C. and a processing pressure of 100 MPa. The release agent fine particle dispersion having a solid content concentration of 10% by mass was obtained.

[Preparation Example 4]
(Preparation of acrylic resin fine particle dispersion)
According to the following method, the amount of polymerization initiator used, the blending ratio of monomers, and the amount of chain transfer agent used are appropriately changed, and acrylic resin fine particle dispersions having physical properties shown in Tables 3 and 4 are used. A to N were prepared.

-Preparation of acrylic resin A 2000-ml flask equipped with a stirrer, a thermometer, a cooling tube, and a nitrogen introduction tube was used as a reaction vessel. As a solvent, styrene, butyl acrylate, and peroxide-based initiator t-butylperoxy-2-ethylhexanoate (manufactured by Arkema Yoshitomi Co., Ltd.) were added to a reaction vessel containing isobutanol. . After raising the internal temperature of the reaction vessel to 95 ° C. (polymerization temperature), the contents of the reaction vessel were stirred for 3 hours. Subsequently, t-butylperoxy-2-ethylhexanoate was further added into the reaction vessel. Thereafter, the contents in the reaction vessel were stirred at 95 ° C. for 3 hours to complete the polymerization reaction, thereby obtaining a resin fine particle dispersion. The obtained resin fine particle dispersion was freeze-dried to obtain an acrylic resin.

-Preparation of fine particle dispersion 200 g of coarsely pulverized product having an average particle size of about 400 μm obtained by coarsely pulverizing the obtained acrylic resin using a turbo mill (manufactured by Turbo Kogyo Co., Ltd.) and an anionic surfactant (lauryl) A slurry was prepared by mixing 20 g of sodium sulfate, Emar 0 (manufactured by Kao Corporation)) and 780 g of ion-exchanged water using a stirring device with a blade (RW20 digital (manufactured by IKA)). The obtained slurry was subjected to treatment three times under the conditions of a heating system temperature of 170 ° C. and a processing pressure of 150 MPa using a nanomizer (NV-200 (manufactured by Yoshida Kikai Kogyo Co., Ltd., added heating system)). Then, an acrylic resin fine particle dispersion having a solid content concentration of 20% by mass was obtained.

[Examples 1 to 15 and Comparative Examples 1 to 9]
Toners used in the image forming methods of Examples 1 to 15 and Comparative Examples 1 to 9 were prepared according to the following procedure.
[Step (I)]
In a 2 L round bottom flask made of stainless steel, 480 g of a polyester resin fine particle dispersion of the types shown in Tables 5 to 7, as a binder resin, 90 g of a release agent fine particle dispersion, 40 g of a pigment dispersion, and a concentration of 25 mass. A 48% aqueous solution of sodium lauryl sulfate (Emar 0 (manufactured by Kao Corporation)) and 542 g of ion-exchanged water were added and mixed at 25 ° C. Next, the mixture in the flask was stirred at a rotation speed of 100 rpm using a stirring blade. The pH of the mixture in the flask was adjusted to 8 using an aqueous sodium hydroxide solution, and the mixture was stirred for 10 minutes. Thereafter, 39 g of a magnesium chloride hexahydrate aqueous solution (flocculating agent) having a concentration of 50% by mass was dropped into the flask over 5 minutes. Next, the mixture in the flask was heated at a rate of 0.2 ° C./min, and the number average particle diameter of the fine particle aggregate measured using Multisizer 3 (manufactured by Beckman Coulter) was 4.5 μm. The temperature was continued until After the number average particle diameter of the fine particle aggregate reached 4.5 μm, the rotation speed of the stirring blade was changed to 200 rpm, and the mixture in the flask was heated to 55 ° C. at a rate of 0.2 ° C./min. . After the temperature is raised to 55 ° C., the mixture is stirred at the same temperature for 1 hour at 200 rpm to unite the toner components contained in the fine particle aggregate and control the shape of the fine particle aggregate into a spherical shape. A dispersion was obtained. For the toner used in the image forming method of Example 1, the average circularity of the toner core particles contained in the toner core particle dispersion obtained in step (I) was 0.932. The average circularity was measured using FPIA-3000 (manufactured by Sysmec Corporation).

(Measurement of storage elastic modulus (G ′ _c ) of toner core particles at 110 ° C.)
Next, for the toner core particles contained in the obtained toner core particle dispersion, the storage elastic modulus (G ′ _c ) of the toner core particles at 110 ° C. was measured according to the following procedure. In addition, as a method for obtaining toner core particles from the toner core particle dispersion, steps similar to the toner mother particle cleaning step and the drying step described later were performed using a part of the toner core particle dispersion. Tables 5 to 7 show the measurement results of the storage elastic modulus (G ′ _c ) of the toner core particles at 110 ° C.

<Method for measuring storage elastic modulus (G ′ _c )>
Using a measuring device (MCR301 (Anton Pearl Japan Co., Ltd.)), the storage elastic modulus was measured under the following conditions. 0.35 g of toner core particles were pressed with a tablet press at 60 kg · f / cm ² for 15 seconds to obtain disk-shaped pellets having a diameter of 20 mm and a thickness of about 1 mm. The obtained pellets were welded to a 20 mm diameter plate (DISPO_20). After welding, the pellet was cooled to 30 ° C. at a rate of 10 ° C./min while applying a constant strain of 0.01% to the pellet. Thereafter, the pellet was heated to 200 ° C. at a rate of 2 ° C./min while increasing the amount of strain applied to the pellet linearly from 0.01% to 5%. The storage elastic modulus of the toner core particles at 110 ° C. was measured from the data acquired through such a process.

[Steps (II) and (III)]
2 g of 2N-hydrochloric acid aqueous solution was added to the toner core particle dispersion in the flask obtained in the step (I) to adjust the pH of the toner core particle dispersion to 4.5. After the pH adjustment, the mass of the solid content of the acrylic resin fine particle dispersion relative to the total mass of the solid content of the polyester resin fine particle dispersion, the release agent fine particle dispersion, and the pigment dispersion is the amount described in Tables 5-7. As described above, acrylic resin fine particle dispersions of the types shown in Tables 5 to 7 were added to the dispersion in the flask. After adding the acrylic resin fine particle dispersion, the contents of the flask were stirred for 15 minutes at a speed of 200 rpm. Thereafter, 1 g of 1-N sodium hydroxide aqueous solution was added to the flask. Next, the contents of the flask were heated to 60 ° C. at a rate of 0.2 ° C./min while stirring at a rate of 200 rpm. After the temperature rise, the contents of the flask were stirred at 200 rpm for 1 hour at the same temperature to obtain toner core particles whose surfaces were coated with acrylic resin fine particles.

[Step (IV)]
3 g of 2N-hydrochloric acid aqueous solution was added to the contents of the flask to adjust the pH of the contents of the flask to 3. Thereafter, the contents of the flask were heated to 69 ° C. at a rate of 0.5 ° C./min while stirring at a stirring rate of 200 rpm. After the temperature increase, the contents of the flask were stirred at 200 rpm for 2 hours at the same temperature. Thereafter, the contents of the flask were cooled to 25 ° C. at a rate of 10 ° C./min, and a toner mother particle dispersion liquid containing toner mother particles having a shell layer on the surface was obtained.

[Step (V): Cleaning step]
Using a Buchner funnel, a wet cake of toner base particles was filtered from the toner base particle dispersion. The wet cake of toner base particles was again dispersed in ion exchange water to wash the toner. The same washing using the ion exchange water of the toner mother particles was repeated 5 times.

[Process (VI): Drying process]
The toner base particle wet cake was dried using a dryer (Perfect Oven PH-200 (manufactured by Espec Corp.)) at 40 ° C. for 72 hours to obtain toner base particles. Regarding the toner used in the image forming method of Example 1, the volume average particle size of the toner base particles obtained in the drying step was 5.5 μm, and the average circularity was about 0.969. The volume average particle diameter and average circularity of the toner base particles were measured using a particle size distribution measuring device (Microtrac UPA150 (Nikkiso Co., Ltd.)).

[Process (VII): External addition process]
The toner base particles obtained in each of Examples and Comparative Examples were subjected to external addition treatment.
Specifically, 100 parts by mass of toner base particles and 0.8 parts by mass of silica (silica 90G manufactured by Nippon Aerosil Co., Ltd. treated with silicon oil and aminosilane) and 5 L Henschel mixer (manufactured by Nippon Coke Industries, Ltd.) Was mixed for 5 minutes at a stirring speed of 30 m / sec to adhere the external additive to the surface of the toner base particles. Thereafter, the mixture after the external addition was sieved using a 300-mesh (aperture 48 μm) sieve to remove coarse powder from the mixture to obtain a toner.

(Measurement of storage elastic modulus (G ′ _t ) of toner particles at 100 ° C.)
With respect to the obtained toner particles, the storage elastic modulus (G ′ _t ) at 100 ° C. of the toner particles was measured by the same method as the measurement method of (G ′ _c ) described above.

<Evaluation of heat-resistant storage stability>
Using the toner prepared according to the above procedure, the heat resistant storage stability of the toner was evaluated according to the following method. The evaluation results are shown in Tables 5-7.
3 g of toner was weighed into a 20 cc plastic bottle and allowed to stand at room temperature for 24 hours. Thereafter, the plastic bottle containing the toner was allowed to stand in a constant temperature bath (DKN302 (manufactured by Yamato Scientific Co., Ltd.)) at 58 ° C. for 3 hours, and then cooled to room temperature. In accordance with the manual of the powder tester (manufactured by Hosokawa Micron Co., Ltd.), the toner is sieved using a sieve having a mesh size of 106 μm under the conditions of a rheostat scale of 3.5 and a time of 30 seconds. Asked. Preservability was evaluated according to the following criteria.
(Residual rate calculation formula)
Residual rate (%) = toner mass remaining on sieve / toner mass before sieving × 100
○ (Pass): Residual rate is 10 mass% or less.
X (failed): Residual rate exceeds 10 mass%.

  In the image forming methods of Examples 1 to 15 and Comparative Examples 1 to 9, the toner prepared according to the above procedure was mixed with a carrier and used as a two-component developer. A two-component developer used in the image forming method was prepared according to the following method.

[Preparation of two-component developer]
The toner and a positively charged toner carrier manufactured by Powdertech Co., Ltd. are mixed with a stirring mixer (Turbler mixer, T2F type (Shinmaru Enterprises Co., Ltd.) so that the mass of the toner with respect to the mass of the two-component developer becomes 10% by mass. The mixture was mixed for 30 minutes under normal temperature and humidity conditions to obtain a two-component developer.

<Fixability evaluation>
Regarding the image forming methods of Examples 1 to 15 and Comparative Examples 1 to 9, the fixability of the toner to the recording medium was evaluated using a two-component developer and an evaluation machine (printer). A printer remodeling machine (LS-C8650 (manufactured by Kyocera Document Solutions Co., Ltd.) from which the fixing device was removed) was used as an evaluation machine. An unfixed solid image of 2.5 cm × 2.5 cm was output on the recording medium so that the toner loading amount was 1.5 mg / cm ² . Next, the fixing device of the printer is used as a fixing jig, and an unfixed solid image is fixed at a fixing temperature 131 under two conditions of a linear speed of 262 mm / second (high speed condition) and a linear speed of 131 mm / second (low speed condition). Fixing was performed on the recording medium at ° C.

The evaluation of the fixability of the solid images of the respective recording media obtained under the high speed condition and the low speed condition was evaluated using the image density measured before and after the rubbing test.
In the rubbing test, a cylindrical metal weight having a mass of 1 kg and a diameter of 50 mm, covered with a cloth, is applied to a part of the solid image formed on the recording medium on which the solid image is fixed. 10 reciprocating frictions were performed. After the rubbing test, the image density of the solid image (density before the rubbing test) that was not subjected to the rubbing test and the image density (density after the rubbing test) of the solid image that was subjected to the rubbing test were measured using a spectral densitometer (X-rite). Measurement was performed using a spectroeye (manufactured by Gretag Macbeth). The fixing rate was calculated from the measured pre-rubbing density and post-rubbing density using the following formula, and the fixability was evaluated based on the following criteria.
Fixing rate [%] = (Density after rubbing test / Density before rubbing test) × 100
○: For solid images under high speed conditions and low speed conditions, the fixing ratio of both is 90% or more.
X: For a solid image under a high speed condition or a low speed condition, either one of the fixing ratios is less than 90%.

Further, in FIG. 3, for the toners used in the image forming methods of Examples 1 to 15 and Comparative Examples 1 to 9, Microsoft (registered trademark) Excel (registered trademark) is used, Tg ₁ is set on the horizontal axis, and Tg on a plane ₂ of a vertical axis shows a graph plotting the Tg ₁ and Tg ₂ for each toner.

According to Examples 1 to 15, the toner core particles containing the binder resin and the shell layer that covers the surface of the toner core particles, the glass transition point (Tg ₁ ) of the binder resin and the material constituting the shell layer. The glass transition point (Tg ₂ ) of the recording medium satisfies the predetermined relationship and is within the predetermined range, and the linear velocity of the recording medium passing between the heating roller and the pressure roller. It can be seen that, when used in combination with an image forming apparatus capable of changing the toner image, the toner image can be satisfactorily fixed on the recording medium regardless of the linear velocity of the recording medium.

In addition, according to Examples 1 to 15, the toner core particles including the binder resin and the shell layer covering the surface of the toner core particles are included, and the glass transition point (Tg ₁ ) of the binder resin and the shell layer are configured. It can be seen that the electrostatic latent image developing toner having a glass transition point (Tg ₂ ) satisfying a predetermined relationship and within a predetermined range is excellent in heat-resistant storage stability.

Also, as shown in FIG. 3, the image forming methods of Examples 3, 13, and Comparative Example 7, the image forming methods of Examples 6, 14, and Comparative Example 8, and Examples 9, 15, and Comparative Example The approximate curve (Tg ₂ = −0.007 (Tg ₁ ) ² +0.182 (Tg) expressed by the above-mentioned formula (1) for the toners having the same Tg ₁ used in the image forming method 9. ₁ ) It can be seen that the toner used in the comparative example having a Tg ₂ higher than +79.735) does not achieve the desired fixing property.

DESCRIPTION OF SYMBOLS 1 Color printer 1a Apparatus main body 2 Paper feed part 3 Image formation part 37 Latent image holding part 38 Exposure part 39 Charging part 4 Fixing part 41 Heating roller 42 Pressure roller 6 Conveyance roller 5 Paper discharge part 7 Image formation unit 71 Development part P Paper

Claims (6)

A heating roller that heats a recording medium to which a toner image formed using a toner for developing an electrostatic latent image is transferred, and a pressure roller that is disposed opposite to the heating roller and pressurizes the recording medium,
An image forming method using an image forming apparatus capable of changing a linear velocity of the recording medium passing between the heating roller and the pressure roller,
The electrostatic latent image developing toner comprises toner core particles containing a binder resin and a shell layer covering the surface of the toner core particles,
The glass transition point (Tg ₁ ) of the binder resin is 25 ° C. or more and 51 ° C. or less,
The glass transition point (Tg ₂ ) of the material constituting the shell layer is 55 ° C. or higher and [−0.0071 (Tg ₁ ) ² +0.182 (Tg ₁ ) +79.735] ° C. or lower. , Image forming method. The toner core particles have a storage elastic modulus at 110 ° C. of 2.0 × 10 ² Pa or more,
The image forming method according to claim 1, wherein the electrostatic latent image developing toner has a storage elastic modulus at 100 ° C. of 5.0 × 10 ² Pa or more.   The image forming method according to claim 1, wherein a ratio of the mass of the shell layer to the total mass of the toner for developing an electrostatic latent image is 5% by mass or more and 30% by mass or less. Consists of a toner core particle containing a binder resin and a shell layer covering the surface of the toner core particle,
The glass transition point (Tg ₁ ) of the binder resin is 25 ° C. or more and 51 ° C. or less,
The glass transition point of the material constituting the shell layer (Tg _2), and at temperatures above 55 ℃, and, ^{_{[- 0.007 (Tg 1) 2 +0.182}} (Tg 1) +79.735 ] ° C. or less , Toner for developing electrostatic latent image. The toner core particles have a storage elastic modulus at 110 ° C. of 2.0 × 10 ² Pa or more,
The electrostatic latent image developing toner according to claim 4, wherein a storage elastic modulus at 100 ° C. of the electrostatic latent image developing toner is 5.0 × 10 ² Pa or more.   6. The electrostatic latent image developing toner according to claim 4, wherein a ratio of a mass of the shell layer to a total mass of the electrostatic latent image developing toner is 5% by mass or more and 30% by mass or less.

Images