JP2676539B2 - Two-component developer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a two-component developer for developing an electrostatic charge image composed of a negatively chargeable toner and an acrylic resin coated carrier.

[Prior Art] Various methods have been described as electrophotography in U.S. Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910, Japanese Patent Publication No. 43-24748, etc. Also, an electrostatic latent image is formed by irradiating the photoconductive layer with a light image corresponding to the original, and then, a colored fine powder called a toner having a polarity opposite to this is attached to the electrostatic latent image. The electrostatic latent image is developed, and if necessary, a toner image is transferred to a transfer material such as paper, and then fixed by heat, pressure, or solvent vapor to obtain a copy.

In the step of developing the electrostatic latent image, the toner particles charged to the opposite polarity to the latent image are attracted by electrostatic attraction and adhered onto the electrostatic latent image. The method of developing with a toner is roughly classified into a method of using a so-called two-component developer in which the toner is dispersed in a medium called a carrier in a small amount, and a so-called one-component developer in which the toner is used alone without using a carrier. There is a method to use.

Generally, the carriers that constitute such a two-component developer are roughly classified into conductive carriers and insulating carriers.

Oxidized or unoxidized iron powder is usually used as the conductive carrier. However, in a developer containing this iron powder carrier, the triboelectric charging property with respect to the toner is unstable and is formed by the developer. There is a disadvantage that fogging occurs in the visible image. That is, with the use of the developer, the toner particles adhere to the surface of the iron powder carrier particles, so that the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectrification becomes unstable. The image density of the visible image decreases and fog increases.

In the conventional developer, a part of the toner particles physically adheres to the surface of the carrier particles to form a film due to collision between particles, mechanical collision such as collision between particles and a developing machine, or heat generated by these. There is a property to do. When this happens,
A film of toner material is gradually accumulated on the surface of carrier particles,
The triboelectrification between the carrier particles and the toner particles is replaced by the triboelectrification between the toners, so that the triboelectrification characteristics of the entire developer are deteriorated, and thus a large amount of toner adheres to the background portion of the copy image, so-called background stain. Phenomenon occurs, and the copy quality deteriorates. Further, when the toner film is formed on the surface of the carrier badly, it is necessary to replace the entire developer, which is a drawback that leads to an increase in cost.

In order to prevent such spent, a method of coating various resins on the surface of the carrier has been conventionally proposed, but a satisfactory method has not been obtained yet.

For example, a carrier coated with a fluorine-based resin such as an ethylene tetrafluoride copolymer has a low critical surface tension, so that the toner is less likely to be spent, but the film-forming property is poor and the carrier core material may be covered sufficiently uniformly. As a result, stable charging characteristics cannot be obtained. Further, the adhesiveness with the core material is weak, and the abrasion resistance is unsatisfactory. Further, due to the relationship with the charging series, the fluororesin-coated carrier cannot have a sufficient charging ability in the negative charging toner.

On the other hand, a carrier coated with an acrylic resin such as a styrene / methacrylate copolymer has a good film-forming property,
It has strong adhesion to the carrier core material and excellent wear resistance. However, since this acrylic resin has a relatively high critical surface tension, the spent of the toner is likely to occur during repeated use, and the life of the developer is somewhat problematic. Further, due to its good film-forming property, the carrier is likely to have a high resistance, and therefore the toner is likely to be separated from the carrier due to charge-up of the toner.

Further, if development is continued for a long time in such a state that the toner is hard to separate from the carrier, it is not preferable because the above-mentioned toner is further promoted into spent toner.

Also, if the carrier has too high resistance, the image density is reduced, the reproducibility of solid halftone is deteriorated, or the carrier is developed on the photoconductor and scratches the photoconductor, or the carrier adheres to the image. Sometimes.

[Problems to be Solved by the Invention] In view of the above-mentioned current problems, an object of the present invention is to solve the following points.

A first object of the present invention is to provide a two-component type developer having an acrylic resin-coated carrier that causes less toner spent.

A second object of the present invention is to provide a two-component developer having an acrylic resin-coated carrier that does not easily charge up.

A third object of the present invention is to provide a two-component developer having an acrylic resin-coated carrier that has stable charging characteristics even after repeated use.

A fourth object of the present invention is to provide a two-component developer having an acrylic resin coated carrier having excellent abrasion resistance.

[Means and Actions for Solving the Problems] The above object is achieved by the following configurations of the present invention.

The present invention provides a two-component developer composed of a negatively chargeable toner and an acrylic resin-coated carrier in which the surface of a carrier core material is coated with an acrylic resin (provided that a mixture of a silicone resin and an inorganic electric resistance adjuster is used. (Except when it further includes a carrier formed by coating the surface of the core material), the acrylic resin-coated carrier has a particle diameter of 0.1 to 5.0 μm and a coefficient of friction of
The present invention relates to a two-component developer characterized by being coated with an acrylic resin in which graphite of 0.19 or less is dispersed.

The two-component developer of the present invention comprises a negatively chargeable toner and an acrylic resin coated carrier.

As the negatively chargeable toner, a known negatively chargeable toner can be used as will be apparent from the examples described later.

In the present invention, graphite is used for the acrylic resin-coated carrier because graphite is scaly, has excellent lubricity, and has high conductivity. It is effective for the mechanism of.

That is, since the flaky graphite is on the surface, the toner is difficult to adhere due to its lubricity, and even if it adheres (spents), it easily peels off because of the scaly high scaly shape. It is easy to come up with a new surface. Further, it is considered that charge is hardly accumulated on the surface of the carrier due to its conductivity, and the separation of the toner from the carrier is promoted.

Further, the larger the particle size, the more remarkable the above properties are, and the effect of the present invention is great, but on the contrary, it becomes difficult to uniformly disperse it in the coat resin, which is unsuitable as an example of addition to the coat resin. Becomes Therefore, the graphite particle size is 0.1
It is necessary to be not less than μm and not more than 5.0 μm, and it is preferably 0.1 μm to 3.0 μm, although it depends on the added amount.

Further, since it has excellent lubricity, the graphite used has a friction coefficient as described in Examples described later.
It is necessary that the particle shape is 0.19 or less. Furthermore, in order to obtain the high conductivity mentioned above, the specific electric resistance is 2 Ω · cm.
Below, graphite of 1 Ω · cm or less is preferable.
The amount of graphite added is 0.1 with respect to the acrylic resin.
〜50wt%, preferably 0.5〜30wt%. If it is 0.1 wt% or less, the effect of the present invention is not remarkable, and if it is 50 wt% or more, the carrier cannot be uniformly coated.

As the acrylic resin to which graphite is added, general ones can be used, for example, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, etc., and further vinyl monomers such as glycidyl methacrylate, methoxyethyl methacrylate, etc. And a homopolymer or a copolymer thereof or a copolymer with a styrene derivative can be used. In particular, styrene-acrylic resin is preferable because it has excellent adhesion to the carrier core material. It is also effective to mix with a fluororesin such as tetrafluoroethylene, if necessary.

As the carrier core material used in the present invention, general materials such as iron powder and ferrite are used, and the particle size is 10 to
1000 μm, preferably 20-200 μm, is suitable.

As a method for coating the surface of the carrier core material with the above-mentioned graphite-dispersed acrylic resin, the resin is dissolved or suspended in a solvent, and further graphite powder is added and sufficiently dispersed by a disperser. And can be applied by a general method such as spraying.

[Examples] Examples using the present invention will be shown below.

Example 1 100 g of a 20% toluene solution of styrene-methyl methacrylate (20:80) and 5 g of graphite (average particle size 2.0 μm, specific electric resistance 0.08 Ω · cm, friction coefficient 0.025) were dispersed in a ball mill pot for 24 hours, A carrier coating solution was prepared.

1 kg of spherical ferrite carrier core material with an average particle size of 100 μm
On the other hand, a spray-coated carrier was obtained using a fluidized bed at a ratio of 20 g of the coating liquid.

This carrier was mixed with a toner for Canon NP-5000 (toner concentration: 2%) to prepare a two-component developer, and the triboelectric charge amount of the toner was measured and found to be -6.5 μc / g. When NP-5000 was used to print 100,000 images using this two-component developer, it was extremely good as shown in Table 1. Only separated and mixed with new toner (toner concentration 2%)
When the triboelectric charge was measured in the same manner as the above method, −
It was 6.2 μc / g, which was almost unchanged from the initial stage, and it was revealed that the carrier did not deteriorate due to the spent toner.

When the surface of only the carrier after 100,000 sheets of durability was observed with an electron microscope, the surface remained smooth and almost no spent such as toner was recognized.

Comparative Example 1 A coated carrier was obtained in substantially the same manner as in Example 1 except that graphite in Example 1 was removed. The carrier was evaluated in the same manner as in Example 1. As a result, as shown in Table 1, both fog and image quality deteriorated as the durability progressed, and the image density also decreased. Ten
It was found that the ability of the carrier to impart tribo to the toner before and after the endurance of 10,000 sheets was the same as that of Example 1 in the initial stage, but was significantly reduced after the endurance. Furthermore, when observed with an electron microscope, the surface of the carrier is uneven, and some of the carrier core material is exposed, and conversely there are parts that are raised due to deposits that are thought to be spent of the toner. , It was mixed.

Example 2 Styrene / methyl methacrylate / ethyl acrylate / 2-hydroxyl ethyl methacrylate (10/60/25 /
To 20 parts by weight of 5), dissolve in a solvent of xylene / butanol = 7/3, mix 10 parts by weight of graphite (average particle size 0.5 μm, specific electric resistance 0.025 Ω · cm, friction coefficient 0.19), After sufficiently dispersing for 24 hours in a ball mill, 5 parts by weight of melamine resin was further dissolved to prepare a carrier coating solution.

This liquid was used in Example 1 in such a proportion that the resin solid content was 2 wt% with respect to 1 kg of a ferrite carrier core material having an average particle diameter of 55 μm.
A coated carrier was obtained by coating in the same manner as in.

When this carrier was used and evaluated in the same manner as in Example 1, good results were obtained as shown in Table 1.

[Advantages of the Invention] As described above, in the two-component developer of the present invention, by using a carrier coated with an acrylic resin in which specific graphite is dispersed in combination with a negatively chargeable toner, It is possible to suppress deterioration of image density, fogging, and deterioration of image quality even after outputting 10,000 or more images, and to guarantee the same quality as the initial quality.

Claims (2)

(57) [Claims] 1. A two-component developer comprising a negatively chargeable toner and an acrylic resin-coated carrier in which the surface of a carrier core material is coated with an acrylic resin (however, a mixture of a silicone resin and an inorganic electric resistance adjusting agent). The case of further including a carrier obtained by coating the surface of a core material by means of the above), wherein the acrylic resin-coated carrier has a particle diameter of 0.1 to 5.0 μm on the surface of the carrier core material and a friction coefficient. Is 0.
A two-component developer characterized by being coated with an acrylic resin in which graphite of 19 or less is dispersed. 2. The graphite has a specific electric resistance of 2Ω.
The two-component developer according to claim 1, which has a size of not more than cm.