JP3102135B2 - Carrier and developer for electrostatic image development - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for developing an electrostatic image used in an electrophotographic copying machine and a developer using the same.

[0002]

2. Description of the Related Art Conventionally, in a two-component developer comprising a positively-chargeable toner and a negatively-chargeable resin-coated carrier, a resin for coating the carrier may be a copolymer of vinylidene fluoride and tetrafluoroethylene or a fluoroalkyl A fluororesin type such as a methacrylate copolymer or a silicone resin type has been proposed (see, for example, JP-A-61-217068, JP-A-62-22682, and JP-A-2-96770). ). Also, Japanese Unexamined Patent Publication No.
Japanese Patent Application No. -92134 proposes coating the carrier surface with a chlorinated or brominated vinyl copolymer, and also exemplifies vinylidene chloride as a monomer of the copolymer. However, the technology specifically disclosed and used is only a carrier coated with a copolymer using vinyl chloride.

[0003]

Conventionally known resin-coated carriers have their respective advantages and disadvantages. For example, fluororesin-based ones have good chargeability, but have drawbacks in charge stability and adhesion to a core material. It is known that the silicone resin-based resin has a poor adhesion to the core material and has a disadvantage that it gradually peels off. Therefore, the copied image is not stable and gradually becomes white stain (hereinafter referred to as fog). All have the disadvantage of lacking durability.

[0004]

As a result of repeated studies to solve the problems of the prior art as described above, the present inventors have found that vinylidene chloride is copolymerized with acrylonitrile and / or an acrylonitrile derivative at a specific ratio. A copolymer, or
Carriers whose surfaces are coated with a resin system containing a copolymer obtained by further copolymerizing other monomers at a specific ratio,
The coated carrier exhibits excellent properties to improve the above-mentioned disadvantages, and the coated carrier can provide a clear copy image with extremely low fog, and further has a performance of extremely increasing the transfer efficiency of toner during copying. And good storage stability and durability, and arrived at the present invention.

That is, the present invention comprises at least a part of a core material coated with vinylidene chloride and a copolymer of vinylidene chloride and at least one monomer having an unsaturated double bond copolymerizable with the vinylidene chloride. A carrier for developing an electrostatic image, wherein the copolymer comprises: (a) vinylidene chloride 70
(B) acrylonitrile and / or acrylonitrile derivative 20 to 60 mol%, and (c) monomer 0 to 4 having an unsaturated double bond copolymerizable therewith.
It can be easily achieved by a carrier for developing an electrostatic image, which is a copolymer comprising 0 mol%, and an electrostatic image developer comprising the carrier and a positively chargeable toner.

Hereinafter, the present invention will be described in detail. First, the carrier of the present invention comprises a binary copolymer consisting of (a) vinylidene chloride and (b) acrylonitrile and / or an acrylonitrile derivative, or (a), (b) and (c) a copolymer copolymerizable therewith. It is characterized by being coated with a resin system containing a multi-component copolymer comprising a monomer having a saturated double bond. In the copolymer, the monomer ratios of (a) vinylidene chloride, (b) acrylonitrile and / or an acrylonitrile derivative, and (c) a monomer having an unsaturated double bond copolymerizable therewith are respectively: a)
70 to 30 mol%, (b) 20 to 60 mol%, (c) 0
４０40 mol%, preferably (a) 60 そ れ ぞ れ
30 mol%, (b) 20 to 50 mol%, (c) 0 to 30
It is good to be mol%. In the case of a binary copolymer,
It is preferable that (a) is 60 to 40 mol% and (b) is 40 to 60 mol%, respectively. If the amount of vinylidene chloride is too large, it becomes close to the properties of vinylidene chloride homopolymer,
Since it is thermally unstable and does not dissolve in most solvents, it is difficult to use it. Even if it is used, it is not preferable because the fluidity of the carrier tends to deteriorate and adversely affect the copied image. In addition, storage stability under high temperature or the like is poor. On the other hand, if the amount of vinylidene chloride is too small, the chargeability of the toner becomes insufficient, and this tends to adversely affect the copied image after the endurance actual copying such as continuous copying of many sheets. (C) If the amount of the monomer is too large, it is not preferable because charging stability is deteriorated and a copied image is adversely affected.

The acrylonitrile derivative in the present invention typically includes methacrylonitrile, that is, (b) acrylonitrile and / or the acrylonitrile derivative includes acrylonitrile alone,
Methacrylonitrile alone or a mixture of acrylonitrile and methacrylonitrile in any ratio can be used.

In the present invention, (c) other monomers copolymerizable with vinylidene chloride include, for example, styrene,
Styrenes such as α-methylstyrene and chloromethylstyrene; methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate,
Hexyl acrylate, octyl acrylate, 2-chloroethyl acrylate, methyl α-fluoroacrylate,
α-ethyl fluoroacrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate,
Α-substituted or unsubstituted alkyl (meth) acrylates such as amyl methacrylate, hexyl methacrylate, octyl methacrylate, and 2-chloroethyl methacrylate; ethyl vinyl ether, 2-chloroethyl vinyl ether, propyl vinyl ether, and butyl Vinyl ethers such as vinyl ether, octyl vinyl ether, cyclohexyl vinyl ether, and phenyl vinyl ether; vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butyrate, vinyl pivalate, and vinyl benzoate; methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl ketone, and butyl Vinyl ketones such as vinyl ketone and phenyl vinyl ketone; ethylene, propylene, isobutene, butadiene,
Olefins such as isoprene; nitrogen-containing compounds such as N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine and the like. These monomers can be used alone or as a mixture of two or more.

Commercially available resins contained in the copolymer of vinylidene chloride and acrylonitrile and / or acrylonitrile derivatives of the present invention include Saran Resin F-310 of Dow Chemical Company and Saran Resin R-202 and R-R of Asahi Kasei Corporation. -241B and the like.
The weight average molecular weight of the copolymer used in the present invention is usually from 6 × 10 ^{4 to} 60 × 10 ⁴ , more preferably from 20 × 10 ^{4, as} measured by gel permeation chromatography (in terms of polystyrene). It is 40 × 10 ⁴ .
If the weight-average molecular weight is too low, the flowability of the coated carrier deteriorates, which is not preferable. If the molecular weight is too high, there is no problem in performance, but the solubility in a solvent is deteriorated, and the coating treatment becomes complicated, which is not preferable.

As a method for producing the copolymer, a usual radical polymerization method is employed, and bulk polymerization, suspension polymerization, emulsion polymerization, solution polymerization and the like are performed. As a coating material for the carrier core material, a composition obtained by blending the above copolymer with another resin or the like can also be used. More specifically, for example, vinylidene fluoride, a blend with a fluorine resin such as vinylidene fluoride-ethylene tetrafluoride copolymer, a silicone resin, an acrylic resin, a polyester resin,
Polycarbonate resin, epoxy resin, phenoxy resin, polyamide resin, polyimide resin, urea resin, alkyd resin, phenol resin, vinyl chloride resin, polysulfone resin, polyether resin, polybutadiene resin,
Examples include blends with other resins such as polystyrene resins and polyacrylonitrile resins, and blends with silica powder, charge control agents, surfactants, lubricants, and the like.
It is preferable that the amount of these blended materials be 50% or less of the copolymer. In order to prevent the dehydrochlorination of the copolymer, stabilizers usually used for stabilizing vinyl chloride, vinylidene chloride and the like can be used. Such stabilizers include, for example, metal soaps, epoxy compounds,
Examples include phosphites and polyols.

Further, as an application of the carrier of the present invention, a resin layer containing a vinylidene chloride-based copolymer and another resin layer can be provided with a multilayer coating resin layer of the carrier. The formation of a film on the carrier core material is performed in substantially the same manner as in a conventional method. For example, the copolymer used in the present invention or a mixture containing the copolymer and the blend material is dissolved or dispersed in an organic solvent to obtain a solid content of 0.1 to 3%.
A coating solution of 0% by weight, more preferably 1 to 5% by weight is prepared, coated on a core material by a dipping method, a dry spray method, a fluid spray method using a flow coater, and the like, and dried. If necessary, heat treatment may be performed at a temperature of up to 100 ° C. after the formation of the film.

As the organic solvent, any organic solvent that can dissolve the copolymer can be used. For example, ketone solvents such as acetone, methyl ethyl ketone, methyl propyl ketone, methyl isopropyl ketone, methyl isobutyl ketone and cyclohexanone; acetate solvents such as ethyl acetate, cellosolve acetate and n-butyl acetate; cyclic ethers such as tetrahydrofuran and dioxane Aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as tetrachloroethylene, trichloroethylene and methylene chloride. These solvents can be used alone or in combination of two or more. Further, these solvents can be used as long as they have a boiling point of about 50 to 150 ° C., but from the viewpoint of the dissolution treatment and the drying treatment after coating, etc., from 60 to 120 ° C.
C. is more preferable.

As the core material of the carrier used in the present invention, all known materials can be used and are not particularly limited. Specifically, ferromagnetic metals such as ferrite, magnetite, iron, cobalt, and nickel; alloys or compounds containing these metals; do not contain ferromagnetic metals, but exhibit ferromagnetism by heat treatment. comprising alloys such, Mn-Cu-Al, so-called Hoisura alloy such as Mn-Cu-Sn: such as metal oxides such as CrO ₂ is preferably exemplified. The particle size of such a carrier is usually about 20 to 500 μm, more preferably about 30 to 200 μm.

The thickness of the carrier coating layer is preferably about 0.05 to 5 μm in a dry state.
More preferably, it is about 3 to 3 μm. 0.05μ
If it is less than m, the durability is not sufficient and the charging stability is poor, so that it is not preferable. The thickness of the coating layer is 5 μm
Even if the value exceeds, there is no substantial problem in performance, but the performance has almost reached the maximum value, and the copolymer is consumed in large quantities, which is not economical.

The carrier of the present invention is used as an electrostatic image developer in combination with a known toner, particularly a positively chargeable toner. Such a toner is obtained by dispersing a colorant in a binder resin. Examples of the binder resin include styrenes such as styrene, parachlorostyrene, and α-methylstyrene; methyl acrylate, ethyl acrylate, n-propyl acrylate, butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, Α-methylene fatty acid monocarboxylic acid esters such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate; vinyl nitriles such as acrylonitrile and methacrylonitrile; Vinyl pyridines such as 2-vinyl pyridine and 4-vinyl pyridine; vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; vinyl methyl ketone, vinyl ethyl methone and methyl isopropenyl ketone Vinyl ketones; unsaturated hydrocarbons such as ethylene, propylene, isoprene and butadiene and their halides; homopolymers consisting of monomers such as halogenated unsaturated hydrocarbons such as chloroprene; copolymers consisting of two or more of these Polymers, and mixtures of two or more of these homopolymers and copolymers are exemplified. Alternatively, rosin-modified phenol-formalin resin, oil-modified epoxy resin, polyester resin, polyurethane resin, polyimide resin, cellulose resin, non-vinyl resins such as polyether resins, and mixtures of these non-vinyl resins and the above-mentioned vinyl resins No.

Examples of the colorant used in the toner include carbon black, nigrosine, aniline blue, calco oil blue, chrome yellow, ultramarine blue, methylene blue, rose bengal, and phthalocyanine blue. The above toner is
If necessary, additives such as waxes, silica, zinc stearate and the like can be further contained or mixed for use. The carrier of the present invention and such a toner are
Usually, the latter is mixed at a ratio of about 0.3 to 20 parts by weight with respect to 100 parts by weight of the former, and used for developing an electrostatic image such as a magnetic brush method or a cascade method.

[0017]

The carrier coating layer comprising a copolymer or a composition containing the copolymer used in the present invention has excellent film strength and good adhesion to a core material. In addition, the chargeability is rapidly increased and high chargeability is imparted to the carrier. Therefore, since the charge stability is excellent, a clear copy image having a high image density and extremely little fog can be obtained. Further, the transfer efficiency of the toner at the time of copying is increased. Further, the storage stability is good and the durability is excellent.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to the following examples.
In the following, “parts” means “parts by weight”. Example 1 A copolymer consisting of 54 mol% of vinylidene chloride and 46 mol% of acrylonitrile was prepared, and gel permeation chromatography HLC-8020 manufactured by Tosoh was used, and tetrahydrofuran was used as a solvent, and a column PL10 μm Mix manufactured by Polymer Laboratories (UK) ( 0.75φ
The number average molecular weight and the weight average molecular weight in terms of polystyrene were measured with two pieces of (× 30 cm). Number average molecular weight is 6.5 ×
The weight-average molecular weight was 10 ⁴ , and the weight-average molecular weight was 32.8 × 10 ⁴ (hereinafter, the molecular weight was measured similarly). The copolymer is dissolved in a mixed solvent of equal amounts of tetrahydrofuran and methyl ethyl ketone to prepare a coating solution having a solid concentration of 1.8%, and then dried by a fluid spray method using a spherical ferrite having an average particle diameter of 100 μm as a carrier core material. Coating was performed so that the film thickness became 2 μm to obtain a resin-coated carrier.

On the other hand, 100 parts of a copolymer resin of styrene and n-butyl acrylate, 5 parts of carbon black, 2 parts of low molecular weight polypropylene, a quaternary ammonium salt-based charge control agent (trade name P-51, manufactured by Orient Chemical Co., Ltd.) Hydrophobic silica fine powder (trade name: R-97, manufactured by Degussa Co., Ltd.) is used for 100 parts of a toner having an average particle diameter of 10 μm comprising 2 parts of kneaded and crushed material.
2) 0.1 part was added and mixed with a Henschel mixer to obtain a silica externally added toner. 4 parts of the silica externally added toner and 100 parts of the resin-coated carrier were mixed to prepare a developer. Subsequently, using a commercially available copying machine (Sharp SF8800) equipped with an organic photoconductor, a real-life durability test was performed, and the image density was measured, the fog was determined, and the toner transfer rate was evaluated. A clear, less fogged image was obtained. Also, the toner transfer efficiency was good. Add 50 g of the developer into a glass bottle and place
A storage stability test was carried out by exposing for 8 hours, and there was no change and the storage stability was good. Hereinafter, evaluation results are shown in Table 1 for each example.

Example 2 A binary copolymer composed of 50 mol% of vinylidene chloride and 50 mol% of acrylonitrile (number average molecular weight 7.0 × 1)
0 ⁴ , weight average molecular weight 34.1 × 10 ⁴ ) was dissolved in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol), treated in the same manner as in Example 1, and coated with a resin having a dry film thickness of 0.7 μm. The carrier was manufactured and subsequently evaluated in the same manner as in Example 1. As a result, a stable and clear image with little fog was obtained throughout. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 3 A binary copolymer comprising 45 mol% of vinylidene chloride and 55 mol% of acrylonitrile (number-average molecular weight 8.1 × 1)
0 ⁴ , weight average molecular weight 38.9 × 10 ⁴ ) was dissolved in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol), treated in the same manner as in Example 1, and coated with a resin having a dry film thickness of 0.6 μm. The carrier was manufactured and subsequently evaluated in the same manner as in Example 1. As a result, a stable and clear image with little fog was obtained throughout. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 4 A binary copolymer composed of 50 mol% of vinylidene chloride and 50 mol% of acrylonitrile (number-average molecular weight: 3.9 × 1)
0 ^4, a weight average molecular weight 18.8 × 10 ⁴⁾ was dissolved in a mixed solvent of methyl ethyl ketone / toluene = 65/35 (Vol), it was treated in the same manner as in Example 1, a dry film thickness of 0.5
A μm resin-coated carrier was manufactured and subsequently evaluated in the same manner as in Example 1. As a result, a stable, clear and less fogged image was obtained throughout. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 5 60 mol% of vinylidene chloride, methacrylonitrile 40
(% Number average molecular weight 5.3 × 1)
0 ^4, a weight average molecular weight 24.7 × 10 ⁴⁾ was dissolved in a mixed solvent of methyl ethyl ketone / toluene = 65/35 (Vol), it was treated in the same manner as in Example 1, a dry film thickness of 0.7
A μm resin-coated carrier was manufactured and subsequently evaluated in the same manner as in Example 1. As a result, a stable, clear and less fogged image was obtained throughout. Also, the toner transfer efficiency was good. The storage stability was also good.

EXAMPLE 6 50 mol% of vinylidene chloride and acrylonitrile 25
Mole% and a mixture of methacrylonitrile 25 mole%
(A number average molecular weight of 4.8 × 10 ^Four,weight
Average molecular weight 23.5 × 10^Four) Is methyl ethyl ketone /
Dissolved in a mixed solvent of toluene = 65/35 (Vol)
And processed in the same manner as in Example 1 to obtain a dry film thickness of 0.5 μm.
A resin-coated carrier was manufactured, and subsequently, as in Example 1.
And evaluated it, it was stable and clear throughout,
Fewer images were obtained. Also, the toner transfer efficiency is good.
Was. The storage stability was also good.

Example 7 1 part of the copolymer of Example 1 and a polyacrylonitrile resin (number average molecular weight 2.3 × 10 ⁴ , weight average molecular weight 8.6)
2 × 10 ⁴ ) One part of the mixture was dissolved in a mixed solvent of dimethylformamide / THF = 2/1 (Vol.),
A resin-coated carrier having a dry film thickness of 2 μm was prepared in the same manner as in Example 1, and then evaluated in the same manner as in Example 1. As a result, a stable, clear and less fogged image was obtained throughout. Also, the toner transfer efficiency was good. or,
The storage stability was also good.

Example 8 55 mol% of vinylidene chloride and acrylonitrile 20
Mol%, 25 mol% methyl methacrylate (number average molecular weight 4.6 × 10 ⁴ , weight average molecular weight 3
8.2 × 10 ⁴ ) was dissolved in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol) and treated in the same manner as in Example 1 to produce a resin-coated carrier having a dry film thickness of 0.3 μm. Evaluation was performed in the same manner as in Example 1. As a result, a stable and clear image with little fogging was obtained throughout. Also, the toner transfer efficiency was good.
The storage stability was also good.

Example 9 A copolymer composed of 60 mol% of vinylidene chloride, 25 mol% of methacrylonitrile and 15 mol% of n-butyl acrylate (number-average molecular weight: 4.1 × 10 ⁴ , weight-average molecular weight: 2)
8.7 × 10 ⁴ ) was treated in the same manner as in Example 1 to produce a resin-coated carrier having a dry film thickness of 2 μm, and then evaluated in the same manner as in Example 1. An image with little fog was obtained. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 10 A copolymer consisting of 46 mol% of vinylidene chloride, 28 mol% of acrylonitrile and 26 mol% of methyl methacrylate (number average molecular weight 4.5 × 10 ⁴ , weight average molecular weight 38.
3 × 10 ⁴ ) was dissolved in a mixed solvent of an equal amount of tetrahydrofuran and toluene and treated in the same manner as in Example 1 to obtain a dry film thickness of 1
μm resin-coated carrier was manufactured, followed by Example 1.
When the evaluation was performed in the same manner as
An image with little fog was obtained. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 11 A copolymer composed of 46 mol% of vinylidene chloride, 25 mol% of acrylonitrile, 29 mol% of methyl methacrylate and 1 mol% of acrylic acid (number-average molecular weight 3.7 × 10 ⁴ , weight-average molecular weight 26. 5 × 10 ⁴ ) was treated in the same manner as in Example 1 to produce a resin-coated carrier having a dry film thickness of 1 μm, and was evaluated in the same manner as in Example 1. As a result, stable, clear, fog-free Fewer images were obtained. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 12 A copolymer composed of 33 mol% of vinylidene chloride, 34 mol% of acrylonitrile and 33 mol% of methyl acrylate (number average molecular weight 4.7 × 10 ⁴ , weight average molecular weight 35.4 ×
10 ⁴ ) is tetrahydrofuran / methyl ethyl ketone =
When dissolved in a mixed solvent of 1/1 (Vol) and treated in the same manner as in Example 1, a resin-coated carrier having a dry film thickness of 0.7 μm was produced. Subsequently, evaluation was performed in the same manner as in Example 1. A stable, clear and less fogged image was obtained throughout. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 13 A copolymer comprising 35 mol% of vinylidene chloride, 36 mol% of methacrylonitrile and 29 mol% of propyl acrylate (number average molecular weight 4.3 × 10 ⁴ , weight average molecular weight 32.
6 × 10 ⁴ ) was dissolved in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol), and
A resin-coated carrier having a dry film thickness of 0.8 μm was manufactured in the same manner as in Example 1. Subsequently, the evaluation was performed in the same manner as in Example 1. As a result, a stable, clear and less fogged image was obtained throughout. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 14 A copolymer consisting of 45 mol% of vinylidene chloride, 30 mol% of methacrylonitrile and 25 mol% of octyl acrylate (number average molecular weight 4.2 × 10 ⁴ , weight average molecular weight 30.
9 × 10 ⁴ ) was converted to methyl ethyl ketone / toluene = 65 /
The resin-coated carrier was dissolved in 35 (Vol) mixed solvent and treated in the same manner as in Example 1 to produce a resin-coated carrier having a dry film thickness of 0.5 μm. A stable, clear and less fogged image was obtained. Also, the toner transfer efficiency was good. The storage stability was also good.

Example 15 A copolymer composed of 40 mol% of vinylidene chloride, 35 mol% of methacrylonitrile and 25 mol% of butyl methacrylate (number average molecular weight 3.4 × 10 ⁴ , weight average molecular weight 25.
8 × 10 ⁴ ) was converted to methyl ethyl ketone / toluene = 65 /
The resin-coated carrier was dissolved in 35 (Vol) mixed solvent and treated in the same manner as in Example 1 to produce a resin-coated carrier having a dry film thickness of 0.5 μm. A stable, clear and less fogged image was obtained. Also, the toner transfer efficiency was good. The storage stability was also good.

Comparative Example 1 A developer was prepared with a silica externally added toner in the same manner as in Example 1 using spherical ferrite not coated with a resin as a carrier, and evaluated in the same manner as in Example 1. The image density decreased as they overlapped. In addition, fog was extremely large from the beginning, and the image was dirty. Further, the transfer efficiency of the toner was poor, and a large amount of untransferred toner was recovered.

Comparative Example 2 Commercially available carrier coated with silicone resin (ferrite core)
When evaluation was performed in the same manner as in Example 1 except for using
Although the image density was almost good, the image was slightly fogged and a slightly dirty image was obtained. In addition, the recovery amount of the untransferred toner was slightly large, and the transfer efficiency of the toner was slightly poor.

Comparative Example 3 Evaluation was conducted in the same manner as in Example 1 except that a commercially available carrier coated with vinylidene fluoride resin (the core agent was ferrite) was used. The transfer efficiency of fog and toner was relatively good. However, the image density was low and inferior.

Comparative Example 4 A binary copolymer composed of 77 mol% of vinylidene chloride and 23 mol% of acrylonitrile (number average molecular weight 3.4 × 1)
0 ⁴ , weight average molecular weight 16.6 × 10 ⁴ ) was dissolved in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol) and treated in the same manner as in Example 1 to obtain a resin-coated carrier having a dry film thickness of 2 μm. Manufacture, followed by Example 1
When the evaluation was performed in the same manner as
An image with little fog was obtained. Also, the toner transfer efficiency was good. However, the storage stability of the developer at 40 ° C. for 48 hours was poor.

Comparative Example 5 A binary copolymer composed of 30 mol% of vinylidene chloride and 70 mol% of acrylonitrile (number-average molecular weight 5.1 × 1)
0 ^4, dissolved weight average molecular weight 25.6 × 10 ⁴⁾ in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol), was treated in the same manner as in Example 1, the resin coating having a dry thickness of 1.0μm A carrier was manufactured and subsequently evaluated in the same manner as in Example 1. As a result, although the initial image and the storage stability were good, the density after 10,000 actual copies was slightly lower and fogging occurred slightly. .

Comparative Example 6 A binary copolymer composed of 25 mol% of vinylidene chloride and 75 mol% of acrylonitrile (number-average molecular weight 6.6 × 1)
0 ⁴ , weight average molecular weight 30.3 × 10 ⁴ ) was dissolved in a mixed solvent of tetrahydrofuran / methyl ethyl ketone = 1/1 (Vol), treated in the same manner as in Example 1, and coated with a resin having a dry film thickness of 0.5 μm. A carrier was manufactured and subsequently evaluated in the same manner as in Example 1. As a result, although the initial image and the storage stability were good, the density after 10,000 actual copies was slightly lower and fogging occurred slightly. .

[0040]

[Table 1]

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-213960 (JP, A) JP-A-49-51951 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/113

Claims (3)

(57) [Claims] 1. A core material is coated at least in part with a resin system containing vinylidene chloride and a copolymer of vinylidene chloride and at least one monomer having an unsaturated double bond copolymerizable with the vinylidene chloride. A carrier for developing electrostatic images, comprising: (a) vinylidene chloride 70
(B) acrylonitrile and / or acrylonitrile derivative 20 to 60 mol%, and (c) monomer 0 to 4 having an unsaturated double bond copolymerizable therewith.
A carrier for developing an electrostatic image, which is a copolymer comprising 0 mol%. 2. The electrostatic image according to claim 1, wherein in the copolymer, (c) the monomer having a copolymerizable unsaturated bond is an acrylate or a methacrylate. Development carrier. 3. An electrostatic image developer comprising the carrier according to claim 1 and a positively chargeable toner.