JPH07109522B2 - Method of developing electrostatic latent image - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developing method for developing an electrostatic latent image formed in an electrophotographic method, an electrostatic printing method, an electrostatic recording method, or the like, In particular, the present invention relates to a method for developing a one-component toner that is preferably used for heat roller fixing.

[Background of technology]

In the field of image forming technology, electrophotography,
A method such as an electrostatic recording method or an electrostatic printing method is known. For example, as an electrophotographic method, US Pat.
A number of methods are described in Japanese Patent Publication Nos. 42-23910 and 43-24748. In electrophotography, a photoconductor made of a photoconductive substance is generally used, an electrostatic latent image corresponding to the original is formed on the photoconductor by various means, and the latent image is developed with toner to form a visible image. It is formed.

Generally, the method of developing such an electrostatic latent image is roughly classified into a wet developing method and a dry developing method. The wet development method is a method of developing using a liquid developer formed by dispersing various pigments and dyes as fine particles in an insulating organic liquid, and the dry development method is a method of developing with a natural or synthetic resin such as carbon black. In this method, a toner containing a colorant dispersed therein is developed using a so-called fine powder powder. This dry development method includes a method of using a one-component type developer containing only toner as a main component and a so-called two-component type developing method of using a mixture of toner and a carrier such as iron powder or glass beads as a developer. is there. The two-component developing method includes a magnetic brush method, a cascade method, etc., and the one-component developing method includes a fur brush method, a magnetic brush method, a powder cloud method, a jumping method, and a magnet dry method using a conductive toner. Etc.

In a developing method using a two-component developer including a toner and a carrier, usually only the toner is consumed, so that the toner concentration in the developer is likely to change, and therefore a control mechanism for appropriately replenishing the toner is required. However, there are various inconveniences from the viewpoint of management of the developer, such as the fact that the toner and the carrier are easily scattered and it is necessary to prevent this.

In order to avoid such problems, there has been proposed a one-component developer which does not require a carrier and is composed only of toner.
The toner of the one-component developer is composed of resin particles in which an additive such as a magnetic material or a colorant is dispersed and contained.
Generally, they are roughly classified into so-called conductive toners having a relatively low resistance and so-called insulating toners having a relatively high resistance due to the difference in developing means.

However, in the former image forming process using a conductive toner, when an electrostatic transfer unit such as a corona transfer device is used to transfer a toner image to a fixing support, disturbance of lines of electric force is likely to occur. Therefore, it is difficult to faithfully transfer the toner image, and as a result, a good image cannot be obtained.

On the other hand, in the latter contact developing methods such as the magnetic brush method and the fur brush method using the insulating toner, the toner easily adheres even to non-images, and so-called fogging is likely to occur. As a developing method for removing such fog, a powder cloud method or a jumping method has been proposed in which the surface of the photosensitive member and the developer are kept in non-contact with each other to fly the toner and develop the toner.

However, in the powder cloud method and the jumping method, although it is possible to improve some fog and the like by using the conventional toner, the toner is agitated in the developing device, the toner is rubbed with the agitating member, and the inner wall of the developing device in many uses. Part of it is scraped off to become fine particles and adheres to the surface of the photoconductor, causing fogging, or so-called filming that adheres to the surface of the photoconductor, adhesion to the cleaning blade, and poor cleaning such as scratching through the cleaning blade. However, a clear image cannot be obtained.

On the other hand, recently, (a) suppressing overheat deterioration of the copying machine, (b) preventing heat deterioration of the photoconductor,
(C) Shorten the warm-up time required to raise the temperature of the heat roller to a temperature at which it can be fixed after the fixing device is activated, and (d) lower the temperature of the heat roller by absorbing heat to the transfer paper. To reduce the power consumption of the fixing heater and reduce the temperature of the heat roller to meet the requirements such as making the size smaller to enable continuous copying over a number of times and (e) increasing the thermal safety. There is a strong demand for enabling the fixing process in a lowered state. Therefore, it is necessary for the toner to be well fixed at a low temperature.

Moreover, in the toner, it can exist stably as a powder without agglomeration under the use or storage environment conditions,
That is, it is necessary to have excellent blocking resistance,
Further, in the heat roller fixing method which is preferable as the fixing method, an offset phenomenon, that is, a part of the toner forming the image at the time of transfer is transferred to the surface of the heat roller, and this is retransferred to the transfer paper which is sent next to form an image. Since the phenomenon of fouling is likely to occur, it is necessary to provide the toner with the performance of preventing the occurrence of the offset phenomenon, that is, the offset resistance.

For example, there is a proposal that the resin used for improving the offset resistance is composed of a low molecular weight polymer component and a high molecular weight polymer component (JP-A-56-158340, JP-A-56-16144 and JP-A-58-158340). No. 202455). However, when a high molecular weight polymer component is introduced into the toner, the offset generation temperature becomes high, which is convenient for the offset resistance, but the fixable temperature becomes high as well, which causes a disadvantage in fixing at a lower temperature. Since such a toner has a brittle low-molecular weight polymer component, a part of the toner component is released due to stirring in the developing device or collision of toner particles to generate fine powder, which causes fogging. Fogging occurs even in the non-contact development method. Further, under high temperature and high humidity conditions, these fine particles and the like film on the surface of the photoconductor and the like, and a clear image cannot be obtained, resulting in poor durability.

Further, for example, JP-A-57-178250, 61-110155, and 61-110156 in the resin obtained by reacting a polymer having a carboxy group and a metal compound, offset resistance, Although there have been attempts to widen the blocking resistance and the allowable fixing temperature range, the one-component developer disclosed in the above publication or the two-component developer using the iron powder carrier is inferior in fixability at low temperature and under high temperature and high humidity conditions. , The triboelectrification is unstable, and the toughness of the toner is lacking, so it is easy to film on the sleeve surface or the photoreceptor surface, and cleaning failure occurs due to fusion to the cleaning blade, resulting in continuous goodness. Image is not obtained and durability deteriorates.

[Object of the Invention]

It is an object of the present invention to provide a developing method which does not cause fogging even after being used many times and does not cause filming on the surface of a photoreceptor or a cleaning member, and can obtain a clear image with good durability. Especially.

Another object of the present invention is to provide a developing method which has good heat roller fixing properties at low temperatures and good offset resistance and blocking resistance.

Another object of the present invention is to provide a developing method having stable triboelectricity and excellent moisture resistance and durability even under high temperature and high humidity environmental conditions.

Another object of the present invention is to provide a developing method having good durability without filming on the surface of the photosensitive member, the surface of the sleeve, the cleaning member and the like even under high temperature and high humidity conditions.

[Structure of Invention]

The above-mentioned object of the present invention is a method for developing an electrostatic charge image, wherein an oscillating electric field is generated in a developing area, and a latent image formed on an image carrier is developed with a one-component magnetic toner on a developer carrying body. The main component resin of the component magnetic toner has a molecular weight of at least two groups of a low molecular weight polymer component and a high molecular weight polymer component, and the molecular weight distribution is the above-mentioned low molecular weight weight in the molecular weight distribution curve by gel permeation chromatography. The maximum value of the united component is 1 × 10 ³ to 2 × 10 ⁴ , the maximum value of the high molecular weight polymer component is 1 × 10 ⁵ to 2 × 10 ⁶ , and the main component resin is ), (B) and (c) is a polyvalent metal salt of the polymer, which is achieved by a method for developing an electrostatic latent image.

(A) Styrene-based monomer (b) Acrylic acid ester-based monomer or methacrylic acid ester-based monomer (c) Monomer represented by the following general formula (A): General formula (A) (In the formula, R ₁ represents a hydrogen atom or a methyl group, L represents a divalent linking group having an ester bond and having 3 or more carbon atoms, and may have a substituent.) The present invention is described in detail below. To do.

In the present invention, an electrostatic charge latent image (hereinafter abbreviated as latent image)
A developer carrying carrier is arranged to face the latent image carrier carrying the developer via a constant space for development, that is, a developing space, and, for example, a magnet for holding a developer is arranged in the developer carrying carrier. Due to the magnetic force of this magnet, a developer layer, which will be described in detail later, is formed of brush-like brushes on the surface of the developer transport carrier, which will be described later, and this developer layer does not contact the latent image carrier. In such a state that the height of the brush of the developer is smaller than the shortest distance between the latent image carrier and the developer carrier in the developing space, the developing space is supplied with an oscillating electric field. To oscillate and disperse the toner particles forming the developer ears by this oscillating electric field to reciprocate between the latent image carrier and the developer carrier.
As a result, the toner particles are made to adhere to the latent image carried on the latent image carrier, and development is carried out to form a toner image.

Then, the toner image is transferred onto a transfer material such as paper, and the transferred image is fixed in a fixing device by, for example, a contact heating fixing method using a heating roller, thereby forming a visible image.

In the developing method including the formation of a toner image by such an oscillating electric field, transfer, and contact heat fixing, the resin as the main component of the toner forms a ionic bond between the carboxy group and the metal atom in the polymer component to form a covalent bond. It is preferable that it has a crosslinked structure with a much looser bond, is easily melted at a low temperature, and has a high melt elastic modulus due to the crosslinked structure at a high temperature. That is, the offset resistance is not deteriorated, and at room temperature conditions such as in the developing device, the toner has a toughness due to the cross-linking structure, so that the wall of the developing device and the collision of the toners with each other or the excess on the sleeve surface are given. Even when rubbing, a part of the toner component is not pulverized and released, so that filming on the surface of the photosensitive member, the surface of the sleeve or the like due to the released toner powder can be suppressed. Further, it has a stable charging property even when it is used for a long period of time, and as a result, a stable and clear image is obtained and the durability is excellent.

However, when the above toner is used under high temperature and high humidity conditions, it cannot be applied to any developing method, and in the contact developing method in which a magnetic brush is formed by an iron powder carrier and the surface of the photoreceptor is rubbed against temperature. ,
It has a drawback that the toner is filmed on the surface of the photoconductor.

The toner according to the present invention exerts the best performance by being applied to the non-contact developing method, and has the drawbacks such as fogging in the non-contact developing method and the fear of frictional electrification under high temperature and high humidity conditions. It solves all the defects of qualitativeness and durability.

The resin contained in the toner applied to the developing method of the present invention is a polyvalent metal salt of a carboxy group present in the polymer component as described above.

The resin contained in the toner has a molecular weight distribution divided into at least two groups of at least a low molecular weight polymer component and a high molecular weight polymer component, and has a low molecular weight in a molecular weight distribution curve measured by gel permeation chromatography (GPC). The maximum value of the polymer component is 1 × 10 ³ to 2 × 10 ⁴ ,
The high molecular weight polymer component has at least two local maxima between 1 × 10 ^{5 and} 2 × 10 ⁶ .

By designing in this way, fixing can be performed at a lower temperature, and since the elastic modulus at the time of melting can be increased, the offset resistance can be further improved, and at the same time, blocking resistance is also good. Can be Further, the resin can be made tougher by the ionic bond and the high molecular weight polymer component, and the generation of fine particles due to the collision with the sleeve or the photoconductor can be suppressed to prevent the sleeve or the photoconductor surface from being contaminated.

When introducing the carboxy group for reacting with the polyvalent metal compound to form an ionic bond, it is sufficient that at least the carboxy group is introduced into the low molecular weight polymer component. Since the fine particles generated from the toner component due to the collision with the sleeve or the surface of the photoconductor are mainly due to the relatively fragile component having a low molecular weight, such a low molecular weight component is crosslinked by at least a metal ion bond to obtain a toughness. By doing so, generation of fine powder, which is a factor of filming, can be suppressed.

As the monomer for obtaining the polymer of the toner main component resin, at least one selected from styrene-based monomers, ester-based monomers such as acrylic acid and methacrylic acid is used as an essential component. It is united. Further, in order to obtain a polymer having a carboxy group, a monomer selected from acrylic acid (including methacrylic acid and the like) and its derivative may be copolymerized in addition to the above-mentioned monomer. As the monomer having a preferred carboxy group, an acrylic acid ester having a hydroxyl group,
A half-ester compound having a structure obtained by an esterification reaction of a methacrylic acid ester or its derivative with a dicarboxylic acid compound.

When a carboxy group is introduced at a position near the end of the main chain as described above, the steric hindrance of the chemical structure is reduced and the reaction with the polyvalent metal compound proceeds efficiently to suppress the residue of the hydrophilic carboxy group. It is possible to generate an effective ionic bond for achieving the object of the present invention, and to have a good crosslinked structure and hydrophobicity.

Examples of the styrene-based monomer include styrene and o-
Methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, 2,3
-Dimethylstyrene, 2,4-dimethylstyrene, pn
-Butylstyrene, p-tert-butylstyrene, pn
-Hexyl styrene, pn-octyl styrene, p-
n-nonylstyrene, pn-decylstyrene, pn
-Dodecylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene and the like can be mentioned. Of these, styrene is particularly preferable.

The toner resin must have appropriate pulverizability during toner production, and the content of the styrene component in the copolymer must be
If the amount is 30% by weight or less, the pulverizability tends to decrease, so the content is usually 30% by weight or more, preferably 40% by weight or more, and the upper limit is generally preferably 95% by weight.

Examples of the acrylic acid ester and methacrylic acid ester include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, lauryl acrylate, acrylic acid. Acrylic esters such as 2-ethylhexyl, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, and methyl α-chloroacrylate; methyl methacrylate,
Ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylamino methacrylate. Examples thereof include methacrylic acid esters such as ethyl and diethylaminoethyl methacrylate.

Examples of the carboxy group-containing compound forming the half-ester compound include malonic acid, succinic acid, and aliphatic dicarboxylic acid compounds such as glutaric acid or aromatic dicarboxylic acid compounds such as phthalic acid, and acrylic acid having a hydroxyl group or A half-ester compound can be obtained by an esterification reaction with a derivative of methacrylic acid.

The dicarboxylic acid compound may have a hydrogen atom substituted with a halogen group element, a lower alkyl group, an alkoxy group, or the like, or may be an acid anhydride.

The hydroxyl group-containing acrylic acid or methacrylic acid derivative may be acrylic acid or methacrylic acid to which 1 mol or 2 mol or more of alkylene oxide such as ethylene oxide or propylene oxide is added, or acrylic acid or methacrylic acid. It may be a hydroxyalkyl ester obtained by esterifying a dihydric alcohol such as propylene glycol.

The preferable half-ester compound can be represented by the following general formula (A).

In the general formula (A), L represents a divalent bonding group having an ester bond in the molecular chain and having 3 or more carbon atoms, and may have a substituent. R ₁ represents a hydrogen atom or a methyl group.

More preferable compounds can be represented by the following formulas (1) to (4).

In the formula, R ₂ and R ₃ represent a hydrogen atom or a methyl group, m represents 1 to 14 and n represents 0 to 8.

In the formula, R ₄ and R ₅ are H or CH ₃ , and h is an integer of 1 to 14,
X represents a hydrogen atom, a halogen group element, a lower alkyl group or an alkoxy group.

In the formula, R ₆ is H or CH ₃ , j is an integer of 3 to 6, and k is an integer of 0 to 8.

In the formula, R ₇ is H or CH ₃ , l is an integer of 3 to 6, Y is H, a halogen group element, a lower alkyl group or an alkoxy group.

Among the half-ester compounds represented by the formulas (1) to (4), the compound represented by the formula (1) is preferable.

Examples of the half-ester compound represented by the formula (1) include succinic acid mono (meth) acryloyloxyethyl ester, succinic acid mono (meth) acryloyloxypropyl ester, glutaric acid mono (meth) acryloyloxyethyl ester, and phthalic acid. Examples thereof include mono (meth) acryloyloxyethyl ester and phthalic acid mono (meth) acryloyloxypropyl ester.

The styrene-based monomer, acrylic acid ester-based monomer,
A polymer obtained from a methacrylic acid ester-based monomer and a half-ester compound obtained by an esterification reaction of an acrylic acid or a methacrylic acid-based derivative having a hydroxyl group and a dicarboxylic acid compound has a content ratio of the monomer unit. The styrene-based monomer is 30 to 95% by weight, preferably 40 to 95% by weight, and the acrylate or methacrylic acid ester monomer is 70 to 5% by weight, preferably 5 to Desirably, it is 50% by weight, and the half-ester compound is 0.5 to 30% by weight, preferably 1 to 20% by weight.

When the content of the acrylic acid ester-based monomer or the methacrylic acid ester-based monomer is more than 70% by weight, or the content of the half-ester compound is less than 0.5% by weight, the resistance to high-temperature fixing is high. The offset property may be deteriorated, and the blocking resistance and the plasticizer resistance may be deteriorated.

The resin contained in the toner of the present invention contains a resin obtained by reacting the above-mentioned polymer having a carboxy group with a polyvalent metal compound as a component.

The metal element in the polyvalent metal compound, Cu, Ag,
Be, Mg, Ca, Sr, Ba, Zn, Cd, Al, Ti, Ge, Sn, V, Cr, Mo, Mn, Fe, Ni,
Co, Zr, Se, etc. are mentioned.

Among these various elements, alkaline earth metals (Be, Mg,
Ca, Sr, Ba) and zinc group elements (Zn, Cd) are preferable, and Mg and Zn are particularly preferable.

Examples of these polyvalent metal compounds include fluorides, chlorides, chlorates, bromides, iodides, oxides, hydroxides, sulfides, sulfites, sulfates, selenides and tellurides of the above-mentioned various elements. , Nitrides, nitrates, phosphides, phosphinates, phosphates, carbonates, orthosilicates, acetates,
Examples thereof include lower alkyl metal compounds such as oxalates, methylated products and ethylated products.

Of these, acetates and oxides are preferable.

The amount of the polyvalent metal compound added cannot be unequivocally varied depending on the type and amount of the monomer constituting the polymer, but for example, the polymer is the styrene monomer,
When the low molecular weight polymer component and the high molecular weight polymer component are composed of the (meth) acrylic acid ester-based monomer and the half ester compound, 0.1 to 1 mol per 1 mol of the half ester compound charged. Is enough.

To react the polyvalent metal compound with the polymer,
For example, a solution containing the polymer obtained by polymerization by a solution polymerization method is mixed with a solution in which the metal compound or the metal compound is dispersed, and the solvent is removed by heating for about 1 to 3 hours, It is advisable to maintain the temperature in the system at about 150 to 180 ° C. for 1 hour or more to complete the reaction. In some cases, the metal compound may be allowed to be present in the reaction system together with a solvent before starting the polymerization, and the polymer obtained as a desolvent and the polyvalent metal compound are roll mills, kneaders, and extruders. You may melt-knead using a.

The resin thus obtained by reacting the polymer and the polyvalent metal compound thus obtained has an ionic bond between the carboxy group and the metal atom contained in the polymer component, and a kind of cross-linked structure due to this ionic bond. Is appearing. This ionic bond is a much slower bond than a covalent bond or the like.

In the polymer molecular weight distribution of the toner main component resin, when the maximum value of the molecular weight distribution of the low molecular weight polymer component is smaller than the above range, the blocking resistance may be deteriorated, and when it is larger than the above range, the fixability may be deteriorated. May decrease. Further, when the maximum value of the molecular weight distribution of the high molecular weight polymer component is smaller than the above range, the offset resistance, durability, and high temperature and humidity resistance may be deteriorated, and when it is larger than the above range, the fixing property is deteriorated. Sometimes.

Further, from the viewpoint of molecular weight distribution, the molecular weight distribution of a polymer composed of a low molecular weight polymer component and a high molecular weight polymer component is as follows: weight average molecular weight (Mw) / number average molecular weight (Mn)
The value of (hereinafter referred to as Mw / Mn) is 3.5 or more, preferably 4.
It is preferably 0 to 40.

In the resin having a bimodal distribution in the low molecular weight portion and the high molecular weight portion, the content of the high molecular weight polymer component is preferably 15% or more, and particularly preferably 15 to 50% by weight of the whole resin. When the content of the high molecular weight polymer component is less than 15% by weight, offset resistance and durability may be deteriorated.

The resin in the present invention may be produced by any production method as long as it has the above-mentioned molecular weight bimodal distribution. For example, a first-stage polymerization in which either one of a high molecular weight polymer component and a low molecular weight polymer component is first produced by polymerization is carried out, and then the produced one polymer component is treated with the other one. It is possible to obtain a polymer having a bimodal molecular weight distribution by dissolving it in a monomer that gives a polymer constituting the polymer component and carrying out the second-stage polymerization to produce the other polymer component. it can.
As described above, the polymer obtained by the two-stage polymerization is presumed to be a mixture of the low molecular weight polymer component and the high molecular weight polymer component uniformly at the molecular level.

This two-stage polymerization can be carried out by, for example, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, etc. Among them, the solution polymerization method is preferable.

On the other hand, a polymer having a bimodal molecular weight can be obtained by mixing a low molecular weight polymer component and a high molecular weight polymer component. Since the polymer may not be uniformly mixed at the molecular level, the polymer obtained in the above two-stage polymerization method is particularly preferable as the polymer in the present invention.

Further, the toner resin in the present invention has a glass transition point
50 to 80 ° C., the glass transition point of the low molecular weight polymer component is 50 ° C. or higher, preferably 55 ° C. or higher, and the high molecular weight polymer component is 65 ° C. or lower, preferably 60 ° C. or lower. It is desirable to have. This is because blocking resistance can be improved by adjusting the glass transition point. The glass transition point can be easily adjusted by appropriately selecting the type of monomer.

Furthermore, the toner resin in the present invention may contain a monomer unit such as vinyl acetate, vinyl propionate, vinyl chloride, or ethylene in the molecular chain within the range not impairing the object of the present invention. However, the polymer of the monomer may be blended. Moreover, a polyester resin or an epoxy resin may be contained.

The toner of the present invention contains a colorant in the above-mentioned specific resin, but may further contain a magnetic material and a property improving agent in the resin, if necessary.

As the colorant, kaobon black, nigrosine dye (CINo.50415B), aniline blue (CINo.5040)
5), Calco Oil Blue (CINo.azoic Blue3), Chrome Yellow (CINo.14090), Ultramarine Blue (CINo.77103), DuPont Oil Red (CINo.261)
05), Quinoline Yellow (CINo.47005), Methylene Blue Chloride (CINo.52015), Phthaloxyanine Blue (CINo.74160), Malachite Green Oxalate (CINo.42000), Lamp Black (CINo.7726).
6), Rose Bengal (CI No.45435), mixtures thereof, and the like. These colorants need to be contained in a sufficient ratio to form a visible image having a sufficient density, and usually 1 to 2 with respect to 100 parts by weight of the resin.
It is about 0 parts by weight.

Examples of the magnetic material include ferrite, magnetite and other iron, cobalt, nickel, and other ferromagnets or alloys, compounds containing these elements, or ferromagnetic materials that do not contain ferromagnetic elements Mention may be made of alloys which become ferromagnetic, for example manganese-copper-aluminum, manganese-copper-tin and other types of alloys called Heusler alloys containing manganese and copper, or chromium dioxide. These magnetic materials are uniformly dispersed in the resin in the form of differential powder having an average particle size of 0.1 to 1 micron. The content is 20 to 70 parts by weight, preferably 40 to 70 parts by weight, per 100 parts by weight of the toner.

Examples of the property improver include fixability improver, charge control agent,
There are others.

Examples of the fixability improver include polyolefin, fatty acid metal salt, fatty acid ester and fatty acid ester wax, partially saponified fatty acid ester, higher fatty acid, higher alcohol, liquid or solid paraffin wax, polyamide wax, polyhydric alcohol ester, silicone. Varnish, aliphatic fluorocarbon, etc. can be used. A wax having a softening point (ring and ball method JIS K2531) of 60 to 150 ° C. is particularly preferable.

As the charge control agent, conventionally known ones can be used, and examples thereof include nigrosine dyes and metal-containing dyes.

Further, the toner of the present invention is preferably used by mixing inorganic fine particles such as a fluidity improver.

The inorganic fine particles used in the present invention have a primary particle diameter of 5 mμ to 2 μ, and preferably 5 mμ to 500 mμ.
Is a particle. The specific surface area by BET method is 20-500
It is preferably m ² / g. The ratio mixed with the toner
It is 0.01 to 5 wt%, preferably 0.01 to 2.0 wt%. Examples of such inorganic fine powders include silica fine powder, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, silica sand, clay, mica, diatomaceous earth, and chromium oxide. , Cerium oxide, red iron oxide, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride, etc., but silica fine powder is particularly preferable.

The silica fine powder referred to here is a fine powder having a Si-O-Si bond, and includes both those produced by the dry method and the wet method. In addition to anhydrous silicon dioxide, any of aluminum silicate, sodium silicate, potassium silicate, magnesium silicate, zinc silicate and the like may be used, but those containing 85% by weight or more of SiO ₂ are preferable.

Specific examples of these silica fine powders include various commercially available silicas, but those having a hydrophobic group on the surface are preferable, for example, AEROSIL R-972, R-974, R-805, R-812 (above Aerosil Co., Ltd. Manufactured by Tarcox) (manufactured by Tarco) and the like. In addition, silane coupling agents, titanium coupling agents, silicone oil, silica fine powder treated with silicone oil having amine in the side chain, and the like can be used.

To give an example of a suitable method for producing a toner according to the present invention, first, a binder resin or one obtained by adding a toner component such as a colorant, if necessary, to
It is possible to obtain a toner having a desired particle diameter by melt-kneading with an extruder, cooling and then finely pulverizing with a jet mill or the like, and classifying this. Alternatively, a toner having a desired particle diameter can be obtained by spraying a product melted and kneaded with an extruder in a molten state with a spray dryer or the like and dispersing it in a liquid.

As the image forming method of the present invention, a developer is prepared by using the above-mentioned specific toner, a latent image is formed and developed by using the developer, and the obtained toner image is transferred. The upper roller, which is electrostatically transferred onto the paper, is fixed by a heating roller fixing device in which the temperature of the upper heating roller is set to a constant temperature to form a copied image.

The toner according to the present invention is particularly preferably used for fixing such that the contact time between the toner on the transfer paper and the heating roller is within 1 second, particularly within 0.5 seconds.

The developer used in the method of the present invention has been described above. Next, a specific developing process for developing, for example, an electrostatic image using such a developer will be described.

The developer carrier for supplying the developer to the developing space is
A conventional one that can apply a bias voltage can be used, and in particular, a structure in which a rotating magnet body having a plurality of magnetic poles is provided inside a sleeve on which a developer layer is carried is preferable. Can be used. In such a developer transport carrier, the rotation of the rotary magnet body causes the developer layer carried on the surface of the sleeve to undulate and move, so that new developer is supplied one after another, and Even if the developer layer on the surface of the sleeve has some unevenness in the layer thickness, the effect is sufficiently covered by the above-mentioned wavy undulation so as not to be a practical problem. Further, it is preferable that the speed at which the developer is conveyed by the rotation of the rotary magnet body or the rotation of the sleeve is almost the same as or faster than the moving speed of the electrostatic image carrier. Further, it is preferable that the rotating magnet body and the sleeve rotate in the same conveying direction. Image reproducibility is better in the same direction than in the opposite direction. However, it is not limited thereto.

Further, the developer layer carried on the developer carrying carrier preferably has a uniform thickness, and for example, the developer adhering on the developer carrying carrier is sufficiently scraped off by a blade for controlling the thickness. A uniform layer is preferable. The gap between the developer carrier and the electrostatic latent image carrier is several tens.
To 2000 μm is preferable, more preferably 50 to 500 μm, and the gap between the developer transport carrier and the electrostatic latent image bearing member is several.
If the width is too narrower than 10 μm, it becomes difficult to form the ears of a magnetic brush that uniformly develops in the developing space, and it is also impossible to supply a sufficient amount of toner particles to the developing space, which eventually stabilizes. If it becomes difficult to develop, and if the gap exceeds 2000 μm, on the contrary, the counter electrode effect will decrease and it will not be possible to obtain sufficient image density. The edge effect of increasing the amount of adhered toner also increases.

Further, the gap and the thickness of the developer layer may be set so that the ears of the magnetic brush do not come into contact with the surface of the electrostatic latent image bearing member and are as close to each other as possible without applying an oscillating electric field. Particularly preferred. This is because it is possible to prevent the toner image from being swept by the rubbing of the magnetic brush and from being fogged.

The oscillating electric field is preferably formed by applying an oscillating bias voltage to the sleeve of the developer carrier. Further, as the bias voltage, it is preferable to use a voltage obtained by superimposing an AC voltage for preventing toner particles from adhering to the non-image portion with an AC voltage for facilitating separation of the toner particles. However, the present invention is not limited to these methods.

An example of a specific apparatus that can be used to perform the developing step in the method of the present invention is shown in FIG. In FIG. 1, reference numeral 1 denotes a drum-shaped electrostatic latent image bearing member made of a photosensitive material such as a material semiconductor, which rotates in the direction of the arrow, and an electrostatic charge image is formed on the surface by a charging exposure device (not shown). It Reference numeral 2 is a sleeve made of a non-magnetic material such as aluminum, and 3 is a magnet body provided inside the sleeve 2 and having a plurality of N and S magnetic poles along its circumference. The sleeve 2 and the magnet body 3 are developer carrier carriers. Is configured. These sleeves 2
The magnet body 2 and the magnet body 3 are rotatable relative to each other. In the illustrated example, the sleeve 2 is rotated in the direction of the arrow, and the magnet body 3 is fixed. The N and S magnetic poles of the magnet body 3 are normally magnetized to a magnetic flux density of 500 to 1500 gauss, and the magnetic force thereof forms a layer of the developer D consisting of brush-like ears on the surface of the sleeve 2, that is, a magnetic brush. To do. Reference numeral 4 is a regulating blade made of a magnetic or non-magnetic material for regulating the height and amount of the magnetic brush, and 5 is a cleaning blade for removing the magnetic brush passing through the developing space A from the sleeve 2. The surface of the sleeve 2 comes into contact with the developer D in the developer pool 6, so that the developer D is supplied, and 7 stirs the developer D in the developer pool 6 to make the components uniform. It is a stirring screw. Developer D in developer pool 6
In the toner hopper 8
The toner particles T are replenished appropriately. 9 is a developer pool 6
The supply roller has a concave portion on the surface on which the toner particles are dropped. Reference numeral 10 is a bias power source for applying a bias voltage to the sleeve 2 via the protection resistor 11. A bias voltage having an AC component that oscillates by the bias power source 10 is applied between the base body 1a of the electrostatic image carrier 1 and the sleeve 2 which are grounded. As the bias voltage, for example, a superimposed voltage of a DC voltage and an AC voltage is used, and the DC component prevents fogging, and the AC component vibrates the magnetic brush to improve the developing effect. For this DC voltage component, a voltage of, for example, 50 to 600 V is generally used, which is substantially equal to or higher than the non-image area potential, and the AC voltage component has a frequency of 100 Hz to 10 kHz.
Preferably a voltage of 100V-5KV at 1-5kHz is used.
The DC voltage component may be lower than the non-image area potential when the toner particles contain a magnetic material. If the frequency of the AC voltage component is too low, the effect of giving vibration will be small, and if it is too high, the developer will not be able to follow the vibration of the electric field and the image density will decrease, making it impossible to obtain a clear high-quality image. Appears. Also, although the voltage of the AC voltage component is related to the frequency as well, the higher it is, the more the magnetic brush vibrates and the more the effect is increased, but if it is too high, fogging tends to occur and insulation such as lightning strike phenomenon occurs. It is not preferable because breakage easily occurs.

In the apparatus as described above, when the gap between the sleeve 2 and the electrostatic image carrier 1 is set to be in the range of several tens to 2000 μm and the latent image on the electrostatic image carrier 1 is developed, The magnetic brush formed on the surface of the sleeve 2 moves on the sleeve 2 while vibrating because the magnetic flux density on the surface changes with the rotation of the sleeve 2, thereby causing the electrostatic charge image carrier 1 to move. Stable and smooth passage through the gap between and, and at that time, a uniform developing effect is given to the surface on the electrostatic image carrying member 1, which enables stable development of high image density.

The example of the apparatus that can be used in the method of the present invention has been described above with reference to FIG. 1, but the present invention is not limited to this. For example, even if several electrode wires are stretched around the developing area between the developer carrier and the electrostatic latent image carrier and a voltage that vibrates is applied to the electrode wire, the magnetic brush is vibrated and the developing effect is achieved. Can be improved. Also in that case, a DC bias voltage may be applied to the developer carrier, or an oscillating voltage having a different frequency may be applied. Further, the method of the present invention can be applied to reversal development as well. In that case, the DC voltage component is set to a voltage substantially equal to the reception potential in the non-image background portion of the electrostatic latent image carrier. Further, the method of the present invention can be applied even when the image to be developed is a magnetic latent image.

〔Example〕

(Synthesis of Resin) Synthesis Example-1 Toluene 500 m in a 3 l separable flask equipped with a thermometer, a stirrer, a nitrogen gas inlet tube and a flow-down condenser.
After adding l, nitrogen gas was introduced from the gas introduction tube to make the inside an inert atmosphere, and then heated in an oil bath to the reflux temperature of toluene. Then, a solution of 195 g of styrene, 75 g of n-butyl acrylate, 30 g of methyl methacrylate and 0.75 g of benzoyl peroxide was placed in the flask and reacted at reflux temperature for 14 hours to obtain a high molecular weight polymer.

Then, a solution of 400 g of styrene, 35 g of α-methylstyrene, 90 g of n-butyl acrylate, 105 g of methyl methacrylate, 70 g of monoacryloyloxyethyl succinate, and 35 g of benzoyl ore oxide was dropped into the flask having the above high molecular weight polymer solution. While carrying out the polymerization reaction, a low molecular weight polymer was obtained.

Next, a solution of 400 g of styrene, 35 g of α-methylstyrene, 90 g of n-butyl acrylate, 105 g of methyl methacrylate, 70 g of monoacryloyloxyethyl succinate, and 35 g of benzoyl peroxide was dropped into the flask having the high molecular weight polymer solution. While carrying out the polymerization reaction. After the solution was added dropwise, a polymerization reaction was performed for 4 hours to obtain a low molecular weight polymer.

Next, 8 g of zinc oxide was added into a flask having a solution containing the high molecular weight polymer and the low molecular weight polymer, and the reaction was carried out for 2 hours while stirring at the reflux temperature.

After completion of the reaction, the toluene solvent was distilled off under reduced pressure, and the carboxy group and the metal compound were reacted to obtain Resin-A of the present invention.

The molecular weight distribution of this resin-A was measured by gel permeation chromatography (HLC-802UR.GMH ₆ column, manufactured by Toyo Soda Co., Ltd.), and the maximum value was 9,200 and 3.4 × 10 ⁵ It was a distribution. The weight average molecular weight (Mw) was 126,000 Mw / Mn was 14.0.

Synthesis Example-2 210 g of styrene as a high molecular weight polymer component, 45 g of n-butyl acrylate, 15 g of n-butyl methacrylate, 30 g of methyl methacrylate, 0.75 g of benzoylpahexoxide
As a low molecular weight polymer composition, 385 g of styrene, 35 g of α-methylstyrene, 70 g of n-butyl acrylate, 70 g of n-butyl methacrylate, 70 g of methyl methacrylate, 70 g of monoacryloyloxyethyl isophthalate, 35 g of benzoyl peroxide, and a metal compound. As zinc acetate 3
Resin-B was obtained in the same manner as in Synthesis Example-1 except that 3 g was used.

This resin-B had the maximum values of the molecular weight distribution at 9,600 and 2.9 × 10 ⁵ , and had Mw 118,000 and Mw / Mn = 12.5.

Synthesis Example-3 225 g of styrene as a high molecular weight polymer component, 60 g of n-butyl acrylate, 15 g of monoacryloyloxypropyl isophthalate, 0.9 g of benzoyl peroxide, 385 g of styrene as a low molecular weight polymer component, 35 g of α-methylstyrene, Resin-C was obtained in the same manner as in Synthesis Example-1 except that 105 g of n-butyl acrylate, 105 g of methyl methacrylate, 70 g of monoacryloyloxypropyl isophthalate and 35 g of benzoyl peroxide were used, and 10 g of zinc oxide was used as the metal compound.

The maximum value in the molecular weight distribution of Resin-C is 9,800 and 3.6 × 10
^{Was 5} . The Mw was 131,000 and Mw / Mn was 13.6.

Synthesis Example-4 170 g of styrene as a high molecular weight polymer component, 30 g of 2-ethylhexyl acrylate, 0.4 of benzoyl peroxide
g, styrene as a low molecular weight polymer component 340 g, α-
Methyl styrene 40g, 2-ethylhexyl acrylate 1
40 g, methyl methacrylate 160 g, monoacryloyloxypropyl isosuccinate 120 g, benzoyl peroxide 40 g, magnesium acetate 13 g as metal compound
Resin-D was obtained in the same manner as in Synthesis Example-1 except that was used.
The maximum molecular weight in the resin-D molecular weight distribution is 11,500.
And 3.8 × 10 ⁵ , and the weight average molecular weight (Mw) is 115,00.
0 and Mw / Mn were 10.5.

Synthesis Example-5 240 g of styrene as a high molecular weight polymer component, 160 g of n-butyl methacrylate, 1.4 g of benzoyl peroxide as a low molecular weight polymer component 235 g of styrene, 30 g of α-methylstyrene, 240 g of n-butyl methacrylate, 60 g of methyl methacrylate, Resin-E was obtained in the same manner as in Synthesis Example-1 except that 35 g of monoacryloyloxyethyl succinate, 30 g of benzoyl peroxide and 4.0 g of zinc oxide were used as the metal compound. The maximum values of the molecular weight in the molecular weight distribution of Resin-E are 10,700 and 2.2 × 10 ⁵ , and Mw is 133,
000 and Mw / Mn were 12.7.

Synthesis Example-6 240 g of styrene, 60 g of n-butyl methacrylate, 0.9 g of benzoyl peroxide as high molecular weight polymer components,
Synthetic example-1 except that 420 g of styrene, 70 g of α-methylstyrene, 105 g of n-butyl acrylate, 105 g of monoacryloyloxyethyl succinate, 28 g of benzoyl peroxide and 13 g of zinc oxide are used as the low molecular weight polymer components and zinc oxide is 13 g as the metal compound. Resin-F was obtained in the same manner as in.

The maximum molecular weight of Resin-F is 9,500 and 2.8 × 10 ⁵ ,
The Mw was 116,000 and the Mn was 12.5.

(Synthesis of Comparative Resin) Comparative Synthesis Example-1 Synthesis Example-1 except that 8 g of zinc oxide was deleted from Synthesis Example-1.
Resin-G was obtained in the same manner as in 1.

Resin-G has maximum values of 9,000 and 3.4 × 10 ⁵ , with Mw of 124,00
0 and Mw / Mn were 14.4.

Comparative Synthetic Example-2 400 g of toluene was placed in a 2 l separable flask, air was replaced with nitrogen gas, and 750 g of styrene, 200 g of n-butyl acrylate and amber were added while heating the system to the boiling point of toluene and stirring. Solution polymerization was carried out while dropwise adding a mixture of 50 g of acid monoacryloyloxyethyl ester and 10 g of benzoyl peroxide as a polymerization initiator over 2.5 hours.

After the addition of the mixture was completed, the mixture was aged for 1 hour while stirring at the boiling point of toluene, and 14.1 g of zinc oxide was added.

Next, the temperature of the system was gradually raised to 180 ° C. and the toluene was removed under reduced pressure to remove styrene-acrylic acid-n.
-Butyl-succinic acid monoacryloyloxyethyl ester copolymer-resin which is a reaction polymer of zinc oxide-H
Got

Comparative Synthetic Example-3 Put 90 g of xylene in a separable flask, further, 75 g of styrene, 20 g of butyl acrylate, 5 g of monobutyl maleate, 0.5 g of divinylbenzene were added, and the gas phase was kept at 80 ° C. after substituting with nitrogen gas, A solution prepared by dissolving 1.2 g of benzoyl peroxide in 10 g of xylene was added, and stirring was continued for 10 hours.
Then, the temperature was raised to 95 ° C. and maintained for 3 hours to complete the polymerization. After cooling, the polymerization solution was poured into a large amount of methanol to separate the precipitate, which was thoroughly dried at 50 ° C. Resin I obtained here had an Mw / Mn of 27 and an Mw of 233,000.

(Production of Toner) 70 parts by weight of each of Resins A to F obtained in Synthesis Examples 1 to 6, 30 parts by weight of magnetite "BL-500" (manufactured by Titanium Industry Co., Ltd.), "Nigrosine EX" (manufactured by Orient Chemical Co., Ltd.) ) 2 parts by weight, polypropylene "Viscor 660P" (manufactured by Sanyo Chemical Industry Co., Ltd.) 2 parts by weight, and Wax-E (manufactured by Hoechst) 2 parts by weight are mixed by a Henschel mixer, and the temperature is 130 ° C with a two-roll mill. After sufficiently melting and kneading, let stand to cool, coarsely pulverize, then finely pulverize with a jet mill, and further classify with wind force to obtain an average particle size.
Toners 1 to 6 according to the present invention having a size of 12.0 μm were obtained.

Comparative Toners (1) and (2) Comparative Toners (1) and (2) were obtained in the same manner as in Example except that the resins G and H were used.

Comparative Toner (3) 100 parts by weight of Resin-I, 0.6 parts by weight of iron (III) acetylacetone, and 60 parts by weight of magnetite were mixed on a roll mill at 150 ° C. for 3 days.
After melt-kneading for 0 minutes, the mixture was cooled and finely pulverized by an air jet type pulverizer to obtain particles of 5 to 20 μm by air classification. This toner is designated as comparative toner (3).

Toners 1 to 6 according to the present invention and comparative toners (1) to
100 parts by weight of each of (3) and 0.5 parts by weight of hydrophobic colloidal silica are externally added as a developer, and a developing device shown in FIG. 1 is used by using a photoreceptor having a negative electrostatic latent image made of an organic semiconductor. The resulting toner image is transferred onto a transfer paper and then fixed by a heating roller fixing device to form a copied image. The minimum temperature and the offset generation temperature (minimum temperature at which the offset phenomenon occurs) were measured.

Minimum fixing temperature: After creating an unfixed image with the above copying machine, the surface layer is a heat roller with a diameter of 50φ formed of Teflon (polytetrafluoroethylene manufactured by DuPont), and the surface layer is a silicone rubber "KE-1300RTV" ( A toner image formed by the sample toner transferred onto a transfer paper of 64 g / m ^{2 with} a fixing device consisting of a pressure roller formed by Shin-Etsu Chemical Co., Ltd., and a linear velocity of 200 mm /
The fixing operation is performed by fixing the heat roller with a linear pressure of 0.8 kg / cm and a nip width of 8 mm in steps of 5 ° C in the temperature setting range of 100 to 240 ° C. The image was rubbed with Kimwipe, and the lowest setting temperature for the fixed image showing sufficient rubbing resistance was defined as the lowest fixing temperature. The fixing device used here does not have a silicone oil supply mechanism.

Offset generation temperature: The measurement of the offset generation temperature is similar to the measurement of the minimum fixing temperature, but after the unfixed image is created by the above copying machine, the toner image is transferred and the fixing process is performed by the above fixing device, and then The operation of sending a blank transfer sheet to the fixing device under the same conditions and visually observing whether or not toner stains occur is repeated with the set temperature of the heat roller of the fixing device being sequentially increased. The set temperature of the temperature at which the stain was generated was defined as the offset generation temperature.

Further, the blocking resistance of the above toner was measured as follows.

Blocking resistance: The blocking resistance test was carried out by leaving it for 1 day under an environmental condition of a temperature of 55 ° C. and a relative humidity of 60% to examine whether or not aggregates were formed.

The above results are shown in Table 1.

Next, using the above developer, a copying test was performed on 100,000 sheets under the environmental conditions of normal temperature and normal humidity (20 ° C, 60% RH) and high temperature and high humidity (30 ° C, 80% RH), and the following evaluations were performed. The results are shown in Tables 2 and 3.

Image quality: The sharpness of the copied image was examined at the beginning and end of the 100,000 times development process.

Filming resistance: Fire filming resistance is determined by observing the surface of the carrier and the cleaning blade of the surface of the carrier and the cleaning blade with an electron microscope or visually at the beginning and the end of the 100,000 times development process to check for the presence of deposits. It was

The results are as shown in Tables 2 and 3. In the table,
Regarding the image quality, "good" means that the image is clear, and "bad" means that the image has a lot of fog and is unclear.

Fog: It was shown by the relative density with respect to a white background partial developed image with a document density of 0.0 (white background reflection density was 0.0).

○ Less than 0.01 △ 0.01 to less than 0.03 × 0.03 or more Cleaning property: The cleaning property was determined by observing the surface of the photosensitive member after cleaning the surface of the photosensitive member with a cleaning member and determining the presence or absence of an adhered substance.

As is clear from the table, the developers 1 to 6 of the present invention are excellent in low-temperature fixing property, anti-offset property, anti-blocking property, and have a wide fixable range, and under environmental conditions of normal temperature and normal humidity and high temperature and high humidity. No fogging, good cleaning performance, no fusing to carrier or photoreceptor surface cleaning blade, excellent triboelectricity, long-term stability and clear image It was excellent in humidity.

In contrast to the results of the developers 1 to 6 according to the present invention, when the comparative toner (1) was used, the minimum fixing temperature was 160 ° C, the offset generation temperature was 230 ° C, and the blocking resistance (good) was obtained. Next, a copy test of 100,000 sheets was carried out at room temperature and normal humidity, but fog started to increase from the 5000th sheet, and after 10,000 sheets, image density decreased and image loss occurred, resulting in an unclear image.

Furthermore, in a 100,000 copy test under hot and humid conditions,
Fog occurred from the initial hundreds of copies, and cleaning failure occurred after 1000 copies, resulting in poor image density and missing images, resulting in unclear images.

Also, in the case of development using comparative toner (2), the minimum fixing temperature
The temperature was 160 ° C, the offset generation temperature was 230 ° C, and the blocking resistance was good. In a 100,000-copy test at room temperature and normal humidity, fog started to increase from 10,000 copies, and after 13,000 copies, the image density decreased and image loss occurred, resulting in an unclear image.

Further, under high temperature and high humidity conditions, after 3000 copies, fogging occurred, image density decreased, and image loss occurred, resulting in an unclear image.

After the test, when the surface of the photoreceptor and the cleaning blade were examined, fusion of toner was found.

Furthermore, the result using the comparative toner (3) shows that the minimum fixing temperature is
The temperature was 150 ° C, the offset generation temperature was 220 ° C, and the blocking resistance was good. In a 100,000-copy test under normal temperature and humidity conditions, fogging started to increase after 50,000 copies, and image defects occurred due to poor cleaning, resulting in unclear images.

Further, under high temperature and high humidity conditions, after 10,000 copies, the fog increased, the image density decreased, and image dropout occurred, resulting in an unclear image.

After the test was completed, the surface of the photoconductor and the cleaning blade were examined, and it was found that fusion due to toner filming had occurred.

[Brief description of drawings]

FIG. 1 is an explanatory sectional view showing an outline of an example of a developing device that can be used for performing a developing step in carrying out the method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Electrostatic latent image carrier, 2 ... Sleeve 3 ... Magnet body, 4 ... Regulation blade 5 ... Cleaning blade 6 ... Developer pool, 7 ... Stirring screw 8 ... Toner hopper, 9 ... Supply roller 10 ... Bias power supply, 11 ... Protective resistance A ... Development space, D ... Developer T ... Toner particles, N, S ... Magnetic pole

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G03G 15/09 Z (56) References JP-A-56-158340 (JP, A) JP-A-57 -178250 (JP, A) JP 61-110155 (JP, A) JP 61-110156 (JP, A) JP 61-181753 (JP, A)

Claims (2)

[Claims] 1. A method for developing an electrostatic charge image in which an oscillating electric field is generated in a developing area to develop a latent image formed on an image carrier with a one-component magnetic toner on a developer carrier, wherein the one-component magnetic toner is used. The main component resin has a molecular weight of at least two groups of a low molecular weight polymer component and a high molecular weight polymer component, and the molecular weight distribution is a molecular weight distribution curve by gel permeation chromatography. The maximum value is 1 × 10 ^{3 to} 2 × 10 ⁴ , the maximum value of the high molecular weight polymer component is 1 × 10 ⁵ to 2 × 10 ⁶ , and the main component resin is the following (a), ( A method for developing an electrostatic latent image, which is a polyvalent metal salt of a polymer obtained from (b) and (c). (A) Styrene-based monomer (b) Acrylic acid ester-based monomer or methacrylic acid ester-based monomer (c) Monomer represented by the following general formula (A) General formula (A) (In the formula, R ₁ represents a hydrogen atom or a methyl group, L represents a divalent linking group having 3 or more carbon atoms having an ester bond, and may have a substituent.) 2. The method for developing an electrostatic latent image according to claim 1, wherein the metal salt is a zinc group metal salt or an alkaline earth metal salt.