JPH09134037A - Developer for electrostatic latent image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize developing characteristics of a developer even when plastic deformation of a polyolefin is caused by introducing a proper amt. of carbon black having a specified oil supply amt. as a conductive fine particles to be added to a coating resin for a carrier. SOLUTION: This developer consists of a carrier comprising magnetic particles coated with a polyolefin and a toner containing a binder resin and a coloring agent. To the coating resin of the carrier, carbon black having 50-300ml/100g oil supply amt. is added by 5-50wt.%. If the oil supply amt. of carbon black is <=50ml/100g, dispersibility of the carbon black in the coating resin decreases, which makes difficult to stably control the volume specific resistance of the carrier. If the oil supply amt. is >=300ml/100g, good dispersibility is obtd. but the structure of the carbon black is easily broken, which render the volume resistance of the carrier unstable for long-term use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for electrostatic latent image used in electrophotography, electrostatic photography, electrostatic printing and the like.

[0002]

2. Description of the Related Art As a developer for forming an image by an electrophotographic method, a two-component developer composed of so-called toner and carrier is often used. As the carrier used here, a carrier in which magnetic particles composed of ferrite, iron powder, or the like is used as it is, or a resin-coated carrier in which the surface of these magnetic particles is coated with a resin is known. Of these, resin-coated carriers are preferably used from the viewpoints of ease of charge control and carrier durability.

Conventionally, styrene / acrylic resins, polyester resins, silicone resins and the like have been widely used as carrier coating resins. Recently, it has been proposed to coat the carrier with polyolefin.

Since the resin itself does not have a polar group, polyolefin has good water repellent property and releasability, and therefore, it is said that it has excellent durability when applied to an electrophotographic carrier.

However, polyolefin is generally used as an insulating material, and when it is used as a carrier coating resin, the volume resistivity, which is the electrical resistance value of the carrier, becomes extremely high. When a carrier having an excessive volume resistivity is used as a carrier for electrophotography, a sufficient amount of development cannot be obtained, which causes insufficient image density. Therefore, in order to solve this problem, Japanese Patent Laid-Open No. 2-18
In 7771, JP-A-6-266168, etc., it is proposed to add conductive fine particles to the coating layer to control the volume resistivity of the carrier. Here, as the conductive fine particles, conductive carbon black is used because the carrier resistance can be relatively easily lowered with a small amount.

Further, when polyolefin is used as a carrier coating resin, it tends to be plastically deformed as a characteristic of the resin itself, which causes a new problem that has not been found in conventional carriers.

[0007] Specifically, there is a problem that when the toner is put into a copying machine as a developer, the polyolefin is deformed by the stress received in the developing machine or at the time of development, and the carrier resistance is changed accordingly. As a result, when the developer is used for a long period of time, the developing performance becomes unstable and problems such as insufficient image density and background fog occur.

As described above, when polyolefin is used as the carrier coating resin, a problem not found in the conventional resin coated carrier occurs, and a developer having sufficiently stable characteristics can be obtained. The current situation is that there are none.

[0009]

SUMMARY OF THE INVENTION According to the present invention, when a developer containing a polyolefin-coated carrier is used for a long period of time, the developing performance becomes unstable and problems such as insufficient image density and background fog occur. SUMMARY OF THE INVENTION It is an object of the present invention to provide a developer for an electrostatic latent image, which solves the above-mentioned problems and has stable developing characteristics for a long period of time.

[0010]

Means for Solving the Problems As a result of earnest research on a polyolefin-coated carrier, the present inventors introduced an appropriate amount of carbon black having an oil absorption in a specific range as conductive fine particles to be added to a carrier-coated resin. As a result, they have found that the dispersed state of the conductive fine particles can be stabilized, and as a result, the development characteristics of the developer can be stabilized for a long period of time even if plastic deformation of the polyolefin occurs, and the present invention has been completed.

Specifically, the object of the present invention has been achieved by adopting the following constitution.

[1] A developer for an electrostatic latent image comprising a carrier in which the surface of magnetic particles is coated with polyolefin and a toner containing a binder resin and a colorant, wherein the coating resin of the carrier has an oil absorption amount of 50-300ml / 100g
The carbon black in the range of 5 to the coating resin
A developer for an electrostatic latent image, characterized in that 50% by weight is added.

[2] The developer for an electrostatic latent image according to claim 1, wherein the carrier coated with the polyolefin is coated by a surface polymerization coating method.

The structure of the present invention will be described in detail below.

As the magnetic particles that are the core material of the carrier used in the present invention, a substance that is strongly magnetized in that direction by a magnetic field is used. Specifically, iron, ferrite, magnetite, nickel, cobalt and other ferromagnetism metals or alloys or compounds containing these metals can be used. Further, the surface of the magnetic particles may be further oxidized or reduced. The term “ferrite” as used herein is a general term for magnetic compounds containing iron and is not limited to spinel type.

The weight average particle size of the magnetic particles is
It is preferably in the range of 40 to 90 μm. Here, the weight average particle size is measured by a laser diffraction particle size analyzer HELO.
It is measured by S (manufactured by SYMPATEC Co., Ltd.).

The polyolefin coating the surface of the magnetic particles is specifically a resin or copolymer resin composed of a known aliphatic hydrocarbon monomer such as ethylene, propylene, butene and cyclopentene, Alternatively, a resin composed of a copolymer containing 50% or less by weight of another vinyl-based monomer can be used. Further, a resin obtained by combining and mixing two or more kinds of these synthesized resins can also be used. Of these,
Particularly preferably, good performance can be obtained by using polyethylene as a coating resin with ethylene as a monomer.

Examples of carbon black added to the coating resin of the carrier used in the present invention include furnace black, lamp black, thermal black, channel black and the like.

The oil absorption amount (dibutyl phthalate (DBP) adsorption) of carbon black added to the coating resin of the carrier used in the present invention is in the range of 50 to 300 ml / 100 g, preferably 80 to 200 ml / 100 g. If it is 50 ml / 100 g or less, the dispersion of carbon black in the coating resin is poor, and it is difficult to stably control the volume resistivity of the carrier. Also, 300m
When the amount is 1/100 g or more, the dispersibility is good, but the structure of carbon black is easily broken, and the volume resistance of the carrier becomes unstable after long-term use. In addition,
The oil absorption of the carbon black used in the present invention is determined by ASTM D-2414-7 using an absorption meter.
It is measured according to 0.

Good performance can be obtained when the primary particle size of carbon black used in the present invention is in the range of 10 to 500 nm, preferably 15 to 250 nm. The primary particle size of carbon black is the number average particle size determined by observation with a transmission electron microscope.

The BET specific surface area of the carbon black used in the present invention measured by the nitrogen adsorption method is 5 to 700 m.
Good performance can be obtained by using ² / g, preferably 25-500 m ² / g.

The pH value of the carbon black used in the present invention is preferably in the range of 5.5 to 9.5.
The pH value of carbon black is measured as follows. An appropriate amount of carbon black is measured into a beaker, 10 ml of water is added to 1 g of carbon black, and the mixture is boiled for 15 minutes. A few drops of ethyl alcohol may be added to make the carbon black wettable. After boiling, the mixture is cooled to room temperature and the supernatant is removed by a gradient method or a centrifugation method to leave a mud. A glass electrode is placed in this mud and the pH is measured. The point to be noted during measurement is that the measured value may vary depending on the insertion position of the electrode, so move the beaker so that the electrode surface and the mud-like surface are in sufficient contact, and the value is measured when the pH becomes constant. To read.

The amount of carbon black added to the coating resin of the carrier used in the present invention is 5 to 5 relative to the coating resin.
It is 0% by weight, preferably 7 to 35% by weight. If the carbon black content is less than 5% by weight,
The control of the volume resistivity of the carrier becomes insufficient, and the volume resistivity values of the individual carrier particles vary widely.
On the other hand, if it is more than 50% by weight, it is difficult to uniformly disperse the carbon black in the coating resin, which may cause problems such as liberation of carbon black, which is not preferable. The amount of carbon black added to the carrier coating resin can be determined by a thermobalance method. As a measuring device, a Shimadzu thermogravimetric measuring device TGA-50 (Co., Ltd.)
Shimadzu) is used. The measurement conditions need to be adjusted according to the type of material to be measured, but when polyethylene is used as the coating resin, the following conditions can be used, for example. About 10 mg of the sample is kept at 50 ° C. for 30 minutes, then heated to 500 ° C. and kept for 15 minutes.
The amount of change in weight during this period is W1. The temperature is further raised to 900 ° C., and held for 15 minutes again. The amount of weight change during this period is W
Let it be 2. From the obtained ratio W2 / W1 of the amount of change in weight, C. B. The content of can be determined. In the measurement, the resin-coated carrier may be directly measured, but if the influence of the magnetic particles is concerned, the resin-coated carrier may be dissolved in hot toluene or the like, and the magnetic particles may be removed with a filter before the measurement. .

The method for producing the carrier used in the present invention is not particularly limited, and a known coating method can be applied. Specifically, for example, a method in which polyolefin is dissolved in a suitable solvent and spray-coated on the surface of magnetic particles, polyolefin powder is electrostatically adhered to the surface of magnetic particles, and the temperature is further adjusted to near or above the melting point of the resin material. A method of mechanically fixing while heating, a method of polymerizing and growing an olefin monomer on the surface of magnetic particles and coating the same (surface polymerization coating method) described in JP-A-60-106808 and the like can be applied.

Of these coating methods, when the method of coating by polymerizing and growing an olefin monomer on the surface of the magnetic particles is used, a resin coating layer having a sufficient thickness can be uniformly formed. It is preferable in that a developer having more stable characteristics can be obtained.

The method of adding carbon black to be added to the carrier coating resin of the present invention is not particularly limited, and an appropriate method may be selected according to the resin coating method. For example, in the case of a melt coating method, carbon black is dispersed and mixed in a solution of a resin, in the case of a mechanical fixing method, resin fine particles and carbon black to be added are mixed, in the case of a polymerization coating method, A method such as adding carbon black to the inside of the polymerization tank during the polymerization reaction can be used. Further, a method of mechanically driving carbon black into the carrier coating layer after coating with the carrier resin can also be used.

Here, the resin coating amount of the carrier is preferably in the range of 1.0 to 10.0% by weight based on the whole carrier.

The volume resistivity of the carrier used in the present invention is 1.0 × 10 ^{8 to} 5.0 × 10 ¹⁴ Ω.
A range of cm is preferred. Furthermore, 1.0 × 10 ⁹ to 1 ×
A range of 10 ¹⁴ Ωcm is preferred.

Here, the method of measuring the volume resistivity of the carrier is, specifically, about 1.0 g of the carrier and 1.0
After filling an insulating cylindrical container of cm ² and measuring the sample height under a load of 500 g, an electric field of DC 100 V is applied to measure the current value. The volume resistivity can be obtained from the obtained sample height and current value by the following "Formula 1".

Volume resistivity value [Ωcm] = {100 [V] / cross-sectional area [cm ² ]} / {current value [A] / sample height [cm]} (Equation 1) The volume resistivity of the carrier In order to adjust, there is a method of adjusting the electrical resistance of carbon black in addition to changing the addition amount of carbon black. The electric resistance of carbon black can be adjusted by a method such as an oxidation treatment or firing in an inert atmosphere. For example, if the surface is oxidized, an insulating layer is formed on the surface of carbon black and the electrical resistance increases.

The weight average molecular weight of the polyolefin coating the carrier used in the present invention is 5.0 × 1.
Good results can be obtained in the range of 0 ^{4 to} 5.0 × 10 ⁶ ,
The range of 1.0 × 10 ^{5 to} 1.0 × 10 ⁶ is more preferable.

The molecular weight distribution and weight average molecular weight of the polyolefin can be measured by gel permeation chromatography (GPC).

Specifically, the GPC model 150C (WA
TERS) was used. O-Dichlorobenzene (Butyl Hydroxy Toluene) as a solvent
Was added), and the measurement temperature was set to 135 ° C. and the measurement flow rate was set to 1.0 ml / min. As a measurement sample,
Prepare a 0.1% by weight sample solution as the sample resin concentration,
0.4 ml was injected into the measuring part. The column of the measurement unit may be selected as necessary and is not particularly limited, but for example, S
hodex A-80M, HT-800P, HT-80
6M (Showa Denko) etc. can be used. It should be noted that impurities (components other than the coating resin such as magnetic particles and functional fine particles added to the coating resin) generated during preparation of the sample solution may be removed by a metal sintering filter before the measurement.

In the measurement of the sample, a calibration curve prepared in advance with plural kinds of monodisperse polystyrene and diphenylmethane is used.

Further, in the present invention, in addition to selecting an appropriate carbon black to be added to the carrier coating resin, by suppressing the deformation of the carrier coating resin surface,
The performance of the developer can be further improved. Specifically, in order to smooth the surface of the carrier-coated resin,
It is effective to apply mechanical stress to the carrier surface.
Here, as the mechanical stress, a known mixer, granulator, crusher or the like can be used. In particular,
For example, Mechanomill (made by Okada Seiko Co., Ltd.), Henschel mixer (made by Mitsui Mining Co., Ltd.), Vertical Granulator (made by Paulec Co., Ltd.), Hybridizer (made by Nara Machinery Co., Ltd.), Mechanofusion system (Hosokawa Micron (made by Hosokawa Micron Co., Ltd.) Co., Ltd.) and the like can be used.
Further, when performing this treatment, if the heating is performed within the range of 50 to 150 ° C. at the same time, the treatment can be completed in a short time.

The toner used in the developer of the present invention is not particularly limited as long as it is a toner that meets the purpose of developing an electrostatic latent image, and a known toner can be used.

The toner is composed of at least a binder resin and a colorant, but may further contain other additives if necessary. The weight average particle size is preferably 1 to
It is 20 μm, more preferably 4 to 15 μm. In addition,
The weight average particle diameter of the toner used in the present invention is the same as in the case of magnetic particles.
Can be found using.

The binder resin constituting the toner is not particularly limited, and various conventionally known resins can be used. For example, a styrene resin, an acrylic resin, a styrene / acrylic copolymer resin, a polyester resin, etc. may be mentioned.

The colorant constituting the toner is not particularly limited, and various conventionally known materials can be used. Examples thereof 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, and rose bengal.

Other additives that can be used as necessary include charge control agents, release agents such as polyolefin wax and natural wax, magnetic powders, dispersion aids for these additives, and other known materials. Can be used.

The method for producing the toner is not particularly limited, and a known method can be used. Specifically, the constituent materials are mixed, melt-kneaded, and then subjected to a cooling step to be pulverized and classified to obtain a toner by a pulverization method for obtaining a toner, emulsion polymerization, suspension polymerization, or the like. A polymerization method or the like can be used.

Further, as the fluidity imparting 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 hydrophobized with a silane coupling agent, a titanium coupling agent, or the like.

As the developer, the above-mentioned toner and the resin-coated carrier are mixed and used. In this case, the toner is preferably mixed and used in a proportion of 2 to 10% by weight based on the whole developer. A known mixer can be used as a mixer for mixing the toner and the resin-coated carrier.

[0044]

EXAMPLES The present invention will be described below with reference to specific examples and comparative examples.

<Production Example of Toner><TonerI> Styrene / n-butyl methacrylate copolymer resin (softening point 132 ° C., glass transition point 60 ° C.) 100 parts by weight carbon black (MA # 8, manufactured by Mitsubishi Kasei Co., Ltd.) ) 8 parts by weight Low molecular weight polypropylene (Viscor 550P, manufactured by Sanyo Kasei Co., Ltd.) 5 parts by weight Charge control agent (TP-302, manufactured by Hodogaya Chemical Co., Ltd.) 3 parts by weight The above materials were thoroughly mixed by a ball mill. Then, the mixture was melt-kneaded with a three-roll kneader heated to 140 ° C. The kneaded product was left standing and cooled, coarsely pulverized using a feather mill, and further finely pulverized by a jet mill. After that, air classification is performed, and the average particle size is 7.
Colored particles of 0 μm were obtained. Then, hydrophobic silica fine particles (H-2050EP, Hoechst Co., Ltd.) were added to the colored particles.
0.5 wt% and titania fine particles (TAF-510, manufactured by Fuji Titanium Co., Ltd.) 0.4 wt% were added and mixed to obtain a positively charged toner I.

<Toner II> 100 parts by weight of polyester resin (Tufton NE-382, manufactured by Kao Corporation) 3 parts by weight of brilliant carmine 6B (C.I.15850) Natural wax (refined carnauba wax No. 1, Noda wax) 3 parts by weight Charge control agent (E-84, manufactured by Orient Chemical Industry Co., Ltd.) 5 parts by weight By the same method as in the production example of Toner I, colored particles having an average particle size of 7.5 μm Got

Thereafter, 0.5% by weight of hydrophobized silica fine particles (R-974, manufactured by Nippon Aerosil Co., Ltd.) was added to the colored particles.
And 0.3% by weight of hydrophobized titania fine particles (T-805, manufactured by Nippon Aerosil Co., Ltd.) were added and mixed to obtain a negatively charged toner.
I got II.

<Production Example of Carrier><Carrier1> In an autoclave, 500 ml of dehydrated n-hexane and 450 g of magnetic particles (magnetite, weight average particle size 65 μm) previously dried under reduced pressure are put and stirred. Next, 2.0 mmol of a Ziegler-Natta catalyst was added and the mixture was stirred to support the catalyst on the surface of the magnetic particles.

Next, 0.22 g of carbon black I shown in the following table was charged from the nozzle in the upper part of the autoclave.
The carbon black I used was one that had been dried under reduced pressure in advance and was mixed with dehydrated n-hexane to form a slurry.

After that, pressure is applied and the mixture is heated at 90 ° C. for 5 minutes.
By continuously supplying ethylene gas for 0 minutes, ethylene was polymerized on the surface of the magnetic particles, and a polyethylene composition containing magnetite and carbon black was obtained. Further, the polyethylene composition obtained here has a mesh size of 106 μm.
The carbon black-containing polyethylene-coated carrier 1 was obtained by removing aggregates with a No. 3 sieve and removing free polyethylene particles with a sieve having an opening of 38 μm.

<Carrier 2 to 8> The same as Carrier 1 except that the type of magnetic particles, the type of carbon black, and the addition amount are changed to those shown in "Table 1" below, and the ethylene polymerization pressure and time are adjusted. Thus, carbon black-containing polyethylene-coated carriers 2 to 8 were obtained.

<Carrier 1+ to 3+> Carbon black-containing polyethylene-coated carriers 1 to 3 were put into a mechanomill (manufactured by Okada Seiko Co., Ltd.) and stirred at a stirring blade rotation speed of 2000 rpm under heating at 80 ° C. A treatment for applying mechanical stress to the carrier surface was performed. This treatment was performed for 60 minutes to obtain carriers 1+ to 3+.

[0053]

[Table 1]

[0054]

[Table 2]

<< Performance Evaluation 1 >> For each of the above carriers,
Positively charged toner I was mixed so that the toner concentration would be 6% by weight, to prepare developers 1 to 8 and 1+ to 3+. Each developer was put into a Konica U-BIX 4155 copier (manufactured by Konica Corp.), and in continuous mode under high temperature and high humidity (30
℃, 80% RH) 100,000 sheets, low temperature and low humidity (10 ℃, 2
A total of 200,000 sheets were copied at 0% RH), and the following evaluations were performed.

[Image Density] A total of 5 at the four corners and the center of the image
A document in which a solid image having a document reflection density of 1.30 was set at each position was copied, the relative reflection density of the output image with respect to a white paper was measured at five positions, and the average value was calculated. A reflection densitometer RD-917 (manufactured by Macbeth Co., Ltd.) was used for the density measurement, and an average image density of 1.30 or more was judged to be good. The evaluation was conducted at the initial stage and at the end of copying.

[Background Fog] The relative reflection densities of five non-image areas near the four corners and the central area of the image with respect to a white paper were measured, and the average value thereof was obtained. A reflection densitometer RD-917 (manufactured by Macbeth Co., Ltd.) was used for density measurement.
A background fog density average value of 0.005 or less was judged to be good. The evaluation was conducted at the initial stage and at the end of copying.

[0058]

[Table 3]

<< Performance Evaluation 2 >> For each of the above carriers,
Negatively charged toner II was mixed so as to have a toner concentration of 6% by weight to prepare developers 1 to 8 and 1+ to 3+. Each developer was put into a Konica U-BIX 6192 copying machine (manufactured by Konica Corp.), and 100,000 sheets under high temperature and high humidity (30 ° C., 80% RH) and low temperature and low humidity (10 sheets) in a single sheet intermittent mode.
A total of 200,000 sheets were copied at 100 ° C. at 20 ° C. and 20% RH, and evaluation was performed in the same manner as Performance Evaluation 1.

[0060]

[Table 4]

As described above, in the developer comprising the toner and the carrier, the oil absorption amount and the addition amount of the carbon black to be added to the polyolefin which is the carrier coating resin are kept within an appropriate range, whereby the volume resistivity of the carrier is improved. It is possible to provide a developer for developing an electrostatic charge image that suppresses changes and exhibits stable developing characteristics for a long period of time.

[0062]

EFFECTS OF THE INVENTION By using the developer of the present invention, development for an electrostatic image having a stable development characteristic for a long period of time without a maximum image density or background fog even when used in a high speed copying machine or in any environment The agent can be obtained.

Claims (2)

[Claims] 1. A developer for electrostatic latent images comprising a carrier in which the surface of magnetic particles is coated with polyolefin and a toner containing a binder resin and a colorant, wherein the coating resin of the carrier has an oil absorption amount of Carbon black in the range of 50-300 ml / 100 g is 5-50 with respect to the coating resin.
A developer for an electrostatic latent image, which is characterized by being added by weight%. 2. The electrostatic latent image developer according to claim 1, wherein the carrier coated with the polyolefin is coated by a surface polymerization coating method.