JP4432802B2 - Photofixing color toner, electrophotographic developer, and image forming method - Google Patents

Description

The present invention relates to an electrophotographic copying machine, a copying machine such as an electrophotographic printer or an electrostatic recording apparatus, a FAX, a light fixing color toner that can be used in a printer, an electrophotographic developer using the same, and an image forming method.
More specifically, the present invention relates to a light fixing light fixing color toner for fixing onto a recording sheet by light fixing, an electrophotographic developer using the same, and an image forming method.

  As an electrophotographic method, an electrostatic charge is applied to a photoconductive body (photosensitive drum, etc.), an electrostatic image is formed by irradiating the photoconductive body with various means, and then, In general, the latent image is developed and visualized using a fine powder called toner, and the toner powder image is transferred onto a recording medium such as paper and then fixed to obtain a printed matter.

  In this fixing step, the toner transferred onto the recording medium is melted by pressurization, heating, solvent vapor, light, etc., and fixed on the recording medium. Here, a photofixing method in which a toner image is irradiated with strong light to melt the toner has attracted attention for the reasons described in the following items (1) to (3).

(1) Since it is non-contact fixing, image bleeding, dust and the like do not occur in the fixing process, and resolution is not deteriorated.
(2) Since no heating is required, there is no waiting time after the device power is turned on, and a quick start is possible.
(3) Fixing is possible regardless of the material and thickness of the recording paper, such as glued paper, preprinted paper, and paper of different thickness.

Currently, the most common method in the light fixing method is a light fixing method using a xenon flash lamp as a light source. The process of fixing the toner on the recording paper in this photofixing method is as follows.
A toner image formed on the surface of a latent image carrier such as a photosensitive drum through exposure and development processes is transferred onto a recording medium. At this time, the toner adheres to the recording medium as an unfixed image and forms an image. For example, if the image is rubbed with a finger, the image is broken.
Next, when the toner image is irradiated with flash light such as a xenon flash, the toner absorbs the light energy of the flash light, softens by heating, and adheres to the recording paper.

  What is important in such optical fixing is to prevent a so-called fixing failure in which the fixed image is peeled off from the recording paper due to bending or rubbing of the recording paper, resulting in deterioration of image quality. In particular, the increase in the demand for color images in recent years is important because the thickness of the toner layer on the recording paper increases. Therefore, it is necessary to design the toner so that the light absorbing ability of the toner is increased, the melting of the toner is promoted at the time of fixing, and the toner sufficiently penetrates the recording paper and is firmly fixed.

  The xenon flash lamp generally used in the photofixing method has a light emission distribution over a wide range from ultraviolet to infrared, but the emission intensity is particularly strong in the near infrared region of 800 to 1000 nm and has high fixing performance. In order to obtain toner, it is required to establish a technique for efficiently absorbing light energy in this region.

In particular, the demand for color prints has increased in recent years, but the colorant used in the light fixing color toner has a sufficiently high light absorption efficiency in the visible light region, but has a low light absorption efficiency in the near infrared region. There is a demand for practical use of a light fixing color toner that can provide good fixability by this method.
In order to meet these requirements, compounds having light absorption ability in the near infrared region, such as aminium salts, indium oxide metal oxides, tin oxide metal oxides, zinc oxide metal oxides, cadmium stannate, A technique (for example, see Patent Documents 1 to 3) that enhances the ability to absorb flash light by incorporating a specific amide compound or the like into the toner as an infrared absorber has been generally used.

  However, even though the infrared absorber has a certain level of absorption ability, it has low ability to transmit the heat generated by infrared absorption to the binder resin (heat transfer ability) and satisfies the fixing property (flash fixing property) by flash light. In order to achieve this, it is necessary to add a large amount of an infrared absorber to the toner or lengthen the light irradiation time.

However, when the amount of the infrared absorber added is increased, the chargeability of the toner is affected. In addition, infrared absorbers may have red or dark green coloration, especially in the case of color toners, adding a large amount of infrared absorber to the toner to improve the infrared absorption ability will affect the toner hue. There was a problem of giving.
Further, the infrared absorber is very expensive, and there is a problem that the toner cost increases when the addition amount increases.

  The method of improving the fixing property by extending the irradiation time is not practical because it is contrary to the recent trend of high speed and energy saving. At present, the color tone as the color toner and the fixing property in the light fixing method are not compatible.

On the other hand, metal oxides such as hematite can be cited as materials having light absorption in the near-infrared region, but they all have a black color or a dark color close to it and cannot be used for color toners.
JP-A-7-191492 Japanese Patent Laid-Open No. 10-39535 JP-A-11-65167

  An object of the present invention is to solve the above problems. That is, an object of the present invention is to provide a photofixing color toner having good photofixability and color reproducibility, a developer using the same, and an image forming method.

The above-mentioned subject is achieved by the following present invention. That is, the present invention
<1> A light fixing color toner comprising an α-type hematite, a binder resin, and an infrared absorber.

<2> The light fixing color toner according to <1>, which includes a color material composed of a dye or a pigment.

<3> The light fixing color toner according to <2>, wherein the color material is a red or magenta color material.

<4> The light fixing color toner according to <1>, wherein the α-type hematite is contained in an amount of 1 to 10 parts by mass with respect to 100 parts by mass of the toner.

<5> The light fixing color toner according to <1>, wherein the infrared absorbing agent is contained in an amount of 0.01 to 10 parts by mass with respect to 100 parts by mass of the toner.

<6> The light fixing color toner according to <2> or <3>, wherein the coloring material is contained in an amount of 1 to 10 parts by mass with respect to 100 parts by mass of the toner.

<7> An electrophotographic developer comprising a carrier and the light fixing color toner according to <1>.

<8> A latent image forming step of forming an electrostatic latent image on the surface of the latent image carrier, and developing the electrostatic latent image formed on the surface of the latent image carrier with a developer having a light fixing color toner. A developing process for forming an image, a transfer process for transferring the toner image formed on the surface of the latent image carrier to the surface of the transfer target, and a toner image transferred on the surface of the transfer target being photofixed on the surface of the recording medium. And an image forming method including a fixing step of forming an image,
An image forming method, wherein the light fixing color toner is the light fixing color toner described in <1>.

<9> The image forming method, wherein the developer having the light fixing color toner is the electrophotographic developer according to <7>.

  Hereinafter, the present invention will be described in detail with respect to a light fixing color toner, an electrophotographic developer, and an image forming method.

(Light fixing color toner)
The light fixing color toner of the present invention is characterized by containing α-type hematite, a binder resin, and an infrared absorber.
The problem as described above occurs only by increasing the amount of the infrared absorber added in order to improve the infrared absorption efficiency.

By the way, in the infrared absorber, electrons in the molecule absorb infrared rays, and the electrons that have absorbed infrared rays enter a so-called excited state with high energy, and then release energy to return to the original state. The energy released at this time becomes heat and the toner is fixed by dissolving the binder resin. The α-type hematite of the present invention has not only the ability to absorb infrared rays, but also the above-mentioned infrared absorption. It has been found that the fixability can be improved by quickly absorbing the thermal energy absorbed by the agent and more efficiently releasing heat into the binder resin.
The reason is not necessarily clear, but it is presumed that the absorption region of light energy possessed by α-type hematite is the infrared region and the energy in this region is easily absorbed.

  In addition, the conventional infrared absorber toner is expensive because the infrared absorber is expensive. However, α-type hematite is less expensive than the conventional infrared absorber. Therefore, the manufacturing cost of the toner can be reduced.

  In addition, the toner of the present invention may contain a coloring material, a fixing auxiliary agent, a charge control agent, and the like as other components, in the same manner as known toners.

Next, various components constituting the toner of the present invention will be described in more detail.
<Α-type hematite>
The toner of the present invention includes α-type hematite (hematite). The α-type hematite (α-Fe ₂ O ₃ ) in the present invention is paramagnetic, has a red color, has a steel ball structure, has very little light absorption in the visible light region, and has a near infrared region of 700 to 2000 nm. Has an absorption peak.

A method for producing iron oxide as a material of α-type hematite is well known. For example, when maghematite (γ-Fe ₂ O ₃ ) having a melting point of 1570 ° C. is ignited in air, a steel ball shape having a red color The structure becomes hematite (α-Fe ₂ O ₃ ). The structure of hematite can be confirmed by dissolving the toner, collecting hematite, and analyzing the recovered hematite crystal structure with an X-ray diffraction apparatus.

The α-type hematite of the present invention can be easily pulverized by a known method, and the preferred volume average particle size is 1 μm or less. The volume average particle size of α-type hematite in the toner is preferably 1 μm or less, more preferably 0.8 μm or less, and still more preferably 0.6 μm or less and 0.05 μm or more. When the volume average particle size is 1 μm or less, the energy of the infrared absorbent can be efficiently transferred to the binder resin, and at the same time, the infrared rays irradiated to the toner can be efficiently absorbed.
Here, the volume average particle diameter refers to a value measured by a laser analysis type particle size distribution.

  The addition amount of α-type hematite is preferably in the range of 0.1 to 20 parts by mass and more preferably in the range of 1 to 10 parts by mass with respect to 100 parts by mass of the toner. If the addition amount is less than 0.1 parts by mass, the heat transfer and absorption performance of the light energy in the near infrared region of the toner may be reduced, leading to poor fixing. On the other hand, when the addition amount exceeds 20 parts by mass, although the photofixability is good, problems such as charging failure and hue change may be caused.

<Infrared absorber>
In order for the toner in the present invention to obtain high infrared absorbing ability, it is essential to add an infrared absorbing agent. Although it does not specifically limit as an infrared absorber, As a specific example, vanadyl naphthalocyanine, aminium, a diimonium, a cyanine, a nickel complex, a phthalocyanine series, an ytterbium oxide compound, etc. are mentioned.

  The addition amount of the infrared absorber is preferably in the range of 0.01 to 10 parts by mass and more preferably in the range of 0.05 to 5 parts by mass with respect to 100 parts by mass of the toner. If the addition amount is less than 0.05 parts by mass, the light energy absorption performance of the near-infrared region of the toner may be deteriorated, resulting in poor fixing. On the other hand, when the addition amount exceeds 10 parts by mass, although the photofixability is good, problems such as charging failure and hue change may be caused.

  The volume average particle size of the infrared absorbent in the toner is preferably 0.8 μm or less, more preferably 0.6 μm or less, and still more preferably 0.4 μm or less. In order to efficiently absorb infrared rays, it is necessary to have a larger surface area, and in order to more efficiently transfer energy to α-type hematite, the distance from α-type hematite in the toner is reduced. If the volume average particle size is 0.8 μm or less, the effect of the present invention can be obtained.

  In addition, since the strongest light emission peak differs according to the kind of light source used for light fixing, the optimal light absorption characteristic of the near infrared region requested | required corresponding to this differs. However, such adjustment of the light absorption characteristics in the near infrared region can be easily performed by controlling the molecular structure of the infrared absorber.

Since the α-type hematite used in the present invention is colored in the visible region in red, when the toner of the present invention contains a color material, a good color gamut can be obtained by using a magenta or red color material.
In particular, cyanine, naphthalocyanine, imonium, and aminium, which are mainly used as infrared absorbers added to conventional toners, exhibit a slightly greenish color in the visible range, so these infrared absorbers have a green complementary color. When used in combination with a certain magenta or red color material, the hue of the toner will become dark, so the color reproducibility will deteriorate, and toner containing these magenta and red color materials using these infrared absorbers will form a color image. It was difficult to use.
On the other hand, since the toner of the present invention contains α-type hematite that exhibits red in the visible range, the above cyanine, naphthalocyanine, imonium as an infrared absorber in a light fixing color toner using a magenta or red coloring material. Even if aminium is used, the change in the hue of the toner can be controlled.

<Binder resin>
There is no restriction | limiting in particular as binder resin used for the toner of this invention. However, it is preferable to use a binder resin having a low acid value. This is because when the acid value of the binder resin is high, the basic organic compound added to improve the infrared absorbing ability of the infrared absorbent is neutralized, and the infrared absorbing ability may not be sufficiently exhibited.

  As such a binder resin, thermoplastic resins made of various natural or synthetic polymer materials can be used, but typically, epoxy resin, styrene-acrylic resin, polyamide resin, polyester resin, polyvinyl resin, polyurethane resin are used. Polybutadiene resin, cyclopolyolefin resin and the like can be used alone or in combination.

  The binder resin of the present invention has a weight average molecular weight of 2,000 to 100,000, more preferably 5,000 to 50,000, and still more preferably 8,000 to 40,000 from the viewpoint of balance with mixed color of the fixed image, color development, penetration into the recording paper and the like. preferable. If the weight average molecular weight exceeds 100,000, the color mixing property and color developability are not improved, and the reproducibility of the secondary color is lowered. If the weight average molecular weight is less than 2000, the amount of penetration into the recording paper increases and the surface glossiness is increased. May decrease, which is not preferable.

  The softening point of the toner of the present invention is preferably in the range of 90 to 140 ° C, more preferably 100 to 120 ° C. Within the above range, color unevenness at the time of fixing a color image after fixing can be suppressed.

  As a preferred resin, a cyclopolyolefin resin is most preferred because it has a low acid value and does not impair the ability of the infrared absorbing agent to absorb infrared rays.

  Cyclopolyolefin means a polyolefin resin having a cyclic structure. Polymers, block copolymers and the like are included. Moreover, the copolymer containing other monomers other than these as a small component may be sufficient, and the modified thing may be sufficient. These cycloolefin copolymer resins can be obtained by a known polymerization method using a metallocene or Ziegler catalyst. For example, it can be synthesized by the methods disclosed in JP-A-5-339327, JP-A-5-9223, JP-A-6-271628, and the like.

  In the present invention, the copolymerization ratio of the α-olefin and the cycloolefin in the cycloolefin copolymer resin can be varied over a wide range. Specifically, the cycloolefin is 2 to 98 mol based on the total of both. %, Preferably in the range of 2.5 to 50 mol%, but these copolymerization ratios can be easily obtained by appropriately setting the reaction charge molar ratio between them. Further, when the cycloolefin copolymer resin is obtained by reacting ethylene as an α-olefin and norbornene as a cycloolefin, the glass transition point (Tg) has a great influence on the charging ratio of both in the reaction. However, when the charging rate of norbornene is increased, Tg tends to increase. Specifically, for example, when the charging ratio of norbornene is about 60% by weight, a Tg of 60 to 70 ° C. is obtained. As Tg of binder resin in this invention, it is preferable that it is 50 to 70 degreeC. Since this binder resin basically has an acid value of almost zero, it is more preferable because the infrared absorbing ability of the infrared absorber can be exhibited.

The acid value of the binder resin is preferably in the range of 0 to 10 mg / KOH, more preferably in the range of 0 to 5 mg / KOH, and particularly preferably in the range of 0 to 1 mg / KOH.
The acid value can be measured according to a conventional method, for example, as follows. First, 1 g of a binder resin sample is weighed into a 100 mL Erlenmeyer flask, and about 50 mL of a mixed solvent of acetone: toluene = 1: 1 is added to dissolve the binder resin. If the solubility is poor, a crushed binder resin may be used. Next, using a mixed indicator of 1% phenolphthalein and titrating with a 0.1 mol / L potassium hydroxide-alcohol solution standardized in advance, the amount of consumption A (mL) of the potassium hydroxide-alcohol solution is reduced. An acid value is calculated | required based on Formula (1).

      Formula (1) Acid value = A (mL) × 0.1 × 56.11

<Color material>
The color material (colorant) used in the toner of the present invention is not particularly limited, and any of dyes, pigments and the like may be used.
For example, in a light fixing color toner, quinacridone (red, magenta), carmine (red, magenta), phthalocyanine (blue, etc.), anthraquinone (red), disazo (red or yellow), monoazo (red), an anilide compound ( Yellow), benzidine (yellow), benzimidazolone (yellow), halogenated phthalocyanine (green), and the like can be used.
In particular, since the hematite used in the present invention exhibits a red color, when a red color material such as quinacridone, carmine 6B, or monoazo is used, a good color can be obtained.

  The color material is preferably in the range of 1 to 10 parts by mass with respect to 100 parts by mass of the toner.

<Charge control agent>
In the present invention, it is preferable to use a colorless or light-colored charge control agent that has a small influence on the hue of the toner. Preferably, a quaternary ammonium salt or the like can be used as a positive charge control agent, and a zinc naphtholate complex, a zinc salicylate complex, a boron compound, calixarene, or the like can be used as a negative charge control agent.
Specific examples include E-81, E-83, E-89, and P-51 manufactured by Orient Chemical Co., N4P manufactured by Clariant Chemical Co., PS201 manufactured by Fujikura Kasei Co., Ltd., and HS2000N1 manufactured by Hodogaya Chemical Co., Ltd. .

<Fixing aid>
In the case where the toner of the present invention is used for fixing by light fixing, a fixing auxiliary agent can be added to the toner in order to improve the fixing property of the toner.
As the fixing aid, those having a low melting point can be used. By using such a material, the fixing property is improved by accelerating the penetration into the recording medium. Such includes a WAX composition. Specifically, ordinary WAX such as polyolefins such as polyethylene and polypropylene, fatty acid esters, paraffin wax, carnauba wax, amide wax, etc. can be widely used as a single substance or a mixture. Among these WAXs, those having a melting point of 150 ° C. or lower are preferable, and those having a melting point lower than the softening temperature of the binder resin are particularly preferable.

<External additive>
As the additive externally added to the toner, any known material that is usually used as an external additive for the toner can be used without particular limitation. For example, inorganic particles such as silica, titania, alumina, and zinc oxide, and polystyrene can be used. Resin particles such as PMMA and melamine resin can be used.

<Toner production method>
Next, a method for producing the toner of the present invention will be described. The toner of the present invention can be produced by a method similar to a known toner production method such as a pulverization method or a polymerization method.
When the pulverization method is used, for example, the toner of the present invention can be prepared as follows. First, the above-described hematite, binder resin, and infrared absorber are mixed with components such as a WAX composition, a colorant, and a charge control agent as necessary, and then the above materials are melt-kneaded using a kneader, an extruder, or the like. . Thereafter, the obtained melt-kneaded product is roughly pulverized and then finely pulverized with a jet mill or the like, and toner particles having a target particle diameter are obtained with an air classifier. Furthermore, the toner of the present invention can be obtained by adding an external additive to the toner particles as necessary.

In the case of using a polymerization method, a suspension polymerization method or an emulsion polymerization method can be mainly used.
When the toner of the present invention is produced using the suspension polymerization method, for example, the toner of the present invention can be produced as follows. First, in addition to monomers such as styrene, butyl acrylate, 2-ethylhexyl acrylate, the above-described hematite and infrared absorbers, cross-linking agents such as divinylbenzene, chain transfer agents such as dodecyl mercaptan, and polymerization initiators, if necessary A colorant, a charge control agent, a release agent and the like are further added to prepare a composition dissolved or dispersed in the monomer.
Thereafter, the monomer composition is put into an aqueous phase containing a suspension stabilizer such as tricalcium phosphate and polyvinyl alcohol, and a surfactant, and a rotor-stator emulsifier, a high-pressure emulsifier, and an ultrasonic emulsifier. A suspension of the composition is prepared using a machine or the like, then deoxygenated in the reaction layer by nitrogen substitution or the like, and then monomer is polymerized by heating to obtain particles. After completion of the polymerization, the obtained particles are washed and dried, and an external additive can be added as necessary to obtain the toner of the present invention.

Further, when the toner is prepared by an emulsion polymerization method, the toner of the present invention can be prepared as follows, for example. First, in a water in which a water-soluble polymerization initiator such as potassium persulfate is dissolved, a monomer such as styrene, butyl acrylate, or 2-ethylhexyl acrylate is added, and a surfactant such as sodium dodecyl sulfate is added as necessary. Polymerization is carried out by heating while stirring to obtain resin particles.
Thereafter, in addition to the above-described hematite and infrared absorber, resin particles are dispersed in a powder obtained by further pulverizing a colorant, a charge control agent, a WAX composition, etc., preferably in a volume average particle size of 1 μm or less as necessary. It is added into the suspension and the pH, agitation strength, temperature, etc. of the suspension are adjusted to heteroaggregate the resin particles and hematite powder to obtain heteroaggregates. Furthermore, the reaction system is heated above the glass transition temperature of the resin particles to fuse the heteroaggregates to obtain toner particles. Thereafter, the toner particles are washed and dried, and an external additive is added as necessary to obtain the toner of the present invention.

The volume average particle diameter D _50V of the toner particles thus produced is preferably in the range of 1 to 10 μm, more preferably in the range of 3 to 7 μm. When D _50v is less than 1 μm, not only the infrared absorber and hematite particles are easily released from the toner particles, but also the fluidity is remarkably deteriorated, the replenishment property, the mixing property with the carrier, etc. are lowered, and the developability is also lowered. There are things to do. On the other hand, if it exceeds 10 μm, the uniformity of the image may decrease.

  The volume average particle size distribution index GSDv of the toner particles is preferably 1.25 or less. When GSDv exceeds 1.25, the resolution is remarkably deteriorated, causing image defects such as toner scattering and fogging.

The volume average particle size D _50v and the volume average particle size distribution index GSDv are, for example, particle size distributions measured with a measuring instrument such as Coulter Counter TAII (manufactured by Beckman Coulter), Multisizer II (manufactured by Beckman-Coulter). A cumulative distribution is drawn from the smaller diameter side with respect to the particle size range (channel) divided on the basis of the particle size, and the particle diameter that becomes 16% cumulative is the volume D _16v and the particle diameter that becomes 50% cumulative is the volume D _50v. In addition, the particle diameter that is 84% cumulative is defined as volume D _84v . Using these, the volume average particle size distribution index GSDv is calculated as ( _D84v / _D16V ) ^1/2 .

Furthermore, the shape factor SF1 of the toner particles in the present invention is preferably in the range of 100 to 140, more preferably in the range of 115 to 135, from the viewpoint of image formability.
The toner shape factor SF1 is obtained by taking toner particles dispersed on a slide glass or an optical microscope image of the toner into a Luzex image analyzer through a video camera, obtaining the maximum length and projected area of 50 or more toners, and calculating the following formula ( It is obtained by calculating by 2) and obtaining the average value.
Formula (2): SF1 = (ML ² / A) × (π / 4) × 100
In the above formula (2), ML represents the absolute maximum length of the toner particles, and A represents the projected area of the toner particles.

(Electrophotographic developer)
The electrophotographic developer of the present invention (hereinafter sometimes abbreviated as “developer”) is a one-component developer composed of the toner of the present invention or a two-component developer composed of a carrier and the toner of the present invention. Either may be sufficient. Hereinafter, the case where the developer of the present invention is a two-component developer will be described in detail.

  The carrier that can be used in the two-component developer is not particularly limited, and a known carrier can be used. For example, a resin-coated carrier having a resin coating layer on the surface of the core material can be exemplified. Further, a resin-dispersed carrier in which a conductive material or the like is dispersed in a matrix resin may be used.

  Coating resins and matrix resins used for carriers include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic. Examples thereof include, but are not limited to, acid copolymers, straight silicone resins composed of organosiloxane bonds or modified products thereof, fluororesins, polyesters, polycarbonates, phenol resins, epoxy resins and the like.

  Examples of the conductive material include metals such as gold, silver and copper, carbon black, titanium oxide, zinc oxide, barium sulfate, aluminum borate, potassium titanate, tin oxide, and carbon black. It is not limited.

  Examples of the core material of the carrier include magnetic metals such as iron, nickel, and cobalt, magnetic oxides such as ferrite and magnetite, and glass beads. However, in order to use the carrier for the magnetic brush method, it is a magnetic material. It is preferable. The volume average particle size of the core material of the carrier is generally 10 to 500 μm, preferably 30 to 100 μm.

  In order to coat the surface of the core material of the carrier with a resin, there may be mentioned a method of coating with a coating layer forming solution in which the coating resin and, if necessary, various additives are dissolved in an appropriate solvent. The solvent is not particularly limited and may be appropriately selected in consideration of the coating resin to be used, coating suitability, and the like.

  Specific resin coating methods include an immersion method in which the carrier core material is immersed in the coating layer forming solution, a spray method in which the coating layer forming solution is sprayed onto the surface of the carrier core material, and the carrier core material is fluidized air. And a kneader coater method in which the carrier core material and the coating layer forming solution are mixed in a kneader coater and the solvent is removed in a kneader coater.

  The mixing ratio (weight ratio) between the light fixing color toner of the present invention and the carrier in the two-component developer is in the range of toner: carrier = 1: 100 to 30: 100, and 3: 100 to 20: A range of about 100 is more preferable.

The developer of the present invention is preferably used so that the toner concentration is in the range of 3% by weight to 15% by weight when the carrier having a resistance value in the range of 10 ⁸ to 10 ¹⁵ Ω is used. . The resistance value of the developer thus adjusted is preferably 10 ¹⁰ Ω or more. By adjusting the resistance value of the carrier, the toner concentration, and the resistance value of the developer within such a range, a good charge amount can be maintained.

(Image forming method)
Next, the image forming method of the present invention will be described. The image forming method of the present invention is not particularly limited as long as the toner of the present invention is used, but specifically, the following image forming method is preferable.
That is, the image forming method of the present invention includes a latent image forming step of forming an electrostatic latent image on the surface of the latent image carrier, and the electrostatic latent image formed on the surface of the latent image carrier as a light fixing color toner developer. A developing process for forming a toner image by developing the toner image, a transferring process for transferring the toner image formed on the surface of the latent image carrier to the surface of the transfer target, and a toner image transferred on the surface of the transfer target It is preferable to include a fixing step of fixing (photofixing) the surface of the medium to form an image (visible image). At this time, the light fixing color toner of the present invention is used as the light fixing color toner.
In the fixing step, thermal fixing can be performed in addition to light fixing.

Each of the above steps can be performed by a known method employed in a conventional image forming method. Further, the image forming method of the present invention may include processes other than the above-described processes such as a cleaning process for cleaning the surface of the latent image carrier.
Since the toner of the present invention is excellent in light fixing property, a known light fixing method such as a flash fixing method or an infrared irradiation fixing method can be used in the fixing step.

  Image formation by the image forming method of the present invention can be performed, for example, as follows when an electrophotographic photosensitive member is used as a latent image carrier. First, the surface of the electrophotographic photosensitive member is uniformly charged by a corotron charger, a contact charger or the like and then exposed to form an electrostatic latent image. Next, the toner particles are attached to the electrostatic latent image by contacting or approaching a developing roll having a developer layer formed on the surface, thereby forming a toner image on the electrophotographic photosensitive member. The formed toner image is transferred onto the surface of a transfer medium such as paper using a corotron charger or the like. Further, the toner image transferred onto the surface of the transfer medium is light-fixed (or heat-fixed) by a light fixing device (or heat fixing device), and an image is formed on the recording medium.

  In forming such an image, for example, when four toners of the present invention comprising cyan, magenta, yellow, and black are used, the light fixing may be performed each time the light fixing color toner image of each color is transferred to the recording medium. Alternatively, it may be performed simultaneously at the same time after transferring all four color light-fixed color toner images to a recording medium in a stacked state.

The light energy at the time of light fixing (hereinafter sometimes referred to as “flash energy”) is the case where the light fixing color toner image of each color is transferred and light fixing is performed (hereinafter referred to as “monochromatic light fixing”). Is preferably in the range of about 1 to 3 J / cm ² , when four-color photofixed color toner images are transferred in a stacked state and photofixed at one time (hereinafter referred to as “four colors”). (Sometimes referred to as “batch photofixing”), it is preferably within a range of about ² to 7 J / cm ² .
Flash energy is less than 1 J / cm ² in monochromatic light fixing, in the case of less than 2J / cm ² in 4-color optical batch fixing may not be satisfactorily fixed. On the other hand, and if it exceeds 3J / cm ² in monochromatic light fixing, if it exceeds 7J / cm ² in 4-color optical batch fixing may or toner voids, burnt like recording medium is generated.

As a light fixing device used for light fixing, a light source (lamp) capable of irradiating near infrared light such as an infrared lamp and a xenon lamp can be used, and one lamp may be used, Two or more may be sufficient.
In addition, it is preferable to use a xenon lamp as the light source in that the light absorption efficiency in the near infrared region of the α-type hematite used in the present invention can be more effectively increased.

In the image forming method of the present invention, at least one kind of toner of the present invention is always used, but when two or more kinds of toners are used, at least one kind of toner may be used.
For example, when a color image (visible image) is formed by light fixing using four colors of light fixing color toners of cyan, magenta, yellow, and black, a book containing a color material as the light fixing color toner of four colors. The toner of the invention can be used.

Examples of the present invention are shown below, but the present invention is not limited by the following examples.
<Preparation of magenta toner particles 1 for photofixing>
・ Cycloolefin resin (manufactured by Ticona, cycloolefin TopasTM, acid value 0 mgKOH / g, Tg104 ° C.) 100 parts by mass ・ Quinacridone pigment (Hostapern RedE2B70, manufactured by Clariant)
5 parts by mass, quaternary ammonium salt (PSY, manufactured by Clariant) 1 part by mass, α-type hematite (R-516P, manufactured by Titanium Industry Co., Ltd.) 0.1 part by mass, polyethylene wax (NP500, manufactured by Mitsui Chemicals) 0.5 Parts by mass

The above was melt-kneaded with a Banbury mixer, and further pulverized and classified to obtain magenta toner particles 1 for photofixing having a volume average particle diameter D ₅₀ of 9 μm.
Moreover, Tg was measured at a temperature increase rate of 10 ° C./min using a differential scanning calorimeter (manufactured by Shimadzu Corporation, DSC-50). Further, D ₅₀ is laser diffraction type particle size distribution measuring apparatus (manufactured by Horiba, Ltd., LA-700) was used for the measurement.

<Preparation of Photofixing Magenta Toner 1>
To 100 parts by mass of the magenta toner particles 1 for photofixing, 0.5 part by mass of hydrophobic silica (HVK2150, manufactured by Clariant) is added as an external additive, and mixed at 30 m / s for 1 minute using a Henschel mixer. As a result, magenta toner 1 for photofixing was obtained.

-Production of Developer 1-
4.5 parts by mass of magenta toner 1 for photofixing and 95.5 parts by mass of ferrite carrier coated with 2% of polymethyl methacrylate resin (weight average molecular weight 80000) were mixed in a V-blender (20 rpm, 10 minutes). Thus, developer 1 was produced.

-Production of developers 2-6-
The amount of α-type hematite was changed to 1 part by mass, 5 parts by mass, 10 parts by mass, 20 parts by mass, and 30 parts by mass, and 99.1 parts by mass and 95.95 parts by mass of the cycloolefin resin used in the magenta toner particles 1 for photofixing. Magenta toner particles 2 to 6 for photofixing were obtained in the same manner as magenta toner particles 1 for photofixing except that they were changed to 1 part by mass, 90.1 parts by mass, and 70.1 parts by mass. Developers 2 to 5 were prepared by the method described above.

-Production of developers 7-13-
The amount of α-type hematite is fixed to 5 parts by mass, and 0.05 parts by mass, 0.1 part by mass, 1 part by mass, 3 parts by mass, 5 parts by mass, 10 parts by mass, and 12 parts by mass of vanadyl naphthalocyanine as an infrared absorber. 95.05 parts by mass, 95.0 parts by mass, 94.1 parts by mass, 92.1 parts by mass, 90.1 parts by mass of the cycloolefin resin used in the magenta toner particles 1 for photofixing And magenta toner particles 7 to 13 were obtained in the same manner as the photofixing magenta toner particles 1 except that they were changed to 85.1 parts by mass and 83.1 parts by mass. Developers 6 to 13 were prepared.

-Production of Developers 14-15-
A method similar to that for magenta toner particles 1 for photofixation, except that 0.1 part by mass of α-type hematite is changed to 1 part of aminium and the cycloolefin resin used in magenta toner particles 1 for photofixation is changed to 99.1 parts by mass. The magenta toner particles for photofixation 14 were changed to 5 parts by mass for α-type hematite and 1 part for aminium, and the cycloolefin resin used for the magenta toner particles 1 for photofixation was changed to 94.1 parts by mass. The light fixing magenta toner particles 15 were obtained in the same manner as the light fixing magenta toner particles 1. Developers 14 to 15 were produced in the same manner as Developer 1, using light fixing magenta toners 14 to 15.

-Production of developer 16-
Photofixing magenta toner particles 1 except that 0.1 part by mass of α-type hematite is changed to 1 part by mass of vanadyl naphthalocyanine and the cycloolefin resin used in the magenta toner particles 1 for photofixing is changed to 95.1 parts by mass. In the same manner, magenta toner particles 16 for photofixing were obtained. Further, developer 16 was produced in the same manner as developer 1.

-Production of developer 17-
Photofixing magenta toner particles 1 except that α-type hematite is changed to 0.5 parts by mass and vanadyl naphthalocyanine 1 part by mass, and the cycloolefin resin used in photofixing magenta toner particles 1 is changed to 94.6 parts by mass. In the same manner as above, magenta toner particles 17 for photofixing were obtained. Developer 17 was prepared in the same manner as Developer 1.

-Production of developer 18-
Same as photo-fixing magenta toner particle 1 except that α-type hematite is changed to 1 part by mass and vanadyl naphthalocyanine 1 part by mass, and cycloolefin resin used for photo-fixing magenta toner particle 1 is changed to 94.1 parts by mass. Thus, magenta toner particles 18 for photofixing were obtained. Developer 18 was produced in the same manner as Developer 1.

-Production of Developer 19-
Same as photo-fixing magenta toner particle 1 except that α-type hematite is changed to 10 parts by mass and vanadyl naphthalocyanine 1 part by mass, and cycloolefin resin used for photo-fixing magenta toner particles 1 is changed to 85.1 parts by mass. Thus, magenta toner particles 19 for photofixing were obtained. Developer 19 was produced in the same manner as Developer 1.

-Production of Developer 20-
The same as magenta toner particle 1 for photofixation, except that α-type hematite was changed to 13 parts by mass and vanadyl naphthalocyanine 1 part by mass, and cycloolefin resin used for magenta toner particle 1 for photofixation was changed to 82.1 parts by mass. Thus, magenta toner particles 20 for photofixing were obtained. Developer 20 was prepared in the same manner as Developer 1.

-Production of Developer 21-
Same as photo-fixing magenta toner particle 1 except that α-type hematite is changed to 14 parts by mass and vanadyl naphthalocyanine 1 part by mass, and cycloolefin resin used in photo-fixing magenta toner particles 1 is changed to 81.1 parts by mass. Thus, magenta toner particles 21 for photofixing were obtained. Developer 21 was produced in the same manner as Developer 1.

-Production of Developer 22-
For the light fixing in the same manner as the light fixing magenta toner particles 9 except that the quinacridone pigment is changed to 0.8 parts by weight and the cycloolefin resin used for the light fixing magenta toner particles 9 is 96.3 parts by weight. Magenta toner particles 22 were obtained. Developer 22 was prepared in the same manner as Developer 1.

-Production of Developer 23-
Photofixing magenta toner in the same manner as the photofixing magenta toner particle 9 except that the quinacridone pigment is changed to 1 part by mass and the cycloolefin resin used in the photofixing magenta toner particle 9 is 96.1 parts by mass. Particles 23 were obtained. Developer 23 was produced in the same manner as Developer 1.

-Production of Developer 24-
Photofixing magenta toner in the same manner as the photofixing magenta toner particle 9 except that the quinacridone pigment was changed to 3 parts by mass and the cycloolefin resin used for the photofixing magenta toner particles 9 was 94.3 parts by mass. Particles 24 were obtained. Developer 24 was produced in the same manner as Developer 1.

-Production of developer 25-
Photofixing magenta toner in the same manner as the photofixing magenta toner particle 9 except that the quinacridone pigment was changed to 7 parts by mass and the cycloolefin resin used for the photofixing magenta toner particles 9 was changed to 90.3 parts by mass. Particles 25 were obtained. Developer 25 was produced in the same manner as Developer 1.

-Production of developer 26-
Photofixing magenta toner in the same manner as the photofixing magenta toner particle 9 except that the quinacridone pigment was changed to 10 parts by mass and the cycloolefin resin used for the photofixing magenta toner particles 9 was changed to 87.3 parts by mass. Particles 24 were obtained. Developer 26 was produced in the same manner as Developer 1.

-Production of developer 27-
The light fixing magenta toner is the same as the light fixing magenta toner particle 9 except that the quinacridone pigment is changed to 12 parts by weight and the cycloolefin resin used in the light fixing magenta toner particles 9 is 85.3 parts by weight. Particles 24 were obtained. Developer 24 was produced in the same manner as Developer 1.

<Examples 1-19 and Comparative Examples 1-8>
An electrostatic latent image is formed on the surface of the latent image carrier using an image forming apparatus (Fuji Xerox Co., Ltd. DocuPrint CF1100 modified machine) equipped with a xenon flash lamp having a high emission intensity in the wavelength range of 700 to 1500 nm. The electrostatic latent image formed on the surface of the image carrier is developed using the developers 1 to 27 to form a toner image, and the toner image formed on the surface of the latent image carrier is transferred to plain paper (NIP- (1500LT, Kobayashi recording paper) and the toner image transferred onto the surface of the plain paper is fixed with a light emission energy of 3 J / cm ² using the xenon flash lamp, and 1 inch square (2. 54 × 2.54 cm □) image was formed.

The fixing rate of the obtained 1-inch square image was evaluated as follows.
First, the optical density (OD1) of the image is measured, and then an adhesive tape (Scotch Mending Tape, manufactured by Sumitomo 3M) is applied on the image, and after 1 minute, the adhesive tape is peeled off. The concentration (OD2) was measured. In addition, the optical density was measured with a spectrocolorimeter (X-Rite 938, manufactured by X-Rite) under the conditions of a light source D50 and 2 ° (backing white).

Next, the fixing rate was calculated from the following equation (3) using the obtained optical density value.
Formula (3): Fixing rate (%) = OD2 / OD1 × 100

In addition, the saturation (C _ab ^* ) is calculated using the following formula (4) after using the L ^* a ^* b ^* color space: tristimulus values obtained by a spectrocolorimeter (X-Rite 938, manufactured by X-Rite). ) To saturation (C _ab ^* ).
Formula (4): Saturation (C _ab ^* ) = √ (a ^{* 2} + b ^{* 2} )

The determination of fixing property and saturation (C _ab ^* ) was performed as follows.
A: Fixing rate is 80% or more and fixing property is particularly good.
○: The fixing rate is 70% or more and less than 80%, and the fixing property is good.
(Triangle | delta): The fixing rate exceeds 60% and is less than 70%, and it is a level which can be used practically.
X: Fixing rate is 60% or less, impractical level.

Saturation (C _ab ^* ) was determined as follows.
A: The saturation is 50 or more, which is particularly good.
○: Saturation is 45 or more and less than 50, which is good.
(Triangle | delta): Saturation exceeds 42 and is less than 45%, and a practical use is possible level.
X: Saturation is 42 or less, impractical level.

  The results of Examples 1 to 19 and Comparative Examples 1 to 8 are shown in Table 1.

Example 20
The binder resin of the toner 9 was changed to a polyester resin (acid value: 10 mg KOH / g, manufactured by Kao, product name: FN119L, softening temperature: 104 ° C.), and toner 28 was prepared in the same manner to prepare developer 28.
Using the prepared developer 28, fixability was measured by the same method as described above. As a result, the fixability was lowered to 65%, but it was a usable level.

Claims (3)

  A photofixing color toner comprising at least α-type hematite, a binder resin, and an infrared absorber.   An electrophotographic developer comprising a carrier and the light fixing color toner according to claim 1. A latent image forming step of forming an electrostatic latent image on the surface of the latent image carrier, and developing the electrostatic latent image formed on the surface of the latent image carrier with a developer containing a light fixing color toner to form a toner image; A developing step for forming, a transfer step for transferring the toner image formed on the surface of the latent image carrier to the surface of the transfer target, and a toner image transferred to the surface of the transfer target for photofixing on the surface of the recording medium, An image forming method including a fixing step of forming an image,
The image forming method according to claim 1, wherein the light fixing color toner is the light fixing color toner according to claim 1.