JP7374655B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus for visualizing an electrostatic charge image.

BACKGROUND ART In recent years, as image forming apparatuses such as copying machines and printers have become widespread, the performance required of image forming apparatuses is not only higher speed and longer life, but also higher image quality.
2. Description of the Related Art As a means of achieving higher image quality in image forming apparatuses, toner particles are becoming smaller in particle size. When the particle size of the toner becomes smaller, it becomes difficult for the toner to be scraped off by a cleaning blade (hereinafter also referred to as "cleaning means") in the cleaning process, and it becomes easier for the toner to slip through the cleaning blade, making cleaning defects more likely to occur.

Furthermore, particles such as silica with a particle size of less than 50 nm are often externally added to the developer as a fluidity imparting agent, and these particles slip through the cleaning means and adhere to the charging means. Once these microparticles adhere, it is difficult to remove them with a cleaning member, a bias, etc., and if they adhere in large quantities and unevenly, the charging in the charging means may become uneven.
As a method for improving cleaning defects, Patent Document 1 proposes a method of adding strontium titanate powder to toner particles. The strontium titanate powder used in these methods has an excellent polishing effect and is effective in preventing filming and fusing caused by toner adhering to the photoreceptor, but it is It was insufficient to remove silica etc. adhering to the means.

Japanese Patent Application Publication No. 2005-338750

One aspect of the present invention is directed to providing an image forming apparatus that can suppress contamination of a charging means and maintain stable image characteristics at a high level.

As a result of extensive studies, the inventors have found that the following configuration is important in order to provide an image forming apparatus that can suppress contamination of the charging means and maintain stable image characteristics at a high level. This heading led to the present invention.
That is, one aspect of the present invention is
an image carrier;
a corona discharge type charging means having a discharge electrode disposed opposite to the image carrier;
A discharge electrode cleaning means that comes into contact with the discharge electrode to clean the surface of the discharge electrode;
an exposure means for forming an electrostatic latent image on the surface of the image carrier that has been charged by the charging means;
a developing means for developing the electrostatic latent image using toner to form a toner image on the surface of the image carrier;
a transfer means for transferring the toner image to a transfer material;
cleaning means for cleaning toner remaining on the surface of the image carrier;
a fixing means for fixing the toner image transferred to the transfer material;
An image forming apparatus having:
The toner has toner particles and strontium titanate particles and silica particles present on the surface thereof,
The strontium titanate particles are
(i) The number average particle diameter (D1T) of the primary particles is 10 nm or more and less than 95 nm,
(ii) the average circularity is 0.700 or more and 0.920 or less,
(iii) It has a maximum peak (a) at a diffraction angle (2θ) of 32.00 deg or more and 32.40 deg or less in CuKα characteristic X-ray diffraction, and the half width of the maximum peak (a) is 0.23 deg or more and 0.2 deg or more. 50deg or less, and the intensity (Ia) of the maximum peak (a) and the intensity (Ix) of the maximum peak in the range of 24.00deg or more and 28.00deg or less of the diffraction angle (2θ) in CuKα characteristic X-ray diffraction. , satisfies the following formula (1),
(Ix)/(Ia) ≦ 0.010... Formula (1)
(iv) When it is assumed that all the elements detected by X-ray fluorescence analysis are contained in oxides, the total content of strontium oxide and titanium oxide when the total amount of all oxides is taken as 100% by mass. is 98.0% by mass or more,
The silica particles have a number average particle diameter (D1S) of primary particles of 5 nm or more and 300 nm or less,
The amount of the strontium titanate particles that separate from the toner when the toner is washed with water is 0.01 times or more and 0.9 times or less the amount of the silica particles that separate from the toner when the toner is washed with water. This is an image forming apparatus.

According to one aspect of the present invention, it is possible to provide an image forming apparatus that can suppress adhesion of external additives to a charging member and maintain stable image characteristics at a high level.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram of a charger according to the present embodiment. It is an external perspective view showing a corona charger. It is a sectional view showing a corona charger. FIG. 3 is a diagram showing the operating state of the corona charger when viewed from the side. It is a schematic block diagram of the discharge wire cleaning member in this implementation. It is a schematic block diagram of the discharge wire cleaning member and support member in this implementation. FIG. 2 is a cross-sectional view of the surface treatment apparatus in this embodiment.

EMBODIMENT OF THE INVENTION Below, with reference to drawings, the form for implementing this invention is illustratively described in detail. However, the dimensions, materials, shapes, and relative arrangement of the components described in this embodiment should be changed as appropriate depending on the configuration of the device to which the invention is applied and various conditions. The scope of the present invention is not limited to the following embodiments.

The image forming apparatus according to the present invention includes:
an image carrier;
a corona discharge type charging means having a discharge electrode disposed opposite to the image carrier;
A discharge electrode cleaning means that comes into contact with the discharge electrode to clean the surface of the discharge electrode;
an exposure means for forming an electrostatic latent image on the surface of the image carrier that has been charged by the charging means;
a developing means for developing the electrostatic latent image using toner to form a toner image on the surface of the image carrier;
a transfer means for transferring the toner image to a transfer material;
cleaning means for cleaning the toner image remaining on the image carrier;
a fixing means for fixing the toner image transferred to the transfer material;
An image forming apparatus having:
The toner has toner particles and strontium titanate particles and silica particles present on the surface thereof.
Strontium titanate particles and silica particles meet the following requirements.

The strontium titanate particles have the following properties (i) to (iv).
(i) The number average particle diameter (D1T) of the primary particles is 10 nm or more and less than 95 nm.
(ii) Average circularity is 0.700 or more and 0.920 or less.
(iii) It has a maximum peak (a) at a diffraction angle (2θ) of 32.00 deg or more and 32.40 deg or less in CuKα characteristic X-ray diffraction, and the half width of the maximum peak (a) is 0.23 deg or more and 0.2 deg or more. 50 deg or less, and the intensity (Ia) of the maximum peak (a) and the maximum peak degree (Ix) in the range of 24.00 deg or more and 28.00 deg or less of the diffraction angle (2θ) in CuKα characteristic X-ray diffraction, The following formula (1) is satisfied.
(Ix)/(Ia) ≦ 0.010...Formula (1)
(iv) When it is assumed that all the elements detected by X-ray fluorescence analysis are contained in oxides, the total content of strontium oxide and titanium oxide when the total amount of all oxides is 100% by mass. is 98.0% by mass or more.

The silica particles have a primary particle number average particle diameter (D1S) of 5 nm or more and 300 nm or less.
The amount of strontium titanate particles that separate from the toner when the toner is washed with water is 0.01 to 0.9 times the amount of silica particles that separate from the toner when the toner is washed with water.

The above-mentioned toner improves the cleaning effect of the cleaning member that comes into contact with the charging means and cleans the surface of the charging means, thereby suppressing contamination of the charging means and improving image forming apparatuses that can maintain stable image characteristics at a high level. can be provided.
The present inventors speculate that the reason why the toner of the present disclosure has solved the above problems is as follows.

The strontium titanate particles included in the toner have a primary particle number average particle diameter (D1T) of 10 nm or more and less than 95 nm, and an average circularity of 0.700 or more and 0.920 or less. By having such strontium titanate particles, the strontium titanate particles that have come off from the toner near the cleaning blade (cleaning member) can appropriately pass through the cleaning blade.

The fact that the number average particle diameter and average circularity of the primary particles of the strontium titanate particles are within the above range indicates that the shape is smaller than that of conventional strontium titanate and has a rounded shape with no corners. . As a result, the particles have a shape that allows them to pass through the cleaning blade more easily than conventional strontium titanate particles.

The strontium titanate particles and silica particles that have passed through the cleaning blade reach the vicinity of the discharge electrode due to the force associated with the rotation of the photoreceptor, the air flow and electric field of the corona charger, which will be described later. The discharge electrode of the corona charger includes a cleaning member that comes into contact with the discharge electrode to clean the surface of the discharge electrode in order to clean deposits. The cleaning member physically scrapes off deposits on the discharge electrode. At this time, strontium titanate particles adhere to the cleaning member.

The cleaning power of the cleaning member to which the strontium titanate particles having the above-mentioned number average particle diameter and average circularity are attached is increased, and the performance for removing deposits such as silica particles attached to the discharge electrode is improved. As a result, contamination of the charging means can be suppressed and stable image quality can be maintained over a long period of time. The number average particle diameter of the primary particles of the strontium titanate particles can be controlled by the concentrations of the titanium raw material and the strontium raw material, the reaction temperature, and the reaction time.

In the present invention, the strontium titanate particles have a maximum peak (a) at a diffraction angle (2θ) of 32.00 deg to 32.40 deg in CuKα characteristic X-ray diffraction, and the half-value width of the maximum peak (a) is , 0.23deg or more and 0.50deg or less. The maximum peak (a) is due to the (1,1,0) plane peak of the strontium titanate crystal.
As a result of intensive studies, the present inventors found that it is very important to control the half-value width to 0.23 deg or more and 0.50 deg or less.

Generally, the half-width of a diffraction peak in X-ray diffraction is related to the crystallite diameter of the object to be measured. One grain of a primary particle is composed of a plurality of crystallites, and the crystallite diameter refers to the size of each crystallite constituting the primary particle.
In the present invention, the term "crystallite" refers to individual crystal grains constituting a particle, and crystallites come together to form a particle. The size of the crystallites is unrelated to the size of the particles (particle size). When the crystallite diameter is small, the half-width becomes large, and when the crystallite diameter is large, the half-width becomes small.

The half width of the diffraction peak in X-ray diffraction of the strontium titanate particles according to the present invention is 0.23 deg or more and 0.50 deg or less, which indicates that the crystallite diameter is smaller than that of conventional strontium titanate particles. There is.
As the crystallite diameter of strontium titanate particles becomes smaller, the number of interfaces (crystal grain boundaries) between crystallites present in the primary particles increases.

Grain boundaries are considered to be points that trap charges. Therefore, when the amount of charge on the toner is small, the grain boundaries tend to trap the charge, so that the amount of triboelectric charge on the toner increases quickly. On the other hand, the inside of the crystallite of strontium titanate particles tends to leak toner charge, so if the toner becomes excessively charged and the amount of charge exceeds the amount of charge that can be trapped by the crystal grain boundaries, the charge will pass through the inside of the crystallite. It is believed that excessive charging of the toner can be controlled.

That is, by controlling the half-width to 0.23 deg or more and 0.50 deg or less, it is possible to achieve the effect of accelerating the rise of charging of the toner and suppressing excessive charging of the toner, which could not be obtained with conventional strontium titanate. I was able to do that. This charging characteristic may also lead to the effect of increasing the cleaning power of the cleaning member due to the adhesion of strontium titanate particles to the cleaning member of the discharge electrode.

When the above-mentioned strontium titanate particles speed up the charge rise of the toner and improve the effect of suppressing excessive charging, the charge amount distribution of the toner becomes sharper. When the toner charge amount distribution becomes sharp, the developability and transferability are improved compared to when the toner charge distribution is broad. As a result of improved transferability, the amount of toner that reaches the photoconductor cleaning (cleaning member) is optimized. In particular, good image formation can be achieved even when used for a long period of time in a low temperature, low humidity environment or a high temperature and high humidity environment.
It is important that the half width of the diffraction peak in X-ray diffraction of strontium titanate particles is 0.23deg or more and 0.50deg or less, preferably 0.25deg or more and 0.45deg or less, more preferably 0.28deg or more. It is 0.40 degrees or less.

In the present invention, the intensity (Ia) of the maximum peak (a) and the intensity (Ix) of the maximum peak in the range of 24.00 deg to 28.00 deg of the diffraction angle (2θ) in CuKα characteristic X-ray diffraction are as follows. It is important to satisfy formula (1).
(Ix)/(Ia) ≦ 0.010... Formula (1)
(Ix) represents the intensity of the peak of SrCO ₃ and TiO ₂ derived from the raw material of the strontium titanate particles.

When (Ix)/(Ia) does not satisfy formula (1), it means that the purity of strontium titanate is low. For example, if SrCO ₃ and TiO ₂ derived from the raw material of strontium titanate remain as impurities, the intensity (Ix) of their maximum peak becomes large, and the formula (1) is no longer satisfied. In this case, impurities are likely to be localized at grain boundaries, and the effect of improving the cleaning power of the above-mentioned cleaning member is reduced.
Formula (1) is
(Ix)/(Ia) ≦ 0.010
It is important that
Preferably,
(Ix)/(Ia) ≦ 0.008
It is. It is preferable that there be no peaks derived from impurities.
(Ix)/(Ia) can be controlled by the mixing ratio of titanium raw material and strontium raw material, reaction temperature, and reaction time. Furthermore, it can be controlled by acid washing the strontium titanate slurry after the reaction.

In addition, in the present invention, strontium titanate contains strontium oxide and titanium oxide, assuming that all the elements detected by fluorescent X-ray analysis are oxides, and the total amount of all oxides is 100% by mass. It is important that the amount is 98.0% by mass or more.
The content being less than 98.0% by mass means that there are many impurities other than strontium titanate inside the crystal. When there are many impurities inside the crystal of strontium titanate, the impurities give distortion to the crystal, and this effect increases the half-width. In this case, although it is possible to increase the half width, it is difficult to control the crystallite diameter to a small size, so the number of crystal grain boundaries decreases, and the effect of improving the cleaning power when it adheres to the cleaning member becomes weak.

By setting the total content of strontium oxide and titanium oxide to 98.0% by mass or more when the total amount of all oxides is 100% by mass, the crystallite diameter of the strontium titanate particles can be controlled to be small. Therefore, the adsorption capacity is improved. The content of strontium oxide and titanium oxide is preferably 98.2% by mass or more. Although the upper limit is not particularly limited, it is preferably 100% by mass or less. The content can be controlled by refining the titanium raw material and reducing impurities.

The image forming apparatus of the present invention can suppress contamination of the charging means by increasing the cleaning effect of the cleaning member that comes into contact with the discharge electrode for corona charging and cleans the surface of the discharge electrode.
The contact nip width between the photoreceptor and the cleaning blade is preferably 7 μm or more and 150 μm or less, more preferably 10 μm or more and 90 μm or less. Further, the average contact surface pressure is preferably 0.05 N/mm ² or more and 0.8 N/mm ² or less, more preferably 0.1 N/mm ² or more and 0.5 N/mm ² or less.
By setting the abutment nip width and average abutment surface pressure between the photoconductor and the cleaning blade within the above ranges, toner can be cleaned and strontium titanate particles can appropriately easily slip through the cleaning blade.

The amount of silica particles separated from the toner when the toner is washed with water is preferably 2.5 or less. By falling within this range, contamination of the charging member can be better suppressed.

It is preferable that the amount of strontium titanate particles separated from the toner when the toner is washed with water is 1.5 or less. By falling within this range, contamination of the charging member can be better suppressed.

(Silica particles)
In the present invention, the number average particle diameter (D1S) of the primary particles of silica particles present on the surface of the toner particles is 5 nm or more and 300 nm or less.
By having the particle size of the silica particles within this range, in addition to obtaining good fluidity, the silica particles form a blocking layer on the cleaning blade, making it possible to control the amount of strontium titanate that slips through.

Preferably, the toner has first silica particles and second silica particles having different number average particle diameters. Specifically, it is possible to have first silica particles having a number average particle diameter (D1S1) of 5 nm or more and 20 nm or less, and second silica particles having a number average particle diameter (D1S2) of 80 nm or more and 120 nm or less. preferable.

When the number average particle diameter of the first silica particles is within this range, the effect of scraping off the strontium titanate particles of the present invention with the cleaning member of the discharge electrode of the corona charger can be maximized.
In addition, since the number average particle diameter of the second silica particles is within this range, the second silica particles form a blocking layer on the cleaning blade, and the amount of the strontium titanate and the like that slips through can be appropriately controlled. I can do it.
Note that the blocking layer is a layer of an external additive formed on the surface of the photoreceptor. The blocking layer formed by the cleaning blade prevents toner remaining on the surface of the photoreceptor from slipping through from the upstream side in the rotational direction of the photoreceptor to the downstream side in the rotational direction of the photoreceptor with respect to the cleaning blade.

The relationship between the number average particle diameter (D1T) of the strontium titanate particles, the number average particle diameter (D1S1) of the first silica particles, and the number average particle diameter (D1S2) of the second silica particles is as follows. It is preferable that formula (2) is satisfied.
D1S2>D1T>D1S1... Formula (2)
As mentioned above, the second silica particles having a large particle size mainly serve to form the blocking layer in the cleaning blade, so they are preferably larger than the strontium titanate particles of the present invention. This allows the strontium titanate particles to pass through the cleaning blade appropriately. Furthermore, since the first silica particles are smaller than the strontium titanate particles of the present invention, the effect of scraping off the strontium titanate with the cleaning member of the discharge electrode in the corona charger is exhibited.

The toner preferably has a number-based median diameter (D50) of 3.0 μm or more and 6.0 μm or less. As the particle size of the toner becomes smaller and it becomes more difficult for the toner to pass through the cleaning blade, the strontium titanate particles exhibit a scraping effect on the cleaning member of the discharge electrode in the corona charger.
Next, preferred embodiments will be described.

(Detailed explanation regarding the production of strontium titanate particles)
The strontium titanate particles are preferably surface-treated for the purpose of hydrophobicization and triboelectrification control, if necessary. That is, examples of the treatment agent include unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane coupling agents, silane compounds having functional groups, and other organosilicon compounds. It will be done. Various processing agents may be used in combination. Among these, treatment with a silane coupling agent is particularly preferred. That is, it is preferable that the strontium titanate be fine particles surface-treated with a silane coupling agent.

Examples of the silane coupling agent include the following. Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4epoxycyclohexyl)ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyl Diethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxy Silane, diphenyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyldiethoxysilane, n-butyltrimethoxysilane, isobutyltrimethoxysilane, trimethylmethoxysilane, n-hexyltrimethoxysilane, n -Octyltrimethoxysilane, n-octyltriethoxysilane, n-decyltrimethoxysilane, hydroxypropyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, trifluoropropyltrimethoxysilane and these Hydrolyzate etc.

Among these, n-octyltriethoxysilane, isobutyltrimethoxysilane, and trifluoropropyltrimethoxysilane are preferred, and isobutyltrimethoxysilane is more preferred. Further, these processing agents may be used alone or in combination of two or more.
Although the surface of the strontium titanate particles can be chemically modified by surface treatment, the crystal structure of the strontium titanate particles is not affected. That is, the surface treatment does not affect the half-width of the maximum peak (a) of strontium titanate. Therefore, in the present invention, fluorescent X-ray measurement of strontium titanate is performed before surface treatment in order to measure impurity elements that affect the crystal structure.

Strontium titanate is produced, for example, by the following method, although there are no particular restrictions on its preparation method.
For example, strontium nitrate, strontium chloride, etc. are added to a titania sol dispersion obtained by adjusting the pH of a hydrous titanium oxide slurry obtained by hydrolyzing an aqueous titanyl sulfate solution. Then, after heating to the reaction temperature, synthesis can be performed by adding an alkaline aqueous solution. Note that the reaction temperature is preferably 60 to 100°C.

In order to control the half width of the maximum peak (a), in the step of adding the alkaline aqueous solution, it is preferable that the time required for adding the alkaline aqueous solution is 60 minutes or less. By controlling the addition rate of the alkaline aqueous solution to 60 minutes or less, particles with a small crystallite size can be obtained.
Furthermore, in the step of adding the alkaline aqueous solution, it is preferable to perform the addition while applying ultrasonic vibration in order to control the half-width. In the reaction process, by applying ultrasonic vibration, the crystal precipitation rate is increased, and particles with a small crystallite diameter can be obtained.

Further, it is preferable to rapidly cool the aqueous solution after the reaction by adding an alkaline aqueous solution in order to control the half-width. Examples of the rapid cooling method include a method of adding pure water cooled to 10° C. or lower until the desired temperature is reached. By rapidly cooling, it is possible to suppress the crystallite diameter from increasing in the cooling process.
On the other hand, a strong processing method (a method of applying a strong mechanical force to inorganic fine particles) may be used as a method of controlling the half width. As the strong processing, methods such as ball milling, high-pressure twisting, drop weight processing, particle impact, and air shot peening can be used.

(Detailed explanation about the production of silica particles)
The silica particles used in the present invention include wet silica produced by a precipitation method, sol-gel method, etc., and dry silica produced by a deflagration method, fumed method, etc., but dry silica is more preferable from the viewpoint of ease of shape control.
Dry silica uses silicon halide compounds and the like as raw materials. As the silicon halogen compound, silicon tetrachloride is used, but silanes such as methyltrichlorosilane and trichlorosilane alone or a mixture of silicon tetrachloride and silanes can also be used as a raw material.

After the raw material is vaporized, the desired silica is obtained through a so-called flame hydrolysis reaction in which it reacts with water produced as an intermediate in an oxyhydrogen flame. For example, it utilizes the thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen and hydrogen, and the reaction formula is as follows.
SiCl ₄ +2H ₂ +O ₂ →SiO ₂ +4HCl
Below, an example of manufacturing the dry silica used in the present invention will be explained.

After supplying oxygen gas to the burner and igniting the ignition burner, hydrogen gas was supplied to the burner to form a flame, and silicon tetrachloride, which was a raw material, was introduced into the flame and gasified. Next, a flame hydrolysis reaction was performed, and the generated silica powder was collected. The number average particle size and shape can be arbitrarily adjusted by appropriately changing the flow rate of silicon tetrachloride, the flow rate of oxygen gas supply, the flow rate of hydrogen gas supply, and the residence time of silica in the flame.
As a method for crushing silica particles, for example, a crusher such as an atomizer (manufactured by Tokyo Atomizer Manufacturing Co., Ltd.) can be used.
The silica particles are preferably surface-treated for purposes such as hydrophobicization and triboelectrification control, using various treatment agents alone or in combination, if necessary. Examples of processing agents include the following. Unmodified silicone varnish, various modified silicone varnishes, unmodified silicone oil, various modified silicone oils, silane coupling agents, silane compounds having functional groups, or other organosilicon compounds.

(Detailed explanation about toner)
Toner particles usually contain a binder resin and a colorant, and if necessary, a release agent, a charge control agent, and the like.

Examples of the binder resin include the following. Styrene resin, styrene copolymer resin, polyester resin, polyol resin, polyvinyl chloride resin, phenol resin, natural resin-modified phenol resin, natural resin-modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, Polyurethane resin, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumaron indene resin, petroleum resin. Preferably used resins include styrene copolymer resins, polyester resins, and hybrid resins in which polyester resins and styrene copolymer resins are mixed or partially reacted. More preferably, the binder resin includes a polyester resin.

A release agent (wax) may be used to impart release properties to the toner.
Examples of waxes include: Aliphatic hydrocarbon waxes such as low molecular weight polyethylene, low molecular weight polypropylene, olefin copolymers, microcrystalline wax, paraffin wax, and Fischer-Tropsch wax; Oxidized waxes of aliphatic hydrocarbon waxes such as oxidized polyethylene wax; Carnauba wax , waxes mainly composed of fatty acid esters such as behenyl behenate, and montanate wax; and waxes that are partially or completely deoxidized from fatty acid esters such as deoxidized carnauba wax.

Additionally, the following may be mentioned: Saturated straight chain fatty acids such as palmitic acid, stearic acid, and montanic acid; unsaturated fatty acids such as branzic acid, eleostearic acid, and valinaric acid; stearyl alcohol, aralkyl alcohol, behenyl alcohol, carnaubil alcohol, seryl alcohol, Saturated alcohols such as sil alcohol; polyhydric alcohols such as sorbitol; fatty acid amides such as linoleic acid amide, oleic acid amide, lauric acid amide; methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide , saturated fatty acid bisamides such as hexamethylene bisstearic acid amide; ethylene bisoleic acid amide, hexamethylene bisoleic acid amide, N,N'-dioleyladipic acid amide, N,N'-dioleylsebacic acid amide, etc. Unsaturated fatty acid amides; Aromatic bisamides such as m-xylene bisstearamide and N,N'-distearylisophthalic acid amide; Aliphatic metals such as calcium stearate, calcium laurate, zinc stearate, and magnesium stearate Salts (generally referred to as metal soaps); Waxes made by grafting aliphatic hydrocarbon waxes with vinyl copolymer monomers such as styrene and acrylic acid; Fatty acids and polyhydric alcohols such as behenic acid monoglyceride Partial esterification products; methyl ester compounds with hydroxyl groups obtained by hydrogenation of vegetable oils and fats, etc.

The wax particularly preferably used in the present invention is an aliphatic hydrocarbon wax. For example, the following are preferred. Low molecular weight hydrocarbons obtained by radical polymerization of alkylene under high pressure or polymerization under low pressure with Ziegler catalysts or metallocene catalysts; Fischer-Tropsch wax synthesized from coal or natural gas; Olefins obtained by thermally decomposing high molecular weight olefin polymers polymer. A synthetic hydrocarbon wax obtained from the distillation residue of hydrocarbons obtained by the Age method from synthesis gas containing carbon monoxide and hydrogen, or a synthetic hydrocarbon wax obtained by hydrogenating these.

Furthermore, those obtained by fractionating the hydrocarbon wax by a press sweating method, a solvent method, a vacuum distillation method, or a fractional crystallization method are more preferably used. Particularly preferred is a wax synthesized by a method that does not involve polymerization of alkylene, in view of its molecular weight distribution.
The wax may be added at the time of producing the toner or the time of producing the binder resin. Further, these waxes may be used alone or in combination of two or more. The wax is preferably added in an amount of 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

The toner of the present invention can be used as any of a magnetic one-component toner, a non-magnetic one-component toner, and a non-magnetic two-component toner.
When used as a magnetic one-component toner, magnetic iron oxide particles are preferably used as the colorant. The magnetic iron oxide particles contained in the magnetic one-component toner include magnetic iron oxides such as magnetite, maghemite, and ferrite, and magnetic iron oxides containing other metal oxides; metals such as Fe, Co, and Ni; Alloys of these metals with metals such as Al, Co, Cu, Pb, Mg, Ni, Sn, Zn, Sb, Be, Bi, Cd, Ca, Mn, Se, Ti, W, and V; Mixtures may be mentioned. The content of the magnetic iron oxide particles is preferably 30 parts by mass or more and 100 parts by mass or less with respect to 100 parts by mass of the binder resin.

Examples of colorants used in non-magnetic one-component toners and non-magnetic two-component toners include the following.
As the black pigment, carbon black such as furnace black, channel black, acetylene black, thermal black, and lamp black is used, and magnetic powder such as magnetite and ferrite is also used.

Pigments or dyes can be used as coloring agents suitable for yellow color. Examples of pigments include the following: C. I. Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 17, 23, 62, 65, 73, 74, 81, 83, 93, 94, 95, 97, 98, 109, 110, 111, 117, 120, 127, 128, 129, 137, 138, 139, 147, 151, 154, 155, 167, 168, 173, 174, 176, 180, 181, 183, 191, C. I. Bat Yellow 1, 3, 20. As a dye, C. I. Examples include Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, and the like. These materials may be used alone or in combination of two or more.

Pigments or dyes can be used as colorants suitable for cyan color. As a pigment, C. I. Pigment Blue 1, 7, 15, 15; 1, 15; 2, 15; 3, 15; 4, 16, 17, 60, 62, 66, etc., C.I. I. Bat Blue 6, C. I. Acid Blue 45 is mentioned. As a dye, C. I. Examples include Solvent Blue 25, 36, 60, 70, 93, and 95. These materials may be used alone or in combination of two or more.

Pigments or dyes can be used as colorants suitable for magenta color. Examples of pigments include the following: C. I. Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 48, 48; 2, 48; 3, 48; 4, 49, 50, 51, 52, 53, 54, 55, 57, 57; 1, 58, 60, 63, 64, 68, 81, 81; 1, 83, 87, 88, 89, 90, 112, 114, 122, 123, 144, 146, 150, 163, 166, 169, 177, 184, 185, 202, 206, 207, 209, 220, 221, 238, 254, etc., C. I. Pigment Violet 19; C. I. Bat Red 1, 2, 10, 13, 15, 23, 29, 35.

Examples of magenta dyes include the following. C. I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 52, 58, 63, 81, 82, 83, 84, 100, 109, 111, 121, 122, etc., C.I. I. Disperse Red 9, C. I. Solvent Violet 8, 13, 14, 21, 27 etc., C.I. I. Oil-soluble dyes such as Disperse Violet 1, C.I. I. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, 40, etc., C. I. Basic dyes such as Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, 28, etc. These materials may be used alone or in combination of two or more.

The content of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.
A charge control agent may be used in the toner. Known charge control agents can be used, examples of which include the following. Azo iron compounds, azo chromium compounds, azo manganese compounds, azo cobalt compounds, azo zirconium compounds, chromium compounds of carboxylic acid derivatives, zinc compounds of carboxylic acid derivatives, aluminum compounds of carboxylic acid derivatives, Zirconium compounds.

The carboxylic acid derivative is preferably an aromatic hydroxycarboxylic acid. Further, a charge control resin can also be used. When using a charge control agent or a charge control resin, it is preferable to use 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin.
Other external additives may be added to the toner as necessary. Examples of such external additives include fine resin particles that function as charging aids, conductivity imparting agents, fluidity imparting agents, anti-caking agents, release agents during heat roller fixing, lubricants, abrasives, etc. Examples include inorganic fine particles. Examples of the lubricant include polyfluoroethylene powder, zinc stearate powder, and polyvinylidene fluoride powder. Examples of the abrasive include cerium oxide powder and silicon carbide powder.
The toner may be mixed with a carrier and used as a two-component developer. As the carrier, a normal carrier such as ferrite or magnetite or a resin-coated carrier can be used. Furthermore, a binder type carrier core in which magnetic powder is dispersed in a resin can also be used.

(Detailed explanation about carrier)
The resin-coated carrier consists of carrier core particles and a coating material that is a resin that covers (coats) the surface of the carrier core particles. Examples of resins used for the covering material include the following. Styrene-acrylic resins such as styrene-acrylic ester copolymers and styrene-methacrylic ester copolymers; Acrylic resins such as acrylic ester copolymers and methacrylic ester copolymers; polytetrafluoroethylene, monochloro Fluorine-containing resins such as trifluoroethylene polymers and polyvinylidene fluoride; silicone resins; polyester resins; polyamide resins; polyvinyl butyral; aminoacrylate resins. Other examples include iomonomer resin and polyphenylene sulfide resin. These resins can be used alone or in combination.

(Detailed explanation of toner manufacturing method)
Here, a procedure for producing toner using a pulverization method will be described.
In the raw material mixing step, predetermined amounts of a binder resin, a colorant, a wax, and, if necessary, other components such as a charge control agent are weighed out, blended, and mixed as materials constituting the toner particles. Examples of the mixing device include a double con mixer, a V-type mixer, a drum-type mixer, a super mixer, a Henschel mixer, a Nauta mixer, and a mechano hybrid (manufactured by Nippon Coke Industry Co., Ltd.).

Next, the mixed materials are melted and kneaded to disperse wax and the like in the binder resin. In the melt-kneading step, a batch-type kneader such as a pressure kneader or a Banbury mixer, or a continuous-type kneader can be used. Single-screw or twin-screw extruders are the mainstream because of their advantage in continuous production. For example, KTK type twin screw extruder (manufactured by Kobe Steel, Ltd.), TEM type twin screw extruder (manufactured by Toshiba Machinery Co., Ltd.), PCM kneader (manufactured by Ikegai Tekko Co., Ltd.), twin screw extruder (manufactured by Ikegai Iron Works Co., Ltd.), (manufactured by K.C.K. Co., Ltd.), Co-kneader (manufactured by Busu Co., Ltd.), and Kneedex (manufactured by Nippon Coke Industry Co., Ltd.).
Further, the resin composition obtained by melt-kneading may be rolled with two rolls or the like, and cooled with water or the like in a cooling step.

Next, the cooled resin composition is pulverized to a desired particle size in a pulverization step. In the pulverization process, the material is coarsely pulverized using a pulverizer such as a crusher, hammer mill, or feather mill, and then finely pulverized using a pulverizer. Examples of fine grinders include Kryptron System (manufactured by Kawasaki Heavy Industries, Ltd.), Super Rotor (manufactured by Nissin Engineering Co., Ltd.), Turbo Mill (manufactured by Turbo Kogyo Co., Ltd.), and air jet type fine grinders. Can be mentioned.
Thereafter, if necessary, the particles are classified using a classifier or a sieve to obtain base particles. Examples of classifiers and sieves include the following: Inertial classification method Elbow Jet (manufactured by Nippon Steel Mining Co., Ltd.), centrifugal classification method Turboplex (manufactured by Hosokawa Micron Co., Ltd.), TSP separator (manufactured by Hosokawa Micron Co., Ltd.), Faculty (manufactured by Hosokawa Micron Co., Ltd.) Classifiers and sieves.

After passing through an adhesion step of adhering strontium titanate particles and silica particles to the surface of the base particles thus obtained, a surface treatment using hot air is performed. Then, if necessary, the toner particles can be classified using a classifier or a sieve to obtain toner particles having strontium titanate particles and silica particles fixed to their surfaces.
In the attachment step, the method of attaching strontium titanate particles and silica particles to the surface of the base particles is not particularly limited, and the base particles, strontium titanate particles, and silica particles are weighed in predetermined amounts, blended, and mixed. .
Further, other inorganic fine particles, a charge control agent, a fluidity imparting agent, etc. may be added at the same time as long as the effects of the present invention are not impaired.

Examples of the mixing device include a double con mixer, a V-type mixer, a drum-type mixer, a super mixer, a Henschel mixer, and a Nauta mixer, each of which is preferably used.
It is more preferable to use a Henschel mixer as the mixing device, since the strontium titanate particles and silica particles can be more uniformly adhered to the surface of the base particles.

As for the mixing conditions, the higher the rotation speed of the mixing blade and the longer the mixing time, the more strontium titanate particles and silica particles are more likely to be uniformly adhered to the surface of the base particles, which is preferable.
However, if the rotational speed of the mixing blade is too high or the mixing time is too long, the frictional heat between the toner and the mixing blade increases, and the temperature of the toner may rise and fuse.
Therefore, it is preferable to actively cool the mixer by providing a mixing blade or a water cooling jacket to the mixer.

The rotation speed of the mixing blade and the mixing time are preferably adjusted to a range where the temperature inside the mixer is 45° C. or less. Specifically, the maximum circumferential speed of the mixing blade is preferably 10.0 m/sec or more and 150.0 m/sec or less, and the mixing time is preferably adjusted within a range of 0.5 minutes to 60 minutes.

In addition, the adhesion process may be performed in one step or in multiple steps of two or more, and the mixing device, mixing conditions, and base particle composition used in each step may be the same or different. It's okay.
In the present invention, the apparatus used for the treatment using hot air has means for melting the surface of toner particles before treatment using hot air, and has a means for melting the surface of toner particles before treatment using hot air, and Any type of device may be used as long as it has a means for cooling with cold air.

An example of such a device is Meteor Rainbow MR Type (manufactured by Nippon Pneumatic Kogyo Co., Ltd.).
Next, one embodiment of a surface treatment method using hot air will be described with reference to FIG. 8, but the method is not limited thereto.
In the present invention, base particles having strontium titanate particles and silica particles attached to their surfaces are subjected to surface treatment using hot air, and the particles having strontium titanate particles and silica particles fixed to their surfaces are called toner particles. . However, in the description of this specification, for convenience, particles before strontium titanate particles and silica particles are fixed to their surfaces may also be referred to as toner particles.

FIG. 8 is an example of a cross-sectional view of the surface treatment apparatus used in the present invention. Specifically, the surface treatment method uses a raw material in which strontium titanate particles and silica particles are attached to the surface of base particles in advance, and supplies the raw material to the surface treatment apparatus.
The toner particles 114 supplied from the toner particle supply port 100 are accelerated by the injection air jetted from the high-pressure air supply nozzle 115, and head toward the air jetting member 102 located below.

Diffusion air is ejected from the air jetting member 102, and the toner particles are diffused outward by this diffusion air. At this time, the state of diffusion of toner particles can be controlled by adjusting the flow rate of injection air and the flow rate of diffusion air.
In addition, cooling jackets 106 are provided around the outer periphery of the toner particle supply port 100, the outer periphery of the surface treatment device, and the outer periphery of the transfer pipe 116 for the purpose of preventing toner particles from fusing.

Note that it is preferable that cooling water (preferably an antifreeze solution such as ethylene glycol) be passed through the cooling jacket.
On the other hand, the surface of the toner particles diffused by the diffusion air is treated by the hot air supplied from the hot air supply port 101.
At this time, the discharge temperature of the hot air is preferably 100°C or more and 300°C or less, more preferably 150°C or more and 250°C or less.

If the temperature of the hot air is less than 100°C, the melting state of the toner particles will be insufficient, and the strontium titanate particles and silica particles will not be sufficiently embedded in the surface of the toner particles, causing the strontium titanate particles and silica particles to melt. Particles may not be able to stick.
If the temperature of the hot air exceeds 300° C., the toner particles will melt too much. Therefore, the degree of embedding of the strontium titanate particles and silica particles on the surface of the toner particles becomes uneven, or the strontium titanate particles and silica particles are completely embedded inside the toner particles. As a result, the fluidity and chargeability of the resulting toner may deteriorate. Furthermore, toner particles tend to coalesce during the manufacturing process, which may result in coarse toner particles or large amounts of toner particles being fused to the inner wall surface of the device.

Further, by adjusting the hot air discharge temperature within the above temperature range, the average circularity of the obtained toner can be controlled to 0.955 or more and 0.980 or less.
The higher the processing temperature, the higher the average circularity of the resulting toner, and the lower the processing temperature, the lower the average circularity of the resulting toner. The degree of circularity tends to increase.

Therefore, it is considered that the degree to which strontium titanate particles and silica particles are buried in the surface of the toner particles differs depending on the average circularity of the toner. However, since the number average particle diameter of the primary particles of the strontium titanate particles and silica particles used in the present invention is within a specific range, the average circularity of the toner is within the above range and is not properly embedded in the surface of the toner particles. It is preferable because it has a high adhesion strength.

The toner particles whose surfaces have been treated with hot air are cooled by cold air supplied from a first cold air supply port 103 provided on the outer periphery of the hot air supply port 101 at the top of the apparatus. At this time, in order to control the temperature distribution within the apparatus and the surface condition of the toner particles, it is preferable to introduce cold air from a second cold air supply port 104 provided on the side surface of the main body of the apparatus. The outlet of the second cold air supply port 104 can have a slit shape, a louver shape, a perforated plate shape, a mesh shape, etc., and the introduction direction can be selected horizontally toward the center or along the device wall depending on the purpose. It is.

At this time, the temperature of the cold air is preferably -50°C or more and 10°C or less, more preferably -40°C or more and 8°C or less. Further, it is preferable that the cold air is dehumidified air. Specifically, the absolute moisture content in the cold air is preferably 5 g/m ³ or less, more preferably 3 g/m ³ or less.
If the temperature of these cold air is less than -50℃, the temperature inside the device will drop too much, and the original purpose of heat treatment will not be achieved sufficiently, making it impossible to melt the surface of the toner particles. There is.
Furthermore, if the temperature of the cold air exceeds 10°C, the toner particles that have been surface-treated with hot air cannot be sufficiently cooled, resulting in coarsening of the toner particles and fusion due to coalescence of the toner particles. There are cases.

Thereafter, the cooled toner particles are sucked by a blower, passed through a transfer pipe 116, and collected by a cyclone or the like.
After performing the surface treatment with hot air in this manner, the toner particles can be classified using a classifier or a sieve if necessary to obtain toner particles having strontium titanate particles and silica particles fixed to their surfaces.

The toner of the present invention further includes at least one of silica particles and titanium oxide particles having a number average primary particle diameter of 5 nm or more and 50 nm or less after surface treatment with hot air. Preferably, it is added externally. This is because it becomes possible to further improve the fluidity of the toner.

<Image forming process>
(Description of each part of the image forming apparatus)
The schematic configuration of the image forming apparatus of this embodiment will be described using FIGS. 1 and 2. FIG. 1 is an overall schematic diagram of an image forming apparatus. FIG. 2 is a schematic diagram of the image forming section.
The image forming apparatus 100 shown in FIG. 1 is an electrophotographic tandem full-color printer. The image forming apparatus 100 includes image forming units PY, PM, PC, and PK that form yellow, magenta, cyan, and black images, respectively. The image forming apparatus 100 generates toner according to an image signal from a document reading device (not shown) connected to the apparatus main body 100A or an external device (not shown) such as a personal computer communicably connected to the apparatus main body 100A. Form an image on a recording material. Examples of the recording material include sheet materials such as paper, plastic film, and cloth.

As shown in FIG. 1, the image forming units PY, PM, PC, and PK are arranged side by side along the moving direction of the intermediate transfer belt 8. The intermediate transfer belt 8 is stretched around a plurality of rollers and is configured to run in the direction of arrow R2. The intermediate transfer belt 8 carries and conveys the primarily transferred toner image as described later. A secondary transfer roller 10 is disposed at a position facing a roller 9 that stretches the intermediate transfer belt 8 across the intermediate transfer belt 8, and is used for secondary transfer that transfers the toner image on the intermediate transfer belt 8 onto a recording material. It constitutes part T2. A fixing device 11 is arranged downstream of the secondary transfer section T2 in the recording material conveyance direction.

At the bottom of the image forming apparatus 100, a cassette 12 containing recording materials is arranged. The recording material is conveyed from the cassette 12 toward the registration roller 14 by the conveyance roller 13 . Thereafter, the registration roller 14 starts rotating in synchronization with the toner image on the intermediate transfer belt 8, and the recording material is conveyed to the secondary transfer section T2.
The four image forming units PY, PM, PC, and PK included in the image forming apparatus 100 have substantially the same configuration except that the developing colors are different. Therefore, here, the image forming section PK will be explained as a representative, and the explanation of the other image forming sections will be omitted.

As shown in FIG. 2, a photosensitive drum 1 is disposed in the image forming section PK. The photosensitive drum 1 is formed to have, for example, an outer diameter of 84 mm and a length of 380 mm, and is rotated in the direction of arrow R1 at a rotation speed of, for example, 450 mm/s. A corona charger 2 , an exposure device 3 , a developing device 4 , a primary transfer roller 5 , and a cleaning device 6 are arranged around the photosensitive drum 1 .
A process of forming, for example, a four-color full-color image using the image forming apparatus 100 configured as described above will be described.

First, when an image forming operation starts, the surface of the rotating photosensitive drum 1 is uniformly charged by the corona charger 2. The corona charger 2 charges the photosensitive drum 1 to a uniform negative dark area potential by irradiating charged particles associated with corona discharge. The charging width of the corona charger 2 in the circumferential direction of the photosensitive drum 1 is, for example, about 30 mm. Details of the corona charger 2 will be described later (see FIGS. 3 to 6). Next, the photosensitive drum 1 is scanned and exposed with a laser beam corresponding to an image signal emitted from the exposure device 3. As a result, an electrostatic latent image is formed on the photosensitive drum in accordance with the image signal. The electrostatic latent image on the photosensitive drum is visualized by toner contained in the developing device 4 and becomes a visible image.

The toner image formed on the photosensitive drum 1 is primarily transferred onto the intermediate transfer belt 8 at a primary transfer portion T1 configured between the primary transfer roller 5 and the primary transfer roller 5 disposed with the intermediate transfer belt 8 in between. At this time, a primary transfer bias is applied to the primary transfer roller 5. Toner remaining on the surface of the photosensitive drum 1 after the primary transfer is removed by a cleaning device 6. The contact nip width between the photosensitive drum 1 and the cleaning blade was set in the range of 10 to 70 μm. Further, the average contact surface pressure was set in a range of 0.2 N/mm ² or more and 1.2 N/mm ² or less. The cleaning blade may have different hardness between the contact surface that contacts the photosensitive drum 1 and the internal hardness that does not contact the photosensitive drum 1. In that case, it is preferable to use a type in which the hardness of the contact surface that contacts the photosensitive drum 1 is increased.

Such operations are sequentially performed at each of the yellow, magenta, cyan, and black image forming sections, and the four color toner images are superimposed on the intermediate transfer belt 8. Thereafter, the recording material accommodated in the cassette 12 is conveyed to the secondary transfer section T2 in accordance with the timing of forming the toner image. Then, by applying a secondary transfer bias to the secondary transfer roller 10, the four-color toner images on the intermediate transfer belt 8 are secondary-transferred all at once onto the recording material.

Next, the recording material is conveyed to the fixing device 11. The fixing device 11 heats and presses the recording material being conveyed. As a result, the toner on the recording material is melted and mixed, and is fixed on the recording material as a full-color image. Thereafter, the recording material is discharged onto the discharge tray 15. In this way, a series of image forming processes is completed.

<Corona charger>
The configuration of the corona charger 2 will be explained using FIGS. 3 to 5. The corona charger 2 is a scorotron type charging device, and FIG. 3 shows the corona charger 2 viewed from the photosensitive drum side. The corona charger 2 is removably installed in the apparatus main body 100A (see FIG. 1) of the image forming apparatus 100, and as shown in FIG. placed in opposing positions.

The corona charger 2 as a charging device includes a pair of shield plates 203 as shield electrodes, a front block 201 arranged on the front side in the insertion direction of the corona charger 2 (arrow X direction in the figure), and a corona charger. 2, and a rear block 202 disposed on the rear side in the insertion direction.
The corona charger 2 has an air flow passing from above to below the charger. Stable corona discharge is achieved by supplying outside air through airflow. The pair of shield plates 203 are formed using stainless steel (SUS), and are spaced from each other at a predetermined interval (for example, about 30 mm) in the width direction of the housing 90 (the direction perpendicular to the rotational axis direction of the photosensitive drum 1, the lateral direction). are arranged to face each other. The shield plate 203, the front block 201, and the back block 202 form an open housing 90 with a substantially U-shaped cross section. The housing 90 has an opening 90a on the side facing the photosensitive drum 1. The front block 201 and the back block 202 can hold a discharge wire 205 (see FIG. 4) and a grid electrode 206, which will be described later, stretched in the longitudinal direction.

<Discharge electrode (discharge wire)>
As shown in FIG. 4, the corona charger 2 includes a discharge wire 205 and a grid electrode 206. A discharge wire 205 serving as a discharge electrode is arranged inside the pair of shield plates 203 (inside the housing). The discharge wire 205 generates corona discharge when a charging voltage is applied from a high voltage power source (not shown). The discharge wire 205 is made of, for example, stainless steel, nickel, molybdenum, tungsten, gold, or the like.
As the diameter of the discharge wire 205 decreases, it becomes more likely to be cut by collisions of ions generated during discharge. Conversely, as the diameter of the discharge wire 205 increases, a higher charging voltage is required to produce a stable corona discharge. However, if the charging voltage is set too high, ozone is likely to be generated due to discharge. In view of the above, the discharge wire 205 is preferably formed to have a diameter of 40 μm to 100 μm. As an example, the discharge wire 205 is a tungsten wire with a diameter of 60 μm. Note that the discharge electrode is not limited to the discharge wire 205 as described above, but may be one having sawtooth teeth formed in a longitudinal direction in an uneven manner.

<Grid electrode>
The grid electrode 206 is disposed between the photosensitive drum 1 and the discharge wire 205, and is removably attached to a casing consisting of a front block 201 and a back block 202 of the charger so as to be close to the surface of the photosensitive drum 1. ing. The grid electrode 206 is attached to the housing 90 so as to be stretched in the rotational axis direction (longitudinal direction) of the photosensitive drum 1 with a predetermined tension.
Specifically, as shown in FIG. 5A, the grid electrode 206 is held by a holding part 207 provided on the front block 201 and a holding part 209 provided on the back block 202. The grid electrode 206 is then removed from or attached to the holding parts 207 and 209 in response to the user operating the knob 208. Furthermore, the knob 208 can adjust the tension with which the grid electrode 206 is stretched through the holding parts 207 and 209.

The grid electrode 206 can control the amount of current flowing to the photosensitive drum side when a high voltage is applied from a high voltage power source (not shown). This controls the charging potential on the surface of the photosensitive drum 1. The closer the grid electrode 206 is to the surface of the photosensitive drum 1, the more effective it is to uniformly charge the surface of the photosensitive drum 1. In this embodiment, the closest distance between the grid electrode 206 and the photosensitive drum 1 is "1.3±0.3 mm." Further, the distance between the grid electrode 206 and the discharge wire 205 was set to 8 mm. In other words, the discharge wire 205 is disposed at a distance of about 9.3 mm from the photosensitive drum 1.

<Discharge electrode cleaning member>
Further, as shown in FIG. 4, the discharge wire 205 of the corona charger 2 has a discharge wire cleaning member 30 (hereinafter also simply referred to as "cleaning member") that contacts the discharge wire 205 and a cleaning member support member (hereinafter referred to as "cleaning member"). , also simply referred to as a "support member") 40.
FIG. 7 is an enlarged view showing the two discharge wire cleaning members 30 attached to the cleaning member support member 40 sandwiching the discharge wire 205. As shown in FIG.

FIG. 6 is an enlarged cross-sectional view of the discharge wire cleaning member 30. As shown in FIG. The discharge wire cleaning member 30 is composed of a support layer 31, an abrasion resistant layer 32, and a polishing layer 33. The support layer 31 is a layer made of elastic sponge rubber. The wear-resistant layer 32 is a layer made of a nonwoven PET material and adhered onto the support layer 31 with a double-sided adhesive tape. The polishing layer 33 is a layer formed by solidifying alumina powder with an epoxy resin on the wear-resistant layer 32. The elastic support layer 31 is preferably made of a flame-retardant material.

As shown in FIG. 7, the polishing layer 33 of the cleaning member 30 is brought into contact with the discharge wire 205 with pressure so as to wrap around the discharge wire 205 due to the elastic force of the support layer 31 and the wear-resistant layer 32. When the discharge wire 205 is cleaned by a cleaning operation in which the cleaning member 30 is moved in parallel with the polishing layer 33 in contact with the discharge wire 205, deposits on the discharge wire 205 are removed and cleaned by the polishing layer. Therefore, if particles of silica or strontium titanate adhere to the discharge wire 205, the cleaning operation is performed while the particles of silica or strontium titanate are retained on the surface of the polishing layer 33.

<Operation of discharge electrode cleaning member>
In this embodiment, immediately after the main switch of the image forming apparatus is turned on and every time 2000 images are formed, the discharge wire cleaning member 30 is placed between the front block 201 and the rear block with the discharge wire 205 sandwiched therebetween. It moves back and forth between block 202 and the like. This reciprocating operation polishes off contaminants attached to the surface of the discharge wire 205.

As mentioned above, the discharge wire cleaning member 30 is supported by the support member 40. As shown in FIGS. 5(a) and 5(b), the support member 40 is connected to the drive screw 217. The drive screw 217 is rotationally driven by the motor M. As the drive screw 217 rotates (forward rotation), the support member 40 moves in the direction of arrow B.
A position detection member 220 is attached to the support member 40, and the positions of the cleaning member 30 and the support member 40 can be detected by position sensors PS1 and PS2.

As the position sensors PS1 and PS2, it is preferable to use, for example, a photo-interrupt type sensor in which a light-emitting part that emits light and a light-receiving part that receives the light emitted from the light-emitting part are arranged facing each other.
When the position sensor PS2 detects the position detection member 220 of the support member 40, the drive screw 217 is driven to reverse rotation, and the cleaning member 30 connected to the support member 40 is moved in the direction of arrow C.

By using the position sensors PS1 and PS2, it is possible to accurately control how many times (how many reciprocations) the cleaning member 30 has cleaned the discharge wire 205. Further, by controlling the rotational drive of the motor M before the cleaning member 30 hits the block 202 or the like, it is possible to avoid the cleaning member 30 from hitting the block 202 or the like.
Further, a cleaning brush 250 for cleaning the grid electrode 206 is also connected to the support member 40 . The cleaning member 30 of the discharge wire 205 and the cleaning brush 250 of the grid electrode 206 clean the discharge wire 205 and the grid electrode 206 as the support member 40 moves.

As the cleaning brush 250, a brush made of resin such as nylon (registered trademark), polyvinyl chloride (PVC), polyphenylene sulfide resin (PPS), etc., which is treated to be flame retardant and woven into a base fabric is used. Note that the cleaning brush 250 is not limited to a brush-like one, and may be, for example, a pad-like one formed of felt or sponge, or a sheet-like one coated with an abrasive such as alumina or silicon carbide.

When the toner having the above-mentioned strontium titanate particles is used, an appropriate amount of the strontium titanate particles as well as the silica particles slip through the cleaning blade. A portion of the particles that have slipped through adhere to the discharge wire 205 due to the influence of the force accompanying the rotation of the photosensitive drum 1, the electric field formed by the discharge of the corona charger 2, air flow, and the like. A cleaning member 30 removes contaminants such as silica attached to the discharge wire 205.

Using cleaning members with the same formulation, the cleaning effects were compared between (1) when only silica particles were attached to the discharge wire 205, and (2) when silica particles and a predetermined amount of strontium titanate particles were attached. As a result, it was found that the cleaning effect of the cleaning member 30 was better in case (2) than in case (1).
This means that the silica particles and strontium titanate particles attached to the discharge wire 205 are removed by the cleaning member 30 and retained by the polishing layer 33 of the cleaning member 30 . It is believed that the strontium titanate particles themselves held in the polishing layer 33 come into contact with the deposits on the discharge wire 205 together with the polishing layer, thereby increasing the efficiency of removing and cleaning the deposits on the discharge wire 205.

Note that in this embodiment, the cleaning member 30 having the polishing layer 33 was brought into contact with the discharge wire 205. However, even without the polishing layer 33, if the characteristics such as the foaming formula and surface roughness of the sponge are properly controlled, a sponge with elasticity or a sheet of urethane or PET (polyethylene terephthalate) with an appropriate thickness can be used as a discharge wire. The cleaning effect can be obtained even if it is brought into direct contact with 205. As for the shape of the cleaning member, the cleaning effect can be obtained even if the cleaning member does not have a shape in which the discharge electrode is sandwiched between the cleaning members, but is made in the shape of a roller and contacts the discharge electrode while rotating. Further, even if the shape of the discharge electrode is not a wire shape, but a serrated electrode, the above-mentioned cleaning effect by the strontium titanate particles can be obtained as long as it is a cleaning member that comes in contact with the discharge electrode for cleaning.
Next, the method for measuring each physical property according to the present invention will be described.

<X-ray diffraction measurement>
The measurement is performed using MiniFlex600 (manufactured by Rigaku Co., Ltd.) under the following conditions.
For the measurement sample, inorganic fine particles (strontium titanate) are placed in a powder state on a non-reflection sample plate (manufactured by Rigaku Co., Ltd.) that does not have a diffraction peak within the measurement range, while being lightly pressed so that it is flat. Once it is flat, place the sample plate into the device.

[Measurement conditions for X-ray diffraction]
Tube: Cu
Parallel beam optical system Voltage: 40kV
Current: 15mA
Starting angle: 3°
End angle: 60°
Sampling width: 0.02°
Scan speed: 10.00°/min
Divergence slit: 0.625deg
Scattering slit: 8.0mm
Light receiving slit: 13.0mm (Open)
The half-value width and peak intensity of the obtained X-ray diffraction peak are calculated using analysis software "PDXL" manufactured by Rigaku Co., Ltd.

<Fluorescent X-ray measurement>
When performing a surface treatment with a silane coupling agent or the like, fluorescent X-ray measurement of inorganic fine particles is performed after the surface treatment agent is removed by solvent cleaning. If untreated particles are available, measurements may be performed using untreated particles.
Elements from Na to U in inorganic fine particles are directly measured in a He atmosphere using a wavelength dispersive X-ray fluorescence spectrometer Axios advanced (manufactured by Spectris Co., Ltd.). Using the liquid sample cup that comes with the device, cover the bottom with a PP (polypropylene) film, add a sufficient amount of the sample, form a layer of uniform thickness on the bottom, and close the lid. Measured under the condition that the output is 2.4kW. The analysis uses the FP (fundamental parameter) method. At this time, it is assumed that all of the detected elements are oxides, and their total mass is 100% by mass. The content (mass %) of strontium oxide (SrO) and titanium oxide (TiO ₂ ) relative to the total mass is determined as an oxide equivalent value using the software UniQuant 5 (ver. 5.49) (manufactured by Spectris Co., Ltd.).

<Method of measuring average circularity>
The average circularity is measured using a flow type particle image analyzer "FPIA-3000" (manufactured by Sysmex Corporation) under measurement and analysis conditions during calibration work.
The measurement principle of the flow type particle image analyzer "FPIA-3000" (manufactured by Sysmex Corporation) is to capture a still image of flowing particles and perform image analysis. A sample added to the sample chamber is delivered to a flat sheath flow cell by a sample suction syringe. The sample sent into the flat sheath flow is sandwiched between the sheath liquid and forms a flat flow. The sample passing through the flat sheath flow cell is irradiated with strobe light at 1/60 second intervals, making it possible to capture still images of flowing particles. Furthermore, since the flow is flat, the image is captured in a focused state. Particle images are captured by a CCD camera, and the captured images are processed at an image processing resolution of 512 x 512 pixels (0.37 μm x 0.37 μm per pixel) to extract the outline of each particle image and create a particle image. The projected area S, perimeter L, etc. of .

Next, the equivalent circle diameter and circularity are determined using the area S and the perimeter L. The equivalent circle diameter is the diameter of a circle that has the same area as the projected area of the particle image, and the circularity C is the value obtained by dividing the circumference of the circle obtained from the equivalent circle diameter by the circumference of the particle projection image. It is defined as and calculated using the following formula.
Circularity C=2×(π×S) ^1/2 /L
When the particle image is circular, the circularity is 1.000, and the greater the degree of unevenness on the outer periphery of the particle image, the smaller the circularity becomes. After calculating the circularity of each particle, the range of circularity from 0.200 to 1.000 is divided into 800 parts, the arithmetic mean value of the obtained circularity is calculated, and this value is defined as the average circularity.
The specific measurement method is as follows.

First, 20 mL of ion-exchanged water from which impure solid matter has been removed is placed in a glass container. This contains "Contaminon N" as a dispersant (a 10% by mass aqueous solution of a pH 7 neutral detergent for cleaning precision measuring instruments consisting of a nonionic surfactant, an anionic surfactant, and an organic builder, Wako Pure Chemical Industries, Ltd. Add 0.2 mL of a diluted solution obtained by diluting (manufactured by )) with ion-exchanged water to about 3 times the mass. Furthermore, 0.02 g of the measurement sample is added, and a dispersion process is performed for 2 minutes using an ultrasonic disperser to obtain a dispersion liquid for measurement. At that time, the temperature of the dispersion liquid is appropriately cooled to a temperature of 10° C. or higher and 40° C. or lower. As the ultrasonic disperser, a tabletop ultrasonic cleaner disperser ("VS-150" (manufactured by Vervo Crea Co., Ltd.)) with an oscillation frequency of 50 kHz and an electrical output of 150 W was used, and a predetermined amount of water was used in the water tank. of ion-exchange water, and add 2 mL of the contaminon N to this water tank.

The flow type particle image analyzer equipped with a standard objective lens (10x magnification) is used for the measurement, and a particle sheath "PSE-900A" (manufactured by Sysmex Corporation) is used as the sheath liquid.
The dispersion liquid prepared according to the procedure is introduced into the flow type particle image analyzer, and 3000 toner particles are measured in the HPF measurement mode (high magnification imaging mode) and total count mode.
Then, the binarization threshold at the time of particle analysis is set to 85%, the analyzed particle diameter is set to an equivalent circle diameter of 1.98 μm or more and 39.96 μm or less, and the average circularity of toner particles, etc. is determined.
In the measurement, automatic focus adjustment is performed using standard latex particles (for example, "RESEARCH AND TEST PARTICLES Latex Microsphere Suspensions 5200A" manufactured by Duke Scientific, diluted with ion-exchanged water) before starting the measurement. Thereafter, it is preferable to perform focus adjustment every two hours from the start of the measurement.

<Method for measuring the number average particle diameter (D1) of primary particles of inorganic fine particles>
The number average particle diameter of the primary particles of the external additive is measured using a transmission electron microscope (TEM) "JEM2800" (manufactured by JEOL Ltd.).
First, the measurement sample is adjusted. Add 1 mL of isopropanol to about 5 mg of external additive, and disperse for 5 minutes using an ultrasonic dispersion machine (ultrasonic cleaner). Next, a measurement sample was prepared by placing one drop of the above dispersion on a microgrid (150 mesh) with a support membrane for TEM and drying it.
Next, images are acquired using a transmission electron microscope (TEM) at an accelerating voltage of 200 kV at a magnification (for example, 200 k to 1 M times) that allows sufficient length measurement of the external additive in the field of view, and randomly The particle size of 100 primary particles of external additives is measured to determine the number average particle size. The particle size of the primary particles may be measured manually or using a measuring tool.

<Measurement of the particle size of primary particles of inorganic fine particles on the toner surface>
The particle size of the primary particles of the inorganic fine particles on the toner surface was determined by observing the inorganic fine particles on the toner using a scanning electron microscope (SEM) "S-4700" (manufactured by Hitachi, Ltd.).
The observation magnification was appropriately adjusted depending on the size of the organic-inorganic composite fine particles, but in a field of view magnified up to 200,000 times, the major diameters of 100 primary particles were measured, and the average value was taken as the number average particle diameter.

<Measurement of median diameter (D50) based on the number of toner>
The median diameter (D50) based on the number of toner particles can be determined by observing a secondary electron image using a scanning electron microscope and subsequent image processing.
The number-based median diameter (D50) of the toner of the present invention was measured using a scanning electron microscope (SEM), S-4800 (manufactured by Hitachi, Ltd.).
Specifically, the toner was fixed in a single layer with carbon tape on a sample stage for electron microscopy observation, platinum was vapor-deposited, and observation was made under the following conditions. Observations were made after performing a flushing operation.

SignalName=SE(U, LA80)
Accelerating Voltage=2000 Volt
Emission Current=10000nA
Working Distance=6000um
LensMode=High
Condenser1=5
ScanSpeed=Slow4 (40 seconds)
Magnification=50000
DataSize=1280×960
ColorMode=Grayscale

For the secondary electron image, the brightness was adjusted to 'contrast 5, brightness -5' on the control software of the scanning electron microscope S-4800, the capture speed/integrated number of images was set to 'Slow 4' for 40 seconds, and the image size was 1280 x 960 pixels. A projected image of the toner was obtained as an 8-bit 256-gradation grayscale image. From the scale on the image, the length of 1 pixel is 0.02 μm, and the area of 1 pixel is 0.0004 μm ² .

Subsequently, the projected area circle equivalent diameter of 100 toner particles was calculated using the obtained secondary electron projection image. Details of the method for selecting 100 toner particles to be analyzed will be described later.
Next, the toner particle group was extracted, and the size of each extracted toner particle was counted. Specifically, first, in order to extract the toner particle group to be analyzed, the toner particle group and the background portion are separated. Select "Measurement" - "Count/Size" of Image-Pro Plus5.1J. In "Brightness range selection" of "Count/Size", set the brightness range in the range of 50 to 255, exclude the low brightness carbon tape part that is reflected as the background, and extract the toner particle group. . When toner particles are fixed by a method other than carbon tape, there is a possibility that the background will not necessarily be a region of low brightness, or that it will partially have the same brightness as the toner particles. However, the boundary between the toner particle group and the background can be easily distinguished from the secondary electron observation image. When extracting, select 4-connection in the "Count/Size" extraction option, enter smoothness of 5, and check "Fill Holes" to remove toner particles and other particles located on all boundaries (outer circumference) of the image. Toner particles that overlap with toner particles are excluded from calculation. Next, the area and Feret diameter (average) were selected from the measurement item "Count/Size", and the area selection range was set to a minimum of 100 pixels and a maximum of 10,000 pixels, and each toner particle to be image analyzed was extracted. One toner particle was selected from the extracted toner particle group, and the size (pixel number: ja) of the portion originating from that particle was determined. Using the obtained ja and the following formula, the projected area circle equivalent diameter _d1 was obtained.
d ₁ = {(4×ja×0.3088)/3.14} ^1/2

Next, in "Brightness range selection" of "Count/Size" of Image-Pro Plus 5.1J, the brightness range was set in the range of 140 to 255, and the high brightness part above one toner particle was extracted. .
Next, the same process was performed on each particle of the extracted particle group until the number of selected toner particles reached 100. When the number of toner particles in one field of view was less than 100, the same operation was repeated for a toner projection image of another field of view.
The 100 toner particles obtained were arranged in ascending order of projected area circular equivalent diameter, and the projected area circular equivalent diameter of the 50th toner particle was defined as the median diameter (D50) based on the number of toner particles of the present invention.

<Method for measuring the amount of strontium titanate salt particles that separate from the toner when the toner is washed with water and the amount of silica particles that separate from the toner when the toner is washed with water>
Toner before washing: Various toners prepared in Examples described below were used as they were.
Toner after water washing: In a 50 mL vial, mix 6 mL of "Contaminon N", 31 g of sucrose liquid (sucrose:pure water = 2:1), and 1 g of toner. Set in a shaker ("YS-8D" manufactured by Yayoi Co., Ltd.) and shaken at 200 rpm for 5 minutes to liberate the toner and external additives. Thereafter, centrifugation is performed at 3700 rpm for 30 minutes using a centrifugal separator ("H-19S" manufactured by Kokusan Co., Ltd.) to separate the toner and the aqueous solution. The toner is collected from the aqueous solution, subjected to vacuum filtration until the detergent contained therein is removed, and then dried at normal pressure of 50° C. for 12 hours or more.

Each of the toner before washing and the toner after washing is molded into pellets with a diameter of 15 mm and a thickness of about 2 mm by applying a pressure of 20 kPa for 1 minute using a molding compressor.
Each pellet was measured using a high-power fluorescent X-ray analyzer (“AXiosmAX” manufactured by Malvern PANalytical) in a mode that examines only the silica element and titanium element, and the fluorescent X-ray intensity of the elements contained in the external additive ( Unit: kcps).
The difference (unit: kcps) between the fluorescent X-ray intensity of the element contained in the toner before washing and the fluorescent X-ray intensity of the element contained in the toner after washing is defined as the amount released.
This release amount measurement involves separating the external additive from the toner by applying a large amount of energy that would not occur when the image forming apparatus is used under normal usage conditions, and measuring the amount of the separated external additive. are being measured.

Measurement conditions for the mode that examines only silica elements Measurement angle 104.1298 to 114.1298°
Step size 0.05°
Measurement time: 50 seconds Measurement potential, current: 25kV, 160mA

Measurement conditions for mode that examines only titanium element Measurement angle 84.1398 to 88.1398°
Step size 0.04°
Measurement time: 20 seconds Measurement potential, current: 40kV, 100mA

[Example 1]
The present invention will be specifically described below based on Examples. However, the present invention is not limited to these examples in any way. In addition, in the following examples, parts and % are based on mass unless otherwise specified.

<Example of manufacturing binder resin>
(Production example of polyester resin)
・Polyoxypropylene (2.2)-2,2-bis(4-hydroxyphenyl)propane: 80.0 mol% based on the total number of moles of polyhydric alcohol
・Polyoxyethylene (2.2)-2,2-bis(4-hydroxyphenyl)propane: 20.0 mol% based on the total number of moles of polyhydric alcohol
・Terephthalic acid: 80.0 mol% based on the total number of moles of polycarboxylic acids
・Trimellitic anhydride: 20.0 mol% based on the total number of moles of polyhydric carboxylic acid

The above materials were put into a reaction tank equipped with a cooling tube, a stirrer, a nitrogen introduction tube, and a thermocouple. Then, 1.5 parts of tin 2-ethylhexanoate (esterification catalyst) was added as a catalyst to 100 parts of the total amount of monomers. Next, after purging the inside of the flask with nitrogen gas, the temperature was gradually raised while stirring, and the mixture was reacted for 2.5 hours while stirring at a temperature of 200°C.
Furthermore, the pressure in the reaction tank was lowered to 8.3 kPa, maintained for 1 hour, cooled to 180°C, allowed to react as it was, and after confirming that the softening point measured according to ASTM D36-86 had reached 110°C. The reaction was stopped by lowering the temperature.

<Production example of toner 1>
- Polyester resin 100.0 parts - 3,5-di-t-butylsalicylic acid aluminum compound 0.1 part - Fischer-Tropsch wax (maximum endothermic peak temperature 90°C) 5.0 parts - C.I. I. Pigment Blue 15:3 5.0 parts After mixing the raw materials shown in the above recipe under specified conditions using a Henschel mixer (model FM75J, manufactured by Nippon Coke Co., Ltd.), (manufactured by Ikegai Co., Ltd.). The obtained kneaded product was cooled and coarsely ground to 1 mm or less using a hammer mill to obtain a coarsely ground product. The obtained coarse material was pulverized using a mechanical pulverizer (T-250, manufactured by Turbo Kogyo Co., Ltd.). Classification was performed using an inertial classification type elbow jet (manufactured by Nippon Steel Mining Co., Ltd.) to obtain toner particles.

Furthermore, the obtained toner particles undergo a process of attaching fine particles such as silica particles and strontium titanate to the surface of the toner particles, and then a surface treatment is performed using hot air to coat the surface with fine particles such as silica particles and strontium titanate. Toner particles on which were fixed were obtained. By adjusting the temperature of the hot air, toner particles with a circularity of 0.960 or more were obtained.
The resulting toner particles 1 had a median diameter (D50) of 5 μm on a number basis. The median diameter (D50) on a number basis is adjusted by changing the conditions of crushing and classification. Furthermore, first and second silica particles and strontium titanate particles were externally added to the toner particles after the hot air treatment.
Further, by changing the external additive formulation and using appropriate manufacturing conditions, toners of the types described below were obtained.
Note that Tables 1 and 2 show the physical properties of the strontium titanate particles and silica particles used in each Example and each Comparative Example.

<Production example of magnetic core particle 1>
・Process 1 (weighing and mixing process):
Fe ₂ O ₃ 62.7 parts MnCO ₃ 29.5 parts Mg(OH) ₂ 6.8 parts SrCO ₃ 1.0 parts Ferrite raw materials were weighed so that the above materials had the above composition ratios. Thereafter, the mixture was ground and mixed for 5 hours in a dry vibration mill using stainless steel beads with a diameter of 1/8 inch.

・Process 2 (temporary firing process):
The obtained pulverized material was made into pellets of approximately 1 mm square using a roller compactor. Coarse powder was removed from the pellets using a vibrating sieve with an opening of 3 mm, then fine powder was removed using a vibrating sieve with an opening of 0.5 mm, and then the pellets were heated in a nitrogen atmosphere (oxygen concentration 0. 01% by volume) at a temperature of 1000° C. for 4 hours to produce calcined ferrite. The composition of the obtained calcined ferrite is as follows.
(MnO) _a (MgO) _b (SrO) _c (Fe ₂ O ₃ ) _d
In the above formula, a=0.257, b=0.117, c=0.007, d=0.393

・Process 3 (pulverization process):
After crushing to about 0.3 mm with a crusher, 30 parts of water was added to 100 parts of calcined ferrite using zirconia beads having a diameter of 1/8 inch, and the mixture was crushed with a wet ball mill for 1 hour. The slurry was ground for 4 hours in a wet ball mill using alumina beads with a diameter of 1/16 inch to obtain a ferrite slurry (finely ground product of calcined ferrite).

・Process 4 (granulation process):
To the ferrite slurry, 1.0 parts of ammonium polycarboxylate as a dispersant and 2.0 parts of polyvinyl alcohol as a binder were added to 100 parts of calcined ferrite, and the mixture was dried with a spray dryer (manufacturer: Okawara Kakoki Co., Ltd.). It was granulated into spherical particles. After adjusting the particle size of the obtained particles, they were heated at 650° C. for 2 hours using a rotary kiln to remove the organic components of the dispersant and binder.

・Process 5 (firing process):
In order to control the firing atmosphere, the temperature was raised from room temperature to 1300°C in 2 hours in an electric furnace under a nitrogen atmosphere (oxygen concentration 1.00% by volume), and then fired at a temperature of 1150°C for 4 hours. Thereafter, the temperature was lowered to 60° C. over a period of 4 hours, the temperature was returned to the atmosphere from the nitrogen atmosphere, and the sample was taken out at a temperature of 40° C. or lower.

・Process 6 (sorting process):
After crushing the aggregated particles, the low-magnetic particles are cut by magnetic separation, and coarse particles are removed by sieving with a sieve with an opening of 250 μm. Magnetic core particles 1 were obtained.

<Preparation of coating resin 1>
1) Cyclohexyl methacrylate monomer 26.8% by mass
2) Methyl methacrylate monomer 0.2% by mass
3) Methyl methacrylate macromonomer 8.4% by mass
(Macromonomer with a weight average molecular weight of 5000 having a methacryloyl group at one end)
4) Toluene 31.3% by mass
5) Methyl ethyl ketone 31.3% by mass
6) Azobisisobutyronitrile 2.0% by mass

Of the above materials, 1), 2), 3), 4), and 5) were placed in a four-neck separable flask equipped with a reflux condenser, thermometer, nitrogen inlet tube, and stirring device, and nitrogen gas was added to the flask. After introducing the mixture into a sufficiently nitrogen atmosphere, it was heated to 80°C. Thereafter, azobisisobutyronitrile was added and the mixture was refluxed for 5 hours for polymerization. Hexane was injected into the obtained reaction product to precipitate the copolymer, and the precipitate was filtered off and dried under vacuum to obtain coated resin 1.
30 parts of the obtained coating resin 1 was dissolved in 40 parts of toluene and 30 parts of methyl ethyl ketone to obtain a polymer solution 1 (solid content 30% by mass).

<Preparation of coating resin solution 1>
・Polymer solution 1 (resin solid content concentration 30%) 33.3% by mass
・Toluene 66.4% by mass
・Carbon black (Regal 330; manufactured by Cabot Corporation) 0.3% by mass (number average particle diameter of primary particles 25 nm, nitrogen adsorption specific surface area 94 m ² /g, DBP oil absorption 75 mL/100 g)
The above material was dispersed in a paint shaker for 1 hour using zirconia beads with a diameter of 0.5 mm. The obtained dispersion liquid was filtered through a 5.0 μm membrane filter to obtain coating resin solution 1.

<Manufacturing example of magnetic carrier 1>
(Resin coating process):
The coating resin solution 1 was put into a vacuum degassing type kneader maintained at room temperature so that the resin component amount was 2.5 parts with respect to 100 parts of the magnetic core particles 1. After the addition, the mixture was stirred at a rotational speed of 30 rpm for 15 minutes, and after a certain amount of the solvent had evaporated (80% by mass or more), the temperature was raised to 80° C. while mixing under reduced pressure, and the toluene was distilled off over 2 hours, followed by cooling.
The obtained magnetic carrier was separated into low-magnetic products by magnetic separation, passed through a sieve with an opening of 70 μm, and then classified with an air classifier to obtain magnetic carriers with a 50% particle size (D50) based on volume distribution of 38.2 μm. I got career 1.

Each toner was added to the magnetic carrier 1 so that the toner concentration was 8.0% by mass, and rotated for 0.5 s ⁻¹ using a V-type mixer (V-10 type: Tokuju Seisakusho Co., Ltd.). The mixture was mixed for 5 minutes to obtain two-component developers 1 to 27 listed in Table 1 below.
[Examples 1 to 22, Comparative Examples 1 to 12]
The following evaluations were performed using the obtained two-component developer. The evaluation results are shown in Tables 1 and 2.

<Explanation of durability test and evaluation method using corona charging method>
Next, the experimental conditions for the durability test and image evaluation using the corona charging method will be briefly explained. In Example 1, the outer diameter of the photosensitive drum was 84 mm, the length was 380 mm, and the output speed of the recording medium was 450 mm/s.
In Example 1, the reciprocating movement of the cleaning member 30 for cleaning was performed in 30 seconds, and the cleaning operation of the discharge wire was performed every 1300 sheets (the cleaning member 30 made one reciprocation). If more than a certain amount of deposits adhere to the discharge wire 205, density unevenness such as streaks will occur on the halftone. Hereinafter, density unevenness such as streaks on halftones due to deposits (contaminants) attached to the discharge wire will be referred to as "wire dirt."

・Evaluation of wire stains The copying machine used for image evaluation is in an environment with a temperature of 23°C and a relative humidity of 5%, and after outputting 1000 images with an image ratio of 10%, the following two types of sample images for evaluating wire stains are output. Five sheets of each were output, 200 sets of these were performed, and density unevenness on the halftone images was evaluated.
First sample image: Analog halftone image with a reflection density measured with X-rite ranging from 0.3 to 0.7 Second sample image: Reflection density measured with X-rite ranging from 0.3 to 0. 7 range digital halftone image

As described above, two types of wire stain evaluation images were used: an analog halftone image and a digital halftone image.
One type is one in which the dark potential VD formed on the surface of the photosensitive drum 1 is directly developed by a charging member (hereinafter referred to as analog HT (halftone)). Specifically, the surface of the photoreceptor drum is charged to a dark area potential VD of approximately -700V, and the developing sleeve potential is set to approximately -720V, thereby developing to the dark area potential VD. Under these conditions, uneven charging caused by dirt on the discharge wire is directly reflected in the image, so dirt can be evaluated under strict conditions.

The other method used a method of forming an image through normal image exposure (hereinafter referred to as digital HT (halftone)). Specifically, the surface of the photoreceptor drum is charged to a dark area potential VD of about -700V, and then the bright area potential VL is set to about -600V by full image exposure. Then, by setting the developing sleeve potential to about -600V, development is carried out to the bright area potential VL.
Both of the above images were adjusted to be halftone images with reflection densities in the range of 0.3 to 0.7 as measured by X-rite.

The evaluation rank was determined as follows.
Rank A: No charging unevenness appears in the image even with analog HT.
Rank B: Line-like unevenness occurs with analog HT, but it does not appear in the image with digital HT.
Rank C: Slight unevenness occurs in digital HT, but there is no problem in practical use.
Rank D: Unevenness and streaks can be clearly seen in digital HT.

As explained above, according to the present invention, in a charging device using a corona charging method such as a copying machine or a printer, wire contamination caused by deposits attached to a discharge wire is suppressed, and image defects are prevented from occurring. It has become possible to provide an image forming apparatus.

1...Photosensitive drum 2...Charging device (corona charger)
30...Cleaning member 40...Supporting member 205...Discharge electrode (discharge wire)
206...Grid electrode

Claims (5)

an image carrier;
a corona discharge type charging means having a discharge electrode disposed opposite to the image carrier;
A discharge electrode cleaning means that comes into contact with the discharge electrode to clean the surface of the discharge electrode;
an exposure means for forming an electrostatic latent image on the surface of the image carrier that has been charged by the charging means;
a developing means for developing the electrostatic latent image using toner to form a toner image on the surface of the image carrier;
a transfer means for transferring the toner image to a transfer material;
cleaning means for cleaning toner remaining on the surface of the image carrier;
a fixing means for fixing the toner image transferred to the transfer material;
An image forming apparatus having:
The toner has toner particles and strontium titanate particles and silica particles present on the surface thereof,
The strontium titanate particles are
(i) The number average particle diameter (D1T) of the primary particles is 10 nm or more and less than 95 nm,
(ii) the average circularity is 0.700 or more and 0.920 or less,
(iii) It has a maximum peak (a) at a diffraction angle (2θ) of 32.00 deg or more and 32.40 deg or less in CuKα characteristic X-ray diffraction, and the half width of the maximum peak (a) is 0.23 deg or more and 0.2 deg or more. 50deg or less, and the intensity (Ia) of the maximum peak (a) and the intensity (Ix) of the maximum peak in the range of 24.00deg or more and 28.00deg or less of the diffraction angle (2θ) in CuKα characteristic X-ray diffraction. , satisfies the following formula (1),
(Ix)/(Ia) ≦ 0.010... Formula (1)
(iv) When it is assumed that all the elements detected by X-ray fluorescence analysis are contained in oxides, the total content of strontium oxide and titanium oxide when the total amount of all oxides is taken as 100% by mass. is 98.0% by mass or more,
The silica particles have a number average particle diameter (D1S) of primary particles of 5 nm or more and 300 nm or less,
The amount of the strontium titanate particles that separate from the toner when the toner is washed with water is 0.01 times or more and 0.9 times or less the amount of the silica particles that separate from the toner when the toner is washed with water. image forming apparatus. Regarding the fluorescent X-ray intensity of silica element measured using a fluorescent X-ray analyzer under the following measurement conditions, the fluorescent X-ray intensity measured using the toner before washing with the toner after washing with water The image forming apparatus according to claim 1 , wherein a value obtained by subtracting 2.5 kcps or less.
Measurement condition:
Sample The toner before washing and the toner after washing are molded into pellets with a diameter of 15 mm and a thickness of about 2 mm by applying a pressure of 20 kPa for 1 minute using a molding compressor.
Measurement angle 104.1298~114.1298°
Step size 0.05°
Measurement time 50 seconds
Measurement potential, current 25kV, 160mA
Regarding the fluorescent X-ray intensity of titanium element measured using a fluorescent X-ray analyzer under the following measurement conditions, the fluorescent X-ray intensity measured using the toner before washing to the fluorescent X-ray intensity measured using the toner after washing The image forming apparatus according to claim 1 , wherein a value obtained by subtracting 1.5 kcps is 1.5 kcps or less.
Measurement condition:
Sample The toner before washing and the toner after washing are molded into pellets with a diameter of 15 mm and a thickness of about 2 mm by applying a pressure of 20 kPa for 1 minute using a molding compressor.
Measurement angle 84.1398~88.1398°
Step size 0.04°
Measurement time 20 seconds
Measurement potential, current 40kV, 100mA
The silica particles are composed of first silica particles having a number average particle diameter (D1S1) of 5 nm or more and 20 nm or less, and second silica particles having a number average particle diameter (D1S2) of 80 nm or more and 120 nm or less,
The relationship between the number average particle diameter (D1T) of the strontium titanate particles, the number average particle diameter (D1S1) of the first silica particles, and the number average particle diameter (D1S2) of the second silica particles is as follows. The image forming apparatus according to any one of claims 1 to 3, which satisfies formula (2).
D1S2>D1T>D1S1... Formula (2) The image forming apparatus according to any one of claims 1 to 4, wherein the toner has a median diameter (D50) on a number basis of 3.0 μm or more and 6.0 μm or less.

Images