JPH08234500A - Carrier for electrostatic latent image developer and its production - Google Patents

Abstract

PURPOSE: To obtain a carrier having stable characteristics over a long period of time because the coating resin is less liable to the reduction of strength and does not cause peeling by uniformly dispersing a large amt. of carbon black and suppressing change with the lapse of time. CONSTITUTION: The surfaces of carrier cores are treated with a catalyst, an olefin monomer is fed to the surfaces of the cores in the presence of carbon black and polyolefin resin is formed by directly polymerizing the olefin monomer on the surfaces of the cores. The carbon black is incorporated into the resin while forming the resin and polyolefin resin coating layers contg. carbon black by 3-60 pts.wt. per 100 pts.wt. resin are formed on the surfaces of the carrier cores to produce the objective carrier having 1×10<1> -9μ10<6> Ω.cm electric resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for an electrostatic latent image developer used for developing an electrostatic latent image in an image forming method utilizing electrophotography.

[0002]

2. Description of the Related Art In electrophotography, generally, a photoreceptor is uniformly charged in the dark, and then the charge potential is lowered by selective image exposure to form an electrostatic latent image based on the difference in charge potential. An image is formed by developing the electrostatic latent image to form a visible image of toner on the surface of the photoconductor, and then transferring and fixing the toner image onto paper or the like.

As the developer, a one-component developer consisting only of toner and a two-component developer consisting of a mixture of toner and carrier are known, and the present invention relates to a carrier used for the two-component developer. In the two-component developer, the carrier plays a role of charging the toner and transporting it to the surface of the photoconductor, and the toner adheres to the surface of the carrier.
When the two-component developer is conveyed to the vicinity of the electrostatic latent image formed on the photoconductor, the toner is electrostatically attracted to the latent image portion and separated from the carrier, and moves to the latent image portion on the photoconductor. Form a visible image.

However, if the suction force between the toner and the carrier is too strong, that is, if the charge amount of the toner is too large, the toner is difficult to separate from the carrier, and the image density may be lowered. Therefore, in order to eliminate such an inconvenience, a method is generally used in which a bias voltage is applied between the developer and the latent image, and the force of the electric field is used to easily move the toner to the latent image. Also,
The development by such a bias electric field is indispensable for the reversal development method which is predominant in printers and digital copying machines, and by lowering the resistance of the carrier, the development efficiency can be improved and at the same time the edge effect is small and uniform. It is possible to obtain various images.

In the sense of a low resistance carrier, a non-coated carrier composed of magnetic material particles such as iron, magnetite and ferrite is known. However, although these non-coated carriers have low resistance, they are apt to cause poor charging, and toner scattering and fog are likely to occur. Also,
Since the weight is large, there is a problem that the toner component easily adheres to the carrier and becomes a spent due to the impact of stirring in the developing machine.

To deal with this, Japanese Patent Laid-Open No. 56-756
59, a method of coating the surface of a magnetic powder with a resin containing a conductive component, as described in JP-A-5-80591.
As described in JP-A No. 5-119539 and JP-A No. 5-119539, a low-resistance carrier is obtained by a method of fixing conductive fine particles to the surface of a carrier core obtained by dispersing magnetic fine particles in a binder resin and then pulverizing them. Is proposed.

However, in order to achieve a desired low resistance by the resin coating containing the conductive component as in the former case, it is necessary to add a large amount of the conductive component and it becomes difficult to uniformly disperse the resin in the resin. The brittleness of the layer makes it easier to peel off due to continuous use. In the latter case,
Even in the carrier having the conductive fine particles fixed to the surface, the conductive fine particles fall off due to stirring in the developing machine, and there is a problem that the initial resistance cannot be maintained.

Further, a monomer is supplied to the surface of a magnetic carrier core such as ferrite in the presence of carbon black, and the monomer is directly polymerized on the surface of the carrier core to form a polyethylene resin, while at the same time being added to the resin. Japanese Patent Laid-Open No. 2-187771 discloses that a carrier for a developer in which carbon black is incorporated to form a resin coating layer containing carbon black on the carrier is manufactured. However, this carrier is not necessarily aimed at lowering the resistance, and the amount of carbon black taken in is relatively small. Therefore, even if it is used in the developing method in which the driving force of the bias electric field is used to attach the toner to the latent image, satisfactory results are not always obtained, and the image density may decrease depending on the combination with the toner and the operating environment temperature. There was a possibility to invite.

Further, when a large amount of carbon black is incorporated into the resin coating layer to reduce the resistance, the resistance value is likely to change with time, and this stable maintenance is required. Further, the carrier having a resin coating layer containing a large amount of carbon black tends to have a reduced strength of the resin coating layer, and the stress due to stirring causes peeling of the resin coating layer during repeated use, resulting in an increase in resistance. There is also a problem.

[0010]

The present invention has a low resistance,
The present invention provides a carrier for an electrostatic latent image developer, which is suitable for a reversal development method in which development is performed under application of a bias electric field.
Further, the present invention is intended to produce the above-mentioned carrier for electrostatic latent image developer, and in particular, there is little change in resistance due to use, and peeling of the coating layer which imparts low resistance. The aim is to produce a resin-coated carrier that does not occur.

[0011]

A carrier for an electrostatic latent image developer according to the present invention is a low resistance carrier having a polyolefin resin coating layer having conductivity on a surface of a magnetic carrier core. The resin coating layer
It is characterized in that carbon black is contained in an amount of 3 to 60 parts by weight with respect to 100 parts by weight of the polyolefin-based resin, and the electric resistance of the carrier is 1 × 10 ^{1 to} 9 × 10 ⁶ Ω · cm.

In the method for producing a carrier for an electrostatic latent image developer according to the present invention, a polyolefin resin coating layer having conductivity is formed on the surface of a magnetic carrier core to produce a low resistance carrier. At this time, the surface of the carrier core is treated with a catalyst, the olefinic monomer is supplied to the surface of the carrier core in the presence of carbon black, and the olefinic monomer is directly polymerized on the surface of the carrier core to form a polyolefin resin. While simultaneously incorporating carbon black into the resin, a polyolefin resin coating layer containing 3 to 60 parts by weight of carbon black per 100 parts by weight of the resin was formed on the surface of the carrier core, and the electric resistance was 1 × 10. The carrier is characterized by being ^{1 to} 9 × 10 ⁶ Ω · cm.

In the above production method, when the olefin-based monomer is polymerized in the presence of carbon black to form the polyolefin-based resin on the surface of the carrier core, carbon black is present from the beginning of the polymerization of the olefin-based monomer. Although it may be good, at the beginning of the polymerization of the olefin-based monomer, the polymerization is started without the presence of carbon black, a thin polyolefin-based resin film is formed on the surface of the carrier core, and then carbon black is introduced into the reaction system. It is desirable to continue the polymerization reaction in the presence of black to form the final polyolefin-based resin coating layer, which makes it possible to efficiently incorporate carbon black into the polyolefin-based resin, resulting in stable properties. A resistance carrier can be manufactured.

That is, in a more preferred embodiment of the method for producing a carrier for an electrostatic latent image developer, according to the present invention, a polyolefin resin coating layer having conductivity is formed on the surface of a carrier core having magnetism to reduce the resistance. When manufacturing a carrier, the surface of the carrier core is treated with a catalyst, and an olefin-based monomer is supplied to the surface of the carrier core in the absence of carbon black to directly polymerize the olefin-based monomer on the surface of the carrier core to form a polyolefin. Starting the formation of a resin coating layer made of a resin, then supplying carbon black, polymerizing an olefin monomer in the presence of carbon black to produce a polyolefin resin, at the same time incorporating carbon black into the resin Finally, 3 to 60 parts by weight of 100 parts by weight of the polyolefin resin is finally added. A resin coating layer containing carbon black allowed formed on the surface of the carrier core, the electrical resistance of 1 ×
It is characterized in that the carrier is 10 ^{1 to} 9 × 10 ⁶ Ω · cm.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The developer carrier of the present invention is a low resistance carrier having a polyolefin-based resin coating layer having conductivity on the surface of a magnetic carrier core. The carrier core is known as a material for a carrier of a two-component developer for electrophotography, for example, a metal such as ferrite, magnetite, iron, nickel or cobalt,
These metals and zinc, antimony, aluminum, lead,
Alloys or mixtures with metals such as tin, bismuth, beryllium, manganese, selenium, tungsten, zirconium and vanadium, metal oxides such as iron oxide, titanium oxide and magnesium oxide, nitrides such as chromium nitride and vanadium nitride, silicon carbide , A mixture with a carbide such as tungsten carbide, a ferromagnetic ferrite, and a mixture thereof can be applied.

The average particle size of the carrier core is preferably such that a carrier of 20 to 100 μm can be obtained after the resin coating layer is formed. The resin for forming the polyolefin resin coating layer having conductivity is not particularly limited,
Polyolefin resins such as polyethylene and polypropylene are suitable. The thickness of the resin coating layer is 0.1-5.
0 μm is preferred.

Further, the resin coating layer contains 3 to 60 parts by weight, preferably 4 to 40 parts by weight of carbon black with respect to 100 parts by weight of the resin. When the content of carbon black is less than 3 parts by weight, it becomes difficult to impart sufficient conductivity, while when it exceeds 60 parts by weight, the resin coating layer is easily peeled off and the carbon black is sufficiently retained in the resin. It becomes difficult to do so, and the printed image is likely to be adversely affected.

What is called conductive carbon black is suitable as the carbon black, and Ketjen Black (Ketjen Black International Co., Ltd.)
Made), Printex (made by Degussa), # 5500
Commercially available products such as (manufactured by Tokai Carbon Co., Ltd.) and MA-100 (manufactured by Mitsubishi Chemical Co., Ltd.) can be used. The average particle size of carbon black is 0.01 to
About 2 μm is preferable, and 0.01 to 1 μm is preferable.
Is.

The above-mentioned carrier for electrostatic latent image developer of the present invention is obtained by utilizing the method described in the above-mentioned JP-A-2-187771 and JP-A-60-106808 or by further improving it. It can be manufactured. That is, an olefin-based monomer is directly polymerized on the surface of a magnetic carrier core to form a polyolefin-based resin on the surface of the magnetic carrier core while simultaneously incorporating carbon black into the resin to form a resin coating. Is continued until a resin coating layer having a desired thickness is formed on the carrier core layer.

In order to directly polymerize the olefinic monomer on the surface of the carrier core, the surface of the carrier core is a catalyst having such a function (hereinafter referred to as a polymerization catalyst).
Need to be processed. As the polymerization catalyst, a highly active catalyst containing titanium and / or zirconium described in JP-A-60-106808 and soluble in a hydrocarbon solvent can be used.

The surface treatment of the carrier core with the polymerization catalyst is also described in detail in JP-A-2-187771, and it can be easily carried out by reacting the carrier core with the polymerization catalyst in a suitable solvent such as normal hexane. You can The polymerization reaction itself of the olefinic monomer can be carried out using an autoclave or the like, but in the present invention, this polymerization reaction is selectively carried out on the surface of the carrier core in the presence of carbon black.

Specifically, in a reaction vessel such as an autoclave, a carrier core surface treated with a polymerization catalyst (hereinafter referred to as an active carrier core) and carbon black are suspended in a polymerization solvent, and trialkyl is suspended in the suspension. The olefin-based monomer is supplied in the presence of a polymerization catalyst component such as aluminum. The olefin-based monomer is selectively polymerized on the surface of the active carrier core while taking in carbon black particles, and the polyolefin-based resin coating containing carbon black grows on the surface of the active carrier core, and finally the polyolefin of the present invention. A system resin coating layer is formed. By controlling the amount of the olefin-based monomer supplied into the polymerization reaction system, the film thickness of the polyolefin-based resin coating layer can be controlled. The thickness of the polyolefin resin coating layer is preferably 0.1 to 5.0 μm, and preferably 0.2.
Is about 3.0 μm.

The content of carbon black in the polyolefin resin coating layer is 3 to 60 parts by weight, preferably 4 to 40 parts by weight, per 100 parts by weight of the polyolefin resin. This content can be controlled by the amount of carbon black suspended in the polymerization reaction system, and is determined to a desired resistance value.

As described above, by directly polymerizing the olefin-based monomer on the surface of the magnetic carrier core to form the polyolefin-based resin and simultaneously incorporating the carbon black polyolefin-based resin into the resin, a large amount of carbon black is uniformly dispersed. The change over time is suppressed, and the strength of the coating resin is not significantly reduced and peeling does not occur, so that a carrier having stable characteristics for a long period of time can be obtained.

In the present invention, carbon black may be allowed to exist in the reaction system and incorporated into the produced polyolefin resin from the start of the polymerization reaction. However, in the initial stage of the polymerization reaction, the polymerization is carried out in the absence of carbon black to form a thin polyolefin resin coating on the surface of the carrier core, and then carbon black is supplied to the reaction system. By the two-step method in which the polymerization reaction is continued in the presence of, the introduced carbon black can be more effectively incorporated into the polyolefin-based resin, and the change in resistance over time can be significantly suppressed, and Since the polyolefin resin coating strength is not significantly reduced and peeling does not occur, it is possible to obtain a carrier having stable properties for a longer period of time.

Specifically, the active carrier core is suspended in a polymerization solvent in an autoclave, and an olefin-based monomer is supplied for polymerization (the amount of the olefin-based monomer is referred to as an initial olefin polymerization amount). Then, suspend the carbon black in the polymerization solvent and introduce it into the autoclave to uniformly suspend it, then supply the olefinic monomer again into the autoclave to restart the polymerization, and to form the resin coating layer having the final thickness. Form. Carbon black (C
The olefinic monomer that is polymerized in the presence of B) is CB
This is called the olefin polymerization amount. In the present invention, the total amount of the above-mentioned initial olefin polymerization amount and the CB-based olefin polymerization amount becomes the total polymerization amount of the olefins used for the polymerization. Is preferably in the range of 0.01 to 0.8 by weight,
Preferably 0.03-0.5, more preferably 0.05
Is about 0.3. If this ratio is smaller than 0.01, the stabilizing effect by the two-step method becomes small, while if it is larger than 0.8, the carbon black is not sufficiently taken in and the desired resistance value cannot be obtained.

[0027]

The carrier for an electrostatic latent image developer of the present invention comprises
It has a low resistance in an appropriate range, imparts an appropriate charge to the toner, and can be suitably used for a reversal development method utilizing a driving force of a bias potential.

Further, according to the method for producing a carrier for an electrostatic latent image developer of the present invention, a large amount of carbon black is uniformly dispersed to suppress a change over time, and peeling is small with a decrease in coating resin strength. As a result, a carrier having stable characteristics for a long period of time can be obtained.

In particular, in the initial stage of the polymerization reaction, the polymerization reaction is carried out in the absence of carbon black to form a thin resin film, after which carbon black is introduced and the polymerization reaction is continued in the presence thereof to form carbon black. By including it in the resin coating layer, the carbon black is more evenly dispersed to further suppress the change in electric resistance over time, and
The effect of preventing the deterioration of the coating resin strength is further enhanced, a more remarkable effect of preventing peeling is obtained, and the characteristics of the carrier are stabilized for a longer period of time.

[0030]

【Example】

(1) Production of Polymerization Catalyst 200 ml of dehydrated n-heptane and 12 in advance were placed in a flask having an inner volume of 500 ml replaced with argon at room temperature.
15 g (25 mmol) of magnesium stearate dehydrated under reduced pressure (2 mmHg) at 0 ° C. is put into a slurry. 0.44 g (2.3 mmol) of titanium tetrachloride was added dropwise with stirring, and then the temperature was started and the reaction was carried out under reflux for 1 hour to obtain a viscous transparent titanium-containing catalyst (polymerization catalyst) solution. .

(2) Evaluation of activity of active catalyst 400 ml of dehydrated hexane and triethylaluminum were added to an autoclave having an internal volume of 1 liter which was replaced with argon.
8 mmol, 0.8 mmol of diethylaluminum chloride, and 0.004 mmol of the titanium-containing catalyst obtained in (1) above as a titanium atom were added and charged.
The temperature was raised to 0 ° C. At this time, the system internal pressure is 1.5 kg / cm
It was ² G. Then, hydrogen is supplied to the device, and 5.5 kg / cm
After boosting to ² G, the total pressure was continuously feeding ethylene so as to maintain the 9.5kg / cm ² G, to obtain a 70g polymer for one hour polymerization. Polymerization activity is 365kg
/ G · Ti / Hr, MFR of the obtained polymer
(Melting flowability at 190 ° C., load 2.16 kg; J
IS K 7210) was 40.

(3) Production of polyethylene-coated carrier Sintered ferrite powder F-300 (Powder Tech Co., Ltd.) was placed in an autoclave having an internal volume of 2 liters, which was replaced with argon.
960 g (average particle size: 50 μm) was added, the temperature was raised to 80 ° C., and drying was performed under reduced pressure (100 mmHg) for 1 hour. Thereafter, the temperature was lowered to 40 ° C., 800 ml of dehydrated hexane was added, and stirring was started. Then diethyl aluminum chloride 5.
The reaction was carried out for 30 minutes by adding 0 mmol and 0.05 mmol of the polymerization catalyst of the above (1) as a titanium atom. Then, the temperature was raised to 90 ° C., and 4 g of ethylene was introduced. At this time, the system internal pressure was 3.0 kg / cm ² G. Then, hydrogen was supplied, the pressure was raised to 3.2 kg / cm ² G, 5.0 mmol of triethylaluminum was added, and the polymerization was started. In about 5 minutes, the system internal pressure dropped to 2.3 kg / cm ² G and became stable. did.

After that, carbon black EC600JD
(Ketjen Black International Co., Ltd.) 6
g in a slurry form with 100 ml of dehydrated hexane, and then continuously feeding ethylene so as to keep the system internal pressure at 4.3 kg / cm ² G for 45 minutes (40 g of ethylene was introduced into the system in total. At that point, introduction was stopped) and polymerization was carried out to obtain 1006 g of carbon black-containing polyethylene resin-coated ferrite.

The dried powder was uniformly black, and it was observed by an electron microscope that the surface of the ferrite was thinly covered with polyethylene and the carbon black was uniformly dispersed in the polyethylene. The composition was measured by TGA (thermobalance) to find that ferrite and carbon black (CB) were 95.4 and 0.6 (wt), respectively.
%)Met. Since the rest is polyethylene (PE), the composition ratio of the three is ferrite: CB: PE = 95.
It means that it is 4: 0.6: 4.0.

Hereinafter, various carriers were prepared by changing the type of CB, the addition amount, and the addition ratio of ethylene before the addition of CB, and the results are shown in Table 1. For the resistance of the carrier, a carrier layer having a thickness of 0.5 cm is provided between electrodes having an electrode area of 5 cm ² and a load of 1 kg, a voltage of 1 to 10 V is applied to the upper and lower electrodes, and converted from the current value flowing there. I asked.

[0036]

[Table 1] Table 1: Manufacturing method of carrier and electronic resistance carbon black Ethylene polymerization amount Coating layer composition Ferrite (CB) Weight ratio Carrier charge (g) CB addition Total polymerization resistance type Addition amount (g) Before (g) Amount (g) PE CB (Ωcm) Example 1 960 EC600JD 6.0 4.0 40.0 100 15 2 × 10 ² 2 960 EC600JD 12.0 4.0 40.0 100 30 4 x 10 ¹ 3 960 EC600JD 2.0 4.0 40.0 100 5 8 × 10 ³ 4 960 EC600JD 1.2 4.0 40.0 100 3 8 × 10 ⁵ 5 960 EC600JD 6.0 2.0 40.0 100 15 3 x 10 ² 6 960 EC600JD 6.0 8.0 40.0 100 15 1 × 10 ² 7 970 EC600JD 4.5 3.0 30.0 100 15 3 × 10 ² 8 920 EC600JD 12.0 8.0 80.0 100 15 9 × 10 ¹ 9 960 XE2 20.0 4.0 40.0 100 50 6 x 10 ¹ 10 960 XE2 8.0 4.0 40.0 100 20 2 x 10 ² 11 960 # 5500 12.0 4.0 40.0 100 30 3 × 10 ³ 12 960 MA-100 12.0 4.0 40.0 100 30 8 × 10 ⁴ 13 960 MA-100 6.0 4.0 40.0 100 15 6 × 10 ⁶ (Note) EC600JD: Carbon black manufactured by Ketjen Black International, trade name Ketjen Black EC600JD XE2: carbon black manufactured by Dexsa, product name Printex XE2 # 5500: carbon black manufactured by Tokai Carbon Co., Ltd. MA-100: Mitsubishi Chemical Corporation ) Carbon black

Comparative Example-1 100 parts by weight of silicone resin and Ketjen Black EC
30 parts by weight of 600 JD was well mixed and dispersed in a toluene solvent with a dispersant to prepare a 1% solution in terms of resin solid content. Ferrite powder F-300 (manufactured by Powder Tech Co., average 50 μm) was put into this solution, and the solvent was removed by heating with good stirring to obtain a carrier coated with a silicone resin. The coated resin was 2 wt% and the carrier resistance was 8 × 10 ¹ (Ωcm).

Comparative Example-2 A carrier was obtained in the same manner except that the carbon black in Comparative Example-1 was changed to # 5500 (manufactured by Tokai Carbon Co., Ltd.). The resistance of this carrier is 4 × 10 ⁴ (Ω
cm).

(4) Evaluation of Carrier Stability [Evaluator] A commercially available medium speed copying machine (45 sheets / min) was modified so that the developing machine could operate independently. [Evaluation] Examples 1 to 13 and Comparative Example in the above-mentioned evaluation machine
After a predetermined amount of 1 and 2 carriers was charged and continuous operation was performed for 50 hours, the carriers were taken out of the developing machine, and the peeling of the coating resin and the change in resistance value were measured. The results of Examples 2 and 11 and Comparative Examples 1 and 2 are shown in Table 2. The peeling of the coating resin was quantified by thermal analysis (TGA). In the carriers of Examples-1 to 13, no peeling of the coating (reduction of the resin) was observed, and almost no increase in the resistance value was observed, whereas in Comparative Examples-1 and 2, the following results were obtained. As shown in the data, a large increase in the resistance value was observed as the resin peeled off and fell off.

[0040]

[Table 2]

Claims (4)

[Claims] 1. A low resistance carrier having a conductive polyolefin-based resin coating layer on the surface of a magnetic carrier core, wherein the polyolefin-based resin coating layer comprises carbon black per 100 parts by weight of the polyolefin-based resin. It contains 3 to 60 parts by weight, and the electric resistance of the carrier is 1 × 10 ^{1 to} 9 × 10.
^A carrier for a low-resistance electrostatic latent image developer, which is ⁶ Ω · cm. 2. The carrier for electrostatic latent image developer according to claim 1, wherein the polyolefin resin is a polyethylene resin. 3. When a low resistance carrier is manufactured by forming a polyolefin resin coating layer having conductivity on the surface of a carrier core having magnetism, the surface of the carrier core is treated with a catalyst and the presence of carbon black is present. An olefin-based monomer is supplied to the surface of the carrier core below, the olefin-based monomer is directly polymerized on the surface of the carrier core to form a polyolefin-based resin, and at the same time carbon black is incorporated into the resin, and thus the resin 100 A polyolefin resin coating layer containing 3 to 60 parts by weight of carbon black per part by weight is formed on the surface of the carrier core so that the electric resistance is 1 × 10 ^1.
A method of manufacturing a carrier for developing an electrostatic latent image, characterized in that the carrier is about 9 × 10 ⁶ Ω · cm. 4. When a low resistance carrier is produced by forming a polyolefin resin coating layer having conductivity on the surface of a magnetic carrier core, the surface of the carrier core is treated with a catalyst to remove carbon black. The olefin monomer is supplied to the surface of the carrier core in the presence of the polymer to directly polymerize the olefin monomer on the surface of the carrier core to start the formation of the resin coating layer made of the polyolefin resin, and then the carbon black is supplied. In the presence of carbon black, an olefin monomer is polymerized to form a polyolefin resin, and at the same time carbon black is incorporated into the resin, and finally 3 to 60 parts by weight of carbon are added per 100 parts by weight of the polyolefin resin. A resin coating layer containing black is formed on the surface of the carrier core, Anticancer ^{1 × 10 1 ~9 × 10 6} Ω · cm manufacturing method of an electrostatic latent image developing Kiaria, characterized in that a carrier.