JP3009453B2 - Electrophotographic yellow toner for negative charging - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a negative charging electrophotographic yellow toner, and more particularly, to a method for maintaining a sharp charge amount distribution for a long period of time, The present invention relates to an electrophotographic yellow toner for negative charging, which has no toner scattering, has a clear hue, is excellent in image reproducibility, and can form a high density image.

(Prior Art) In the field of commercial electrophotographic copying and electrophotographic printing, a method of forming a positively charged electrostatic image is generally adopted in order to minimize the amount of ozone generated during charging. And
Therefore, as a developing toner used for developing the electrostatic image, a negative charging toner is widely used.

On the other hand, in recent years, laser beam printers and digital copiers have been developed, and in such image forming apparatuses,
The operation of writing a latent image on a negatively charged organic photoreceptor with a laser and performing reversal development with a negatively charged toner has been adopted, and a higher quality negatively charged toner has been required.

The developing toner is formed by granulating a resin composition containing a fixing resin, a colorant and a charge control agent as essential components to a toner particle size, generally an average particle size of 5 to 15 μm. In the case of a negative charging toner, a toner having a negative charge control action during frictional charging is used as a charge control agent.

In the conventional toner charge control method, the control of the average value of the toner charge amount of the entire toner is controlled by selecting the type of charge control agent and adjusting the amount of addition. However, in this method, even if it is possible to control the average value of the charge amount of the entire toner, it is very difficult to exactly control the distribution of the charge amount of the toner particles.

Conventionally, it is already known that a toner particle contains a plurality of charge control agents having a charging performance of opposite polarities. For example, JP-A-54-34243 discloses an electrostatic charge comprising toner and a carrier. An image developer is described in which the toner is a negatively chargeable toner containing a dye which is positively charged by friction with a carrier.

JP-A-57-196264 discloses an electrically insulating fixing medium, an electrically insulating magnetic one-component developer comprising a magnetic material powder and a charge control agent dispersed in the fixing medium. The developer, wherein the charge control agent comprises a combination of a negative or positive charge control agent and a charge control agent of the opposite polarity in a weight ratio of 1: 0.05 to 1: 1.5. Have been.

Further, recently, full-color development for forming an image by superimposing magenta, cyan, yellow, and black color toners has been performed. Among such full-color toners, cyan toner, magenta toner,
In addition, an organic colorant is mainly used as a colorant in a yellow toner, and carbon black is mainly used as a colorant in a black toner.

(Problems to be Solved by the Invention) In the conventional negative charging toner, the type and amount of the charge control agent are adjusted so that the average value of the charge amount is a value that can be sufficiently satisfied. In addition, the tendency that the distribution of the charge amount becomes considerably wide is inevitable. Of particular concern here is that
The charge amount is much higher than the average value, and a highly charged toner that is not consumed for development is necessarily generated at a certain frequency (distribution amount). Another problem is that a low-charged toner having a charge amount considerably lower than the average value and causing toner scattering is generated at a certain frequency.

The former highly charged toner particles are strongly adsorbed to the surface of the carrier particles and exist in a state in which they are hardly separated, and significantly impair the frictional charging performance of the carrier particles. Therefore, even if the toner has relatively few problems at the beginning of the development,
As the development time elapses, the ratio of uncharged or low-charged toner becomes higher, and problems such as toner scattering, fogging, and image density reduction occur.

In the method of combining a positively chargeable dye (charge control agent) with a charge control agent for negative charging, which is found in the prior art, the distribution of the charge amount can be freely shifted to a higher charge amount side or a lower charge amount side. Even if the advantage of obtaining the toner can be obtained, this method is still sufficiently satisfactory from the viewpoint that the distribution of the toner charge amount is sharpened and the generation of the highly charged toner and the low charged toner is suppressed to a level that is negligible or negligible. It was not something you could do.

Further, in a color toner, an organic colorant is used, but is often denatured by a mechanical impact force or a heat generated by a stirring operation in a developing device,
As a result, the charging characteristics of the toner fluctuate, and the state may not be maintained even if the charge amount distribution is sharp and good in the initial step.

In addition, a desired color and image (full-color image) are obtained by superimposing the color toners of each color (cyan, yellow, magenta).
However, if the charging characteristics of the toner fluctuate, the toner will not be developed (transferred) to the area to be developed (transferred) in the developing step and the transfer step, and will not be reproduced in a desired color.

Accordingly, an object of the present invention is to solve the above-mentioned disadvantages of the conventional yellow toner for negative charging, to appropriately adjust the charge amount of the toner, and to keep the average value of the charge amount of the toner in an optimum range with respect to prevention of toner scattering and image density. At the same time, the distribution of the toner charge amount is sharp, and a high-density image with good color development and a clear hue can be obtained with almost no high-charge toner not used for development or low-charge toner that causes toner scattering. An object of the present invention is to provide a charging yellow toner.

Another object of the present invention is to provide a negative charging yellow toner which has a sharp distribution of toner charge amount, has a fast rise of charge during charging, and has excellent image reproducibility with little deterioration in charging characteristics during long-term operation. To provide toner.

(Means for Solving the Problems) According to the present invention, in a negative charging electrophotographic toner containing a fixing resin, a colorant, and a negative charge control agent, the colorant is a benzidine pigment. The negative charge control agent is a metal compound of an aromatic oxycarboxylic acid, and is incompatible with the fixing resin but has dispersibility and a positive charge control action. A quaternary ammonium salt containing an anion as a charge control aid,
An electrophotographic yellow toner for negative charging, which is contained in a toner, is provided.

The metal compound (A) of the aromatic oxycarboxylic acid and the charge control auxiliary (B) are present in a weight ratio of A: B = 1: 0.05 to 1: 1, especially 1: 0.1 to 1: 0.7. It is preferable to use 0.5 to 5 parts by weight, especially 2 to 4 parts by weight in total, per 100 parts by weight of the fixing resin.

(Action) The negative charging electrophotographic yellow toner of the present invention contains, as essential components, a fixing resin, a colorant mainly composed of a benzidine pigment, and a negative charge control agent. It is remarkable that it contains, together with the charge control agent, a charge control auxiliary agent which is incompatible with the fixing resin but has a dispersibility and a charge control action of a polarity opposite to that of the negative charge control agent. It is a characteristic. That is, the present invention provides a positive charge controlling substance which is incompatible with the fixing resin but is dispersible, instead of the conventionally used positive charging dye which is compatible with the fixing resin. Is combined with a charge control agent for negative charge as a charge control aid, the charge amount of the toner can be suitably adjusted, and the distribution of the charge amount of the toner can be significantly sharper than that of a conventional toner. The present invention is based on the novel finding that the generation of highly charged toner not used for development and low charged toner which causes toner scattering can be effectively suppressed.

Making the charge amount distribution of the toner significantly sharper than the conventional one is particularly important when obtaining a full-color image (multicolor image) by superimposing toners. That is, in a full-color image, if any toner adheres (exists) to an unnecessary area in the development and transfer steps, the color of the image obtained by superposition changes and the image is not faithfully reproduced on the original.

FIG. 2 shows the charge control agent for negative charging (Comparative Example 1).
FIG. 3 shows the toner A using the toner A alone, FIG. 3 shows the toner B using the positive charge dye (see Comparative Example 2) in combination with the negative charge controller, and FIG. 5 is a graph showing the results of measuring the distribution of the charge amount of toner C using a charge control assistant (see Example 1) that satisfies the requirements of the present invention. Table 1 below summarizes the characteristic values of the charge amount distribution for these toners A, B, and C.

In this specification, the distribution of the charge amount of the toner is obtained by the following method.

Measurement of charge amount distribution The charge amount measuring device will be described below. As shown in FIG.
The apparatus includes a separating unit 2 for separating the toner from the developer, a measuring unit 3 for measuring the charge amount distribution of the separated toner, and a suction device 10 such as an air pump.

The separating unit 2 and the measuring unit 3 are separated by a partition plate 7, and the housing 1 is located slightly below the partition plate 7.
A communication hole 1a for introducing air into the housing 1
Is provided. An air rectifying filter 8 is provided slightly below the communication hole 1a.

The separating unit 2 is provided with the developer held on the magnet 4,
The compressed air is blown by the air needle 5, and only the lightweight toner is blown up and scattered, leaving the carrier magnetically attracted to the magnet 4.

A funnel 6 supported by a partition plate 7 is provided between the separation unit 2 and the measurement unit 3. The receiving port 6d at the upper end of the funnel 6 protrudes above the partition plate 7, and the front recess 6a at the lower end penetrates the filter 8 and faces the measuring unit 3 side.

The measuring unit 3 applies a DC power source R to the pair of electrode rods 9a and 9b embedded in the side wall of the housing 1,
A horizontal parallel electric field is formed between the electrode rods 9a and 9b. 10 is a filter.

The suction device 11 is connected to the communication hole 1a from outside the housing 1.
A main airflow that flows to the measuring section 3 through the rectifying filter 8 and the airflow that sucks the toner into the funnel 6 are formed above the funnel 6.

According to this charge amount measuring device, the toner particles separated by the separating unit 2 and collected by the funnel 6 and introduced into the measuring unit 3 fall vertically by the airflow by the suction device 11, and fall into the electrode rod 9a, It passes between 9b and lands on the filter 10. At this time, the toner particles fall in the horizontal parallel electric field between the electrode rods 9a and 9b while receiving the horizontal Coulomb force H and the vertical gravity V according to the charge amount. The light is dispersed on the filter 10 at positions corresponding to the mass and the charge amount. Then, from the distribution of the falling positions of the toner particles, the charge amount distribution of the toner is calculated by image processing.

The charge distribution curves in FIGS. 1, 2 and 3 are measured by this method.

That is, in the toner A using the negative charge controlling agent alone, as shown in FIG. 2, a large amount of the highly charged toner in the a region exists, and a large proportion of the oppositely charged toner and the 0 charged toner in the d region are present. include. In addition, in the toner B of the prior art in which a positive charge dye is combined with a negative charge control agent, the average value of the charge amount can be shifted to the lower charge amount side as shown in FIG. 3, but the distribution width is wide. It is almost the same as toner A,
Although the amount of the highly charged toner in the area a decreases, it is still present, and the proportion of the oppositely charged toner or the 0 charged toner in the area d increases. On the other hand, in the toner C of the present invention in which a negative charge control agent and a non-phase fixing positive charge control material for fixing are combined as an auxiliary agent, as shown in FIG. It can be understood that the presence amount increases, the width of the charge amount distribution becomes extremely narrow, and the amount of the highly charged toner in the region a and the amount of the oppositely charged toner and the amount of the 0 charged toner in the region d can be reduced (eliminated here).

Table 1 shows that the above toners A, B, and C were used to continuously copy 1000 sheets using a laser beam printer LPX-1 (manufactured by Mita Kogyo Co., Ltd.) modified machine (improved to the reversal development system). The image density (ID), the image fogging density (FD), and the state of toner scattering around the developing device at the time of performing the above were evaluated.

From FIGS. 1 to 3 and Table 1, it is confirmed that the toner of the present invention can be improved to a preferable charging characteristic capable of suppressing the fluctuation of image density, image fogging and toner scattering.

With the toner of the present invention, there is no change in image density, no fogging, and no toner scattering even during the long-term development, as well as at the beginning of development, and it has a remarkable effect on the charging characteristics and its deterioration prevention. Is shown.

In the toner of the present invention, the fact that the distribution of the charge amount is sharpened by using the charge control aid for the positive charge, which is incompatible with the fixing resin, was found as a phenomenon as a result of numerous experiments. Although the reason is not clear, the positively chargeable dye compatible with the fixing resin has no effect of sharpening the distribution, and the aromatic oxycarboxylic acid as the negative charge control agent is compatible or dispersed. It is presumed that the dispersion structure in which the positive charge control agent is dispersed in a macroscopic particle size in the matrix thus formed acts to reduce the number of highly charged toners and negatively charged toners. . In general, one of the significant drawbacks of combining a negative charge control agent with a positive charge control agent as an auxiliary is that, even if the charge on the toner particles is ultimately controlled to be negative, When the developer is stirred in a developing device, the rise of charge is delayed.
On the other hand, in the toner having the composition and the dispersion structure of the present invention, the rise of the charge when the developer is started to be stirred and the charging is started is similar to the negatively chargeable toner containing only the negatively chargeable charge controlling agent. It also has the advantage of being fast.

In the present invention, it is also important to use a metal compound of an aromatic oxycarboxylic acid as a charge control agent for negative charging, and to use a benzidine pigment as a coloring agent. Features can be further enhanced.

That is, the metal compound of the aromatic oxycarboxylic acid and the benzidine pigment do not significantly affect the electrical properties of the fixing resin, and have excellent thermal stability. The structure can be kept stable, and the charge amount distribution can be kept sharp and stable without being denatured by the impact force, heat or the like in the continuous stirring action.

(Preferred Embodiment of the Invention) Charge Control Aid The charge control aid used in the present invention is incompatible with the fixing resin but has dispersibility and reverse polarity to that of the negative charge control agent. , And specifically, a quaternary ammonium salt is used.

Such quaternary ammonium salts include: In the formula, R represents a lower alkyl group or a benzyl group under the condition that at least one of them is a long-chain alkyl group or a long-chain alkenyl group, and at least two of them are a lower alkyl group or a benzyl group. , A long-chain alkyl group or a long-chain alkenyl group, and A ^- represents an oxygenate anion.

The compound represented by these can be mentioned. Examples of the oxyacid anion include anions such as phosphorus oxyacids such as orthophosphoric acid and pyrophosphoric acid, and molybdic acid, tungstic acid, antimonic acid and bismuthic acid. These quaternary ammonium salts are particularly suitable for the purpose of sharpening the distribution of the charge amount without delaying the rise of the charge of the toner.

Charge Control Agent A metal compound of an aromatic oxycarboxylic acid is used as the negative charge control agent used in combination with the charge control aid. Examples of the metal compound of an aromatic oxycarboxylic acid include metal salts of oxybenzoic acid such as salicylic acid, paraoxybenzoic acid, and metaoxybenzoic acid, metal complex salts, oxy-1-naphthoic acid, oxy-2-naphthoic acid, and 3-oxy. Examples thereof include metal salts and metal complex salts of -2-naphthoic acid.

Among these, a metal salt or a metal complex salt of salicylic acid can be preferably used, and particularly, a salt of salicylic acid and zinc or a zinc complex compound is preferably used.

In addition, any negative charge control agent known per se can be used on the condition that it does not hinder color development and hue development of the colorant.

In the present invention, the charge control agent and the charge control aid
It is preferred to use 1: 0.05 to 1: 1, especially 1: 0.1 to 1: 0.7 weight ratio, and to use these combinations in total of 1 to 5 parts by weight, particularly 2 to 4 parts by weight per 100 parts by weight of the fixing resin. Should be present in an amount of

Fixing Resin As the fixing resin, a known fixing resin which is not compatible with the charge control assistant but exhibits dispersibility is used. Since these fixing resins charge the toner with a negative charge, it is desirable that the fixing resin has a tendency to be charged with a negative charge. For example, a styrene resin, an acrylic resin, or a styrene-acryl copolymer resin may be used. Commonly used.

As the styrene monomer used for these resins,
The following formula In the formula, R ₁ is a hydrogen atom, a lower (C 4 or less) alkyl group or a halogen atom, and R ₂ is a hydrogen atom or a substituent such as a lower alkyl group or a halogen atom. For example, styrene, vinyltoluene, α-methylstyrene, α-chlorostyrene, vinylxylene, vinylnaphthalene and the like can be mentioned. Among them, styrene is preferred.

On the other hand, as the acrylic monomer, the formula Wherein, R ₃ represents a hydrogen atom or a lower alkyl group, R ₄
Is a hydrogen atom or a substituted or unsubstituted alkyl group having up to 18 carbon atoms, such as ethyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylic Acids, methacrylic acid and the like. As the acrylic monomer, in addition to those described above, other ethylenically unsaturated carboxylic acids or anhydrides thereof,
For example, maleic acid, fumaric acid, crotonic acid, itaconic acid and their acid anhydrides can be used.

Styrene-acrylic copolymer resin is one of the suitable resin media, and styrene monomer (A) and acrylic monomer (B) are A: B = 50: 50-90. :Ten,
In particular, the range is preferably 60:40 to 35:15. Further, the resin used generally preferably has an acid value of 0 to 25. Further, from the viewpoint of fixability, it is preferable that the glass transition temperature (Tg) is 50 to 75 ° C.

Colorant As the colorant contained in the resin, one or more colorants for yellow containing a benzidine-based pigment as a main component are used.

Specific examples of the benzidine pigments include CI Pigment Yellow 13 (Benzidine Yellow GR), CI Pigment Yellow 14 (Vulcan First Yellow G), CI Pigment Yellow 17, CI Pigment Yellow 55, CI Pigment Yellow 12 and CI Pigment Yellow 83. And the like.

By using a benzidine-based pigment as a main component, there is also obtained an advantage that yellow color is well developed, the hue is clear, there is no fading, and the durability is excellent.

Toner The particle diameter of the toner particles, as measured by a Coulter counter, is preferably in the range of 5 to 15 μm, particularly 7 to 12 μm in terms of volume-based median diameter, and the particle shape was produced by a melt-kneading / pulverization method. It may be amorphous or spherical, produced by a dispersion or suspension polymerization method.

The toner of the present invention exhibits excellent chargeability when used as a two-component magnetic developer in combination with a magnetic carrier known per se. As the magnetic carrier, a ferrite carrier or an iron powder carrier is used, and these can be used either uncoated or resin-coated. Generally, ferrite carriers are preferred.

Conventionally, as ferrite, for example, iron oxide zinc (ZnFe
₂ O ₄ ), iron oxide yttrium (Y ₃ Fe ₅ O ₁₂ ), iron cadmium oxide (CdFe ₂ O ₄ ), iron cadmium oxide (Gd ₃ Fe ₂ O ₁₂ ),
Copper iron oxide (CuFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), nickel iron oxide (NiFe ₂ O ₄ ), iron neodymium oxide (NdFeO ₃ ),
Barium iron oxide (BaFe ₁₂ O ₁₉ ), magnesium iron oxide (M
gFe ₂ O ₄ ), iron manganese oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ), and the like. Mg, Mn
And a soft ferrite containing at least one metal component selected from the group consisting of Ni, and preferably two or more, such as copper-zinc-magnesium ferrite.These ferrites are also used in the present invention. It is preferably used.

Various types of coating resins for magnetic carriers, such as acrylic resins, styrenic resins, silicone resins, fluorine resins, and various amino-modified resins, are known. The charge of the resin-coated magnetic carrier is positively controlled. Accordingly, it is preferable that the toner charge is indirectly controlled to be negative. Needless to say, in the present invention, even if such a carrier coat resin layer does not exist, the control of the electric charge is performed effectively and surely. The carrier's saturation magnetization is
It is preferably in the range of 40 to 75 emu / g, especially 45 to 70 emu / g. As the magnetic carrier, a ferrite carrier that satisfies the above conditions, particularly a spherical ferrite carrier, is preferable, and its particle size is 20 to 140 μm, particularly 50 to 100 μm.
m is desirable.

The mixing ratio between the toner and the magnetic carrier varies depending on the physical properties of the toner and the magnetic carrier, but is preferably in the range of generally 1:99 to 10:90, more preferably 2:98 to 5:95 by weight. . Further, it is generally desirable that the electric resistivity of the whole developer is in the range of 5 × 10 ^{9 to} 5 × 10 ¹² Ω · cm, preferably 5 × 10 ^{9 to} 5 × 10 ¹¹ Ω · cm.

In developing an electrostatic image, after mixing the toner and the magnetic carrier, a magnetic brush having a predetermined length is formed on a developing sleeve having a magnet roll therein, and the magnetic brush and a photoconductor having an electrostatic image are formed. The magnetic brush and the electrostatic image holding photoreceptor are brought close to each other in a printing operation or in an electric field to which an oscillating electric field is applied.

(Effects of the Invention) According to the present invention, for negative charging electrophotography, a fixing resin, a colorant containing a benzidine pigment as a main component, and a metal compound of an aromatic oxycarboxylic acid as a negative charging control agent are used. In the yellow toner, a charge control auxiliary agent which is incompatible with the fixing resin but has a dispersibility and a charge control action of a polarity opposite to that of the negative charge control agent is contained in the toner. Thereby, the charge amount of the toner can be appropriately adjusted, various disadvantages of the conventional negatively charged toner can be solved, and the average value of the charge amount of the toner is in the optimal range with respect to the prevention of toner scattering and the image density. There is provided a negatively charged toner having a sharp distribution and having substantially no highly charged toner that is not used for development and lowly charged toner that causes toner scattering. The toner of the present invention achieves the advantages that the distribution of the toner charge amount is sharp, that the charge rises quickly during charging, and that the charging characteristics are less deteriorated during long-term operation.

(Example 1) Styrene-acrylic copolymer as fixing resin 10
0 parts by weight, CI Pigment Yellow 1 as colorant
75 parts by weight, 2 parts by weight of zinc compound of salicylic acid as charge control agent for negative charge, 2 parts by weight of low molecular weight polypropylene, quaternary ammonium of the following formula as charge control aid incompatible with fixing resin 0.5 parts by weight of salt Was melt-kneaded by a twin-screw extruder, and the kneaded product was cooled, pulverized and classified to obtain a toner having an average particle diameter of 11 μm. The average particle diameter of the toner and the resin coating is 85 μm.
The ferrite carrier was mixed and stirred at a toner concentration of 4.5% to obtain a developer, and the charge amount distribution was measured by a toner charge amount distribution measuring device shown in FIG. FIG. 1 shows the result.

Next, the above-mentioned developer was modified with a laser beam printer LPX-1 manufactured by Mita Kogyo Co., Ltd. equipped with an organic photoreceptor for negative charging (remodeled to a reversal development system) (photoreceptor surface potential: −
(700 V, developing bias potential: -500 V), and continuous image formation was performed on 1000 sheets, and the image characteristics were observed. As a result, a good image was obtained without any decrease in image density, image fogging, and toner scattering shown in Table 1. Was. Further, when the continuous image formation of 50,000 sheets was performed and the fluctuation of the toner charge amount distribution was traced,
As shown in the figure, the toner charge amount distribution stably changed in the initial to 5,000 sheets without generating many defectively charged toner particles.

(Example 2) In Example 1, 5 parts by weight of CI Pigment Yellow 13 was used as a coloring agent, and 2 parts by weight of a zinc compound of alkyl salicylic acid was used as a charge control agent for negative charging. As a charge control aid, the following formula 4
A toner was prepared in the same manner as above, except that the ammonium salt was 0.5 part by weight.

Thereafter, a developer was obtained in the same manner as in Example 1, and image characteristics were observed by continuous image formation on 1000 sheets.
Fluctuations in the toner charge amount distribution during continuous image formation on sheets were tracked. As a result, the toner charge amount distribution was sharp, and the charge distribution with little high-charge area toner or 0 to reverse polarity toner was maintained, and a good image was always formed.

(Comparative Example 1) A toner was prepared in the same manner as in Example 1, except that no charge control auxiliary agent was used. The toner charge amount distribution was measured in the same manner as in Example 1. The results are shown in FIG. Further, in observing the image characteristics by forming 1000 continuous images, the image density was unstable. Further, image fogging and toner scattering also occurred.

Comparative Example 2 A toner was prepared in the same manner as in Example 1, except that 0.5 parts by weight of CI Solvent Yellow 56 compatible with the fixing resin was used instead of the charge control aid. Then, the toner charge amount distribution was measured in the same manner as in Example 1, and the result was as shown in FIG. Further, in observation of image characteristics by continuous image formation of 1000 sheets, image fog and toner scattering were severe. Although the image density was satisfactory to some extent, density unevenness occasionally occurred.

(Comparative Column 3) A toner was prepared in the same manner as in Example 1, except that 5 parts by weight of CI Pigment Yellow 138 was used as a coloring agent. Then, in the same manner as in the embodiment, the image characteristics were observed by forming a continuous image of 1000 sheets, and the fluctuation of the toner charge amount distribution by forming the continuous image of 50,000 sheets was tracked.
The results shown in the figure were obtained.

In the continuous image formation of 1000 sheets, a good image similar to that of Example 1 was obtained. However, the distribution of the toner charge amount gradually deteriorated from around 8000 sheets and became broad, and the image became inferior from around 10,000 sheets.

Comparative Example 4 A toner was prepared in the same manner as in Example 1, except that 2 parts by weight of a chromium-containing azo dye was used as a negative charge control agent. Then, in the same manner as in the example, the image characteristics by the continuous image formation of 1000 sheets were observed, and the variation of the toner charge amount distribution by the continuous image formation of 50,000 sheets was traced. Although a good image similar to that of No. 1 was obtained, the toner charge amount distribution gradually deteriorated, and the image became poor after about 13,000 sheets.

 FIG. 7 shows the charge amount distribution.

Comparative Example 5 A toner was produced in the same manner as in Example 1, except that 2 parts by weight of an aluminum complex salt of an aromatic dicarboxylic acid was used as a negative charge control agent. Then, in the same manner as in the example, the image characteristics by the continuous image formation of 1000 sheets were observed, and the fluctuation of the toner charge amount distribution by the continuous image formation of 50,000 sheets was traced. A good image was obtained in the same manner as described above, however, the distribution of the toner charge amount gradually deteriorated, and the image became inferior from around 25,000 sheets.

As described above, according to the examples and comparative columns, the toner of the present invention maintains a sharp charge amount distribution stably even when copying operation is repeated, and shows poor toner (highly charged toner, lowly charged toner, etc.).
It can be seen that a good image can be repeatedly formed without occurrence of image formation.

[Brief description of the drawings]

FIG. 1 is a diagram showing a characteristic curve of a toner charge amount distribution of the present invention, and FIG. 2 is a diagram showing a characteristic curve of a toner charge amount distribution using a negative charge control agent alone. FIG. 3 is a diagram showing a characteristic curve of a charge amount distribution of a toner using a charge controlling agent for negative charging and a dye having positive charging (compatible with a fixing resin), and FIG. FIG. 2 is a schematic layout diagram of a charge amount measuring device used for measuring a charge amount distribution of a toner. FIG. 5 is a diagram showing a charge amount distribution characteristic curve of the toner of the present invention before and after printing, and FIGS. 6 and 7 show the variation of the charge amount distribution characteristic curve of the comparative toner. FIG.

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akihiro Watanabe 1-2-2, Tamazo, Chuo-ku, Osaka-shi, Osaka Mita Kogyo Co., Ltd. (72) Inventor Yoshihisa Kuramae 1-2-2, Tamazuki, Chuo-ku, Osaka, Osaka No. 28 Mita Kogyo Co., Ltd. (56) References JP-A-1-155361 (JP, A) JP-A-2-22670 (JP, A) JP-A-53-127726 (JP, A) JP-A-62 -53944 (JP, A) JP-A-54-134441 (JP, A) JP-A-59-136747 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/08 CA (STN)

Claims (4)

(57) [Claims] 1. A negative charging electrophotographic toner containing a fixing resin, a colorant and a negative charge control agent, wherein the colorant is a benzidine pigment, and the negative charge control agent is aromatic. A metal compound of oxycarboxylic acid, which is incompatible with the fixing resin, but has a dispersibility and a quaternary ammonium salt containing an oxyacid anion having a positive charge control action. An electrophotographic yellow toner for negative charging, which is contained in a toner as a control assistant. Wherein said quaternary ammonium salt has the formula ^{_{(R) 4 -N - · A}} - wherein, R is 4 at least one long chain alkyl group or long chain alkenyl groups in the, A lower alkyl group, a benzyl group, a long-chain alkyl group or a long-chain alkenyl group, provided that at least two of the four groups are a lower alkyl group or a benzyl group, and A ^- represents an oxygenate anion The yellow toner according to claim 1, which is represented by: 3. A method according to claim 1, wherein the charge control agent for negative charge and the charge control auxiliary agent are 1:
2. The yellow toner according to claim 1, wherein the yellow toner is present in a weight ratio of 0.05 to 1: 1 and 0.5 to 5 parts by weight in total per 100 parts by weight of the fixing resin. 4. The yellow toner according to claim 1, wherein the charge control agent for negative charging is a zinc compound of salicylic acid.