JP2007240852A - Toner and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide toner for preventing its base particles and inorganic fine particles from adhering to the contact static charger and an image forming method, capable of preventing occurrence of fogging back ground for an image forming device, having a positive static charger to charge the surface of a photoreceptor in contact. <P>SOLUTION: This toner is positive charge toner used in an image forming device 10, having a contact positive static charger 14 to charge the surface of a photoreceptor 12 in contact. It contains base particles and an outer additive agent, and this outer additive agent contains silica and stearic acid calcium of a charging amount of 10 μC/g or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a toner used in an image forming apparatus including a contact charging unit that comes into contact with the surface of the photoreceptor to positively charge the surface of the photoreceptor, and an image forming method using the toner.

  The image forming apparatus includes a charging unit that charges the surface of the photosensitive member, an exposure unit that exposes the surface of the photosensitive member to form an electrostatic latent image, and an electrostatic latent image formed by attaching toner to the electrostatic latent image. An image forming apparatus comprising: a developing unit that develops toner as a toner image; a transfer unit that transfers a toner image from a photoconductor to a transfer target; and a cleaning unit process that cleans the surface of the photoconductor using a cleaning blade. It has been.

Recently, a contact charging means such as a charging roller, which generates less ozone than the conventional charger wire system, has been adopted as the charging means.
Further, the toner used in the image forming apparatus is required to have fluidity, chargeability, and the like. As the toner, a toner containing toner base particles having high circularity and inorganic fine particles such as silica and titanium oxide as external additives is known.

However, when the toner is used in an image forming apparatus having a charging roller, the following problems occur.
(I) Since the circularity of the toner base particles is high, the toner base particles are easy to slip through the cleaning blade and easily adhere to the charging roller.
(Ii) Inorganic fine particles that have passed through the cleaning blade tend to adhere to the charging roller. Since the inorganic fine particles have high electric resistance, when the inorganic fine particles adhere to the charging roller, the charging ability of the charging roller is hindered, the surface potential of the photoreceptor is lowered, and background fogging occurs.

The following methods have been proposed as a method for removing deposits on the charging roller.
(1) A method in which a charging voltage having a polarity opposite to that at the time of image formation is applied to a charging roll, and the deposit on the charging roller is electrostatically returned to the photosensitive member side to be removed (Patent Document 1).
(2) A method of mechanically removing deposits on the charging roller by bringing a cleaning elastic blade into contact with the charging roller (Patent Documents 2 and 3).

  However, in the method (1), the deposit on the charging roller may not be sufficiently removed. In the method (2), an elastic blade for cleaning is required, leading to an increase in cost; there is a problem that the adhered material is pressed against the charging roller by the elastic blade and fixed.

It is known that a metal soap (a fatty acid metal salt such as a stearic acid metal salt) is added to a toner as a lubricant for the purpose of improving the cleaning property of the photoconductor and preventing the adhesion to the photoconductor (patent) References 4-6). However, even when a toner to which metal soap is added is used in an image forming apparatus having a charging roller, toner base particles or inorganic fine particles may adhere to the charging roll and cause background fogging.
Japanese Patent Laid-Open No. 5-181351 JP-A-6-342237 Japanese Patent Laid-Open No. 10-123800 JP 2004-163807 A JP 2002-169330 A JP 2001-100452 A

  Accordingly, an object of the present invention is to provide adhesion of toner mother particles and inorganic fine particles to the contact charging means in an image forming apparatus including a contact charging means that positively charges the surface of the photoreceptor by contacting the surface of the photoreceptor. It is an object of the present invention to provide an image forming method in which generation of toner to be suppressed and generation of background fog is suppressed.

  The toner of the present invention is a positively chargeable toner used in an image forming apparatus provided with a contact charging unit that comes into contact with the surface of the photoreceptor to positively charge the surface of the photoreceptor, and includes toner base particles and an external additive. The external additive contains silica and calcium stearate having a charge amount of 10 μC / g or more.

  The image forming method of the present invention comprises a charging step in which a contact charging means is brought into contact with the surface of the photoconductor to positively charge the surface of the photoconductor, and an exposure step in which the surface of the photoconductor is exposed to form an electrostatic latent image. And an image forming method comprising: a developing step of developing the electrostatic latent image as a toner image by attaching toner to the electrostatic latent image; and a transfer step of transferring the toner image from the photosensitive member to the transfer target. The toner according to claim 1 is used.

The toner of the present invention suppresses adhesion of toner base particles and inorganic fine particles to the contact charging means in an image forming apparatus having a contact charging means that positively charges the surface of the photoreceptor by contacting the surface of the photoreceptor. Can do.
According to the image forming method of the present invention, the occurrence of background fog is suppressed.

<Toner>
The toner of the present invention is a positively chargeable toner used in an image forming apparatus provided with a contact charging unit that comes into contact with the surface of the photoreceptor to positively charge the surface of the photoreceptor, and includes toner base particles and an external additive. And a toner containing silica and calcium stearate having a charge amount of 10 μC / g or more as the external additive.

(Toner mother particles)
The circularity of the toner base particles is preferably 0.96 or more. By setting the circularity of the toner base particles to 0.96 or more, the fluidity of the toner becomes high, the transfer efficiency is high, and an image with excellent image quality can be obtained. The circularity is obtained from the following equation.
Circularity = perimeter of a circle having the same projected area as the particle image / perimeter of the projected image of the particle.

  The volume average particle diameter of the toner base particles is preferably 8 μm or less. By setting the volume average particle diameter of the toner base particles to 8 μm or less, an image having excellent image quality can be obtained. The volume average particle diameter is measured by a pore electrical resistance method.

  The toner base particles contain a binder resin and a color pigment. The toner base particles may contain a release agent, a charge control agent, magnetic powder, and the like as necessary.

  Examples of the binder resin include styrene resins, acrylic resins, styrene-acrylic copolymer resins, olefin resins such as polyethylene and polypropylene, vinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, Thermoplastic resins such as polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, styrene-butadiene resins; bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins And epoxy resins such as cycloaliphatic epoxy resins, and thermosetting resins such as cyanate resins.

Color pigments include black pigments such as carbon black, acetylene black, lamp black and aniline black; yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Yellow pigments such as Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, etc .; Orange pigments such as Rembrilliant Orange GK; Bengala, Cadmium Red, Lead Tan, Mercury Cadmium, Permanent Red 4R, Risor Red, Pyrazolone Red Red pigments such as watch red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B; purple pigments such as manganese purple, fast violet B, methyl violet lake; bitumen, cobalt Blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, indanthrene blue BC and other blue pigments; chrome green, chromium oxide, pigment green B, malachite green lake , Green pigments such as Final Yellow Green G; white pigments such as zinc white, titanium oxide, antimony white, zinc sulfide; barite powder, barium carbonate, clay, silica , White carbon, talc, extender pigments such as alumina white and the like.
The amount of the color pigment is usually 2 to 20 parts by mass and preferably 5 to 15 parts by mass with respect to 100 parts by mass of the binder resin.

Examples of the release agent include waxes and low molecular weight olefin resins. Examples of waxes include polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylene bis fatty acid amide compounds, natural waxes, and the like. Examples of the low molecular weight olefin-based resin include polypropylene, polyethylene, propylene-ethylene copolymer and the like having a number average molecular weight in the range of 1,000 to 10,000, preferably 2,000 to 6,000. Polypropylene is preferred.
The amount of the release agent is preferably 2 to 6 parts by mass and more preferably 3 to 5 parts by mass with respect to 100 parts by mass of the binder resin.

  As the positive charge control agent, 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, phthalazine, quinazoline, quinoxaline, etc. Azine Fast Red FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azine Fast Red FC Direct dyes composed of azine compounds such as Nylon Brown GR, azine dark green BH / C, azine deep black EW, azine deep black 3RL; nigrosine compounds such as nigrosine, nigrosine salt, nigrosine derivatives; nigrosine BK, nigrosine NB, nigrosine Z, etc. Acid dyes composed of nigrosine compounds of the following: metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride; A resin or oligomer having a carboxylate; a resin or oligomer having a carboxyl group;

Examples of the negative charge control agent include organometallic complexes or chelate compounds, such as aluminum acetylacetonate, iron (II) acetylacetonate, chromium 3,5-ditertiary butylsalicylate, and the like, and acetylacetone metal complexes. A salicylic acid metal complex or salt is preferred.
The amount of the charge control agent is usually 1 to 8 parts by mass and preferably 2 to 5 parts by mass with respect to 100 parts by mass of the binder resin.

When the toner of the present invention is used as a magnetic one-component developer, the toner base particles may contain magnetic powder.
Examples of the magnetic powder include ferrite, magnetite, and other metals or alloys exhibiting ferromagnetism, such as iron, cobalt, and nickel, or compounds containing these elements; Alloys exhibiting magnetism, such as chromium dioxide, etc. The amount of magnetic powder is preferably 50 to 100 parts by mass with respect to 100 parts by mass of the binder resin.

Examples of the method for producing the toner base particles include known production methods such as a polymerization method, a pulverization classification method, a melt granulation method, and a spray granulation method. Toner base particles having a circularity of 0.96 or more can be easily produced. A polymerization method is preferred from the viewpoint of production.
In the polymerization method, a monomer, a polymerization initiator, a color pigment, and other components as necessary are dispersed in water to prepare a suspension or an emulsion, which is heated to heat the monomer. In this method, a dispersion of toner base particles is obtained by polymerization.

(External additive)
The external additive in the present invention is an external additive containing silica and calcium stearate having a charge amount of 10 μC / g or more.

As silica, known silica particles used as an external additive for toner may be used.
The amount of silica is preferably 0.4 to 1.5 parts by mass with respect to 100 parts by mass of toner base particles.

The metal stearate has different charging properties depending on the metal as follows.
+ Side: calcium>magnesium> zinc:-side.
In the present invention, calcium stearate having a positive polarity is used. When calcium stearate adheres to contact charging means such as a charging roller, toner mother particles and silica of the same polarity are electrically repelled because calcium stearate is positive polarity, and toner mother particles and silica adhere to the contact charging means. Is suppressed. Further, since calcium stearate has the same polarity as the toner base particles, the charge amount of the toner base particles is not adversely affected.

The charge amount of calcium stearate is 10 μC / g or more, preferably 23 μC / g or more. The upper limit is 100 μC / g. By setting the charge amount of calcium stearate to 10 μC / g or more, adhesion of toner base particles and silica to the contact charging means can be sufficiently suppressed. The charge amount of calcium stearate is measured as follows.
After putting 10 g of spherical ferrite carrier (FK-150, manufactured by Powder Tech Co., Ltd.) and 0.5 g of calcium stearate into a plastic container with a capacity of 20 CC, stirring for 10 minutes at a rotational speed of 100 pm, the charge amount of calcium stearate was measured using a QM meter. To measure.
Further, the detection of calcium stearate in the toner can be performed with a fluorescent X-ray analyzer.

The volume average particle diameter of calcium stearate is preferably 16 μm or less. By setting the volume average particle diameter of calcium stearate to 16 μm or less, calcium stearate is less likely to be detached from the toner base particles, and as a result, calcium stearate is transported to the contact charging means together with the toner base particles and is sufficiently adhered to the contact charging means. To do.
The volume average particle diameter of calcium stearate is measured using a laser diffraction / scattering particle size distribution measuring apparatus.

  The amount of calcium stearate is preferably 0.01 to 0.5 parts by weight and more preferably 0.02 to 0.1 parts by weight with respect to 100 parts by weight of the toner base particles from the viewpoint of chargeability and cleaning properties. By making the amount of calcium stearate 0.01 parts by mass or more, the effect of preventing adhesion of toner and silica to the contact charging means is sufficiently exhibited. By setting the amount of calcium stearate to 0.5 parts by mass or less, absorption of moisture under high temperature and high humidity can be suppressed, and a decrease in charge amount of toner base particles can be suppressed.

  As the external additive, other external additives may be used as long as the effects of the present invention are not impaired. Examples of other external additives include titanium oxide, alumina, and metal soap excluding calcium stearate having a charge amount of 10 μC / g or more.

<Image forming method>
The toner of the present invention is used in an image forming apparatus including a contact charging unit that comes into contact with the surface of the photoreceptor and positively charges the surface of the photoreceptor.
As the image forming apparatus, for example, as shown in FIG. 1, a drum-shaped photoreceptor 12, a contact charging unit 14 that contacts the surface of the photoreceptor 12 and positively charges the surface of the photoreceptor 12, and a photosensitive An exposure means 16 for exposing the surface of the body 12 to form an electrostatic latent image; a developing means 18 for developing the electrostatic latent image as a toner image by attaching toner to the electrostatic latent image; The image forming apparatus 10 includes a transfer unit 20 that transfers the image from a transfer member 12 to a transfer target (not shown) 12 and a cleaning blade 22 that cleans the surface of the photoconductor.

As the photoconductor 12, an inorganic photoconductor such as selenium or amorphous silicon; an organic photoconductor in which a single-layer or multi-layer photoconductor containing a charge generator, a charge transport agent, a binder resin, etc. is formed on a conductive substrate. Etc.
Examples of the contact charging unit 14 include a charging roller and a charging brush.
As the exposure unit 16, the development unit 18, the transfer unit 20, and the cleaning blade 22, known ones may be used.
Examples of the image forming apparatus include a copying machine, a facsimile machine, and a laser beam printer.

An image forming method using the image forming apparatus 10 will be described below.
First, the surface of the photoreceptor 12 is positively charged by the contact charging means 14 (charging process). Next, the surface of the photoreceptor 12 is exposed by the exposure means 16 to form an electrostatic latent image (exposure process). Next, the developing means 18 attaches toner to the electrostatic latent image and develops the electrostatic latent image as a toner image (developing step). Next, the toner image is transferred from the photoconductor 12 to the transfer target by the transfer means 20 (transfer process). Next, the surface of the photoreceptor 12 is cleaned using the cleaning blade 22. The above steps are repeated.

  In the image forming method, calcium stearate contained in the toner is transported to the contact charging means together with the toner mother particles and adheres to the contact charging means 14. When calcium stearate adheres to contact charging means such as a charging roller, since calcium stearate has a positive polarity, toner and silica having the same polarity are electrically repelled, and adhesion of toner and silica to the contact charging means is suppressed. As a result, the charging ability of the contact charging means is not hindered by silica, and the surface potential of the photoreceptor is suppressed from being lowered, so that the occurrence of background fog is suppressed.

  Since the toner of the present invention described above contains calcium stearate having an electrification amount of 10 μC / g or more as an external additive, it makes contact with the surface of the photoreceptor to positively charge the surface of the photoreceptor. In an image forming apparatus including a charging unit, adhesion of toner mother particles and inorganic fine particles to the contact charging unit can be suppressed.

  In the image forming method of the present invention, in the image forming apparatus including the contact charging unit that positively charges the surface of the photoconductor by contacting the surface of the photoconductor, the toner base particles to the contact charging unit and Since toner that suppresses the adhesion of inorganic fine particles is used, the occurrence of background fogging can be suppressed.

Each measurement and evaluation in the examples was performed as follows.
(Volume average particle diameter of toner base particles)
The volume average particle diameter of the toner base particles was measured using Multisizer type III (manufactured by Coulter Counter). Specifically, it measured by the following method.
As an electrolytic solution, 1% NaCl aqueous solution was prepared using sodium chloride (reagent grade 1). As a dispersant, 0.1 to 5 ml of a surfactant (preferably alkylbenzene sulfonate) was added to 100 to 150 ml of the electrolytic solution, and 0.5 to 50 mg of a measurement sample toner was added and suspended. Disperse the suspended electrolyte with an ultrasonic disperser for about 1 to 3 minutes, and then measure the particle size distribution of toner particles using the Multisizer III type with an aperture of 100 μm to determine the volume distribution of the toner. Asked.

(Circularity of toner base particles)
The circularity of the toner base particles was measured using FPIA-2100 (manufactured by Sysmex Corporation). Specifically, it measured by the following method.
First, 20 mg of toner mother particles were placed in a measurement container, and 10 ml of a sheath liquid as a dispersion medium was added thereto and stirred, followed by dispersion treatment at 60 W for 3 minutes with an ultrasonic disperser to obtain a dispersion.
For the measurement, the dispersion was adjusted so that the concentration of the toner base particles was 3,000 to 10,000 particles / μL, and the flow type particle image analyzer “FPIA-2100” manufactured by Sysmex Corporation was used. The circularity was measured for 1,000 to 10,000 particles having a circle diameter (equivalent circle diameter) of 1 μm or more having the same circumference as the two-dimensional projection image of the particles. The average value of the circularity of the individual particles thus obtained was determined as the average circularity.

(Volume average particle diameter of metal stearate)
The volume average particle size of the stearic acid metal salt was measured using a laser diffraction / scattering particle size distribution analyzer “LA-700” (manufactured by Horiba, Ltd.).
(Charge amount of stearic acid metal salt)
10 g of spherical ferrite carrier (FK-150, manufactured by Powder Tech Co., Ltd.) and 0.5 g of calcium stearate were placed in a polycontainer having a capacity of 20 CC and stirred for 10 minutes at a rotation speed of 100 pm. The charge amount of the stearic acid metal salt was measured using a QM meter (Trek Corp., 210HS).

(Image evaluation)
The following evaluation machines were used for image evaluation.
Evaluator: A modified LBP-2410 manufactured by Canon (positive charging system, see the drawing of Japanese Patent No. 3332870 for a sectional view),
Line speed: 151 mm / sec,
Photoconductor: positively charged amorphous silicon drum, surface potential + 300V,
Charging roller: Epichlorohydrin rubber having a diameter of 12 mm and an electric resistance of 3 × 10 ⁷ Ω.

The charging roller was brought into contact with the photosensitive member with a biting amount of 0.2 mm and was driven by the photosensitive member. Further, a sine wave of Vpp 1.1 kV, frequency 1.3 kHz, and Vdc 400 V was applied to the charging roller.
Toner was set in an evaluation machine, and the following items were evaluated.

(Skin cover)
After outputting 3000 sheets of a Duty 5% original, a blank sheet was output. The reflection density of the white paper before output and the reflection density of the white paper after output were measured, and the background fog (FD) was obtained from the following equation. The reflection density was measured using TC-6DS (manufactured by Tokyo Denshoku).
F. D. = Reflection density of blank paper after output-Reflection density of blank paper before output.

[Production Example 1]
80 parts by mass of styrene, 20 parts by mass of 2-ethylhexyl methacrylate, 5 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, MA-100), 3 parts by mass of low molecular weight polypropylene (manufactured by Sanyo Chemical Co., Ltd., Viscol 660P), charge control agent (Orient A mixed solution of 5 parts by mass of N-07 and 1 part by mass of divinylbenzene (crosslinking agent) manufactured by Kagaku Co., Ltd. was sufficiently dispersed with a ball mill, and then 2,2-azobis (2,4-dimethyl) as a polymerization initiator. 2 parts by weight of valeronitrile) were added. The mixed solution is added to 400 parts by mass of ion-exchanged water, and 5 parts by mass of tribasic calcium phosphate and 0.1 part by mass of sodium dodecylbenzenesulfonate are added as a suspension stabilizer. A suspension was prepared by stirring at 6000 rpm for 45 minutes. The suspension was heated at 70 ° C. for 10 hours while stirring at 100 rpm in a nitrogen atmosphere to polymerize the monomer. The resulting dispersion was acid washed to remove tricalcium phosphate. The volume average particle diameter of the toner base particles in the dispersion was 7.5 μm. The dispersion was filtered, and the recovered powder was washed and dried to obtain toner base particles. The sphericity of the toner base particles was 0.975.

[Production Example 2]
The following metal stearate salt was pulverized with a jet mill and then applied to a classifier to obtain a metal stearate salt having a predetermined volume average particle size.
Calcium stearate (metal content: 7%),
Magnesium stearate (metal content: 11%),
Zinc stearate (metal content: 12%).

[Examples 1 to 4, Comparative Examples 1 to 9]
To 100 parts by mass of toner base particles, 0.8 part by mass of silica (manufactured by Nippon Aerosil Co., Ltd., RA200HS) and 0.05 part by mass of a metal stearate shown in Table 1 are added and stirred using a Henschel mixer. The toner was obtained by mixing. Image evaluation was performed using the obtained toner. The results are shown in Table 1.

[Comparative Example 10]
A toner was obtained in the same manner as in Example 1 except that no metal stearate was added. Image evaluation was performed using the obtained toner. The results are shown in Table 1.

  Since the toners of Examples 1 to 4 contain calcium stearate having a charge amount of 10 μC / g or more as an external additive, adhesion of toner mother particles and inorganic fine particles to the contact charging means is suppressed. D. Was kept low.

Since the toner of Comparative Example 1 contains calcium stearate having an electrification amount of less than 10 μC / g as an external additive, adhesion of toner mother particles and inorganic fine particles to the contact charging means cannot be suppressed. D. Became high.
Since the toners of Comparative Examples 2 to 9 contain a metal stearate other than calcium stearate as an external additive, adhesion of toner mother particles and inorganic fine particles to the contact charging means cannot be suppressed. D. Became high.
Since the toner of Comparative Example 10 does not contain a metal stearate as an external additive, adhesion of the toner base particles and inorganic fine particles to the contact charging means cannot be suppressed. D. Became high.

  The toner of the present invention is useful for an image forming apparatus provided with a contact charging unit that comes into contact with the surface of the photoreceptor to positively charge the surface of the photoreceptor, and the toner of the present invention can suppress the occurrence of background fog. In addition, an image with excellent image quality can be obtained.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Photoconductor 14 Contact charging means

Claims (2)

A positively chargeable toner used in an image forming apparatus having a contact charging means for positively charging the surface of the photosensitive member by contacting the surface of the photosensitive member;
Contains toner base particles and external additives,
A toner in which the external additive contains silica and calcium stearate having a charge amount of 10 μC / g or more. A charging step in which the contact charging means is brought into contact with the surface of the photoreceptor to positively charge the surface of the photoreceptor;
An exposure step of exposing the surface of the photoreceptor to form an electrostatic latent image;
A developing step of developing the electrostatic latent image as a toner image by attaching toner to the electrostatic latent image;
A transfer step of transferring a toner image from a photoreceptor to a transfer target,
An image forming method using the toner according to claim 1 as the toner.

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