JPH0895285A - Electrophotographic toner - Google Patents

Abstract

PURPOSE: To provide a new electrophotographic toner having an especially small particle diameter and excellent in electrostatic chargeability and stability of a charged state as well as flowability. CONSTITUTION: Fine hydrophobic silica particles treated with hexamethyldisilazane and fine titanium oxide particles are added to toner particles. The fine titanium oxide particles are fine titanium oxide particles (a) treated with polyhydric alcohol, fine titanium oxide particles (b) satisfying A/B<1.6 [where A is the specific surface area (m<2> /g) of the particles and B is the primary particle diameter (nm)], fine titanium oxide particles (c) having resistivity of 10<6> -10<8> Ω.cm or fine titanium oxide particles (d) having 5-80μC/g absolute value of the quantity of electric charges and the same polarity as that of the toner after electrostatic charge when the particles are mixed with a magnetic carrier and electrostatically charged.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic toner, and more particularly to an electrophotographic toner having a small particle size for the purpose of improving the quality of a formed image.

[0002]

2. Description of the Related Art An electrophotographic toner used as a two-component developer together with a magnetic carrier in an image forming apparatus such as an electrostatic copying machine or a laser beam printer utilizing the so-called electrophotographic method is usually used in a fixing resin. A colorant such as carbon black, a charge control agent, or the like is added to the above, and the mixture is granulated to a predetermined particle size.

Further, such an electrophotographic toner has fluidity,
In order to improve properties such as chargeability and charge stability, surface treatment is performed with an external additive composed of fine particles having a particle size smaller than that of the toner particles. Recently, small-sized electrophotographic toners having a particle size of 9 μm or less are being put to practical use for the purpose of further improving the quality of formed images. Since the fluidity is poorer than that of the toner, the toner is liable to be agglomerated and blocked. In addition, since electrophotographic toner having a small particle size is unstable in charging property as compared with a normal toner, toner scattering due to poor charging or image defects such as fogging in which toner adheres to a blank portion of a formed image. There is also a problem that is likely to occur.

In order to solve such a problem, it has been studied to use silica fine particles and titanium oxide fine particles as an external additive in a toner having a small particle diameter. In such a combined system, the silica fine particles mainly serve to improve the fluidity of the toner particles and increase the bulk of the charge amount. Further, the titanium oxide fine particles assist the charge transfer between the toner particles to equalize the charge amount of the entire toner particles, so that the highly charged toner exceeding the predetermined charge amount or vice versa does not reach the predetermined charge amount. It functions to stabilize the charging by preventing the generation of the weakly charged toner and the reversely charged toner which is charged to the opposite polarity.

[0005]

However, according to the studies made by the present inventors, it has been found that a sufficient effect cannot be obtained by simply using silica fine particles and titanium oxide fine particles in combination. That is, as usual silica fine particles for external addition, hydrophobic silica fine particles capable of imparting moisture resistance and storability to an electrophotographic toner are preferably used, and such hydrophobic silica fine particles include, for example, silicon tetrachloride and the like. A fumed silica obtained by combustion hydrolysis in a gas phase using a volatile silicon compound as a raw material is treated with an organochlorosilane such as dichlorodimethylsilane or an organosiloxane such as dimethylpolysiloxane to obtain a surface Examples thereof include highly hydrophobic silica fine particles produced by blocking silanol groups, and arc-process silica fine particles obtained by burning silicon monoxide volatilized from an arc furnace.

However, all of the above-mentioned conventional hydrophobic silica fine particles are easily aggregated and difficult to uniformly adhere to the surface of the toner particles, so that a large amount must be added to impart sufficient fluidity to the toner particles. . Therefore, excessive hydrophobic silica fine particles adhere around the titanium oxide fine particles to prevent the titanium oxide fine particles from adhering to the surface of the toner particles, or the titanium oxide fine particles directly contact with other toner particles. As a result of hindering contact, the effect of assisting charge transfer between toner particles cannot be sufficiently obtained due to the addition of titanium oxide fine particles.

In addition to the fact that a large amount of hydrophobic silica fine particles having the effect of increasing the charge amount is added, the charge amount of the entire toner becomes too high and the charge amount distribution widens, so that the highly charged toner Also, weakly charged toner, reversely charged toner, and the like are generated, and image defects such as toner scattering and fog occur. Further, if a large amount of titanium oxide fine particles is added to prevent this, the charge amount of the entire toner is reduced, so that an image defect occurs in which the image density of the formed image is reduced.

An object of the present invention is to provide a novel electrophotographic toner having a particularly small particle size, excellent fluidity, and excellent chargeability and charge stability.

[0009]

Means and Actions for Solving the Problems In order to solve the above problems, the inventors first examined hydrophobic silica fine particles. As a result, the hydrophobic silica fine particles produced by blocking the silanol groups on the surface by treating with hexamethyldisilazane are less likely to aggregate and easily adhere evenly to the surface of the toner particles. In addition, it is possible to impart sufficient fluidity to the toner particles with a small amount of addition, and since it is not necessary to add excessively, there is no generation of hydrophobic silica fine particles adhering to the surface of the titanium oxide fine particles. , It does not interfere with the function of assisting charge transfer between toner particles.

Then, as a result of further examination of titanium oxide fine particles to be combined with the above-mentioned hydrophobic silica fine particles, the present invention has been completed. That is, the electrophotographic toner of the present invention is characterized in that the above-mentioned hydrophobic silica fine particles and titanium oxide fine particles treated with a polyhydric alcohol are externally added to the toner particles.

Another electrophotographic toner of the present invention is
The above-mentioned hydrophobic silica fine particles and titanium oxide fine particles satisfying the formula (1) are externally added to the toner particles. A / B <1.6 (1) [where A is the specific surface area (m ² / g) of the titanium oxide fine particles measured by the BET method, and B is the primary particle diameter (nm) of the titanium oxide fine particles. In still another electrophotographic toner of the present invention, the toner particles have the above-mentioned hydrophobic silica fine particles and a resistivity of 10 ⁶
It is characterized by externally adding titanium oxide fine particles of 10 ⁸ Ω · cm.

Further, still another electrophotographic toner of the present invention comprises, in the toner particles, the above-mentioned hydrophobic silica fine particles,
The absolute value of the charge amount when mixed and charged with the magnetic carrier used for charging the toner particles is 5 to 80 μC / g,
In addition, titanium oxide fine particles having the same charging polarity as that of the toner are externally added.

In such an electrophotographic toner, the titanium oxide fine particles treated with polyhydric alcohol, which are combined with the hydrophobic silica fine particles treated with hexamethyldisilazane, do not easily agglomerate and are uniform on the surface of the toner particles together with the hydrophobic silica. Therefore, it has an excellent effect of assisting charge transfer between toner particles. Further, the titanium oxide fine particles satisfying the above formula (1) have the formula (1)
The surface is smoother than that of a porous material that does not satisfy the above condition, and the charge transfer is performed smoothly [The charge transfer due to titanium oxide fine particles is mainly generated on the surface], and thus the charge transfer between the toner particles is also assisted. Excellent effect.

Further, since the titanium oxide fine particles having a resistivity of 10 ⁶ to 10 ⁸ Ω · cm have an appropriate charge transfer ability with respect to the toner particles, the charge transfer between the toner particles is similar to the former two. It has an excellent effect of helping. Further, the absolute value of the charge amount when mixed with the magnetic carrier used for charging the toner particles and charged is 5 to 80 μC / g.
In addition, since the titanium oxide fine particles whose charging polarity is the same as the charging polarity of the toner also have appropriate chargeability and charge transfer ability with respect to the toner particles, as in the former three cases, the toner particles are It has an excellent effect of helping charge transfer.

Therefore, the electrophotographic toner of the present invention in which any one of the above-mentioned four kinds of titanium oxide fine particles is combined with the above-mentioned hydrophobic silica fine particles has excellent fluidity, and also has excellent chargeability and charge stability. It will be excellent. The present invention will be described below. As the hydrophobic silica fine particles, those produced by treating the surface of the silica fine particles with hexamethyldisilazane as described above to block the silanol groups on the surface are used. Specific examples of such hydrophobic silica fine particles include Aerosil R812 and RX200 manufactured by Nippon Aerosil Co., Ltd.

As the silica fine particles which are the basis of the above-mentioned hydrophobic silica fine particles, for example, fumed silica obtained by combustion hydrolysis in a gas phase using a volatile silicon compound such as the above-mentioned silicon tetrachloride as a raw material. It is preferably used. In order to treat the surface of the silica fine particles with the above hexamethyldisilazane, both of them may be reacted in a reaction tower of a fluidized bed.

As described above, the above-mentioned hydrophobic silica fine particles are less likely to aggregate as compared with the conventional hydrophobic silica, and therefore have an excellent effect of improving the fluidity of the toner particles, and at the same time, most of them have silanol groups. Since it does not exist, it is highly hydrophobic and can significantly improve the humidity resistance and storage stability of the electrophotographic toner. The particle size of the hydrophobic silica fine particles is not particularly limited in the present invention, but the average particle size of the primary particles is, for example, about 5 to 50 nm when the fumed silica is used due to its manufacturing method. In order to obtain stable charging characteristics and fluidity, it is preferable that the particle size variation is small and the particle size distribution is sharp within the above particle size range.

If the particle size of the hydrophobic silica fine particles is less than the above range, the hydrophobic silica fine particles may aggregate. On the contrary, if it exceeds the above range, the effect of improving the fluidity of the toner particles is insufficient. May be. The particle size of the hydrophobic silica fine particles is 7 to 30 n in the above range in order to obtain stable charging characteristics and fluidity as described above.
It is preferably m, and more preferably 10 to 20 nm.

The addition amount of the hydrophobic silica fine particles to the toner particles is 0.
It is preferably about 01 to 5 parts by weight. If the amount of the hydrophobic silica fine particles added is less than the above range, the effect of improving the fluidity of the toner particles by the hydrophobic silica fine particles becomes insufficient, and there is a risk of blocking the toner as agglomerates. Further, the effect of raising the bulk of the charge amount as a whole cannot be obtained, and the charge amount of the entire toner is reduced, which may cause an image defect in which the image density of the formed image is reduced.

On the other hand, when the addition amount of the hydrophobic silica fine particles exceeds the above range, excessive hydrophobic silica fine particles are generated and adhere to the surface of the titanium oxide fine particles, and the toner is formed by the titanium oxide fine particles. As a result of hindering the function of facilitating the charge transfer between particles, the charge amount of the entire toner becomes too high, and the distribution of the charge amount spreads, and the above-mentioned highly charged toner, weakly charged toner, reverse charged toner, etc. are generated,
Image defects such as toner scattering and fogging may occur.

In the above range, the amount of the hydrophobic silica fine particles added is preferably 0.05 to 2 parts by weight, and more preferably 0.1 to 1 part by weight, based on 100 parts by weight of the toner particles. Is more preferable. As the titanium oxide fine particles, as described above, (a) titanium oxide fine particles treated with a polyhydric alcohol, (b) titanium oxide fine particles having a smooth surface, which satisfies the formula (1), (c) resistivity is 10 ⁶ to 10 ⁸
The absolute value of the charge amount when mixed with the titanium oxide fine particles of Ω · cm and (d) the magnetic carrier used for charging the toner particles is 5 to 80 μC / g, and the charging polarity is , Titanium oxide fine particles having the same charge polarity as the toner are used.

Among the above, the titanium oxide fine particles of (a) are obtained by, for example, sintering the titanium oxide fine particles, and then pulverizing and classifying the fine particles on the surface of the fine particles, for example, by the formula (2): CH ₃ —CH ₂ Treatment with a polyhydric alcohol such as trimethylolpropane represented by C (CH ₂ OH) ₃ (2) or pentaerythritol represented by the formula (3): C- (CH ₂ OH) ₄ (3) It can be obtained.

In order to treat the surface of the titanium oxide fine particles with the polyhydric alcohol, the polyhydric alcohol may be added and mixed in the final pulverizing step. By this mixing, the -OH group of the polyhydric alcohol is bonded to the hydrophilic group on the new surface of the titanium oxide fine particles generated by the pulverization, and the aggregation property of the titanium oxide fine particles is reduced. The particle size of the titanium oxide fine particles of (a) is not particularly limited in the present invention, but the average particle size of the primary particles is preferably about 10 to 200 nm.

If the particle size of the titanium oxide fine particles is less than the above range, the titanium oxide fine particles may aggregate. On the contrary, if the particle size exceeds the above range, the surface of the photoreceptor is scraped by the titanium oxide fine particles, so-called drum. Scraping may occur. In order to obtain stable charging characteristics and fluidity as described above, the particle size of the titanium oxide fine particles is preferably 20 to 100 nm even within the above range, and 30
More preferably, it is -80 nm.

The amount of titanium oxide fine particles added to the toner particles is 0.0 per 100 parts by weight of the toner particles.
It is preferably about 1 to 10 parts by weight. If the addition amount of the titanium oxide fine particles is less than the above range, the effect of assisting the charge transfer between the toner particles by the titanium oxide fine particles becomes insufficient, the charge amount of the entire toner becomes too high, and the distribution of the charge amount spreads. However, the high-charged toner, the weakly-charged toner, the reversely-charged toner, and the like are generated, which may cause image defects such as toner scattering and fog.

On the other hand, when the addition amount of the titanium oxide fine particles exceeds the above range, the charge amount of the entire toner is reduced as described above, so that the image density of the formed image may be lowered and an image defect may occur. is there. Even within the above range, the addition amount of titanium oxide fine particles is preferably 0.05 to 3 parts by weight with respect to 100 parts by weight of toner particles,
More preferably, it is 0.1 to 2 parts by weight.

Among the four types of titanium oxide fine particles, the titanium oxide fine particles (b) are, as described above, the specific surface area A (m ² / g) measured by the BET method and the primary particle diameter B (nm).
Must satisfy the formula (1): A / B <1.6 (1). In the case of a porous material having a ratio A / B of 1.6 or more, charge transfer is not smoothly performed,
The effect of assisting charge transfer between toner particles cannot be obtained.

The titanium oxide fine particles having the ratio A / B within the above range are produced by adjusting the sintering conditions for producing the titanium oxide fine particles by sintering the titanium oxide fine particles as described above. That is, as the sintering temperature is higher and the sintering time is longer, the surface of the titanium oxide fine particles changes from a porous state to a smooth state, and the A / B becomes smaller. The particle size of the titanium oxide fine particles of (b) is not particularly limited in the present invention, but for the same reason as the titanium oxide fine particles of (a) above,
The average particle size of the primary particles is preferably about 10 to 200 nm, more preferably 20 to 100 nm, and further preferably 30 to 80 nm.

The addition amount of the titanium oxide fine particles to 100 parts by weight of toner particles is preferably about 0.01 to 10 parts by weight, and 0.05 to 3 parts by weight for the same reason as above. Is more preferred,
More preferably, it is 0.1 to 2 parts by weight. Among the four types of titanium oxide fine particles, the titanium oxide fine particles (c) are
It must have a resistivity of 10 ⁶ to 10 ⁸ Ω · cm.

If the resistivity of the fine particles of titanium oxide is less than the above range, the charge amount of the entire toner is reduced, and an image defect occurs in which the image density of the formed image is reduced. On the contrary, if the resistivity exceeds the above range, The effect of assisting the charge transfer between the toner particles becomes insufficient, the charge amount of the entire toner becomes too high, and the distribution of the charge amount spreads, so that the highly charged toner, the weakly charged toner, the oppositely charged toner, etc. are generated. Image defects such as toner scattering and fogging occur.

In order to adjust the resistivity of the titanium oxide fine particles within the above range, a treatment agent for making the surface of the titanium oxide fine particles hydrophobic, such as a silane-based, titanate-based, aluminum-based or zircoaluminate-based treatment agent. It suffices to change the type of various coupling agents, silicone oil, etc., or adjust the addition amount of the treating agent.
To treat the surface of the titanium oxide fine particles with such a treating agent, the titanium oxide fine particles are forcibly stirred by a blender or the like, and the treating agent alone or a diluted solution thereof is added dropwise or sprayed to further mix the mixture. The dry method is preferably employed, in which the product is dried in an oven, and then again stirred with a blender or the like to disintegrate. Further, a wet method in which titanium oxide fine particles and a treating agent are mixed in an appropriate organic solvent and then dried and crushed may be employed.

When the surface of the titanium oxide fine particles is coated with a resin coating layer for making it hydrophobic, the proportions of antimony and tin oxide added for conductivity adjustment in the coating layer are changed. Also, the resistivity of the titanium oxide fine particles can be adjusted. The particle size of the titanium oxide fine particles of (c) is not particularly limited in the present invention.
For the same reason as the titanium oxide fine particles of (a), the average particle size of the primary particles is preferably about 10 to 200 nm, more preferably 20 to 100 nm, and 30 to
More preferably, it is 80 nm.

The amount of the titanium oxide fine particles added to 100 parts by weight of the toner particles is preferably about 0.01 to 10 parts by weight, and 0.05 to 3 parts by weight for the same reason as above. Is more preferred,
More preferably, it is 0.1 to 2 parts by weight. Among the four types of titanium oxide fine particles, the titanium oxide fine particles (d) are
The absolute value of the charge amount when mixed and charged with the magnetic carrier used for charging the toner particles is 5 to 80 μC / g,
In addition, the charging polarity is limited to the same as the charging polarity of the toner. That is, the titanium oxide fine particles for negatively charged toner have a charge amount limited to -5 to -80 [mu] C / g, and the titanium oxide fine particles for positively charged toner have a charge amount of +5.
Limited to +80 μC / g.

When the absolute value of the charge amount of the titanium oxide fine particles is less than the above range or the charge polarity is opposite to the charge polarity of the toner, the charge amount of the entire toner is reduced and the image density of the formed image is lowered. On the contrary, when the amount exceeds the above range, the charge amount of the toner as a whole becomes too high, and the distribution of the charge amount is widened, so that the highly charged toner, the weakly charged toner, the oppositely charged toner, etc. are generated. As a result, image defects such as toner scattering and fogging occur.

The absolute value of the charge amount of the titanium oxide fine particles is preferably 8 to 70 μC / g, and more preferably 10 to 60 μC / g, even within the above range. As can be seen from the above description, the value of the charge amount defined here is not an absolute value specific to the titanium oxide fine particles, but a relative value that changes depending on the type of magnetic carrier used. That is, titanium oxide fine particles whose absolute value of the charge amount is within the above range when mixed and charged with the magnetic carrier that is actually used for charging the toner particles may be used. A conventionally known measuring method such as a so-called blow-off method can be used for measuring the charge amount.

As a method for adjusting the charge amount of the titanium oxide fine particles, considering that the charge amount changes depending on the resistivity of the titanium oxide fine particles, the above-described method of adjusting the resistivity of the titanium oxide fine particles is preferable. Adopted by.
That is, when mixed with the magnetic carrier that is actually used for charging the toner particles, the charge amount should be within the above range,
The resistivity of the titanium oxide fine particles may be adjusted.

The particle size of the titanium oxide fine particles of (d) is
Although not particularly limited in this invention, for the same reason as the titanium oxide fine particles of (a) above, the average particle diameter of the primary particles is preferably about 10 to 200 nm, preferably 20 to 20 nm.
The thickness is more preferably 100 nm, further preferably 30 to 80 nm. Also, the addition amount of the titanium oxide fine particles to 100 parts by weight of the toner particles is preferably about 0.01 to 10 parts by weight, and is 0.05 to 3 parts by weight for the same reason as above. Is more preferable, and 0.1 to 2 parts by weight is even more preferable.

As the toner particles to which the hydrophobic silica fine particles and the titanium oxide fine particles described above are externally added, any known toner conventionally used in the dry developing method can be used. Such a toner is usually manufactured by dispersing additives such as a colorant in a fixing resin. Examples of the fixing resin include styrene polymers, acrylic polymers, styrene-acrylic polymers, chlorinated polystyrene, olefin polymers such as polypropylene and ionomers, polyvinyl chloride, polyesters, polyamides, polyurethanes, and epoxies. Examples thereof include resins, diallyl phthalate resins, silicone resins, ketone resins, polyvinyl butyral resins, phenol resins, rosin-modified phenol resins, xylene resins, rosin-modified maleic acid resins and rosin esters. Among these, an acrylic polymer or a styrene-acrylic polymer is preferable because of easy pulverization and control of the molecular weight distribution. In the case of a full-color toner, polyester having excellent color mixing property is preferable.

In the case of a black toner, examples of the colorant dispersed in the fixing resin include acetylene black, carbon black, aniline black and the like. Further, magenta, cyan, and yellow pigments are used as full-color colorants. Among these, magenta colorants include C.I. I. Pigment Red 49,
C. I. Pigment Red 57, C.I. I. Pigment Red 81, C.I. I. Pigment Red 122, C.I. I.
Solvent Red 19, C.I. I. Solvent Red 4
9, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Examples include Disperse Red 15 and the like. Among these, especially C.I. I. Pigment Red 122 and other quinacridone pigments are preferably used in terms of tint as a magenta colorant.

As the cyan colorants, for example, C.I. I. Pigment Blue 15, C.I. I. Pigment Blue 16, C.I.
I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 25, C.I. I. Direct Blue 86 etc. can be mentioned. Among these,
C. I. Pigment Blue 15 and other copper phthalocyanine pigments are preferably used in terms of tint as a cyan colorant.

Examples of yellow colorants include C.I. I. Pigment Yellow 1, C.I. I. Pigment Yellow 5, C.I.
I. Pigment Yellow 12, C.I. I. Pigment Yellow 15, C.I. I. Pigment Yellow 17 and the like, and inorganic pigments such as yellow iron oxide and ocher. Examples of dyes include C.I. I. Nitro dyes such as Acid Yellow 1 and C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I.
Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 16, C.I. I. Solvent Yellow 19, C.I. I. Solvent yellow 21
Oil-soluble dyes such as Among these, especially C.I.
I. Pigment Yellow 12 and other benzidine pigments are preferably used in terms of tint as a yellow colorant.

The amount of the colorant added is preferably 1 to 30 parts by weight, and 2 to 2 parts by weight based on 100 parts by weight of the fixing resin.
It is more preferably 0 part by weight. Typical additives other than the colorant include a charge control agent and an offset preventive agent. The charge control agent is blended to control the triboelectric chargeability of the toner, and there are two types, one for controlling the positive charge and one for controlling the negative charge, depending on the charging characteristics of the toner.

As the charge control agent for controlling the positive charge, an organic compound having a basic nitrogen atom, for example, a basic dye,
Examples include aminopyrine, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes and the like. As the charge control agent for negative charge control, nigrosine base, oil black, oil-soluble dyes such as spirone black, metal-containing azo dyes, metal naphthenates, metal salts of alkylsalicylic acid,
Examples include fatty acid soap and resin acid soap.

The amount of the charge control agent added is 100% for the fixing resin.
It is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on parts by weight. The offset preventing agent is blended in order to impart an offset preventing effect to the toner. Examples of the anti-offset agent include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Of these, aliphatic hydrocarbons having a weight average molecular weight of about 1,000 to 10,000 are preferable. Specifically, low molecular weight polypropylene, low molecular weight polyethylene, paraffin wax, and 4 carbon atoms.
It is suitable to use one or a combination of two or more kinds of low molecular weight olefin polymers composed of the above olefin units and silicone oils.

The amount of the anti-offset agent added is preferably 0.1 to 10 parts by weight, more preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the fixing resin.
When magnetic powder is added, a magnetic toner as a one-component developer can be obtained. The magnetic substance is a substance that is strongly magnetized in that direction by a magnetic field, and is preferably chemically stable, and is preferably a fine powder having a particle size of 1 μm or less, particularly about 0.01 to 1 μm. As a typical magnetic material,
In addition to iron oxides such as magnetite, hematite and ferrite, metals such as iron, cobalt and nickel, or these metals and aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium and calcium. , Alloys with manganese, selenium, titanium, tungsten, vanadium, and mixtures thereof.

The amount of the magnetic powder added is 100% for the fixing resin.
It is preferably 20 to 300 parts by weight, more preferably 50 to 150 parts by weight, based on parts by weight. In addition, various additives such as a stabilizer may be blended in an appropriate ratio. The particle size of the toner particles is not particularly limited in the present invention, but as described above, a small particle size toner having a particle size of 9 μm or less is preferable in order to obtain a high quality image. Considering the improvement of image quality, the particle size of the small particle size toner is
Within the above range, it is particularly preferably 4 to 9 μm,
It is more preferably 6 to 8 μm.

However, the constitution of the present invention can be applied to ordinary electrophotographic toners other than the above-mentioned small particle size,
In that case, the particle size of the toner particles may be in the above range or more. The electrophotographic toner of the present invention is produced by surface-treating the above toner particles with the above-mentioned hydrophobic silica fine particles and titanium oxide fine particles. The surface treatment is carried out by blending the above-mentioned respective components in the above-mentioned addition ratio and stirring and mixing. Various mixing devices can be used, and examples thereof include a Henschel mixer and a V-type mixer.

The hydrophobic silica fine particles and the titanium oxide fine particles can be mixed with the toner particles at the same time, but in order to uniformly attach both fine particles to the surface of the toner particles, either one of the fine particles is first added to the toner particles. It is preferable that the toner is mixed with and adhered to the surface thereof, and then mixed with the other fine particle toner particles and adhered to the surface thereof. The electrophotographic toner of the present invention thus obtained is suitable for use as both a one-component developer and a two-component developer.

When used as a one-component developer, the electrophotographic toner of the present invention, which has been surface-treated with toner particles containing or not containing a magnetic material as described above, may be used as it is. On the other hand, to obtain a two-component developer, the electrophotographic toner of the present invention surface-treated as described above may be mixed with a carrier.

Examples of the carrier include glass beads, magnetic particles such as oxidized or non-oxidized iron powder, ferrite and cobalt, or the surface thereof made of synthetic resin (acrylic, styrene-acrylic, fluorine-based, silicone-based, Those coated with a resin such as polyester are used. Such carriers are typically 50-2000μ.
It has a particle size of m. When using a two-component developer, the toner concentration is preferably 2 to 15% by weight.

[0051]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Example 1, Comparative Examples 1 to 7 <Production of Toner Particles> 100 parts by weight of a polyester resin as a fixing resin, 5 parts by weight of a quinacridone pigment as a colorant, and salicylic acid as a charge control agent for negative charge control After melting and kneading 2 parts by weight of the zinc compound and crushing,
Classification was performed to produce toner particles having an average particle size of 8 μm. <Production of Toner for Electrophotography> 100 parts by weight of the toner particles obtained in the production of the above toner particles and 0.5 parts by weight of hydrophobic silica fine particles having an external additive amount shown in Table 1 are stirred and mixed with a Henschel mixer. After that, titanium oxide fine particles having an external amount shown in Table 1 were further added and mixed by stirring to produce a negatively charged toner for electrophotography.

In Table 1, the reference numerals in the column of hydrophobic silica fine particles indicate the following hydrophobic silica fine particles. I: Hydrophobic silica fine particles treated with hexamethyldisilazane, average particle diameter of primary particles is 12 nm. II: Hydrophobic silica fine particles treated with dimethyldichlorosilane, average particle diameter of primary particles is 16 nm.

III: Hydrophobic silica fine particles treated with dimethylpolysiloxane, average primary particle size 16 nm. Further, in Table 1 above, the reference numerals in the column of titanium oxide fine particles indicate the following titanium oxide fine particles, respectively. i: Titanium oxide fine particles treated with trimethylolpropane, average particle diameter of primary particles is 50 nm.

Ii: Titanium oxide fine particles coated with aluminum oxide, average particle diameter of primary particles is 50 nm. iii: Titanium oxide fine particles treated with octyltrimethoxysilane, average particle diameter of primary particles is 50 nm. The following tests were carried out on the electrophotographic toners of the above Examples and Comparative Examples to evaluate the characteristics. Fluidity Test The fluidity of the electrophotographic toners of Examples and Comparative Examples was measured using the apparatus shown in FIG.

This apparatus is provided with a hopper 1 on which sample toner is placed.
And a toner replenishing roller 2 arranged in the bottom opening 11 of the hopper 1 and a tray 3 provided below these. The toner replenishing roller 2 is a metal cylinder having a diameter of 20 mm and having an uneven surface, and is configured to drop the sample toner from the hopper 1 to the tray 3 by rotating. Then, a predetermined amount of electrophotographic toner is placed on the hopper 1, the toner replenishing roller 2 is rotated at a constant speed, the amount of toner that falls on the tray 3 during a constant time is obtained, and the fluidity of the toner is evaluated. It is a thing. In this measurement, the rotation speed of the toner replenishing roller 2 is set to 3 per minute.
The rotation was set, and the amount of toner falling on the tray 3 was measured for 5 minutes. The results show that the greater the amount of toner that has fallen, the higher the fluidity of the toner. Measurement of Fogging Density The electrophotographic toners of the above Examples and Comparative Examples were mixed with a coating carrier (a surface of ferrite particles was coated with styrene-acrylic resin, average particle size: 65 μm) to obtain a toner concentration of 4% by weight. % Two-component developer, which is used as an electrostatic copying machine (model number DC-4 manufactured by Mita Industry Co., Ltd.).
585), image formation is performed 20000 times,
The image density in the margin of the final formed image was measured using a reflection densitometer (RD-918 manufactured by Macbeth Co.). Toner Scattering Observation The state in the copying machine after the above-mentioned 20,000 times of image formation was visually judged and evaluated according to the following criteria.

B: No toner scattering Δ: Toner is slightly scattered. ×: There is toner scattering. Table 1 shows the above results.

[0057]

[Table 1]

Examples 2 and 3 and Comparative Examples 8 to 12 Example 1 and Comparative Example except that titanium oxide whose ratio A / B is the value shown in Table 2 was used in an externally added amount shown in the same table. Negatively charged electrophotographic toners were prepared in the same manner as in Examples 1 to 7. Then, with respect to the electrophotographic toners of the respective Examples and Comparative Examples, the fluidity test, the fogging density measurement, and the toner scattering observation tests were conducted to evaluate the characteristics. The results are shown in Table 2.

[0059]

[Table 2]

Examples 4 and 5, Comparative Examples 13 to 17 Example 1 was repeated, except that titanium oxide having a resistivity [Ω · cm] shown in Table 3 was used in an externally added amount shown in the same table. Then, negatively charged electrophotographic toners were prepared in the same manner as in Comparative Examples 1 to 7. Then, with respect to the electrophotographic toners of the respective Examples and Comparative Examples, the fluidity test, the fogging density measurement, and the toner scattering observation tests were conducted to evaluate the characteristics. The results are shown in Table 3.

[0061]

[Table 3]

Examples 6 to 8 and Comparative Examples 18 to 21 Amount of charge when mixed with the coating carrier [μC
/ G] is the value shown in Table 4, except that the externally added amount shown in the same table is used, Example 1 and Comparative Examples 1 to 1
A negatively charged electrophotographic toner was prepared in the same manner as in No. 7.
Then, with respect to the electrophotographic toners of the respective Examples and Comparative Examples, the fluidity test, the fogging density measurement, and the toner scattering observation tests were conducted to evaluate the characteristics. The results are shown in Table 4.

[0063]

[Table 4]

[0064]

As described above in detail, the toner for electrophotography of the present invention uses a combination of specific hydrophobic silica fine particles and specific titanium oxide fine particles as an external additive externally added to the toner particles. Therefore, in addition to being excellent in fluidity, it is also excellent in charging property and charging stability. Therefore, the constitution of the present invention can be suitably applied to the electrophotographic toner having a small particle diameter for the purpose of improving the image quality.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating an outline of an apparatus for evaluating fluidity of toner.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Nishino 1-2-2 Tamatsukuri, Chuo-ku, Osaka-shi, Osaka Mita Industry Co., Ltd.

Claims (4)

[Claims] 1. A toner for electrophotography, wherein hydrophobic silica fine particles treated with hexamethyldisilazane and titanium oxide fine particles treated with a polyhydric alcohol are externally added to the toner particles. 2. A toner for electrophotography, wherein hydrophobic silica fine particles treated with hexamethyldisilazane and titanium oxide fine particles satisfying the formula (1) are externally added to the toner particles. A / B <1.6 (1) [where A is the specific surface area (m ² / g) of the titanium oxide fine particles measured by the BET method, and B is the primary particle diameter (nm) of the titanium oxide fine particles. ] 3. A toner particle comprising hydrophobic silica fine particles treated with hexamethyldisilazane, and a resistivity of 10 ⁶ to 10 ^6.
An electrophotographic toner comprising titanium oxide fine particles of ⁸ Ω · cm added externally. 4. The toner particles are mixed with a hydrophobic silica fine particle treated with hexamethyldisilazane and a magnetic carrier used for charging the toner particles, and when charged, the absolute value of the charge amount is 5 to 5. A toner for electrophotography, which comprises externally added titanium oxide fine particles having a charge polarity of 80 μC / g and the same charge polarity as the toner.