JP2552491B2 - Carrier for developing electrostatic images - Google Patents

Description

The present invention relates to a carrier for developing an electrostatic image, that is, a carrier which constitutes an electrostatic image developer together with a toner.

[Prior Art] In electrophotography, an electrostatic charge image is formed by imagewise exposure after applying a uniform surface charge to a photoconductor composed of a photoconductive element in a dark place, and the electrostatic charge image is developed with a developer. By doing so, a visible image is formed.

The method of developing such an electrostatic image can be roughly classified into a liquid developing method and a dry developing method. The liquid developing method is a method in which development is performed using a liquid developer in which various pigments and dyes are dispersed as fine particles in an insulating organic liquid, and the dry developing method is a method in which carbon black is contained in a natural or synthetic resin. This is a method using fine powdered electrophoretic powder, usually called toner, which contains a coloring agent such as a dispersion. In the latter method, the toner is charged to the opposite polarity to the charge of the electrostatic charge image, and the charged toner is electrostatically attached to the electrostatic charge image to form a visible image. In this dry development method, a method using a so-called one-component developer containing only the toner as a main component and a so-called two-component developer in which a carrier composed of iron powder or glass beads is mixed with the toner is used. The method includes a hair brush method, an impression method, and a powder cloud method, and the latter includes a magnetic brush method and a cascade method.

By the developing method as described above, the visible image formed by adhering the toner to the electrostatic charge image is transferred to the photoreceptor as it is, or after being transferred to paper or other image support, heat,
It is fixed by pressure, solvent vapor and the like.

The present invention relates to a carrier for a two-component developer used in a magnetic brush method, a cascade method or the like among the above-mentioned developing methods, that is, a carrier mixed with a toner and used for developing an electrostatic image. .

The electrostatic charge image developing carrier can be roughly classified into a conductive carrier and an insulating carrier. Oxidized or unoxidized iron powder is usually used as the conductive carrier. However, the developer containing the iron powder carrier has unstable triboelectric charging characteristics with respect to the toner. There is a drawback that fogging occurs in the visible image formed by the method. That is, since the toner particles adhere to the surface of the iron powder carrier particles due to friction with the toner and are contaminated, the electric resistance of the carrier particles increases, the bias current decreases, and the triboelectrification characteristics become further unstable. , The image density of the visible image is reduced, and the fog is increased. Therefore, when copying is continuously performed by an electronic copying machine using a developer containing an iron powder carrier, the developer is deteriorated in a few times of copying, and it is necessary to replace it at an early stage, resulting in high cost. Become.

On the other hand, as the insulating carrier, a carrier in which the surface of core particles generally made of a magnetic material is coated with a coating layer of an insulating resin is typical. In the developer containing the insulating carrier as a component, the toner particles adhere to the surface of the carrier particles very little to be contaminated, and it is possible to control the frictional charging characteristics of the carrier and the toner, and to improve the durability. This is advantageous in that it is particularly suitable for high-speed electronic copiers in that it has excellent service life and a long service life.

As the insulating resin forming the coating layer on the core particles, a styrene-based polymer as shown in JP-A-47-13954,
Acrylic polymers or styrene-acrylic copolymers are preferable because they have high adhesion to core particles.

[Problems to be Solved by the Invention] However, the insulating carrier coated with the above-mentioned polymer or copolymer is disadvantageous in that the speed at which the toner is mixed and stirred with the toner to give an electric charge, that is, the so-called charge rising speed is slow. Have. When the speed of the rise of the charge is slow, the amount of the toner that is not charged or the toner that does not have a sufficient charge increases in the developer, and the toner separates from the carrier with copying, causing so-called toner scattering. The toner scattering pollutes the inside of the machine, and in a remarkable case, it is discharged to the outside of the machine and pollutes the surrounding environment.

In view of the above problems, it is an object of the present invention to provide a carrier for developing an electrostatic charge image, which has a long service life and a high charge rising speed.

[Means for Solving the Problems] The above object can be achieved by using a carrier for electrostatic image development containing a fatty acid metal salt on the surface of a carrier coated with a styrene-acrylic copolymer as a magnetic material.

The carrier according to the present invention is, for example, a carrier produced by coating a solution of at least one selected from styrene-acrylic copolymers in a suitable solvent on the surface of the magnetic material, and then evaporating the solvent at a desired temperature. It can be produced by a method of adding a fatty acid metal salt and mixing and stirring at an appropriate strength. Further, the carrier according to the present invention is a solution in which at least one selected from styrene-acrylic copolymers is dissolved in a suitable solvent, a fatty acid metal salt is further micro-dispersed, and this solution is applied to the surface of the magnetic material, and then the solvent is used. It can also be produced by evaporating.

Any styrene-acrylic copolymer may be used in the present invention, but it has a weight average molecular weight of 5,000 to 50.
Those of 0000 are preferable. If the average molecular weight is less than 5,000, the strength of the resin is poor and the film is easily broken.
If it exceeds 500,000, the solubility in a solvent is poor and it is difficult to form a film. Typical styrenic compounds serving as constituent units of styrene-acrylic copolymers include styrene, α-methylstyrene, vinyltoluene, 4-bromostyrene, 4-chloro-5-fluorostyrene, 2-chlorostyrene, 2 , 5-dichlorostyrene, 2,5-difluorostyrene, 2,4-dimethylstyrene, 4-ethoxystyrene, 4-ethylstyrene, 4-hexyldecylstyrene, 3-oxymethylstyrene, 4-iodostyrene, 4 -Isoventoxy styrene, 4-nonadecyl styrene, a mixture thereof and the like can be mentioned.

Methyl acrylate is used as a typical substituted or unsubstituted acrylate and methacrylate compound which is a constituent unit of a styrene-acrylic copolymer.
Ethyl acrylate, tert-butyl acrylate, neopentyl acrylate, α-chloromethyl acrylate, isobutyl acrylate, cyclohexyl acrylate, dodecyl acrylate, hexyl decyl acrylate, isopropyl acrylate, tetradecyl acrylate, ethylene glycol dimethacrylate , Sec-butyl acrylate, 2-
n-tert-butylaminoethyl methacrylate, 2-butyl methacrylate, glycidyl methacrylate, 2-chloroethyl methacrylate, 3,3-dimethylbutyl methacrylate, 2-ethylhexyl methacrylate, 2-methoxyethyl methacrylate, pentyl methacrylate, Methyl methacrylate, ethyl methacrylate, methacrylic acid n-
Examples include butyl, isobutyl methacrylate, isopropyl methacrylate, propyl methacrylate, 2-ethylhexyl acrylate, and mixtures thereof.

Styrene-acrylic polymers have good coating properties, especially copolymers of styrene and methyl methacrylate having very good coating properties. Examples of the fatty acid constituting the fatty acid metal salt used in the present invention include caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid,
There are palmitic acid, margaric acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid and mixtures thereof, and the metal salts are lithium, sodium, potassium, copper, silver, magnesium, calcium, zinc, strontium, Examples thereof include metal salts of cadmium, barium, aluminum, tin, lead, iron, nickel and the like, but are not limited thereto. Among these, a metal salt of stearic acid is particularly effective and effective for improving the rate of rise in charging.

In the present invention, the amount of the fatty acid metal salt contained on the carrier surface is preferably in the range of 0.001% by weight to 0.04% by weight based on the whole carrier. If the fatty acid metal salt is less than 0.001% by weight, the effect of increasing the charge rising speed is insufficient, and if it is more than 0.04% by weight, the charging order of the carrier gradually fluctuates, and the desired charge to the toner is obtained. It becomes difficult to give sex.

The amount of fatty acid metal salt on the carrier surface can be quantified as follows. As an example, a method for determining zinc stearate on the carrier surface will be described.

1. Take about 5g of carrier in a 100cc beaker and stir it.

2. Add a proper amount of acetone and place a magnet on the bottom of the beaker to fix the carrier on the bottom of the beaker to prevent the carrier from flowing out and elute only the carrier coating layer.

Repeat operation 3.2 to completely remove the coating layer.

4. Dry the remaining carrier cores in the beaker on the hot plate.

5. Precisely weigh the carrier core.

6. Obtain the coverage from the following formula.

About 100 g of carrier is placed in a 7.1-liter beaker and the coating layer is eluted in the same manner as in 2.

8. Remove the solvent from the eluted solution with an evaporator and dry under reduced pressure.

9. Pellet the remaining resin and quantify the amount of zinc stearate in the resin by X-ray fluorescence analysis.

10. Zinc stearate content in carrier (wt%)
Ask for.

Other fatty acid metal salts can be quantified in the same manner as described above.

Examples of the magnetic material used in the present invention include iron, nickel, ferrite and cobalt. The particle size of the magnetic material is 30 to 1000 μm, preferably 40 to 200 μm after the resin is coated. If the particle size is less than 30 μm, the carrier has a small magnetization, so that scattering from the sleeve or adhesion to the photoconductor is likely to occur, and if it exceeds 1000 μm, the image quality becomes rough.

Any toner may be used as the toner constituting the developer in combination with the carrier of the present invention.
In particular, those having fine particles of hydrophobized silica, alumina, titania or the like on the surface are preferable because the charging rising speed is faster and a clear image can be obtained.

[Examples] The effects of the present invention will be described with reference to the following examples, but the present invention is not limited to these embodiments.

(Production Example 1) The monomer composition ratio of styrene and methyl methacrylate was
A coating liquid was prepared by dissolving 15 g of a styrene-methyl methacrylate copolymer having a weight average molecular weight of 120,000 at 40:60 in 300 ml of methyl ethyl ketone, and a spherical ferrite F-150 (manufactured by Nippon Iron Powder Co., Ltd.) was used as a spira coater (Ta (Manufactured by Seiko Co., Ltd.) to produce a carrier having a coating layer with an average film thickness of 1.0 μm. This is called "carrier A".

(Production Example 2) 1 kg of carrier A and 50 mg of zinc stearate "Zinc stearate S" (manufactured by NOF CORPORATION) were put in a V-type mixer "micro-type transparent mixer" (manufactured by Tsutsui Rikagaku Co., Ltd.) to rotate at 70 rp.
Mixing at m for 20 minutes to produce a carrier with zinc stearate on the surface. This is called “carrier B”.

(Production Example 3) A carrier was produced in the same manner as in Production Example 2 except that zinc stearate was 5 mg. This is called “carrier C”.

(Production Example 4) A carrier was produced in the same manner as in Production Example 2 except that zinc stearate was 10 mg. This is called "carrier D".

(Production Example 5) A carrier was produced in the same manner as in Production Example 2 except that zinc stearate was 500 mg. This is called “carrier E”.

(Production Example 6) A carrier was produced in the same manner as in Production Example 2 except that aluminum stearate (manufactured by Tokyo Kasei Kogyo Co., Ltd.) was used instead of zinc stearate. This is called “carrier E”.

(Production Example 7) A carrier was produced in the same manner as in Production Example 2 except that zinc stearate was changed to sodium stearate (manufactured by Tokyo Chemical Industry Co., Ltd.). This is referred to as “carrier G”.

(Production Example 8) Production Example 1 except that the styrene-methyl methacrylate copolymer was changed to a styrene polymer having a weight average molecular weight of 130,000.
A carrier having a coating layer having an average film thickness of 1.1 μm was manufactured in the same manner as in. This is referred to as “carrier H”.

(Production Example 9) A carrier was produced in the same manner as in Production Example 2 except that the carrier A was changed to the carrier H. This is called “carrier I”.

(Production Example 10) A carrier having a coating layer with an average film thickness of 1.0 µm was produced in the same manner as in Production Example 1 except that the styrene-methyl methacrylate copolymer was changed to a methyl methacrylate polymer having a weight average molecular weight of 120,000. This is called “carrier J”.

(Production Example 11) A carrier was produced in the same manner as in Production Example 2 except that the carrier A was changed to the carrier J. This is referred to as “carrier K”.

(Production Example 12) A carrier having a coating layer with an average film thickness of 1.1 µm was prepared in the same manner as in Production Example 1 except that spherical iron powder DSP-138 (made by Dowa Iron Powder Co., Ltd.) was used instead of the spherical ferrite F-150. Manufactured. This is called “carrier L”.

(Production Example 13) A carrier was produced in the same manner as in Production Example 2 except that the carrier A was changed to the carrier L. This is called “carrier M”.

(Manufacture of Toner) Resin having a composition ratio of styrene, methyl methacrylate and butyl acrylate of 70:15:15 and a weight average molecular weight of 120,000 and a number average molecular weight of 6600, 100 parts by weight, carbon black Mogal L (manufactured by Cabot Corporation) ) 10 parts by weight and 3 parts by weight of polypropylene wax 660P (manufactured by Sanyo Kasei Co., Ltd.) were mixed, kneaded, ground and classified to obtain a toner having an average particle size of 10 μm.
100 parts by weight of this toner and 0.8 parts by weight of hydrophobic silica R-972 (manufactured by Nippon Aerosil Co., Ltd.) were mixed with a Henschel mixer.

 This toner is designated as "toner A".

299g terephthalic acid and polyoxypropylene (2,2)
-2,2-bis (4-hydroxyphenyl) propane 211g
And 82 g of pentaerythritol are placed in a round bottom flask equipped with a thermometer, a stirrer made of stainless steel, a nitrogen gas introduction tube made of glass and a downflow condenser, and this flask is set to a mantle heater, and a nitrogen gas introduction tube is set. Nitrogen gas was further introduced to raise the temperature while maintaining the inside of the flask in an inert atmosphere. Then dibutyltin oxide.
Add 05 g, and follow the reaction at the softening point to a temperature of 200
The reaction was carried out at ℃ to produce a polyester resin having a chloroform insoluble content of 17% by weight. This is designated as "polyester resin A". The ring and ball softening point of this polyester resin A (according to the method of JIS K 1351-1960) was 131 ° C.

100 parts by weight of this polyester resin A, 10 parts by weight of carbon black "Mogal L" (manufactured by Cabot) and 3 parts by weight of low molecular weight polypropylene "Viscor 660P" (manufactured by Sanyo Chemical Co., Ltd.) were melt-kneaded, pulverized and classified to obtain an average particle size. Diameter 10 μm
Toner was obtained.

100 parts by weight of this toner and 0.8 parts by weight of hydrophobic silica R-972 were mixed with a Henschel mixer. This toner is referred to as “toner B”.

100 parts by weight of a resin having a composition ratio of styrene, methyl methacrylate and butyl acrylate of 70:15:15, a weight average molecular weight of 120,000, and a number average molecular weight of 6600, and 10 parts by weight of carbon black Mogal L (manufactured by Cabot). Mix 3 parts by weight of polypropylene wax 660P (manufactured by Sanyo Kasei)
After kneading and pulverizing and classifying, a toner having an average particle size of 10 μm was obtained. 100 parts by weight of this toner, 0.8 parts by weight of hydrophobic silica R-972 (manufactured by Nippon Aerosil Co., Ltd.) and 0.1 part by weight of zinc stearate zinc stearate S were mixed with a Henschel mixer.

 This toner is designated as "toner C".

The toner A, the toner B, the toner C and the carrier A
The charge rising speed and the toner scattering state were measured using the developers each of which is combined with M.

The combinations of toner and carrier are shown in Table 1 below.

To measure the charge rising speed, put 19 g of carrier and 1 g of toner in a 20 cc glass sample tube, amplitude 30 cm, speed 1
Mix with a mixer that reciprocates at 30 strokes / min, Was used as an index.

Regarding the toner scattering status, electrophotographic copying machine U-Bi
Performed a live-action test of 20,000 copies using the x1600, 1
The state of toner scattering after ten thousand and twenty thousand copies is shown in the following six stages.

Table 2 shows the experimental results.

As described above, all of the comparative carriers have a slow charge rise and cause a large amount of toner scattering, whereas the carriers of the present invention have a fast charge rise and a good performance with little toner scattering.

[Advantages of the Invention] As described in detail above, the carrier of the present invention exhibits good performance in which the rate of charge rise is high, the amount of toner scattering is small, and the service life is long.

Front page continuation (72) Inventor Hiroki Kabashima 2970 Ishikawa-cho, Hachioji City, Tokyo Konishi Roku Photo Industry Co., Ltd. (56) Reference JP-A-58-216261 (JP, A)

Claims (1)

(57) [Claims] 1. A carrier for developing an electrostatic charge image, comprising a magnetic material coated with a styrene-acrylic polymer, wherein the surface of the carrier contains a fatty acid metal salt.