JPH0862899A - Electrophotographic developer - Google Patents

Abstract

PURPOSE: To obtain an electrophotographic developer not reducing the quantity of electric charges even in an environmental change and suppressing the occurrence of image defects such as the blurring of the rear end of an image part while attaining a high image density and a low fog density. CONSTITUTION: This electrophotographic developer consists of at least a toner and a carrier consisting of two kinds of carriers (A), (B) different from each other in the variation of the water content due to an environmental change. When the variation of the water content of the carrier A causing a relatively small variation of the water content due to an environmental change and that of the carrier B causing a relatively large variation are represented by WA (g/m<2> ) and WB(g/m<2> ), respectively, and the variation of the water content of the toner is represented by Wt (g/m<2> ), the relation of WA<Wt <WB is established.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer, and more particularly to an electrophotographic developer carrier.

[0002]

2. Description of the Related Art In a two-component developing system comprising a toner (hereinafter also referred to as colored particles) and a carrier, the toner is provided with a charge amount necessary for development by utilizing frictional charging with a carrier. However, it has been unavoidable that the amount of electrification of the toner has changed in the developers so far due to changes in the environment, that is, temperature and humidity.

For example, the reason why the amount of charge of a negatively charged toner in a high humidity environment decreases is that the degree of change in the chargeability of the toner and the carrier due to environmental changes is different. Since the charging order of water is located on the plus side of the toner and the carrier, when the water is adsorbed in a high humidity environment, the chargeability of the toner and the carrier changes to the plus side. At this time, if the change widths of the toner and the carrier are equal, the charge amount of the toner should not change. However, in reality, the toner has a larger water adsorption property than the carrier, and thus the change range of the charging property is different, and the charge amount of the toner is reduced in most cases in high humidity.

For this reason, even if a developer capable of obtaining a good copy image under normal temperature and normal humidity is used, the charge amount is decreased under the high temperature and high humidity environment, and the image density is decreased, the fog and the image area are deteriorated. Image defects such as blurring of the trailing edge occurred, and it was difficult to obtain good image quality in all environments.

Recently, in order to eliminate waste toner,
A copying machine having a so-called recycling mechanism that collects the toner that is not transferred and remains on the drum and returns it to the developing device for reuse has been put into practical use. This is because it also uses toner with deteriorated charging characteristics. A developer used in a developing device having a recycling mechanism is required to have a smaller environmental dependency.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, does not cause a decrease in charge amount even under environmental changes, achieves high image density and low fog density, It is an object of the present invention to provide an electrophotographic developer that suppresses the occurrence of image defects such as edge blurring.

[0007]

The above object of the present invention can be achieved by the following constitutions.

(1) In an electrophotographic developer comprising at least a toner and a carrier, the carrier is composed of two types of carriers having different changes in water content due to environmental changes, and among the two types of carriers, water inclusion due to environmental changes. The change in water content of carrier A with a relatively small change in water content and the change in water content of carrier B with a relatively large change in water content are respectively calculated as W _A (g /
m ² ), W _B (g / m ² ), and the change in water content of the toner is represented by W _t (g
/ M ² ), WA _A <W _t <W _B is satisfied.

(2) | (W _B −W _t ) − (W _t −W _A ) |
The electrophotographic developer according to (1), wherein ≦ 0.10.

[0010] ^{(3) 0.05 × 10 -2 ≦} W t -W A ≦ 2.0 × 10
^-2 , and 0.2 × 10 ^-2 ≤ W _B -W _t ≤ 0.10. The electrophotographic developer according to (1) above.

The present invention will be described in detail below.

In the present invention, the two types of carriers have different water content changes, and one has a water content change smaller than the toner (hereinafter referred to as carrier A) and the other has a water content change larger than the toner (hereinafter referred to as carrier B). Therefore, the change in chargeability due to the change in humidity is different.
That is, the carrier A, the carrier B, and the toner each have their charging order moved to the positive side due to moisture absorption, but the carrier A having a small water content change moves to the plus side, which is smaller than the toner, and thus the water content change. The large carrier B moves to the plus side more than the toner.
As a result, the chargeability of the toner and the carrier A is lower under high humidity, and the chargeability of the toner and the carrier B changes to higher under high humidity, and the developer as a whole has low chargeability. It is possible to reduce the change in charge amount under high humidity.

It is also conceivable to use as the carrier coating material a material whose water content change due to the environment is the same as that of the toner. In this case, however, the carrier coating material becomes a material similar to the toner to obtain the required charge amount. Is difficult. However, by using two types of carriers having different changes in water content, both the charge amount and its environmental dependence can be improved.

Here, the water content change of the carrier A and the carrier B is W _A (g / m ² ), W _B (g / m ² ), respectively, and the water content change of the toner is W _t (g / m ² ). ² )
(W _B −W _t ) − (W _t −W _A ) | ≦ 0.10 is preferable, and | (W _B −W _t ) − (W _t −W _A ) | ≦ 8.0 × 10 ⁻² Is more preferable. If the left side of this equation is too large, the effect of the present invention is difficult to be exhibited.

Further, (W _t -W _A ) is 0.05 × 10 ^{-2 to} 2.0 × 1.
It is preferably 0 ^-2 , and more preferably 0.20 x 10 ^{-2 to} 1.0 x 10 ^-2 . Further, (W _B -W _t) is 0.2 × 10 ^-2 ~
It is preferably 0.10, further 0.50 × 10 ^-2 ~ 8.0 × 1
It is more preferably 0 ^-2 .

[0016] wherein when (W _t -W _A) or (W _B -W _t) is too large, it is possible to necessarily the toner or carrier itself moisture content of increases, the powder fluidity, cohesion Cause problems with sex.

When (W _t -W _A ) or (W _B -W _t ) is too small, as described above, when a material whose water content change due to the environment is the same as that of the toner is used as the carrier coating material. Causes the same problem as.

The term "environmental change" as used in the present invention means a change in temperature and humidity, and has a great effect on the change in water content of the carrier and toner.

<Measurement Method of Water Content> The water content of the present invention is preferably measured by the Karl Fischer coulometric titration method.

As a measuring instrument for measuring the water content of the present invention, an automatic heating vaporized moisture measuring system AQS-724 manufactured by Hiranuma Sangyo Co., Ltd. was used.

0.5 g of the sample whose humidity has been adjusted is added to a glass 20 m.
l Weigh accurately in a sample tube and cover with Teflon-coated silicone rubber packing. At this time, in order to correct the amount of water contained in the air, two empty sample tubes covered with the same packing are prepared at the same time when the lid is covered.

The water sent from the moisture vaporizer was heated under the conditions of a heating temperature of 110 ° C. and a carrier gas (nitrogen gas) flow rate of 150 ml / min and titrated under the conditions of INTERVAL = 25 seconds and TIMER = 1 minute. The generated liquid is Hydranal Aqualite R
S, the counter electrode liquid is aqualite C.

The water content W (g / m ² ) is calculated according to the following formula.

W = [(A−B) / C] · R · ρ / 6 A: Moisture amount detected in the sample tube containing the sample (g) B: Moisture detected in two empty sample tubes Average value of amount (g) C: Sample amount (g) R: Volume average particle size of toner or carrier (m) ρ: Density of toner or carrier (g / m ³ ) <Change in water content due to environment> Sample temperature 10 ° C, relative humidity 20
%, Or the temperature is 30 ° C. and the relative humidity is 80%. Then, following the above method,
Temperature 10 ° C., the water content W _L after standing at 20% relative humidity, temperature 30
° C., determined a water content W _H after standing at 80% relative humidity, defined as the water content changes according to the difference _{(W H -W L) (g} / m 2) the environment of the present invention.

<Method for Measuring Charge Amount> The charge amount in the present invention is determined by placing a sample obtained by mixing toner and carrier in a measuring cell having a stainless steel mesh screen and using nitrogen gas to obtain an internal pressure of 0.2 kg / cm. Blow off for 6 seconds at a pressure of ² and measure the charge and mass of the scattered powder.

<Method of Measuring Carrier Particle Size> The average particle size of the carrier particles of the present invention means an average particle size on a volume basis,
It is measured by a laser diffraction particle size distribution measuring device "HELOS" (manufactured by SYMPATEC) equipped with a wet dispersion machine.

<Toner Particle Size Measuring Method> The average particle size of the toner of the present invention is the Coulter counter particle size distribution measuring device T.
It can be determined as the volume average particle diameter when using the A-II type and using an aperture of 100 μm.

<Determination of Carrier and Toner Density> The density of the carrier and toner of the present invention can be determined by measuring with a dry automatic densitometer Acupic 1330 (Micromeritics) using helium gas. In the case of the above toner, 1 to 5 g, and in the case of the above carrier, 10 to 20 g of the sample is precisely weighed and then sufficiently purged to 10 cm.
^{Put in} the sample cell of ³ and measure the density of the sample. For accurate measurement, the measurement was performed 20 times, and the average value was used as the measurement result.

Next, the toner of the present invention will be described in detail.

As the raw material of the toner used in the present invention, all known materials can be used, but the desired toner can be obtained by appropriately using a binder resin, a colorant, a magnetic substance, a charge control agent, a release agent and the like. Can be obtained.

First, as the binder resin, for example, polyester resin, styrene-alkyl acrylate resin,
Styrene-alkyl methacrylate resin, styrene-butadiene resin, styrene-acrylonitrile resin, styrene-acryl-polyester resin, styrene-acryl-
Crystalline polyester graft resin, polyurethane resin,
Epoxy resin, silicone resin, polyvinyl chloride, polyamide, polyvinyl butyral, rosin, modified rosin,
Examples thereof include phenol resin and xylene resin.

Examples of the colorant include carbon black, chrome yellow, DuPont oil red, quinoline yellow, phthalocyanine blue, and magnetic materials.

The magnetic material is a metal or alloy exhibiting ferromagnetism such as iron, cobalt and nickel including ferrite and magnetite, a compound containing these elements, or a material containing no ferromagnetic element, but is appropriately heat-treated. Examples thereof include alloys exhibiting ferromagnetism, for example, alloys called Heusler alloys containing manganese and copper such as manganese-copper-aluminum and manganese-copper-tin.

As the charge control agent, a nigrosine dye, a quaternary ammonium salt compound, an alkylpyridinium compound and an organic salt or complex containing a metal having a valence of 2 or more can be used.

Further, examples of the releasing agent include low molecular weight polyethylene having a number average molecular weight (the number average molecular weight is a polystyrene molecular weight conversion value in high temperature GPC) of 1500 to 5000, low molecular weight polypropylene, low molecular weight polyethylene- Polyolefin wax such as polypropylene copolymer, high-melting paraffin wax such as microwax and Fischer-Tropsch wax, ester wax such as fatty acid lower alcohol ester, fatty acid higher alcohol ester, and fatty acid polyhydric alcohol ester, amide wax, etc. Can be used.

In the present invention, the above-mentioned raw materials are appropriately blended, and colored particles are obtained through the steps of mixing, melting, cooling, pulverizing and classifying. Alternatively, the colored particles can be obtained by a method of dissolving and dispersing the raw materials in a solvent and polymerizing the raw materials.

Next, inorganic fine particles and, if necessary, other substances are mixed as an external additive. Examples of the inorganic fine particles used in the present invention include silica, alumina, titania, barium titanate, magnesium titanate, and the like. Examples thereof include calcium titanate, strontium titanate, zinc oxide, cerium oxide, antimony trioxide, zirconium oxide, silicon carbide and silicon nitride.
The inorganic fine particles may be hydrophobized before use, and hydrophobized silica is particularly preferable. In recent years, as a photoreceptor,
Negatively chargeable organic photoconductors are becoming mainstream, and accordingly, toners having positive chargeability are required. Therefore, the chargeability of the hydrophobic silica fine particles is also required to be positively chargeable, for example, an amino-modified silane coupling agent,
Hydrophobic silica surface-treated with amino-modified silicone oil, polysiloxane ammonium salt, organopolysiloxane and amine-modified silicone compound such as 3-aminopropyltriethoxysilane can be preferably used. Other external additives include zinc stearate, lubricants such as polyvinylidene fluoride, and fixing aids such as low molecular weight polypropylene.

The amount of the inorganic fine particles of the present invention used is preferably 0.01 to 5 parts by weight, and more preferably 0.05 to 2 parts by weight, based on the total weight of the toner.

As the carrier constituting the two-component developer of the present invention, conventionally known carriers can be used. Examples of the carrier include particles of ferromagnetic metals such as iron, nickel and cobalt, alloys containing these metals, particles of ferromagnetic metal compounds such as ferrite and magnetite, vinylidene fluoride-4 fluorinated ethylene copolymer, tetrafluoro Fluorine resin such as ethylene, 2,2,2-trifluoroethyl methacrylate, pentafluoropropyl methacrylate, silicone varnish, alkyd modified silicone varnish, epoxy modified silicone varnish, polyester modified silicone varnish,
Silicone resin such as acrylic modified silicone varnish, urethane modified silicone varnish, reactive silicone resin,
Acrylic acid and methacrylic acid alkyl alcohol,
It is preferable to use a carrier coated with a polymer or copolymer of an esterified product with a halogenated alkyl alcohol, an alkoxyalkyl alcohol, an aralkyl alcohol, an alkenyl alcohol, etc., a polymer or a copolymer of styrene and its derivative, etc. it can. The volume average particle size of the carrier is preferably in the range of 20 to 200 μm,
Particularly, the range of 30 to 150 μm is preferable.

The addition rate of the coating material to the carrier of the present invention is preferably 0.5 to 10% by weight, more preferably 1 to 5% by weight.

As means for increasing the water content change of the present invention, a highly hydrophilic inorganic compound such as magnesium oxide or hydrophilic silica is added to the carrier coating, or an ester group, a carboxyl group, an amide group or the like is added. Examples thereof include a method of adding an organic compound such as a homopolymer or a copolymer of a monomer having a hydrophilic group into the carrier coating agent.

Among the compounds that increase the water content change, magnesium oxide is preferable because it is easy to control the water content change.

As means for reducing the change in water content of the present invention, in addition to the above-mentioned fluororesins and silicone resins,
The use of an alkyl methacrylate-based material having a bulky structure of an alkyl group as a coating material for a carrier can be mentioned. The alkyl group preferably has 3 to 8 carbon atoms, and more preferably the alkyl group has a cyclic structure. Specific compounds include 2-
There are ethylhexyl methacrylate, isobutyl methacrylate, cyclopropyl methacrylate, cyclobutyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, cycloheptyl methacrylate and the like, but cyclohexyl methacrylate is particularly preferable.

The mixing ratio of the two types of carriers of the present invention having different changes in water content is determined so that an appropriate amount of charge can be obtained and the change due to the environment is small, but the carrier of the present invention with large changes in water content. The weight ratio of the carrier having a small change in water content to the carrier is preferably 10:90 to 90:10.

The charge amount of the toner of the present invention is 15 to 35 so that an appropriate image density can be obtained and the image quality is not impaired.
(Μc / g) is preferable.

The toner concentration of the present invention is preferably 2 to 10 parts by weight, more preferably 3 to 8 parts by weight, based on 100 parts by weight of the entire developer. The toner particle diameter of the present invention is preferably 5 to 15 μm.

[0047]

The present invention will be described in detail below with reference to examples, but the embodiments of the present invention are not limited thereto.

An example of producing the toner and carrier used in this example is shown below.

<Preparation Example 1 of Toner> Copolymer of styrene / n-butyl acrylate / methyl methacrylate (weight ratio = 70/20/10) 100 parts by weight Carbon black 12 parts by weight Polypropylene (number average molecular weight 4000) 2 parts by weight Parts 2 parts by weight of ethylenebisstearic acid amide The above components were mixed, melted, kneaded, crushed and classified to obtain colored particles having a volume average particle diameter of 8.5 μm. Further, 1.0 part by weight of negatively-charged silica hydrophobized with hexamethyldisilazane was added to 100 parts by weight of the colored particles to obtain a toner 1.

Preparation Example 2 of Toner Polycondensation reaction of 275 parts by weight of terephthalic acid and 110 parts by weight of trimellitic acid as carboxylic acid components, and 50 parts by weight of ethylene glycol and 135 parts by weight of neopentyl glycol as diol components. 100 parts by weight of the obtained polyester resin, 9 parts by weight of carbon black, 3 parts by weight of carnauba wax and 3 parts by weight of ethylenebisstearic acid amide were mixed, melted, kneaded, pulverized, classified and externally added in the same manner as in Example 1. The toner 2 having a volume average particle diameter of 8.5 μm was obtained by the treatment. For the external addition treatment, negatively charged silica hydrophobized with octyltrimethoxysilane was used at a ratio of 0.6 parts by weight to 100 parts by weight of the colored particles.

<Toner Preparation Example 3> 155 parts by weight of terephthalic acid, 30 parts by weight of succinic acid and 27 parts by weight of trimellitic acid as polyvalent carboxylic acid components, and 280 parts by weight of bisphenol A propylene oxide and bisphenol A ethylene as diol components. 100 parts by weight of a polyester resin obtained by polycondensation reaction with 120 parts by weight of oxide, 9 parts by weight of carbon black, 3 parts by weight of carnauba wax, and 3 parts by weight of ethylenebisstearic acid amide were mixed and melted in the same manner as in Example 1. Then, kneading, pulverization, classification and external addition were performed to obtain a toner 3 having a volume average particle diameter of 8.5 μm. For the external addition treatment, negatively charged silica hydrophobized with octyltrimethoxysilane was used at a ratio of 0.4 parts by weight to 100 parts by weight of the colored particles.

Preparation Example 4 of Toner Styrene-2-ethylhexyl acrylate-dimethylaminoethyl methacrylate copolymer (molar ratio = 80/15/5) 100 parts by weight Monoazo red pigment 4 parts by weight Polypropylene 6 parts by weight The above components Were mixed, melted, kneaded, pulverized, and classified to obtain colored particles having a volume average particle diameter of 7.5 μm. To 100 parts by weight of the colored particles, 1.0 part by weight of positively charged silica whose surface was treated with an amino-modified silane coupling agent was added to obtain a red toner.

<Production Example 1 of Carrier> Styrene / cyclohexyl methacrylate (molar ratio = 1/9) copolymer 2.2 parts by weight Core material particles (spherical ferrite particles) 100 parts by weight Put it in the mold mixer,
After mixing and stirring at 30 ° C. for 5 minutes under the condition that the peripheral speed of the horizontal rotor was 8 m / s, the mixture was heated to 100 ° C. and stirred for 20 minutes to produce a resin-coated carrier having an average particle diameter of 62 μm. This is carrier 1.

<Preparation Example 2 of Carrier> Styrene / methyl methacrylate (molar ratio = 4/6) copolymer 1.8 parts by weight Magnesium oxide 0.2 parts by weight Core material particles (spherical ferrite particles) 100 parts by weight A carrier 2 having an average particle diameter of 62 μm was produced in the same manner as the carrier 1 in the compounding ratio.

<Preparation Example 3 of Carrier> Copolymer of methyl methacrylate / cyclohexyl methacrylate (molar ratio = 5/5) 1.9 parts by weight Core material particles (spherical magnetite particles) 100 parts by weight Carrier in the above mixing ratio A carrier 3 having an average particle size of 62 μm was manufactured in the same manner as in 1.

<Preparation Example 4 of Carrier> Copolymer of styrene / methyl methacrylate (molar ratio = 4/6) 0.6 part by weight Magnesium oxide 0.4 part by weight Hydrophilic silica 1.0 part by weight Core material particles (spherical magnetite particles) 100 By weight The carrier 4 having an average particle size of 62 μm was produced by the same method as that for the carrier 1 with the above compounding ratio.

Preparation Example 5 of Carrier Silicone varnish 100 parts by weight Toluene 100 parts by weight Ferrite 1000 parts by weight was mixed with the resin solution prepared in the above mixing ratio, and then dried in an atmosphere at 90 ° C. 20
The silicone resin was baked by leaving it in an electric furnace at 0 ° C. for 30 minutes to prepare a carrier 5 having an average particle size of 52 μm.

<Production Example 6 of Carrier> Copolymer of styrene / methyl methacrylate (molar ratio = 2/8) 0.4 parts by weight Magnesium oxide 0.6 parts by weight Hydrophilic silica 1.0 parts by weight Core material particles (spherical magnetite particles) 100 By weight In the same manner as for the carrier 1, the carrier 6 having an average particle diameter of 62 μm was produced with the above-mentioned compounding ratio.

<Production Example 7 of Carrier> Styrene-2-ethylhexyl acrylate (molar ratio = 50:50) / vinylidene fluoride-tetrafluoroethylene (molar = ratio 75:25)
Is 40/60 weight ratio of toluene-MEK (weight ratio 1: 1) 20
% Solution and spherical ferrite are coated by a spray method using a fluidized bed at a mixing ratio such that the solid content of the coating agent / ferrite is 3/100 weight ratio, and the carrier 7 having an average particle diameter of 72 μm is used. Got

<Preparation Example 8 of Carrier> Methyl methacrylate / cyclohexyl methacrylate (molar ratio = 7/3) copolymer 2.0 parts by weight Core material particles (spherical ferrite particles) 100 parts by weight By the same method as the carrier 1,
A carrier 8 having an average particle size of 62 μm was manufactured.

<Preparation Example 9 of Carrier> Methyl methacrylate / butyl methacrylate (molar ratio = 9/1) copolymer 2.5 parts by weight Core material particles (spherical ferrite particles) 100 parts by weight Carriers having the above compounding ratio A carrier 9 having an average particle size of 62 μm was manufactured by the same method as in 1.

<Preparation Example 10 of Carrier> Copolymer of styrene / butyl acrylate (molar ratio = 8/2) 1.9 parts by weight Core material particles (spherical ferrite particles) 100 parts by weight Carrier 1 with the above compounding ratio A carrier 10 having an average particle diameter of 62 μm was manufactured by the same method as described above.

Table 1 shows the change in water content depending on the environment of the toner and carrier prepared as described above. In addition, Table 1
The values shown in ( ² ) are shown as the values for both water content and change in water content (× 10 ² ).

[0064]

[Table 1]

Example 1 Toner 1 prepared as described above
5 parts by weight, 30 parts by weight of carrier 1 and 2 parts of carrier
65 parts by weight were mixed to obtain a developer 1.

This developer has a temperature of 10 ° C. and a relative humidity of 20.
% Environment, the temperature was 30 ° C., and the relative humidity was 80%. In addition, the above two-component developer at a temperature of 30
Electrophotographic copying machine "U-" that has a mechanism to collect and recycle the residual toner after transfer at 80 ° C and 80% relative humidity
"Bix5070" (manufactured by Konica Corporation) was used to carry out an actual shooting test to evaluate the image density of the copied image, the background fog, and the trailing edge blur.

-Evaluation Method and Evaluation Criteria- (Image Density) As the image density, the density of a copy image having a document density of 1.42 was measured using a Macbeth densitometer. A document density of 1.42 is an acceptable level above 1.3.

(Background fog) For the background fog, the relative density of the white background portion of the copied image to new paper was measured. When the density corresponding to background fog is 0.010 or less, there is no practical problem.

(Blur at the rear end) The blur at the rear end has a density of 0.
7. A document with a size of 20 mm x 20 mm was copied, and the degree of blurring of the edge on the side where the paper is subsequently discharged was visually determined. The case where there is a faint mark is ○, and the case where there is no blur is ×.

A durability test was conducted on 100,000 sheets of this developer 1, and good images were obtained as in the initial stage.

Example 2 6 parts by weight of toner 2, 50 parts by weight of carrier 3, and 44 parts by weight of carrier 4 were mixed to prepare developer 2, and the same evaluation as in example 1 was carried out. It was Further, a durability test of 100,000 sheets was conducted for this developer 2, and a good image was obtained as in the initial stage.

Example 3 6 parts by weight of toner 3, 38 parts by weight of carrier 5, and 56 parts by weight of carrier 6 were mixed to prepare developer 3, and the same evaluation as in example 1 was carried out. It was The charge amount of this developer was measured in an environment of a temperature of 10 ° C. and a relative humidity of 20% and in an environment of a temperature of 30 ° C. and a relative humidity of 80%. In addition, the above two-component developer, temperature 30 ℃, relative humidity
In an 80% environment, "U-Bix5070" (manufactured by Konica Corporation) was used for a real-life test, and the same evaluation as in Example 1 was performed for the image density of the copied image, background fog, and trailing edge blur. Further, a durability test was conducted on 100,000 sheets of this developer 3, and a good image was obtained as in the initial stage except that the developer spilled from the developing device (due to insufficient fluidity of the developer). Was obtained.

Example 4 A developer 4 was prepared by mixing 6 parts by weight of the toner 4, 75 parts by weight of the carrier 7, and 19 parts by weight of the carrier 8.

This developer has a temperature of 10 ° C. and a relative humidity of 20.
% Environment, the temperature was 30 ° C., and the relative humidity was 80%. Further, this developer 4 was electrophotographic copying machine "U-Bix" under the environment of temperature 30 ° C. and relative humidity 80%.
1012 "(manufactured by Konica Corp.) was used to perform a live-copy test, and the same evaluation as in Example 1 was performed for the image density, background fog, and trailing edge blur of the copied image. Further, a durability test was conducted on 100,000 sheets of this developer 4, and a good image was obtained as in the initial stage.

<Example 5> 5 parts by weight of toner 2, 45 parts by weight of carrier 1 and 50 parts by weight of carrier 3 were mixed to prepare a developer 5, and the same evaluation as in example 3 was carried out. It was

<Example 6> 5 parts by weight of toner 1, 38 parts by weight of carrier 2, and 57 parts by weight of carrier 9 were mixed to prepare developer 6, and the same evaluation as in example 3 was carried out. It was

Example 7 6 parts by weight of Toner 1 and 94 parts by weight of Carrier 10 were mixed to prepare Developer 7, and the same evaluation as in Example 3 was carried out.

The results are shown in Table 2 below.

[0079]

[Table 2]

As is clear from Table 2, the present invention uses two types of carriers having different changes in water content due to environmental changes, so that the environmental dependence of the charge amount is small, the image density is high, and the fog density is low. Thus, a good electrophotographic developer can be obtained without causing image defects such as blurring of the trailing edge of the image area. On the other hand, the comparative example has a large environmental dependency of the charge amount as compared with the present invention, and therefore, the image density is lowered in a high temperature and high humidity environment, the fog density is high, and the image defect such as the blurring of the trailing edge of the image portion is caused. Is generated, which means that it is not suitable for practical use.

[0081]

EFFECTS OF THE INVENTION According to the present invention, there is no reduction in charge amount even under environmental changes, and while high image density and low fog density are achieved, electrophotography which suppresses the occurrence of image defects such as blurring at the trailing edge of the image area. A developer for use can be provided.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masafumi Uchida 2970 Ishikawa-cho, Hachioji-shi, Tokyo Konica Stock Company

Claims (3)

[Claims] 1. An electrophotographic developer comprising at least a toner and a carrier, wherein the carrier comprises two types of carriers having different water content changes due to environmental changes.
Among the types of carriers, the water content change of carrier A whose water content change is relatively small due to environmental change and the water content change of carrier B whose water content change is relatively large are respectively W _A (g / m ² ), W
_A developer for electrophotography, wherein W _A <W _t <W _B is established, where _B (g / m ² ) and the change in water content of the toner are W _t (g / m ² ). 2. | (W _B −W _t ) − (W _t −W _A ) | ≦ 0.10
The electrophotographic developer according to claim 1, wherein 3. a _{^{0.05 × 10 -2 ≦ W t -W}} A ≦ 2.0 × 10 -2, and in claim 1, characterized in that a _{^{0.2 × 10 -2 ≦ W B -W}} t ≦ 0.10 The described electrophotographic developer.