JP3119705B2 - Carrier for electrostatic latent image developer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for an electrostatic latent image developer, and more particularly, to a dry two-component developer for developing an electrostatic latent image such as electrophotography and electrostatic recording. Improved carrier.

[0002]

2. Description of the Related Art Conventionally, as a method of developing an electrostatic latent image using toner, a cascade developing method (US Pat.
No. 8552) or a magnetic brush developing method (US Pat.
No. 74063) is known. In each of these methods, a two-component dry developer is used.

[0003] In this two-component dry developer, fine toner particles are held on the surface of relatively large carrier particles by an electric force generated by friction between the two particles. The attraction force of the toner particles in the direction of the latent image due to the electric field generated by the image overcomes the bonding force between the toner particles and the carrier particles, and the toner particles are attracted and adhered on the electrostatic latent image to visualize the electrostatic latent image. Things. Then, the developer is repeatedly used while replenishing the toner consumed by the development.

In this case, the toner particles must have the correct chargeability and charge magnitude so as to be preferentially attracted to the desired image area on the photoconductor. In addition, the carrier must always frictionally charge the toner particles with a desired polarity and a sufficient charge amount during long-term use. However, in the conventional developer, a part of the toner particles physically adheres to the surface of the carrier particles due to mechanical collisions such as collisions between particles or collisions between the particles and the developing mechanism or heat generated by these collisions, thereby forming a film. There is a property to form. In such a situation, the toner is gradually accumulated on the surface of the carrier particles, and the frictional charge between the carrier particles and the toner particles is replaced by the frictional charge between the toners,
The triboelectric charging characteristic of the entire developer is deteriorated, so that a so-called background stain phenomenon that a large amount of toner adheres to the background portion of the copy image occurs, and the copy quality is reduced. Further, if the formation of the toner film on the carrier surface becomes severe, the entire developer must be replaced, which is a disadvantage that leads to an increase in cost.

[0005] In order to prevent such spent, there have been proposed methods of coating the surface of the carrier with various resins, but no satisfactory method 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. Therefore, the life of the developer is not so long. Also, since the carrier coated with the ethylene tetrafluoride polymer has a low surface tension, it is difficult for the toner to be spent, but since the ethylene tetrafluoride polymer is located at the most negative side in the triboelectric series, the toner is negatively charged. It cannot be used when charging is intended to be carried out. Further, a carrier coated with a coating layer containing a silicon resin has been proposed as having a low surface tension. For example, an unsaturated silicon resin, organosilicon, silanol, or the like mixed with a styrene / acrylic resin to coat the carrier surface (US Pat. No. 356253)
No. 3), a carrier whose surface is coated with a polyphenylene resin and an organosilicon terpolymer resin (US Pat. No. 3,847,127), and a carrier coated with a coat layer containing a silicon resin and a nitrogen-containing resin having positively-charging properties. (JP-A-55-127567) and a carrier whose surface is coated with a resin-modified silicone resin (JP-A-55-127567).
No. 157751) and the like.

As described above, the use of a resin-coated carrier improves the spent resistance, but has the disadvantage that the carrier has a high resistance, so that the edge effect is likely to occur and the reproducibility of a wide black area and a halftone area is poor. is there. Also, the counter charge at the time of toner detachment becomes excessively large, so that carrier adhesion to a non-image portion due to electrostatic development easily occurs. In particular, this phenomenon occurs remarkably at a high bias.

To solve this drawback, it has been proposed to mix a conductive substance such as carbon black in the coating layer. For example, one coated with a material mainly composed of porous carbon black and a resin (Japanese Patent Laid-Open No.
And coated with a silicone resin containing carbon black subjected to coupling treatment (Japanese Patent Application Laid-Open No. 62-182759).

As described above, when the surface of the carrier is coated with a silicon resin containing carbon black, the resistance of the carrier can be easily adjusted, and the edge effect and the adhesion of the carrier can be improved. However, when the resistance is lowered, there is a problem that the carrier adheres to the image area. Furthermore, if carbon black is added too much to lower the resistance of the carrier, the coat film becomes weak and the film is abraded, and the repeated use of the developer fluctuates the resistance of the carrier, so that a stable image cannot be obtained. Occur. On the other hand, if the resistance of the carrier is too low, the charge amount of the developer is remarkably reduced by storage over time. For example, when a developer that has been manufactured for a long time (for example, one month) has been used in a copying machine, the charge amount has decreased. As a result, the thinning of lines due to an increase in the amount of adhered toner, background contamination, and toner scattering have occurred. I do. Further, when the developer contained in the copying machine is placed under high temperature and high humidity, the charge amount sharply decreases and a stable image cannot be obtained. Furthermore, there is a problem that the amount of charge greatly varies depending on environmental conditions during the production of the developer, and a stable developer cannot be obtained.

[0009]

[Problems to be solved by the invention]

(1) The present invention has been made in view of the above points, and has as its object to suppress the electric resistance of a coating layer of a carrier to be low, and to prevent the edge effect and the strong prevention action against carrier adhesion from being impaired at all. The present invention provides a carrier for a dry developer having excellent stability over time and production stability.

(2) The present invention provides a carrier for a dry developer which is excellent in carrier adhesion to an image area despite the low electric resistance of a coating layer of the carrier. (3) Further, the present invention provides a long-life dry developer carrier that is resistant to abrasion of a coating film by minimizing the amount of carbon black added.

According to the present invention, there is provided a carrier for an electrostatic latent image developer having a core material surface coated with a silicon resin containing two types of carbon blacks having different average particle sizes, as described in the claims, Particularly, it is a carrier for an electrostatic latent image developer using furnace black having a specific range of surface area and a specific range of oil absorption.

Acetylene black is a conventionally known conductive carbon black which is obtained by thermal decomposition of acetylene, and is a carbon black having a small amount of impurities in the carbon black and a high carbon content. The carbon content is at least 99%, preferably at least 99.3%. Commercial products of such acetylene black include Denka Black granules and Denka black powder, manufactured by Denki Kagaku Kogyo, and Anacar manufactured by Postman.
There is a bon.

Furnace black is also a conventionally known carbon black having high conductivity, and is generally carbon black obtained by incompletely burning a residue of crude oil at high temperature and carbonized, and has a surface area determined by a nitrogen adsorption method (carbon black handbook). : Carbon Black Association, May 25, 1972,
2nd edition test method specific surface area measurement method P513-P514)
Is 50 to 500 m ² / g, and the DBP oil absorption is 5
0 to 200 ml / 100 g, more preferably 100 to 400 m ² / g, and a DBP oil absorption of 100
２００200 ml / 100 g. Commercial products of such furnace black include Cabot's MONAR.
CH700,800,880,900,1000, RE
GAL330,660, BLACK PEARLS70
0,800,880,1000, # 4 from Mitsubishi Kasei Kogyo
0,44,45, Degussa's Corax P, Prin
tex60, Printex L, PrintexL-
6 and others.

[0014]

The silicon resin may be added alone or as a blend of furnace black and acetylene black to reduce the resistance of the silicon resin and impart conductivity. However, the addition of furnace black alone inhibits the cross-linking reaction of the silicon resin, thus lowering the strength of the silicon coating. Therefore, in a silicon-coated carrier using furnace black as a charge-imparting material, a large amount of carbon black cannot be added, so that it is difficult to sufficiently lower the resistance.

On the other hand, when acetylene black is added alone, it does not inhibit the crosslinking reaction of the silicone resin. Therefore, in contrast to the case where furnace black is solely added, wear of the coating layer is less than that of a carrier whose surface is coated only with silicon resin, and the effect of reinforcing the coating can be seen by adding acetylene black to the silicon resin. However, in the case of a carrier whose surface is coated with a resin solution in which acetylene black alone is added to a silicone resin, the charge amount of a developer prepared by mixing with the toner varies depending on the silicone resin (mainly viscosity), manufacturing conditions and manufacturing environment. It fluctuates greatly.

Therefore, a carrier whose surface is coated with a silicone resin to which a mixture of acetylene black and furnace black has been added has been proposed (JP-A-61-260254).
issue). This carrier has a higher strength of the coating layer than a silicon resin-coated carrier to which furnace black alone is added, and has less wear of the coating layer when the developer is repeatedly used, and has excellent durability. Also, compared to a silicon resin-coated carrier to which only acetylene black has been added, the charge amount of the developer has less fluctuation during production and is stable.
However, according to this invention, the silicon coating layer does not have an appropriate resistance unless carbon black is added in an amount of 5 to 10 parts by weight with respect to 100 parts by weight (in terms of solid content) of the silicon resin.
The reason is that acetylene black is also furnace black (surface area 800 m ² / g or more, DBP oil absorption 300
(m / 100 g or more), the pulverized particle size is very fine and the dispersion stability is excellent. However, since the particle size is small, the resistance cannot be reduced unless a large amount of carbon black is added. In addition, a carrier containing a relatively large amount of carbon black is significantly deteriorated with time during storage of the charge amount of the developer. Therefore, even if the optimal charge amount is given at the time of manufacturing, the charge amount decreases until it is actually used in a copying machine.
Toner scattering occurs. Furthermore, since the carbon black used has a large surface area and easily absorbs moisture in the air, there is a problem in production stability at the time of coating. Therefore, there is a limit to the amount of carbon black added to the silicone resin film, and there is no carrier that can completely satisfy both image quality, production stability of developer, and stability over time.

Therefore, the inventor studied how to reduce the amount of carbon black to be added, how to lower the resistance, and also to suppress the deterioration of the charge amount with time during storage, and as a result, invented the following method.

First, a method was considered in which the overall resistance of the silicon coating layer was not lowered to the target, but rather the resistance was partially lowered by adding carbon black having a particle size equal to or larger than the coating layer. However, porous carbon blacks that have been mainly used so far tend to have a fine particle size, so that furnace black having a relatively small surface area and a small DBP oil absorption is used. Preferably, the surface area by nitrogen adsorption is 50 to 500 m ² / g and D
The BP oil absorption is preferably 50 to 200 ml / 100 g. Further, as the average particle diameter, 1.0 to
The effect is even greater when adjusted to be 1.5 times. By using this means, the resistance of the carrier can be reduced even if the amount of carbon black used is kept small, and the edge effect can be improved and the carrier can be prevented from adhering to the image area. However, carrier adhesion on the high bias side is hardly improved. Therefore, to improve high bias carrier adhesion,
A core material is coated with a resin solution in which finely ground acetylene black is dispersed in a silicon resin together with furnace black. The average particle size of the acetylene black added at this time is adjusted to 0.1 to 0.5 μm. Generally, unless a relatively large amount of carbon black having a small particle diameter is added, the effect of lowering the resistance does not appear. However, in the case of the present invention, the resistance has been lowered to the target by the above-mentioned method, and it is not necessary to reduce the resistance by adding acetylene black. 3 to 10 parts by weight (based on 100 parts by weight of silicone resin)
Is required, but in this method, 0.5 to 5.0 parts by weight may be added. In order to further obtain an optimum image quality, the ratio B / C of the furnace black (B) to the film thickness (C) of the coating layer and the acetylene black (A) and the furnace black ( The product (B / C) * (A + B) with the sum A + B of B) is 0.75 to
It is preferably in the range of 5.0.

As described above, the object was achieved by adding two kinds of carbon blacks having different average particle diameters to the silicon coating. Conventionally, as a method of dispersing carbon black in a coating solution, a wet pulverization method has been generally used. However, when the wet grinding method is used, it is difficult to stabilize the resistance because the particle size distribution tends to have a two-peak distribution, and the average particle size tends to vary depending on the viscosity and temperature of the liquid. When two types of carbon black are used as in this patent, it is almost impossible to arbitrarily change the particle size by a wet method. In the dry method, it is also easy to prevent coarse particles from being mixed in by coarse powder classification.

The particle size of the carbon black was measured by a general sedimentation type particle size distribution analyzer. The silicone resin used in the present invention may be any conventionally known silicone resin, including straight silicone consisting only of an organosiloxane bond and silicone resin modified with alkyd, polyester, epoxy, eletan, and the like. . For example, as a commercial product, straight silicone resin is KR271, KR255, K
R152, Toray Dow Corning Silicone SR24
And modified silicone resins such as KR206 (Alkyd modified) and KR520 of Shin-Etsu Chemical Co., Ltd.
8 (acrylic modification), ES1001N (epoxy modification), KR305 (urethane modification), SR2115 (epoxy modification) of Toray Dow Corning Silicone, SR
2110 (alkyd denaturation).

In the present invention, the carrier particles coated with the silicone resin include non-metals such as sand, cobalt, iron, copper, nickel, zinc, aluminum, brass and glass having an average particle size of 10 to 1000 μm, preferably 30 to 500 μm. Conventionally used materials such as metals and metals, metal alloys are widely used, and as a method for forming a silicon resin coating layer, a coating layer composition is fluidized on the surface of the particles, and a conventionally known method such as a dipping method is used. What is necessary is just to apply by means.

As the toner used together with the carrier of the present invention, a toner obtained by a conventionally known method is used.
Specifically, it is obtained by well mixing a resin component, a coloring agent such as carbon black necessary for forming a visible image, kneading with a hot roll mill, cooling, individualizing, pulverizing and classifying.

The amount of the carrier and the toner used is preferably such that the toner particles adhere to the surface of the silicone resin of the carrier particles and occupy 30 to 90% of the surface area of the carrier particles.

[0025]

EXAMPLES The present invention will be described below by producing carriers according to Examples and Comparative Examples and comparing their properties.

Each component was mixed so as to have each composition shown in Table 1 below to prepare a coating layer forming solution. The carbon black was adjusted to an arbitrary particle size by a dry pulverization method. Next, this solution was made into spherical ferrite 5000 having an average particle size of 100 μm.
The surface of a part by weight was coated with a fluidized bed type coating apparatus, heated at a temperature shown in Table 1 for 2 hours, and then crushed to obtain a resin-coated carrier.

In Comparative Examples 1 to 6, the dry pulverization method was used as in the examples, but in Comparative Example 7, a wet pulverization method was used. Specifically, each component was dispersed by a homomixer for 30 minutes to prepare a liquid.

Among the silicone resins listed in Table 1, KR206 is an alkyd-modified silicone resin manufactured by Shin-Etsu Chemical Co., Ltd.

SR2400: Straight silicone resin manufactured by Dow Corning Toray Silicone Co., Ltd.

Of the carbon blacks listed in Table 1, Printex L-6: furnace black manufactured by Degussa Co., having a surface area of 265 m ² / g by nitrogen adsorption, DBP
The oil absorption is 123 ml / 100 g.

Black Pearls 700: Furnace black manufactured by Cabot Co., having a surface area of 200 m ² / g by a nitrogen adsorption method and a DBP oil absorption of 117 ml / 10
0 g.

Black Pearls 2000: Furnace black manufactured by Cabot Corporation, surface area by nitrogen adsorption method is 1050 m ² / g, DBP oil absorption is 330 ml /
100 g.

Denka black granularity: acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. The carbon content of carbon black is 99.5%.

On the other hand, the composition of the toner is as follows: 80 parts of a copolymer of styrene and n-butyl methacrylate, 10 parts of carbon black, 3 parts of a 2: 1 type chromium complex dye of a monoazo dye, and 3 parts. Was prepared. Then, 2.5 parts of this toner was mixed with 100 parts of each carrier shown in Table 1 below to prepare a developer.

[0035]

[Table 1]

These developers were left in an environment of 30 ° C. and 90%, and the change with time in the charge amount was examined. Further, using FT-4820 manufactured by Ricoh, initial images were obtained immediately after production and after leaving for 7 days. The results are shown in Table 2 below.

[0037]

[Table 2]

As is clear from Table 2, the carriers with a large amount of carbon black added (Comparative Examples 1, 3, 5, 7)
Tend to have a low charge amount. Furthermore, the amount of charge is significantly reduced with time. On the other hand, in Examples, the addition amount of carbon black is small, the charge amount is high, and the decrease with time is small.

On the other hand, regarding the image quality, Comparative Examples 1, 3,
In Nos. 5 and 7, thin lines are thickened due to a decrease in the charge amount. On the other hand, in Examples and Comparative Examples 2, 4, and 6, there is little decrease in the charge amount, and there is no problem with thickening of thin lines.

Further, regarding the carrier adhesion in the non-image area, in the example, all were good, while in comparative example 2,
At 4 and 6, carrier adhesion occurs. This is because the amount of carbon black added to reduce the deterioration of the charge amount over time was reduced. Similarly, carrier adhesion to the image area occurs in Comparative Examples 1, 3, 5, and 7. This is because the charge amount has decreased over time.

As described above, in the comparative example, both the stability of the charge amount and the image quality cannot be achieved. On the other hand, the carrier whose surface is coated with a silicon resin to which two types of carbon blacks having different average particle diameters are added as in the example can achieve both the stability of the charge amount and the image quality.

Next, the step of developing and transferring the latent image on the OPC photoreceptor was repeated 120,000 times while replenishing toner with the developer. The results are shown in Table 3 below.

[0043]

[Table 3]

As is clear from Table 3, the embodiment of the present invention is different from the carriers of Comparative Examples 1 and 2 whose surface is coated with a silicon resin to which only furnace black is added, in that the coating layer of the carrier is obtained by repeatedly using the developer. Of the developer, the amount of charge of the developer before and after repeated use is small, and the image quality is good.

Further, the carriers of Comparative Examples 3 and 4 whose surfaces were coated with a silicone resin to which only acetylene black had been added had little shaving of the carrier coating layer due to repeated use of the developer. Has the same durability. Further, in Comparative Example 5, since acetylene black was added together with furnace black, the degree of film shaving was better than in Comparative Examples 1 and 2. However, since a large amount of carbon black was added to lower the resistance, the durability was inferior to the examples.

Table 4 shows the results of the production stability (environmental fluctuation) during coating.

[0047]

[Table 4]

(Note) The charge amount was measured by measuring 100
50 g into a ball mill stirrer, and 1.5 g of the toner.
After stirring for 0 minute, the developer was taken out and its charge amount was measured.

The resistance was expressed as a logarithmic value of the volume resistivity (Ωcm). For example, 1 × 10 ¹¹ Ωcm is 1
1.0 (log Ωcm).

The environmental fluctuation rate is a fluctuation rate of the physical properties of the carrier coated with the silicon resin under the environment of 30 ° C. and 80% and the physical properties of the carrier coated with the environment of 15 ° C. and 30%. (See the formula below)

[0051]

(Equation 1)

As is clear from Table 4, in the examples of the present invention, there is little variation due to the amount of charge and the environment at the time of resistance coating as compared with the comparative example, and a carrier with stable physical properties can be obtained throughout the year.

[0053]

As is evident from the above, the carrier of the present invention containing two types of carbon black having different average particle diameters in the coating layer of the present invention, when used as a developer, has a charge amount with time. Higher quality copies can be provided with less deterioration. In addition, the carrier has excellent durability. In addition, a carrier of stable quality is always obtained throughout the year.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-260254 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/10

Claims (2)

(57) [Claims] 1. A latent image carrier for a developer having a surface coated with a silicone resin containing carbon black, be one which contains two kinds of carbon blacks different in average particle size in the coating layer, the Carbon black
With cetylene black (A) and furnace black (B)
Yes, the surface area of furnace black by nitrogen adsorption
50-500 m ² / g and DBP oil absorption of 50
A carrier for an electrostatic latent image developer, wherein the carrier weight is from 200 ml / 100 g . 2. The carbon black (A) has an average particle size of 0.1 to 0.5 μm, and the (B) has an average particle size of 0.5 to 2.
Is 0 .mu.m, carrier of claim 1, wherein the ratio of the average particle size of the carbon black (A) and (B) is characterized in that it is a 0.1 ≦ (A / B) ≦ 0.5.