JP2728933B2 - Magnetic developer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic developer for visualizing an electrostatic latent image in an image forming method such as electrophotography and electrostatic recording.

(Background technology)

2. Description of the Related Art In recent years, as image forming apparatuses such as electrophotographic copying machines have become widespread, the uses thereof have been diversified, and requirements for image quality have become strict. 2. Description of the Related Art In copying images such as ordinary documents and books, it is required to reproduce very finely and faithfully without crushing or breaking even fine characters. In particular, when the latent image on the photoreceptor of the image forming apparatus is a line image of 100 μm or less, thin line reproducibility is generally poor, and the line image is not yet sufficiently sharp. Recently, in an image forming apparatus such as an electrophotographic printer using a digital image signal, a latent image is formed by collecting dots of a constant potential, and a solid portion,
The halftone portion and the light portion are expressed by changing the dot density. However, if the toner particles do not adhere exactly to the dots and the toner particles protrude from the dots, the gradation of the toner image corresponding to the dot density ratio of the black portion and the white portion of the digital latent image cannot be obtained. There is a problem. Furthermore, when the resolution is improved by reducing the dot size in order to improve the image quality, the reproducibility of a latent image formed from minute dots becomes more difficult, and the resolution and gradation are poor, and the sharpness is low. Image tends to be lacking.

Although the image quality is good in the early stage, the image quality may deteriorate while copying or printing out. It is considered that this development is caused by the fact that only toner particles which are easily developed are consumed first while copying or printing is continued, and the toner particles having poor developability accumulate and remain in the developing machine.

Heretofore, some developers have been proposed for the purpose of improving image quality. JP-A-51-3244 proposes a non-magnetic toner intended to improve image quality by regulating the particle size distribution. In the toner, 8 to
The toner mainly has a particle diameter of 12 μm, and is relatively coarse. With this particle diameter, it is difficult for the present inventors to closely “glue” the latent image, and the particle diameter of 5 μm or less is 30 μm.
From the characteristic that the particle size distribution is not more than 5% by number when the particle size is 20% or more, the particle size distribution is also broad, which tends to lower the uniformity. In order to form a clear image using such a coarse toner particle and a toner having a broad particle size distribution, it is necessary to fill the gap between the toner particles by thickly overlapping the toner particles. There is also a problem that it is necessary to increase the image density, and the amount of toner consumption required to obtain a predetermined image density increases.

Also, Japanese Patent Application Laid-Open No. 54-72054 proposes a non-magnetic toner having a sharper distribution than the former,
The size of particles having an intermediate weight is as coarse as 8.5 to 11.0 μm, and there is still room for improvement as a high-resolution toner.

In Japanese Patent Application Laid-Open No. 58-1229437, the average particle size is 6 to 10 μm.
Non-magnetic toners having the largest number of particles of 5 to 8 μm have been proposed, but the number of particles of 5 μm or less is as small as 15% by number or less, and an image lacking sharpness tends to be formed.

According to the study of the present inventors, it has been found that toner particles having a size of 5 μm or less clearly reproduce the outline of the latent image and have a main function of dense toner adhesion to the entire latent image. In particular, in the electrostatic latent image on the photoreceptor, due to the concentration of lines of electric force, the contoured edge portion has a higher electric field intensity than the inside, and the sharpness of the image quality is determined by the quality of the toner particles collected in this portion. According to the study of the present inventors, it has been found that the amount of particles of 5 μm or less is effective in solving the problem of sharpness of image quality.

Also, in U.S. Pat.No. 4,299,900, 20-35 μm
A jumping development method using a developer having 10 to 50% by weight of a magnetic toner has been proposed. In other words, the toner particle size suitable for frictionally charging the magnetic toner, uniformly and thinly applying the toner layer on the sleeve, and further improving the environmental resistance of the developer has been devised. However, considering stricter requirements such as reproducibility of fine lines and resolution, it is not sufficient, and further improvements are required.

On the other hand, in recent years, a toner for reversal development has been desired for application to a digital copying machine, and the transfer current has to be weakened in order to prevent a photosensitive memory from being caused by transfer charging, which is a problem peculiar to reversal development. As a result, transferability becomes a problem, and various proposals have been made to reduce the affinity between the photosensitive member and the developer.

It has been proposed to add silicon oil-treated silica fine powder as disclosed in JP-A-49-42354. However, when the silica fine powder is used, although the transferability is improved, there are many aggregates, the aggregates are crushed in the developer, and untreated or insufficiently processed silica fine powder is generated, Decreases the temperature characteristics of the developer. In particular, it has a point to be improved such as lowering of image density under high humidity.

It has also been proposed to add a silica fine powder which has been subjected to a silicon oil treatment after a hydrophobic treatment. Use of this silica fine powder can overcome the above-mentioned problems under high humidity. However, when added to magnetic toner having a volume average particle size of 5 to 8 μm under low humidity and printed out, there is no problem with about 1,000 copies, but when more than 3,000 copies are made, the charge amount becomes too high and the image density becomes too high. It has points to be improved such that it gradually decreases.

As a result of the present inventors' examination of these problems,
Using a toner with a fine particle diameter, after hydrophobizing, adding a silica fine powder that has been treated with silicon oil, and then adding a silica fine powder having a trimethylsiloxyl group and a pH of 7 or more to the system in which the silica fine powder is added. It has been found that the above problems can be overcome.

[Object of the invention]

An object of the present invention is to provide a magnetic developer which solves the above-mentioned problems.

It is a further object of the present invention to provide a magnetic developer having high image density, excellent fine line reproducibility, and excellent gradation.

A further object of the present invention is to provide a developer capable of maintaining a stable high image density without depending on the environment.

Further, an object of the present invention is to provide a developer which can be transferred well even at a weak transfer current without fusing toner particles to the surface of a photoreceptor even when a copy image is continuously taken for a long period of time. It is in.

[Summary of the Invention]

More specifically, the present invention relates to an insulating magnetic toner having at least a binder resin and a magnetic material, and a silica fine powder (A) which has been subjected to a hydrophobic treatment and then to a silicone oil treatment in a magnetic developer containing at least a silica fine powder. And silica fine powder (B) having a trimethylsiloxyl group and having a pH of 7 or more per 0.6 parts by weight per 100 parts by weight of the insulating magnetic toner.
6 parts by weight are mixed, and the magnetic developer has a BET specific surface area of 1.
It has 8~3.5m ² / g, has a triboelectric charging characteristic of -20~-35μc / g, a density 0.4~0.52g / cm ³ loose apparent, the true specific gravity
1.45 to 1.8 g / cm ³ , and the insulating magnetic toner has a volume average particle diameter of 6 to 8 μm and contains 17 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less; 10.0
5 to 50% by number of magnetic toner particles having a particle diameter of 8 μm, and magnetic toner particles having a particle diameter of 12.7 μm or more
The magnetic toner particles having a content of 2.0% by volume or less and a particle size of 5 μm or less [Wherein N represents the number% of magnetic toner particles having a particle size of 5 μm or less, V represents the volume% of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. . Here, N indicates a positive number of 17 to 60. ] It has a particle size distribution satisfying the following.

The magnetic developer of the present invention can faithfully reproduce even a fine line of a latent image formed on a photoreceptor, or even when printout is continued, high image quality can be achieved without depending on the environment. Is maintained, and even when copying is continued for a long period of time, sufficient transfer can be performed even with a weak transfer current without toner fusion to the photoreceptor, and a good copy image can be obtained.

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

That is, one feature of the magnetic developer of the present invention is that 17 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less. Conventionally, 5 μm
The following magnetic toner particles are difficult to control the charge amount, impair the fluidity of the magnetic toner, and actively decrease as a component that scatters the toner and stains the machine, as well as a component that causes image fogging. Was thought to be necessary.

However, studies by the present inventors have revealed that magnetic toner particles having a size of 5 μm or less are essential components for forming high-quality images.

For example, using a magnetic toner having a particle size distribution ranging from 0.5 μm to 30 μm, the surface potential on the photoreceptor is changed, and from a large development potential contrast in which a large number of toner particles are easily developed, to a halftone, and further, a very small amount. A latent image with a changed surface potential on the photoreceptor was developed to a small development potential contrast where only toner particles were developed, and the developed toner particles on the photoreceptor were collected. The toner particle size distribution was measured. It has been found that there are many magnetic toner particles, especially magnetic toner particles of 5 μm or less. In other words, when magnetic toner particles having a particle size of 5 μm or less, which are most suitable for development, are smoothly supplied to the development of the latent image on the photoreceptor, the toner is faithful to the latent image and does not protrude from the latent image, and is truly reproducible And excellent images can be obtained.

In the magnetic toner of the present invention, 6.35 to 10.08
One feature is that particles in the range of μm are 5 to 50% by number. This is related to the need for the presence of magnetic toner particles having a particle size of 5 μm or less, as described above. The magnetic toner particles having a particle size of 5 μm or less strictly cover the latent image and have an ability to faithfully reproduce the latent image. However, in the latent image itself, the electric field strength of the edge portion around the latent image is higher than that of the central portion, so that the toner particles may be thinner inside the latent image than in the edge portion, and the image density may appear to be light. In particular, 5μ
The tendency is strong for magnetic toner particles of m or less. However, the present inventors have found that this problem can be solved and made clearer by containing 5 to 50% by number of toner particles in the range of 6.35 to 10.08 μm.
That is, it is considered that the toner particles having a particle size in the range of 6.35 to 10.08 μm have a moderately controlled charge amount with respect to the magnetic toner particles having a particle size of 5 μm or less.
The toner is supplied to the inner side of the latent image where the electric field intensity is smaller than the edge portion, and a small amount of the toner particles on the edge portion is compensated for, so that a uniform developed image is formed. This provides a sharp image with excellent gradation.

Further, for particles having a particle size of 5 μm or less, N / V = −0.05 N + k between the number% (N) and the volume% (V).
(However, one of the characteristics is that the magnetic toner of the present invention satisfies the relationship of 4.6 ≦ k ≦ 6.7; 17 ≦ N ≦ 80).
FIG. 1 shows this range, and together with other features, the magnetic developer containing the magnetic toner according to the present invention having a particle size distribution that satisfies this range is excellent for a digital latent image formed from excellent minute spots. Excellent developability can be achieved.

The present inventors have studied the state of the particle size distribution of 5 μm or less and have found that there is a state of existence of the fine powder most suitable for achieving the object as shown by the above formula. In other words, for a certain value of N, a large N / V indicates that particles of 5 μm or less are widely included, and a small N / V indicates that the abundance ratio of particles near 5 μm. Is high, indicating that there are few particles with a particle size smaller than that, the value of N / V is in the range of 1.6 to 5.85, and N is
When the ratio is in the range of 17 to 60 and the above relational expression is further satisfied, good fine line reproducibility and high resolution are achieved.

Further, for magnetic toner particles having a particle diameter of 12.7 μm or more, the content is preferably set to 2.0% by volume or less, and as small as possible.

The magnetic developer of the present invention solves the conventional problems, and can withstand recent severe demands for high image quality.

 The configuration of the present invention will be described in more detail.

Magnetic toner particles having a particle size of 5 μm or less have a total particle number of 17 to
The number is preferably 60% by number, preferably 25% to 60% by number, and more preferably 30% to 60% by number. When the number of magnetic toner particles having a particle diameter of 5 μm or less is less than 17% by number, the amount of magnetic toner particles effective for high image quality is small. In particular, as the toner is used by continuing printout, the effective magnetic toner particle component is reduced. Decrease, the balance of the particle size distribution of the magnetic toner as shown in the present invention deteriorates,
Image quality gradually decreases. If it exceeds 60% by number, the magnetic toner particles tend to aggregate with each other,
Since the toner mass is larger than the original particle size, the image quality becomes rough, the resolution is reduced, or the density difference between the edge portion and the inside of the latent image is increased, so that the image tends to be slightly hollow.

Further, particles in the range of 6.35 to 10.08 μm are 5 to 50% by number.
And preferably 8 to 40% by number. 50
If the number is more than the number%, the image quality is deteriorated, and the development is performed more than necessary, that is, the toner is excessively adhered. As a result, the reproducibility of fine lines is reduced and the toner consumption is increased. On the other hand, if it is less than 5% by number, it becomes difficult to obtain a high image density. The number% (N) of the magnetic toner particles having a particle size of 5 μm or less
%) And volume% (V%), there is a relationship of N / V = −0.05N + k, which indicates a positive number in the range of 4.6 ≦ k ≦ 6.7. Preferably, 4.6 ≦ k ≦ 6.2, and more preferably, 4.6 ≦ k ≦ 5.7. As indicated above, 17 ≦ N ≦ 60, preferably 25 ≦ N
≦ 60, more preferably 30 ≦ N ≦ 60.

When K <4.6, the number of magnetic toner particles having a particle diameter smaller than 5.0 μm is small, and the image density, resolution, and sharpness are poor. The appropriate presence of fine magnetic toner particles, which was conventionally considered unnecessary, contributes to the closest packing of the toner in development and contributes to the formation of a uniform image without roughness. In particular, by uniformly filling the fine lines and the contours of the image, the sharpness is further enhanced visually.
That is, when K <6.7, the characteristics are inferior due to the lack of the particle size distribution component.

From another aspect, in production, it is necessary to cut a large amount of fine powder by classification or the like to satisfy the condition of K <4.6, which is disadvantageous in terms of yield and toner cost.
When K> 6.7, the presence of more fine powder than necessary
As printout is repeated, the image density tends to decrease. Such development occurs when excessive fine powdered magnetic toner particles having an unnecessary charge are charged and adhered to the developing sleeve, thereby hindering normal magnetic toner from being carried on the developing sleeve and applying charge. Conceivable.

The particle diameter of the magnetic toner particles having a particle diameter of 12.7 μm or more is preferably 2.0% by volume or less, more preferably 1.0% by volume or less, and further preferably 0.5% by volume or less. If it is more than 2.0% by volume, it will hinder the reproduction of fine lines. Further, the volume average diameter of the magnetic toner is 6 to 8 μm, and this value cannot be considered separately from the above-mentioned respective constituent elements. If the volume average particle diameter is less than 6 μm, there is a problem that the amount of toner applied on the transfer paper is small and the image density is low in digital latent images having a high image area ratio, such as graphic images. This is considered to be due to the same reason as described above for lowering the density inside the edge portion of the latent image. When the volume average particle size exceeds 8 μm, the resolution of fine spots of 100 μm or less is not good, and there are many spots on non-image areas. At the beginning of the printout, if the user keeps using it at best, the image quality tends to deteriorate.

Although the particle size distribution of the toner can be measured by various methods, in the present invention, the measurement was performed using a Coulter counter.

In other words, the Coulter Counter TA is used as a measuring device.
-Use type II (manufactured by Coulter), connect an interface (manufactured by Nikkaki) and a CX-1 personal computer (manufactured by Canon) that output the number distribution and volume distribution, and use primary sodium chloride as the electrolyte. Prepare 1% NaCl aqueous solution. As a measurement method, 0.1 to 5 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes using an ultrasonic disperser, and the Coulter Counter TA II type was used, and a particle size distribution of 2 to 40 μ particles based on the number using a 100 μ aperture as an aperture was used. Measure
Then the values according to the invention were determined.

On the other hand, the silica fine powder (A) subjected to the hydrophobizing treatment and then subjected to the silicon oil treatment and the silica fine powder having a trimethylsiloxyl group and having a pH of 7 or more used in the present invention have an effect of maintaining a high image density in a high humidity environment. Also, even when copying is performed for a long period of time, there is an effect that the toner is prevented from being fused to the surface of the photoreceptor and the image on the photoreceptor is transferred well even with a weak transfer current. Although the detailed reason for the former effect is unknown, it has a trimethylsiloxyl group, and
Silica fine powder with a pH of 7 or more is characterized by low chargeability while maintaining hydrophobicity.This property moderately moderates toner and silica fine powder with high chargeability and satisfies humidity characteristics as a developer. It is thought that it is hurting.

In particular, the magnetic toner having a particle size used in the present invention has a higher charge amount and tends to aggregate more than conventionally known magnetic toners having a volume average particle size of more than 8 μm, and as the particle size decreases, the surface area increases. The addition of a fluidizing agent is essential.

Although the detailed reason for the latter effect is unknown, the silica fine powder (A) is used during the development, transfer, and cleaning steps of the latent image on the photoreceptor performed each time a copy is taken.
The silicone oil contained is appropriately supplied to the surface of the photoreceptor to form a thin coating, reduce the frictional resistance between the surface of the photoreceptor and the cleaning member, and prevent the adhesion between the surface of the photoreceptor and the toner particles. It is thought that the toner particles effectively act on the surface of the photoreceptor so that the toner particles can be easily separated from the surface of the photoreceptor. Further, the fine silica powder (B) having a low charging ability is removed so as to scrape off fine deposits which may be nuclei of toner fusion to the surface of the photoreceptor, and further, it is possible to remove the roller between the toner particles and the surface of the photoreceptor. It has a role as described above, and serves to assist the separation of toner particles from the surface of the photoreceptor.

Also, as the printout speeds up,
The toner tends to increase in charge, and the use of silica treated with silicone oil alone tends to cause problems such as unevenness and a decrease in density, especially at low temperature and low humidity.

The present inventors have found that the charge-up phenomenon under low humidity can be prevented by using a silica fine powder having a trimethylsilyl group at the surface of pH 7 or more in combination.

The true density of the magnetic toner according to the present invention is 1.45 to 1.8 g / cm ³ . Preferably from 1.55~1.75g / cm ^3. Within this range, the magnetic toner having the specific particle size distribution of the present invention can exhibit effects in terms of high image quality and durability stability in the reversal development system in the presence of a magnetic field. When the true density of the magnetic toner is less than 1.45, the weight of the magnetic toner particles themselves is too light, and in reversal development, the fine lines are liable to be crushed, jumped, and deteriorated in resolving power due to fogging and excessive toner particles. Also, the true density of magnetic toner
If it is larger than 1.8, the image density is low, the image lacks sharpness such as breaks in thin lines, and the magnetic force is relatively large, so that the toner ears are likely to be long or branched, and in this case, When a digital latent image is developed, the image quality is disturbed, and the image is likely to be rough.

The true density of the magnetic toner can be measured by any of several methods. In the present application, the following method was adopted as an accurate and simple method when measuring fine powder.

A stainless steel cylinder with an inner diameter of 10 mm and a length of about 5 cm, a disk with an outer diameter of about 10 mm and a height of 5 mm (A) that can be closely inserted into it, and a piston with an outer diameter of about 10 mm and a length of about 8 cm (B)
Prepare The disk (A) is placed at the bottom of the cylinder, then about 1 g of the measurement sample is placed, and the piston (B) is gently pushed. A force of 400 kg / cm ² is applied to this with a hydraulic press, and the product is compressed for 5 minutes and taken out. The weight of the compressed sample is weighed (wg), the diameter (Dcm) and the height (Lcm) of the compressed sample are measured with a micrometer, and the true density is calculated by the following equation.

In order to obtain better developing characteristics, the magnetic toner of the present invention has a residual magnetization σ _{r of 1} to 5 emu / g, preferably 2 to 4.
A 5 emu / g, a saturation magnetization sigma _s is 20~40emu / g, it is preferable that the coercive force H _c satisfies the magnetic properties of 40-100 Erusutetsudo (e). The measurement of the magnetic properties is performed with a measurement magnetic field of 1000 oersted.

When a heating and pressing roller fixing device having a device for applying oil is used as the fixing resin used in the magnetic toner according to the present invention, the following binder resins for toner can be used.

For example, polystyrene, poly-p-chlorostyrene,
Styrenes such as polyvinyltoluene and their substituted homopolymers; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, 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 copolymers such as copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers; polyvinyl chloride, phenolic resins, naturally-modified phenolic resins, and naturally-modified maleic resins 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 heat and pressure roller fixing method in which little oil is applied, so-called offset development in which a part of the toner image on the toner image support member is transferred to the roller, and adhesion of the toner to the toner image support member are important issues. is there. These problems must be taken into account at the same time because toners that fix with less heat energy tend to block or cake during storage or in a developer. The physical properties of the binder resin in the toner are most greatly involved in these phenomena. However, according to the study of the present inventors, when the content of the magnetic substance in the toner is reduced, the toner image supporting member is fixed at the time of fixing. The adhesion of the toner to the toner is improved, but offset tends to occur, and blocking or caking tends to occur. Therefore, in the present invention, when using the heating / pressing roller fixing method in which almost no oil is applied, the selection of the binder resin is more important. Preferred binders include crosslinked styrenic copolymers or crosslinked polyesters.

Examples of the comonomer for the styrene monomer of the styrene copolymer include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, and methacrylic acid. Acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, a monocarboxylic acid having a double bond such as acrylamide or a substituted product thereof; for example, maleic acid, butyl maleate, Dicarboxylic acids having a double bond such as methyl maleate, dimethyl maleate and the like and their substituted products; for example, vinyl chloride, vinyl acetate,
Vinyl esters such as vinyl benzoate; ethylenic olefins such as ethylene, propylene, butylene; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone; vinyl methyl ether, vinyl ethyl ether; Vinyl monomers such as vinyl isobutyl ether and the like; alone or two or more vinyl monomers are used.

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

When a pressure fixing method is used, a binder resin for a pressure fixing toner can be used. For example, polyethylene, polypropylene, polymethylene, polyurethane elastomer, ethylene-ethyl acrylate copolymer, ethylene-vinyl acetate copolymer can be used. Coalescent, ionomer resin, styrene-butadiene copolymer, styrene-isoprene copolymer, linear saturated polyester, paraffin and the like.

In the magnetic toner of the present invention, it is preferable that a charge control agent is blended (internally added) to the toner particles or mixed (externally added) with the toner particles for use. The charge control agent makes it possible to control the optimal charge amount according to the development system. In particular, in the present invention, it is possible to further stabilize the balance between the particle size distribution and the charge, and by using the charge control agent The function separation and the complementarity for higher image quality for each particle size range described above can be further clarified.

As the negative charge controlling agent that can be used in the present invention, for example, a metal complex or a salt of a monoazo dye or a metal complex or a salt of salicylic acid, alkylsalicylic acid, dialkylsalicylic acid or naphthoic acid is used.

The above-mentioned charge control agent (having no action as a binder resin) is preferably used in the form of fine particles. In this case, specifically, the number average particle diameter of the charge control agent is preferably 4 μm or less (more preferably 3 μm or less).

When internally added to the toner, such a charge control agent is used in an amount of 0.1 to 10 parts by weight (more preferably 0.1 to 5 parts by weight) based on 100 parts by weight of the binder resin.
Parts by weight).

As the silica fine particles (A) used in the present invention, both a so-called dry method produced by vapor phase oxidation of a silicon halide and a so-called wet silica produced from water glass or the like and a dry silica called a fumed silica can be used. However, dry silica having few silanol groups on the surface and inside and having no production residue is preferable. In the case of fumed silica, for example, it is also possible to obtain a composite fine powder of silica and another metal oxide by using another metal halide such as aluminum chloride or titanium chloride together with a silicon halide in the production process. Is also included.

In order to treat the silica fine particles (A) with a hydrophobic treatment, a conventionally known hydrophobic treatment method is used, and the silica fine particles (A) are chemically treated with an organosilicon compound or the like which reacts or physically adsorbs the silica fine powder. As a preferred method, the silica fine powder generated by the vapor phase oxidation of the silicon halide is treated with a silane coupling agent or simultaneously with the silane coupling agent and treated with an organosilicon compound. Examples of the silane coupling agent include hexamethyldisilazane and dimethyldichlorosilane.

Finally, the degree of hydrophobicity of the treated silica fine powder was determined as a degree of hydrophobicity measured by a methanol titration test, 30
It is preferred that the developer containing such fine silica powder exhibits a uniform and triboelectric chargeability in a sharp and uniform manner when it is hydrophobized so as to show a value within the range of -80.

Here, the methanol titration test is an experimental test for confirming the degree of hydrophobicity of silica fine powder having a hydrophobicized surface.

The "methanol titration test" defined herein for evaluating the degree of hydrophobicity of the treated fine silica powder is performed as follows. 0.2 g of the test silica fine powder is added to 50 ml of water in a 250 ml Erlenmeyer flask. Methanol is titrated from the vial until all of the 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 the suspension of the entire amount of the fine silica powder in the liquid, and the degree of hydrophobicity is expressed as the percentage of methanol in the liquid mixture of methanol and water at the end point.

As a method of further treating the silica fine particles (A) with silicon oil, a conventionally known technique can be used. For example, the silica fine powder and the silicon oil are mixed using a mixer, the silicon oil is sprayed into the silica fine powder using a spray, or the silicon oil is dissolved in the solvent and then mixed with the silica fine powder. However, the present invention is not limited to these. The silicone oil used is of the general formula R: an alkyl group having 1 to 3 carbon atoms R ': a silicon oil-modified group such as alkyl, halogen-modified alkyl, phenyl, and modified phenyl R ″: an alkyl group or an alkoxy group having 1 to 3 carbon atoms, for example, dimethyl Examples include silicone oil, alkyl-modified silicone oil, α-methylstyrene-modified silicone oil, chlorophenyl silicone oil, and fluorine-modified silicone oil.

The silicone oil preferably has a viscosity at 25 ° C. of 50 to 1000 centistokes. If the temperature is less than 50 centistokes, heat is applied, and a portion of the liquid evaporates, deteriorating the charging characteristics. On the other hand, at 1000 centistokes or more, handling becomes difficult due to the processing operation.

The silica fine particles (B) used in the present invention have a trimethylsiloxyl group. The pH is preferably 7 or more, preferably 7.5 or more. For example, Taranox 500 manufactured by Talco
And is preferably used.

Here, the pH is measured by suspending 4 parts by weight of the sample in 96 parts by weight of a mixed solvent of water and acetone (1: 1) and measuring the suspension with a pH meter.

The above silica fine particles (A) and (B) have a particle size of 0.001 μm.
m to 2 μm, preferably 0.005 μm
m to 0.2 μm is preferred.

The content in the developer is 0.6 to 1.6 parts by weight, preferably 0.8 to 1.4 parts by weight in terms of the total amount of the silica fine particles (A) and (B) based on 100 parts by weight of the toner. The ratio of (A) to (B) is (A) :( B) = 95: 5 to 30:70, preferably 90; 10 to 40; 60.

The magnetic developer of the present invention having at least silica fine powder and insulating magnetic toner has a BET specific surface area of 1.8 to 3.5 m ² / g by a nitrogen gas adsorption method, and has a triboelectric charging property of −20 to −35 μc / g. It has an apparent density of 0.4 to 0.52 g / cm ³ and a true specific gravity of 1.45 to 1.8 g / cm ³ .

If the triboelectric charge is less than −20 μc / g, a sufficient charge for development cannot be obtained on the developer carrying member, and the image density is low from the beginning. If it is more than −35 μc / g, the charge amount of the developer near the carrier on the developer carrier is increased by repeating the image formation, so that a so-called charge trap that inhibits the proper charging of the developer on the carrier. This phenomenon causes the image density to gradually decrease. This development is likely to occur when developing a digital latent image, which is the development of a dot latent image, and is remarkable in a low potential contrast reversal development system using an OPC photosensitive member.

When the BET specific surface area of the developer of the present invention by the nitrogen gas adsorption method is less than 1.8 m ² / g, it takes time to obtain a sufficient amount of charge for development on the developer carrier, and the initial concentration is thin and fog is reduced. There are many images. On the other hand, if it is larger than 3.5 m ² / g, the reflection power with the sleeve is increased, and the development rate is reduced, and as a result, the image density is reduced.

In the measurement of the BET specific surface area in the present invention, QVANTACHROM
It was determined by the BET one-point method using a specific surface area meter Autosorb 1 manufactured by Company E.

Further, the true specific gravity of the developer of the present invention is 1.45~1.8g / cm ^3, prone to fog also line width is the resolution deteriorates thicker in method of developing by applying an AC bias in the magnetic field is less than 1.45 .

If it is larger than 1.8, line fading is likely to occur, and the image density also decreases. The loose apparent density of the developer of the present invention is
0.4 to 0.52 (preferably 0.45 to 0.5), which is characteristic in that the loose apparent density is smaller than the true specific gravity. The porosity calculated from the true specific gravity and the loose apparent density is 62
Preferably it is ~ 75%.

 The porosity (εa) is calculated by the following equation.

The solid apparent density is preferably in the range of 0.8 to 1.0, and the porosity (εp) at this time is preferably 40 to 50%.

If εa is less than 62%, the toner is not sufficiently loosened by stirring inside the developing device, and if it is more than 75%, toner scattering and toner leakage are likely to occur.

If εp is less than 40%, the developer is liable to be jammed inside the developing device, and the developer is not supplied to the developer carrier smoothly, so that white drop is likely to occur. On the other hand, if it is more than 50%, the same amount of developer is included, so that a larger developing device capacity is required, which hinders downsizing of the printer.

In the present invention, the loose apparent density and the solid apparent density (pack bulk density) are measured using a powder tester manufactured by Hosokawa Micron Co., Ltd. and a container attached to the powder tester, according to the procedure described in the instruction manual for the powder tester. Means the value measured according to

The tribo value of the magnetic developer is measured by the following method. In other words, it has a main particle size of 1 g of a magnetic developer and 200 to 300 meshes that are left overnight in an environment of 23.5 ° C. and 60% RH.
9 g of non-resin-coated carrier iron powder (for example, EFV200 / 300 manufactured by Nippon Iron Powder Co., Ltd.) is precisely weighed in the above environment, and sufficiently weighed in a polyethylene wide-mouth bottle having a volume of about 50 c.c. Hold it in your hand and shake it up and down about 50 times for about 20 seconds)
Mix.

Next, as shown in Fig. 3, a 400 mesh screen 3
About 0.5 g of the mixture is placed in a metal measuring container 32 having a metal cover 3 and a metal lid 34 is provided. At this time, the weight of the entire measurement container 32 is weighed and set as W ₁ (g). Next, in the suction device 31 (at least a portion in contact with the measuring container 32 is an insulator), the pressure of the vacuum gauge 35 is adjusted to 250 mmH by adjusting the air volume control valve 36 by suctioning from the suction port 37.
g. In this state, suction is sufficiently performed to remove the magnetic developer by suction. At this time, the potential of the electrometer 39 is set to V (volt). Here, 38 is a capacitor whose capacity is C (μF).
And Also. Weigh the entire measuring container after aspiration W
₂ (g). The triboelectric charge of this magnetic developer (μc /
g) is calculated as follows.

The magnetic toner of the present invention may optionally contain additives. Dyes conventionally known as colorants,
Pigments can be used, and usually 0.5 to 20 parts by weight per 100 parts by weight of the binder resin may be used. As other additives, for example, a lubricant such as zinc stearate, or an abrasive such as cerium oxide or silicon carbide or a fluidity imparting agent such as colloidal silica or aluminum oxide;
Anti-caking agent, or for example carbon black,
There is a conductivity imparting agent such as tin oxide.

In addition, wax-like substances such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, microcrystalline wax, carnauba wax, sasol wax, and paraffin wax are used for the purpose of improving the releasability at the time of hot roll fixing.
Addition of about 5 wt% to the magnetic toner is also a preferred embodiment of the present invention.

Further, the magnetic toner of the present invention may also serve as a colorant, but contains a magnetic material. Examples of the magnetic material contained in the magnetic toner of the present invention include iron oxides such as magnetite, γ-iron oxide, ferrite, and iron-rich ferrite;
Metals such as iron, cobalt, nickel or these metals and aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, kangan, selenium, titanium, tungsten, vanadium Alloys with various metals and mixtures thereof.

To prepare the toner for developing an electrostatic image according to the present invention, a magnetic powder and a vinyl-based or non-vinyl-based thermoplastic resin, a pigment or a dye as a colorant as needed, a charge control agent, and other additives Are mixed sufficiently by a mixer such as a ball mill and then melted, kneaded and kneaded using a hot kneader such as a heating roll, a kneader or an extruder to make the resins compatible with each other. Is dispersed or dissolved, and after cooling and solidifying, pulverization and strict classification are performed to obtain the magnetic toner according to the present invention.

An image forming method to which the magnetic developer of the present invention can be preferably applied will be described with reference to FIGS. The surface of the photoreceptor is negatively charged by the primary charger 2, a digital latent image is formed by image scanning by exposure 5 with a laser beam, and a developing sleeve 4 including a magnetic blade 11 and a magnet 14 is provided. The latent image is developed with a one-component magnetic developer 10 of a container 9. In the developing section, between the conductive substrate 16 of the photosensitive drum 1 and the developing sleeve 4, an alternating bias, a pulse bias and / or a DC bias are applied by the bias applying means 12. When the transfer paper P is conveyed and reaches the transfer section, the transfer charger 3 charges the transfer paper P with a positive polarity from the rear surface (the surface opposite to the photosensitive drum side), thereby loading the negatively charged toner image on the surface of the photosensitive drum. Is electrostatically transferred onto the transfer paper P. The transfer paper P separated from the photosensitive drum 1 is fixed on the transfer paper P by the heating and pressing roller fixing device 7.

The one-component developer remaining on the photosensitive drum after the transfer process is removed by a cleaning device 8 having a cleaning blade. After the cleaning, the photosensitive drum 1 is neutralized by the erase exposure 6, and the process starting from the charging process by the primary charger 2 is repeated again.

The electrostatic image holding member (photosensitive drum) has a photosensitive layer 15 and a conductive substrate 16 and moves in the direction of an arrow. Rotate to go in the same direction as the surface. Inside the non-magnetic cylinder 4, a multi-pole permanent magnet (magnet roll) 14 as a magnetic field generating means is arranged so as not to rotate. The one-component insulative magnetic developer 10 in the developing device 9 is applied on a non-magnetic cylindrical surface, and triboelectric charges are given to the toner particles by friction between the surface of the sleeve 4 and the toner particles. Further, the thickness of the developer layer is reduced (30 μm to 30 μm) by disposing an iron magnetic doctor blade 11 close to the cylindrical surface (interval: 50 μm to 500 μm) and opposed to one magnetic pole position of the multipole permanent magnet. The developer layer is formed so as to be non-contact with the gap between the electrostatic holding member 1 and the developing carrier 4 in the developing section so as to be non-contact. By adjusting the rotation speed of the cylinder 4, the surface speed of the sleeve is made substantially equal to or close to the speed of the electrostatic image holding surface. The opposed magnetic poles may be formed by using permanent magnets instead of iron as the magnetic doctor blades 11. Biasing means for applying an AC bias or a pulse bias between the developer carrier 4 and the electrostatic image holding surface in the developing section;
12 may be applied. This AC bias is f 200
Up to 4,000 Hz, V _PP should be 500 to 3,000 V.

At the time of transfer of the toner particles in the developing portion, the toner particles are transferred to the electrostatic image side by an electrostatic force of the electrostatic image holding surface and an action of an AC bias or a pulse bias.

Instead of the doctor blade 11, an elastic blade made of an elastic material such as silicone rubber may be used to regulate the thickness of the developer layer by pressing to apply the developer on the developer carrier.

Hereinafter, the present invention will be described in more detail based on Production Examples and Examples.

Production Example 1 After the above materials were mixed well in a blender, they were kneaded with a biaxial kneading extruder set at 150 ° C. The obtained kneaded material was cooled, coarsely pulverized by a cutter mill, and then finely pulverized by using a fine pulverizer using a jet stream, and the obtained finely pulverized powder was classified by a fixed wall type air classifier to classify. A powder was produced. Further, the obtained classified powder is strictly classified and removed simultaneously by a multi-division classifier utilizing a Coanda effect (an elbow jet classifier manufactured by Nittetsu Mining Co., Ltd.) to simultaneously remove the fine powder and coarse powder.
3 μm negatively-chargeable magnetic toner No. 1 was obtained.

Table 1 shows data obtained by measuring the obtained negatively chargeable insulating No. 1 using a Coulter Counter TA II type having a 100 μ aperture as described above.

The multi-segment classifier used in the present embodiment and the classification process by the classifier will be described with reference to FIGS. 5 and 6. FIG. 5 and 6, the multi-segment classifier 40 has a side wall having a shape indicated by 52 and 54, a lower wall has a shape indicated by 55, and a side wall 53 and a lower wall 55 respectively. Knife edge type classification edges 47, 48 are provided, and the classification zones are divided into three by these classification edges 47, 48. A raw material supply nozzle 46 that opens to the classification chamber is provided below the side wall 52, and a Coanda block 56 that is bent downward in the direction of extension of the tangent to the bottom of the nozzle to draw a long elliptical arc is provided. Classification room upper wall
57 is a knife edge type inlet edge to the lower part of the classification chamber.
In addition to the above, the air intake pipe that opens to the classification chamber
44, 45 are provided. The inlet pipes 44, 45 are provided with first and second gas introduction adjusting means 50, 51 such as dampers, and static pressure gauges 58, 59, respectively. Discharge pipes 41, 42, and 43 having discharge ports that open into the room are provided on the lower surface of the classifying chamber so as to correspond to the respective dividing areas. The classified powder is introduced under reduced pressure from the supply nozzle 46 into the classification region, and moves along the curved line 60 by the action of the Coanda effect of the Coanda block 56 due to the Coanda effect and the action of the high-speed air flowing in at that time. The powder was classified into a black fine powder 42 and an ultra fine powder 43 having a predetermined volume average particle size and a particle size distribution.

Production Example 2 Using the above materials and the same method as in Production Example 1, a negatively chargeable insulating magnetic toner No. 2 having a volume average particle diameter of 7.8 μm (particle size distribution is shown in Table 1) was obtained.

Production Example 3 The above substance was used in the same manner as in Example 1 to obtain a negatively chargeable insulating magnetic toner No. 3 having a volume average particle diameter of 11.9 μm (particle size distribution is shown in Table 1).

Examples 1 to 5 and Comparative Examples 1 to 3 A magnetic toner was prepared by using the insulating magnetic toners No. 1, No. 2, and No. 3 and the silica fine powders (A) and (B) shown in Table 2. The silica fine powders (A) and (B) were mixed with a Hensiel mixer to obtain a magnetic developer shown in Table 2.

In Examples 1 to 3, silica fine powder (B) was used.
As a silica fine powder having a trimethylsiloxyl group, Taranox 500 manufactured by Talco Co., Ltd. (used in a lot of pH 8.0) was used. In Example 4, a taranox of pH 8 lot was used as a silica fine powder (B). 500 was heated to pH 7.5, and in Example 5, as a silica fine powder (B), Taranox 5 of a pH 9.0 lot was used.
00 was used. Further, in Comparative Example 1, Taranox 500 of a pH 9.0 lot was used as the silica fine powder (B), and in Comparative Example 2, the pH was set as the silica fine powder (B).
In the comparative example 3, untreated silica fine powder of pH 4.0 (AEROSIL130 manufactured by Nippon Aerosil Co., Ltd.) was used as the silica fine powder (B) using 8.0 lot of Taranox 500.

Next, for each of these adjusted developers, primary charge of -700 V is performed on the surface of the laminated organic photoconductor (OPC) photosensitive drum using a modified machine of a Canon LBP-8AJ1 laser beam printer. A digital latent image is formed by setting the electric potential at the laser light exposure portion to -100 V, and a DC bias of -500 V and an AC bias (1800 Hz, peak-to-peak 1600 V) are applied, and the developing sleeve (made of stainless steel) at the developing portion is exposed to light. 300μ closest gap to drum
m and the thickness of the developer layer on the sleeve in the developing section in a state where no bias was applied was set to about 100 μm, and development was performed.

The diameter of the laser spot at the time of latent image formation was 50 μm.
And

 The results are shown in Table 3.

Evaluation method: (a) Fog: The difference between the whiteness of a white background portion of the transfer paper measured by a reflectometer (manufactured by Tokyo Denshoku Co., Ltd.) and the whiteness after printing a solid white was defined as fog.

○: 0 to less than 2% (good) △: 2 to 3% (practical) ×: more than 3% (poor) (b) Transfer: Develops “surprise” characters of about 3 mm in length and width and plain paper (128g /
m ² ), the image was fixed, and the fixed image was observed with a magnifying glass.

：: There is no missing part in the image forming the character “surprise”.

Δ: The image constituting the character “surprise” has some missing parts.

×: There are many missing parts in the image constituting the character “surprise”.

(C) Fusion of toner on photoreceptor: Observation of the occurrence of fusion of toner on the surface of the photoreceptor, and visual observation of the degree of influence on the printout image.
It was rated on a scale.

 ：: No fusion of toner occurred on the surface of the photoconductor.

Δ: toner fusion was observed on the surface of the photoreceptor, but there was little effect on the printout image.

×: Many toner fusions were observed on the surface of the photoreceptor, and image defects occurred in the printout image.

(D) Reproducibility of 100 μm fine line: A thin line of about 100 μm was printed, the average line width of 100 lines was determined, and the evaluation was made based on the fluctuation width in which 90% or more of the line width was reduced.

○: Within ± 6% △: Within ± 12% ×: Over ± 12%

[Brief description of the drawings]

FIG. 1 is a view showing the range of the content ratio of particles of 5 μm or less in the magnetic toner according to the present invention. FIG. 2 is a schematic view of a device for measuring a charge amount of a developer according to the present invention. FIG. 3 is a schematic explanatory view of an image forming apparatus to which the magnetic developer of the present invention can be preferably applied, and FIG. 4 is an enlarged view of a developing section of the apparatus shown in FIG. 5 and 6 are schematic illustrations of a multi-segment classifier used for classifying magnetic toner in the embodiment.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeshi Takiguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Naoto Kitamori 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside the corporation

Claims (1)

(57) [Claims] 1. A magnetic developer containing at least an insulating magnetic toner having at least a binder resin and a magnetic substance, and a silica fine powder, which has been subjected to a hydrophobic treatment and then a silicone oil treatment, and a silica fine powder (A). It has a trimethylsiloxyl group and has a pH of 7
The above-mentioned silica fine powder (B) is used as an insulating magnetic toner 100
Parts by weight per 0.6 to 1.6 are mixed parts, the magnetic developer has a BET specific surface area ^{1.8~3.5m 2 / g, -20~-35μc} / g
With a triboelectric charging characteristic of 0.4 to 0.52 g / c
m ³ , a true specific gravity of 1.45 to 1.8 g / cm ³ , and the insulating magnetic toner has a volume average particle size of 6 to 8 μm and a
magnetic toner particles having a particle size of 12.7 μm or more, containing 17 to 60% by number of magnetic toner particles having a particle size of 1 m or less and 5 to 50% by number of magnetic toner particles having a particle size of 6.35 to 10.08 μm. Particles are contained in 2.0% by volume or less, and 5 μm
The following magnetic toner particle group has the following formula [Wherein N represents the number% of magnetic toner particles having a particle size of 5 μm or less, V represents the volume% of magnetic toner particles having a particle size of 5 μm or less, and k represents a positive number of 4.6 to 6.7. . Here, N indicates a positive number of 17 to 60. ] A magnetic developer characterized by having a particle size distribution satisfying the following.