JPH0373968A - Coating carrier - Google Patents

Abstract

PURPOSE:To stably obtain good triboelectrification and the low surface energy characteristic of a coating resin by incorporating a carbon black into the inner layer of a resin coating layer consisting of two layers. CONSTITUTION:The carbon black is incorporated into the inner layer of the resin coating layer consisting of the two layers; the inner layer and the outer layer. The exposing of the carbon black to the surface of the resin coating layer is obviated to prevent the degradation of triboelectrification. In addition, the effect of decreasing the electric resistance as the entire part of the coating carrier is sufficiently obtd. even if the layer where the carbon black exists is in the inner layer and, therefore, the preferable low surface energy is obtd. and the good triboelectrification is stably obtd. while the exposing of the carbon black is prevented by the outer layer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a carrier constituting a developer used in electrophotography, electrostatic recording, electrostatic printing, etc.
The present invention relates to a coated carrier having a resin coating layer on the surface of magnetic particles.

[Conventional technology]

A two-component developer consisting of a toner and a carrier is known as a developer used in electrophotography, etc. However, from the viewpoint of improving durability, such a carrier is made of magnetic particles. A coated carrier having a resin coating layer on its surface is advantageously used.

As the resin for the resin coating layer, it has been proposed to use a fluorine-containing resin with low surface energy properties in order to prevent toner substances from adhering to the carrier surface and stabilize the triboelectric charging properties of the carrier. (Japanese Unexamined Patent Publications No. 58-208754, No. 60-176048)
Publication No. 60-16617, Publication No. 59-2407
(See Publication No. 58, etc.)

However, since the fluorine-containing resin in such a coating carrier has high insulating properties, its electrical resistance as a carrier increases, and as a result, the amount of triboelectric charge imparted to the toner becomes excessive, resulting in poor developability. However, there is also the problem that the bias voltage applied between the photoreceptor and the developing device in the developing area does not act sufficiently, which tends to cause fog in the resulting copied image. In particular, in recent years, devices such as laser printers that carry out the development process by lowering the charged potential of the photoreceptor than before have become popular. The occurrence of fog becomes noticeable.

That is, when the charged potential of the photoreceptor is low, the so-called V, which indicates the correlation between the charged potential V of the photoreceptor and the image density,
A developer with a large slope in the -D curve is required, and in order to achieve this, it is necessary to reduce the electrical resistance of the coating carrier.

However, as a technique for reducing the electrical resistance of a coating carrier, a technique has been proposed in which conductive fine particles are contained in a resin coating layer (Japanese Unexamined Patent Application Publication No. 1986-1999).
No. 200245, No. 57-40267, No. 5
No. 8-108549, No. 55-163544, No. 59-223452, No. 54-7343, No. 61-219055, No. 63-28117
(See Publication No. 3, etc.)

[Problem to be solved by the invention]

However, in a coating carrier having a resin coating layer containing conductive fine particles, the conductive fine particles present on the surface of the resin coating layer are easily detached, and the detached conductive fine particles adhere to the toner and cause the toner to become damaged. There is a problem of worsening triboelectric charging properties. Furthermore, since conductive fine particles are present on the surface of the resin coating layer, there is a problem that the low surface energy characteristics of the coating resin are not fully exhibited.

If the triboelectric charging properties of the coating carrier change or the low surface energy characteristics are not exhibited in this way, it becomes difficult to impart a suitable triboelectric charge to the toner, and the coating carrier must be replaced at an early stage. This will cause inconvenience.

The present invention has been made based on the above circumstances, and its purpose is to stably exhibit good triboelectric charging properties and low surface energy properties of the coating resin when used repeatedly many times. The objective is to provide a coated carrier that can

[Means to solve the problem]

In order to achieve the above object, the present invention employs a coating carrier in which a resin coating layer consisting of two layers, an inner layer and an outer layer, is provided on the surface of magnetic particles, in which the inner layer contains carbon black. do.

The outer layer is preferably made of a low surface energy resin.

That is, in the present invention, the resin coating layer has a two-layer structure of an inner layer and an outer layer, and the inner layer is particularly selected and contains carbon black, thereby preventing carbon black from being exposed on the surface of the resin coating layer. This prevents the deterioration of triboelectric charging properties, and as will be understood from the explanation of the examples below, even if the carbon black is present in the inner layer, the effect of reducing the electrical resistance of the coating carrier as a whole can be sufficiently achieved. It was completed after confirming that the

As described above, according to the present invention, the electrical resistance can be reduced by the inner layer in which carbon black is present, and the outer layer can prevent the exposure of carbon black while obtaining preferable low surface energy properties, and the synergistic effect of these can be achieved. As a result, it is possible to obtain a developer that has a large slope in the so-called V-D curve and can stably obtain good triboelectrification and properties.

Therefore, even when applied to a developing process in which the charged potential of a photoreceptor is lowered, which has become popular in recent years, images can be stably formed many times without causing fog or toner scattering. .

Furthermore, since carbon black is not present in the outer layer, cracks in the outer layer, which tend to occur when carbon black is present, do not occur, and the durability of the carrier is improved in terms of mechanical strength.

As the magnetic particles that are the core material of the coating carrier, conventionally used ones can be used, and in particular,
Particles such as ferrite and magnetite can be preferably used.

The resin constituting the inner layer of the resin coating layer (hereinafter referred to as "inner layer resin") is preferably one that has good adhesion to magnetic particles from the perspective of increasing film strength, and from the perspective of increasing the dispersibility of carbon black. Among these, those having high compatibility with the carbon black are preferred. in particular,
Styrene resins such as styrene-butadiene resins, styrene-acrylic resins, acrylic resins, and the like can be preferably used.

The carbon black contained in the inner layer includes conventionally commercially available furnace black, acetylene black,
Any type of material such as channel black or thermal black may be used, but from the viewpoint of significantly reducing electrical resistance, the specific resistance should be 1 of that of the inner layer resin.
Carbon black having a molecular weight of /105 or less is preferable.

Further, from the viewpoint of improving dispersion stability, the primary particle diameter of carbon black is preferably 200 nm or less.

The content ratio of carbon black is preferably 1 to 50 M1B, particularly preferably 10 to 30 parts by weight, based on 100 parts by weight of the inner layer resin. Within this range, the effect of reducing electrical resistance by carbon black is fully exhibited.

The resin that constitutes the outer layer of the resin coating layer (hereinafter referred to as "outer layer resin"). From the viewpoint of effectively preventing adhesion of toner substances, resins having low surface energy properties are preferred. Specifically, polytetrafluoroethylene, tetrafluoroethylene/hexafluoroethylene copolymer, polytrifluorochloroethylene, polyvinylidene fluoride, tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer, fluorinated Silicone resins such as vinylidene-tetrafluoroethylene copolymers, fluorine-containing resins having groups substituted with fluorine atoms in side chains, dimethyl silicone resins, and methylphenyl silicone resins can be used. Among the above fluorine-containing resins, especially acrylic acid-1, -3,
A copolymer of -trihydroperfluoro-n-propyl and 1,1-dihydroperfluoro-n-propyl acrylate, a 1,1-dihydroperfluoroethyl acrylate polymer, etc. are preferred.

The thickness of the inner layer is about 0.4-2.9pm, and the thickness of the outer layer is 0.
．． 1~2.6I! The thickness is preferably about M, and the total thickness of the resin coating layer is preferably about 0.5 to 3.0p.

As a means for forming the resin coating layer, either a wet coating method or a dry coating method can be employed.

〔Example〕

Examples of the present invention will be described below along with comparative examples, but the present invention is not limited to these embodiments. In addition,
In the following, "parts" represent "parts by weight."

Example 1 In a solution of 15 g of styrene/methyl methacrylate copolymer dissolved in 300% of methyl ethyl ketone, 3 g of carbon black with a specific resistance of 1/10''' of the inner layer resin and a particle size of 24 nm was dispersed using an ultrasonic homogenizer. Then, a coating solution for the inner layer was prepared.

Using this inner layer coating liquid, an inner layer having an average thickness of 1 p was formed on the surface of spherical ferrite particles using a spira coater to obtain a -order carrier.

Next, 12 g of acrylic acid-1,1,3-)dihydroperfluoro-n-propyl/acrylic acid-1゜1-dihydroperfluoro-n-propyl copolymer (low surface energy resin) was added to 50 g of acetone. A coating liquid for the outer layer was prepared by dissolving it in the following.

Using this outer layer coating liquid, an outer layer is formed on the surface of the inner layer of the secondary carrier using a spira coater, so that the average particle size is IQO,n with a resin coating layer having a total average thickness of about 2 μm. A coating carrier C1 was obtained.

Example 2 In Example 1, the coating liquid for the outer layer was changed to acrylic acid-1, acrylic acid-1,
A coating carrier C2 was obtained in the same manner except that the coating liquid for the outer layer was prepared by dissolving 02 g of the 1-dihydroperfluoroethyl polymer low surface energy resin in 500 d of acetone.

Example 3 A coating carrier C3 was obtained in the same manner as in Example 1 except that the carbon black was changed to 3 g of carbon black having a specific resistance of 1/10'' of the inner layer resin and a particle size of 3 Or+m.

Example 4 A coating carrier C4 was obtained in the same manner as in Example 2, except that the carbon black used in Example 3 was changed to 3 g of carbon black.

Example 5 A coating carrier C5 was obtained in the same manner as in Example 1 except that the carbon black was changed to 3 g of carbon black having a specific resistance of 1/10'' of the inner layer resin and a particle size of 25 μm.

Example 6 A coating carrier C6 was obtained in the same manner as in Example 2, except that the carbon black used in Example 5 was changed to 3 g of carbon black.

Example 7 A coating carrier C7 was obtained in the same manner as in Example 1 except that the carbon black was changed to 3 g of carbon black having a specific resistance of 1/10'' of the inner layer resin and a particle size of 30 μm.

Example 8 A coating carrier C8 was obtained in the same manner as in Example 2, except that the carbon black used in Example 7 was changed to 3 g of carbon black.

Comparative Example 1 A comparative coating carrier C1 was obtained in the same manner as in Example 1, except that the inner layer coating liquid was prepared without containing carbon black.

Comparative Example 2 A comparative coating carrier C2 was obtained in the same manner as in Example 2, except that the inner layer coating liquid was prepared without containing carbon black.

Comparative Example 3 Acrylic acid-1,1,3-)dihydroverfluoro-n
-Propyl/acrylic acid-1,1-dihydroperfluoro-n-propyl copolymer 12 g Total acetone 500
- The specific resistance is 1/101' of the inner layer resin.
A coating liquid was prepared by dispersing 3 g of carbon black having a secondary particle size of 24 μm using an ultrasonic homogenizer.

Using this coating liquid, a resin coating layer with an average thickness of 21 parts M was formed on the surface of spherical ferrite particles using a spira coater, and a comparison coating carrier having one resin coating layer and an average particle size of 100 parts M was formed. Obtained C3.

Comparative Example 4 In Example 1, the coating liquid for the outer layer was changed to acrylic acid-1, acrylic acid-1,
The carbon black used for the inner layer (ratio Resistance = 1/10''' of inner layer resin, -order particle diameter = 24 nm) 2.
Comparative coating carrier C4 was obtained in the same manner except that the coating liquid for the outer layer was prepared by dispersing 4 g using an ultrasonic homogenizer.

Comparative Example 5 15 g of styrene/methyl methacrylate copolymer was mixed with 300 mj of methyl ethyl ketone! A solution dissolved in the above was used as an inner layer coating liquid, and using this inner layer coating liquid, an inner layer having an average thickness of 1 nm was formed on the surface of spherical ferrite particles using a Subira coater to obtain a -order carrier.

Next, using the outer layer coating liquid used in Comparative Example 4, an outer layer was formed on the surface of the inner layer of the secondary carrier using a spira coater, thereby forming an average particle having a resin coating layer with a total average film thickness of about 2p. A comparison coating carrier C5 having a diameter of 100 μm was obtained.

<Actual Photography Test> Two-component developers were prepared by mixing each of the carriers obtained in the above Examples and Comparative Examples with toner at a ratio such that the toner concentration was 4% by weight. The toner used was obtained as follows.

That is, 100 parts of styrene/methyl methacrylate/butyl acrylate copolymer resin, 10 parts of carbon black, and 3 parts of polypropylene wax were mixed, ground, crushed, and classified to obtain a powder with an average particle size of 10 μm. Further, 100 parts of this powder and 0.8 parts of hydrophobic silica fine particles were mixed in a Henschel mixer to obtain a toner.

Using each of the above two-component developers, an electrophotographic copying machine "U-8ix 1017J (manufactured by Konica ■)" was used.
The potential of the black background part (image part) of the photoreceptor is 1400V, and the potential of the white background part (
A photographic test was conducted under conditions of a potential of 150 V (non-image area) and a bias voltage of 1150 V in the development area, and the following items were evaluated.

(2) Durability of carrier Carrier durability was determined by measuring the change in the amount of charge of the developer when a 100,000-sheet photographic test was conducted. In other words, the smaller the change in the amount of charge, the better the durability of the carrier.

■Image fog This was determined by measuring the change in relative density of the white background area (non-image area) of the copied image when a 100,000-sheet photocopy test was conducted.In other words, the smaller this change is, the more likely the carrier is triboelectrically charged. and its stability is excellent.

■ Developability This was determined by measuring the change in the relative density of the black background area (image area) of the copied image when a 100,000-sheet photocopy test was conducted.In other words, the smaller this change is, the better the carrier's developability and frictional electrification. Excellent properties and stability.

■Toner scattering When a live-photograph test was conducted with 10,000 sheets, the state of toner scattering after the test was completed was evaluated on the following six scales.

That is, the less toner scatters, the better the triboelectric charging properties and stability of the carrier.

A: No scattering was observed at all.

B: Some scattering is observed around the developing device, but no scattering is observed in other areas.

C: Scattering is observed around the developing device and some scattering is also observed in other parts, but no problems are observed in both copy quality and maintainability.

D = Scattering is observed throughout the copying machine, and some ground blur due to dirt in the optical system is observed.

E: Considerable scattering occurred throughout the copying machine, and soil blur due to contamination of the optical system was clearly observed, and copies were stained due to contamination of the conveyance section.

F: Scattered toner is discharged outside the copying machine and contaminates the surrounding area.

The results are shown in Table 1.

As can be understood from Table 1, the coated carriers of Examples 1 to 8 not only have a resin coating layer consisting of two layers, an inner layer and an outer layer, on the surface of the magnetic particles, but also carbon black in the inner layer. Because it contains the compound, stable triboelectric chargeability and developability are exhibited even when images are formed many times, and high-density images can be stably formed without fogging or toner scattering. The durability of the carrier is greatly improved.

On the other hand, since the coating carriers of Comparative Examples 1 and 2 do not contain any carbon black, the bias voltage does not work sufficiently and developability is poor, resulting in low image density and significant fogging. be.

Since the coating carrier of Comparative Example 3 contains carbon black in one resin coating layer, the triboelectric charging property and stability thereof are poor, and the occurrence of fog and toner scattering is significant.

The coated carrier of Comparative Example 4 contains carbon black not only in the inner layer but also in the outer layer, and the coated carrier of Comparative Example 5 contains carbon black in the outer layer rather than the inner layer. Since carbon black is present on the surface of the resin coating layer in the carrier, after one layer has been copied 10,000 times, the amount of illumination triboelectricity decreases significantly, the image density also decreases significantly, and fogging and toner scattering occur. is remarkable.

〔Effect of the invention〕

According to the invention of claim 1, the resin coating layer has a two-layer structure of an inner layer and an outer layer, and especially carbon black is contained in the inner layer, so that carbon black is not exposed on the surface of the resin coating layer. , the effect of reducing electrical resistance by carbon black is stably exhibited, stable triboelectric chargeability and developability are exhibited even when images are formed many times, fogging and toner scattering do not occur, and the durability of the carrier is improved. Improves sex. Furthermore, since carbon black is not present in the outer layer, cracks in the outer layer are less likely to occur, and the durability of the carrier is improved in terms of mechanical strength as well.

These excellent performances can be stably exhibited even when applied to a developing process where the photoreceptor is charged at a low potential, such as in a laser printer.

According to the second aspect of the invention, the low surface energy property of the outer layer effectively prevents adhesion of toner substances, so that even more excellent durability is exhibited.

Claims (2)

[Claims] (1) A coating carrier comprising a resin coating layer consisting of two layers, an inner layer and an outer layer, on the surface of magnetic particles, wherein the inner layer contains carbon black. (2) The coated carrier according to claim 1, wherein the outer layer is made of a low surface energy resin.