JP3333973B2 - Electrophotographic carrier - 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 used for developing an electrostatic latent image formed by electrophotography.

[0002]

2. Description of the Related Art In recent years, there has been an increasing need for electrophotographic developers with high durability in order to minimize the amount of used developer discarded from the viewpoint of environmental protection, in addition to reducing the cost per copy. I have. Therefore, conventionally, for example, Japanese Patent Laid-Open No. 55-118047
No. 55-163544, No. 60-170865, No. 62-106475,
As described in JP-A-63-235962 and JP-A-63-27859, a technique of providing a resin coating layer on magnetic particles has been widely used.

[0003]

However, in response to the recent demand for higher durability, it is not sufficient to provide only a resin layer.

[0006] The long-term stabilization of the charge amount cannot be said to be sufficient by merely providing the resin layer, and the charge amount decreases during continuous use, causing many image defects.

[0005] In some cases, this may cause blocking of the developer in the developing machine.

In order to extend the durability of the developer, it is necessary to solve these problems.

An object of the present invention is to provide a highly durable resin-coated carrier capable of stabilizing the charge amount for a long period of time and obtaining a high-quality image without defects.

It is a further object of the present invention to provide a resin-coated carrier which does not cause developer blocking even after long-term use.

It is a further object of the present invention to provide a resin-coated carrier having a high production yield that does not cause carrier blocking or adherence to the inner walls of the device even during the production of the resin-coated carrier.

It is a further object of the present invention to provide a resin-coated carrier free of off-flavors when using a copying machine.

[0011]

SUMMARY OF THE INVENTION The above object has been achieved in a reduced pressure atmosphere.
An electrophotographic carrier comprising a resin coating layer formed on a surface of magnetic particles by a dry coating method under a reduced pressure atmosphere using resin fine particles dried under air , wherein the amount of residual monomer in the coating layer is reduced. An electrophotographic carrier characterized in that the amount of the body is 200 ppm or less with respect to the total amount of the resin forming the coating layer.

As the magnetic particles that can be used in the present invention, substances that are strongly magnetized in the direction by a magnetic field can be used.

Specifically, ferromagnetic metals such as iron, ferrite, and magnetite, such as nickel and cobalt, or alloys or compounds containing these metals;
An alloy which does not contain a ferromagnetic element but becomes ferromagnetic by heat treatment, for example, a Heusler alloy such as manganese-copper-aluminum or manganese-copper-tin, chromium dioxide, or the like can be used.

[0014] Ferrite here is a general term for magnetic compounds containing iron, and is not limited to the spinel type.

Of these, ferrite has a relatively low magnetization and is less likely to damage a toner having a small particle size, so that the durability of the developer is improved.

Further, since ferrite has a smaller specific gravity than iron powder or nickel powder, it can be easily mixed and stirred with the toner, so that the toner concentration in the developer becomes uniform and the charge amount with the toner is optimized. It is preferable in performing.

The ferrite has a saturation magnetization of 10 to 80 emu / g in an external magnetic field of 1000 Oe,
The coercive force is preferably 0.1-100 Oersted,
Furthermore, the specific resistance is 1 × 10 ⁶ to 10 ¹¹ ohm · cm and the specific gravity is 4.0 to
Preferably it is 5.5.

The magnetic particles that can be used in the present invention include:
It is preferable to use one having a volume average particle size of 30 to 100 μm, preferably 50 to 80 μm.

The reason is that if the volume average particle diameter of the carrier is too small, the carrier is liable to adhere to the latent image carrier, causing image defects such as scratches on the photoreceptor. On the other hand, if the volume average particle size is too large, the specific surface area of the carrier becomes small, making it difficult to appropriately frictionally charge a required amount of toner, and causing image defects such as background fog.

As the resin for coating magnetic particles that can be used in the present invention, a resin obtained by a known polymerization method can be used.

As the resin that can be used in the present invention, known resins can be used. Specifically, styrene resins, acrylic resins, vinyl resins, ethylene resins, polyamide resins, polyester resins Or a resin composed of a copolymer or a mixture of two or more of these.

Specific examples of the method for producing the resin include solution polymerization, suspension polymerization, emulsion polymerization, bulk polymerization, and in-situ polymerization.
A polymerization method or the like can be used.

As a method of coating the surface of the magnetic particles with the obtained resin, a known coating method can be used.

[0024]

However, it is more preferable to use a known dry coating method.

Specifically, the dry coating method means that the finely divided coating resin is not dissolved in a solvent or the like,
This is a method in which a coating resin is electrostatically attached to the surface of the magnetic particles, and thereafter, one or both of heat and mechanical stress are applied to the particles, thereby coating the surface of the magnetic particles with a resin layer.

In general, the dry coating method does not require ventilation or other operations as compared with the wet coating method, and thus has the advantage that the coating can be performed in a closed system and the coating can be performed in a relatively low humidity condition in a short time.

However, when the dry coating method is applied to the present invention, in addition to the above-mentioned advantages, by performing the coating under reduced pressure as necessary, during the process,
That is, since the amount of the residual monomer in the resin can be controlled simultaneously with the coating, it can be said that the coating method is more preferable than the wet coating method.

When the dry coating method is applied, the method for producing the resin for coating is not particularly limited as long as the method can obtain fine resin particles.
Those having a range of 0.01 to 1 μm are preferred. Further, it is more preferable to use an emulsion polymerization method from the viewpoint of the fineness and homogeneity of the obtained resin fine particles.

The coating amount of the magnetic particles is preferably 0.1 to 10% per unit weight of the magnetic particles.

In the present invention, as an essential requirement, the amount of the residual monomer in the resin coating layer of the magnetic particles should be 200 ppm or less, more preferably 150 ppm or less, based on the total amount of the resin forming the coating layer.
pm or less, and when the amount of the residual monomer exceeds 200 ppm, long-term stabilization of the charge amount cannot be obtained, and in long-term use, toner scattering occurs and ground fogging occurs on an image. The amount of the residual monomer is defined as follows. The method of forming the carrier coating layer is such that the resin fine particles dried under a reduced pressure atmosphere are used.
Use is applied when performing the dry type method under a reduced pressure atmosphere.

Further, there may be a case where adverse effects such as occurrence of blocking in the developing machine and generation of offensive odor during use of the copying machine may occur.

The amount of the residual monomer in the resin coating layer is 200 p.
In order to reduce the amount to pm or less, a residual monomer reduction operation may be performed as necessary during the production process of the resin-coated carrier.

Specifically, before coating on the surface of the magnetic particles,
The residual monomer reduction operation may be performed in any one of the steps after coating the magnetic particle surface and the step after coating the magnetic particle surface, or in two or more steps.

As a residual monomer reducing operation, a known method can be used. As an example, a heating and drying operation in an atmosphere at a temperature equal to or higher than the glass transition point of the resin can be used. More preferably, the operation is performed under a reduced pressure atmosphere. The reduced pressure atmosphere referred to here means that the pressure is equal to or less than the atmospheric pressure.
(Pascal) It is good to be below.

However, when a resin whose residual monomer content has been adjusted to 200 ppm or less in advance is used as the resin for coating magnetic particles, the operation of reducing the residual monomer during the carrier production step can be omitted.

The amount of the residual monomer can be quantified by a gas chromatography method. When quantifying the amount of residual monomer in the magnetic particle coating layer by gas chromatography, a method of directly measuring magnetic particles having a resin coating layer is also possible, but the magnetic particle coating layer may be appropriately measured. Dissolved in a solvent such as chloroform or tetrahydrofuran to separate the magnetic particles beforehand.
Taking the method of removing helps to improve the measurement accuracy.

The volume average particle diameter of the magnetic particles can be measured by a laser diffraction particle size distribution analyzer “HELOS” <JEOL
The volume average particle diameter of the resin fine particles is measured by a laser scattering particle size distribution analyzer “LPA-3000 / 31”.
00 "(manufactured by Otsuka Electronics Co., Ltd.).

[0039]

The carrier for electrophotography according to the present invention has the above-mentioned structure, so that the charging performance of the carrier does not decrease, and at the time of manufacture, adhesion to the inner wall of the apparatus and blocking of the developer in the developing machine are caused. Therefore, a high-quality image can be stably obtained during long-term image formation. Also,
Since there is no unpleasant odor when using the copying machine, a comfortable working environment can be provided. The reason why such an effect can be obtained is not necessarily clear, but the adverse effect when the residual monomer is present in excess of the limit, for example, because the residual monomer becomes plastic, the constituent components of the toner or the toner This is presumed to be because the external additives added to the surface are taken in, and adverse effects such as affecting the charging property and causing blocking are removed.

[0040]

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

First, resin fine particles used for manufacturing carriers for Examples and Comparative Examples were prepared as follows.
That is, fine particles of styrene / methyl methacrylate = 6/4 copolymer resin having an average primary particle diameter of 0.1 μm obtained by an emulsion polymerization method were used, and the drying time thereof was changed in three ways as shown in Table 1 to obtain 120%. Drying under reduced pressure was carried out in an atmosphere at ℃ to prepare resin fine particles A, B and C having different residual monomers.

FIG. 1 is a structural view of a high-speed stirring mixer with a jacket for temperature control used for producing the carriers of the examples and comparative examples. FIG. 2 is an enlarged plan view of the horizontal rotating body of the stirring mixer.

In FIG. 1, reference numeral 11 denotes an upper cover of the main body.
Has a raw material input port 12, input valve 13, filter 14, inspection port 15
Is provided. The charging valve 13 is opened, and the raw material is charged from the charging port 12. The charged raw material is stirred by the horizontal rotating body 18 with stirring blades driven by the motor 22. In the horizontal rotating body 18, as shown in FIG. 2, the stirring blades 1 arranged at a central portion 18d at an angular interval of 120 ° from each other.
8a, 18b and 18c are connected, and these stirring blades are mounted at an angle of 35 ° with respect to the plane of the bottom 10a.

For this reason, the raw material is scraped upward by the rotation of the horizontal rotating body 18 and collides with the upper inner wall of the main body container 10 and falls. The agitation is promoted and the agglomeration is broken.
The raw material undergoes a collision with the horizontal rotating body 18 and the vertical rotating body 19 with the stirring blades, the inner wall of the container, and the collision of the raw materials to form a coating layer on the magnetic particles.

In FIG. 1, 16 is a thermometer, 20 is a carrier outlet, 21 is a discharge valve, 23 is an exhaust port in the container, 24 is a vacuum pump,
25 and 26 are exhaust valves.

(Examples 1 and 2 and Comparative Examples 1 and 2) <Carrier for Example 1> (a) In the mixing step, the raw material input port 12 was
Ferrite core particles with an average particle size of 60 μm (98% by weight)
A raw material composed of fine resin particles A (2% by weight) having an average primary particle size of 0.1 μm was charged into the main vessel 10, and the peripheral speed of the horizontal stirring blade was 6 m / sec, and the mixture was stirred and mixed at room temperature and pressure for 10 minutes. .

Next, as a film formation step (b), the inside of the vessel 10 is heated to 120 ° C. by passing a heat medium through a temperature control jacket, the peripheral speed of the stirring blade is increased to 12 m / sec, and the Stir and mix for minutes.

Next, (c) as a step after film formation, the peripheral speed of the stirring blade was returned to 6 m / sec under normal pressure, cooling water was flowed through the jacket 17 to return the inside of the container 10 to normal temperature. Got a career.

<Carrier for Example 2> The resin fine particles of the raw material were resin fine particles B, and the container 10 in the film forming step (b) was used.
The carrier for Example 2 was obtained in the same manner as the carrier for Example 1 except that the internal pressure was reduced to 100 Pa (Pascal) by operating the vacuum pump 24 and the stirring and mixing time was set to 120 minutes.

<Carrier for Comparative Example 1> A carrier for Comparative Example 1 was obtained in the same manner as the carrier for Example 2 except that the stirring and mixing time in the film formation step (b) was set to 40 minutes.

<Carrier for Comparative Example 2> A comparison was made in the same manner as the carrier for Example 2 except that the resin fine particles as the raw material were resin fine particles C, and the stirring and mixing time in the film forming step (b) was 60 minutes. The carrier for Example 2 was obtained.

The residual amounts of the monomers in the carrier coating layers of Examples 1 and 2 and Comparative Examples 1 and 2 were measured by chromatography "GC-14A" manufactured by Shimadzu Corporation, and the results are shown in Table 1. Indicated. The production yields of the carriers of Examples 1 and 2 and Comparative Examples 1 and 2 were measured, respectively, and the results are shown in Table 1.

The percentage of the ratio of the discharged product carrier (g) to the charged raw material (g) was defined as the production yield.

<Each Developer for Examples and Comparative Examples> Each of the carriers for Examples 1 and 2 and Comparative Examples 1 and 2 was 1728 g.
And 72 g of the following polyester toner were mixed by a V-type mixer to obtain four types of developers for Examples 1 and 2 and Comparative Examples 1 and 2.

Polyester toner: 88% by weight of polyester, 10% by weight of carbon black, and 2% by weight of polypropylene are thoroughly mixed, kneaded with a dissolution kneader, then cooled, pulverized and classified to obtain a volume average particle size of 8.0%. In order to further impart fluidity and chargeability to those adjusted to μm,
A toner obtained by externally adding 0.5% by weight of silica fine particles was used as a toner.

<Actual photo test> Next, an electrophotographic copying machine "U-Bix5082" manufactured by Konica Corporation was sequentially filled with the above four types of developers, and 50,000 copies of Examples 1 and 2 and Comparative Examples 1 and 2 were prepared. The four types of actual test were performed, and the developer at the time and after 50,000 copies were collected, and the charge amount (μC / g) of each developer was obtained by a blow-off method. The results are shown in Table 1. Was. Also, the image quality of the image after 50,000 copies is visually determined,
The results are shown in Table 1.

[0057]

[Table 1]

(Comparative Examples 3, 4 and Example 3) <Carriers for Comparative Examples and Examples> The carrier for Comparative Example 2 was divided into three parts, and the three parts were sequentially placed in a vacuum dryer.
The drying time under reduced pressure was changed as shown in Table 2 at 120 ° C. under reduced pressure of 100 Pa (Pascal) to obtain three types of carriers for Comparative Examples 3, 4 and Example 3.

The amount (ppm) of residual monomer in the coating layer of each of the three carriers after drying under reduced pressure was measured by the chromatography, and the results are shown in Table 2 together with the values before the drying under reduced pressure. . Table 2 also shows the time required for drying each carrier under reduced pressure.

<Each Developer for Comparative Examples and Examples> Each of the three types of carriers and the polyester toner used in Example 1 were used. The same developer was obtained.

<Actual photo test> As in the case of the first embodiment, the above three types of developers are sequentially filled in a "U-Bix5082" copying machine, and 50,000 copies of each of Comparative Examples 3, 4 and 3 of the third embodiment are made. In the same manner as in Example 1, the actual amount of the developer was measured at the initial stage and after 50,000 copies (μC / g), and the image quality after 50,000 copies was evaluated. It was shown to.

[0062]

[Table 2]

Tables 1 and 2 show that, in the case of fine resin particles, at the time of formation of the coating layer or at any point after the formation of the coating layer, the residual amount of the monomer in the resin was adjusted to 200 ppm or less. Each carrier has a stable triboelectric charge amount as a developer over a long period of use and excellent image quality at the time of image formation, but finally the residual amount of the resin monomer in the coating layer Is 200p
It is understood that each carrier of Comparative Example exceeding pm has an unstable triboelectric charge amount when used as a developer when used for a long period of time, has a lot of background fogging during image formation, and sometimes causes blocking or the like, which is not preferable. You.

[0064]

As is clear from the above description, according to the carrier for electrophotography of the present invention, when used as a developer, a stable and appropriate amount of triboelectric charge is ensured from time to time. No toner scattering or fogging
High-quality images can be obtained stably for a long time.
An excellent effect such as no occurrence of blocking in the developing machine and no generation of offensive odor in the copying machine can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a high-speed stirring mixer applied to the production of a carrier of the present invention.

FIG. 2 is an enlarged plan view of a horizontal rotating body 18. FIG.

[Explanation of symbols]

 10 Main body container 11 Main body lid 12 Raw material input port 13 Input valve 14 Filter 15 Inspection port 16 Thermometer 17 Temperature control jacket 18 Horizontal rotating body with stirring blades 18a, 18b, 18c Stirring blade 18d Central part 19 Vertical rotating body 20 Carrier outlet 21 Exhaust valve 22 Motor 23 Exhaust port 24 Vacuum pump 25 Exhaust valve 26 Exhaust valve

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-61260 (JP, A) JP-A-5-249749 (JP, A) JP-A-2-2576073 (JP, A) JP-A-2- 160032 (JP, A) JP-A-63-235959 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/113

Claims (1)

(57) [Claims] Claims: 1. Resin fine particles dried under reduced pressure atmosphere
Use, on the surface of the magnetic particles, a carrier for electrophotography formed by forming a resin coating layer by a dry coating method under reduced pressure atmosphere, the amount of the residual monomer in the coating layer, the coating layer An electrophotographic carrier, wherein the amount is 200 ppm or less based on the total amount of resin to be formed.