GB2136981A - Magnetic Toner for Developing Latent Electrostatic Images - Google Patents

Abstract

A one-component magnetic toner for developing latent electrostatic images comprises a ferromagnetic material, a resin binder, and from 0.01 to 5% by weight, based on the total weight of the toner, of a fatty acid metal salt and/or a fatty acid amide. The toner is used to develop latent electrostatic images in development apparatus comprising a member which contacts the toner and triboelectrically charges it.

Description

SPECIFICATION Magnetic Toner for Developing Latent Electrostatic Images The present invention relates to a magnetic toner for developing latent electrostatic images in electrophotography, electrostatic recording, electrostatic printing and the like. More particularly, it relates to a one-component type, high resistivity magnetic toner for developing latent electrostatic images by tribo-electrically charging the toner particles, for instance, by a fixed member in the development section of a development apparatus.

Conventionally, methods for developing latent electrostatic image in electrophotography, electrostatic recording and electrostatic printing may be classified into the dry development method and the wet development method. The dry method may be further subdivided into two classes. In one class, a two-component developer is employed and in the other class, a one-component developer is employed. The method in which a two-component developer is employed is capable of yielding high quality images in a relatively stable manner. However it has the shortcomings that, occasionally, inferior images are produced due to deterioration of the carrier component of the developer and changes in the ratio of toner to carrier in the developer.

In order to avoid such shortcomings, various development methods have been proposed, in which a one-component developer consisting of a toner is employed. Of these methods, development methods in which a magnetic toner is employed are in general use. In such methods, a high resistivity magnetic toner is triboelectrically charged by the friction between the toner particles and, for instance, a toner layer thickness regulation member in a development section, and latent electrostatic images are developed with the triboelectrically charged magnetic toner, for instance as disclosed in Japanese Patent Publication No. 55-34421 and Japanese Utility Model Publication No. 56-43815.Conventional development methods using such magnetic toners, however, have the shortcomings that toner particles adhere and are fixed, for instance, to the toner layer thickness regulation member, so that the thickness of the toner layer on a sleeve member becomes uneven, and uniform and sufficient charging of the toner for an extended period of time becomes impossible, and the quality of the developed images is not always good since undeveloped lines are observed in the developed images.

Furthermore, in a magnetic toner of this kind, there may be employed a positive charge control agent, a representative example of which is an oil-soluble dye such as nigrosine type dye. Since the positive charge control agent, however, is hardly soluble in the resin components of the toner, it is extremely difficult to disperse the charge control agent uniformly throughout the toner. When the distribution of the positive charge control agent is not uniform in the toner, non-uniform charging of the toner and fogging of the developed images are caused, by which the clarity of the images is impaired.

It is an object of the present invention to provide an improved magnetic toner for developing latent electrostatic images.

It has now been found that the incorporation of from 0.01 to 5% by weight of a metal salt of a fatty acid and/or a fatty acid amide into a one component magnetic toner serves to reduce adhesion of the toner to parts of a development apparatus and to generally enhance the quality of images produced using the toner.

According to the invention, therefore, there is provided a one component magnetic toner formed of particles comprising (a) a ferromagnetic material, (b) a resin binder, and (c) from 0.01 to 5% by weight, based on the total weight of the toner, of a metal salt of a fatty acid and/or a fatty acid amide.

The magnetic toner of the invention contains from 0.01 to 5% by weight of a fatty acid salt and/or amide. If the amount of fatty acid salt and/or amide is less than 0.01 wt.%, the object of the invention cannot be attained. On the other hand, if the amount exceeds 5 wt.%, the toner may be excessively charged to a positive polarity and as a result, the toner may adhere, for instance to a sleeve, the toner loses its fluidity and the obtained image density decreases.

Examples of resins that can be used as resin components of the toners of the present invention include: polymers of styrene and substituted styrenes, such as polystyrene, poly(p-chlorostyrene) and polyvinyl toluene; copolymers of styrene with, for example, p-chlorostyrene, propylene, vinyltoluene, vinylnaphthalene, methyl acrylate, ethyl acrylate, butyl acrylate, octyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl dichloromethacrylate, acrylonitrile, vinyl ethyl ether, vinyl methyl ketone, butadiene, isoprene, acrylonitrile indene, maleic acid and maleic acid esters;; poly(methyl methacrylate), poly(butyl methacrylate), polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyesters, polyurethanes, polyamides, epoxy resins, polyvinyl butyral, polyacrylic acid resins, rosin, modified rosins, terpene resins, phenol resins, aliphatic or alicyclic hydrocarbon resins, aromatic petroleum resins, chlorinated paraffin, paraffin wax and the like. The above resins can be used alone or in combination.

The ferromagnetic component of the toner comprising fine particles of any material that can be intensely magnetized in a magnetic field in the magnetic direction thereof, such as ferrite, magnetite, iron, cobalt, nickel, alloys containing such magnetic substances and a wide variety of alloys that exhibit intense ferromagnetic properties when submitted to heat treatment or other treatments. It is preferable that the average particle size of the ferromagnetic material in the toner be from 0.1 to 3 microns and that it forms from 15 to 60% by weight of the toner.

The toner may also contain a positive charge control agent and, for this purpose, conventional charge control agents can be used, such as quaternary ammonium salts, organic dyes, particularly base dyes and salts thereof. Specific examples of positive charge control agents include benzyldimethylhexadecylammonium chloride, decyltrimethyl ammonium chloride, nigrosine base, nigrosine hydrochloride, Safranine and Crystal Violet.

The fatty acid metal salts and/or amides can be uniformly dispersed within the toner particles by mixing them with the other components of the toner from the beginning or by mixing such other components first to form toner particles and then mixing these toner particles with the fatty acid salt and/or amide so that the salts and/or amides are deposited on the surface of the toner particles The fatty acid metal salts and/or amides serve to prevent or reduce the adhesion of the toner to members which triboelectrically charge the toner particles, and the salts and amides themselves have positive charging properties. Therefore, in the presence of the salts and/or amides, the toner can be positively charged in a stable manner and can yield high quality clear images for a long period of time without causing fogging of the image or undeveloped lines in the images.

Examples of fatty acid metal salts for use in the invention include barium stearate, calcium stearate, zinc stearate, aluminium stearate, magnesium stearate, lithium stearate, lead stearate, barium laurate, calcium laurate, zinc laurate, magnesium laurate, lithium laurate, lead laurate, calcium palmitate, magnesium palmitate and dibasic lead stearate. Of the above, zinc stearate, magnesium stearate and calcium stearate are most preferred.

Examples of fatty acid amides for use in the invention include stearamide, palmitamide, oleamide, linolamide, oxystearamide, erucamide, behenamide, lauramide, ethylenebisstearamide, ethylenebisoleamide, methylenebisstearamide, ethylenebislauramide, hexamethylenebisstearamide, N-stearylstearamide, N-oleylstearamide, N,N-distearinadipamide and butylenebisstearamide. Of the above, ethylenebisstearamide is most preferred.

When the fatty acid salts and amides are used in combination it is preferable that the weight ratio of salt to amide be from 10:90 to 90:10, more preferably from 20:80 to 40:60.

The magnetic toner of the invention is triboelectrically charged by the frictional contact of the toner particles with, for instance, a toner layer thickness regulating member. It is preferable that a development sleeve by which the magnetic toner is carried be made of a number of small electroconductive members, each of which is electrically insulated, formed on a dieiectric layer.

Furthermore, it is preferably that the toner layer thickness regulation member be made of an elastic member, for instance, a thin blade made of steel, that can be attracted magnetically towards the development sleeve by inner magnets disposed within the development sleeve.

In order that the invention may be well understood, the following examples are given by way of illustration only.

EXAMPLE 1 The components listed below were well mixed in a blender and the mixture was then kneaded at a temperature in the range from 1 400C to 1 500C by two heated rollers.

Parts Styrene-butyl methacrylate copolymer 53.0 Nigrosine 2.0 Tri-iron tetroxide 45.0 After cooling to room temperature, the mixture was roughly crashed by a cutter mill and was then finely grounded to powder by a pulverizer by use of jet stream.

The thus prepared powder mixture was subjected to pneumatic classification, to give a core magnetic toner with an average particle size from 5 to 20 micrometres.

1,000 parts of the core magnetic toner and 1 part of zinc stearate were mixed in a mixer, to give a magnetic toner according to the invention.

The thus prepared magnetic toner was triboelectrically charged by the friction between the toner particles themselves, between the toner particles and a toner layer thickness regulation member, and between the toner particles and a development sleeve. Latent electrostatic images formed on an organic photoconductor were developed with the triboelectrically charged magnetic toner, so that toner images were formed on the photoconductor. The toner images were then transferred to a sheet of plain paper and were then fixed thereto by the application of heat.

The image density of the thus obtained images was 1.40. The images were free from fogging and undeveloped lines. The images were of excellent quality and had high resolution. By repeating the above-mentioned procedure, 50,000 copies were made. The initial high image quality was maintained throughout the making of the 50,000 copies. No adhesion of the toner to the development sleeve and the toner layer regulation member was observed, nor was adhesion of the toner, in the form of a film, to the photoconductor observed.

COMPARATIVE EXAMPLE The procedure of Example 1 was repeated, except that the zinc stearate employed in Example 1 was not mixed with the core magnetic toner, to give a comparative magnetic toner.

Using this comparative magnetic toner, image formation was conducted in the same manner as described in Example 1. The initial image density was 0.80 and undeveloped lines and fogging of the images were observed. The initial image density decreased as the copying was continued. Furthermore, adhesion of the toner to the development sleeve, the toner layer thickness regulation member and the photoconductor were observed. The thickness of the toner layer on the development sleeve was not uniform and some streaks were observed in the surface of the layer.

EXAMPLE 2 The following components were well mixed in a blender and the mixture was kneaded at temperatures in the range from 1 400C to 1 500C by two heated rollers.

Parts Styrene-butyl methacrylate copolymer 52.0 Nigrosine 2.0 Tri-iron tetroxide 45.0 Magnesium stearate 1.0 After cooling to room temperature, the mixture was roughly crashed by a cutter mill and was then finely ground to a powder by a pulverizer by use of jet stream.

The thus prepared powder mixture was subjected to pneumatic classification, to give a magnetic toner with an average particle size ranging from 5 to 20 micrometres.

Images were produced on plain paper from this toner by the method described in Example 1.

The image density of the thus obtained images was 1.25. The image were free from fogging and undeveloped lines. The images were of excellent quality and had high resolution. When 50,000 copies were made, the initial image quality was maintained throughout the process. No adhesion of the toner to the development sleeve and the toner layer regulation member was observed nor was adhesion of the toner, in the form of a film, to the photoconductor observed.

EXAMPLES 3-5 Core magnetic toners were prepared, following the procedure described in Example 1, from the components listed in Table 1. Toners were prepared from these core toners by the addition of a metal salt of a fatty acid as listed in Table 1 and following the procedure of Example 1.

TABLE 1 Example 1 2 3 Polymer (amount Polystyrene Poly(methyl- Polyvinyl in parts) (58) methacrylate) chloride (58.8) (53.5) Charge control Nigrosine Spirit Black Oil Black HBB agent (amount (2.0) AB2 (1.5) in parts) (1.2) Ferromagnetic Zinc ferrite Zinc ferrite Tri-iron material (40) (40) tetroxide (amounts in (45) parts) Fatty acid salt Magnesium Calcium Zinc laurate (amounts in stearate stearate (10) parts per 1000 (0.5) (1) parts of core toner) Image formation was carried out using each toner following the procedure described in Example 1.

In each case, high quality images were obtained and the toner did not adhere to the development sleeve, the toner layer thickness regulation member or the photoconductor. In the 50,000 copying test, the high image quality and the initial image density were substantially maintained throughout the test.

The initial image density and the image density at the 50,000th copy are set out in Table 2.

TABLE 2 Initial Image Image Density of Example Density 50,000th Copy 3 1.23 1.25 4 1.35 1.30 5 1.15 1.12 EXAMPLES 6-8 Toners were prepared from the compositions listed in Table 3 following the procedure of Example 2.

Images were formed from the toners following the procedure of Example 1 and in each case high quality images were obtained and the toner did not adhere to the development sleeve, the toner layer thickness regulating member or the photoconductor. In the 50,000 copying test, the high image quality and the initial image density were substantially maintained during the test. The initial image density and that at the 50,000 th copy are shown in Table 3.

TABLE 3 Example 6 2 8 Polymer (parts) Styrene/butyl Polystyrene Poly(methyl methacrylate (56.3) methacrylate copolymer (58.3) (57.0) Charge control Nigrosine Spirit Black Spirit Black agent (parts) (2.0) AB2 AB2 (1.2) Ferromagnetic Zinc ferrite Tri-iron Zinc ferrite material (part) (40) tetroxide (40) (40) Fatty acid Zinc stearate Lithium Calcium salt (parts) (1.0) (2.5) (0.5) Initial image 1.40 1.25 1.30 density Image density 1.30 1.20 1.28 at 50,000th copy EXAMPLE 9 1,000 Parts of a core magnetic toner prepared as described in Examples 1 and 5 part of ethylenebisstearamide were mixed in a mixer, to give a magnetic toner according to the invention.

The thus prepared magnetic toner was subjected to image formation tests as described in Example 1.

The image density of the thus obtained images was 1.40. The images were free from fogging and undeveloped lines. The images were of excellent quality and had high resolution. The initial image quality was maintained throughout the process'of making the 50,000 copies. No adhesion of the toner to the development sleeve or the toner layer regulation member was observed, nor was. adhesion of the toner, in the form of a film, to the photoconductor observed.

EXAMPLE 10 A magnetic toner was prepared as described in Example 2 except that the magnetic stearate was replaced by the same amount of stearamide. The toner was subjected to the image formation tests as described in Example 1.

The image density of the thus obtained images was 1.25. The images were free from fogging and undeveloped lines. The images were of excellent quality and had high resolution. The initial image quality was maintained throughout the process of making the 50,000 copies. No adhesion of the toner to the development sleeve or the toner layer regulation member was observed, nor was adhesion of the toner, in the form of a film, to the photoconductor observed.

EXAMPLES 11-13 Core magnetic toners were produced as described in Example 1 using the formulations of Examples 3, 4 and 5. The toner was mixed with an amide, as listed in Table 4, following the procedure of Example 9 to give toners which were then tested as described in Example 1. In each case, high quality images were obtained and the toner did not adhere to the development sleeve, toner layer thickness regulation member or photoconductor. In the 50,000 copying test, the high image quality and initial image density were substantially maintained throughout the test. The initial image density and that at the 50,000th copy are shown in Table 4.

TABLE 4 Example 11 12 13 Core toner As in Example 3 As in Example 4 As in ExampleS Amide (parts Hexamethylene- Oleamide Ricinoleamide per 1000 parts bisstearamide (8) (15) of the toner) (5) Initial image 1.32 1.25 1.23 density Image density 1.30 1.28 1.18 at 50,000th copy EXAM.PLES 14-16 Magnetic toners were produced as described in Example 10 from the components listed in Table 5. The toners were each tested as described in Example 1. In each case, high quality images were obtained and the toner did not adhere to the development sleeve, toner layer thickness regulation member or photoconductor. In the 50,000 copying test, the high image quality and initial image density were substantially maintained through the test. The initial image density and that at the 50,000th copy are shown in Table 5.

TABLE 5 Example 14 15 16 Polymer (parts) Styrene/butyl Polystyrene Poly(methyl methacrylate (51.0) methacrylate) copolymer (53.8) (55.0) Charge control Nigrosine Spirit Black Spirit Black agent (parts) (2.0) AB2 (1.2) (1.2) Ferromagnetic Zinc ferrite Tri-iron Zinc ferrite material (parts) (40) tetroxide (40) (45) Amide Ethylene Hexamethylene Ricinoleamide bisstearamide bisstearamide (5.0) (3.0) (2.8) Initial image density 1.4 1.30 1.18 Image density of 1.42 1.25 1.22 50,000th copy EXAMPLE 17 1,000 Parts of the core magnetic toner of Example 1 were mixed with 1 part of a 30:70 mixture of ethylene bisstearamide and calcium stearate to give a magnetic toner. The toner was then tested as described in Example 1.

The image density of the obtained images was 1.40. The images were free from fogging and undeveloped lines. The images were of excellent quality and had high resolution. The initial image quality was maintained throughout the process of making the 50,000 copies. No adhesion of the toner to the development sleeve or the toner layer regulation member was observed, nor was adhesion of the toner, in the form of a film, to the photoconductor observed.

EXAMPLE 18 A toner was prepared as described in Example 2 except that 52.5 parts of the styrene/butyl methacrylate was employed and the magnesium stearate was replaced by 0.5 parts of a 40:60 mixture of methylene bisstearate and zinc stearate.

The toner was tested as described in Example 1. The image density of the thus obtained images was 1.25. The images were free from fogging and undeveloped lines. The images were of excellent quality and had high resolution. The initial image quality was maintained throughout the process of making the 50,000 copies. No adhesion of the toner to the development sleeve or the toner layer regulation member was observed, nor was adhesion of the toner, in the form of a film, to the photoconductor observed.

EXAMPLES 19-21 Core magnetic toners were produced as described in Example 1 using the procedures of Examples 3, 4 and 5. The toners were mixed with fatty acid salts and amides, as listed in Table 6, following the procedure of Example 17 to give toners which were then tested as described in Example 1. In each case, high quality images were obtained and the toner did not adhere to the development sleeve, toner layer thickness regulation member or photoconductor. In the 50,000 copying test, the high image quality and image density were substantially maintained throughout the test. The initial image density and that at the 50,000th copy are shown in Table 6.

TABLE 6 Example 19 20 21 Core toner As in Example 3 As in Example 4 As in Example 5 Amide (parts Ethylene Methylene Ethylene per 1,000 parts bislauramide bisstearamide bisstearamide of core toner) (1.5) (4) (1.5) Salt (parts Magnesium Zinc laurate Calcium per 1,000 parts stearate (6) stearate of core toner) (3.5) (3.5) Initial image density 1.30 1.28 1.28 Image density at 1.23 1.21 1.21 1,000th copy EXAMPLES 22-24 Magnetic toners were produced as described in Example 1 8 from the components listed in Table 7.

The toners were each tested as described in Example 1. In each case, high quality images were obtained and the toner did not adhere to the development sleeve, toner layer thickness regulation member or photoconductor. In the 50,000 copying test, the high image quality and image density were substantially maintained throughout the test. The initial image density and that at the 50,000th copy are shown in Table 7.

TABLE 7 Example 22 20 24 Polymer (parts) Styrene/butyl Polystyrene Poly(methyl methacrylate (52.8) methacrylate copolymer (56.8) (55.0) Charge control Nigrosine Spirit Black Spirit Black agent (parts) (2.0) AB2 AB2 (1.2) (1.2) Ferromagnetic Zinc ferrite Tri-iron Zinc ferrite material (40) tetroxide (40) (parts) (45) Amide (parts) Ethylene Methylene Ethylene bisstearamide bisstearamide bislauramide (1.2) (0.3) (0.4) Salt (parts) Zinc stearate Zinc stearate Calcium (1.8) (0.7) stearate (1.6) Initial image density 1.20 1.25 1.28 Image density at 1.18 1.20 1.23 50,000th copy

Claims (10)

1. A one-component magnetic toner comprising a ferromagnetic material, a resin binder, and from 0.01 to 5% by weight, based on the total weight of the toner, of a fatty acid metal salt and/or a fatty acid amide.

2. A toner as claimed in claim 1 , in which the fatty acid metal salt is barium stearate, calcium stearate, zinc stearate, aluminium stearate, magnesium stearate, lithium stearate, lead stearate, barium Faurate, calcium laurate, zinc laurate, magnesium laurate, lithium laurate, lead laurate, calcium palmitate, magnesium palmitate or dibasic lead stearate.

3. A magnetic toner as claimed in claim 1 or claim 2, in which the fatty acid amide is stearamide, palmitamide, oleamide, linolamide, oxystearamide, erucamide, behenamide, lauramide, ethylenebisstearamide, ethylenebisolea mide, methylenebissteara mide, ethylenebislauramide, hexamethylene-bisstearamide, N-stearylstearamide, N-oleylstearamide, N,N-distearinadipamide or butylenebisstearamide.

4. A magnetic toner as claimed in any one of the preceding claims and containing a mixture of fatty acid metal salt and fatty acid amide, the weight ratio of said salt to said amide being from 10:90 to 90:10.

5. A magnetic toner as claimed in any one of the preceding claims, in which the ferromagnetic material comprises ferromagnetic particles having an average particle size of 0.1 to 3 micrometres in an amount of 15 to 60% by weight, based on the weight of the toner.

6. A magnetic toner as claimed in any one of the preceding claims comprising a positive charge control agent which is benzyldimethyl-hexadecylammonium chloride, decyltrimethyl ammonium chloride, nigrosine base, nigrosine hydrochloride, Safranine or Crystal Violet.

7. A magnetic toner as claimed in claim 1, substantially as hereinbefore described with reference to the Examples.

8. A method of developing a latent electrostatic image by contacting it with a triboelectrically charged toner in electrographic development apparatus comprising a member which contacts the toner and at least partially triboelectrically charges it, in which the toner is a one-component toner as claimed in any one of the preceding claims.

9. A method as claimed in claim 8, in which the said member takes the form of thin steel blade.

10. A method as claimed in claim 8 substantially as hereinbefore described with reference to the Examples.