JP3286849B2 - Carrier for electrostatic latent image development - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for electrostatic latent images used in electrophotography, electrostatic printing, and the like, and more particularly to a carrier for developing electrostatic latent images.

[0002]

2. Description of the Related Art Conventionally, a so-called two-component dry developer comprising a mixture of carrier particles and toner particles is well known. In this two-component dry developer, fine toner particles are held on the surface of a relatively large particle by the electric force generated by friction between the two particles, and an electrostatic latent image is formed when approaching the electrostatic latent image. The attraction force of the toner particles in the latent image direction due to the applied electric field overcomes the bonding force between the toner particles and the carrier particles, and the toner particles are adsorbed and adhered on the electrostatic latent image to visualize the electrostatic latent image. It is. And
The developer is used repeatedly while replenishing the toner consumed by the development.

[0003] Generally, metal oxides such as magnetite and ferrite are widely used as carrier materials for two-component developers, and have a smaller apparent density than iron powder carriers and the like, resulting in a lighter weight developer. Therefore, when the developer is stirred in the developing device, there is an advantage that the stirring resistance is reduced. Furthermore, compared to the iron powder carrier, the magnetic properties, the residual magnetic flux density is low, the coercive force is small, and as a result, the area of the hysteresis loop is small, and the initial characteristics are always retained for the magnetization reversal and magnetization history. Have the following characteristics. Magnetite, ferrite, and the like are oxides and therefore chemically stable, and are unlikely to undergo a chemical change due to ozone, NOx, and the like generated in the copying machine.

However, such oxide carriers such as ferrite and magnetite also cause mechanical collisions such as collisions between developer particles due to high-speed development and multiple-sheet copying, or collisions between developer particles and a developing machine, or the like. As a result, the toner film is formed on the surface of the carrier due to the heat generated by the action of the toner, so-called spent occurs, and the charging characteristics of the carrier are reduced with use time, and toner scattering, background fogging and the like occur.

In order to prevent such spent,
Conventionally, methods for coating the surface of core particles with various resins have been proposed, but no satisfactory one has yet been obtained. For example, a carrier coated with a resin such as a styrene-methacrylate copolymer or a styrene polymer has excellent charging characteristics, but has a relatively high critical surface tension of the surface, and also causes spent during repeated copying. The life as a developer was not so long. Also, a carrier coated with an ethylene tetrafluoride polymer is unlikely to cause spent toner, but since the tetrafluoroethylene polymer is located at the most negative side in the triboelectric series, the toner should be negatively charged. Cannot be used.

On the other hand, a method of coating the carrier surface with a material having a low surface energy such as silicone has been devised. However, such a resin-coated carrier has the following two disadvantages. It was observed.
The first drawback is that when used as a developer due to the high electrical resistance of the carrier, image quality is poor due to edge development and reduced charge accumulation. The second drawback is that the carrier coat film wears over time due to mechanical friction such as friction between the developer particles due to high-speed development and multiple-sheet copying, or friction between the developer particles and the developing machine, That is, the charging characteristics deteriorated.

The former disadvantage of the coated carrier can be improved by dispersing a conductive substance in the coating layer. That is, when a certain degree of conductivity is imparted to the carrier, the carrier acts as a developing electrode, and the developing is performed in a state where the developing electrode and the surface of the photoreceptor to be developed are in close contact with each other. Even a large area black part is faithfully reproduced as the original.

Conventionally, carbon, tin oxide and the like have been used as such a conductive material. However, when such a conductive material is dispersed in a coating layer of a carrier, the following defects occur.

Generally, the toner and the carrier are charged when they come into contact with each other. In this case, when the electric resistance of the carrier decreases, the charge generated in the toner is attenuated through the carrier, and the charge amount cannot be maintained. Further, there is a disadvantage that the conductive material is separated from the coating layer due to use over time and the charge amount is changed. In order to solve this drawback, Japanese Patent Application Laid-Open No. 62-182759 has improved carbon by treating it with aminosilane, amino-modified silicone oil, or the like. there were.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent background contamination and toner scattering, to prevent image quality from deteriorating due to edge development and charge accumulation development, and to prevent peeling of the coating layer and conductivity even during continuous use. An object of the present invention is to provide a carrier for developing a negatively charged electrostatic latent ume that is stable in triboelectric charging because no fine powder is detached, and can provide an image having high fidelity equivalent to that of an initial image. Another purpose is to develop an electrostatic latent image which is stable even when the carrier coating layer is worn during continuous use, so that triboelectric charging is stable and an image with high fidelity equivalent to the initial image can be obtained. To provide a career.

[0011]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that, in an electrophotographic carrier having a silicone resin coating layer, a silicone resin coating layer containing a conductive fine powder and a silane coupling agent is used. It has been found that the above problem can be solved by providing a concentration gradient in which the silane coupling agent gradually decreases from the inside to the outside in the thickness direction of the silicone resin coating layer. That is, according to the present invention, it has a silicone resin coating layer containing a conductive fine powder and a silane coupling agent, furthermore, the concentration of the silane coupling agent, the thickness direction of the silicone resin coating layer, From inside to outside
A carrier for developing an electrostatic latent image, characterized in that the carrier has a density gradient that gradually becomes thinner .

In the present invention, the use of carbon black as the conductive fine powder provides durability, does not deteriorate image quality due to edge development or charge accumulation development, and provides stable triboelectric charging even when used over time. Thus, a two-component developing carrier for electrophotography exhibiting excellent properties can be obtained.

In the present invention, since the aminosilane coupling agent having an amino group is used as the silane coupling agent, it is durable, has no image quality deterioration due to edge development or charge accumulation development, and can be used over time. As a result, a two-component developing carrier for electrophotography exhibiting stable negative triboelectric charging was obtained.

Further, by using the aminosilane coupling agent having an epoxy group as the silane coupling agent, the silane coupling agent is durable, has no deterioration in image quality due to edge development or charge accumulation development, and is stable even when used over time. For electrophotography exhibiting improved positive triboelectricity 2
A carrier for component-based development is obtained.

That is, the present invention maintains the advantages of the conventional silicone resin-coated carrier by coating the surface of the core particles with a silicone resin containing a conductive fine powder and a silane coupling agent. In addition, by imparting conductivity to the carrier, accumulation and development of electric charge in the carrier, peeling of the coating layer, and detachment of the conductive fine powder are effectively suppressed.

Further, according to the present invention, the concentration gradient of the silane coupling agent is controlled in the thickness direction of the silicone resin coating layer .
The silane coupling agent is exposed to the surface even if the carrier coat film is worn because the thickness is gradually reduced from the side to the outside, so that the polarity is controlled by the polarity having the silane coupling agent. By increasing the portion on the carrier surface, the toner can be charged to a desired charge amount.

In particular, when an aminosilane coupling agent having a positive polarity group is used, there is an advantage that the positive charge characteristic of the carrier increases with the abrasion of the film, and the toner is easily negatively charged. It is more convenient to obtain a negatively charged toner having the same.

Further, when an epoxy silane coupling agent having a negative polarity group is used, there is an advantage that the negative charge characteristic of the carrier increases with the abrasion of the film, and the toner is easily charged positively. It is more convenient to obtain a positively charged toner having the same.

In the present invention, in order to obtain a desired stable negatively chargeable toner, the concentration range of the concentration gradient of the aminosilane coupling agent in the thickness direction of the silicone resin coating layer is set to 0.5% by weight to 10% by weight. It is more convenient to make the weight%.

In particular, in order to obtain a desired stable positively chargeable toner, the concentration range of the concentration gradient of the epoxy silane coupling agent in the thickness direction of the silicone resin coating layer is set as follows:
It is more convenient to use 0.5% by weight to 10% by weight.

Here, when the concentration is less than 0.5% by weight, the ratio of the portion of the silane coupling agent controlled by the polarity, which is controlled by the polarity, to the carrier surface is small. When the concentration is not higher than 10% by weight, the appearance rate of the silane coupling agent on the surface is too large, that is, the charging effect is too large to obtain a desired charge amount.

The carrier core particles coated with the silicone resin in the present invention may be conventionally known particles, for example, ferromagnetic metals such as iron, cobalt and nickel; alloys and compounds such as magnetite, hematite and ferrite;
Glass beads and the like can be mentioned. The average particle size of these core particles is usually 10 to 1000 μm, preferably 30 to 500 μm.
μm. The amount of silicone resin used is
Usually, it is 1 to 10% by weight based on the carrier core particles.

The silicone resin used in the present invention may be any of the conventionally known silicone resins.
KR280, KR282, KR285, KR251, K
R155, KR220, KR201, KR204, KR
205, KR206, SA-4, ES1001, ES1
001N, ES1002T, KR3093 and SR2100, SR2101, SR210 manufactured by Toray Silicone Co., Ltd.
7, SR2110, SR2108, SR2109, SR
2400, SR2410, SR2411, SH805,
SH806A, SH840 or the like is used. As a method for forming the silicone resin layer, the silicone resin may be applied to the surface of the carrier core particles by a spraying method, an immersion method, or the like, as in the related art.

The coating layer composition is prepared by adding a conductive fine powder and a silane coupling agent to a silicone resin solution and dispersing the mixture with an appropriate mixer.

As the conductive fine powder dispersed in the coating layer, conventionally known carbon black may be used, and examples thereof include contact black, furnace black and thermal black. The conductive fine powder dispersed in the coating layer has a content of 0.1%.
The particles having a particle size of about 01 to 5.0 μm are preferred, and 0.01 to 30 parts by weight are preferably added to 100 parts by weight of the silicone resin, more preferably 0.1 to 20 parts by weight.

The silane coupling agent is a compound represented by the formula: X-Si-Rn (n: an integer of 1 to 3), where X is a functional group that reacts with an organic substance, and R is an alkoxy group or chlorine. Is an atom. In particular, when a developer having a negative polarity is obtained, an aminosilane coupling agent having an amino group at X is desirable. In particular, when a developer having a positive polarity is obtained, an epoxy silane coupling agent having an epoxy group is desirable.

As specific examples of the silane coupling agent used in the present invention, compounds having the following structures can be used.

[0028]

[Table 1- (1)]

[Table 1- (2)]

[Table 1- (3)]

In the present invention, the concentration gradient of the silane cuffling agent in the thickness direction of the silicone resin coating layer is set to the inner side.
The method of changing the concentration of the silane coupling agent in the resin coating layer forming liquid during the formation of the resin coating layer in the fluidized bed type coating apparatus is to gradually decrease the concentration of the silane coupling agent in the fluidized bed coating apparatus. And a method in which the resin coating forming solution is changed by changing the silane cup agent concentration into several times to form a resin coating layer in a layer structure, and the like. is not. All parts are parts by weight.

Next, a production example of a carrier having several silicone resins in the coating layer will be described. These can be performed by known means.

Production Example 1 Composition of coating layer forming liquid Silicon resin solution 100 parts Carbon black 3 parts Toluene 100 parts The above formulation was dispersed with a homomixer for 30 minutes to prepare a resin coating layer forming liquid. A silane coupling agent (1) was added to the solution, and a resin coating layer forming solution was gradually added to the total of 2 parts during the formation of the resin coating layer so that the concentration of the silane coupling agent was gradually reduced. , Average particle size 100μ
The surface of 1,000 parts of a spherical ferrite having a particle size of m was coated using a fluidized bed type coating apparatus, and was used as a carrier A.

Production Examples 2 to 18 The components shown in Table 2 below and 100 parts of toluene were mixed and dispersed with a homomixer for 30 minutes to prepare a coating layer forming solution.

[Table 2] Carrier prescription

With respect to Production Examples 2 to 7 and 10 to 16, the above resin coating layer forming solution was applied to the surface of 1,000 parts of spherical ferrite having an average particle diameter of 100 μm by using a fluidized bed type coating apparatus in the same manner as in the above carrier A. A resin coating layer forming solution is gradually added to the silane coupling agent to change the concentration of the silane coupling agent to form a coating layer, and the carriers B, C, D,
E, F, G, J, K, L, M, N, O, P were obtained. Regarding Production Examples 8 and 17, the surface of 1000 parts of spherical ferrite having an average particle diameter of 100 μm was coated using a fluidized bed type coating apparatus as before, without applying a concentration gradient of the silane coupling agent. Q was obtained.

With respect to Production Examples 9 and 18, Carriers I and R were prepared by using the same resin coating solution as Carrier K but without the addition of a silane coupling agent.

[0036]

The present invention will be described in more detail with reference to the following examples. Example 1 80 parts of a polyester resin 20 parts of a styrene-acrylate copolymer 20 parts 8 parts of a carbon black 2 parts of a metal-containing monoazo dye The mixture of the above composition was sufficiently stirred and mixed in a Henschel mixer, and then the mixture was roll-milled at a temperature of 130 to 140 ° C. 3
After heating and melting for 0 minutes and cooling to room temperature, the obtained kneaded material was pulverized and classified to obtain a toner having a particle size of 5 to 20 μm. Silicone carrier A 97.5 was added to 2.5 parts of the toner.
Were mixed with a ball mill to obtain a developer.

Next, the above developer was set in an FT7570 made by our company, and development was performed. As a result, clear and high-quality images were obtained.
The image did not change even after 300,000 sheets of images were displayed. Also, when the charge amount of the toner was measured by a blow-off method,
The initial charge amount is −27.9 μC / g, and the charge amount of the toner after running 300,000 sheets is −25.3 μC / g.
g and the initial value were hardly different. The thickness of the carrier coating film at this time was about 0.1 μm worn from the beginning.

Example 2 75 parts of a polyester resin 15 parts of a styrene-acrylate copolymer 15 parts of carbon black 8 parts of a metal-containing monoazo dye 1.5 parts The mixture of the above composition was sufficiently stirred and mixed in a Henschel mixer, and then 130-140 using a roll mill. About 3 at a temperature of ℃
After heating and melting for 0 minutes and cooling to room temperature, the obtained kneaded material was pulverized and classified to obtain a toner having a particle size of 5 to 20 μm. To 2.5 parts of this toner, silicone carrier B 97.5 was used.
The developer was prepared in the same manner as in Example 1, and a similar image output test was performed. As a result, clear and high-quality images were obtained, and the image remained unchanged even after 300,000 images were output.

When the charge amount of the toner was measured by a blow-off method, the initial charge amount was -26.2 μC / g, and the charge amount of the toner after running 300,000 sheets was-
24.6 μC / g was almost the same as the initial value. In addition, the thickness of the carrier coating film at this time is about 0.
It was worn by 1 μm.

Example 3 80 parts of a polyester resin 20 parts of a styrene-acrylate copolymer 20 parts of carbon black 8 parts of a metal-containing monoazo dye 1 part After sufficiently stirring and mixing the mixture having the above composition in a Henschel mixer, the mixture was heated to 130 to 140 ° C. with a roll mill. About 3 at temperature
After heating and melting for 0 minutes and cooling to room temperature, the obtained kneaded material was pulverized and classified to obtain a toner having a particle size of 5 to 20 μm. To 2.5 parts of the toner, a silicone carrier C 97.5 was used.
The developer was prepared in the same manner as in Example 1, and a similar image output test was performed. As a result, clear and high-quality images were obtained, and the image remained unchanged even after 300,000 images were output.

When the charge amount of the toner was measured by a blow-off method, the initial charge amount was −27.4 μC / g, and the charge amount of the toner after running 300,000 sheets was −
At 27.6 μC / g, there was almost no difference from the initial value. In addition, the thickness of the carrier coating film at this time is about 0.
It was worn by 1 μm.

Comparative Example 1 A developer was obtained and an image test was performed in the same manner as in Example 3, except that the carrier H having no concentration gradient of the aminosilane coupling agent of the carrier was used. A clear image was obtained. From around 200,000 sheets, fogged and unclear images were obtained. When the charge amount was measured in the same manner as in Example 3, the initial charge amount was −26.1.
μC / g, but after 300,000 sheets, −18.3 μC / g
g. The thickness of the carrier coating film at this time was about 0.1 μm worn from the beginning.

Comparative Example 2 A developer was obtained and an image test was conducted in the same manner as in Example 3, except that Carrier I was used except for the aminosilane coupling agent. The initial image is
A clear image without fog was obtained, but from around 10,000 sheets,
The image was fuzzy and unclear. When the charge amount was measured in the same manner as in Example 3, the initial charge amount was -2.
It was 0.1 μC / g, but -100.3 μm after 30,000 sheets.
C / g. Further, the thickness of the carrier coating film after 100,000 sheets was worn by about 0.2 μm from the beginning.

Example 4 85 parts of a polyester resin 15 parts of a styrene-acrylate copolymer 15 parts of a carbauba wax freed of a fatty acid 3 parts of a carbon black 8 parts of a metal-containing monoazo dye 1.5 parts A mixture of the above composition was sufficiently stirred and mixed in a Henschel mixer. After that, a roll mill is used at a temperature of 130 to 140 ° C. for about 3 hours.
After heating and melting for 0 minutes and cooling to room temperature, the obtained kneaded material was pulverized and classified to obtain a toner having a particle size of 5 to 20 μm. To 2.5 parts of this toner, 97.5 parts of silicone carrier D
The developer was prepared in the same manner as in Example 1, and a similar image output test was performed. As a result, clear and high-quality images were obtained, and the image remained unchanged even after 300,000 images were output.

When the charge amount of the toner was measured by a blow-off method, the initial charge amount was -28.4 μC / g, and the charge amount of the toner after running 300,000 sheets was-
28.2 μC / g, almost no difference from the initial value. In addition, the thickness of the carrier coating film at this time is about 0.
It was worn by 2 μm.

Example 5 A developer was prepared in the same manner as in Example 4 except that the carrier F was used in which the concentration range of the concentration gradient of the silane coupling agent in the resin coating layer was lower than 0.5 wt%. And subjected to an image test. As a result, a clear image without fogging was obtained, and the image did not change even after 100,000 sheets of images were output. When the charge amount was measured in the same manner as in Example 4, the initial charge amount was -27.1 μC / g.
After 50,000 sheets, it was -21.0 μC / g.

Example 6 A developer was obtained in the same manner as in Example 4 except that the carrier G in which the concentration range of the concentration gradient of the silane coupling agent in the resin coating layer was higher than 10 wt% was used. When an image test was carried out, a clear image without fog was obtained, and the image did not change even after 100,000 sheets of images were output. When the charge amount was measured in the same manner as in Example 4, the initial charge amount was −29.8 μC / g.
After 100,000 sheets, it was −34.3 μC / g.

Example 7 85 parts of polyester resin 10 parts of styrene-acrylate copolymer 7 parts of polypropylene I. Pigment Blue 15 3 parts Salicylic acid derivative zinc salt 2 parts The mixture having the above composition is thoroughly stirred and mixed in a Henschel mixer, and then roll-milled at a temperature of 130 to 140 ° C. to about 3 parts.
After heating and melting for 0 minutes and cooling to room temperature, the obtained kneaded product was pulverized and classified to obtain a blue toner having a particle size of 5 to 20 μm.
To 2.5 parts of the toner, a silicone carrier E9 was used.
A developer was prepared in 7.5 parts in the same manner as in Example 1, and a similar image output test was performed. As a result, a clear high-quality image was obtained, and the image remained unchanged even after 100,000 sheets of the image were output.

When the charge amount of the toner was measured by a blow-off method, the initial charge amount was −25.6 μC / g, and the charge amount of the toner after running 100,000 sheets was −
It was 25.1 μC / g, which was almost the same as the initial value. In addition, the thickness of the carrier coating film at this time is about 0.
It was worn by 1 μm.

Example 8 93 parts of epoxy resin 5 parts of phthalocyanine blue 5 parts of quaternary ammonium salt 2 The mixture of the above formulation was melted and kneaded with a hot roll at 120 ° C., then cooled and solidified, crushed by a jet mill, and classified. As a result, a toner having a particle size of 5 to 20 μm was obtained. 2.5 parts of this toner was mixed with 97.5 parts of silicone carrier J in a ball mill to obtain a developer. This developer was set in a copier FT7570 manufactured by our company and an image test was performed. As a result, clear and high-quality images were obtained, and the image remained unchanged even after 200,000 sheets of images were output.

When the charge amount of the toner was measured by the blow-off method, the initial charge amount was +26.8 μC / g, and the toner charge amount after running 200,000 sheets was +2.
24.3 μC / g was almost the same as the initial value. Further, the thickness of the carrier coating film after 200,000 sheets was worn by about 0.1 μm from the initial stage.

Example 9 A developer was obtained in the same manner as in Example 8, except that the carrier K to which the epoxy coupling agent was added, and an image test was performed. As a result, a clear image without fog was obtained. The image was obtained and remained unchanged after 200,000 images were displayed.

Comparative Example 3 A developer was obtained and an image test was performed in the same manner as in Example 9 except that the carrier Q having no concentration gradient of the aminosilane coupling agent was used. As the initial image, a clear image without fog was obtained, but from about 300,000 sheets, an unclear image with fog was obtained. When the charge amount was measured in the same manner as in Example 9,
The initial charge amount was +26.1 μC / g, but after 300,000 sheets, it decreased to +18.3 μC / g. At this time, the thickness of the carrier coating film is about 0.1 μm from the beginning.
Was worn.

Comparative Example 4 A developer was obtained and an image test was conducted in the same manner as in Example 9 except that the carrier R was used except for the aminosilane coupling agent. The initial image is
A clear image without fog was obtained, but from around 10,000 sheets,
The image was fuzzy and unclear. When the charge amount was measured in the same manner as in Example 9, the initial charge amount was +2.
0.1 μC / g, but after 30,000 sheets, +10.3 μC / g
C / g. Further, the thickness of the carrier coating film after 100,000 sheets was worn by about 0.2 μm from the beginning.

Example 10 Styrene-n-butyl methacrylate copolymer 88 parts Carbon black 10 parts Metal complex compound 2 parts A mixture of the above formulation was prepared in the same manner as in Example 8 by 5 to 20 μm.
m was obtained. For 3.5 parts of this toner,
96.5 parts of silicone carrier L was mixed with a ball mill to obtain a developer. Next, when an image test was performed on this developer in the same manner as in Example 8, the initial charge amount was +2.
The charge amount of the toner after running 300,000 sheets was +22.7 μC / g, which was almost the same as the initial value. Further, the thickness of the carrier coating film after 200,000 sheets was worn by about 0.1 μm from the initial stage.

Example 11 Styrene-n-butyl methacrylate copolymer 88 parts Carbon black 10 parts Quaternary ammonium salt 2 parts A mixture of the above formulation was prepared in the same manner as in Example 8 by 5 to 20 μm.
m was obtained. 2.5 parts of this toner and 97.5 parts of a silicone carrier M were mixed in a ball mill, a developer was prepared in the same manner as in Example 8, and a similar image test was performed. As a result, clear high-quality images were obtained. The image did not change even after 300,000 sheets of images were output. When the charge amount of the toner was measured by a blow-off method, the initial charge amount was +24.1 μC / g, and the toner charge amount after running 300,000 sheets was +23.7 μC / g, which is almost the same as the initial value. Did not. Further, the thickness of the carrier coating film after 200,000 sheets was worn by about 0.1 μm from the initial stage.

Example 12 The development was performed in the same manner as in Example 11, except that the carrier O was used in which the concentration range of the concentration gradient of the silane coupling agent in the resin coating layer was lower than 0.5 wt%. When the agent was obtained and an image test was performed, a clear image without fog was obtained. The image did not change even after 100,000 sheets of images were output. When the charge amount was measured in the same manner as in Example 11, the initial charge amount was +27.1 μC / g, but was +21.8 μC / g after 150,000 sheets.

Example 13 A developer was used in the same manner as in Example 11, except that the carrier P was used in which the concentration range of the concentration gradient of the silane coupling agent in the resin coating layer was higher than 10 wt%. As a result of the image test, a clear image without fogging was obtained. The image did not change even after 100,000 sheets of images were output. When the charge amount was measured in the same manner as in Example 11, the initial charge amount was +29.8 μC / g, but was +36.3 μC / g after 300,000 sheets.

[0058]

According to the carrier for electrophotographic development of the present invention, an image having the same quality as the initial image can be obtained after continuous copying, stable triboelectricity can be obtained, and a clear copy image can be obtained. Is obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masami Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (56) References JP-A-60-19156 (JP, A) JP-A Heihei 3-217856 (JP, A) JP-A-60-15973 (JP, A) JP-A-60-73631 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/113

Claims (5)

(57) [Claims] 1. A silicone resin coating layer containing a conductive fine powder and a silane coupling agent, wherein the concentration of the silane coupling agent is from inside to outside with respect to the thickness direction of the silicone resin coating layer. A carrier for developing an electrostatic latent image, characterized in that the carrier has a density gradient that gradually decreases toward . 2. The electrostatic latent image according to claim 1, wherein the conductive fine powder is carbon black, and the silane coupling agent is an aminosilane coupling agent to impart a negative charge to the toner. Development carrier. 3. The carrier for developing an electrostatic latent image according to claim 2, wherein the concentration of the aminosilane coupling agent in the silicone resin coating layer has a gradient in the range of 0.5% by weight to 10% by weight. . 4. The electrostatic latent image according to claim 1, wherein the conductive fine powder is carbon black, and the silane coupling agent is an epoxy silane coupling agent to impart toner positive charge. Development carrier. 5. The electrostatic latent image developing device according to claim 4, wherein the concentration of the epoxysilane coupling agent in the silicone resin coating layer has a gradient in the range of 0.5% by weight to 10% by weight. Career.