JPH11242363A - Carrier for electrophotographic developer and electrophotographic developer using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for an electrophotographic developer having a slight change in resistance, the quantity of electric charges and flowability and capable of maintaining initial image characteristics in long-time resistivity to printing and to provide an electrophotographic developer using the carrier. SOLUTION: A carrier core material is coated with a silicone resin contg. a quaternary ammonium salt catalyst to obtain this carrier for an electrophotographic developer. Since the quaternary ammonium salt catalyst is used for the silicone resin, the hardening and crosslinking of the silicone resin can be made to proceed slowly and therefore, since coating strength and adhesive strength to the core material can be enhanced, the obtd. carrier has a light change in physical carrier properties such as the quantity of electric charges, resistance and flowability in long-time resistivity to printing. The objective developer using the carrier has a slight change in image density and fogging even in the long-time resistivity to printing and maintains initial image characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for a two-component electrophotographic developer used for a copying machine, a printer and the like, and an electrophotographic developer using the carrier.

[0002]

2. Description of the Related Art An electrostatic image two-component developer used in an electrophotographic system is composed of a toner and a carrier. The carrier is mixed and stirred with the toner in a developing tank to give a desired charge to the toner. And a carrier material that carries the charged toner to the electrostatic latent image on the photoconductor and forms a toner image.

[0003] The carrier remains on the magnet in the developing tank,
The toner is returned to the developing tank again, mixed and stirred again with the newly supplied toner, and used repeatedly.

Therefore, in order to stably maintain a desired image quality during the printing life, it is required that the characteristics of the carrier be stable during the use period.

As such a carrier, a carrier in which a carrier core material is coated with a resin has been proposed. However, since the developer is constantly subjected to stress such as collision between particles or collision with a developing device and a photoreceptor during the printing life,
The toner component adheres to the carrier surface due to the impact and the heat generated by the impact, causing so-called spent. In addition, the resin film is peeled off by these impacts, and charging characteristics, resistance characteristics,
Fluidity changed, and the initial image could not be stably maintained.

For example, styrene / acrylic copolymers, styrene / butadiene copolymers, polyurethane resins, etc., which have been proposed as coating resins, have a high surface tension and cause a spent phenomenon in which toner adheres to the carrier surface. The resistance is increased, causing toner to adhere to a white background portion of an image, so-called fogging, and causes deterioration of image characteristics.

[0007] Fluororesins are relatively useful for spent, but they have low coating strength, poor adhesion to the core material, and are often peeled off, resulting in excessively low resistance. The initial image could not be maintained.

On the other hand, a silicone resin having a low surface tension which is effective for spent is proposed, but the silicone resin itself is liable to wear, and the electric resistance, the charge amount, the fluidity, etc., in long-time printing are increased. No stability was obtained, and the initial image characteristics could not be maintained.

Further, in order to stabilize the charging characteristics of the silicone resin, JP-A-60-76754 and JP-A-61-284775 propose to add an organic tin compound. The organic tin compound makes the coating very hard by accelerating the curing of the silicone resin.However, it becomes very brittle due to impact. A large initial image cannot be maintained.

Further, in order to maintain the charge amount, Japanese Patent Application Laid-Open No.
JP-A-8-168056 and JP-A-4-204666 propose that a quaternary ammonium salt be incorporated into the skeleton of a resin. However, it was not possible to increase the strength of the coating film, and it was not possible to maintain the initial image in a long press life as described above.

Further, a carrier coated with a resin generally has high resistance, so that it is difficult to obtain a sufficient image density, and there is a problem that a fogging phenomenon easily occurs. In addition to the problem that resistance tends to change during long-term printing,
Japanese Patent Application Laid-Open No. 56-126843 proposes a method of adjusting the initial electric resistance by adding a conductive agent to a coating resin and stabilizing the resistance characteristics in printing durability.

However, even when a resin to which a conductive agent is added is coated, the acrylic resin or the fluororesin has a poor holding property of the conductive agent in addition to the same reason as described above. There is a problem that the agent is detached and the initial image cannot be maintained.

Further, Japanese Patent Application Laid-Open No. 61-204643 proposes adding a conductive agent to a silicone resin. As a curing catalyst for silicone resins, organotin-based or titanium-based catalysts are generally used.However, these catalysts are too strong, and the curing speed is too fast, so that the conductive agent cannot be sufficiently contained. The conductive agent was hardened, and the conductive agent could not be sufficiently held, and the conductive agent was detached due to stress in the developing tank, causing a rapid change in resistance, thereby causing the deterioration of image characteristics to be accelerated.

[0014]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an electrophotographic developing apparatus capable of maintaining the initial image characteristics in a long printing run with a small change in resistance, charge amount and fluidity as described above. An object of the present invention is to provide a carrier for an agent and an electrophotographic developer using the carrier.

[0015]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above object is achieved by the following invention.

That is, the present invention provides a carrier for an electrophotographic developer, wherein a carrier core material is coated with a silicone resin containing a quaternary ammonium salt-based catalyst.

Further, the present invention provides an electrophotographic developer comprising the above carrier and toner.

Further, the present invention provides a carrier for an electrophotographic developer, wherein the carrier core material is coated with a silicone resin containing preferably 0.5 to 5% by weight of a quaternary ammonium salt catalyst. This is an electrophotographic developer using this.

Furthermore, when a conductive agent for adjusting the resistance and the chargeability is used, the carrier core material is coated with a silicone resin containing the above quaternary ammonium salt catalyst, so that it can be used for a long time. An object of the present invention is to provide an electrophotographic developer carrier that can be maintained in printing and an electrophotographic developer using the same.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In the present invention, the carrier whose core material is coated with a silicone resin containing a quaternary ammonium salt-based catalyst is not particularly limited, and the silicone resin used here is not particularly limited. And a modified silicone resin modified with methylphenyl silicone resin, acryl, epoxy, urethane, polyethylene, alkyd, and the like.

The quaternary ammonium salt catalyst used in the present invention can be represented by the following general formula.

Embedded image

Here, R _{1 to} R ₄ represent a hydrogen atom, an alkyl group, an allyl group and derivatives thereof. X represents a sulfate ion, a nitrate ion, an organic sulfate ion, an organic nitrate ion, an organic carboxylate ion or the like. Among them, the above R _{1 to} R
₄ is preferably an alkyl group, particularly preferably 1 to 1 carbon atoms.
4 alkyl group. X is preferably an organic carboxylate ion, and particularly preferably an organic carboxylate ion having 1 to 4 carbon atoms.

Examples of the quaternary ammonium salt include tetramethylammonium acetate, tetraethylammonium acetate, tetrapropylammonium acetate, tetrabutylammonium acetate, and tetramethylammonium propanate.

By using such a quaternary ammonium salt-based catalyst, the degree of crosslinking and curing of the silicone resin can be gradually increased in the coating step and the heating step, and the adhesion to the carrier core material is improved. be able to. In addition, the film strength can be sufficiently increased by gradually promoting curing and crosslinking. further,
By controlling the content of the quaternary ammonium salt-based catalyst, the adhesion strength to the core material and the coating strength can be further improved. The content of the quaternary ammonium salt-based catalyst is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight.
If the content of the quaternary ammonium salt-based catalyst is less than 0.2% by weight, the effect cannot be sufficiently obtained. If the content is more than 10% by weight, the effect of the catalyst is too strong and the coating strength becomes brittle.
Similarly, even when the conductive agent is contained, by using the quaternary ammonium salt-based catalyst as described above, the conductive agent can be sufficiently mixed into the resin while the resin is crosslinked and cured, and the conductive agent can be used. It is possible to increase the retention of the active agent. In this case, if the content of the catalyst is less than 0.2% by weight, the effect of the catalyst cannot be sufficiently obtained. If the content is more than 10% by weight, the curing is too fast, so that the sufficient retention of the conductive agent cannot be obtained.

Examples of the conductive agent used for adjusting the resistance and chargeability of the carrier include conductive carbon, boride such as titanium boride, and oxide such as titanium oxide, iron oxide and chromium oxide. Can be used, but conductive carbon is particularly preferred. As the conductive carbon, specifically known carbon blacks can be used, for example, furnace black, acetylene black,
Channel black and the like are exemplified. The content of the conductive agent is preferably 0.5 to 100 parts by weight, more preferably 1 to 50% by weight, and particularly preferably 5 to 20% by weight, based on the silicone resin. When the content of the conductive agent is 0.
If it is less than 5% by weight, sufficient conductivity cannot be obtained.
If it is more than 00% by weight, it cannot be sufficiently retained in the resin.

The carrier core material used in the present invention is not particularly limited, and examples thereof include iron powder, ferrite powder, and magnetite powder. Cu, Zn, Mg, Mn, Ca, L
Ferrite powder using i, Sr, Sn, Ni, Al, Ba, Co or the like is preferably used. There are no restrictions on the shape, surface properties, particle size, magnetic properties, resistance value, chargeability, etc. of the carrier core material.

The coating amount of the silicone resin with respect to the carrier core material is 0.0
The content is preferably 5 to 10.0% by weight, particularly preferably 0.1 to 7.0% by weight. It is necessary to adjust the coating thickness of the silicone resin in accordance with the specific surface area of the carrier core material to reduce the exposed portion of the carrier core material, thereby reducing the developer resistance, charge amount, and fluidity. The change can be reduced. This coating thickness is preferably 0.02 to 2.0 μm.

As a method of coating the silicone resin, it is common to dilute the silicone resin in a solvent and coat the surface of the carrier core material. The solvent used here may be any solvent that is soluble in the silicone resin, and examples thereof include toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and methanol. Also, on the carrier core material surface,
The method of coating the resin diluted with the solvent is applied by an immersion method, a spray method, a brush application method, a kneading method, or the like, and thereafter, the solvent is volatilized. In the present invention, it is particularly preferable to use a fluidized bed type coating apparatus. By using such a coating apparatus, the uniformity of the coating film thickness can be improved. Note that the surface of the carrier core material can be coated with the resin powder by a dry method instead of a wet method using such a solvent.

When the above-mentioned silicone resin is coated on the surface of the carrier core and then baked, either an external heating method or an internal heating method may be used. For example, a fixed or fluid electric furnace, a rotary kiln electric furnace or a burner furnace may be used. Often,
Alternatively, baking by microwave may be used. The baking temperature depends on the silicone resin used,
A temperature higher than the melting point or the glass transition point is required, and in the case of a thermosetting or condensation type, it is necessary to raise the temperature to a temperature at which curing sufficiently proceeds.

In this way, after the surface of the carrier core material is coated with the silicone resin and baked, the carrier is cooled, crushed and the particle size is adjusted to obtain the carrier coated with the silicone resin.

The carrier of the present invention is mixed with a toner and used as a two-component developer for electrophotography. The toner used here is a toner in which a charge control agent, a colorant, and the like are dispersed in a binder resin.

The binder resin used for the toner is not particularly limited. For example, polystyrene,
Chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylate copolymer, styrene-methacrylic acid copolymer, rosin-modified maleic resin, epoxy resin, polyester resin, polyethylene resin, polypropylene resin, polyurethane resin, etc. Is mentioned. These are used alone or in combination.

Any suitable charge control agent can be used. For example, in the case of a positively charged toner, there are a nigrosine dye, a quaternary ammonium salt, and the like.
In the case of a negatively charged toner, a metal-containing monoazo dye or the like can be used.

As the coloring agent, conventionally known dyes and pigments can be used. For example, carbon black,
Examples include phthalocyanine blue, permanent red, chrome yellow, and phthalocyanine green. In addition, external additives such as silica fine powder and titania can be added according to the toner in order to improve the fluidity and aggregation resistance of the toner.

The method for producing the toner is not particularly limited. For example, a binder resin, a charge control agent, and a colorant are sufficiently mixed by a mixer such as a Henschel mixer, and then melt-kneaded by a twin-screw extruder or the like. After cooling, pulverizing and classifying, adding an external additive and mixing with a mixer or the like.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on embodiments and the like.

Example 1 A silicone resin (manufactured by Dow Corning Toray Silicone Co., Ltd.) was added with conductive carbon (manufactured by Ketjen Black International) at 15% by weight based on the solid content of the silicone resin. Resin 1 was obtained by adding 2% by weight of a quaternary ammonium salt-based catalyst (tetramethylammonium acetate).

A manganese-based ferrite core material having an average particle size of 60 μm was coated with 1.5% by weight of the above resin by a fluidized bed coat, and heated at 250 ° C. for 2 hours to obtain Carrier 1.

Example 2 A resin 2 was obtained in the same manner as in Example 1 except that a quaternary ammonium salt catalyst (tetramethylammonium acetate) was added at 5% by weight based on the solid content of the silicone resin. Further, a carrier 2 was obtained in the same manner as in Example 1 using this resin.

Example 3 A quaternary ammonium salt catalyst (tetramethylammonium acetate) was added in an amount of 0.2% by weight based on the solid content of the silicone resin.
Resin 3 was obtained in the same manner as in Example 1. Further, using this resin, a carrier 3 was obtained in the same manner as in Example 1.

Example 4 A quaternary ammonium salt catalyst (tetraethylammonium acetate) was added to the same silicone resin as in Example 1 (manufactured by Dow Corning Silicone Toray Co., Ltd.) at 10% by weight based on the solid content of the silicone resin. Was added to obtain Resin 4. Further, using this resin, a carrier 4 was obtained in the same manner as in Example 1.

Comparative Example 1 A manganese-based ferrite core material having an average particle size of 60 μm was prepared by using only the same silicone resin as that of Example 1 (manufactured by Dow Corning Toray Silicone Co., Ltd.).
It was coated with a 5% by weight fluidized bed coat and heated at 250 ° C. for 2 hours to obtain Carrier 5.

Comparative Example 2 Resin 6 was obtained in the same manner as in Example 1, except that an organic tin salt catalyst (cybutyltin dilaurate) was used as a catalyst. Further, a carrier 6 was obtained in the same manner as in Example 1 using this resin.

Comparative Example 3 A resin 7 was obtained in the same manner as in Example 1 except that a titanium-based catalyst (titanium tetrabutoxy monomer) was used as a catalyst. Further, using this resin, a carrier 7 was obtained in the same manner as in Example 1.

[Evaluation Results] Carriers 1 to 7 obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were mixed with a polyester toner so that the toner concentration became 5% by weight, and a commercially available OPC photoconductor was obtained. A printing durability test was carried out with a reversal developing PPC mounted. Table 1 shows the results.

In Table 1, the methods for measuring the physical properties of the carrier and the image characteristics were performed based on the following. Charge: A blow-off powder charge measuring device manufactured by Toshiba Chemical Corporation was used. Resistance: An SM-5E super megohmmeter manufactured by Toa Denpa Kogyo KK was used. Fluidity: In accordance with JIS-Z2502 “Testing method for metal powder fluidity”. Image density: The solid image density was measured with a Macbeth densitometer. Fog: Fog on a white background image was measured using a colorimetric colorimeter Z-300 manufactured by Nippon Denshoku Industries Co., Ltd. or an apparatus equivalent thereto.

The overall evaluation in Table 1 was based on the following. ◎: Little change in image characteristics. ：: An image having a slight change in image characteristics but at an acceptable level. ×: The image characteristics are changed and are unacceptable. XX: A level worse than X.

[0048]

[Table 1]

As shown in Table 1, Examples 1 to 4
Compared with Comparative Examples 1 to 3, the change in resistance, charge amount, fluidity, image density and fog is small and a good image is maintained even in long-time printing.

[0050]

As described above, in the carrier for an electrophotographic developer of the present invention, the use of a quaternary ammonium salt catalyst as the silicone resin allows the curing and crosslinking of the silicone resin to proceed gradually. As a result, since the coating strength and the adhesion strength to the core material can be increased, changes in carrier physical properties such as charge amount, resistance and fluidity during long press life are small. Further, the developer of the present invention using such a carrier has a high image density even in a long press life,
Fog change is small and the initial image characteristics are maintained.

Claims (4)

[Claims] 1. A carrier for an electrophotographic developer, wherein a carrier core material is coated with a silicone resin containing a quaternary ammonium salt catalyst. 2. The carrier for an electrophotographic developer according to claim 1, wherein the quaternary ammonium salt catalyst is contained in the silicone resin in an amount of 0.5 to 5% by weight. 3. The carrier for an electrophotographic developer according to claim 1, wherein a conductive agent is contained in the silicone-based resin. 4. An electrophotographic developer comprising the carrier according to claim 1, 2 or 3, and a toner.