JPH021874A - Electrophotographic toner - Google Patents

Abstract

PURPOSE:To reduce drops of image density and quality due to increase of a number of copies by using carbon black having a specified oil absorption value and a specified surface area value for the colorant of a toner. CONSTITUTION:The electrophotographic toner is formed by binding each constituent, that is, as the colorant, the carbon black and the binder resin for fixing the colorant to a transfer paper. The carbon black has an oil absorption of 300-500(ml/100g) DBP and a surface area of 900-1,300(m<2>/g), thus permitting the carbon black to be high and large in the oil absorption and the surface area, to restrain deterioration of conductivity of the toner even if it is broken in the kneading step of the manufacturing process of the toner, and accordingly, to reduce deteriorations of the image density and quality accompanied by increase of a number of copies.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrophotographic toner used in electrophotographic apparatuses such as electrostatic transfer copying machines and laser printers.

[Conventional technology]

Conventional electrophotographic toner (hereinafter referred to as toner) is -
In addition to integrating each material constituting the toner, C contains a binder resin agent for fixing the colorant on the transfer paper, a colorant for imparting color to the toner, and a substance for imparting chargeability to the toner. It consists of a charge control agent and a release agent for preventing offset caused by toner adhering to the surface of the fixing roller. Then, these materials are mixed, melted and kneaded, the kneaded material is pulverized, and then classified to produce granules having a predetermined particle size.

Carbon black is used as the coloring agent in black toner used for monochrome copying, and conventionally, this carbon black has a density of 20 to 250 (m!/100g) D
Has an oil absorption amount of B P and 10 to 600 (m/g)
A material having a surface area (BET) of

[Problem to be solved by the invention]

However, since the structure of the conventional carbon black is destroyed during the kneading process of toner production, the DBP oil absorption is reduced to approximately half, and furthermore, its conductivity is lost. For this reason, the volume resistivity value of the obtained toner increases, and in the frictional charging with the carrier in the two-component development method, the amount of charge increases more than necessary. Therefore, when a large number of copies are made, there is a problem in that image density and image quality deteriorate as the number of copies increases.

Incidentally, the DBP oil absorption amount is determined as follows. First, 0.5 g of carbon black is placed on a glass plate, linseed oil is added dropwise thereto, and the mixture is mixed with a steel spatula. At this time, linseed oil is slowly dripped from a 2 mR biuret. Next, pull up the spatula and the paste will form a mound. Furthermore, linseed oil is dripped until the pile of paste bends downward when an impact is applied, such as by hitting it against a glass plate. The amount of linseed oil added as described above is converted into weight, expressed as a percentage with respect to the weight of carbon black, and this is defined as the DBP oil absorption amount.

Also, the surface area (BET) was calculated by S. in 1938.

Brunauer, P., H., Emmett, E.
.

BET which is a series of relational expressions submitted by Te1l++vr
It is derived from the VI wear isotherm equation.

[Means to solve the problem]

In order to solve the above-mentioned problems, the electrophotographic toner according to the present invention integrates each material constituting the toner, and also includes a binder resin agent for fixing the colorant onto the transfer paper;
In an electrophotographic toner containing at least a colorant that imparts color, the colorant has a content of 300 to 500%.
(m 1 /100g) It is a structure made of carbon black having an oil absorption amount of DBP and a surface area (BET) of 900 to 1300 (m/g).

[For production]

According to the above configuration, the carbon black used as a colorant in this toner has a larger oil absorption and surface area than carbon blanks used in conventional toners, and has a surface area of 300 to 500 (mf/100g). )
DBP oil absorption and 9oo to 1300 (m/g)
surface area (BET). It has been confirmed that by using such carbon black, it is possible to suppress a decrease in the conductivity of the obtained toner even if the carbon black is destroyed in the kneading step during the toner manufacturing process. Therefore, according to the present toner, when a large number of copies are made, it is possible to reduce the decrease in image density and the decrease in image quality that accompanies an increase in the number of copies. Specifically, the oil absorption amount of 20 to 250 (mj!/100g) DBP and the surface area (BET of 100 to 600 (of/g))
) and 300
~500 (mj!/100g) DBP oil absorption and
Preferably, 1 to 10 weight percent of the above carbon black having a surface area (BET) of 900 to 1300 (m2/g) is added and used as a coloring agent.

[Example 1] A first embodiment of the present invention will be described below.

Toner for electrophotography according to the present invention (hereinafter referred to as toner)
In addition to integrating the various materials that make up the toner, a binder resin agent is used to fix the colorant onto the transfer paper, a charge control agent is used to impart chargeability to the toner, and the toner is applied to the surface of the fixing roller. It consists of a release agent to prevent offset caused by adhesion, a first colorant and a second colorant to impart color to the toner, and a surface treatment agent to impart fluidity etc. to the toner. .

The above binder resin is a styrene/acrylic resin material, the charge control agent is a nigrosine material, the release agent is polypropylene, the first colorant is furnace carbon, and the second colorant is Lion (Tarusha Kotschen Black manufactured by Kotschen, Co., Ltd. and colloidal silica are used as the surface treatment agent.Furnace carbon as the first coloring agent is 70 (ml/100g) D
The oil absorption amount of B P and the surface area (B
ET). Ketschen black as the second colorant was 330 (ml/100g) D
The oil absorption amount of B P and the surface area (B
ET). Then, the blending ratio of each material is the first
As shown in the table.

Table 1 A method for manufacturing the present toner having the above structure will be described below.

First, each material except for the surface treatment agent shown in Table 1 above was mixed in a Henschel mixer, and the mixture obtained by this mixing step was melted and kneaded in a twin-screw extrusion kneader. The mixture was cooled and integrated.Then, the integrated kneaded material was coarsely pulverized, further pulverized into particles using an air jet type pulverizer, and then classified to obtain particles of a predetermined particle size. Then, 0.08 parts by weight of colloidal silica was added to these particles and mixed to obtain a first toner.

Next, as a toner for comparison with the first toner, 6.5 parts by weight of Furnace Carbon, which is the first colorant, and 0.5 parts by weight of Ketchen Blank, which is the second colorant, in the first toner were replaced. Then, 7 parts by weight of furnace carbon as the first colorant was added, and a second toner was produced in the same manner as described above.

Then, using the first toner and the second toner, 2000
When copies were made and the image density, black solid area adhesion amount, and charge amount were compared, the results shown in Table 2 were obtained.

(Margin below) Table 2 [Example 2] The third toner according to this example, like the first toner described above, contains a binder resin agent, a charge control agent, a release agent, and a first colorant. , a second coloring agent, and a surface treatment agent, and each of these materials is contained in the proportions shown in Table 3. and,
The third toner was produced in the same manner as the first toner.

From the results in the same table, the second toner for comparison showed a decrease in image density and the amount of black solid area adhesion after 2000 copies compared to the initial stage of copying, whereas the first toner according to the present invention showed There was no decrease in them at all. Furthermore, the first toner exhibits less change in charge amount as the number of copies increases than the second toner, and maintains a stable charge amount. Therefore,
It was found that good images could be stably obtained with the first toner.

Next, as a toner for comparison with the above third toner, 6 parts by weight of Furnace Carbon, which is the first colorant, and 1 part by weight of Ketchen Black, which is the second colorant, in the third toner.
A fourth toner was prepared in the same manner as described above except that 7 parts by weight of furnace carbon, which is the first colorant, was added instead of 7 parts by weight.

Similarly, 2000 copies were made using the third toner and the fourth toner, and the image density, amount of black solid area adhesion, and amount of charge were compared, and the results shown in Table 2 were obtained. .

From the results in the same table, it can be seen that the third toner for comparison shows a decrease in image density and the amount of black edge adhesion after 2000 copies compared to the initial stage of copying, while the third toner according to the present invention shows There was almost no decrease in them. Further, the third toner has less change in the amount of charge associated with an increase in the number of copies, and maintains a stable amount of charge than the fourth toner. Therefore, it was found that, like the first toner, good images could be stably obtained with the third toner.

〔Effect of the invention〕

As described above, the electrophotographic toner of the present invention integrates the various materials constituting the toner, as well as a binder resin agent for fixing the colorant onto the transfer paper and a colorant for imparting color. In the electrophotographic toner which contains at least 300 to 500 of the above colorant (ml/100g
) has an oil absorption amount of DBP, and has an oil absorption of 900 to 1300 (
It is composed of carbon black having a surface area of m/g).

Therefore, even if the carbon black is destroyed in the kneading step during the toner manufacturing process, it is possible to suppress a decrease in the conductivity of the resulting toner. As a result, when a large number of copies are made, a decrease in image density and a decrease in image quality due to an increase in the number of copies is reduced, and it is possible to obtain a good image.

Claims (1)

[Scope of Claims] 1. Electrophotography that integrates the various materials constituting the toner and includes at least a binder resin agent for fixing the colorant on the transfer paper and a colorant for imparting color. In the toner for
It has an oil absorption amount of BP of 900 to 1300 (m^2/
g) An electrophotographic toner comprising carbon black having a surface area (BET) of: