JPH02103561A - Electrostatic charge image developing toner - Google Patents

Abstract

PURPOSE:To obtain uniform chargeability characteristics and good potential stability by uniformly dispersing a colorant made of agglomerates of a specified carbon black into a binder resin. CONSTITUTION:The colorant composed of the agglomerates 2 of the carbon black having an average particle diameter of 0.05-0.5mum is uniformly dispersed into the binder resin 3. If the colorant contains the small agglomerates 2 near in diameter to the primary particles 1 of the carbon black or the large agglomerates near to the toner particles, sufficient volume resistivity cannot be obtained. It is controlled to regulate 70% of the agglomerates 2 in the number distribution in the range of x+ or -5xmum, where x is the average particle diameter of the agglomerates 2, thus permitting a uniform and narrow distribution of charge and superior potential stability to be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a toner for developing electrostatic images in electrophotography, and particularly to a toner having excellent charge retention properties.

<Prior Art> Many methods have been known for electrophotography, but in general, an electrostatic latent image is formed on a photoreceptor by various means using a photoconductive substance, and then the electrostatic latent image is formed on a photoreceptor. The latent image is developed using toner, the toner image is transferred to a transfer material such as paper as needed, and then fixed by heat, pressure, etc. to obtain a copy. The development methods in this case can be roughly divided into two component development methods that use a developer consisting of a magnetic carrier and toner, and one-component development methods that use a developer that uses only magnetic or non-magnetic toner and does not require a carrier. There is. The toners used for these are colored particles that are finely pulverized to about 5 to 25 μm and contain a binder resin and a colorant as main components.

In recent years, in electrophotographic copying machines, it has been desired to increase the copying speed and to extend the life of toner from the viewpoint of maintenance of the copying machine.

To this end, each toner particle must have good charging properties, i.e.
It is necessary to have a uniform charging level and excellent charge retention. In other words, if the charging characteristics are uneven, toner particles that do not contribute to copying are generated, which accumulate and appear as deterioration of the life characteristics. In order to prevent this, measures have been taken to use various charge control agents, additives, surface treatment agents, etc. in order to impart good charging characteristics to the toner. However, using these methods not only complicates the composition of the toner, but there are also concerns that they may have negative effects, and even if these methods are used, the current lifespan of toner is limited to tens of thousands of copies. .

The inventors of the present invention believe that there is a limit to the above-mentioned considerations from the viewpoint of materials in order to achieve good charging characteristics of toner and, ultimately, to extend its lifespan. We conducted a detailed study of the structure of toner particles, that is, the dispersion state of carbon black as a coloring agent in the binder resin, dyes and pigments as charge control agents, and other additives such as polypropylene as a mold release agent. . the result,
In particular, it has been confirmed that carbon black affects the uniformity of charge amount and volume resistivity of the 1-ner depending on its dispersion state, and has an adverse effect on charging characteristics and life characteristics. For example, as shown in FIG. 2, carbon is dispersed non-uniformly in various forms ranging from primary particles 1 to large aggregates 2. That is, if the dispersion is poor, the amount of carbon in each toner particle becomes non-uniform, making it impossible to obtain uniform charging characteristics, and the volume resistivity becomes small, resulting in poor charge retention. Therefore, in order to improve this, carbon bra
When the toner particles are dispersed as uniformly as possible in the form of primary particles, the amount of carbon between toner particles becomes uniform, uniform charging characteristics are obtained, and the volume resistivity also tends to increase. However, in this case, if the total amount of carbon black is increased in order to obtain sufficient blackness as a toner, the distance between the uniformly dispersed carbon black particles becomes quite close, resulting in charge retention. It was found that sufficient volume resistivity could not be obtained. Therefore, it has been found that when carbon black is used as a colorant in a toner, a toner having a volume resistivity sufficient to obtain good charge retention cannot be obtained as long as a normal dispersion method is used.

<Problems to be Solved by the Invention> In view of the above circumstances, the present invention provides an electrostatic image developing toner having a uniform charge amount with a narrow charge amount distribution and excellent charge retention.

<Means for Solving the Problems> The present invention was discovered as a result of intensive studies on the dispersion state of carbon black in a binder resin. This is a toner for developing an electrostatic image, characterized in that a coloring agent is uniformly dispersed in a binder resin.

First of all, the dispersion state of carbon black in the binder resin, which is a feature of the present invention, is such that carbon black has an average diameter of 0.
．． It is important to disperse it as aggregates of 0.05 to 0.5 μm. Here, it is necessary that the carbon black aggregates be contained uniformly in the toner particles. If it contains many large aggregates, sufficient volume resistivity, which is the object of the present invention, cannot be obtained. Furthermore, it is preferable that the size of the carbon black aggregates be as uniform as possible in order to reduce variations among toner particles, and the average diameter of the carbon black aggregates dispersed in the binder resin is defined as X. When X±
It is preferable that 70% of the aggregates are contained in the range of 0.5×μm in terms of number distribution, and it is particularly preferable that 80% or more of the aggregates are contained. If the amount is less than 70%, that is, if the distribution of carbon black aggregates becomes wide and the dispersion becomes uneven, sufficient uniformity in the amount of charge to achieve the purpose of the present invention cannot be obtained, and In this case, sufficient charge retention properties cannot be obtained, and therefore, the life characteristics are also adversely affected. Secondly, it is important that the carbon black aggregates be uniformly dispersed, in other words, that the distances between the dispersed aggregates be relatively equal. That is, in the present invention, the dispersion state of carbon black in the binder resin is as shown in FIG. 3
It is most preferable that the aggregates are dispersed in the liquid, the aggregates are relatively uniform in size, and that such aggregates are uniformly dispersed.

The toner of the present invention has the above structure,
It consists of at least a colorant and a binder resin, and various additives such as a charge control agent, a mold release agent to prevent roll offset, and a lubricant to improve fluidity can be used as necessary.

The carbon black used in the carbon black aggregate constituting the toner of the present invention is not particularly limited in type and properties, such as channel black and furnace black, and is limited to carbon black that has been conventionally used for toners. Any material may be used as long as it can obtain the blackness as an I-ner and the dispersion state which is a constituent feature of the present invention.

As the binder resin, polystyrene and styrene substituted homopolymers or copolymers thereof, styrene monomers and other monomers such as propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid and their esters,
Resins such as copolymers with methacrylic acid and its esters, polyvinyl chloride, polyvinyl acetate, polyesters, polyolefins, rosin-modified maleic acid resins, epoxy resins, silicone resins, urethane resins, phenolic resins, and xylene resins are used. .

Furthermore, various conventionally known dyes and pigments such as nigrosine 1 and quaternary ammonium salts for positive polarity, and metal complex salts of monoazo and disazo dyes for negative polarity are used as charge control agents, and as mold release agents. is a low molecular weight polyolefin, and examples of the lubricant include various additives such as finely powdered silica and fluororesin finely powdered powder.

To produce the toner in which carbon black aggregates are dispersed in the binder resin of the present invention, carbon black is predispersed at a high concentration in the binder resin using a master bunch method.

That is, a pre-kneaded material containing carbon black aggregates is prepared by pre-dispersing carbon black in a resin at a high concentration of 125 wtX or more (master bunch method). Next, the pre-kneaded product is added to the binder resin together with other additives, and kneaded using the conventional toner manufacturing method.
Toner is manufactured by crushing and classifying. In addition, at this time, it is necessary to control the crosstalk conditions appropriately so that the carbon black aggregates are not completely dispersed, taking into account the melt viscosity of the resin, the dispersion state of the carbon black aggregates in the pre-kneaded material, etc. .

The toner of the present invention obtained in the above manner has a dispersed state in which carbon black is present in a particularly single layer, so it has a higher volume resistivity than conventional toners of the same composition. Good charge retention, which is one of the following, can be obtained. In addition, the volume resistivity is 1.0×
It is preferable that it is 10119 cm or more. If the resistance value is lower than 101 Ωcm, the charge retention property will be poor, which will adversely affect the object of the present invention.

In the present invention, the methods for measuring volume resistivity, average diameter of aggregates, etc. are as follows.

(1) Toner Volume Specific Resistance Measurement Method Using 2.5 g of the sample, pressurize (200 kg, 30 seconds) to form toner pellets with a diameter of 25 mm and a thickness of 4 to 4.5 mm to form a sample. Next, using the solid electrode 5E-70 (manufactured by Ando Electric), a bridge method (manufactured by GR, Capacitan) was applied.
The conductance G of the sample is measured by applying 10 V and I Kc to the above sample using the CE Measurement System. Volume resistivity ρ is calculated from the obtained conductance G using the following equation.

(2) Method for measuring the dispersion state, particle size distribution, and average diameter of carbon black aggregates After embedding the sample toner in epoxy resin and curing the epoxy resin, prepare sections with a thickness of about 0.3μ using a microtome. Then, this section was examined using a transmission electron microscope at 20,000 yen.
Take a 2x photo, enlarge it 3x to make a 60.000x photo, and observe the dispersion state.

Using this photograph, image analysis is performed using an image analysis system PIAS (manufactured by Nippon PC Systems 01) to measure the diameter of the carbon black aggregate. Image analysis is repeated for 10 visual fields to determine the number distribution of carbon black aggregates and their average diameter.

<Examples> Next, the present invention will be explained by examples. Note that all parts indicating blending ratios represent parts by weight.

Example 1 Styrene butyl acrylate copolymer resin A (styrene/)tylacrylate = 9/1. The melt viscosity is 5
Preliminary dispersion of carbon black was carried out using a pressure kneader for 10 minutes using a mixture of 100 parts of carbon black (Poise at 130°C) and 40 parts of carbon black (manufactured by Mitsubishi Kasei Corporation, #40), and pre-kneading containing carbon black aggregates was performed. I made something.

Next, the following composition was premixed and kneaded at a temperature of 40°C (PCM-30, using only a screw), and then pulverized and
The toner of the present invention was classified and had an average particle diameter of 11 μm (using a Coulter counter, volume average particle diameter).

Example 2 The following composition was premixed and kneaded at a temperature of 120°C (PC
The toner of the present invention having an average particle size of 11 μm was obtained by pulverization and classification.

Example 3 A mixture of 100 parts of styrene butyl acrylate copolymer resin A and 40 parts of carbon black (manufactured by Mitsubishi Kasei Corporation, #40) was predispersed for 60 minutes using a pressure kneader to form carbon black aggregates. A pre-kneaded product containing the following was prepared.

Next, the following composition was premixed, kneaded in the same manner as in Example 2, and pulverized and classified to obtain the toner of the present invention having an average particle size of 11 μm.

Comparative Example The following composition was premixed, kneaded in the same manner as in Example 2, and crushed and classified to produce a comparative toner having an average particle size of 11 μm.

The volume resistivity and carbon black dispersion state of the toners of Examples 1 to 3 and Comparative Example prepared as described above were investigated. In addition, a developer was prepared by mixing 94 parts of carrier (Ferrite Carrier 100/300, manufactured by Nippon Tetsuko Co., Ltd.) and 6 parts of toner, and a copying machine (manufactured by Sharp Corporation, 5F
-8200). These results are shown in Table 1. In the toner of the present invention, the dispersion state of carbon black is as shown in Fig. 1, and the carbon black exists as aggregates, and the volume resistivity is lower than that of the toner of the comparative example. It is as high as 101Ω・Cl11 or higher. In addition, good image quality with little background fogging was obtained, and this is thought to be due to the charging characteristics due to the difference in the dispersion state of carbon black.

(Margins below) Furthermore, when repeated copy tests were conducted on the toners of Example 3 and Comparative Example using the combination of the developer and copying machine described above, the toner of Example 3 produced good copies even after 50,000 copies. There was almost no change in the toner charge amount, but after 30,000 copies of the toner of the comparative example, the background fog was severe and the image quality deteriorated significantly, and the toner charge amount changed so much that the copy test was discontinued.

Note that the image quality evaluation in Table 1 is based on the following.

(1) Image density: Density of 5Bφ image area measured by Macbeth densitometer (2) Background fog: Difference in Hunter whiteness between non-image area and before copying <Effects of the invention> The toner of the present invention is a carbon black aggregate. Because the particles are uniformly dispersed, the toner has a high volume resistivity, and it is possible to obtain good images with little fog.In addition, it has good charging characteristics with little variation in individual toner particles, and excellent life characteristics. This is the toner obtained.

[Brief explanation of the drawing]

Figures 1 and 2 are model diagrams of transmission electron micrographs showing the dispersion state of carbon black in toner particles. Figure 1 is for the toner of the present invention, and Figure 2 is for the conventional toner. belongs to. ■... Primary particles of carbon black, 2... Carbon black aggregates, 3... Binder resin. Patent applicant: Tomoekawa Paper Mills Co., Ltd.

Claims (1)

[Scope of Claims] 1) A toner for developing electrostatic images, characterized in that a colorant made of carbon black aggregates having an average diameter of 0.05 to 0.5 μm is uniformly dispersed in a binder resin. . 2) The toner for developing an electrostatic image according to claim 1, wherein the carbon black aggregates contain 70% or more of the aggregates within a range of x±0.5x μm, where x is the average diameter of the carbon black aggregates. 3) The toner for developing an electrostatic image according to claim 1 or 2, having a volume resistivity of 1.0×10^1^1 Ω·cm or more.