JPH0814712B2 - Positively charged magnetic toner - Google Patents

Description

TECHNICAL FIELD The present invention relates to a positively chargeable magnetic toner used in electrophotography, electrostatic recording and the like.

BACKGROUND ART Conventional electrophotographic methods include U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 (U.S. Pat. No. 3,666,363) and Japanese Patent Publication No. 43-24748 (U.S. Pat. No. 4,071,3).
No. 61), etc., a number of methods are known. Generally, a photoconductive substance is used to form an electric latent image on a photoconductor by various means, and then, The latent image is developed with toner to form a visible image, and if necessary, the toner image is transferred to a transfer material such as paper and then fixed by heating, pressure or the like to obtain a copy.

Various developing methods are known in which an electrostatic latent image is visualized using toner. For example, a magnetic brush method described in U.S. Pat.No. 2874063, a cascade developing method described in No. 2618552 and a powder cloud method described in No. 2221776, a fur brush developing method. A large number of developing methods such as a method and a liquid developing method are known. Among these developing methods, a magnetic brush method, a cascade method, a liquid developing method and the like, which use a developer mainly composed of toner and a carrier, have been widely put into practical use. Each of these methods is an excellent method of obtaining a good image relatively stably, but has the common problems of the two-component developer such as deterioration of the carrier and fluctuation of the mixing ratio of the toner and the carrier.

To solve this problem, it consists of toner only 1
Various developing methods using a component-based developer have been proposed, but among them, many are excellent in the method using a developer composed of magnetic toner particles.

U.S. Pat. No. 3,909,258 proposes a developing method using a magnetic toner having electrical conductivity. In this method, a conductive magnetic toner is supported on a cylindrical conductive sleeve having magnetism inside, and the conductive magnetic toner is brought into contact with an electrostatic image for development. At this time, in the developing portion, a conductive path is formed by the toner particles between the surface of the recording material and the surface of the sleeve, and the electric charge is introduced from the sleeve to the toner particles through the conductive path, and the conductive path is formed between the electrostatic image and the image area. The Coulomb force causes the toner particles to adhere to the image area and be developed. The developing method using the conductive magnetic toner is an excellent method that avoids the problems associated with the conventional two-component developing method. However, since the toner is conductive, the developed image can be transferred from a recording medium to plain paper or the like. There is a problem that it is difficult to transfer electrostatically to the final supporting member.

As a developing method using a high-resistance magnetic toner that can be electrostatically transferred, there is a developing method using dielectric polarization of toner particles. However, such a method is practically difficult because it has a problem that the developing speed is slow and the density of the developed image cannot be sufficiently obtained.

As another developing method using a high-resistance magnetic toner, a method of frictionally charging the toner particles by friction between the toner particles, friction between the toner particles and the sleeve, etc., and developing the toner particles by contacting them with an electrostatic image holding member It has been known. However, these methods have the following problems: the number of times of contact between the toner particles and the friction member is small, and triboelectric charging is likely to be insufficient, and the charged toner particles are liable to agglomerate on the sleeve due to the strong Coulomb force between the sleeve and the sleeve. And it was practically difficult.

However, in Japanese Patent Laid-Open No. 55-18656, a new developing method has been proposed which eliminates the above-mentioned problems. This involves applying a very thin coat of magnetic toner on a sleeve, tribocharging it and then developing it in close proximity to the electrostatic image. This method increases the chances of contact between the sleeve and toner by applying a very thin coating of magnetic toner on the sleeve, and enables sufficient triboelectrification. By moving the toner particles to each other to sufficiently agglomerate the toner particles with each other and sufficiently rubbing with the sleeve, and by supporting the toner by magnetic force and developing it by facing it without contacting the electrostatic image, an excellent image can be obtained. Is what you get.

In the conventionally known jumping development method, if copying is repeatedly performed, the uniformity of the developer layer carried on the developer carrier may be impaired in some cases, resulting in streak coating in the circumferential direction of the carrier. Defects may occur, the thickness of the carried developer layer may be extremely thick compared to the initial stage, and uneven spots may occur or coating defects such as sawtooth waves may occur. The former is observed as a white streak in an image when developed, and the latter is observed as a hanspot-like or soothing wavy density unevenness. Although this phenomenon hardly occurs in ordinary repeated copying, it may occur particularly in continuous use under an environment of extremely low temperature and low humidity for a long time, and also causes a decrease in image density in continuous use, which is not preferable. .

Further, even at high temperature and high humidity, the thickness of the developer layer often changes and becomes thin, which often causes a decrease in image density, which is not preferable. As a result of studying this point, it was found that the adhesion of the developing powder onto the sleeve and the transfer of the developing powder from the sleeve were changed.

More specifically, such a phenomenon is caused by a non-uniform portion of the triboelectric charge amount in the developer layer carried on the carrier due to a change in environmental conditions. That is, under environmental conditions of ultra-low temperature and low humidity, a component having an extremely large triboelectrification charge of the developer generated by friction between the surface of the carrier and the developer is generated. The extremely large component of such triboelectric charge easily accumulates, and this is due to continuous durability.
This affects the uniformity of the developer coating on the upper layer portion of the developer layer and the easiness of development, and as a phenomenon, the white streaks, spot-like unevenness, and rough wavy coating defects occur. Further, the decrease in the thickness of the developer layer at high temperature and high humidity also occurs due to non-uniform triboelectric charging between the developer and the carrier, and is due to instability of the triboelectric charge amount of the developer near the surface of the carrier. .

In addition, due to the uneven charge amount of the developer,
A ground fog phenomenon occurs, which is a serious problem on the image. In recent years, the functions of copiers have become diversified, so that a part of an image is erased by exposure and the like, and then another image is inserted into the part to make multiple copies, or the periphery of the transfer paper is removed. In terms of function, the occurrence of fog in a white portion of an image that should be removed is a serious problem in terms of color tone and image quality.

That is, when an image having a polarity opposite to the latent image potential with respect to the development reference potential is applied by strong light such as an LED or a fuse lamp to erase the image, fogging occurs at that portion. further,
When multiple copies are made with multiple colors, color mixing occurs, and the sharpness of the image is impaired.

In particular, in the case of a magnetic toner having a positive chargeability, the triboelectric charge amount distribution tends to be broad and non-uniform due to the dispersion state of the magnetic substance contained in the toner, and the environmental conditions such as temperature and humidity The triboelectric charge amount is likely to become more unstable. In recent years, with the increasing use of photoreceptors using organic photoconductors (OPCs), development of positively chargeable magnetic toners that solve the above problems has been desired.

In addition, OPC photoconductors have been made more durable in recent years, and positively chargeable toners are being applied to machines that are faster than conventional ones. In this case, not only in the development of a digital latent image to be described later, but also in the development of an analog latent image, a positively chargeable toner having a high durability capable of withstanding a large number of copies than ever before, or a developer containing the same. Is required.

Image quality such as background fog, reversal fog, and rubbish tends to deteriorate in direct proportion to increase in process speed, and is particularly remarkable in reversal fog. It is speculated that this development is caused by the fact that there is less chance of rubbing between the toner and the toner carrier with the increase in the process speed, and the development becomes shorter, so that the toner cannot obtain sufficient and uniform charging. It

Further, in a high-grade machine, a method of using static electricity is often used in the step of separating the drum and the paper after transferring the image formed on the photosensitive drum onto the transfer paper. In this case, before transferring the toner from the photosensitive drum onto the paper,
A new process (post-charging) for uniformly charging the same charge as the developer is added. In such an image forming process, if the toner is present as fog on the drum, it will not be transferred onto the paper in the conventional image forming process, but will be transferred onto the paper due to the addition of the charging process. , Appears as a fog in the final image. In such an image forming process, it is necessary to control the triboelectric charge amount more sharply than the conventional toner, and it is extremely difficult to use the conventional toner as it is in a copying machine having a post-charging process. The current situation.

In addition, recently, as the demand for image quality improvement has increased, image forming apparatuses such as electrophotographic printers using digital image signals are being used. When a conventional positively chargeable toner is used, the non-uniformity of the charge amount, which is likely to occur on the surface of the toner particles between the toner particles or between the toner and a toner carrier such as a sleeve, is digital. When developing an electrostatic latent image formed by an image signal, it becomes clear that a particular problem occurs, and a developer having a more uniform charge has been desired.

That is, when the image signal is a digital signal, the latent image is formed by gathering dots having a constant potential, and the solid portion, the halftone portion, and the light portion are expressed by changing the density of each dot. Therefore, any part is basically formed from an electrostatic latent image having substantially the same potential in the case of binary.

Also in this method, there is an increasing demand for further improvement in image quality.
It has become necessary to measure the improvement in gradation reproducibility using the multivalued dither method based on values. This multi-valued dither method is useful for removing false contours that are likely to occur in highlights, or for simultaneously reproducing an image in which halftones and line images are mixed, without reducing the gradation. It is also an indispensable technique for improving the resolution by reducing the size.

The concept of the dither matrix in the multi-value dither method will be described with reference to FIGS. 1 (a) and 1 (b). FIG. 1 (a) is a 2 × 2 ternary dither matrix, and regions S ₁ , S ₂ , and S ₃ respectively represent ternary density levels of white, gray, and black. FIG. 1 (b) shows 2 ×
This is a 4-valued dither matrix of 2 and includes areas S ₁ , S ₂ ,
S ₃ and S ₄ are white, light gray, dark gray, and black, respectively.
It represents the density level of the value. Dot size
16 dots / mm.

2 (a) and (b) and FIGS. 3 (a) and (b),
Exposure intensity distribution when ternary recording is performed in an optical scanning electrophotographic printer (FIG. 2 (a), FIG. 3 (a))
And the potential distribution of the electrostatic latent image corresponding thereto (FIGS. 2B and 3B). Second
The broken lines in FIGS. 3A and 3A represent the signal output for outputting a light beam for forming a multi-valued latent image, and FIG. 2A shows the luminance for controlling the laser output. a gray level corresponding to S ₂ of FIG. 1 by the modulation (a) (hereinafter referred to as "M" level), the black level to S ₃ (hereinafter "H
It is a method of obtaining "level"). For example, the M level is obtained with a laser output that is 1/2 of the H level. On the other hand, FIG. 3A shows a method of obtaining M level and H level by pulse width modulation for controlling the laser output time. This is obtained, for example, by setting the M level to have a pulse width that is 1/2 of the H level.

The potential distributions of the latent image formed by the light beam having the exposure intensity distributions of FIGS. 2 (a) and 3 (a) are as shown in FIGS. 2 (b) and 3 (b), respectively. The M-level latent image contrast due to the pulse width modulation shown in FIG. 3B tends to be smaller than the H level due to the decrease in the MTF (modulation transfer function) of the latent image. Therefore, the image density after the development at the M level is almost the same gray as the image density at the M level in FIG.

Fig. 4 shows the development characteristics (Vs-
FIG. 2 (b) and FIG. 3 (b).
In order to reproduce the M-level and H-level latent images (the respective potential contrasts are represented by), particularly when the H level cannot be sufficiently high, a relatively gamma (latent image potential) is used.
A Vs-Dp characteristic (indicated by a solid line in the figure) having a large inclination of the image density Dp with respect to Vs is required. However, when a conventional toner or developer for developing an analog latent image is used, in many cases, it tends to show development characteristics as shown by a solid line, in which case various problems such as a decrease in image density and sharpness are caused. .

Also, when developing a latent image represented by the density of digital dots, compared to the conventional analog latent image
Precise control of the Vs-Dp curve is required. First, in order to develop a digital latent image, the slope (gamma) of the Vs-Dp curve needs to be made larger than before, and it is necessary to control so that this slope does not change. However, the non-uniformity of the electric charge generated in the toner using the conventional magnetic powder is due to Vs-Dp
This is an obstacle to increasing the slope of the curve, and causes a state in which the slope is likely to change.

When the slope of the Vs-Dp curve is small, H-level dots cannot be reproduced at sufficiently high density. If the difference between the H level and the M level cannot be sufficiently reproduced,
As shown in FIG. 3 and FIG. 3, the potential of the edge portion of the dot is lower than that of the central portion, which causes problems such as poor image cutting at the edge portion of the dot. The resulting image is low, lacks sharpness, and has low resolution. Further, this non-uniformity of electric charges causes the Vs-Dp curve to fluctuate when the number of times of copying is increased or the working environment fluctuates, which causes the above-mentioned problems.

OBJECT OF THE INVENTION An object of the present invention is to provide a stable triboelectric charge amount between toner particles, between a toner and a toner carrier such as a sleeve, and a sharp and uniform triboelectric charge amount distribution. Another object of the present invention is to provide a positively chargeable magnetic toner capable of controlling a suitable charge amount.

Still another object is toner that enables faithful development to a digital latent image, that is, the slope of the Vs-Dp curve during development is large, and it is possible to increase the density difference between dots, and The object is to provide a positively chargeable magnetic toner whose parts are sharply reproduced.

Still another object is to provide a positively chargeable magnetic toner that maintains the initial characteristics even when the toner is continuously used for a long period of time and has no fluctuation in the Vs-Dp curve.

Still another object is to provide a positively chargeable magnetic toner with less fog and reversal fog even in an image forming process including post-charging.

Still another object is to provide a positively charged magnetic toner that reproduces a stable image that is not affected by changes in temperature and humidity.

Still another object is to provide a positively chargeable magnetic toner excellent in storage stability, which retains initial characteristics even after long-term storage.

That is, the present invention comprises a magnetic powder having magnetic particles containing silicic acid or silicate converted to silicon element in an amount of 0.05 to 10 weight percent, and a positive charge control substance. The present invention relates to a characteristic positively chargeable magnetic toner.

The positively chargeable magnetic toner of the present invention having the above-mentioned constitution has a uniform triboelectric charge amount, can control the triboelectric charge amount suitable for the developing system, and only gives a high density image without fog. In addition, it enables stable image reproduction even when environmental conditions change.

The reason why such effects are obtained in the toner of the present invention is not clear, but it is presumed as follows.

That is, the magnetic particles constituting the magnetic powder used in the toner of the present invention, by the inclusion of silicic acid or silicate,
(Compared to magnetic powder used in conventional magnetic toner)
The composition and structure inside the particles become uniform, which not only sharpens the particle size distribution of the magnetic powder particles but also reduces the cohesiveness of the particles themselves, making them extremely uniform in the toner (or the binder resin that constitutes the toner). Disperse into.

Therefore, the toner particles of the present invention have physically and chemically uniform surface characteristics, and a stable and uniform charge can be imparted very easily, so that a high-density image free from fog can be obtained, and It is estimated that a stable image can be given even when the environmental conditions change.

Further, in the conventional magnetic toner containing a general magnetic powder, there is a tendency that toner particles that partially exhibit a negatively charged fog phenomenon are likely to occur, but in the toner of the present invention, The generation of such fog is substantially eliminated.

The reason is presumed as follows. That is, between the toner particles containing the conventional magnetic powder, when the positive charge control agent and the magnetic powder contact or rub against each other, they are partially triboelectrically charged to the positive charge and the negative charge, respectively. Toner particles that are electrically charged (causing fog) are generated.

On the other hand, in the positively chargeable magnetic toner of the present invention, the magnetic particles containing silicic acid or silicate exhibiting hydrophilicity are triboelectrically charged by contact with the positively chargeable control agent and partially Magnetic particles are evenly charged, the magnetic particles are uniformly dispersed in the toner particles, and the magnetic particles have a hydrophilic silicic acid or silicate. The negative charge can be easily leaked between the positive charge control agent and the sleeve. Therefore, it is presumed that the toner of the present invention can stably hold the positive charge based on the triboelectric charge with the sleeve of the developing machine, and gives a clear toner image substantially free from fog.

Hereinafter, the present invention will be further described with reference to the drawings as necessary. In the following description, “part” and “%” representing the quantitative ratio are based on weight unless otherwise specified.

DETAILED DESCRIPTION OF THE INVENTION The positively chargeable magnetic toner of the present invention comprises a magnetic powder composed of magnetic particles containing silicic acid or silicate in an amount of 0.05 to 10 (weight)% in terms of silicon element, and a positively chargeable magnetic toner. It contains a control substance as an essential component.

The magnetic powder used in the present invention needs to contain silicic acid or silicate in an amount of 0.05 to 10% in terms of silicon element, and more preferably 0.1 to 5%.

If the abundance of silicon element in the magnetic particles is less than 0.05%, it becomes difficult to produce the effect of containing a silicon element,
It is not possible to obtain uniform dispersion of magnetic powder in the toner, while
When the abundance ratio exceeds 10%, the moisture resistance of the toner decreases.

In the present invention, the abundance of the silicic acid or silicate contained in the magnetic particles in terms of silicon element is measured by the following method.

Approximately 5 g of magnetic powder is sampled in the beaker of No. 1 (this is referred to as Ag), and 3N hydrochloric acid aqueous solution is added to make it to be one. Keep the temperature at about 50 ° C and continue the reaction with stirring until everything is dissolved and clear. Plasma emission spectroscopy (ICP) was used to determine the amount of dissolved silicon element (this was calculated as Bmg
/ l) and measure. The abundance of elemental silicon with respect to the weight of the magnetic powder is calculated by the following equation.

Existence rate of elemental silicon (%) = {B / (A × 1000)} × 100 When analyzing the magnetic powder contained in the toner, an organic solvent such as xylene that dissolves the resin component of the magnetic toner is used. And the toner are mixed, the solution in which the resin component of the magnetic toner is dissolved is filtered through a 20 A filter paper, and the solution in which the resin component of the magnetic toner is dissolved is collected to collect the magnetic powder remaining on the 20 A filter paper. The collected magnetic powder is treated in an atmosphere of 600 ° C. to remove organic components, and the obtained magnetic powder is analyzed by the above method, whereby the abundance ratio of the elemental silicon is measured.

As the magnetic powder used in the present invention, a powder of a ferromagnetic element, or an alloy or compound containing these, which contains a silicon compound is preferably used. For example, iron, such as magnetite, γ-iron oxide, and ferrite, alloys and compounds such as cobalt, nickel, and manganese, and other ferromagnetic alloys, which are conventionally known as magnetic materials, are made to contain silicon element in the manufacturing process. You can use one. Among them, magnetic iron oxide containing a silicon element by involving a silicon compound in the form of silicic acid or silicate in the production process is preferably used.

These are fine powders and have a BET specific surface area of 0.1 to ²⁰ m ² / g, preferably ^{2 to 20} m ² / g. In addition, the saturation magnetization σs is 70 emu / g or more, and the measurement magnetic field 1KOe
Is preferably 5 to 200 Oe.

In the magnetic iron oxide according to the present invention, the apparent bulk density is
0.10 to 0.38 g / cc is preferred, and particularly preferably 0.10 to 0.30 g / cc.
g / cc is good. Within this range, the effect of the present invention is more exerted as a magnetic iron oxide mainly containing octahedral particles having a low cohesiveness and an excellent dispersibility.

Further, the toluene dispersibility of the magnetic iron oxide used in the present invention is such that the sedimentation length after 1 hour shows a value of 20 mm or less, preferably 10 mm or less. In such a case, magnetic iron oxide can be satisfactorily dispersed in the binder resin component.

The average particle size of the magnetic iron oxide used in the present invention is 0.1 to 2.0.
μm is preferable, and 0.1 to 0.6 μm is more preferable. If the average particle size is too small (less than 0.1 μm), the particles easily aggregate and the environment resistance deteriorates. Average particle size is too large (2.0μ
and larger than m), when dispersed in a binder resin and used,
The toner particles may be excessively projected or unevenly distributed on the surface of the toner particles, which is not preferable, and the blackness may decrease as a hue.

In the present invention, the apparent bulk density of magnetic iron oxide is measured as follows.

Using a bulk density measuring device of a powder tester (manufactured by Hosokawa Micron), set a 710 μm sieve, add crushed magnetic iron oxide little by little onto the sieve, and swing about 1 m
While vibrating at m, continue to the attached cup until there is a heap. After stopping, the surface of the powder is ground with the attached blade and weighed. The internal volume of the cup is 100 cc, the tare value of the cup is subtracted to obtain the sample weight, and the apparent bulk density is calculated by the following formula.

Apparent bulk density (g / cc) = magnetic oxide weight (g) / 100 (c
c) In the present invention, the dispersibility of magnetic iron oxide in toluene is measured as follows.

Approximately 1 g of sample is weighed and a settling tube with a stopper (16.5 mmφ x 105 mm
(H, with scale) and add toluene to make 10 ml. After stoppering and shaking thoroughly, stand vertically and stand still. At the same time as the start of standing, the stopwatch is pushed, the distance between the liquid surface and the sedimentation interface after a predetermined time is read, and this value is used as a measure of the dispersibility of the magnetic iron oxide in toluene.

In the present invention, the measurement of the average particle diameter of the magnetic oxide and the observation of the shape are performed as follows.

Using a sample treated with a collodion film copper mesh with a transmission electron microscope (Hitachi H-700H), an image is taken at 10,000 times at an applied voltage of 100 KV, and the baking magnification is set to 3 times and the final magnification is set to 30,000 times. The shape is then observed, the maximum length of each particle is measured, and the average thereof is taken as the average particle diameter.

The magnetic powder as described above may be used in an amount of about 20 to 200 parts, particularly preferably 30 to 150 parts, based on 100 parts of the binder resin.

Further, even if the surface of these magnetic powders is treated with a treating agent such as a silane coupling agent, a titanium coupling agent, a titanate, an aminosilane, a hydrophobic polymer, a surfactant (including a fatty acid metal salt), etc. good.

In particular, isopropyltriisostearoyl titanate (TTS), aluminum stearate and the like are preferable.
By these treatments, the environment resistance and dispersibility can be improved, and the charging ability can be adjusted.

On the other hand, when the positive charge control material described later does not act as a binder resin, the toner of the present invention contains a binder resin.

As the binder resin used in the positively chargeable magnetic toner of the present invention, a known binder material for toner can be used when a pressure heating roller fixing device having an oil coating device is used. .

For example, polystyrene, poly-p-chlorostyrene,
Homopolymers of styrene such as polyvinyltoluene and its substitution products; styrene-p-chlorostyrene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene copolymers, styrene-acrylic acid ester copolymers, styrene -Methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone Styrene-based copolymers such as copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, natural modified phenolic resins, natural resin modified malein Acid resin, Acrylic Resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethane, polyamide resins, furan resins, epoxy resins, xylene resins, polyvinyl butyral, terpene resin, coumarone-indene resins, and petroleum resins.

In the heating and pressure roller fixing method in which oil is hardly applied, the so-called offset phenomenon in which a part of the toner image on the toner image supporting member is transferred to the roller and the adhesion of the toner to the toner image supporting member are important problems. is there. Toners that fix with less heat energy usually tend to be blocked or caked during storage or in a developing device, so these problems must be taken into consideration at the same time. The physical properties of the binder substance in the toner are most involved in these phenomena. However, according to the research conducted by the present inventors, when the content of the magnetic substance in the toner is reduced, as described above, at the time of fixing, Although the adhesion of the toner to the toner image supporting member is improved, offsetting is likely to occur, and blocking or caking is likely to occur. Therefore, when using the heating and pressure roller fixing method in which the oil is hardly applied in the present invention, the selection of the binding substance is more important. Preferred binder materials are cross-linked styrenic copolymers or polyesters.

Examples of the comonomer of this styrene-based copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid, A monocarboxylic acid having a double bond such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, and acrylamide, or a substituted product thereof; for example, maleic acid, butyl maleate, maleic acid. Dicarboxylic acids having a double bond such as methyl and dimethyl maleate and substituted compounds thereof; vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc .; ethylene, propylene, butylene, etc. Ethylenic olefins such;
For example, vinyl ketones such as vinyl methyl ketone and vinyl hexyl ketone; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether, vinyl isobutyl ether and the like;

Here, as the cross-linking agent, a compound having two or more polymerizable double bonds is mainly used, and examples thereof include aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; for example, ethylene glycol diacrylate and ethylene glycol diethylene. Double bonds such as methacrylate and 1,3-butanediol dimethacrylate
Carboxylic acid ester having one; a divinyl compound such as divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone; and a compound having three or more vinyl groups; used alone or as a mixture.

When the pressure fixing method is used, a known binder resin for pressure fixing toner can be used, and examples thereof include polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-acetic acid. Examples thereof include vinyl copolymers, ionomer resins, styrene-butadiene copolymers, styrene-isoprene copolymers, linear saturated polyesters and paraffins.

Examples of the positive charge control agent used in the present invention include nigrosine and its modified products; tributylbenzylammonium-1.
-Quaternary ammonium salts such as hydroxy-4-naphthosulfonate and tetrabutylammonium tetrafluoroborate; diorganotin oxides such as dibutyltin oxide, dioctyltin oxide and dicyclohexyltin oxide; dibutyltin borate, dioctyltin borate, dicyclohexyltin borate Etc. can be used alone or in combination of two or more kinds. Among these, organotin-based charge control agents such as diorganotin oxide and diorganotin borate are particularly preferably used.

Also, the general formula R ₁ : H, CH ₃ R ₂ : R ₃ a homopolymer of a monomer represented by a substituted or unsubstituted alkyl group; or a copolymer with a polymerizable monomer such as styrene, acrylic acid ester, methacrylic acid ester as described above. Polymers can be used as positive charge control agents, in which case these charge control agents also have the effect of (all or part of) a binder resin (thus acting as a binder resin). (A positive charge controlling agent is also referred to herein as a positive charge controlling agent including the positive charge controlling agent).

It is preferable to use the above-mentioned charge control agent (which does not function as a binder resin) in the form of fine particles. In this case, the number average particle size of the charge control agent is preferably 2/3 or less (more preferably 1/2 or less) of the number average particle size of the toner. The number average particle diameter of this charge control agent is, specifically, 10
It is preferably not more than μm (more preferably not more than 5 μm).

When internally added to the toner, such a charge control agent is preferably used in an amount of 0.1 to 20 parts (more preferably 0.5 to 10 parts) per 100 parts of the binder resin.

Further, it is preferable to add fine silica powder to the positively chargeable magnetic toner of the present invention. In the toner in which the magnetic powder (for example, magnetic oxide) according to the present invention, the positive charge control agent, and the silica fine powder are combined, the triboelectric charge amount is controlled with higher performance than the conventional toner, and the charging is stabilized. It is possible to

As the silica fine powder, silica fine powder produced by a dry method or a wet method can be used, but from the viewpoint of filming resistance and durability, it is preferable to use the silica fine powder by the dry method.

The dry method referred to here is a method for producing fine silica powder produced by vapor phase oxidation of a silicon halogen compound. For example, in a method utilizing a thermal decomposition oxidation reaction of silicon tetrachloride gas in oxygen hydrogen, the basic reaction formula is as follows.

SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl In this manufacturing process, for example, by using another metal halogen compound such as aluminum chloride or titanium chloride together with a silicon halogen compound, a composite fine powder of silica and another metal oxide is obtained. It is possible to obtain, and they are included.

Examples of commercially available silica fine powder produced by vapor phase oxidation of a silicon halogen compound used in the present invention include those commercially available under the following trade names.

AEROSIL 130 (Japan Aerosil Co., Ltd.) 200 300 380 OX50 TT600 MOX80 MOX170 COK84 Ca-O-SiL M-5 (CABOTO Co. Co.) MS-7 MS-75 HS-5 EH-5 Wacker HDK N 20 V15 (WACKER-CHEMIE) GMBH) N20E T30 T40 D-C Fine Silica (Dow Corning Co.) Fransol (Fransil) On the other hand, there are various conventionally known methods for producing the silica fine powder used in the present invention by a wet method. Applicable. For example, if sodium silicate is decomposed by an acid, and if it is shown by a general reaction formula (the reaction formula is abbreviated below), Na ₂ O ・ XSiO ₂ + HCl + H ₂ O → SiO ₂・ nH ₂ O + NaCl, other ammonium salts of sodium silicate or alkali Decomposition by salts, method of generating alkaline earth metal silicate from sodium silicate, then decomposing with acid to silicic acid, method of converting sodium silicate solution into silicic acid by ion exchange resin, natural silicic acid or There is a method of using silicate.

As the silica fine powder referred to here, anhydrous silicon dioxide (silica) and other silicates such as aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, and zinc silicate can be applied.

Examples of commercially available silicic acid fine powders synthesized by the wet method include those commercially available under the following trade names.

Carpretx Shionogi Nepseal Nippon Silica Tokseal, Huainseal Soda Tokuyama Vita Seal Taki Manure Shiruton, Shirunetsuku Mizusawa Chemical Starsil Kamijima Kagaku Himesir Ehime Pharmaceutical Syloid Fuji Debison Kagaku Hi-Sil Pittsburgh Plate Glass Co. (Pittsburgh)
Plate Glass) Durosil Fiillstoff-Gesellschaft Marquart Ultrasil (Ultraseal) (Fuyrustotsuf Gezershyaft Marukoruto) Manosil (Manosir) Hardman and Holden (Hardman and Holden) Hoesch (Hetsuyu) Chemische Fabrik Hoesch K-G・ Fair Creek Het Shiyu Sil-Stone Stoner Rubber Co. Nalco Nalco Chem.Co. Quso Philodelphia Quartz Co.35 Imla ) Illinois Minerals Co. (Illinois Minerals) Calsium Silikat Chemische Fabrik Hoesch.K-G (Calcium Zilikart) (Hiemitsushie Fabryu Hetsushiyu) Calsil Fortafil Imperial Chemical Industries.Ltd. (Imperial Chemical Industries) Microcal (Microcal) Joseph Crosfield & Sons.Ltd. (Jesef Crossfield and Sons) Manosil (Manosir) Hardman and Holden (Hardman and Holden) Vulkasil ( Burkazir) Farbenfabriken Bryer, AG Tufknit Durham Chemicals.Ltd. Silmos Shiraishi Kogyo Starletx Kamijima Chemical Phlycosyl Polywood Manure Measured by the BET method among the above fine silica powders Specific surface area of 30m ² / g) or more due to nitrogen adsorption (especially 50 to 400m ² / g)
Those in the range of give good results.

Conventionally, examples of adding fine silica powder produced by vapor phase oxidation of a silicon halogen compound to a developer are known. However, even with a toner having a positive charge control agent,
Addition of such silica negatively changes the chargeability, and is sometimes unsuitable for visualizing a negative electrostatic charge image or visualizing a positive electrostatic charge image by reversal development.

As a method for obtaining a positively chargeable silica fine powder, a method of treating the above-mentioned untreated silica fine powder with a silicone oil having an organo group having at least one nitrogen atom in a side chain, or a nitrogen-containing silane cup is used. There is a method of treating with a ring agent or a method of treating with both of them.

In the present invention, the positively chargeable silica has a positive triboelectric charge when measured by the blow-off method.

As the silicone oil having a nitrogen atom in the side chain used for treating the silica fine powder, silicone oil having at least a partial structure represented by the following formula can be used.

(In the formula, R ₁ represents hydrogen, an alkyl group, an aryl group or an alkoxy group, R ₂ represents an alkylene group or a phenylene group, R ₃ and R ₄ represent hydrogen, an alkyl group or an aryl group, and R ₅ Represents a nitrogen-containing heterocyclic group) The alkyl group, aryl group, alkylene group and phenylene group may have an organo group having a nitrogen atom, and may be substituted with halogen or the like within a range not impairing the charging property. It may have a group.

The nitrogen-containing silane coupling agent used in the present invention is
Generally, it has a structure represented by the following formula.

RmSYn (R represents an alkoxy group or halogen, Y represents an amino group or an organo group having at least one nitrogen atom, m and n are integers of 1 to 3, and m + n =
It is 4. ) Examples of the organo group having at least one nitrogen atom include an amino group having an organic group as a substituent, a nitrogen-containing heterocyclic group, or a group having a nitrogen-containing heterocyclic group. As the nitrogen-containing heterocyclic group, there are an unsaturated heterocyclic group and a saturated heterocyclic group, and known ones can be applied. Examples of the unsaturated heterocyclic group include the following.

Examples of the saturated heterocyclic group include the followings.

The heterocyclic group used in the present invention is preferably a 5-membered ring or a 6-membered ring in view of stability.

Examples of such treating agents include aminopropyltrimethoxysilane, aminopropyltriethoxysilane, dimethylaminopropyltrimethoxysilane, diethylaminopropyltrimethoxysilane, dipropylaminopropyltrimethoxysilane, dibutylaminopropyltrimethoxysilane, mono Butylaminopropyltrimethoxysilane, dioctylaminopropyltrimethoxysilane, dibutylaminopropyldimethoxysilane, dibutylaminopropylmonomethoxysilane, dimethylaminophenyltriethoxysilane, trimethoxysilyl-
γ-propylphenylamine, trimethoxysilyl-γ
-Propylbenzylamine and the like, and the nitrogen-containing heterocycle having the structure described above can be used. Examples of such compounds include trimethoxysilyl-γ-propylpiperidine and trimethoxysilyl-γ-propylmorpholine. , Trimethoxysilyl-γ-propylimidazole and the like.

The amount of the treated silica fine powder applied is 0.01 to 10 parts with respect to 100 parts of the positively chargeable magnetic toner, and particularly preferably 0.03 to 5 parts is excellent in stability. Shows a positive chargeability. To describe a preferable mode of addition, it is preferable that 0.01 to 3 parts of the treated silica fine powder adhere to the surface of the toner particles with respect to 100 parts of the positively chargeable magnetic toner. The untreated silica fine powder described above can be used in the same application amount.

Further, the fine silica powder used in the present invention may be treated with a silane coupling agent and a treating agent such as an organic silicon compound for the purpose of hydrophobizing, if necessary, and a known method may be used. , Treated with the above-mentioned treating agent that reacts or physically adsorbs with the silica fine powder. As such a treating agent, for example, hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyldimethylchlorosilane, Brommethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilane, dimethylethoxysilane, dimethyldimethoxy. Silane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldisiloxane,
1,3-diphenyltetramethyldisiloxane, and 1
For example, there is dimethylpolysiloxane having 2 to 12 siloxane units per molecule, and each unit located at the terminal has a hydroxyl group bonded to Si for one unit. These are used alone or as a mixture of two or more.

Finally, the hydrophobicity of the treated silica fine powder is the hydrophobicity measured by the methanol titration test,
When hydrophobized so as to exhibit a value in the range of 30 to 80, the developer containing such silica fine powder exhibits a sharp and uniform triboelectric charge amount, which is preferable.
Here, the methanol titration test is for confirming the degree of hydrophobicity of silica fine powder having a hydrophobized surface.

In order to evaluate the hydrophobicity of the treated silica fine powder, the "methanol measurement test" defined in this specification is performed as follows.

0.2 g of the fine silica powder to be tested is added to 50 ml of water in an Erlenmeyer flask having a volume of 250 ml. Methanol is filled from the burette until the total amount of silica has been wetted. At this time, the solution in the flask is constantly stirred with a magnetic stirrer.
The end point is observed by suspending the total amount of silica fines in the liquid, and the degree of hydrophobization is expressed as the percentage of methanol in the liquid mixture of methanol and water when the end point is reached.

In the electrostatic charge image developing developer obtained by adding the positively chargeable silica fine powder to the positively chargeable magnetic toner containing the magnetic powder containing the silicon element and the positive chargeability control agent, particularly excellent characteristics are That is, even after continuous use for a long period of time, a decrease in image density is not seen and a high quality image in the initial stage can be maintained. It is presumed that this is because the triboelectric charge amount is constant and the distribution is sharp in the developer in which the positively chargeable magnetic toner and the positively chargeable silica fine powder are combined.

The toner of the present invention may further contain various additives, if necessary. Such additives include charge control,
It is added for the purpose of coloring, toning, imparting fluidity, etc., and includes carbon black, various dyes and pigments, metal complexes, plasticizers and the like.

Next, a method for producing the toner particles of the present invention will be described. First, a toner composition including magnetic powder and a charge control agent (a binder resin or the like as necessary) is premixed using a mixer such as a ball mill. The obtained mixture is kneaded using a melt-kneader such as a roll mill. After cooling, it is roughly crushed to a size of several mm or less using a crusher such as a hammer mill, and then finely crushed using a supersonic jet crusher. The obtained particles are fine particles of about 0.1 to 50 μm and are classified to obtain a toner. At this time, the pulverization is controlled to set the particle size distribution before classification, and the classification is set according to the specific gravity of the toner and the feed amount, whereby a toner having a predetermined particle size distribution can be obtained.

At the time of the classification, as a material used for cutting on the fine powder side, Alpine Co., trade name, Microplex 132MP, Donaldson Co., trade name Acucut A-12, or Hosokawa Iron Works Co., Ltd. trade name Micron Separator MS-1.
There is a wind classifier etc.

As a product for cutting the coarse powder side, Alpine Co., Ltd. product name Microplex 400MP or Micron Separator
There are wind classifiers such as MS-1 and classifiers with sieves such as Blower Shifter manufactured by Taikosha.

The above is one example of the method for producing the toner used in the present invention, and various methods such as a toner by a suspension polymerization method and a toner by a microcapsule method are possible in addition to this.

In the present invention, the charge amount of the toner layer per unit area on the carrier and the weight of the toner layer were determined by using a so-called suction type Faraday cage method.

In this suction type Faraday cage method, the outer cylinder is pressed against the toner carrier to suck all the toner on a certain area on the carrier, and the toner is collected on the filter of the inner cylinder.
The weight of the toner layer per unit area on the toner carrier can be calculated from the weight increase of the filter. At the same time, the amount of charge per unit area on the toner carrier can be obtained by measuring the amount of charge accumulated in the inner cylinder that is electrostatically shielded from the outside (for example, the suction-type Faraday cage method Electrophotographic Society Paper Vol.11.No1)
Have been introduced).

An example of producing the magnetic powder containing silicon element used in the present invention is shown below.

Production Example 1 0.8 M FeSO ₄ aqueous solution 1 in a ₄ l three-necked flask,
Oxidation was performed at about 70 ° C. while blowing steam and oxygen into a system in which 0.02 M sodium silicate aqueous solution 1 and 0.85 M caustic soda aqueous solution 1 were mixed. The obtained black powder was filtered, washed with water, and dried at 50 ° C. to obtain a magnetic iron oxide powder containing 0.4% by weight of silicic acid and sodium silicate in terms of silicon element.

The apparent bulk density of this magnetic iron oxide is 0.25 g / cc, and the dispersibility in toluene is 7 mm with a sedimentation length of 1 hour, the average particle size is 0.28 μm, and BET.
The specific surface area was 7.9 m ² / g.

Production Example 2 The procedure of Production Example 1 was repeated except that a 0.06 M aqueous sodium silicate solution was used instead of the 0.02 M aqueous sodium silicate solution. Silicic acid and sodium silicate were converted to elemental silicon. As a result, magnetic iron oxide powder containing 1.0 weight percent was obtained.

The apparent bulk density of this magnetic iron oxide is 0.27 g / cc, the dispersibility in toluene is 5 mm with a sedimentation length of 1 hour, the average particle size is 0.26 μm, and BET
The specific surface area was 8.2 m ² / g.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples, but this does not limit the present invention at all, and all parts in the following formulations are parts by weight.

Example 1 The above materials were well mixed with a blender and then kneaded with two rolls heated to 150 ° C. The resulting kneaded product is allowed to cool naturally, roughly crushed with a cutter mill, crushed with a fine crusher using a jet stream, and further classified with an air classifier to obtain a volume average particle diameter of 12 μm ( Number average particle size about 10μ
m) black powder (that is, positively charged magnetic toner) was obtained.

To 100 parts by weight of this black powder, 0.5 parts by weight of positively charged hydrophobic dry colloidal silica was added and mixed with a Henschel mixer to obtain a positively charged magnetic toner with silica added.

By applying this toner to a commercial copying machine NP-3525, it can be used under normal conditions of normal temperature and humidity (23.5 ℃, 60%), low temperature and low humidity (15 ℃, 10%), high temperature and high humidity (32.5 ℃, 85%). Image drawing was performed.

As shown in the table below, the charge amount of the toner on the developing sleeve did not change significantly in any environment, and the image density was stable.

Further, even after the repeated copying of 50,000 sheets, the image quality did not change significantly, and the background fog and the reverse fog in the white part due to the area designation function did not pose a problem.

It should be noted that the toner is hardened with epoxy resin, and the
When a reflection image was observed with a scanning microscope using a thin film section of μ, it was found that the magnetic powder particles were uniformly dispersed in the toner particles.

Example 2 In the same manner as in Example 1 except that the magnetic powder of Production Example 2 was used instead of the magnetic powder of Production Example 1 used in Example 1,
A positively chargeable magnetic toner was obtained and evaluated.

As a result, as shown in the table below, both the charge amount and the image density were stable. Also, repeated copying did not cause any serious problems.

Example 3 Using the above materials, a positively chargeable magnetic toner was obtained and evaluated in the same manner as in Example 1.

As a result, as shown in the table below, both the charge amount and the image density were stable.

Also, repeated copying did not cause any serious problems.

Example 4 In Example 1, dibutyltin borate (number average particle size of about 4 μm) was used instead of nigrosine, and as a hydrophobic colloidal silica, a silicone oil having a partial structural unit represented by the following formula: A silica externally added positively charged magnetic toner was obtained and evaluated in the same manner as in Example 1 except that finely charged positively charged silica powder treated with (nitrogen atom equivalent 83 viscosity at 80 cps) was used.

As a result, as shown in the table below, a stable charge amount,
It was the image density. In addition, the ground fog and the reverse fog were good throughout the durable copying.

Example 5 Using the toner of Example 4, an image was obtained and evaluated by an electrophotographic printer using an amorphous silicon photoconductor. When measured by the blow-off method, the tribo value of the developer was +8.5 μc.

FIG. 5 shows an embodiment of an electrophotographic printer to which the developer of the present invention can be applied. With reference to FIG. 5, the electric signal input to the laser modulation unit 1 is output as a modulated laser beam, and the scanner mirror 2 and the f.theta. Lens 3 scan the photosensitive drum 4 in the longitudinal direction. The photosensitive drum 4 rotates in the direction of the arrow, enabling two-dimensional scanning with the laser beam.

Amorphous silicon, selenium, Cd
S, organic photoconductors, etc. are used, and are specially published for sensitivity to the wavelength of semiconductor lasers (780 nm to 800 nm). In this embodiment, an amorphous silicon photoconductor is used as such a photoconductor, and the surface of the photoconductor is leveled by the AC static eliminator 5 and then charged to 380 V by the charger 6. After that, laser beam exposure is performed to image the photoreceptor.
A dot latent image is formed by a ternary dither method by a scanning method. The ternary M level is formed by pulse width modulation of the laser light as shown in FIG. The latent image potential was 250v for H level and 120v for M level.

Such a dot latent image was subjected to reversal development by a developing device 9 or 10 for a one-component insulating magnetic toner containing the above-described developer of the present invention containing toner. At this time, a developing bias of 280 V was applied as a direct current component.

The image thus developed is then transferred onto a transfer paper 12 by a transfer charger 11, and is then transferred by a fixing device 13 to the transfer paper 12.
It was established in. Further, the toner remaining on the photosensitive drum 4 without being transferred is collected by the cleaner 14.

The image thus formed on the transfer paper shows an image density of 1.48 at the H level and 0.62 at the M level, the image density of the solid portion is sufficiently high, the dots are sharply cut, and as a guide for the reproduction of the halftone. The photographic image was also reproduced neatly.

Further, 100,000 copies were repeatedly made, but in the obtained image density, the fluctuation of the H level was within ± 0.10 and the fluctuation of the M level was within ± 0.15, and a large change in the Vs-Dp characteristics was recognized. There wasn't. Furthermore, the environmental conditions are 35 ° C, 85% and
When the temperature was set to 15 ° C and 10%, good images were obtained in the same manner as at room temperature and normal humidity, and no significant change was observed even after repeated use of 100,000 sheets.

Also, this developer was stored for half a year, but it did not change significantly from the initial characteristics.

Also, fog and reversal fog did not become a problem through durability.

Example 6 To 100 parts by weight of the black fine powder obtained in Example 1 was added 0.4 part by weight of hydrophobized wet silica to prepare a silica externally added positively charged magnetic toner. The prepared magnetic toner showed good developing characteristics.

Comparative Example 1 The procedure of Example 1 was repeated, except that the magnetic powder of Example 1 was replaced by the magnetic powder obtained in substantially the same manner as in Production Example 1 except that the aqueous sodium silicate solution was omitted.

Compared with the case of Example 1, there was a slight background fog at room temperature and normal humidity. Under the low temperature and low humidity environment conditions of 15 ° C and 10%, the background fog increased, and at the same time, high temperature and high humidity of 32.5 ° C and 85%. Under environmental conditions, the density was as low as 1.08 from the beginning, and dropped to 0.87 due to durable copying.

It should be noted that the toner is hardened with epoxy resin, and the
When a reflection image was observed with a scanning microscope using a thin film section of μ, magnetic particles were unevenly distributed in the toner particles in an aggregated state, and a wide area where magnetic particles were not observed was observed.

The aggregates obtained in the above examples are summarized in the table below.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 (a) and 1 (b) are diagrams showing the concept of a multivalued dither matrix, and FIGS. 2 (a) and 2 (b) and FIGS. 3 (a) and 3 (a). FIG. 4B is a graph showing a characteristic graph showing an exposure intensity distribution and a potential distribution of an electrostatic latent image when three-value recording is performed, and FIG. 4 is a graph showing a developing property of a multivalued latent image. FIG. 5 is a diagram schematically showing a specific example of an electrophotographic printer to which the toner of the present invention is applied. 1 ... Laser modulation unit, 2 ... Scanner mirror, 4 ...
Photosensitive drum, 5 ... AC static eliminator, 6 ... Charging device, 9 ... Developing device,
11 ... Transfer charger.

Claims (5)

[Claims] 1. A positive electrode characterized by containing a magnetic powder having magnetic particles containing silicic acid or silicate in an amount of 0.05 to 10 weight percent in terms of silicon element, and a positive charge control material. Chargeable magnetic toner. 2. The positively chargeable magnetic toner according to claim 1, wherein the magnetic particles are magnetic iron oxide particles. 3. The positively chargeable magnetic toner according to claim 1 or 2, wherein the magnetic powder has an average particle diameter of 0.1 to 0.6 μm. 4. The positively chargeable magnetic toner contains a binder resin, magnetic powder and a positively chargeable control agent.
4. The positively chargeable magnetic toner according to any one of items 1 to 3. 5. The positive charge control agent according to claim 1, wherein the number average particle diameter of the positive charge control agent is 2/3 or less of the number average particle diameter of the positive charge magnetic toner. Chargeable magnetic toner.