JPH11305491A - Electrophotographic developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such an electrophotographic developer and an image forming method that an olefin resin-coated carrier is mixed with a toner to prepare the electrophotographic developer having excellent fluidity, fast electrification property, and especially maintaining high image density for continuous copying in a low temp. and low humidity environment without producing background fog, while making use of the intrinsic feature of the olefin resin-coated carrier that the surface is hardly contaminated. SOLUTION: This electrophotographic developer consists of an olefin resin- coated carrier containing fine particles fixed to the surface, and a toner containing at least a binder resin and a coloring agent. The fixing index R of the fine particles to the resin-coated carrier is controlled to 70 to 100. Thereby, the intrinsic feature of the olefin resin-coated carrier that the surface is hardly contaminated is made use of, and the carrier is mixed with the toner to prepare the developer having excellent fluidity and fast electrification property. The obtd. developer has excellent effect such as to maintain high image density during continuous copying process, especially in a low temp. and low humidity environment, without producing background fog.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic developer used for electrophotography, electrostatography, electrostatic printing, and the like, and an image forming method.

[0002]

2. Description of the Related Art Conventionally, in order to prevent fatigue deterioration of a two-component type electrophotographic developer (hereinafter simply referred to as a developer) when the carrier is repeatedly used, various resins such as an acrylic resin or a silicone resin are provided on the surface of the carrier. Are known. However, carriers coated with these resins have a problem in that they tend to deteriorate due to fatigue during long-term use. Therefore, a resin-coated carrier coated with a polyolefin-based resin instead of the above resin has been developed. The polyolefin-based resin-coated carrier has the advantage that the surface thereof is less likely to be contaminated with toner and the like and the carrier characteristics are stable, as compared with the resin-coated carrier coated with another resin.

However, since the polyolefin resin generally has a low glass transition temperature, its flowability when used as a developer is inferior to that of a developer using a carrier coated with another resin, and charge generation is slow. There's a problem. This problem is remarkable in a low-temperature and low-humidity environment.

[0004] This problem occurs in image formation by electrophotography, particularly when an original having a high image density is set and image formation is continuously performed, that is, in a use mode in which toner consumption is intense. This causes a problem that the generation of the charged toner is delayed, and the toner that is not sufficiently charged is used for image formation. In the case of forming an image in such a mode, not only a sufficient image density cannot be obtained but also a problem that toner adheres to a non-image portion and contaminates a background portion of an output image (causing background fog). I do.

Japanese Patent Laid-Open Publication No. Hei 6-266168 proposes a technique for incorporating fine particles into the resin coating layer of the above-mentioned olefin resin-coated carrier. It is described that the fluidity when mixed with a developer to improve the fluidity is improved.

[0006]

However, as a result of diligent studies conducted by the present inventors, the fine particle-containing polyolefin-based resin-coated carrier described in the above publication has an effect of improving the fluidity and chargeability when this is used as a developer. The present invention was completed by noticing that the fine particles were simply contained in the resin coating layer, but was realized by stably adhering the fine particles on the surface of the carrier particles. .

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above circumstances. It is an object of the present invention to mix a developer with a toner while making the most of the inherent characteristic of an olefin resin-coated carrier that the surface is hardly contaminated. The developer is excellent in fluidity and rapid generation of charge, and maintains a high image density, especially during continuous copying under a low-temperature and low-humidity environment, and does not cause background fog. An object of the present invention is to provide an image forming method used.

[0008]

The above object is achieved by the following constitution.

1. In an electrophotographic developer composed of an olefin-based resin-coated carrier having fine particles fixed on its surface and a toner containing at least a binder resin and a colorant, a fixation index R of the fine particles on the resin-coated carrier Is from 70 to 100.

[0010] 2. 2. The electrophotographic developer according to item 1, wherein at least organic fine particles are used as the fine particles adhered to the surface.

3. Wherein the step of fixing and containing the fine particles on the surface of the resin-coated carrier includes the step of fixing and containing the fine particles by stirring the resin-coated carrier with a stirring blade while heating. Or the developer for electrophotography according to 2.

4. 4. An image forming method, comprising: forming a magnetic brush with the electrophotographic developer according to any one of the above 1 to 3, and developing an electrostatic image formed on the electrophotographic photosensitive member. .

Hereinafter, the present invention will be described in detail.

In the present invention, an olefin resin is used as a coating resin of the resin-coated carrier in a developer comprising a toner and a resin-coated carrier described later, and the degree of fixation R is 70 to 100 on the surface of the resin-coated carrier. It is characterized in that fine particles are fixed and contained.

[Olefin-Based Resin-Coated Carrier] <Magnetic Particles> As the magnetic particles as the core material of the resin-coated carrier used in the present invention, for example, a substance which is strongly magnetized in the direction by a magnetic field can be used.
Specifically, ferrite such as iron powder particles, Zn ferrite, Ni ferrite, Cu ferrite, Mn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Cu-Zn ferrite, Ni-Zn ferrite, Mn-Cu-Zn ferrite Known materials such as particles and magnetite particles can be used.

<Coating resin> As the coating resin of the resin-coated carrier used in the present invention, a known olefin resin can be used. Specifically, polymers of olefin monomers such as ethylene, propylene, 1-butene, 1-hexene, 1-octene, 4-methyl-1-pentene, 2-methyl-1-butene, 1-decene and 1-octadecene And a copolymer selected from two or more of these. In particular, when polyethylene is used, particularly good results can be obtained.

[0017] The resin coating amount of the magnetic particles is preferably in the range of 0.5 to 10 wt% based on the entire resin-coated carrier.

The preferred molecular weight of the above coating resin is 50,000 to 1,000,000 as a weight average molecular weight Mw.
0, the number average molecular weight Mn is 10,000 to 500,
000.

The ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn is preferably in the range of 2.0 to 10.0.

The weight average molecular weight and the number average molecular weight of the resin are determined by gel permeation chromatography (G
PC). In the measurement, a calibration curve prepared in advance from a plurality of types of monodisperse polystyrene and diphenylmethane is used.

<Resin Coating Method on Resin-Coated Carrier> The resin coating method on the resin-coated carrier is not particularly limited, and a known resin coating method can be applied. Specifically, for example, (a) a method of dissolving a coating resin in an appropriate solvent and applying it to the surface of the magnetic particles; and (b) electrostatically attaching a coating resin powder to the surface of the magnetic particles. A method of mechanically fixing the material while heating it to near or above the melting point of the material; (Surface polymerization coating method) (d) There is a method using two or more of these methods in combination.

<Composition of Fine Particles> Known fine particles can be selected and used as fine particles fixed to and contained on the surface of the resin-coated carrier used in the present invention. Specifically, carbon black fine particles, silica, titania,
Metal oxide fine particles such as alumina, metal nitride fine particles such as silicon nitride, metal carbide fine particles such as silicon carbide, boron carbide and titanium carbide, acrylic resin and styrene resin,
Including styrene / acrylic copolymer resin, ester resin, urethane resin, phenol resin, carbonate resin, ketone resin, fluorine resin such as fluorinated methacrylate and vinylidene fluoride, melamine resin,
One or more kinds of organic fine particles made of a formaldehyde resin, a silicone resin or a modified product thereof can be used. If necessary, the surface may be hydrophobized with a coupling agent or silicone oil.

Of these, good results can be obtained when the organic fine particles are used alone or 50% by weight or more of the total fine particles are used as the organic fine particles. Organic fine particles have better environmental stability of charging. Among them, it is preferable to use organic fine particles having a three-dimensional crosslinked structure in the molecular structure, such as a crosslinked acrylic resin, a crosslinked melamine resin, a crosslinked urethane resin, and the like. In addition, as a method for imparting a crosslinked structure to the organic fine particles, in the case where the organic fine particles cannot be obtained by using only the selected main raw material monomer, the organic fine particles can be obtained by using a known crosslinker at the time of manufacturing the fine particles.

<Average Primary Particle Size of Fine Particles> The average primary particle size of the fine particles contained on the surface of the resin-coated carrier used in the present invention is preferably in the range of 0.05 to 0.5 μm. More preferably, it is in the range of 0.1 to 0.4 μm. The average primary particle size of the fine particles is determined by observing 200 or more particles with an electron microscope, determining the fixed direction diameter of each particle, and then determining the number average particle size thereof.
Further, the fine particles used in the present invention are preferably substantially spherical, and the fine particles are substantially spherical when the long diameter Dl and the short diameter D of the particles obtained by microscopic observation.
The ratio Ds / Dl to s is defined to be in the range of 0.5 to 1.0.

<Fixed Particle Index R of Carrier> In the present invention, the fixed particle index R of the fine particles fixed on the surface of the resin-coated carrier is from 70 to 100 when the particle-containing resin-coated carrier of the present invention has a ( When the aqueous dispersion (containing an appropriate amount of surfactant) was further dispersed using a homogenizer “US-150T” (manufactured by Nippon Seiki Seisaku-sho, Ltd.), the fine particle dispersion separated from the carrier was light-transmitted by the following measurement method. It means that the value measured at a ratio is 70 to 100.

Here, a specific method of measuring the sticking degree index R of the fine particles is as follows. That is, 5 g of a resin-coated carrier containing fine particles on its surface and 20 cc of water to which an appropriate amount of a surfactant has been dropped are added to a 50 cc glass beaker to obtain a mixed solution. Thereafter, ultrasonic waves are applied to the mixed solution for 60 seconds by a homogenizer “US-150T” (manufactured by Nippon Seiki Seisakusho KK) to forcibly deteriorate the mixed solution. In addition,
The diameter of the oscillator of the above homogenizer is 20 mmφ, the current value is 100 μA, and the height of the oscillator is adjusted to the bottom of the beaker and almost to the center of the liquid level. Next, the supernatant liquid of the mixed liquid forcedly degraded by the homogenizer is separated and collected without diluting, and set on a spectrophotometer “U-3500” (manufactured by JASCO Corporation), and the light having a wavelength of 500 nm is set. Is determined for the light transmittance. The light transmittance obtained by this operation is defined as a fine particle fixation index R.

<Method of Incorporating Fine Particles in Resin-Coated Carrier> In the present invention, the method of incorporating fine particles near the carrier surface is not particularly limited, and a known method can be used. In particular,
For example, using (A) a known mixer such as a Henschel mixer or a vertical granulator, a method of fixing to the carrier surface after resin coating, (B) using a known surface modifying device such as a hybridizer or an ong mill, A method in which the carrier is contained on the carrier surface after resin coating, a method in which the carrier is covered with a mixed resin obtained by mixing (C) the fine particles and the coating resin, and the like, so that the carrier is contained in the carrier surface can be applied. Further, two or more of these methods may be used in combination. Further, any of a dry method and a wet method may be used as necessary.

Among them, a method of applying a stress to the carrier surface by rotating the stirring blade to fix and contain the fine particles is particularly preferable.
It is.

Further, in the case of the above (A) or (B), through a two-stage process of a low-speed stirring process and a high-speed stirring process,
The dispersion uniformity of the fine particles can be improved, and better results can be obtained.

In the case where fine particles are fixedly contained on the surface of the resin-coated carrier, a more stable contained state can be obtained by heating as necessary.

<Fixed amount of fine particles on resin-coated carrier>
In the present invention, the amount of fine particles fixedly contained on the surface of the resin-coated carrier varies depending on the specific gravity of the fine particles,
Often 0.05 to
It is preferably in the range of 5.0 wt%. Note that the content is more preferably in the range of 0.1 to 3.0 wt%.

[Toner] The toner used in the present invention includes:
Known ones can be used. Specifically, a toner comprising at least the following binder resin and colorant,
Further, if necessary, a release agent, a charge control agent, a fluidizing agent, a magnetic substance, a lubricant, a cleaning aid, and the like may be contained by internal addition or external addition.

<Binder Resin> Preferred binder resins are as follows.
For example, a styrene resin, an acrylic resin, a styrene / acrylic copolymer resin, a polyester resin and the like can be mentioned.

<Colorant> The colorant constituting the toner is not particularly limited, and various conventionally known materials can be used. Examples include carbon black, nigrosine dye, aniline blue, calcoil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, rose bengal, and the like.

<Other Additives> Other additives that can be used as required include charge control agents, release agents such as polyolefin waxes and natural waxes, magnetic powders, and dispersion aids for these additives. Can be

Further, as a fluidizing agent, inorganic fine particles or organic fine particles may be added to the toner surface. As the inorganic fine particles, inorganic oxide particles such as silica, titania, and alumina are preferable. Furthermore, these inorganic fine particles may be subjected to a hydrophobic treatment with a silane coupling agent, a titanium coupling agent, or the like.

<Method of Manufacturing Toner> The method of manufacturing the toner is not particularly limited, and a known method can be used. Specifically, a pulverization method in which the constituent materials are mixed, melt-kneaded, and then cooled, pulverized, and classified to obtain a toner, and a polymerization method in which emulsion polymerization or suspension polymerization is performed to obtain a toner are used. it can.

[Developer] The developer of the present invention is prepared by mixing the above resin-coated carrier and toner. Here, in mixing the resin-coated carrier and the toner, a conventionally known mixer can be used, and a mixer which exerts less stress on the developer at that time is preferable. Specifically, a Henschel mixer is used. A rotation type mixer such as a V-type mixer, a W-cone mixer, and a rocking mixer can obtain better results than a high-speed stirring type such as a mixer. Also,
The mixing ratio of the resin-coated carrier and the toner is preferably in the range of 2 to 20% by weight of the toner with respect to the developer.

[Image Forming Method] In the image forming method of the present invention, an electrostatic latent image is preferably formed on a photoreceptor, and the electrostatic latent image is developed with the developer of the present invention to form a toner image. And
The toner image is transferred onto a transfer paper and fixed to form an image. In the above-described image forming method, a known method can be used as a developing method for developing an electrostatic latent image formed on a photoreceptor, and a magnetic brush method is used as a method for transporting a developer to a developing area. It is preferred to use In this case, a contact developing method in which a magnetic brush formed by a developer directly contacts a photoreceptor forming an electrostatic latent image to perform development, and a non-contact method in which a developing method is close but not in contact Any of the developing methods may be used.

[0040]

EXAMPLES [Preparation of Resin Coated Carrier A] A resin coating solution in which 15% by weight of carbon black was dispersed in a resin solution obtained by heating and melting a polyethylene resin in toluene was prepared.
Using a Spira coater (Okada Seiko), average particle size 65μm
Was provided with a polyethylene resin coating layer on the surface of the spherical magnetite particles. Then, the mixture was passed through a sieve having an opening of 106 μm to remove aggregates in the polyethylene resin-coated particles, thereby obtaining a polyethylene resin-coated carrier A. In addition, the polyethylene resin coating amount of the obtained polyethylene resin-coated carrier A was 3.5 wt% with respect to the whole carrier.

[Preparation of Resin-Coated Carrier B1] Spherical crosslinked melamine / formaldehyde resin fine particles (average primary particle diameter 0.21 μm) were added to the polyethylene resin-coated carrier A obtained by the above-described preparation procedure, and the weight of the resin-coated carrier A Into a vertical granulator VG-25 (Nara Machinery Works) at a rate of 0.25 wt%.
The number of revolutions of the stirring blade was set to 500 rpm, and
Stirred dry for minutes. Subsequently, the temperature was raised to 100 ° C,
The stirring blade was set at a rotation speed of 1000 rpm, and a further 120
Stirred dry for minutes. After that, the carrier B1 containing the fine particles fixed on the surface by natural cooling to room temperature was obtained. Note that the fine particle fixation index R of the carrier B1 is 8
4.8.

[Preparation of Resin-Coated Carriers B2 and B3] A carrier B2 containing fine particles fixed on the surface in the same manner as in Carrier Preparation Example B1 except that the processing conditions for fine particles were changed to the conditions shown in Table 2. And B3 were obtained. In addition,
The fine particle fixation index R of the carriers B2 and B3 is respectively
98.5 and 68.0.

[Resin coated carriers C1 to C3, D1, D
2. Preparation of E1, E2] Resin-coated carriers C1 to C3, D1, D2, E1, E2 containing fine particles fixed in the same manner as in Carrier Preparation Example B except for the conditions shown in Tables 1 and 2.
I got The fine particle fixation index R of the carriers C1 to C3 is 82.1, 96.4, and 64.5, and the fine particle fixation index R of the carriers D1, D2, E1, and E2 is 7
2.2, 57.0, 80.8 and 78.3.

[Preparation of Resin-Coated Carriers F1 and F2] A polymethyl methacrylate resin-coated carrier was prepared in the same manner as in the preparation of the polyethylene resin-coated carrier A, except that a polymethyl methacrylate resin was used instead of the polyethylene resin. F1 was obtained. The resin coating amount of the resin-coated carrier F1 was 2.0% by weight based on the entire carrier. Thereafter, a fine particle-containing resin-coated carrier F2 was obtained in the same manner as the resin-coated carrier B1, except that titanium oxide fine particles (average primary particle size: 0.1 μm) were used in an amount of 0.5 wt% based on the weight of the resin-coated carrier F1. Note that the fine particle fixation index of the resin-coated carrier F2 was 80.2.

[Preparation of Resin-Coated Carrier G1] Instead of polyethylene resin as the carrier-coated resin, 95.0% by weight of a silicone resin and 5.0% by weight of the titanium oxide fine particles used in the preparation example of the carrier F2 were used. Was prepared in the same manner as in the preparation example of the polyethylene resin-coated carrier A except that a resin coating solution in which was mixed in a toluene solvent in advance was used to obtain a fine particle-containing silicone resin-coated carrier G1. In addition, the coating amount of the fine particle-containing silicone resin of the carrier G1 was 1.0 wt% with respect to the entire carrier, and as a result, the fine particle content was 0.05 wt% with respect to the entire carrier. The fine particle fixation rate was 76.
It was 0%.

The composition, shape, average primary particle size and addition amount of the fine particles used for producing the resin-coated carriers C1 to C3, D1, D2, E1, E2, F2 and G1 obtained as described above (however, G1 Are shown in Table 1 below.

[0047]

[Table 1]

Table 2 below shows the treatment conditions of the above-mentioned resin-coated carriers containing fine particles and the value of the fine particle fixation index R.

[0049]

[Table 2]

[Preparation of Toner] 1 part by weight of a charge control agent (T-77: Orient Chemical Industry) per 100 parts by weight of styrene / acrylic copolymer resin, and low molecular weight polypropylene (Biscol 660P: Sanyo Chemical) as a release agent 3 parts by weight and 10 parts by weight of carbon black (Black Pearl L: Cabot) as a colorant were mixed and melt-kneaded by a biaxial kneader. Thereafter, through cooling and crushing steps, fine crushing and air classification were performed to obtain colored particles having a weight average particle size of 7.5 μm.

0.3 parts by weight of hydrophobic silicon oxide fine particles (R805: Nippon Aerosil) and 0.6 parts of hydrophobic titanium oxide fine particles (T805: Nippon Aerosil) were added to the above colored particles.
Parts by weight and 0.1 part by weight of zinc stearate fine particles (Type S: Nippon Oil & Fat) were externally added and mixed with a Henschel mixer to obtain a negatively charged toner used in Examples.

[Preparation of Developer] Each of the resin-coated carriers A, B1 to B-B is adjusted so that the toner concentration in the developer becomes 5 wt%.
3, C1 to C3, D1, D2, E1, E2, F2, G1
And the above-mentioned toner are charged into a V-type mixer.
Minutes, negatively charged developers A, B1 to B3, C1 to C
3, D1, D2, E1, E2, F2, and G1 were produced.

[Evaluation of Performance] Developers A and B1 to B
3, C1 to C3, D1, D2, E1, E2, F2, G1
About 650 g each of the commercially available copier Konica
A4 with 50% blackening area ratio mounted on 7050 (Konica)
Manuscripts should be continuously printed in an environment with a temperature of 10 ° C and humidity of 20% RH.
A real copy evaluation of 00 copies was performed.

At this time, the relative reflection density of the output image with respect to a blank sheet was measured at two places, ie, a solid portion (relative reflection density 1.30) and a background portion (relative reflection density 0.00) of the document. The evaluation was performed twice at the initial stage and twice for the 1000th sheet.

Here, for the density measurement, a reflection densitometer RD-9 was used.
18 (Macbeth), and the solid portion has a relative reflection density of 1.
A good image was judged to be good at 30 or more, and a good image was 0.005 or less for the background portion.

Table 3 shows the results of the performance evaluation.

[0057]

[Table 3]

From Table 3, it can be seen that the developer of the embodiment is continuous 1000
In the process of repeated image formation of the sheets, the density of the solid image portion did not decrease and the fog of the background portion did not increase, which is excellent. However, in the developer of the comparative example, the density decrease of the solid image portion and the background portion did not occur. It can be seen that the increase in fog is remarkably poor in practicality.

[0059]

As demonstrated by the examples, according to the developer and the image forming method of the present invention, the toner is mixed with the toner and developed while utilizing the inherent characteristics of the olefin resin-coated carrier that the surface is less likely to be contaminated. It has excellent fluidity when used as an agent and has a rapid charge generation, and has excellent effects such as maintaining a high image density and preventing background fog, especially during continuous copying under a low-temperature and low-humidity environment. .

Claims (4)

[Claims] 1. An electrophotographic developer comprising an olefin-based resin-coated carrier having fine particles fixed on the surface thereof and a toner containing at least a binder resin and a colorant, wherein the fine particles are applied to the resin-coated carrier. Index R of
Is from 70 to 100. 2. The electrophotographic developer according to claim 1, wherein at least organic fine particles are used as the fine particles adhered to the surface. 3. The method according to claim 1, wherein the step of fixing and containing the fine particles on the surface of the resin-coated carrier includes the step of fixing and containing the fine particles by stirring the resin-coated carrier with a stirring blade while heating. The electrophotographic developer according to claim 1, wherein the developer is an electrophotographic developer. 4. A process for forming a magnetic brush with the electrophotographic developer according to claim 1 and developing an electrostatic image formed on an electrophotographic photosensitive member. Characteristic image forming method.