JPH10301336A - Production of carrier for developing electrostatic latent image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure stable image quality at low temp. and humidity over a long period by heating coating resins on carrier core particles at a temp. above the glass transition temps. of the resins and then carrying out rapid cooling. SOLUTION: The surfaces of carrier core particles are coated with a resin soln. contg. two or more coating resins to form resin layers and the layers are heated at a temp. above the glass transition temps. of the resins, preferably at a temp. in the range of 100-200 deg.C. The layers are then rapidly cooled to a temp. below the glass transition temps. at >=30 deg.C/min cooling rate. This rapid cooling is preferably carried out to 50 deg.C at >=30 deg.C/min, preferably 40-100 deg.C/min cooling rate. Molecular motion in the coated resins is activated by the heating and the activated molecules are fixed as they are by the following rapid cooling to form the surface structure of the coating layers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrostatic latent image developing carrier used for developing an electrostatic latent image in electrophotography and electrostatic recording, and to a method for producing the same. The present invention relates to a carrier for developing an electrostatic latent image.

[0002]

2. Description of the Related Art An electrophotographic method includes a charging step of imparting chargeability to a photoreceptor, an exposure step of forming an electrostatic latent image on the photoreceptor, a developing step of developing the electrostatic latent image with toner, and a step of developing the developed image. The method includes a transfer step of transferring the image to a support such as paper, a fixing step of fixing the transferred image on the paper, and a cleaning step of removing the toner remaining on the photoconductor.

As the developer used in the electrophotographic method, there are two kinds of one-component developer and a two-component developer composed of a toner and a carrier, and the charge control is easy and the reliability is high. From the viewpoint, two-component developers are widely used. The role of the carrier used in the two-component developer is, for example, to impart electric charge to the toner by triboelectric charging and to transport the toner to the photoconductor, and it is particularly important to control the amount of charge to the toner.

In general, low temperature and low humidity (for example, 5
It is known that the toner charge amount is higher than the initial value at a temperature of (.about.15 DEG C., 25 to 35 RH%). If the charge amount of the toner is too high, the electrostatic adhesion between the toner and the carrier increases, and the toner is not sufficiently developed on the photoconductor, leading to deterioration of image quality. Further, so-called carrier adhesion, in which the carrier adheres to the photoconductor, occurs due to electrostatic attraction between the charge remaining on the carrier after the toner development and the non-image portion of the photoconductor. This leads to fatal image defects.

In general, as a method for controlling the charge amount of a carrier to a toner, it has been proposed to combine two or more kinds of carrier coating resins (see Japanese Patent Application Laid-Open Nos. 7-199545 and 7-209918). . But,
The carrier controlled by this method cannot suppress an increase in the toner charge amount under low temperature and low humidity, and cannot substantially improve the image quality.

On the other hand, a carrier coated with a thermosetting resin is instantaneously heated at a temperature higher than the curing temperature of the resin by 50 ° C. or more to completely cure the resin and prevent contamination of the photoreceptor. (See JP-A-5-11508 and JP-A-5-127431) or by coating the carrier core material with a coating resin solution heated to a temperature equal to or higher than the glass transition point of the coating resin. A method has been proposed in which the resin coating is stabilized to make the chargeability and the charge distribution uniform (see JP-A-5-273790). However, in any of these methods, no special consideration is given to the cooling rate after the heat treatment, and since the cooling is performed to room temperature by cooling, a certain improvement is obtained at room temperature and normal humidity and high temperature and high humidity. Although observed, image stability over a long period of time at low temperature and low humidity could not be substantially improved.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention solves the above-mentioned drawbacks, assures charging control for toner, and suppresses carrier adhesion to a photoreceptor. An object of the present invention is to provide a carrier for developing an electrostatic latent image capable of obtaining stable image quality over a period and a method for manufacturing the same.

[0008]

Means for Solving the Problems The present inventors have studied various conditions for producing a carrier in which the surface of the carrier core particles is coated with two or more kinds of resins. After heat treatment at a higher temperature, rapid cooling allowed the image quality to be improved at low temperatures and low humidity.

That is, in the present invention, a resin solution containing two or more kinds of coating resins is applied to the surface of carrier core particles to form a resin layer, and a heat treatment is performed at a temperature higher than the glass transition point of the coating resin. And carrying out the heat treatment and then cooling to a temperature lower than the glass transition point at a cooling rate of 30 ° C./min or more in the method for producing a carrier for developing an electrostatic latent image. This is a method for producing a carrier for use.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The two or more resins used in the present invention are appropriately selected from general soluble resins in consideration of the amount of charge to the toner. Styrenes such as styrene, chlorostyrene and methylstyrene; methyl methacrylate, propyl acrylate,
Α such as lauryl acrylate, methacrylic acid, acrylic acid, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate and ethyl methacrylate
-Methylene aliphatic monocarboxylic esters; nitriles such as acrylonitrile and methacrylonitrile; 2-
Vinylpyridines such as vinylpyridine and 4-vinylpyridine; vinyl ethers; vinyl ketones; olefins such as ethylene, propylene and butadiene; homopolymers or copolymers of silicones such as methylsilicon and methylphenylsilicon; Copolymers of vinyl-based fluorine-containing monomers such as vinylidene, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, monochloroethylene, and trifluoroethylene; and known coating resins such as polyesters containing bisphenol, glycol, and the like And two or more types can be appropriately combined.

Among these coating resins, a combination of polymethyl methacrylate and polystyrene is particularly preferred. When two types of coating resins are combined, the composition ratio is preferably in the range of 3: 7 to 7: 3 by weight.

[0012] The carrier core particles used in the present invention include metal particles such as ferrite powder, iron powder, magnetite powder, glass beads, Ni-Fe alloy, Co-Fe alloy, and Al-Fe alloy, and magnetic powder made of resin. Magnetic powder-dispersed carrier core particles dispersed therein can be used.

[0013] Further, the particle size distribution of the carrier can be ensured by selecting using a centrifugal classifier, an inertial classifier, or a sieve. When the carrier particle size is small,
Carrier scattering is likely to occur, and if a large particle size carrier is used, the magnetic brush becomes rough and the image quality deteriorates.
Therefore, the average particle size of the carrier is suitably in the range of 10 to 100 μm, preferably 20 to 50 μm.

The heat treatment in the present invention is carried out at a temperature higher than the glass transition temperature of two or more kinds of coating resins,
It is performed at a temperature in the range of 0 to 200 ° C. Even if the heat treatment is performed at a temperature lower than the glass transition point, the charge cannot be controlled. If the heat treatment is performed at a temperature higher than 200 ° C., the carriers aggregate, which is not preferable.

The quenching after the above-mentioned heat treatment is carried out by increasing the cooling rate from the above-mentioned heat treatment temperature to a temperature lower than the glass transition point, preferably to 50 ° C., at 30 ° C./min or more, preferably 40 to 100 ° C./min. Select in the range. When the cooling rate is less than 30 ° C./min, the charge amount of the toner at a low temperature and a low humidity shows a high value from the beginning and keeps a high value thereafter, so that the development amount is reduced and the image quality is reduced. Carriers tend to adhere to the photoconductor. Further, in order to make the cooling rate higher than 100 ° C./min, it is necessary to use liquid nitrogen or the like, and the cost is extremely increased.

According to the present invention, the above-mentioned heat treatment
The molecular movement between two or more kinds of coating resins becomes active, and the rapid cooling thereafter fixes the activated molecules as they are and forms the surface structure of the coating, thereby obtaining the above characteristics. It is considered possible.

In the present invention, a method of mixing a resin solution containing two or more kinds of coating resins and carrier core particles includes a rotating blade capable of applying a forced shear force to a mixture of the coating resin and the carrier core particles. A device provided with a stirring blade such as a scraper in a mixing tank is suitable, and specific examples thereof include a batch type kneader, a ribbon blender, and a pony mixer.

As the means for heating the mixture, a method of heating in an electric furnace, a method in which a jacket is attached to a mixing tank to circulate steam, a heating medium, and the like to conduct heat transfer, and a method in which hot air is supplied to the mixing tank. Examples include a direct heating method of blowing, but are not limited thereto. Examples of the cooling means include a method in which the heat medium in the jacket of the mixing tank is switched to a refrigerant and a method in which cool air is blown into the mixing tank or the electric furnace, but is not limited thereto.

The carrier of the present invention is mixed with
Used as a component developer. The toner is obtained by dispersing a colorant in a binder resin. Examples of the binder resin used in the toner include styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, propylene, butylene, and isobutylene; Vinyl esters such as vinyl acetate and vinyl benzoate; methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, dodecyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methacrylic acid Α-methylene aliphatic monocarboxylic acid esters such as dodecyl; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone Which homopolymer or copolymer can be exemplified. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide resin, modified rosin, paraffin wax and the like can be mentioned.

The coloring agents used in the toner include carbon black, aniline black, aniline blue, calcoil blue, chrome yellow, ultramarine blue,
Representative examples include DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, and rose bengal.

The toner components other than the colorant include charge control agents such as salicylic acid metal salts, metal-containing azo compounds, nigrosine, and quaternary ammonium salts, and offset polymers such as low molecular weight polypropylene, low molecular weight polyethylene, and wax. Known components such as an inhibitor can be added, and among them, the weight average molecular weight is 500 to 5000.
Is particularly effective.

In the production of the toner, the above-mentioned toner materials are blended, mixed using a Banbury mixer, a kneader coater, a CM mixer extruder, etc., melt-kneaded, and pulverized and classified to obtain an average particle size of about 30 μm or less. In particular, it is preferable to use fine particles of 3 to 20 μm.

The toner fine particles thus obtained may include a fluidizing agent such as silica, titania, and alumina, a cleaning aid such as polystyrene fine particles, polymethyl methacrylate fine particles, and polyvinylidene fluoride fine particles, and a transfer aid such as a transfer aid. Additives can be used, and among them, hydrophobic silica having a primary average particle size of 5 to 30 nm is particularly effective.

[0024]

EXAMPLES The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 12 parts by weight of polymethyl methacrylate (molecular weight = 150,000, Tg = 73 ° C.) and poly-4-methylstyrene (molecular weight = 80,000, Tg = 5 ° C.) 1
2 parts by weight were dissolved and mixed in 200 parts by weight of toluene to prepare a resin solution. Next, 1000 parts by weight of ferrite carrier core particles having a weight average particle diameter of 40 μm were mixed with the resin solution
The parts by weight were stirred and mixed while reducing the pressure in a batch kneader to remove the solvent, thereby producing carrier particles. The carrier particles are transferred from the kneader to a container and placed in an electric furnace,
The temperature was set at 150 ° C. and maintained for 2 hours. After the heat treatment, the operation of the electric furnace was stopped, and cool air was blown to cool the carrier particles to room temperature. At this time, the cooling time from 150 ° C. to 50 ° C. is 2 minutes and 10 seconds, and the cooling rate is 4 minutes.
6.2 ° C./min.

Example 2 The carrier material of Example 1 was mixed in a kneader provided with a jacket to produce carrier particles. Next, circulate the heating medium through the kneader,
The temperature in the tank was set to 150 ° C., and the heat treatment was performed while stirring the carrier particles for 2 hours. Thereafter, the heat medium was switched to a refrigerant controlled at 5 ° C., and the carrier particles were cooled to room temperature. At this time, the required cooling time from 150 ° C. to 50 ° C. was 3 minutes, and the cooling rate was 33 ° C./min.

[Comparative Example 1] The carrier material of Example 1 was mixed in a batch-type kneader to prepare carrier particles, and then the carrier particles were placed in an electric furnace, set at 150 ° C and held for 2 hours. did. Thereafter, the temperature of the electric furnace was set at 30 ° C. to cool the carrier. At this time, 150 ° C to 5
The time required for cooling to 0 ° C. is 4 minutes, and the cooling rate is 25 minutes.
° C / min.

Comparative Example 2 In Example 1, poly-4-
A carrier was produced in the same manner as in Example 1 except that the blending of methylstyrene was omitted and polymethyl methacrylate (molecular weight = 150,000, Tg = 73 ° C.) was changed to 24 parts by weight.

Example 3 In Example 1, the coating resin was nylon 6-6 (molecular weight = 120,000, Tg = 63 ° C.).
12 parts by weight and poly-4-methylstyrene (molecular weight = 8
(Tg = 85 ° C.) A carrier was manufactured in the same manner as in Example 1 except that the weight was changed to 12 parts by weight.

(Production of Toner) Binder resin (styrene-n
86% by weight of butyl methacrylate), 8% by weight of carbon black (manufactured by Cabot, BPL), 2% by weight of a charge control agent (manufactured by Orient Chemical Co., Bontron NO4), and 66% of polypropylene wax (manufactured by Sanyo Chemical Industries, Ltd.)
0P) Using 4% by weight, an average particle size of 9 by a kneading and pulverizing method.
A μm toner was obtained.

(Evaluation) A developer was prepared by mixing the toner and the carriers of Examples 1 to 3 and Comparative Examples 1 and 2 so that the toner concentration became 9%. The image quality maintenance test
Fuji Xerox V under low humidity (10 ° C, 18% humidity)
Using an IVACE500 modified machine, the above developer was used to measure the initial charge amount of the toner, the charge amount of the toner after copying 150,000 sheets, carrier adhesion, and image density. The results are shown in Table 1.

The evaluation index of carrier adhesion was the area ratio of carrier particles on the background. To measure the area ratio,
An image analyzer (LUZEX-5000, manufactured by NIRECO) was used. The criterion for determining the area ratio of the carrier particles is 0.5
%, ○: 0.5 to 1.0%, and X: greater than 1.0%. If it is 1.0% or less, there is little effect on image quality and there is no problem in practical use.

The image density was measured for a solid image using a reflection densitometer (X-RITE 310, manufactured by X-Rite). Regarding the image density, 1.5 or more was rated as ○, 1.2 or more and less than 1.5 as ○, and less than 1.2 as ×. If it is 1.5 or more, both solid images and line images are sufficient, and if it is 1.0 or more, there is no problem in practical use.

[0034]

[Table 1]

As is clear from Table 1, in Examples 1 to 3, the charge amount of the toner under low temperature and low humidity is appropriately low from the beginning and is kept low thereafter, so that the carrier adhesion can be substantially suppressed. In Comparative Example 1 in which the cooling rate was slower than the range of the present invention, and in Comparative Example 2 in which one type of coating resin was used alone, the charge amount of the toner was initially low. And then kept high, carrier adhesion occurred and the desired image density could not be ensured.

Comparative Example 3 A carrier was manufactured in the same manner as in Example 1 except that the temperature in the electric furnace was set to 90 ° C. At this time, the cooling time from 90 ° C. to 50 ° C. is 1 minute and 15 seconds, and the cooling rate is 32 ° C./m
was in.

Example 4 A carrier was manufactured in the same manner as in Example 1 except that the temperature in the electric furnace was set to 120 ° C. At this time, 120 ° C to 50 ° C
Cooling time is 2 minutes and cooling rate is 35 ° C./mi
n.

Example 5 A carrier was manufactured in the same manner as in Example 1, except that the temperature in the electric furnace was set to 180 ° C. At this time, 180 ° C to 50 ° C
The cooling time is 3 minutes and 30 seconds, and the cooling rate is 37 ° C.
/ Min.

Comparative Example 4 A carrier was manufactured in the same manner as in Example 1 except that the temperature in the electric furnace was set to 230 ° C. However, at this time, aggregates were observed. The cooling time from 230 ° C. to 50 ° C. was 4 minutes, and the cooling rate was 45 ° C./min.

(Evaluation) A developer was prepared by mixing the toner and the carriers of Examples 4 and 5 and Comparative Examples 3 and 4 so that the toner concentration became 9%. The image quality maintenance test
Fuji Xerox V under low humidity (10 ° C, 18% humidity)
Using an IVACE500 modified machine, the above developer was used, and the initial charge amount of the toner, the charge amount of the toner after copying 150,000 sheets, carrier adhesion, and image density were measured in the same manner as described above. The results are shown in Table 2.

[0041]

[Table 2]

As is evident from Table 2, the heat treatment temperature of the present invention is 120 ° C. and 18 ° C. within the range of 100 ° C. to 200 ° C.
In Examples 4 and 5 in which the heat treatment was performed at 0 ° C., the charge amount of the toner under low temperature and low humidity was appropriately low from the beginning and was kept low thereafter, so that the carrier adhesion could be substantially suppressed and the image density was low. In Comparative Example 3 where the heat treatment was performed at 90 ° C. and Comparative Example 4 where the heat treatment was performed at 230 ° C., the charge amount of the toner was high from the beginning and is maintained high thereafter. And the desired image density could not be secured.

[0043]

According to the present invention, it is possible to provide a carrier having a stable image quality over a long period of time under low temperature and low humidity by adopting the above-mentioned structure. became.

Claims (3)

[Claims] 1. A resin solution containing two or more kinds of coating resins is applied to the surface of carrier core particles to form a resin layer,
In a method for producing a carrier for electrostatic latent image development by performing a heat treatment at a temperature higher than the glass transition point of the coating resin,
A method for producing a carrier for developing an electrostatic latent image, wherein the carrier is cooled to a temperature lower than the glass transition point at a cooling rate of 30 ° C./min or more after the heat treatment. 2. The method according to claim 1, wherein the heat treatment is performed at a temperature of 100 to 200 ° C., and then cooled to a temperature lower than the glass transition point at a cooling rate of 30 to 100 ° C./min. A method for producing a carrier for developing an electrostatic latent image. . 3. A carrier for developing an electrostatic latent image, the chargeability of which is controlled by a combination of two or more kinds of coating resins produced by the method of claim 1.