Toner Number:7,160,663 from the United States Patent and Trademark Office (PTO) owispatent

Title: Toner

Abstract: A toner includes toner particles and an inorganic fine powder mixed with the toner particles. The toner particles contain a binder resin, a coloring agent, a releasing agent, and a sulfur-containing resin. The toner particles contain at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum, and phosphorus and satisfy the relationship: 4.ltoreq.T/S.ltoreq.30 wherein T represents the total content of the element in ppm, and S represents the content of sulfur in ppm. The weight-average particle diameter (D4) of the toner is in the range of 3 to 10 .mu.m. The average circularity of the toner is within the range of 0.950 to 0.995.

Patent Number: 7,160,663 Issued on 01/09/2007 to Komoto,   et al.

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Inventors:	Komoto; Keiji (Shizuoka, JP), Katsuta; Yasushi (Shizuoka, JP), Mikuriya; Yushi (Shizuoka, JP), Kaburagi; Takeshi (Shizuoka, JP), Tosaka; Emi (Shizuoka, JP)
Assignee:	Canon Kabushiki Kaisha (Tokyo, JP)
Appl. No.:	10/808,401
Filed:	March 25, 2004

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Foreign Application Priority Data

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Jul 29, 2003 [JP]			2003-281761
Feb 25, 2004 [JP]			2004-049917

Current U.S. Class:	430/109.1 ; 430/108.6; 430/108.7
Current International Class:	G03G 9/087 (20060101)
Field of Search:	430/109.1,108.6,108.7,137.15

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References Cited [Referenced By]

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U.S. Patent Documents

	4883735		November 1989		Watanabe et al.
	5858597		January 1999		Mizoh et al.
	6638674		October 2003		Komoto et al.
	6667146		December 2003		Tosaka et al.
	2002/0048010		April 2002		Inaba et al.
	2003/0186152		October 2003		Ohno et al.

Foreign Patent Documents

	56-13945		Apr., 1981		JP
	63-184762		Jul., 1988		JP
	00-56518		Feb., 2000		JP
	001-343788		Dec., 2001		JP
	2-108019		Apr., 2002		JP

Primary Examiner: Goodrow; John L
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto

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Claims

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What is claimed is:

1. A toner comprising: (a) toner particles comprising a binder resin, a coloring agent, a releasing agent, and a sulfur-containing resin; and (b) an inorganic fine powder mixed with the toner particles, wherein i) the toner particles contain at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum, and phosphorous and satisfy the relationship: 4.ltoreq.T/S.ltoreq.30 wherein T is from 100 to 1,000 ppm and represents the total content of said element, and S represents the sulfur content in terms of ppm; ii) the weight-average particle diameter (D4) of the toner is in the range of 3 to 10 .mu.m; and iii) the average circularity of the toner is within the range of 0.950 to 0.995.

2. The toner according to claim 1, wherein the following relationship is satisfied: (S-f).gtoreq.(S-m) wherein (S-f) represents the sulfur content in finer particles obtained by air-classifying the toner and (S-m) represents the sulfur content in the toner, the finer particles being air-classified particles satisfying the following relationship: {D4 of the toner.times.0.7}.ltoreq.D4 of the finer particles.ltoreq.{D4 of the toner.times.0.8}.

3. The toner according to claim 1, wherein the following relationship is satisfied: 0.0003.ltoreq.E/A.ltoreq.0.0050 wherein E represents the content of sulfur on the toner surfaces and A represents the content of carbon on the toner surfaces in terms of atomic percent measured by X-ray photoelectron spectrometry.

4. The toner according to claim 1, wherein the following relationship is satisfied: 0.0005.ltoreq.F/A.ltoreq.0.0100 wherein F represents the content of nitrogen on the toner surfaces and A represents the content of carbon on the toner surfaces in terms of atomic percent measured by X-ray photoelectron spectrometry.

5. The toner according to any one of claims 1 to 4, wherein the following relationship is satisfied: 1.ltoreq.F/E.ltoreq.8 wherein F represents the content of nitrogen on the toner surfaces and E represents the content of sulfur on the toner surfaces in terms of atomic percent measured by X-ray photoelectron spectrometry.

6. The toner according to claim 5, wherein the following relationship is satisfied: 1.ltoreq.F/E.ltoreq.6.

7. The toner according to claim 5, wherein the following relationship is satisfied: 2.ltoreq.F/E.ltoreq.8.

8. The toner according to claim 5, wherein the following relationship is satisfied: 2.ltoreq.F/E.ltoreq.6.

9. The toner according to claim 1, wherein the inorganic fine powder is one of silica, titanium oxide, alumina, and a complex oxide thereof.

10. The toner according to claim 1, wherein the inorganic fine powder is hydrophobized inorganic fine powder.

11. The toner according to claim 10, wherein the inorganic fine powder is hydrophobized with a silane compound and/or silicone oil.

12. The toner according to claim 1, wherein the inorganic fine powder comprises silica, and the percentage of free silica is within the range of 0.05% to 5.00% based on the number of the silica.

13. The toner according to claim 1, wherein the average circularity of the toner is in the range of 0.960 to 0.995.

14. The toner according to claim 1, wherein the mode circularity of the toner is at least 0.99.

15. The toner according to claim 1, wherein the weight-average particle diameter (D4) is in the range of 4 to 8 .mu.m.

16. The toner according to claim 1, wherein the toner is nonmagnetic.

17. The toner according to claim 1, wherein the toner particles are prepared in an aqueous medium.

18. The toner according to claim 17, wherein the toner particles are prepared by suspension polymerization.

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Description

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a toner for use in recording processes such as electrophotographic processes, electrostatic recording processes, electrostatic printing processes, and the like.

2. Description of the Related Art

To date, many electrophotographic recording processes are known. In a typical electrophotographic process, an electrical latent image is formed by a variety of methods on a member for carrying an electrostatic image, hereinafter simply "photosensitive member", using a photoconductive material, and is developed into a visible toner image using a toner. The toner image is transferred onto a suitable recording medium, such as paper, and is then fixed on the recording medium by application of heat, pressure, or the like, to obtain a copy.

Examples of the methods for forming visible toner images from electrical latent images include cascade development; magnetic-brush development; pressure development; magnetic-brush development with a two-component developer containing a carrier and a toner; noncontact single-component development in which toner is transferred from a toner supporting member onto a photosensitive member without the photosensitive member making contact with the toner supporting member; contact single-component development in which a toner supporting member is pressed against a photosensitive member to transfer the toner by an electric field; and jumping development using a magnetic toner.

Recent technical trends require electrophotographic apparatuses, such as printers, to have higher resolutions as measured in dots per inch (dpi). The desired resolutions are now 1,200 dpi and 2,400 dpi, which are higher than the 300 dpi and 600 dpi conventionally required. Higher resolutions require finer development systems. Moreover, recent copying machines incorporate digital technology to achieve advanced functions. In particular, copying machines now use lasers to produce electrostatic images to achieve higher resolutions. As with printers, copy machines also require high-resolution, fine development systems.

Furthermore, the field of electrophotography has seen rapid development of color printing. Since color images are developed by adequately superimposing yellow, magenta, cyan, and black toners, toners are required to have characteristics suitable for such development (hereinafter referred to as "development characteristics"), which are different from those required in a single toner process. Accordingly, the electrification of the toners must be uniformly controlled.

In order to control the electrification of toners, charge control agents are conventionally used. In general, charge control agents can be roughly classified into two types, namely, (i) complex compounds having complex structures in which ligand components coordinate with central metals and (ii) polymer compounds containing polar functional groups that function as the charging sites. Complex compounds are crystalline and exhibit low compatibility with binder resins; accordingly, a toner production method must be carefully selected and controlled to uniformly disperse such complex compounds. In contrast, charge control agents of a polymer compound type, which are highly compatible with resins, can easily form homogeneous dispersions; accordingly, fewer limitations are imposed on the process using this type of agent. An example of the polymer compound charge control agent is a resin containing a polymerizable polymer of a particular structure. For example, Japanese Patent Laid-Open No. 63-184762 discloses such a polymer compound charge control agent.

In an electrophotographic process, a toner image produced on a photosensitive member by development is transferred onto a recording member in a transfer step. The remaining toner in the image area and the fogging toner in the non-image area on the photosensitive member are removed in a cleaning step and stored in a waste toner storage. In a conventional cleaning step, a blade, a fur-brush, a roller, or the like has been used. These components require a large space and prevent size reduction of the apparatuses. Moreover, from the standpoint of ecology, a system with less waste toner and a toner having high transfer efficiency while causing less fogging are desired.

The transfer efficiency is known to decrease due to degradation in releasability of the toner from the photosensitive drum. The degradation occurs when the circularity or sphericity of the toner is low because a toner with low circularity or sphericity increases the area of contact between the toner and the photosensitive drum. Moreover, since the surface of such a toner has large irregularities, charges concentrate on edges and the so-called image force at the locations corresponding to these edges increases as a result.

The process of achieving high toner circularity differs depending on the method for making the toner. Methods for making commercial toners can be roughly classified into pulverization methods and polymerization methods. In pulverization methods, a binder resin, a coloring agent, and the like are thoroughly mixed by melting to obtain a homogeneous mixture. The mixture is then pulverized in a fine grinding mill and classified with a classifier to obtain a toner having a predetermined particle diameter. The toner obtained by the pulverization methods has irregularities in the surface since the surface has fractures resulting from milling. Accordingly, an additional process, such as applying mechanical impact, heat, or the like, is necessary to improve the surface quality and to achieve sufficiently high circularity.

Polymerization methods can be classified into two types, namely, association/aggregation methods and suspension polymerization methods. In the association/aggregation method, resin particles, a coloring agent, a releasing agent, and the like are associated or aggregated into particles of a predetermined diameter in an aqueous medium containing emulsion-polymerized resin particles as the binder resin component. In the suspension polymerization method, a polymerizable monomer composition containing a coloring agent, a releasing agent, a polymerization initiator and the like dispersed or dissolved in a polymerizable monomer (binder resin component) is prepared. The polymerizable monomer composition is then placed in an aqueous medium, formed into droplets of a predetermined diameter by application of shear force, and is suspension-polymerized to provide a toner.

The toner prepared by the association/aggregation method also has irregularities on the surface; thus, an additional process of heating the toner, adding another polymerizable monomer composition to perform seed polymerization, or the like is necessary to improve the surface quality. The toner prepared by suspension polymerization methods has fewer irregularities and is more spherical compared to other toners since the toner is polymerized in droplets. No additional process is required to achieve high circularity. An example of this type of toner is disclosed in Japanese Patent Laid-Open No. 2001-343788. As is described above, a toner capable of uniform electrification and having high transfer efficiency can be prepared by suspension polymerization using a charge control agent of a polymer compound type. An example of such a technique is disclosed in Japanese Patent Laid-Open No. 2000-056518.

Moreover, a toner can be stably and efficiently prepared by suspension polymerization using a water-insoluble inorganic salt as the dispersion stabilizer. Such a technique is disclosed in Japanese Patent Laid-Open No. 2002-108019.

As is described above, the transfer efficiency can be improved by increasing the circularity of the toner. However, some of the toner will remain on the photosensitive member after the transfer step unless the transfer efficiency is 100%. Thus, a cleaning step for removing the remaining toner is necessary. In the cleaning step, a toner having high circularity and thus high flowability is difficult to remove since the toner can pass under the cleaning blade. Accordingly, when the toner has high charge, an image force operates between the image carrying member and the toner, and thus the toner becomes difficult to remove in the cleaning step.

On the other hand, when the toner has low charge, the toner tends to scatter into a development unit or the like, thereby contaminating the interior of the printer, copy machine, or the like. The contamination may cause image quality degradation, image contamination, and defects in the apparatus.

Thus, a highly circular toner prepared with a charge control agent of a polymer compound type rarely satisfies all of the properties required in development, charging, and cleaning.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a toner that exhibits stable charge characteristics regardless of the environment, forms high quality images, causes less scattering, and can be easily removed in the cleaning step.

In particular, the present invention provides a toner containing toner particles and an inorganic fine powder mixed with the toner particles. The toner particles contain a binder resin, a coloring agent, a releasing agent, and a sulfur-containing resin. The toner particles contain at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum, and phosphorus and satisfy the relationship: 4.ltoreq.T/S.ltoreq.30 wherein T represents the total content of the element in ppm, and S represents the sulfur content in ppm. The weight-average particle diameter (D4) of the toner is in the range of 3 to 10 .mu.m. The average circularity of the toner is within the range of 0.950 to 0.995.

Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments (with reference to the attached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example of a development apparatus used in the present invention.

FIG. 2 is a schematic diagram of an image forming apparatus including an intermediate transfer drum for simultaneously transferring multiple toner images onto a recording medium.

FIG. 3 is a schematic diagram of an intermediate transfer belt.

FIG. 4 is a schematic diagram of an image forming apparatus including a plurality of image forming units for respectively forming toner images of different colors, in which the toner images are superimposed on one another by sequentially transforming the toner images onto a recording medium.

FIG. 5 is a schematic diagram of an image forming apparatus including a transfer belt, which functions as a secondary transfer means for simultaneously transferring four color toner images from an intermediate transfer drum to a recording medium.

FIG. 6 is a schematic diagram of an image forming apparatus of a contact development type that uses a single-component nonmagnetic toner employed in the Examples herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A toner of the present invention contains a sulfur-containing resin and is constituted from particles having a high circularity and a diameter within a predetermined range. In the toner, the ratio of the sulfur content to the total content of at least one element selected from the group consisting of magnesium, calcium, barium, zinc, aluminum, and phosphorus is adjusted within a predetermined range to achieve sufficient development characteristics and charge properties, while facilitating cleaning and preventing scattering of the toner inside the apparatus. The toner achieves these effects when used in a full-color printer.

In general, a charge control agent of a polymer compound type has a resistance higher than that of a complex compound and thus produces overcharged toner particles by charge transfer. Since the overcharged particles tightly adhere onto the photosensitive member, the toner cannot be completely removed from the surface of the photosensitive member, which results in cleaning failure. A conventional method that uses a toner prepared by suspension polymerization and a charge control agent of a polymer compound type is known in which degradation of image characteristics in a high-temperature high-humidity environment is said to prevented by regulating the amount of the remaining dispersion stabilizer. However, this method does not teach the correlation between the polymer compound charge control agent and the cleaning failure in a low-temperature and low-humidity environment.

The present inventors have examined the correlation between the polymer compound charge control agent and cleaning failure at a low-temperature and low-humidity environment. The Inventors have also investigated toner scattering, which is technically difficult to overcome. As a result, the inventors have discovered a toner which is free of cleaning failure and toner scattering and which can produce high-quality images irrespective of the environment.

The present invention will now be described in detail.

A toner becomes increasingly difficult to remove from a photosensitive member as the circularity of toner particles increases. This tendency is accelerated in a low-temperature-low-humidity environment due the following reasons. In a development unit, a toner is transferred onto a photosensitive member, during which a toner component having a higher charge tightly adheres to the surface of the photosensitive member due to the high image force. In a low-temperature-low-humidity environment, a toner can be readily overcharged and the percentage of the overcharged component in the toner increases as a result. Thus, the toner tightly adhered on the photosensitive member cannot be removed with a cleaning blade or a cleaning roller, thereby resulting in cleaning failure.

Cleaning failure may be prevented by decreasing the charge of the toner; however, this causes degradation of development properties and toner scattering in a high-temperature and high-humidity environment.

The inventors have carefully investigated the overcharged component in the toner and have discovered a method for optimizing the charge of the overcharged component in the toner containing a polymer compound charge control agent. A polymer compound charge control agent generally has a slightly nonuniform distribution in the number of charge sites. Among the components of the charge control agent, a component containing a large number of charge sites induces the production of an overcharged component in the toner. Thus, a predetermined percentage of at least one element selected from magnesium, calcium, barium, zinc, aluminum, and phosphorus is added to interact with the component containing a large number of charge sites. As a result, the amount of the overcharged component in the toner can be reduced without decreasing the total charge of the toner while preventing cleaning failure and toner scattering. The present invention is made based on the fact that the aforementioned particular elements readily interact with the component containing a large number of charge sites in the charge control agent. The inventors have also found that an organic dispersion stabilizer used in toner fabrication can be used as the element capable of interacting with the polymer compound charge control agent.

The toner of the present invention yields the above-described effects due to the following reasons. A toner having smaller particles is advantageous in obtaining a superfine or high resolution image and a toner having a high circularity is advantageous for uniform charging. A toner with smaller particles and high circularity thus forms a superfine image. However, such a toner is likely to cause cleaning failure. Moreover, when such a toner is used with a polymer compound charge control agent, frequent cleaning failures occur due to its high resistance and the presence of the overcharged component in the toner in a low-temperature and low-humidity environment.

In the toner of the present invention, the relationship between the amount of sulfur, which promotes electrification, and the amount of the component that inhibits electrification is controlled to prevent both cleaning failure and toner scattering. Here, the component that inhibits electrification is at least one element selected from magnesium, calcium, barium, zinc, aluminum, and phosphorus, hereinafter simply referred to as "Group 1 element".

The ratio of the content T of the Group 1 element in the toner particles to the sulfur content S in the toner particles, i.e., the ratio T/S, must be in the range of 4 to 30. The balance between the amount of the Group 1 element primarily functioning as the leak site and the amount of sulfur functioning as the charge site is strongly related to prevention of cleaning failure and toner scattering when the toner has a diameter within a predetermined range and an average circularity within a predetermined range. When the ratio T/S is smaller than 4, the sulfur content is excessively small relative to the content of the Group 1 element functioning as the leak site. This may result in excess charge-up, cleaning failure, and image quality degradation due to the overcharged component in the toner. When the ratio exceeds 30, the Group 1 element functioning as the leak site becomes excessive. Accordingly, the charge of the toner does not reach the level required in electrophotographic processes, resulting in toner scattering and lower image quality. In order to control the ratio T/S, the content of the sulfur and the content of the Group 1 element in the toner must be controlled.

In a suspension polymerization toner fabrication method preferred in the present invention, the T/S is determined from the interaction between the polymer compound charge control agent and the Group-1-element-containing compound used as the suspension stabilizer. In this method, the ratio T/S varies according to the distribution of sulfur atoms even though the amount of sulfur is fixed at a predetermined level.

For example, when the charge control agent contains a large amount of a high-charge-site component in which the distance between adjacent charge sites is small and the concentration of neighboring charge sites is high, the high-charge-site component when placed into contact with the Group 1 element tends to surround the Group 1 element due to a strong interaction between the high-charge-site component and the Group 1 element and due to the short distance between the adjacent charge sites, thereby yielding a large ratio T/S. When this tendency is amplified, the Group 1 element becomes completely hidden and no longer functions as the leak site for leaking charges, resulting in excess charge-up. Since most of the charge sites of the charge control agent interact with the Group 1 element, the number of charge sites decreases, and the charge can no longer be controlled. This may cause toner scattering due to a decreased charge in a high-humidity environment or may cause cleaning failure due to excess charge-up in a low-humidity environment.

In the present invention, the combination of the polymer compound charge control agent and the Group 1 element yields an adequate interaction and is most suitable for achieving the effects of the present invention. Although the reason for this is not clearly known, the inventors assume that the ionic radius, the electro-negativity, or the like of the Group 1 element causes such effects.

When the distance between adjacent charge sites is adequate and the interaction with the Group 1 element is sufficiently weak, the polymer compound charge control agent no longer surrounds the Group 1 element, and charge sites can function properly. Moreover, the amount of the remaining Group 1 element can be decreased. Since certain positions of the charge sites readily interacting with the Group 1 element tend to have a charge site density, the distribution of toner charge can be narrowed due to the concentration of the charge sites.

However, when the distribution of the charge sites becomes completely uniform, the interaction between the Group 1 element and sulfur becomes excessively weak. Accordingly, the amount of the Group 1 element decreases; the ratio T/S decreases; charge-up occurs due to deficiency of the leak sites; and extensive cleaning failure and image quality degradation occur as a result. The inventors have comprehensively considered all of the aforementioned phenomena in defining the range of T/S capable of preventing degradation of the image quality. Moreover, in suspension-polymerized toners, components with higher polarity tend to appear on the surface of particles. Thus, when the sulfur-containing resin exists on the toner surface, the above-described effects of the invention can be further promoted.

The value T (ppm) of the Group 1 element is preferably in the range of 100 to 2,000 since T exceeding 2,000 causes toner scattering and T less than 100 causes cleaning failure. More preferably, T is in the range of 100 to 1,500 and most preferably 100 to 1,000. In the present invention, values T and S are determined as follows. A calibration curve is drawn using a standard sample by fluorescent X-ray analysis, and each value is determined based on the calibration curve. The analysis is carried out according to Japanese Industrial Standards (JIS) K 0119 (1987) using a fluorescent X-ray analyzer, SYSTEM 3080 (manufactured by Rigaku Corporation)

In general, finer toner particles whose diameter is smaller than the average tend to spread over the background, thereby causing fogging. The inventors have found through extensive investigations that the toner of the present invention can prevent fogging and cleaning failure since the sulfur content in the finer toner particles is sufficiently large. The exact reason for this phenomenon is not clear, but the inventors consider that charges of the finer particles are responsible for this phenomenon. In the present invention, cleaning failure can be prevented when the following relationship is satisfied: (S-f).gtoreq.(S-m) wherein (S-f) represents the sulfur content in finer particles obtained by air-classifying the toner and (S-m) represents the sulfur content in the toner. In the present invention, the finer particles are air-classified particles, which satisfy the following relationship: {D4 of the toner.times.0.7}.ltoreq.D4 of the finer particles.ltoreq.{D4 of the toner.times.0.8}, wherein D4 represents the weight average particle diameter.

In the present invention, the "sulfur-containing resin" refers to a resin preferably having a peak top in the range of 1,000 or more in terms of polystyrene-equivalent molecular weight by gel permeation chromatography described below, wherein sulfur is contained in a component eluted within the above-described range. The sulfur atoms on the particle surfaces preferably have a bond energy peak top in the range of 166 to 172 eV measured by X-ray photoelectron spectrometry described below. In particular, the sulfur atoms preferably have a valence number of 4 or 6, and more preferably a valence number of 6. Regarding the bonding state of the sulfur atoms, sulfone, sulfonic acid, sulfonate, sulfuric ester, and sulfate ester are preferred. Sulfonic acid, sulfonate, sulfuric ester, and sulfuric ester, and sulfate ester are particularly preferred.

The toner of the preset invention preferably contains nitrogen atoms on the toner surface in addition to the sulfur atoms. The nitrogen atoms have a bond energy peak top in the range of 396 to 403 eV measured by X-ray photoelectron spectrometry described below. Moreover, the ratio of the content F of the nitrogen atoms on the toner surface to the content E of the sulfur atoms on the toner surface in terms atomic percent, i.e., the ratio F/E, preferably satisfies the relationship, 1.ltoreq.F/E.ltoreq.8 measured by the X-ray photoelectron spectrometry described below. The nitrogen atoms in the toner of the present invention are preferably contained as amines or amides, and more preferably as amides.

When the above relationship is satisfied, the toner can exhibit good development characteristics and high transferability without being adversely affected by the environment and can provide high-quality images over a long term.

The sulfur-containing resin is essential for the toner of the present invention to exhibit sufficient development characteristics. In order to maximize the effect, sulfur atoms should be on the toner surface to best contribute to the toner charging. The inventors have also found that nitrogen atoms are desirable for the toner to maintain sufficient development characteristics in various operating environments. This is presumably because nitrogen atoms promote charging through unshared electron pairs at the initial stage of charging, but inhibit charging through interaction with sulfur atoms during overcharge, i.e., excess charge-up. At a ratio F/E less than 1, the effect of promoting charging is insufficient and the charge tends to be excessively low in high- and low-humidity environments. At a ratio F/E exceeding 8, the effect of the nitrogen atoms to inhibit charging becomes excessively strong, resulting in insufficient charging.

In order to control the ratio F/E, the percentage E and/or the percentage F can be adjusted as follows. The percentage E may be adjusted by changing the sulfur content in the sulfur-containing resin, changing the bonding state of the sulfur atoms, adjusting the amount of the sulfur-containing resin, or increasing the polarity of the sulfur-containing resin to be sufficiently higher than those of other materials. The percentage F may be adjusted by changing the nitrogen-containing functional groups in the nitrogen-containing substance, the amount of nitrogen, or the amount of the nitrogen-containing substance. The percentage F can also be controlled by increasing the polarity of the nitrogen-containing substance to be sufficiently higher than those of the other materials. Adjusting the percentage E or F as noted above can be done using conventional techniques known to the artisan.

The ratio F/E may be adjusted by controlling the sulfur atoms and nitrogen atoms contained in one compound, one monomer, and the like or may be adjusted by mixing other compounds, monomers, and the like.

More preferably, 2.ltoreq.F/E.ltoreq.6 is satisfied.

In the present invention, the optimum range of the sulfur content of the toner particle surfaces can be defined by X-ray photoelectron spectrometry described below. In particular, the ratio of the sulfur content E on the toner particle surfaces to the carbon content A on the toner particles surfaces in terms of atomic percent measured by X-ray photoelectron spectrometry, i.e., the ratio E/A, is preferably in the range of 0.0003 to 0.0050. The ratio E/A can be controlled in the above-described range by adjusting the average particle diameter of iron oxides, the sulfur content in the binder resin, or the amount of the sulfur-containing monomer in accordance with conventional techniques. At a ratio less than 0.0003, the charge may be insufficient. At a ratio exceeding 0.0050, the charge becomes less dependent upon humidity.

The optimum range of the nitrogen content of the toner particle surfaces can also be defined by, for example, X-ray photoelectron spectrometry. The ratio of the nitrogen content F of the toner particle surfaces to the carbon content A on the toner particles surfaces in terms of atomic percent is preferably in the range of 0.0005 to 0.0100. At a ratio less than 0.0005, sufficient charge cannot be readily obtained. At a ratio exceeding 0.0100, the charge becomes less dependent upon humidity.

The ratio F/E, the ratio E/A, and the ratio F/A can be determined through surface composition analysis by X-ray photoelectron spectrometry, also known as electron spectroscopy for chemical analysis (ESCA). The apparatus used and the conditions employed in the ESCA are as follows: Apparatus: X-ray photoelectron spectrometer 1600 S, manufactured by Physical Electronics Industries, Inc. (PHI) Measuring conditions: MgK.alpha. (400 W) as X-ray source Spectral region: 800 .mu.m.phi.

In calculating the atomic density at the surfaces, the intensity of the peak top in the bond energy range of 166 to 172 eV is used for sulfur, the intensity of the peak top in the bond energy range of 396 to 402 eV is used for nitrogen, and the intensity of the peak top in the bond energy range of 280 to 290 eV is used for carbon.

In this invention, the surface atomic density is calculated from the peak intensity of each element using relative sensitivity factors provided by PHI. Prior to measurement, the toner is preferably washed with ultrasonic sound to remove external additives from toner particle surfaces, isolated using a filter or the like, and dried.

Examples of the sulfur-containing monomer for making the sulfur-containing resin of the present invention include styrene sulfonic acid; 2-acrylamide-2-methylpropane sulfonic acid; 2-methacrylamide-2-methylpropane sulfonic acid; vinyl sulfonic acid; methacrylic sulfonic acid; and a maleic acid amide derivative, a maleimide derivative, and a styrene derivative having the following structures:

maleic acid amide derivative

##STR00001## maleimide derivative

##STR00002## styrene derivative

##STR00003## (Binding site is either ortho or para.)

The sulfur-containing resin of the present invention may be a homopolymer of any one of the monomers described above or a copolymer containing one of the above-described monomers and a separate monomer. Examples of the separate monomer that forms a copolymer with the above-described monomers include polymerizable vinyl monomers such as monofunctional polymerizable monomers and multifunctional polymerizable monomers.

Monomers containing sulfonic groups, in particular, (meth)acrylamide containing sulfonic groups, are preferred in order for the toner to obtain target circularity and average particle diameter.

The amount of the sulfur-containing monomer in the sulfur-containing resin of the present invention is preferably in the range of 0.01 to 20 percent by weight, more preferably 0.05 to 10 percent by weight, and most preferably 0.1 to 5 percent by weight based on the weight of the sulfur-containing resin in order to achieve target charge and target average circularity.

Examples of the aforementioned monofunctional polymerizable monomer include styrene; styrene derivatives such as .alpha.-methylstyrene, .beta.-methylstyrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, 2,4-dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-n-nonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, and p-phenylstyrene; acryl polymerizable monomers such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, n-amyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, n-octyl acrylate, n-nonyl acrylate, cyclohexyl acrylate, benzyl acrylate, dimethylphosphate ethyl acrylate, diethylphosphate ethyl acrylate, dibutylphosphate ethyl acrylate, and 2-benzoyloxy ethyl acrylate; methacryl polymerizable monomers such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, iso-propyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, n-amyl methacrylate, n-hexyl methacrylate, 2-ethyl hexyl methacrylate, n-octyl methacrylate, n-nonyl methacrylate, diethylphosphate ethyl methacrylate, and dibutylphosphate ethyl methacrylate; methylene aliphatic monocarboxylic ester; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, and vinyl formate; vinyl ethers such as vinylmethylether, vinylethylether, and vinylisobutylether; and vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and vinyl isopropyl ketone.

Examples of the multifunctional polymerizable monomer include diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, tripropylene glycol diacrylate, polypropylene glycol diacrylate, 2,2'-bis-(4-acryloxy diethoxy)phenyl)propane, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, tetraethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, 1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate, polypropylene glycol dimethacrylate, 2,2'-bis(4-(methacryloxy diethoxy)phenyl)propane, 2,2'-bis(4-methacryloxy polyethoxy)phenyl)propane, trimethylolpropane trimethacrylate, tetramethylolmethane tetramethacrylate, divinylbenzene, divinylnaphthalene, and divinyl ether.

The sulfur-containing resin is preferably prepared by using the styrene derivative as the monomer among the above-described monomers. The sulfur-containing resin is preferably prepared by mass polymerization, solution polymerization, emulsion polymerization, suspension polymerization, ion polymerization, or the like. Solution polymerization is particularly preferred for its ease of operation.

The sulfur-containing resin containing sulfonic acid groups has the following structure: X(SO.sub.3.sup.-)nmY.sup.k+ wherein X represents a polymer moiety derived from the above-described polymerizable monomer, Y.sup.+ represents a counter ion, k represents the valence number of the counter ion, m and n each represent an integer, and n is k.times.m. Preferable examples of the counter ion include a hydrogen ion, a sodium ion, a potassium ion, a calcium ion, and ammonium ion.

In the sulfur-containing resin, the acid number (mgKOH/g) of the polymer containing sulfonic acid groups is preferably in the range of 3 to 80, more preferably 5 to 40, and most preferably 10 to 30.

At an acid number less than 3, sufficient charge controlling effect cannot be obtained and environmental characteristics become poor. At an acid number exceeding 80, particles made by suspension polymerization using a composition containing such a polymer have irregular shapes, resulting in a decrease in circularity. Thus, the releasing agent appears on the toner particle surfaces, thereby degrading the development characteristics.

The amount of the sulfur-containing resin is preferably 0.05 to 20 parts by weight, and preferably 0.1 to 10 parts by weight per 100 parts by weight of the binder resin. At a content less than 0.05 part by weight, sufficient charge controlling effect can rarely be obtained; at a content exceeding 20 parts by weight, the average circularity decreases, and the developing and transfer properties become degraded. The content of the sulfur-containing resin in the toner can be determined by capillary electrophoresis or the like.

The weight-average molecular weight (Mw) of the sulfur-containing resin is preferably 2,000 to 10,000. At a weight average molecular weight less than 2,000, the flowability of the toner decreases and the transferability is degraded as a result. At a weight average molecular weight exceeding 10,000, the resin requires a longer time before becoming dissolved into the monomer, the dispersibility of the pigment decreases, and tinting power of the toner decreases.

The sulfur-containing resin preferably has a glass transition temperature (Tg) in the range of 50 to 100.degree. C. At a glass transition temperature less than 50.degree. C., the flowability, the storage stability, and the transferability of the toner are degraded. At a glass transition temperature exceeding 100.degree. C., images cannot be sufficiently fixed when the area of toner printing is large.

The volatile content of the sulfur-containing resin is preferably in the range of 0.01 to 2.0% since a complex process for removing volatile-component is necessary to reduce the volatile content to less than 0.01% and insufficient charging, particularly, insufficient charging after the toner is left to stand for a certain period of time, results if the volatile content exceeds 2.0% in a high-temperature and high-humidity environment. The volatile content of the sulfur-containing resin here is calculated from a decrease in weight of the resin after an hour of heating at a high temperature (135.degree. C.).

The method for extracting the sulfur-containing resin prior to measuring the molecular weight or the glass transition temperature of the sulfur-containing resin is not particularly limited. Any suitable method may be employed.

The average circularity of the toner of the present invention will now be explained.

The toner of the present invention preferably has an average circularity in the range of 0.950 to 0.995. A toner constituted from particles having an average circularity of 0.950 or more exhibits superior transferability. This is because the area of the contact between the toner particles and the photosensitive member is small, and the adhesive force of the toner particles to the photosensitive member resulting from image force, van der Waals force, or the like can thus be decreased. Accordingly, such a toner can exhibit high transfer efficiency while reducing the toner consumption.

Moreover, since toner particles having an average circularity of 0.950 or more have fewer edges on the surfaces and localization of charges within one particle rarely occurs, the charge distribution becomes narrower and a latent image can be faithfully developed. The average circularity is more preferably 0.960 or more. However, sufficient effects may not be obtained even when the average circularity is high if the circularity of predominant particles is low. Accordingly, the mode circularity, which will be described hereinafter, is preferably 0.99 or more. At a mode circularity of 0.99 or more, the predominant particles have a circularity of 0.99 and can yield sufficient effects.

On the other hand, a toner constituted from particles whose average circularity exceeds 0.995 can rarely suppress cleaning failure due to its high circularity.

In the present invention, the average circularity is used as a reference that can easily express the shape of particles in a quantitative manner. In the present invention, a flow particle image analyzer FPIA-2100 manufactured by Toa Iyo Denshi is used for measurement. The circularity a.sub.i of each of particles having an equivalent circle diameter of 3 .mu.m or more is calculated from equation (1), and the sum of the circularity of particles is divided by the number m of particles to obtain the average circularity a, as shown by equation (2):

.times..times..times..times..times..times..times..times..times..times..tim- es..times..times..times..times..times..times..times..times..times..times..- times..times..times..times..times..times..times..times..times..times. ##EQU00001##

The circularities of individual particles measured are allotted to sixty-one circularity classes ranging from 0.40 to 1.00 at an interval of 0.01 to obtain a circularity frequency distribution. The circularity of the maximum frequency is defined as the "mode circularity".

In calculating the average circularity and the mode circularity, the image analyzer FPIA-1000 employed in the present invention employs a calculation method in which particles are classified into sixty-one circularity classes ranging from of 0.40 to 1.00 according to the circularity of individual particles measured, and the average circularity and the mode circularity are calculated using the medians and the frequencies of individual classes. This calculation method has a negligibly small margin of error in calculating the average circularity and the mode circularity. In the present invention, the measured circularities of individual particles are directly used in calculating the average and mode circularities according to the above-described process in order to simplify data handling, i.e., to decrease the time required for calculation and to simplify the operation expression.

The procedures for measurement are as follows. Dispersion liquid is prepared by dispersing 5 mg of a developer in 10 ml of an aqueous solution containing about 0.1 mg of a surfactant. The dispersion liquid is exposed to ultrasonic sound waves (20 kHz, 50 W) for five minutes to yield a dispersion liquid density of 5,000 to 20,000 particle/.mu.l, followed by calculation of the average circularity and the mode circularity of a particle group having an equivalent circle diameter of at least 3 .mu.m using the above-described analyzer.

In the present invention, the average circularity indicates the degree of surface irregularities of developer particles. The circularity is 1.000 when a particle is perfectly spherical. The circularity decreases as the surface shape becomes irregular.

In the present invention, only the circularity of a particle group having an equivalent circle diameter of 3 .mu.m or more is determined. This is because particles having an equivalent circle diameter of less than 3 .mu.m contain large amounts particles of external additives independent of the toner particles and the circularity of the toner particles cannot be accurately determined due to these external additives.

The explanation of the toner particle diameter will now be presented.

The toner of the present invention must have a weight-average particle diameter D4 in the range of 3 to 10 .mu.m in order to achieve higher image quality and to faithfully develop fine dots of latent images. The weight-average particle diameter D4 is more preferably in the range of 4 to 8 .mu.m. A toner having D4 of less than 3 .mu.m frequently remains in a large amount on the photosensitive member after transfer due to low transfer efficiency. Moreover, such a toner will cause wearing of the photosensitive member during the step of contact charging and obstruct control of the toner fusing. Since individual toner particles tend to be unevenly charged due to an increase in toner surface area and degradation of flowability and mixing characteristics, fogging and degradation of transferability occur, resulting in image blurring. Thus, such a toner is not suitable for the present invention. In contrast, a toner having D4 exceeding 10 .mu.m easily spreads over characters or line images and thus rarely yields high resolution. A toner having D4 of 8 .mu.m or more tends to exhibit lower reproducibility of individual dots as the resolution of the apparatus becomes higher.

The weight-average particle diameter and the number-average particle diameter of the toner of the present invention may be determined using a Coulter Counter TA-II or a Coulter Multisizer available from Coulter Corporation, or by employing various other methods. For example, the diameters may be determined as follows. An interface for outputting the particle number distribution and volume distribution, manufactured by Nikkaki Corporation, is connected to a personal computer PC9801 (manufactured by NEC Corporation). The electrolyte is a 1% NaCl aqueous solution prepared using primary sodium chloride. For example, ISOTON R-II manufactured by Coulter Scientific Japan can be used. The measurement is carried out as follows. To 100 to 150 ml of the electrolytic aqueous solution described above, 2 to 20 mg of a test sample is added. The electrolytic aqueous solution with suspended test sample is processed in a ultrasonic disperser for one to three minutes to disperse the test sample into the electrolytic aqueous solution. The volume and the number of toner particles having a diameter of 2 .mu.m or more are determined with the above-described Coulter Multisizer using a 100-.mu.m aperture to determine the volume distribution and the particle distribution. The weight-average particle diameter D4 is calculated based on the volume distribution of the particles within the range of the present invention, and the number-average particle diameter D1 is calculated from the particle distribution within the range of the present invention.

The toner particles of the present invention are preferably made by polymerization. The toner of the present invention may be made by pulverization, but toner particles made by pulverization generally have irregular shapes and require an additional process, such as a mechanical process or thermal process, to achieve an average circularity of 0.950 to 0.995 as required in the present invention. Thus, polymerization processes are preferred in making toner particles of the present invention.

Examples of the polymerization method for making toner particles include direct polymerization, suspension polymerization, emulsion polymerization, emulsion aggregation polymerization, and seed polymerization. Suspension polymerization is particularly preferred since the particle diameters can be well balanced with the particle shape. In suspension polymerization, a homogeneous polymer composition containing a polymerizable monomer and a coloring agent (a polymerization initiator, a crosslinking agent, a charge control agent, or other additives may be added if necessary) is prepared, and the monomer composition is dispersed into a continuous layer, e.g., a water phase, containing a dispersion stabilizer using a suitable stirrer to perform polymerization so as to obtain a toner having a desired particle diameter. The toner prepared by suspension polymerization, hereinafter referred to as the "polymer toner", consists of uniform spherical toner particles; thus, a toner having an average circularity of 0.950 to 0.995 and a mode circularity of at least 0.99 can be easily made by suspension polymerization. Since such a toner has relatively uniform charge distribution, it also achieves high transferability. If necessary, particles made by suspension polymerization may be blended with a polymerizable monomer and a polymerization initiator to prepare core-shell structure particles.

The toner of the present invention preferably contains 0.5 to 50 parts by weight of a releasing agent per 100 parts by weight of a binder resin. Examples of the binder resin include, as described below, various waxes.

The toner image transferred onto a recording medium is fixed onto the recording medium by application of energy, such as heat and/or pressure, to obtain a semipermanent image. A heat-roller fusing or thin-film belt fusing is frequently used for fixing toner images.

Toner particles having a weight-average particle diameter of 10 .mu.m or less can produce superfine images but such fine toner particles become entrapped in gaps of fibers of the paper when paper is used as the recording medium. Accordingly, the toner particles cannot receive sufficient heat from the heat rollers, frequently resulting in low temperature offset. High resolution and resistance to offset can be simultaneously achieved by adding an adequate amount of releasing agent in the toner of the present invention.

Examples of the releasing agent suitable for the toner of the present invention include petroleum wax, such as paraffin wax, microcrystalline wax, and petrolatum, and derivatives thereof; montan wax and derivatives thereof; hydrocarbon wax prepared by a Fischer-Tropsch process and derivatives thereof; polyolefin wax, such as polyethylene, and derivatives thereof; and natural wax, such as carnauba wax and candelilla wax, and derivatives thereof. The derivatives include oxides, block copolymers with vinyl monomers, and graft conversion products. Further examples of the releasing agent include higher aliphatic alcohols; aliphatic acids such as stearic acid, and palmitinic acid, and compounds thereof; acid amide wax, ester wax, hydrogenated caster oil, and derivatives thereof; vegetable wax; and animal wax. Among these waxes, those having an endothermic peak in the range of 40 to 110.degree. C. in differential thermal analysis are preferred, and those having an endothermic peak in the range of 45 to 90.degree. C. are particularly preferred.

When the content of the releasing agent is less than 0.5 part by weight per 100 parts by weight of the binder resin, low-temperature offset cannot be sufficiently prevented. At a content exceeding 50 parts by weight, long-term storage ability is degraded, and other toner materials cannot be homogeneously dispersed. Moreover, the toner flowability and image quality are degraded.

The maximum endothermic peak temperature of the wax component is measured according to ASTM D 3418-8. For example, DSC-7 manufactured by PerkinElmer Inc. is used for measurement. The temperature correction at the detector unit is done using the melting points of indium and zinc. The calorie is adjusted using the temperature of the melting point of indium before actual measuring of the melting point so that a precise value can be measured. An aluminum pan is used to accommodate a sample, and an empty aluminum pan is prepared for comparison. The temperature is increased at a rate of 10.degree. C./min.

The glass transition temperature (Tg) of the sulfur-containing resin is calculated from a differential scanning calorimetry (DSC) curve obtained during second heating. The glass transition temperature is determined as the intersection between the DSC curve and the median line between the base line before the endothermic peak and the base line after the endothermic peak.

The toner of the present invention must include a coloring agent in order to have tinting power. Preferable examples of the coloring agent of the present invention include the following organic pigment or dye.

Examples of cyan coloring agents include the following organic pigments and dyes: copper phthalocyanine compounds and derivatives thereof; anthraquinone compounds; and lake compounds of basic dyes thereof. Specific examples thereof include C.I. Pigment Blue 1, C.I. Pigment Blue 7, C.I. Pigment Blue 15, C.I. Pigment Blue 15:1, C.I. Pigment Blue 15:2, C.I. Pigment Blue 15:3, C.I. Pigment Blue 15:4, C.I. Pigment Blue 60, C.I. Pigment Blue 62, and C.I. Pigment Blue 66.

Examples of magenta coloring agents include the following organic pigments and dyes: condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone, quinacridone compounds, lake compounds of basic dyes, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. Specific examples thereof include C.I. Pigment Red 2, C.I. Pigment Red 3, C.I. Pigment Red 5, C.I. Pigment Red 6, C.I. Pigment Red 7, C.I. Pigment Violet 19, C.I. Pigment Red 23, C.I. Pigment Red 48:2, C.I. Pigment Red 48:3, C.I. Pigment Red 48:4, C.I. Pigment Red 57:1, C.I. Pigment Red 81:1, C.I. Pigment Red 122, C.I. Pigment Red 144, C.I. Pigment Red 146, C.I. Pigment Red 150, C.I. Pigment Red 166, C.I. Pigment Red 169, C.I. Pigment Red 177, C.I. Pigment Red 184, C.I. Pigment Red 185, C.I. Pigment Red 202, C.I. Pigment Red 206, C.I. Pigment Red 220, C.I. Pigment Red 221, and C.I. Pigment Red 254.

Examples of yellow coloring agents include the following organic pigments and dyes: condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and allylamide compounds. Specific examples thereof include C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 17, C.I. Pigment Yellow 62, C.I. Pigment Yellow 74, C.I. Pigment Yellow 83, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, C.I. Pigment Yellow 95, C.I. Pigment Yellow 97, C.I. Pigment Yellow 109, C.I. Pigment Yellow 110, C.I. Pigment Yellow 111, C.I. Pigment Yellow 120, C.I. Pigment Yellow 127, C.I. Pigment Yellow 128, C.I. Pigment Yellow 129, C.I. Pigment Yellow 147, C.I. Pigment Yellow 151, C.I. Pigment Yellow 154, C.I. Pigment Yellow 168, C.I. Pigment Yellow 174, C.I. Pigment Yellow 175, C.I. Pigment Yellow 176, C.I. Pigment Yellow 180, C.I. Pigment Yellow 181, C.I. Pigment Yellow 191, and C.I. Pigment Yellow 194.

These coloring agents can be used alone or in combination. They may be used in the form of a solid solution. The coloring agent for use in the toner of the present invention is selected based on hue angle, color saturation, lightness, lightfastness, OHP transparency, and dispersibility into the toner. The amount of the coloring agent is preferably 1 to 20 parts by weight per 100 parts by weight of the binder resin.

Examples of black coloring agents include carbon black, magnetic material, and a material colored black by mixing the above-described yellow, magenta and cyan coloring agents. When the magnetic material is used as the black coloring agent, unlike other coloring agents, 30 to 200 parts by weight of the magnetic material is added per 100 parts by weight of the binder resin.

Examples of the magnetic material include oxides of iron, cobalt, nickel, copper, magnesium, manganese, aluminum, and silicon. Among these oxides, those containing iron oxide as the primary component, e.g., ferroso-ferric oxide, .gamma.-iron oxide, and the like, are particularly preferred. Moreover, the magnetic material may additionally contain silicon, aluminum, or other metal elements. The BET specific surface area of magnetic particles determined by nitrogen adsorption measurement technique is preferably 2 to 30 m.sup.2/g and more preferably 3 to 28 m.sup.2/g. The Mohs hardness of the magnetic particles is preferably 5 to 7.

The magnetic particles may be octahedral, hexahedral, spherical, spicular, squamous, or the like in shape. Among them, particles with low anisotropy, such as octahedral particles, hexahedral particles, spherical particles, and particles having no regular form, are preferred since such particles increase the image density. The average particle diamete