CA2052571A1 - Electrophotographic toner - Google Patents

Abstract

Abstract The electrophotographic toner in accordance with the present invention comprises a binder resin, a coloring agent, an electric charge controlling agent and a release agent, said electric charge controlling agent being represented by the following general for-mula (1):

Description

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20~257~

Title of the Invention Electrophtographic Toner Backqround of the Invention The present invention relates to an electropho-tographic toner, and more particularly to an electro-photographic toner to be used for an image forming apparatus such as an electrostatic copying apparatus, a laser printer or the like.
In the image forminy apparatus above-mentioned, an electrostatic latent image formed on the surface of a photoreceptor by exposure to light is let come in contact with an electroph~tographic developer by a developping device. Toner in the electrophotographic developer is electrostatically sticked to the electro-static latent image. This causes the electrostatic latent image to be turned into a toner image. Then, the toner image is transferred to paper from the sur-face of the photoreceptor and fixed on the paper, thus achieving image forming.
As an electrophotographic toner, there may be generally used toner particles containing a binder resin, a coloring agent such as carbon black or the like, an electric charge controlling agent, a release agent, a flowability imparting agent as necessary and Z05~57~

the like. As the electric charge controlling agent, there is generally used an azo-type metal complex salt dye (azo-type chromium dye or the like).
To improve the flowability of the toner parti-cles, silica fine powder, particularly hydrophobicsilica fine powder, is generally mixed with and dis-persed in the toner particles.
However, such a conventional electrophotographic toner presents the problems that the electric charge characteristics are not stabilized to provoke fog, decrease in image density, toner scattering or a so-called letter dispersion, i.e., spots as formed by the toner scattering around reproduced letters, so that stable images cannot be obtained. In particular, when a black toner containing carbon black as a coloring agent is used, the problems above-mentioned are re-markable.

Summary of the Invention It is an object of the present invention to pro-vide an electrophotographic toner with which there can be obtained stable images free from fog, decrease in image density, letter dispersion, toner scattering and the like.
To achieve the object above-mentioned, the in-"'''''``' ~' ' "" ' ` ' -: - ......

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ventors have studied hard and paid their attention to the pH value of an azo-type metal complex salt dye used as the electric charge controlling agent. The inventors have found the novel fact that the electric charge characteristics and humidity resistance of a toner and dispersibility of the electric charge con-trolling agent in the resin vary with this pH value to cause a variety of problems such as defective image (insufficient image density, fog and the like), toner scattering and the like.
The electrophotographic toner in accordance with the present invention contains, as the electric charge controlling agent, a compound represented by the fol-lowing general formula (1) and presenting a pN value in a range from 3 to 5:

~ _ ~ ~ R ~ N= N $~
O~ ~0 ~ ( 1) /Y\ Z

~ ~R~' 20S~571 [wherein Rl, R2, R3 and R4 may be the same as or dif-ferent from one another, and each is a hydrogen atom, a halogen atom or the following group:

- S O 2 ~ ~

(wherein R5 and R6 may be the same as or different from one another, and each is an alkyl or aryl group), and R , R2, R3 and R4 should not be simultaneously a hydrogen atom; Y is a Cr, Fe, Co, Zn or Ti atom; Z is a cation selected from the group consisting of an ammonium ion, a hydrogen ion, a potassium ion and a~
sodium ion.]
For a toner containing carbon black as the co-loring agent, it is preferable to use carbon black of which pH value is in a range from 6 to 11, in addition to the use of the electric charge controlling agent having a pH in the range mentioned earlier.
When hydrophobic silica fine powder is mixed with and dispersed in toner particles containing, as the electric charge controlling agent, the compound (1) having a pH value in a range from 3 to 5, the pH
value of the hydrophobic silica is preferably in a .
.

- ' 20~;~57~

range from 3.5 to 4.5.
The pH value above-mentioned may be measured in accordance with the method set forth in JIS K 6221.
More specifically, 10 g of a sample is added to 100 ml S of distilled water. The sample-water mixture is then boiled for 15 minutes and cooled to a room tempera-ture, after which pH value is measured.

Detailed nescription of the Present Invention Since the compound of the general formula (1) presents a pH value in a range from 3 to 5, it can be uniformly dispersed, as the electric charge control-ling agent, in the binder resin of the toner. Accord-ingly, the electrophotographic toner in accordance with the present invention can be stabilized in elec-tric charge characteristics.
If the pH value of the compound (1) is less than 3, the toner is lowered in humidity resistance. If the pH value is greater than 5, the dispersibility of the compound (1) in the binder resin is defective. In both cases above-mentioned, there are caused the problems such as decrease in image density, letter disperslon, toner scattering and the like.
The pH value of the compound of the general for-mula (11 is greatly influenced by the polar group con-.. . . ........... . . . . .

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nected to this compound. When the polar group is anelectron attractive group (e.g., a halogen atom), the pH value is liable to decrease. It is therefore re-quired to select the respective groups such that the pH value is located in the range above-mentioned.
Table 1 shows the relationship between the combination of the substituting groups and the pH value. It is however noted that the pH value varies with a trace amount of a by-product included in the course of pro-duction of the compound (1) or with the presence ofunreacted substances, and is therefore not a definite value.
Table 1 Rl R2 R3 R pH

Cl H H Cl Cr H _3.1 - 4.9 H H *1 Cl Fe H 3.6 - 4.9 H *2 H Cl Co Na 4.1 - 4.9 *3 H H Cl Ni R _ 4.2 - 4.9 *1 -SO2N(CH3)2 *2 -SO2N(C2H5]2 *3 -SO2N~C5Hll)2 -:

2 C)5;~57~

When there is used, as the coloring agent, car-bon black of which pH value is less than 6, the humi-dity resistance of the toner is not sufficient. When there is used, as the coloring agent, carhon black of which pH value is greater than 11, the dispersibility of the compound (1) and the carbon black in the binder resin is lowered. In both cases above-mentioned, there are caused the problems of fog, decrease in image den-sity, letter dispersion, toner scatterin~ and the like.
When hydrophobic silica finé powder is to be mixed with and dispersed in toner particles contain-ing, as the electric charge controlling agent, the compound tl) of which pH value is in a range from 3 to lS 5, it is preferable to use hydrophobic silica fine powder of which pH value is in a range from 3.5 to 4.5. In this case, the electric charge characteristics are stabilized to produce stable images. More speci-fically, if the pH values of the compound of the gen-eral formula (1) and the hydrophobic silica fine pow-der are below the ranges above-mentioned, the amount of negative electric charge becomes great, causing the toner to be separated from the carrier with difficul-ty. This provokes the problem of decrease in image .: ~

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density. If both pH values exceed the ranges above-mentioned, the amount of negative electric charge be-comes small, causing the toner to be insufficiently sticked to the carrier. This provokes the problem of toner scattering, fog or the like.
Examples of the halogen atom include a fluorine atom, a chloride atom, a bromine atom and an iodine atom.
Examples of the alkyl group include methyl, eth-yl, propyl, isopropyl, butyl, t-butyl, pentyl and hexyl groups, each having 1 to 6 carbon atoms.
Examples of the aryl group include phenyl, tol-yl, xylyl, biphenyl, naphthyl, antolyl and phenantolyl groups.
lS As the electric charge controlling agent, the compound (1) is used in an amount from 0.5 to 8 parts by weight, preferably from 1 to 3 parts by weight, for 100 parts by weight of binder resin. If the blending ratio of the compound (1) is smaller than the range above-mentioned, the electric charge characteristics become unstable. If the blending ratio of the compound (1) is greater than the range above-mentioned, the carrier is sticked to the toner, thereby to provoke toner scattering, fog and the like.
The toner is produced by a method of mixing a -2~5~57~

binder resin, a coloring agent, the compound tl) as an electric charge controlling aqent, a release agent (an off-set preventive agent) and an additive such as a flowability imparting agent or the like to be used as necessary, and pulverizing the mixture into particles having a predetermined particle size. More specific-ally, the toner is produced by previously mixing and kneading the components above-mentioned uniformly with the use of a dry blender, a Henschel mixer, a ball mill or the like, uniformly melting and kneading the resultant mixture with the use of a kneading device such as a Banbury mixer, a roll, a single- or double-shaft extruding kneader or the like, cooling and grinding the resultant kneaded body, and classifying the resultant ground pieces as necessary. The toner may also be produced by suspension polymerization or the like.
Examples of the binder resin include styrene resins (monopolymers and copolymers containing styrene or a styrene substituent) such as polystyrene, chloro-polystyrene, poly-~-methylstyrene, a styrene-chloro-styrene copolymer, a styrene-propylene copolymer, a styrene-butadiene copolymer, a styrene-vinyl chloride copolymer, a styrene-vinyl acetate copolymer, a sty-rene-maleic acid copolymer, a styrene-acrylate copoly-2C)5;~57~

mer (a styrene-methyl acrylate copolymer, a styrene-ethyl acrylate copolymer, a styrene-butyl acrylate copolymer, a styrene-octyl acrylate copolymer, a sty-rene-phenyl acrylate copolymer or the like), a sty-S rene-methacrylate copolymer (a styrene-methyl meth-acrylate copolymer, a styrene-ethyl methacrylate co-polymer, a styrene-butyl methacrylate copolymer, a styrene-phenyl methacrylate copolymer or the like), a styrene-~-methyl chloroacrylate copolymer, a styrene-acrylonitrile-acrylate copolymer and the like. Exam-ples of the binder resin further include polyvinyl chloride, low-molecular-weight polyethylene, low-mole-cular-weight polypropylene, an ethylene-ethyl acrylate copolymer, polyvinyl butyral, an ethylene-vinyl ace~-tate copolymer, rosin modified maleic acid resin,phenyl resin, epoxy resin, polyester resin, ionomer resin, polyurethane resin, silicone resin, ketone res-in, xylene resin, polyamid resin and the like. The examples above-mentioned may be used alone or in com-bination of plural types. In the examples above-men-tioned, there may be preferably used styrene resin, particularly a styrene-(meth)acxylate copolymer and more particularly a styrene-methyl methacrylate-butyl-acrylate copolymer. In particular, there may be pre-ferably used a styrene-methyl methacrylate-butylacryl-~ ' ` ~ ' ' .
-: '' 2~)5~57~

ate copolymer containing 75 to 85 % by weight of sty-rene, 0.5 to S % by weight of methylmethacrylate and 10 to 20 ~ by weight of butylacrylate.
Examples of the coloring agent include: a black coloring agent such as carbon black (furnace black, channel black, thermal, gas black, oil black, acetyl-ene black), lamp black, aniline black or the likei a brown coloring agent as obtained by mixing red, yellow and black coloring agents. Of these, the black color-ing agent may be particularly suitably used. Thecoloring agent may be used in an amount of 1 to 20 parts by weight and preferably 3 to lS parts by weight for 100 parts by weights of the binder resin.
Examples of the release agent (off-set prevent-ing agent) include aliphatic hydrocarbon, aliphaticmetal salts, higher fatty acids, fatty esters, its partially saponified substances, silicone oil, a vari-ety of waxes and the like. Of these, there is pre-ferably used a low-molecular-weight aliphatic hydro-carbon of which weight average molecular weight isfrom about 1,000 to about 10,000. More specifically, there is suitably used one or a combination of plural types of a low-molecular-weight polypropylene, low-molecular-weight polyethylene, paraffin wax, a low-molecular-weight olefin polymer composed of an ~:~5~571 olefin unit having 4 or more carbon atoms and the like. The release agent may be used in an amount of 0.1 to 10 parts by weight and preferably from 1 to 5 parts by weight for 100 parts by weight of the binder S resin.
As conventionally done, the toner particles may have sizes in a range from 3 to 35 ~m and preferably from 5 to 25 ~m, but it is preferable that the distri-bution of toner particle sizes satisfies the following formula:
N < -172.7C + 1.45 [wherein N is the percentage by the number of toner particles of which sizes as measured with a coulter counter exceed 16 ~m, and C is surface dye density (g/g) of the toner particles]
When the distribution of toner particle sizes is in the range above-mentioned, it is possible, in view of the relationship with the surface dye density, to further eliminate variations in electric charging characteristics of the toner.
To obtain toner particles presenting a distri-bution of particle sizes which satisfies the formula above-mentioned, the ground toner particles may be classified to remove particles having sizes greater than 16 ~m, or toner particles may be ground such that 2~15~57~

the peak of the toner particle-size distribution is shifted to a smaller-size zone to reduce the content of particles having sizes greater than 16 ~m.
According to the present invention, as the hy-drophobic silica fine powder to be mixed with and dis-persed in the toner particles, there may be used sili-ca fine powder of which surface is treated with, for example, a (poly)alkyl group, a (poly)alkylsilil group, a (poly)alkylsilane or silicone oil. Prefer-ably, there may be used silica fine powder of whichsurface has been treated with a compound having a pol-ymethylsilil group such that the powder becomes hydro-phobic. Such powder i8 higher in hydrophobic nature than conventional silica fine powder treated with a compound having a low-molecular-weight alkyl group.
As a commercially available product of such si-lica fine powder, there may be mentioned "Cabosil TS720" manufactured by Cabot Co., Ltd. This product is hydrophobic fumed silica fine powder, which is obtain-ed by treating high-purity fumed silica fine powder (99.8~ SiO2) with an organic silicone compound, and on the surface of which a polymethylsilil group is pre-sent to increase the hydrophobic nature of the surface of the silica fine powder.
The particle sizes of the silica fine powder so .... .. . . . :

2C~5~5~

treated as to be hydrophobic are suitably in a range from 0.01 to 0.04 ~m.
The pH value of the hydrophobic silica fine pow-der varies with a variety of factors wl~ich are not always clarified. However, it is known that the sur-face functional group is influenced by reaction by-products.
The hydrophobic silica fine powder may be added in an amount of 0.01 to S % by weight and preferably from 0.05 to 1 % by weight for the total amount of toner. If the amount of the hydrophobic silica fine powder is greater than the range above-mentioned, the amount of electric charge is excessive. If this amount is smaller than the range above-mentioned, the effect of improving the toner flowability cannot be expected.

Examples The following description will discuss in more detail the electrophotographic toner in accordance with the present invention with reference to Examples and Comparative Examples.
Examples 1 to 9 and Comparative Examples 1 to 8 , 2~5~S71 (Component) (% by Weight) Styrene-acrylic copolymer 86 Carbon black 10 Off-set preventive agent 2 (Low-molecular-weight polypropylene~
Charge controlling agent (Compound (1)) 1.5 Hydrophobic silica 0.5 The component_ above-mentioned were mixed. The mixture was molten and kneaded with a double-shaft kneader, and then cooled, ground and classified to prepare toner particles having the average particle size of 10 ~m. Table 2 shows the substituting groups contained in the compounds (1) used, as the electric charge controlling agent, in Examples 1 to 9 and Com-parative Examples 1 to 8. Table 3 shows the pH values of carbon black and the compounds (1) used. Each pH
value was measured in the manner that 10 g of a sample was added to 100 ml of distilled water and the sam-ple-water mixture was then boiled for 15 minutes on a hot plate and cooled to a room temperature, after which pH value was measured with a glass electrode pH
meter. The pH value of the hydrophobic silica fine powder used was 4.1.
The moisture contents of the resultant electro-photographic toners thus obtained were measured under , . . . . , .. . ... . . . . . . -205~57~

the cGndition of ambient temperature/ambient humidity (temperature : 20C, humidity : 65%, hereinafter referred to as N/N) and under the condition of high temperature/high humidity ~temperature : 35C, humidi-ty : 85~, hereinafter referred to as H/H), respective-ly, according to the Karl Fischer method. Table 3 shows the results.
The following evaluation tests were conducted on the electrophotographic toners obtained in Example 1 to 9 and Comparative Examples 1 to 8. Table 3 shows the test results.

(1) Test of Dispersibility The circumference of each of the electrophoto-graphic toners was covered with and solidified by epo-xy resin. Each of the toners as cut with a microtome was observed with a transmission-type electro micro-scope. The toner dispersibility was evaluated accord-ing to the following cr teria:
O : Extremely finely dispersed O : Substantially finely dispersed ~ : Some large particles observed X : Many large particles observed (2) Test of Image Density Each of the electrophotographic toners was mixed Z~5~57~

with a carrier to prepare a developer having a toner density of 3%. With an electrophotographic copying apparatus ~DC-7085 manufactured by Mita Industrial Co~, Ltd.) using (i) each developer above-mentioned as a start developer and (ii) the same toner as that con-tained in the start developer as a resupply toner, a solid-black document was continuously copied for 150,000 pieces under the condition of ambient tempera-ture/ambient humidity (N/N), i.e., temperature of 20C
and humidity of 65~, except that intermediate 8000 copied pieces from 16001st piece to 24000th piece were taken at temperature of 35C and humidity of 85%
(H/H). Every thousandth copied pieces were extracted, as samples, from 150,000 copied pieces for each of the developers and were measured as to the density values thereof with a reflection densitometer (TC-6D manufac-tured by Tokyo Denshoku Co., Ltd.). The averages were calculated for these samples for all the developers.

(3) Test of Fog Density With the use of the reflection densitometer above-mentioned, the density of the blank spaces of each sample obtained in Test of Image Density was measured to measure fo~ density. The averages were calculated for the samples for all the developers.

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(4) Test of Letter Dispersion All the samples obtained in Test of Image Densi-ty were visually checked for a so-called letter dis-persion of toner spots.

(5) Test of Toner Scattering For each developer, there were checked (i) the blank spaces of the reproduced image of the 150,000th piece, and (ii) the inside of the copying apparatus after 150,000 copies had been taken. The toner dis-persibility was evaluated according to the following criteria:

~pparatus Reproduced Inside Image O : No toner scattering No toner scattering observed observed O : Some toner scattering "
observed : Toner scattering Sporadic ~oner scat-observed tering observed X : Many toner scattering Continuous toner scat-observed tering observed 2QS257~

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Table 3 ( 3J3 ) __ Fog Density Letter Toner Total Disper- Scatter- Evalua-N/N H/H sion inq tion .
Example 1 0.002 0.004 None O
-Example 2 0.003 0.004 None 0 Example 3 0.001 0.003 None ~ 0 Example 4 0.001 0.002 None O 0 Example 5 0.003 0.004 Little O O
-Example 6 0.002 0.004 Little O O
_ Example 7 0.001 0.003 None O
Example 8 _0.003 0.004 Little O O
Example 9 0.002 0.003 Little O _ O
Comp. Ex.l 0.011 0.019 Sporadic X X
Comp. Ex.2 0.012 0.017 Sporadic ~ X
Comp. Ex.3 0.014 0.022 Contiuous X_ X
Comp. Ex.4 0.016 0.026 Continuous X X
Comp. Ex.5 0.013 0.023 Sporadic ~ X
Comp. Ex.6 0.012 0.022 Sporadic X X_ Comp. Ex.7 0.014 0.021 Sporadic ~ X
Comp. Ex.8 0.011 0.023 Sporadic ~ X
"Comp. Ex." means "Comparative Example".

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It is understood from Table 3 that each of the electrophotographic toners of Examples 1 to 9 contain-ing, as the electric charge controlling agent, the compound (1) presenting a pH value in a range from 3 S to 5, is superior in dispersibility to the electropho-tographic toners of Comparative Examples 1 to 8 con-taining a compound presenting a pH value which devi-ates from the range above-mentioned. Further, each of the toners of Examples l to 9 presents less variations of moisture content under both conditions of ambient temperature/ambient humidity (N/N) and high tempera-ture/high humidity (H/H), and is therefore excellent in humidity resistance.
It is also understood that the reproduced images obtained with the use of the electrophotographic toners of Examples 1 to 9 are superior in any of image density, fog density, letter dispersion and toner scattering to the reproduced images obtained with the use of the electrophotographic toners of Comparative Examples 1 to 8.
It is also understood that variations between reproduced images obtained under the ambient tempera-ture/ambient humidity (N/N) condition and reproduced images obtained under the high temperature/high humi-dity (H/H) condition both with the use of each of the ,' ' ' .
.

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electrophotographic toners of Examples 1 to 9, are less than variations between reproduced images ob-tained under the ambient temperature/ambient humidity (N/N) condition and reproduced i~ages obtained under the high temperature/high humidity (H/H) condition both with the use of each of the electrophotographic toners of Comparative Examples 1 to 8. Thus, stable reproduced images can be obtained with the toners of Examples 1 to 9.
It is also understood that, out of the electro-photographic toners of Examples 1 to 9, the toners of Examples 1 to 4 and 7 using carbon black presenting a pH value in a range from 6 to 11 are particularly excellent.

Examples 10 (Component)(% by Weight) Styrene-acrylic copolymer 85 Carbon black 10 Off-set preventive agent 3 (Low-molecular-weight polypropylene) Chromium-containing azo dye (pH 4.9) 2 The components above-mentioned were molten and kneaded with a double-shaft kneader, and then prepared as toner particles having the averag~ toner particle 20S;;~57~

size of 10 ~m with a jetmil. Table 4 shows the groups contained in the chromium-containing azo dye used as the electric charge controlling agent. The pH value of the carbon black was 8.5.
Silica fine powder so treated as to be hydropho-bic (particle size of 0.02 ~m, pH of 3.7, Cabosil TS-720 manufactured by Cabot Co., Ltd.) was mixed with and dispersed in the toner particles thus prepared in an amount of 0.5 % by weight for the total amount of the toner particles, thus preparing a toner.
Examples 11 to 13 and Comparative Examples 9 to 16 Toners were prepared in the same manner as in Example 10 except that there were used (i) metal-con-taining azo dyes which respectively contained groups shown in Table 4 and of which pH values are shown in Table 6 and (ii) hydrophobic silica fine powders of which pH values are shown in Table 6.

2~5~57~

Table 4 5~ Groups of Compound ~1) Rl R2 R3 R4 Y Z+
Examples 10 Cl H H Cl Cr H
Examples 11 Cl H H Cl Cr H
Examples 12 Cl H H Cl Cr H+
Examples 13 Cl H H Cl Cr H
Comparative Examples 9 Cl H H Cl Cr NH4 Comparative +
Examples 10 Cl Cl Cl H Fe Na Comparative +
Examples 11 H Cl Cl Cl Co Comparative +
Examples 12 H H Br H Zn NH4 Comparative +
Examples 13 H Cl Br H Co H
Comparative +
Examples 14 Cl H Cl Cl Zn K
Comparative Examples 15 Cl H H Cl Cr Comparative +
Examples 16 Cl H H Cl Cr H

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Evaluation Tests Ferrite carrier having the average particle size of 80 ~m was blended with each of the toners of ~xam-ples 10 to 13 and Comparative Examples 9 to 16. Each mixture was uniformly mixed and agitated to prepare a two-component developer presenting toner density of 4~. With the use of an electrophotographic copying apparatus (DC-3255 manufactured by Mita Industrial Co., Ltd.) using each of the developers thus prepared, an original document was copied ~otally 80,000 pieces under different operating conditions under which a predetermined number of copied pieces were respective-ly taken. All the copied pieces were checked for image density, fog density, amount of electric charge and toner scattering for each of the operating conditions.
More specifically, the copying operation was carried out with the operating condition changed in the order shown in Table 5 for a predetermined number of pieces, and the reproduced images were checked for the items above-mentioned. It is however noted that the measured values of the images reproduced under the N/N condi-tion were those obtained after 80,000 pieces were copied.

21D5;~571 Table S
.
Copying Mark OperatingNumber of Order ConditionCopied Pieces 1 N/N Ambient Temp. & 8,000 Ambient Humidity ~20C & 65%~
2 L/L Low Temp. & 8,000 Low Humidity (10C & 45%) 3 H/H High Temp. &8,000 High Humidity (35C & 85%) _ _ 4 N/N Ambient Temp. & 56,000 Ambient Humidity (20C & 65%) The respective tests were conducted in the fol-lowing manners.
(1) Measurement of Image Density (I.D.) Each image density was measured with the use of ~;' a reflection densitometer (TC-6D manufactured by Tokyo Denshoku Co., Ltd.) ~2) Measurement of Fog Density (F.D.) With the use of the reflection densitometer above-mentioned, the density of blank portions of each reproduced image was measured and defined as fog den-sity.
(3) Amount of Electric Charge The amount of electric charge was measured with .~

.. . . . . .. . ... . ..... . . . . ........ . . . . .

, 2~S;~:57~.

a blow-off electric charge measuring instrument manu-factured by Toshiba Chemical Co., Ltd.
(4) Toner Scattering The inside of the copying apparatus and the sur-face of each reproduced image were visually checked for toner scattering, and evaluated according to the following criteria:

Apparatus Reproduced Inside Image O : Substantially no toner No toner scattering scattering observed observed O : Slight toner scattering "
observed : Some toner scattering "
observed : Toner scattering Toner scattering observed observed X : Many toner scattering Toner blanking observed observed The test results are shown in Table 6.

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:

' - ' ' ' Z~5~i7~

It is apparent from Table 6 that, by adjusting the pH values of the hydrophobic silica fine powder and the electric charge controlling agent within re-spective predetermined ranges, the electric charge characteristics can be stabilized to remarkably im-prove the image density and toner scattering.

.

Claims (7)

1. An electrophotographic toner comprising a binder resin, a coloring agent, an electric charge controlling agent and a release agent, said electric charge controlling agent being represented by the fol-lowing general formula (1):
(1) [wherein R1, R2, R3 and R4 may be the same as or dif-ferent from one another, and each is a hydrogen atom, a halogen atom or the following group:
(wherein R5 and R6 may be the same as or different from one another, and each is an alkyl or aryl group), R1, R2, R3 and R4 should not be simultaneously a hy-drogen atom; Y is a Cr, Fe, Co, Zn or Ti atom; Z+ is a cation selected from the group consisting of an am-monium ion, a hydrogen ion, a potassium ion and a sodium ion.], said electric charge controlling agent being a compound of which pH value is in a range from 3 to 5.

2. An electrophotographic toner according to Claim 1, wherein the compound of the general formula (1) is contained in an amount of 0.5 to 3 parts by weight for 100 parts by weight of binder resin.

3. An electrophotographic toner according to Claim 1, wherein the distribution of toner particle sizes is in a range represented by the following form-ula:
N < -172.7C + 1.45 [wherein N is the percentage by the number of toner particles of which sizes as measured with a coalter counter exceed 16 µm, and C is surface dye density (g/g) of the toner particles].

4. An electrophotographic toner according to Claim 1, wherein the coloring agent is carbon black of which pH value is in a range from 6 to 11.

5. An electrophotographic toner according to Claim 1, wherein hydrophobic silica having a pH value in a range from 3.5 to 4.5 is mixed with and dispersed in said toner.

6. An electrophotographic toner according to Claim 5, wherein the hydrophobic silica is fine powder of 0.01 to 0.04 µm.

7. An electrophotographic toner according to Claim 5, wherein the hydrophobic silica is contained in an amount of 0.01 to 5 % by weight for the amount of all toner particles.