JP2992921B2 - Electrophotographic carrier and two-component developer - 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 in a developer used for developing an electric latent image or a magnetic latent image in an electrophotographic method or an electrostatic printing method, and more particularly to a method for improving durability and image quality. It relates to a markedly improved electrophotographic carrier and a two-component developer.

[0002]

2. Description of the Related Art A carrier constituting a two-component developer is as follows.
The carrier is roughly divided into a conductive carrier and an insulating carrier.As the conductive carrier, oxidized or unoxidized iron powder is usually used.In a developer containing the iron powder carrier as a component,
There is a drawback that the triboelectric charging property with respect to the toner is unstable and that a visible image formed by the developer is fogged. That is, with the use of the developer, toner particles adhere and accumulate (spent toner) on the surface of the iron powder carrier particles, so that the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectric charging property is increased. Becomes unstable, and as a result, the image density of the visible image formed decreases and fog increases. Therefore, when copying is continuously performed by an electronic copying apparatus using a developer containing an iron powder carrier, the developer deteriorates in a small number of times, so that it is necessary to replace the developer at an early stage, which results in a high cost. It will be.

[0003] A typical example of an insulating carrier is a carrier obtained by uniformly covering the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, or ferrite with an insulating resin. In a developer using this carrier, toner particles are less likely to fuse to the surface of the carrier than in the case of a conductive carrier, and at the same time, it is easy to control the triboelectric charging property between the toner and the carrier, and the durability is high. This is advantageous in that it is particularly suitable for high-speed electronic copiers in that it has excellent service life and a long service life.

There are various characteristics required for the insulating carrier, but particularly important characteristics are appropriate chargeability, impact resistance, abrasion resistance, good adhesion between the core and the coating material, and good charge distribution. Uniformity and the like.

In view of the above-mentioned required characteristics, conventionally used insulating carriers still have a problem to be improved, and the perfect carrier has not been known so far.
For example, examples in which an acrylic resin or the like is used as a carrier coating material are disclosed in JP-A-47-13954 and JP-A-60-1985.
-208765. In addition, those which particularly describe the molecular weight are disclosed in
It is disclosed in, for example, Japanese Patent Application Laid-Open No. 0-208767, and it is known that the chargeability of a coated carrier is stabilized by controlling the molecular weight to be constant. However, in order to attach the coating resin to the carrier core material, it is easily affected by the conditions of the apparatus and the environment in which the coating is performed, particularly humidity. Even if these are strictly controlled, the resin is stably attached to the core material. At present, there is no satisfactory material for providing sufficient chargeability and durability.

[0006]

SUMMARY OF THE INVENTION The main object of the present invention is to provide a carrier for electrophotography which is improved in the above-mentioned conventional disadvantages, in particular, in chargeability, uniformity of charge distribution, mechanical strength, and adhesion to a core material. And a two-component developer.

[0007]

The present inventors have conducted various studies and studies in order to improve the above-mentioned conventional disadvantages.
It has been found that giving a polymer, which is a coating material, a specific molecular weight peak is effective in improving various required characteristics of the coated carrier, and the present invention has been completed.

That is, the present invention relates to an electrophotographic carrier in which a carrier core material is coated with a resin, wherein the coating resin has a weight average molecular weight of 50,000 to 250,000 and is determined by gel permeation chromatography (GPC). When the molecular weight distribution is 10,000 to 60,000 by weight, the maximum value of the low molecular weight component and 1
An electrophotographic carrier characterized by being a resin having a maximum value of a high molecular weight component in the range of from 10,000 to 300,000.

Further, the present invention provides a two-component developer containing a toner and a carrier, wherein the carrier has a carrier core material coated with a resin, and the coated resin has a weight average molecular weight of 50,000 to 25,000. A resin whose molecular weight distribution by gel permeation chromatography (GPC) has a maximum value of a low molecular weight component at 10,000 to 60,000 and a maximum value of a high molecular weight component at 100,000 to 300,000. The present invention relates to a two-component developer, which is a certain electrophotographic carrier.

If a carrier coating material having a weight average molecular weight of more than 300,000 has been used so far, the adhesion to the core material is poor and the charge rises slowly, so that the charge amount during running decreases. As a result, fogging occurs early and fouling occurs in the machine, which is not desirable. On the other hand, when the weight average molecular weight is less than 10,000, peeling due to internal destruction of the coating layer is remarkable, and carrier and developer It has been found that this is not preferable because it causes a shortened life.

The molecular weight distribution of the resin is also important, and it has been found that it is effective to have a certain range of molecular weight distribution for stable adhesion of the resin to the core material. That is, when the molecular weight distribution is sharp, the adhesive force to the core material during coating tends to be weak, and when the molecular weight distribution is broad, the adhesive force to the core material increases,
The carrier is liable to be contaminated with toner, the amount of toner adhered to the surface of the carrier after printing has been large, and the triboelectricity tends to decrease.

Therefore, although the use of resins having an intermediate molecular weight distribution is being studied, sufficient durability has not yet been obtained.

In order to solve the properties of the coating material, the inventors of the present invention have proposed a high molecular weight component having toner contamination resistance and a low molecular weight component having an effect of increasing the adhesion strength to a core material as a carrier coating resin. It has been found that it is extremely effective to coexist with and. Further, in order to obtain the effect, it is important to have a peak on each of the high molecular weight side and the low molecular weight side, thereby greatly improving the durability.

The molecular weight distribution of the resin can be measured by using GPC (gel permeation chromatography).

[0015] Until now, as for the coating resin having excellent adhesion to the carrier core material, the lower the Tg (glass transition point), the better, and the higher the Tg, the lower the adhesion, especially the Tg. For resins above 140 ° C,
It has been confirmed that the adhesiveness is weak, and even when coating is performed by heating to Tg or more, the coating film is easily cracked during use, and the coating resin is peeled off from the core material.

On the other hand, a carrier-coated resin having a low Tg of less than 55 ° C. is excellent in adhesion to a core material, but easily causes toner adhesion (spent) to a carrier,
Further, particularly under high temperature conditions, the hardness of the resin is insufficient, the fluidity of the carrier itself is deteriorated, the charge-imparting ability is low, and there is a practical problem. Therefore, the Tg of the coating resin used in the present invention is desirably 55 ° C. or more and 140 ° C. or less.

As the polymer component used in the coating resin of the carrier of the present invention, the following can be used.

That is, alkyl styrene such as styrene, methyl styrene, dimethyl styrene, trimethyl styrene, ethyl styrene, diethyl styrene, triethyl styrene, propyl styrene, butyl styrene, hexyl styrene, heptyl styrene, octyl styrene, fluorostyrene, chlorostyrene, etc. Halogenated styrenes such as styrene, bromostyrene, dibromostyrene and iodostyrene; and styrene-based monomers such as nitrostyrene, acetylstyrene and methoxystyrene; acrylic acid, methacrylic acid, α-ethylacrylic acid, crotonic acid, α-methylcroton Acid, α-ethylcrotonic acid, isocrotonic acid, tiglic acid, addition-polymerizable unsaturated aliphatic monocarboxylic acid such as ungeric acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, Saconic acid, glutaconic acid, addition-polymerizable unsaturated aliphatic dicarboxylic acids such as dihydromuconic acid; the above-mentioned addition-polymerizable unsaturated carboxylic acids and alcohols, for example, methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, amyl alcohol, hexyl alcohol, Alkyl alcohols such as heptyl alcohol, octyl alcohol, nonyl alcohol, dodecyl alcohol, tetradecyl alcohol, and hexadecyl alcohol; halogenated alkyl alcohols obtained by partially halogenating these alkyl alcohols; methoxyethyl alcohol; ethoxyethyl alcohol; ethoxyethoxyethyl alcohol , Methoxypropyl alcohol, alkoxyalkyl alcohols such as ethoxypropyl alcohol, benzyl alcohol, Esters with aralkyl alcohols such as phenylethyl alcohol and phenylpropyl alcohol, alkenyl alcohols such as allyl alcohol and crotonyl alcohol, especially alkyl acrylate, alkyl methacrylate, alkyl fumarate, alkyl maleate and the like Are preferred examples; amides and nitriles derived from the addition-polymerizable unsaturated carboxylic acids; aliphatic monoolefins such as ethylene, propylene, butene, and isobutylene; vinyl chloride, vinyl bromide,
Vinyl iodide, 1,2-dichloroethylene, 1,2-dibromoethylene, 1,2-diiodoethylene, isopropenyl chloride, isopropenyl bromide, allyl chloride, allyl bromide, vinylidene chloride, vinyl fluoride, fluoride Halogenated aliphatic olefins such as vinylidene; 1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene;
Conjugated diene-based aliphatic diolefins such as 2,4-hexadiene and 3-methyl-2,4-hexadiene; 2-vinylpyridine, 4-vinylpyridine, 2-vinyl-6-methylpyridine, 2-vinyl-5- Methylpyridine, 4-
Butenylpyridine, 4-pentylpyridine, N-vinylpiperidine, 4-vinylpiperidine, N-vinyldihydropyridine, N-vinylpyrrole, 2-vinylpyrrole, N-vinylpyrroline, N-vinylpyrrolidine, 2-
Vinylpyrrolidine, N-vinyl-2-pyrrolidone, N-
Nitrogen-containing vinyl monomers such as vinyl-2-piperidone and N-vinylcarbazole can be exemplified. These can be used alone or in combination of two or more.

Examples of the polymerization initiator used for producing the coating resin of the present invention include azo compounds such as azobisisobutyronitrile, cumene hydroperoxide, t-butyl hydroperoxide, dicumyl peroxide, di-t- Known initiators such as peroxides such as butyl peroxide, benzoyl peroxide, lauroyl peroxide and the like are used. In addition, combinations with ionizing radiation such as γ-rays and accelerated electron beams and various sensitizers are also used.

The compounding amount of the polymerization initiator such as an azo compound and a peroxide may be a so-called catalyst suitable amount, and is generally preferably used in an amount of 0.1 to 10% by weight per charged monomer. The polymerization reaction temperature may be a known one, and a temperature of 40 to 140 ° C. is generally sufficient. The stirring of the reaction system may be gentle stirring so that a homogeneous reaction occurs as a whole, and the polymerization is carried out by replacing the reaction system with an inert gas such as nitrogen to prevent the polymerization from being inhibited by oxygen. You may. Then, the obtained polymer is recovered, and if necessary, the polymer is immersed in a highly volatile solvent which is compatible with the monomer and does not dissolve the polymer component, and is stirred.

The preferred solvent is conveniently selected depending on the resin component of the resin particles to be produced and the polymerizable monomer used, but is preferably water, methanol, ethanol, propanol, butanol, isobutanol, tert-butanol, hexanol, or the like. Alcohols such as octanol, n
-Hexane, pentane, heptane, octane, isooctane, decane, 2,2'-dimethylbutane, aliphatic hydrocarbons such as cyclohexane, benzene, toluene, aromatic hydrocarbons such as xylene, dichloromethane, dichloroethane, carbon tetrachloride, Halogenated hydrocarbons such as chlorobenzene, dioxane, dimethyl ether, diethyl ether, tetrahydrofuran, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,
Various solvents such as ethers such as ethylene glycol dimethyl ether and ethylene glycol diethyl ether, ketones such as acetone, methyl ethyl ketone and cyclohexanone, acetonitrile, formamide, dimethylformamide and diethylformamide are used. The above solvents may be used alone, but depending on the resin, two or more solvents can be used as a mixed solvent.

As a method for obtaining a resin having two peaks as a molecular weight distribution, a method of mixing two kinds of resins having different weight average molecular weights or a known multi-stage polymerization method is used, but is not particularly limited. When a multi-stage polymerization method is used, either the high molecular weight side or the low molecular weight side may be polymerized first. In addition, as a coating procedure, a method in which coating, drying, and baking steps are repeated and applied in two or more steps can be used, in which case a low molecular weight component is applied first, and then a high molecular weight component is applied. Is also effective in satisfying the characteristics required for the above-mentioned coat carrier.

The coating amount of the coating resin according to the present invention with respect to the carrier core material is such that the resin solid content is 0.05% by weight to 10% by weight, preferably 0.2% by weight to 5% by weight. 0.0
If the amount is less than 5% by weight, the effect of coating the carrier core material with the resin is not sufficient, and the coating amount exceeding 10% by weight is meaningless, and an excess amount of the resin alone may be present from the viewpoint of production. Absent.

The weight average particle size of the carrier core material used is 17 to 200 μm, preferably 20 to 65 μm. The measurement of the particle size distribution of the carrier is based on JIS-H2601. Also, the average particle size is obtained from the measured particle size distribution,
It is calculated according to the following formula.

[0025]

(Equation 1)

The material of the magnetic particles used as the core material of the carrier of the present invention is 98% or more of Cu—Zn—Fe (metal composition ratio (5-20) :( 5-20) :( 30-8)
Ferrite particles having the composition of 0)) are preferable for easy surface uniformization and stable charging ability, but are not particularly limited, and may be flat, spongy, coin-like, spherical, spherical, etc. Iron oxide powder of various shapes, copper, manganese, cobalt,
Ferrite containing one or more of nickel, zinc, tin, magnesium, lead, strontium, barium, lithium and the like, particles made of a mixture of various resins and magnetic powder, and the like can be used.

For coating the core material with a resin, for example, the core material is immersed in a solution obtained by dissolving one or more of the polymers produced as described above in a suitable solvent, Thereafter, a method of removing the solvent, drying and baking at a high temperature, or a method of suspending the core material in a fluidized bed, spray-coating the copolymer solution, drying and baking at a high temperature can be used. In these methods, the high-temperature baking treatment is performed at about 80 to 240 from the viewpoint of removing residual monomers and increasing the adhesion strength between the core material and the copolymer layer.
It is preferable to carry out the treatment at a temperature of ° C.

The carrier of the present invention thus obtained is mixed with a toner and used as a magnetic brush developer for developing an electrostatic latent image.

As the toner, any toner usually used in electrophotography, in which a colorant is dispersed in a binder resin, can be used, and is not particularly limited.

When a two-component developer is prepared by mixing the carrier and the toner according to the present invention, the mixing ratio is 1.0% by weight to 12% by weight, preferably 2% by weight, as the toner concentration in the developer. Good results are usually obtained with ９9% by weight. When the toner concentration is less than 1.0% by weight, the image density is low and cannot be used practically. When the toner concentration is more than 12% by weight, fog and scattering in the machine are increased, and the service life of the developer is shortened.

Hereinafter, the measuring method according to the present invention will be described.

1) Measuring method of triboelectric charge amount The measuring method will be described in detail with reference to the drawings.

FIG. 1 is an explanatory view of an apparatus for measuring a triboelectric charge amount of a toner. First, 50 g of a mixture of toner and carrier whose weight ratio is to be measured in a ratio of 1:19 is placed in a polyethylene bottle having a capacity of 50 to 1000 ml in a metal measuring container 22 having a 500-mesh screen 23 at the bottom. , 30 times and 500 times by hand, about 0.5 to 0.9 g of the mixture (developer) is put therein, and the metal lid 24 is closed. At this time, the weight of the entire measurement container 22 is weighed and set as W ₁ (g). Next, in the suction device 21 (at least a portion in contact with the measurement container 22 is an insulator), the suction port 27 is provided.
The pressure of the vacuum gauge 25 is adjusted to 250 mmAq by adjusting the air volume control valve 26. In this state, suction is sufficiently performed, preferably for about 2 minutes, to remove the toner by suction. The potential of the electrometer 29 at this time is set to V (volt). Here, 28 is a capacitor whose capacity is C (μF). Further, the weight of the whole measurement container after suction is weighed to be W ₂ (g). The triboelectric charge (μC / g) of this toner is calculated as shown in the following equation.

Amount of triboelectric charge of toner (μC / g) = (C × V) / (W ₁ −W ₂ )

2) Method for measuring molecular weight distribution In the present invention, the molecular weight distribution of a chromatogram by GPC (gel permeation chromatography) using THF as a solvent is measured under the following conditions.

That is, the column was stabilized in a heat chamber at 40 ° C., and THF (tetrahydrofuran) as a solvent was added to the column at this temperature at 0.8 ml / min.
And then inject about 100 μl of a THF sample solution for measurement. In measuring the molecular weight of the sample, the molecular weight distribution of the sample was calculated from the relationship between the logarithmic value of a calibration curve prepared from several kinds of monodisperse polystyrene standard samples and the count number. As a standard polystyrene sample for preparing a calibration curve, for example, one having a molecular weight of about 10 ² to 10 ⁷ manufactured by Tosoh Corporation or Showa Denko KK, and it is appropriate to use a standard polystyrene sample having at least about 10 points. is there. An RI (refractive index) detector is used as the detector. As the column, it is preferable to combine a plurality of commercially available polystyrene gel columns. For example, showex GPC KF-801, 802, manufactured by Showa Denko KK
803, 804, 805, 806, 807, 800P combination, two Tosoh GMH _XL and TSKge
_{lG1000H (H XL), G2000H (} H XL), G3
_{000H (H XL), G4000H (} H XL), G5000
H (H _XL ), G6000H (H _XL ), G7000H (H
_XL ) and TSKguardcolumn.

The sample is prepared as follows.

The sample is placed in THF, left for several hours, shaken sufficiently, mixed well with THF (until the sample is no longer united), and allowed to stand for 12 hours or more. At this time, TH
The time of leaving in F is set to 24 hours or more. Then, a sample processing filter (pore size 0.45 to
0.5 μm, for example, Myshoridisk H-25-
5 The product passed through Tosoh Co., Ltd., and can be used as a sample of GPC. The sample concentration is
The resin component is adjusted to be 0.5 to 5 mg / ml.

[0039]

Embodiments of the present invention will be described below. Average molecular weight means weight average molecular weight. Further, both the high molecular weight side peak value and the low molecular weight side peak value indicate the respective peak values of the weight molecular weight by GPC.

Example 1 In xylene at 120 ° C., 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, DTBP (di-t
A mixture of 0.1 part by weight of (-butyl peroxide) was added dropwise over 3 hours. Thereafter, the mixture was polymerized at a boiling point for 4 hours, and dried under vacuum to remove xylene to obtain a polymer A.
Next, 70 parts by weight of polymer A, methyl methacrylate 75
Parts by weight, 25 parts by weight of butyl acrylate, BPCP
[2,2-bis (4,4-di-t-butylperoxy)
Cyclohexyl) propane] was added dropwise to xylene and polymerized at a polymerization temperature of 130 ° C. for 5 hours. The average molecular weight was 190,000 and the peak value on the high molecular weight side was 25.
A resin having a peak value on the low molecular weight side of 30,000 was obtained. The obtained resin was diluted with xylene to a resin solid content of 15%.

The coating solution was applied to spherical ferrite particles having an average particle size of 45 μm and having a Cu—Zn composition with a coating machine (Spiracoater manufactured by Okada Seiko Co., Ltd.).

The obtained coated carrier was dried at 60 ° C. for 1 hour to remove the solvent, and further heated at 140 ° C. for 1 hour to obtain a resin-coated carrier.

The resin coating amount of the obtained carrier was 0.62.
%, And it was confirmed by observation with an electron microscope that the ferrite core material was uniformly coated with the resin.

On the other hand, 4 parts by weight of a polyester resin phthalocyanine pigment obtained by condensing 100 parts by weight of propoxylated bisphenol and fumaric acid and 4 parts by weight of a chromium complex of di-tert-butylsalicylic acid were sufficiently premixed by a Henschel mixer. The mixture was melt-kneaded by a shaft extrusion kneader, cooled, coarsely pulverized to about 1 to 2 mm using a hammer mill, and then finely pulverized by an air jet pulverizer. Further, the obtained finely pulverized product was classified to obtain a negatively triboelectrically charging cyan powder having a weight average particle size of 8.3 μm.

100 parts by weight of the above colored powder and 0.7 parts by weight of hydrophobic titanium oxide fine powder were mixed to obtain a cyan toner. The cyan toner and the above-described carrier were allowed to stand in an N / N (23 ° C./60%) environment, mixed at a toner concentration of 5%, and the charge amount was measured.

The carrier and the cyan toner were mixed at a toner concentration of 5% to prepare a developer, and an image area ratio of 50% was obtained using a color copying machine CLC-500 (manufactured by Canon).
23% / 60% using the original manuscript
Table 1 shows the results of image formation on 40,000 sheets. From Table 1, it can be seen that the above-mentioned developer has a small variation in the printing durability test and is very good.

The following comparative examples and examples are also shown in Table 1.

Example 2 In xylene at 120 ° C., 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, 0.08 of DTBP
A part by weight of the mixed solution was added dropwise over 3 hours. Thereafter, the mixture was polymerized at a boiling point for 5 hours, and dried under vacuum to remove xylene, thereby obtaining a polymer B. Next, 75 parts by weight of polymer B,
A uniform mixture of 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.1 part by weight of BPCP was dropped into xylene, polymerized at a polymerization temperature of 130 ° C. for 6 hours, and had an average molecular weight of 230,000 and a peak value on the high molecular weight side of 27. A copolymer having a peak value of 550,000 on the low molecular weight side was obtained.

This was further diluted with xylene to prepare a carrier coating resin solution having a resin solid content of 15%.
When a carrier was manufactured and evaluated in the same manner as in Example 1 except that this resin solution was used, a good image was obtained even after copying 40,000 sheets.

Example 3 A mixture of 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate and 0.2 parts by weight of DTBP was dropped into xylene at 120 ° C. over 2.5 hours, and then kept at the boiling point for 2 hours. The resulting mixture was polymerized and dried under vacuum to remove xylene, thereby obtaining a polymer C. Next, 75 parts by weight of polymer C, 75 parts by weight of methyl methacrylate, and 2 parts of butyl acrylate
A homogeneous mixture of 5 parts by weight and 0.2 parts by weight of BPCP was dropped into xylene and polymerized at a polymerization temperature of 130 ° C. for 4 hours.
A copolymer having an average molecular weight of 80,000, a peak value on the high molecular weight side of 110,000, and a peak value on the low molecular weight side of 20,000 was obtained.

This was diluted with xylene to obtain a resin solid content of 15%.
When the carrier was manufactured and evaluated in the same manner as in Example 1, the fogging was slightly increased after 40,000 sheets of images were produced, but the image density and image quality were stable and good. Obtained.

Example 4 A mixture of 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.1 part by weight of DTBP was dropped into xylene at 120 ° C. over 4 hours, and then 5.
Polymerization was carried out at a boiling point of 5 hours to obtain a polymer DI having a peak of one molecular weight at 250,000. Apart from this, 1
A mixture of 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.1 part by weight of BPCP was dropped into xylene at 30 ° C. over 2 hours, and then 4.
Polymerization was carried out at a boiling point of 5 hours to obtain a polymer D-II having a peak of one in 30,000 molecular weight.

By sufficiently mixing the two kinds of resins, a resin having an average molecular weight of 200,000, a high molecular weight side peak of 250,000 and a low molecular weight side peak of 30,000 was obtained. This resin was diluted with xylene to prepare a carrier coating resin solution having a resin solid content of 15%.

When a carrier was manufactured and evaluated in the same manner as in Example 1 except that this resin solution was used, the image density was slightly increased after copying 40,000 sheets, but the image quality was not deteriorated. Good results were obtained.

Example 5 Polymer DI having one peak at a molecular weight of 250,000 and polymer D having one peak at a molecular weight of 30,000 used in Example 4
-II Each diluted with xylene, resin solid content 15%
The solution was used.

First, a resin coating was performed in the same manner as in Example 1 using the polymer D-II solution. After drying and baking, the polymer DI was further applied thereon, followed by drying and baking again. Got a career.

Using this carrier, the same evaluation as in Example 1 was performed. As a result, a good image with fine images was obtained, and no deterioration in image quality was observed even after copying 40,000 sheets.

Comparative Example 1 Polymer DI of Example 4 (having one peak at a molecular weight of 250,000) was diluted with xylene to prepare a carrier coating resin solution having a resin solid content of 15%.

Except that this resin solution was used, a carrier was manufactured and evaluated in the same manner as in Example 1. As a result, the image quality was inferior to those of Examples 1 to 5, particularly in terms of fineness. Was almost satisfactory after the copying of 40,000 sheets.

However, after the copying of 40,000 sheets, the reproduction of the halftone portion (intermediate color) of the document was clearly lower than in the first embodiment.

Comparative Example 2 The polymer D-II of Example 4 (having one peak at a molecular weight of 30,000) was diluted with xylene to prepare a resin solution for carrier coating having a resin solid content of 15%.

A carrier was manufactured and evaluated in the same manner as in Example 1 except that this resin solution was used. As a result, a good image was obtained in the initial stage, but fog slightly increased after copying 40,000 sheets. Deterioration was also observed in terms of image fineness compared to the initial stage.

Comparative Example 3 75 parts by weight of the polymer B of Example 2, 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, BPCP
Polymerization was carried out at a polymerization temperature of 130 ° C. for 9 hours using 0.1 part by weight of the homogeneous mixture to obtain a copolymer having an average molecular weight of 100,000, a peak value on the high molecular weight side of 250,000, and a peak value on the low molecular weight side of 110,000. . This was further diluted with xylene, and the resin solid content was reduced to 15
% Of a carrier coating resin solution was prepared.

A carrier was manufactured and evaluated in the same manner as in Example 1 except that this resin solution was used.
In addition to the initial image, the fineness of the initialized image was slightly inferior, and the reproduction of the halftone portion (intermediate color) tended to be slightly worse.

Comparative Example 4 In xylene at 120 ° C., 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.4 parts by weight of DTBP were added dropwise over 1.5 hours, and then kept at the boiling point for another 1.5 hours. The polymer was polymerized and dried under vacuum to remove xylene to obtain a polymer E. Next, a homogeneous mixture of 50 parts by weight of polymer E, 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.9 parts by weight of BPCP was dropped into xylene, and polymerized at a polymerization temperature of 130 ° C. for 5.5 hours.
A copolymer having an average molecular weight of 60,000, a high molecular weight side peak of 70,000, and a low molecular weight side peak of 30,000 was obtained. This was further diluted with xylene to prepare a carrier coating resin solution having a resin solid content of 15%.

A carrier was manufactured and evaluated in the same manner as in Example 1 except that this resin solution was used. As a result, fog was slightly increased after 40,000 copies were formed.

Comparative Example 5 In xylene at 120 ° C., 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, 0.08 of DTBP
A part by weight of the mixed solution was added dropwise over 6 hours, and then polymerized while maintaining the boiling point for 5.5 hours, and dried under vacuum to remove xylene to obtain a polymer F. Next, a homogeneous mixed solution of 75 parts by weight of polymer F, 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.2 parts by weight of BPCP was dropped into xylene, and polymerized at a polymerization temperature of 130 ° C. for 6 hours to obtain an average molecular weight of 30. A copolymer having a molecular weight of 400,000, a high molecular weight peak of 400,000, and a low molecular weight peak of 30,000 was obtained. This was further diluted with xylene to prepare a carrier coating resin solution having a resin solid content of 15%.

A carrier was manufactured and evaluated in the same manner as in Example 1 except that this resin solution was used.
5, the uniformity of the halftone portion was slightly poor, but no significant deterioration was observed even after 40,000 images were printed.

Comparative Example 6 A mixture of 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.1 part by weight of DTBP was added dropwise to xylene at 120 ° C. over 4 hours, and then kept at the boiling point for further 4 hours for polymerization. Then, vacuum drying was performed to remove xylene, thereby obtaining a polymer G. A homogeneous mixture of 40 parts by weight of polymer G, 75 parts by weight of methyl methacrylate, 25 parts by weight of butyl acrylate, and 0.2 parts by weight of BPCP was dropped into xylene, and polymerized at a polymerization temperature of 130 ° C. for 3 hours, and the average molecular weight was 200,000. Thus, a copolymer having a peak on the high molecular weight side of 250,000 and a peak on the low molecular weight side of 50,000 was obtained. This was further diluted with xylene to prepare a carrier coating resin solution having a resin solid content of 15%.

A carrier was produced and evaluated in the same manner as in Example 1 except that this resin solution was used. As a result, fog increased after 40,000 sheets of images were formed.

The evaluation of fog was performed using REFL manufactured by Tokyo Denshoku Co., Ltd.
The measurement was performed using ECTOMETER MO DELTAC-6DS, and the cyan toner image was calculated using the following formula using an amber filter. The smaller the value, the less fog.

Fog reflectance (%) = reflectivity of standard paper (%) − reflectivity of non-image portion of sample (%)

[0073]

[Table 1]

[0074]

According to the present invention, by using a carrier coating material having a molecular weight distribution of two peaks by GPC of a coating resin, sufficient adhesion to a carrier core material, spent resistance, and crack resistance are achieved. It is possible to achieve both.

First, the chargeability and the uniformity of the charge distribution are superior to those of the conventional coated carrier, that is, the charge saturation time is significantly reduced. Further, the adhesion between the core material and the coating is excellent, the mechanical strength is high, and the contamination by the toner based on the coating is suppressed, so that the life of the carrier is long, and as a result, a developer with a long life can be obtained. .
Further, the carrier of the present invention can be manufactured by a simple process such as immersion in a solution, spray application of the solution, or heat treatment as necessary.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an apparatus for measuring a triboelectric charge amount of a toner.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-269547 (JP, A) JP-A-63-217360 (JP, A) JP-A-4-338972 (JP, A) 83260 (JP, A) JP-A-5-265259 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 9/10

Claims (2)

(57) [Claims] 1. An electrophotographic carrier in which a carrier core material is coated with a resin, wherein the coating resin has a weight average molecular weight of 5
The molecular weight distribution by gel permeation chromatography (GPC) is as follows: the maximum value of the low molecular weight component is 10,000 to 60,000 and the maximum value of the high molecular weight component is 100,000 to 300,000. An electrophotographic carrier, characterized in that the carrier is a resin having the same. 2. A two-component system containing a toner and a carrier.
In the developer, the carrier has a carrier core material coated with a resin,
The coating resin has a weight average molecular weight of 50,000 to 250,000,
Gel permeation chromatography (GP
The molecular weight distribution according to C) is as low as 10,000 to 60,000 by weight.
The maximum value of the high molecular weight component and the maximum value of the high molecular weight component
Carrier for electrophotography which is a resin having
A two-component developer.