GB2091435A

GB2091435A - Toner for developing electrostatic latent images

Info

Publication number: GB2091435A
Application number: GB8136380A
Authority: GB
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 1980-12-18
Filing date: 1981-12-02
Publication date: 1982-07-28
Also published as: DE3149575A1

Abstract

Sharp images with low fog can be obtained by developing electrostatic images with a toner comprising particles of a colouring agent and a resin having a ratio of longer diameter/shorter diameter of from 1.00 to 1.05, the particle size being in the range from 1 to 30 microns and at least 70% by weight of the particles having a size within the range of the mean particle size +/-3 microns. In preferred embodiments, the resin comprises a polymer having a ratio weight average molecular weight/number average molecular weight of at least 3.5; and/or comprises a component of high molecular weight (generally over 50,000) and a component of low molecular weight (generally under 150,000).

Description

SPECIFICATION Toner for developing electrostatic latent images The present invention relates to a toner for developing electrostatic latent images, and more particularly to a toner for developing electrostatic latent images in the electrophotographic process, electrostatic recording process, electrostatic printing process and the like, The method for developing electrostatic latent image may be broadiy classified into two; one is called the liquid developing method which uses a developer prepared by finely dispersing various pigments or dyes into an insulating solvent, and the other is the so-called dry developing method such as the cascade developing method, furbrush developing method, magnetic brush developing method, impression developing method, and powder developing method, impression developing method, and powder cloud developing method, wherein powdery developers called the dry toner are used which may be prepared by dispersing coloring agents such as carbon black and the like into natural or synthesized resins, and the present invention relates to the toner used in the latter; i.e., the dry developing method.

The dry toner has generally been produced in such a manner that a pigment such as carbon black is fusedly mixed with a thermoplastic resin to make a uniformly dispersed product, which is then pulverized by means of an appropriate pulverizer into a powder form having a particle size required as toner.The toner produced in this manner may have various excellent advantages, but at the same time has various disadvantages; for example, there are restrictions on the use of materials for the production of the toner, the restrictions being such that the production of the toner requires such conditions that the material must be fluidized at an appropriate temperature so as to enable the pigment to be uniformly mixed thereinto because of the need for the fusing and pulverizing process; and the desired particle size must be obtained at a considerable rate by means used in the pulverization of the mixture system.However, when an easily pulverizable material is used, the material tends to be further pulverized while inside the electrophotographic copying apparatus, thereby causing fog to appear on the copied image, while when an easily fusible material is merely used, it causes the caking of toner and stain on the surface of the photoconductive layer (toner filming).

And when a pigment that has been embedded in the resin appears out on the surface at the time of pulverization, the appearance may sometimes produce uneven triboelectric characteristics locally and in addition may give rise to a question on the moisture resistance depending on the kind of the pigment used. Furthermore, more significant disadvantages are such that the toner produced by the pulverization has the indeterminate form which tends to produce aggregation of the toner particles, which aggregation may sometimes act as an undesirable factor against such characteristics as the stabilization.

of the toner in storage, the dispensability of the toner at the time of being supplied, the toner transfer efficiency, the sharpness of the developed toner image, and the cleanability when the toner is repeatedly used, the disadvantages in actuality having large undesirable influences upon the obtained toner image quality such as especially the resolution, sharpness, fog and the like.

In contrast to the toner produced in the manner of the foregoing pulverization, the production of toners by the so-called polymerization method has been proposed as described in, e.g., Japanese Patent Publications No. 10231/1961, No. 51 830/1972, No. 14895/1976, No.17735/1978, No.

17736/1978 and No. 17737/1978, which are on the basis of the so-called suspension polymerization method which produces toners in such a way that a mixture of a monomer, polymerization initiator, coloring agent and the like is suspended into water and polymerized to thereby produce toners.Such toners obtained by the polymerization, although they cover the foregoing defects of the toner produced by the pulverization, create such a different drawback that they become deteriorated along with the change in the quantity of charge in successive copying operations; that is, with respect to the rate of toner being consumed in order from larger particle sizes thereof, the toner is significantly faster than the toner in the indeterminate form, so that the toner's change in the quantity of charge at the time of successive copying operations is larger, giving undesirable results to the image in running operations.

Especially when the toner is recycled there occur the deterioration of image densities and fog.

It is an object of the present invention to provide a toner for developing electrostatic latent images which has overcome the above-described drawbacks of the toners.

It is another object of the present invention to provide a toner for developing electrostatic latent image having an excellent property of flowability.

It is a further object of the present invention to provide a toner for developing electrostatic latent image capable of producing toner images excellent in resolution, sharpness and having little or no fog.

It is still another object of the present invention to provide a toner for developing electrostatic latent image having satisfactory image transfer efficiency.

It is a still further object of the present invention to provide a toner for developing electrostatic latent image with little change in the quantity of charge at the time of successive copying operations.

It is an additional object of the present invention to provide toner for developing electrostatic latent image having good recovering characteristics.

The above-mentioned objects of the present invention may be accomplished by a toner for developing electrostatic latent image (hereinafter referred to as the toner of the present invention) having as substantially globular toner particles as the ratio between the longer diameter thereof (a) and the shorter diameter thereof (b) is in the range of 1.00 Se/b 5 1.05, the particle size ranging from 1 to 30 microns, 70% by weight of the toner being in the particle size range of the principal particle size + 3 microns.

When the ratio of the longer diameter (a) to the shorter diameter (b) of the toner particle of the present invention exceeds 1.05, the toner becomes substantially the same as that in the indeterminate form, producing undesirable effects upon the flowability, transfer efficiency, resolution and sharpness compared to the toner of the present invention with the particles in the foregoing diameter ratio of 1.005a/b < = a/b % 1.05.

When the toner contains particles smaller in diameter than 1 micron, it produces much fog, whereas when it contains particles larger than 30 microns, it brings about such undesirable results as a coarse-grained image and poor resolution.

And when the toner contains less than 70% by weight, particularly less than 65% by weight, of particles in the size range of the principal particle size + 3 microns, the change in the quantity of charge at the time of successive copying operations becomes large, bringing undesirable results to the running copying characteristics as well as to the toner recovery characteristics.

The percent by weight toner within the range of the principal particle size + 3 microns expressed in the present invention means that when the mean particle diameter of the toner is X microns, what percent of the total amount of the toner is occupied by those toner particles ranging from X - 3 to X + 3 microns.

The toner of the present invention contains normally a resin (preferably a thermoplastic resin), coloring agent, and further at need charge controlling agent, releasing agent, magnetic material and the like.

The method for the production of the toner of the present invention includes the spray dry process and suspension polymerization process, but the latter is most suitably applicable, which is such that a polymerization composition comprising a polymerizable monomer, coloring agent, charge controlling agent, polymerization initiator and the like is dispersed into water, and the dispersed mixture is then suspended in the presence of a dispersion stabilizer by stirring at the rate of from 3,000 to 10,000 r.p.m. by means of a disperser capable of giving a high rate of shear, and when a required particle size distribution is found obtained by viewing through a microscope, the stirring rate is slowed down to, e.g., 100 to 800 r.p.m., and the mixture is heated to a temperature of from 40 to 850C to thereby complete the polymerization and is then washed, filtered and dried, whereby the objective toner of the present invention is obtained.

Polymerizable monomers applicable to the present invention include, for example, styrenes such as e.g., styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, p-ethyl styrene, 2,4-dimethyl styrene, p-n-butyl styrene, p-tert-butyl styrene, p-n-hexyl styrene, p-n-octyl styrene, p-n-nonyl styrene, p-n-decyl styrene, p-n-dodecyl styrene, p-methoxy styrene, p-phenyl styrene, p-chlorostyrene, 3,4dichlorostyrene, and the like; vinyl naphthalenes; monoolefins such as ethylene, propylene, butylene, isobutylene, and the like; vinyl halide such as vinyl chloride, vinyl bromide, vinyl fluoride and the like; vinyl esters such as vinyl acetate, vinyl propionate, vinyl venzoate, vinyl butyrate, and the like; amethylene aliphatic monocarboxylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethyl-hexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl a-chloroacrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethyl-hexyl methacrylate, stearyl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, N,N-dimethyl-aminoethyl methacrylate, and the like; acrylic or methacrylic acid derivatives such as acrylonitrile, methacrylonitrile, acrylamide, and the like; vinyl ethers such as vinyl-methyl ether, vinyl-ethyl ether, vinyl-isobutyl ether, and the like; vinyl ketones such as vinyl-methyl ketone, vinyl-hexyl ketone, methyl-isopropenyl ketone, and the like; and N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole; N-vinyl indole, N-vinyl pyrrolidene, and the like.

As coloring agents applicable to the present invention there may be arbitrarily used appropriate pigments or dyes such as carbon black (including prepolymerized or grafted-polymerized carbon black), nigrosine dye, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and mixtures thereof. The toner is required to contain these coloring agents in so sufficient quantities as to enable the formation of visible images in the development process.

In addition, for the toner of the present invention, a charge control agent such as hydrophobic silica may also be used, and besides, other known toner characteristics improving agents may be used when necessary.

And in the present invention, for one-component developing toner useful magnetic material may be used. In one-component developing toner, magnetic material can be used as the coloring agent.

Such magnetic material is those which, according to the magnetic field applied, are strongly magnetized in the direction thereof and which should preferably be black and well dispersed into a resin to be chemically stabilized, and should be obtainable in the fine particulate form smaller in particle size than 1 1j. To meet such requirements magnetite (triiron tetraoxide) may be most suitably used Magnetic or magnetizable materials may be typified by such metals as cobalt, iron, nickel; alloys and mixtures of such metals as aluminum, cobalt, steel, lead, magnesium, nickel, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, vanadium; metallic compounds comprising such metallic oxides as.aluminum oxide, iron oxide, copper oxide, nickel oxide, zinc oxide, titanium oxide, and magnesium oxide; refractory nitrides such as vanadium nitride, chromium nitride; carbides such as tungsten carbide and silica carbide; and ferrite, and mixtures of these materials.

The quantities of these ferromagnetic materials to be incorporated into the toner are desired to be from about 50 to 300 parts by weight, most preferably from 70 to 200 parts by weight per 100 parts by weight of the resin component used.

The particle size and particle size distribution of the toner are governed by the degree of shearing, shearing period, type of the disperser used, the using quantity and the kind of the dispersion-stabilizing agent used, the proportion of the monomer used and water, the viscosity of the polymerization composition and the like. And it is known that the higher the shearing rate, the larger the using quantity of the dispersion-stabilizing agent, the smaller the proportion of the polymerization composition and water, and the smaller the viscosity of the polymerization composition, the smaller does the resulting particle size become.

However, these factors have interactions therebetween, and it is difficult to control all the factors, so that the shearing is applied with viewing through a microscope to find the point of obtaining the desired particle size and particle size distribution, and the stirring rate is slowed down to the normal stirring speed to continue the polymerization - this is the most suitable way for obtaining the toner of the present invention.

In the electrophotographic process, fixing takes place after the development of an electrostatic latent image with the use of a toner, but the fixation is generally carried out either by fusing directly the toner image formed by developing on a photosensitive body or an a dielectric material of by fusing the toner image on a sheet such as paper, said toner image being transferred onto said sheet from a photosensitive body or a dielectric material. The fusing of the toner image at this time is effected either by bringing the image into contact with a solvent vapor or by heating the image, the heating being generally carried out in the manner of either non-contact heating in an electric furnace or of heating with pressure by heat rollers.

The heating with pressure by the heat roller, generally called the heat roller fixing method, is to fix the toner image in such a manner that the image on a sheet to be fixed is put through and brought into pressed contact with a heat roller that is coated over the entire surface thereof with a material that enables parting property from the toner. This method, since the surface of the heat roller and the toner image on a sheet to be fixed are brought into pressed contact with each other, provides so good heat efficiency at the time of fusing the toner image onto the sheet that a rapid fixing may be carried out, so that the method is suitably applicable to such an image transfer type electrophotographic copying machine as intended particularly for high speed image reproductions.However, in this method, because the surface of the fixing roller and the toner image in a fused-by-heating condition are brought into pressed contact with each other, there may sometimes occur the so-called offset phenomenon which is such that part of the toner image is transferred to be attached onto the surface of the fixing roller, and the attached part of the image is then transferred onto the subsequent sheet. To avoid such a phenomenon, the surface of the roller must be subjected to the following treatment, which is essential for the heat roller fixing method.

To avoid the attachment of the toner onto the surface of the fixing roller, there has heretofore been employed such a treatment that, for example, a material excellent in the parting property from such a toner as comprising fluoro-carbon resin is formed over the surface of the roller, onto which is further supplied an offset prevention agent such as silicone oil, thus covering the surface of the roller with a liquid membrane.This method, although effective for the prevention of the offset phenomenon, has such drawbacks that the method makes the construction of a copying apparatus complex due to the need for providing the apparatus with means to remove the odor produced by heating from the offset preventing agent as well as with means to supply the liquid, and also makes the copying apparatus much expensive in order to meet the requirement for obtaining consistently satisfactory reproduction results. However, in the case where the offset preventing agent is not supplied, the toner is attached onto the surface of the fixing roller to produce an offset phenomenon, so that it is now the fact that the supply of the offset preventing agent is inevitably made in despite of these drawbacks.

On the other hand, there have been proposals for the use of various additives intended for the prevention of the offset phenomenon as described in, for example, Japanese Patent Publications No.

11492/1 976 and No. 47622/1976. The art in these proposals has effects in the kneading method, but places such restrictions on the use of additives that because in the method for the production of toners by the suspension polymerization the reaction takes place in the condition that all various necessary additives including coloring agents are incorporated into the polymerizable monomer, such compounds as having no effects on the polymerization reaction must be selected or any compounds hard to be dissolved into monomers cannot be used.

It is more one of another object of the present invention to provide a toner for developing electrostatic latent image capable of carrying out a highly efficient satisfactory heating roller fixing method without producing any offset phenomenon of the toner even in the case of using a fixing roller whose surface is supplied with no offset preventing agent.

The above more object of the present invention may be accomplished by the toner of present invention whose particles are in the form as substantially globular as the ratio between the longer particle diameter (a) and the shorter particle diameter (b) is 1.00 ~ a/b < 1.05, and whose particle sizes range from 1 to 30 microns, and which contains 70% by weight toner having the particle sizes in the range of the principal particle size + 3 microns, and which also contains a,-unsaturated ethylenically monomer as the principal resin component thereof, the weight average molecular weight thereof being not less than 80,000.

In the course of studying the method for the production of the toner in accordance with the suspension polymerization method, we analyzed toner resins produced in various polymerization conditions, and as a result we have found that the use of those resins having the molecular weight within a certain range is effective for the prevention of the offset phenomenon, and thus we have accomplished the present invention; that is, we have found that when the molecular weight of the produced resin is small, an offset phenomenon is observed at the time of fixation, paper becomes coiling around the roller, the toner sometimes becomes aggregated and the flowability becomes degraded, and thus the toner becomes unable to be provided for development.

The toner is generally composed of a resin component, coloring agent component such as pigments or dyes and additive component comprising a plasticizer, charge controlling agent and the like for controlling the physical and developing characteristics of the toner, the said resin component including various natural resin and synthetic resin, which may be used in single or in the form of an appropriate mixture.

The tonerofthe invention contains ,/3-unsaturated ethylenically monomers as a principal resin component unit thereof having the weight average molecular weight of 80,000 or more; that is, the resin of the present invention is incorporated into the toner in the proportion of about 60% by weight, preferably at least 75% by weight, to the whole resin component content of the toner, whereby the foregoing objects of the present invention may be attained; particularly the offset phenomenon of the toner to the heat fixing roller may be effectively prevented.

A characteristic of the present invention is that the toner comprises a:,/3-unsaturated ethylenically monomer as the principal component thereof, but the resin may have either a single polymer produced by polymerizing one monomer alone or a copolymer obtained by polymerizing two or more kinds of monomers, or further may be a mixture of such a single polymer with such a copolymer.

Other characteristic of the present invention is that the toner of the present invention is of the weight average molecular weight (Mw) of 80,000 or more. This value, when the toner of the invention fs of either a single polymer or a copolymer, is the value owned by either of the polymers, while when the toner of the present invention is of a mixture of these polymers, is the value of the whole mixed polymers; that is, in the case of such a mixture of the polymers, the polymers each does not necessarily have to be 80,000 or more but the value possessed by the whole mixture will do as long as it is in the foregoing range.

The value of Mw may be determined by various methods, but the result varies slightly according to the method used. The present invention, therefore, hereby specifies the value of Mw shall be determined in accordance with the following method: All values shall be those determined in accordance with the gel permeation chromatography (GPC) in such conditions that a solvent (tetrahydrofuran) is made to flow at the flowing rate of 1.2 ml/min at the temperature of 400C and then 300 ,ul of a tetrahydrofuran sample solution containing the resin sample in the concentration of 0.2 9/20 ml is poured into the column to thereby carry out a measurement.In determining the molecular weight of the sample, a measuring condition shall be selected so that the molecular weight distribution of the sample falls under such the range that the calibration curve indicating the relations between the logarithm and counted numbers of the weight, which has been prepared by use of severai singly dispersed polystyrene reference samples, become linear.

In addition, the reliability of the measurement may be assured by confirming that the Mw/Mn of NBS706 polystyrene reference sample [Mw = 28.8 x 104, Mn (number average molecular weight) = 13.7 x 104, Mw/Mn =2.11] used in the above measuring conditions becomes 2.11 + 0.10.

As the column for the GPC, any of those columns meeting the foregoing conditions may be used, such as, e.g., TSK-GEL, GMH6 (manufactured by Toyo Soda Mfg. Co., Ltd.).

Such resins as containing as the principal component thereof a-methylene aliphatic monocarboxylic acid esters or aromatic vinyl compounds and a-methylene aliphatic monocarboxylic acid esters are effectively applicable to the present invention, and such a resin as containing these monomers together and further at least about 30 mole% styrenes is especially usable in the present invention because it is not only capable of preventing the occurrence of offset phenomenon but is excellent in such manufacturing characteristics as triboelectric effect and uniform dispersibility of additives which are required for toner.

In producing the toner of the present invention, in order to produce the toner having the Mw of 80,000 or more, although conditions for obtaining the Mw are unable to be uniformly determined due to the fact that such various conditions as the kinds and combination of the polymerizing monomers used, the kinds and the adding quantities of such coloring agents as carbon black, the adding quantities of other additives including polymerization initiator, the temperature and time of the polymerization reaction and so forth are complicatedly entangled, the conditions, taking into account the fact that generally in the case of a large quantity of the polymerization initiator and of a high polymerization temperature, the weight average molecular weight becomes smaller, may be determined, for example, in such a manner that after the quantities of monomers, coloring agents, and other additives required for the toner are kept constant, the quantity of the polymerization initiator and the polymerizing temperature are varied to thereby carry out several times experiments for determining the conditions whereby a desired weight average molecular weight may be obtained.

On the other hand, the particle size and particle size distribution of the toner are governed by the degree of shearing, shearing period, type of the disperser used, the using quantity and the kind of the dispersion-stabilizing agent used, the proportion of the monomer used and water, the viscosity of the polymerization composition and the like. And it is known that the higher the shearing rate, the larger the using quantity of the dispersion-stabilizing agent, the smaller the proportion of the polymerization composition and water, and the smaller the viscosity of the polymerization composition, the smaller does the resulting particle size become.

However, these factors have interactions therebetween, and it is difficult to control all the factors, so that the shearing is applied with viewing through a microscope to find the point of obtaining the desired particle size and particle size distribution, and the stirring rate is slowed down to the normal stirring speed to continue the polymerization -- this is the most suitable way for obtaining the toner of the present invention.

And also the above-mentioned object for an offset preventing of the present invention may be accomplished by a toner for developing an electrostatic latent image having as particles as the ratio between the longer diameter thereof (a) and the shorten diameter thereof (b) is 1.00 < a/b S 1.05 and the particle size ranging from 1 to 30 microns, and containing 70% by weight toner having the particle size in the range of the principal particle size + 3 microns, the value of ths weight average molecular weight (Mw)/ the number average molecular weight (Mn) of the polymer being 3.5 or more as principal resin.

According to a preferred embodiment of the present invention, the toner of the present invention contains as the principal resin such a polymer as containing a high molecular weight component (resin) and low molecular weight component (resin), the content of the high molecular weight component having the Mw of 1 50,000 or more being 550% by weight of the amount of the polymer.

The use of the electrostatic image developing toner of the present invention permits highly efficient, satisfactory heat-roller fixing with no offset phenomenon nor coiling of paper sheets around the fixing roller even when no offset preventing agent is supplied to the surface of the fixing roller, so that not only may the mechanism of the fixing means be simplified but, e.g., the accuracy, stability and reliability of a rapid copying apparatus into which such fixing means is incorporated may be improved and besides, the cost of producing such apparatus may be reduced. Accordingly, the toner of the present invention has the advantage that it fairly facilitates the designing of high speed copying apparatus.

The toner is generally comprises a resin component, coloring agent component such as pigments or dyes, and additive component comprising a plasticizer, charge control agent and the like for controlling the physical and developing characteristics of the toner, the said resin component including various natural resins and polymerized resins, which may be used singly or in the form of an appropriate mixture, and also there are cases where the toner uses as the resin component thereof a polymer itself colored by being coupled with a dye.

According to a preferred embodiment of the present invention, the toner of the present invention contains as the component unit thereof an "B-unsaturated ethylenically monomer and contains a resin in which the molecular weight distribution of the principal resin consists of a low molecular weight component and a high molecular weight component, the Mw/Mn thereof being 3.5 or more, and particularly contains the resin of the present invention as the principal resin component; that is, the toner of the present invention contains the resin of the present invention in the quantity oi at least 60% by weight, preferably at least 75% by weight to the total amount of the resin component of the toner, thereby preventing the offset phenomenon of the toner to the heat-fixing roller as well as the coiling of paper sheets around the fixing roller.

The resin of preferred embodiment, as mentioned above, is of the molecular weight distribution consisting of a low molecular weight component and a high molecular weight component the Mw/Mn thereof being 3.5 or more. This value, when the resin of the present invention is composed of one single polymer or one copolymer, is the value the respective polymers posses, while when the resin of the present invention is composed of mixed polymers, is the value of the whole mixed polymers; that is, in the case of mixed polymers, the value of the Mw/Mn of each of the polymers to be mixed need not necessarily be 3.5 or more but of the whole will do as long as it is within the foregoing range.The molecular weight of the low molecular weight component of the resin of the present invention, in terms of weight average molecular weight, is less than 1 50,000, preferably in the range of from 10,000 to 1 50,000, while the molecular weight of the high molecular weight component, in terms of weight average molecular weight, is more than 150,000, preferably from 200,000 to 500,000, and the proportion of both component contents is such that the high molecular weight component is in the range of from 5 to 50% by weight, preferably from 10 to 40% by weight, and the low molecular weight component is in the range of from 95 to 50% by weight, preferably from 90 to 60% by weight.

The preferred embodiment of present invention uses a resin containing the low molecular weight component and the high molecular weight component The low molecular weight component plays the effective role of lowering the softening point of the toner of the present invention to thereby enable the lowering of the temperature of the fixing roller, thus permitting the energy-saving of the copying apparatus used. And the lowering of the molecular weight causes the resin itself to become softer, leading to the improvement in the condition of the fixation with pressure by the fixing roller.On the other hand, the high molecular weight component plays the effective role of preventing the offset phenomenon as well as the coiling of paper sheets around the fixing roller; that is, the high molecular resin is the component hard to be fused by heat and therefore has parting property against the fixing roller. However, when the high molecular weight resin is used in the quantity exceeding 50% by weight, the resin becomes hard to be fused by the heat roller, thus causing a poor fixation.

The resin of the present invention has the Mw/Mn of at least 3.5, but those having the weight average molecular weight Mw of from 10,000 to 2U0,000 are desired. In addition, the values of Mw, Mn and Mw/Mn may be determined in various ways and slightly vary according to the measurement method used. The present invention hereby specifies the values of Mw, Mn and Mw/Mn shall be determined by the above mentioned measurement procedure.

The above object for offset preventing of the present invention may be accomplished by an electrostatic image developing toner having a substantially globular particles as the ratio between the longer diameter thereof (a) and the shorter diameter thereof (b) is in the range of 1.00 ~ a/b < 1.05 and the particle sizes ranging from 1 to 30 microns, and containing 70% by weight toner having the particle sizes in the range of the principal particle size + 3 microns, the principal resin of the said toner being a uniform mixture of a low molecular weight component with a high molecular weight component, the weight average molecular weight (Mw)/number average molecular weight (Mn) of the said toner being 3.5 or more, the glass transition point of the said high molecular component being in the range of from 30 to 700 C.

According to a preferred embodiment of the present invention, in the toner of the present invention, the weight average molecular weight of the high molecular weight component is 1 50,000 or more, and the polymer is contained in the toner in the proportion of 550% by weight to the principal resin.

On the other hand, when the glass transition point of the toner is less than 450C, there occurs a tendency to bring about blocking due to the cold flow phenomenon, which will have undesirable influence upon the storage of the toner; -that is, the substantially globular toner used in the present invention has as low a softening point as 1 500C or less and as high a glass transition point as 450C or more. These physical characteristics may be attained by a toner containing the principal resin component composed of a copolymer of, e.g., 65-95% by weight styrene, 5-35% by weight methacrylic acid ester and/or acrylic acid ester.If the styrene content is smaller than the 65% by weight it becomes difficult to control the glass transition point to 450C or higher, whereas if it is larger than the 95% by weight it becomes hard to control the softening point to 1 500C or lower, and therefore in both cases the toner of the present invention cannot be obtained.

The principal resin component content of the toner of the present invention is desired to be at least about 60% or more by weight, preferably 75% or more by weight to the total amount of the resin component of the toner.

In order to form an image, for example, in accordance with the electrophotographic process, using the toner of the present invention, there may be used a selenium photosensitive body; a photosensitive body produced by providing a conductive support thereon with a photosensitive layer prepared by dispersing into a binder such an inorganic photoconductive material as zinc oxide, cadmium sulfide, cadmium selenide, cadmium sulfide-selenide, lead oxide, mercury sulfide and the like; or a photosensitive body produced by providing a conductive support thereon with a photosensitive layer prepared by incorporating into a binder resin such an organic photoconductive material as anthracene, polyvinyl carbazole and the like.The entire surface of such a photosensitivebody is charged by a corona generator, using either a corotron or scorotron charger, and is then imagewise exposed to light or the like to thereby form an electrostatic latent imee thereon. The electrostatic latent image is then developed with, e.g., a developer composed of a mixture of the toner of the present invention with glass beads or with iron carriers by, e.g., the cascade method or magnetic brush method. The resulting toner image, under, e.g., corona discharge, is then brought into pressed contact with a paper to be transferred thereonto. The toner image formed on the paper is subsequently heated to be fixed by a heat roller fixing means. Generally, as the fixing roller, there may be effectively used one having a smooth surface formed by the use of such a fluororesin as, e.g., Teflon Registered Trade Mark (manufactured by DuPont), EFP (manufactured by DuPont), Fluon (manufactured by ICI), Kel-F (manufactured by 3M), Daiflon (manufactured by Daikin) and the like, or of such a relatively hard silicone rubber as KE--1300RTV (manufactured by Shin-etsu Chemical Industries Co., Ltd.), or if necessary, one having the surface made of metal.

The present invention is illustrated with reference to examples below. In addition, the term "part(s)" hereinafter described means "part(s) by weight" unless otherwise noticed.

EXAMPLE 1 Styrene 100 parts Carbon black &num;30 (manufactured by Mitsubishi Chemical Industries, Ltd.) 5 parts 2,2'-azobis(2,4-dimethyl valeronitrile) 3 parts Hydrophobic silica aerosyl R-972 (charge control agent, manufactured by DEGUSSA) 1 part The above materials were mixed to prepare a polymerization composition. On the other hand, 3 parts of tricalcium phosphate and 0.04 part of sodium dodecyl benzene sulfonate were put in a 2-liter separable flask, and distilled water was added to the mixture. To this was added the above composition and the mixture was stirred by means of a TK Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). The stirring was replaced by a normal rate stirring at the point where the particles in the desired size were found obtained by viewing through a microscope.The mixture was then heated up to 600C and subjected to polymerization reaction at this temperature over a period of 10 hours with 100 r.p.m.

stirring. No change in the particle size was observed until the completion of the polymerization reaction.

After completion of the polymerization reaction, the solid product particles were subjected to treatment by hydrochloric, filtering and washing to thereby obtain negative two-component toner samples No. 1 to No. 6.

The thus obtained toner was of particles substantially in the globular form; the ratio of the longer particle diameter (a) to the shorter particle diameter (b) was within the range of 1.00 < a/b 5 1.05.

Subsequently, the relations between the number of revoiutions of TK Homomixer, the stirring periods, particle sizes and particle size distributions are shown in Table 1.

TABLE 1

% by weight Mean toner within Stirring particle Particle principal Sample Revolutions period size size particle size No. (r.p.m.) (min.) (jut) (P) + 3,a 1 3,000 120 15 5 to 40 70% 2 4,000 60 13 5to35 72% 3 5,000 60 10 1 to 30 75% 4 6,000 30 10 1 to 30 68% 5 7,000 20 10 0.1 to 35 65% 6 8,000 10 10 0.1 to 35 63% The percent by weight toner within the principal particle size + 3y indicated herein above means that if the mean particle diameter of the toner is 10y, what percent of the total amount of the toner is occupied by those toner particles ranging 7y to 13 .

Image tests were made by use of U-Bix V (manufactured by Konishiroku Photo Industry Co., Ltd.) on the samples No. 1 to No. 6 for the resolution, fog, and the change in the quantity of charge at the time of successive copying operations. The results are shown in Table 2.

TABLE 2

Change in qty. of charge in Fog successive copyings Sample Resolution reflection (initial > after 10,000 No. lines/mm density shts) 1 4 0.03 16 Sc/g --- > 22 c/g 2 5 0.03 18 c/g --- > 22 c/g 3 7 0.02 20 c/g --- > 20 c/g A 6 0.02 20 c/g --- > 26 c/g 5 5 0.06 20 c/g --- > 30 c/g 6 5 0.08 20 sslc/g ~32,uc/g Sample No. 3 had an excellent resolution and little fog, and no deterioration of the image density occurred even in successive copying operations.No change in the quantity of charge was observed even after copying 10,000 sheets.

EXAMPLE 2 Polystyrene 100 parts Carbon Black &num;30 5 parts Hydrophobic silica aerosyl R-972 1 part The above materials were fused, kneaded and pulverized, and then classified by means of a classifier so that the particle sizes are from 1 to 30,u ,and the toner contains 70% by weight particles with the sizes in the range of the principal particle size + 3y, whereby a negatively charged twocomponent toner sample No. 7, which was subsequently subjected to a spray-drying treatment to be made globular to thereby obtain samples No. 8 and No. 9 as shown in Table 3.

TABLE 3

Sample Ratio between longer diameter (a) No. and shorter diameter (b) Resolution 7 2.0 and more 5 lines/mm 8 1.5 and more 6 lines/mm 9 1.05 7 Lines/mm These samples were subjected to image tests in the same manner as in Example 1, then the results showed that sample No. 9 had satisfactory results in flowability, sharpness and resolution as compared to samples No. 7 and No. 8.

EXAMPLE3 Styrene 50 parts Methyl methacrylate 30 parts n-butyl methacrylate 20 parts Carbon Black &num;30 5 parts Azobisisobutylonitrile 3 parts Hydrophobic silica aerosyl R-972 1 part The above materials were mixed to prepare a polymerization composition, which was then treated in the same manner as in Example 1 to thereby obtain a negative-polarity two-component toner. The obtained toner particles are substantially in the biobular form; the ratio between the longer particle diameter (a) and shorter particle diameter (b) was in the range of 1.00 < a/b ~ 1.05.The toner particle sizes as a result of the measurement by means of a coulter counter was in the range of from 1 to 30 microns, and the quantity of the toner falling under the range of the principal particle size +3 microns was 75% by weight.

The results obtained by testing the obtaining toner, using U-Bix V showed that the resolution was 7 lines/mm, fog was 0.02, and the change in the quantity of charge was as little as from -20,uC/g in the initial stage to -21 yC/g after copying 1 0,000 sheets, and no deterioration of the image density was observed.

EXAMPLE 4 Styrene 90 parts 4-vinyl pyridine 10 parts Carbon Black &num;2300 5 parts Azobisisobutylonitrile 3 parts Triiron tetraoxide powder, Mapicoblack BL-500 (Titanium Industry Co., Ltd.) 70 parts The above materials were mixed to prepare a polymerization composition, which was then treated in the same manner as in Example 1 to thereby produce a positive-polarity one-component toner. The toner particles were substantially in the globular form; the ratio between the longer particle diameter (a) and the shorter particle diameter (b) was in the range of 1.00 < a/b < 1.05.

The particle sizes of the resulting toner, as a result of the measurement by means of a coulter counter, were in the range of from 1 to 30 microns, and the quantity of the toner covered by the range of the principal particle size + 3 microns was 75% by weight.

The results obtained by testing the toner, using U-Bix T (manufactured by Konishiroku Photo Industry Co., Ltd.), showed that the resolution was 6 lines/mm, fog was 0.02, and the change in the quantity of charge at the time of successive copying operations was a little as from 16,uC/g in the initial stage to 17yC/g after copying 1 0,000 sheets, and no deterioration of the image density was observed.

EXAMPLE 5 Polymerization compositions as indicated in Table 4 were prepared by the use of styrene and butyl methacrylate as monomers to be polymerized, Carbon Black &num;30 as a coloring agent, and 2,2'-azobis (2,4-dimethyl valeronitrile) as a polymerization initiator.

TABLE 4

Polymerization composition and Polymerizing conditions Butyl conditions Sample method Coloring Sample Styrene acrylate agent Initiator Temp. Period Toner (A) 100 - 5 3 65"C 8 parts parts parts parts Toner (B) 100 - 5 3 50;;C 8 parts parts parts hours Toner (C) 100 - 5 2 50"C 7 parts parts parts hours Toner (D) 100 - 5 1 50'C 8 parts parts part hours Toner (E) 80 20 5 3 63C 6.5 parts parts parts parts hours Toner (F) 80 20 5 2 çc 7 parts parts parts parts hours Toner (G) 80 20 5 1 50"C 7 parts parts parts part hours Toner ------------------ (H) 80 20 5 2 50or 8 parts parts parts parts parts Toner (1) 80 20 5 1.5 50C 8 parts parts parts parts hours On the other hand, 3 parts of tricalcium phosphate and 0.04 part of sodium dodecyl benzene sulfonate were put in a 2-liter separable flask, to the mixture were added distilled water and the foregoing polymerization composition, and the resulting mixture was stirred by means of a TK Homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.) to disperse the components thereof with viewing through a microscope.Upon confirming the point where a desired particle size was obtained, the homomixer was replaced by a normal-speed stirrer to stir the mixture at the rate of 100 r.p.m. and then the dispersed mixture was subjected to the polymerization reaction in the conditions indicated in Table 4. Until the completion of the reaction, no change in the particle size was observed. After completion of the polymerization, the obtained solid particles were subjected to treatment by hydrochloric acid, filtering and then washing, whereby a two-component toner was obtained.

Every particle of the resulting toner was substantially in the globular form; the ratio between the longer particle diameter (a) and the shorter particle diameter (b) was in the range of 1 S a/b 5 1.05. The results obtained with the use of a coulter counter on the mean particle size, particle size distribution, the quantity of the toner having the particle sizes in the range of the principal particle size + 3y, and the weight average molecular weight of the toner were as shown in Table 5, wherein the percent by weight of the toner within the principal particle size + 3y means that when the average particle diameter of the toner is 1 Ou, what percent of the whole toner is occupied by those having the particle diameters in the range of from 7y to 13y.

TABLE 5

Me % by wt. toner Wt. average Mean Particle within principal mo I ecu I ar \ particle size particle wt. of resin Sample do size distribution size + 3 (Mw) Toner (A) 11 3 to 25 77 4.8 x 104 Toner(B) 13 5 to 30 75 9.9x104 Toner (C) 11 3 to 25 80 15.3 x 104 Toner (D) 12 5 to 25 79 23.4 x 104 ~ Toner (E) 10 3 to 23 76 6.5 x 104 ~ Toner (F) 1 11 3 to 25 81 142x104 Toner (G) 12 5 to 25 83 25.1 x104 Toner (H) 12 5 to 40 57 13.8 x 104 Toner (1) 12 3 to 35 61 17.2 x 104 Each of the toners shown in Table 5 was mixed with resin-coated iron powder carriers having the particle size of from about 50 to 80y to prepare a developer, which was then used to develop an electrostatic latent image formed in accordance with the ordinary electrophotographic process to thereby carry out image tests on the resolution, fog, changes in the quantity of charge (the initial after copying 10,000 sheets) during the successive copying operations using a copier provided with toner-recycling means, and image densities. The thus obtained results are shown in Table 6.

As apparent from the table, the toners of the samples (B), (C), (D), (F) and (G), because of small ranges of the particle size distributions, have little fog, no change in the quantity of charge, and enable good images having satisfactory image densities, whereas the control toners (H) and (I), because of wide ranges of the particle size distributions, have much fog, and particularly the toner (H) shows deterioration of the resolution as well as of the image density because of the fluctuation in the quantity of charge.

TABLE 6

Charge in quanti ty,of \ charge (,aC tg) Resolution After Anti lines 10,000 Image offset mm Fog Initial copies density effect Toner (A) 7 0.02 20 21 good poor Toner (B) 7 0.02 20 19 good good Toner (C) 7 0.02 21 20 1 good good Toner (D) 7 0.02 20 20 good good Toner (E) 7 0.02 19 20 good poor poor Toner (.F) 7 0.02 20 21 good good Toner (G) 7 0.02 20 20 good good Toner (H) 5 0.05 18 25 lowered good Toner (I) 7 0.05 20 27 (owe red good Regarding the offset preventing effect, after developing the electrostatic latent image, the toner image was transferred onto a transfer paper sheet, which was then brought into pressed contact with a fixing roller heated up to a temperature of from 165 to 1 750C, the roller being coated on the surface thereof with a fluoro-carbon resin (EFP, manufactured by DuPont), whereby the toner image was fusedly fixed.Subsequently, in order to examine whether or not the fused toner image was transferred onto the surface of the fixing roller to bring about an offset phenomenon, after completion of the respective fixing operations, a plain transfer paper sheet with no toner image was brought into pressed contact with the fixing roller in the same manner as in above, thereby observing the presence of stain on the transfer paper sheet caused by offset phenomenon of the toner, and as the result, as indicated in Table 6, in the case where toners (A) and (E) were which have lower weight average molecular weight, there were observed stains on the transfer paper sheets caused by the offset phenomenon of the toners, whereas the toners (B), (C), (D), (F) and (G), and other toners (H) and (I) produces no offset phenomenon.The results were not changed even when the fixing operations were repeated in the same manner.

In addition, blocking tests were made on the samples in an incubation cabinet kept at the temperature of 500C, but all the samples showed no blockings nor cakings.

EXAMPLE 6 Styrene 80 parts n-butyl methacrylate 20 parts Carbon Black #30 5 parts 2,2'-azobis-(2,4-dimethyl- valeronitrile) 3 parts Hydrophobic silica aerosyl R-972 1 part The above materials were mixed to prepare a polymerization composition. On the other hand, 3 parts of tricalcium phosphate and 0.04 part of sodium dodecyl benzenesulfate were put in a 2-liter separable flask, and to the mixture were added distilled water and then the foregoing polymerization composition.The obtained mixture was stirred by means of a TK Homomixer, and when, with viewing through a microscope, the required particle size and required particle size distribution were obtained, the homomixer was replaced by a normal stirrer, the mixture was heated up to 600C and subjected to the polymerization reaction at this temperature over a period of 10 hours with the normal stirring rate of 100 r.p.m., thus completing the polymerization reaction. During the reaction period no change in the particle size was observed.

Upon completion of the polymerization, the solid particles were subjected to treatment by hydrochloric, fiitering and then washing to thereby obtain a negative-polarity two-component toner. The obtained toner was of substantially globular toner particles whose ratio between the longer diameter (a) and the shorter diameter (b) was within the range of 1.00 5 a/b 5 1.05. The obtained toner particle sizes measured by means of a coulter counter was from 1 to 30 microns, and the quantity of the toner within the range of the principal particle size + 3 microns was 75% by weight. In addition, the softening point and the glass transition point of the toner was 1 350C and 590C, respectively.

The obtained toner was subjected to image tests by use of an electrophotographic copier U-Bix V.

The results of the test showed that the resolution was 7 lines/mm, fog was 0.02, the change in the quantity of charge at the time of successive copying operations was as little in the range as of from 20,uc/g in the initial stage to 21 c"g after copying 10,000 sheets, and the image densities were not deteriorated. In the test for the fixation with the use of the heat roller of the U-Bix V in the condition of 1 600C with the speed of 1 22 mm/sec., the result showed the toner had a satisfactory fixing ability. And the blocking test carried out in an incubation cabinet kept at the temperature of 500C showed no blocking of the toner particles.

Styrene 100 parts Carbon Black &num;30 5 parts 2,2'-azobis-(2,4-dimethyl valeronitrile) 3 parts Hydrophobic silica aerosyl R-972 1 part The above materials were mixed to prepare a polymerization composition, which was then polymerized in the same manner as in Example 6 to thereby obtain a toner having the particle size and particle size distribution required for the present invention. The softening point and the glass transition point of the toner were 1 600C and 800 C, respectively.

The heat roller of the U-Bix V was used in the condition of 1 600C with 1 22 mm/sec. to carry out fixing tests, then the results showed that the toner was unthoroughly fixed.

Styrene 60 parts n-butyl methacrylate 40 parts Carbon Black #30 5 parts 2,2'-azobis-(2,4-dimethyl- valeronitrile) 3 parts Hydrophobic silica aerosyl R-972 1 part The above materials were mixed to prepare a polymerization composition, which was then polymerized in the same manner as in Example 1 to thereby produce a toner having the particle size and particle size distribution required. The softening point and the glass transition point of the resulting toner were 11 00C and 430C, respectively. The blocking test made in an incubation cabinet kept at 500C showed blocking of the toner.

EXAMPLE 7 In a 1-liter separable flask, 100 ml of a 0.1 moVliter aqueous trisodium phosphate solution was diluted by the addition of 600 ml of distilled water, and to the aqueous solution with stirring were slowly added 18.7 ml of a 1.0 ml/liter aqueous calcium chloride solution and then a 0.1 g of a 10% sodium dodecyl benzenesulfonate to thereby prepare a dispersion medium [S]. To the obtained mixture was added to be dispersedly suspended a polymerization composition composed of 80 g of styrene, 20 g of n-butyl methacrylate and 0.3 g of benzoyl peroxide, and after replacing the air inside the flask by nitrogen gas the suspension was heated up to 800C and at this temperature was subjected to polymerization reaction over a period of 20 hours.Upon completion of the reaction, the polymerized product was cooled, dehydrated and washed repeatedly, whereby a high molecular weight resin [A] was obtained.

On the other hand, another same dispersion media [S] was prepared. Subsequently, 80 parts of styrene, 20 parts of n-butyl methacrylate, 5 parts of Carbon Black &num;30, one part of aerosyl R-972, 5 parts of 2,2'-azobis-(valeronitrile), 6 parts of dodecyl mercaptan and 30 parts of the foregoing high molecular weight resin [A] are mixed together to sufficiently disperse the carbon black to thereby prepare a polymerization composition, which was then added to the foregoing dispersion medium and the thus obtained mixture, with stirring by means of a TK Homomixer at the rate of 3,500 r.p.m., was heated to 650C, and at this temperature the stirring was continued for 30 minutes.After that, the stirring was replaced by a normal speed stirring by a normal stirrer at the rate of 100 r.p.m. to carry out the polymerization, keeping the same temperature, over a period of 8 hours, thus completing the polymerization. Upon completion of the polymerization, the product was cooled, the solid was filtered and immersed in a 5% aqueous dilute hydrochloric acid solution to decompose the calcium phosphate therein, then washed until the washing water becomes neutral, and then dehydrated to be dried, thereby obtaining a toner [1] of the present invention having the average particle diameter of 12 microns.

The resin of the obtained toner [1] had the Mw/Mn of 16.5, Mw of 90,000 and the softening point of 1 380C (the value obtained by a flow tester).

Control 1 A polymerization composition composed of 8 parts of styrene, 20 parts of n-butyl methacrylate, 5 parts of Carbon Black #30, one part of Aerosyl R-972, 3 parts of 2,2'-azobis-(valeronitrile), with the use of the foregoing dispersion medium [S], was subjected to suspension polymerization at 600C over a period of 1 5 hours thereby to produce a Control toner 1.

The resin of the obtained Control toner 1 had the Mw/Mn of 3.2, Mn of 52,000 and softening point of 1410C.

EXAMPLE 8 Toner [2] was obtained in quite the same manner as in Example 7 with the exception that 5 parts of the high molecular weight resin [A] synthesized in Example 7, 80 parts of styrene, 20 parts of n-butyl methacrylate, 5 parts of Carbon Black &num;30, one part of Aerosyl R-972, 5 parts of 2,2'-azobis (valeronitrile), and 6 parts of dodecyl mercaptan were used. ~~~ The resin of the obtained toner [2] of the present invention had the Mw/Mn of 10.8, Mw of 47,000 and softening point of 1 350C.

EXAMPLE 9 Toner [3] was prepared in quite the same manner as in Example 7 with the exception that the high molecular weight resin [A] in Example 7 was used in the quantity of 40 parts.

The resin of the obtained toner [3] had the Mw/tWn of 1 8.6, Mw of 120,000 and softening point of 1430C.

In addition, each of the toners obtained in Examples 7,8 and 9, and in Control 1 was in the - substantially globular particle form with the ratio between the longer diameter thereof (a) and the shorter diameter thereof (b) being in the range of 1.00 S a/b S 1.05, the toner particle sizes were in the range of from 1 to 30yam, determining by the measurement with counter, and the content of the particles within the range of the principal particle size + 3,um was 70% by weight.

Test 1 Three parts each of the toners [1], [2] and [3] and of the Control toner 1 and 97 parts of iron powder carrier with the average particle size of from 50 to 801um were mixed to prepare a developer. Each of these prepared developers was used to develop an electrostatic latent image formed in accordance with the ordinary electrophotographic process, and the thus developed toner image was transferred onto a transfer paper, the surface of which was brought onto pressed contact with a fixing roller coated on the surface thereof with FEP (tetrafluoroethylene-hexafluoropropylene copolymer, manufactured by DuPont) heated at a temperature of from 160 to 1 700C to thereby fusedly fix the toner image.

Subsequently, in order to examine whether or not the fusedly fixed toner image is transferred onto the surface of the fixing roller to bring about an offset phenomenon, after the respective fixing operations, a plain transfer paper with no toner image was brought into pressed contact with the fixing roller in the same condition as the above, and thus the occurrence of offset phenomenon on the transfer paper was observed.

As the result, in the case where the toner of Control 1 was used, a stain was found produced on the transfer paper due to the offset phenomenon, but in the case of toners [1] and [3], any stain due to offset phenomenon was not found at all on the transfer paper. Where toner [2] was used, little or no offset phenomenon was found on the transfer paper, while even though found, it had no influence upon the reproduced image.

Further, tests were made on the coiling of paper sheets around the fixing roller, then the Control toner 1 brought about the coiling phenomenon, whereas toners [1], [2] and [3] did not produce the coiling phenomenon at all.

And, image tests were made on toners [1] and [3], using an electrophotographic copier U-Bix V, and the results showed that the resolution was 7 lines/mm, fog was 0.02 (reflection density), the changes in the quantity of charge at the time of successive copying operations were so small that in toner [1] the change was from 2o5yclg in the initial state to 22.5,uc/g after copying 10,000 sheets and in toner [3] the change was from 21 .0,uc/g in the initial stage to 23.0yc/g after copying 10,000 sheets, so that the image densities were not deteriorated.

Test 2 In order to observe the storage stability of the toner, each of the toners was allowed to stand for 24 hours in an incubation cabinet in the atmospheric condition at the temperature of 500C with relative humidity of 60%. The results of the test showed that toners [1], [2] and [3] did not produce any aggregated lumps at all.

SYNTHESIS EXAMPLE 1 In an ordinary anchor-shaped stirrer-provided flask there were prepared 340 ml of an aqueous solution containing 1% by weight tricalcium phosphate,0.01 by weight NL-R (sodium dodecyl benzene sulfonate) to the following monomer: a monomer mixture composed of 80 parts of styrene, 20 parts of n-butyl acrylate and 1.6 parts of lauryl peroxide was added to the above-prepared aqueous solution with stirring at the rate of 200 r.p.m., and the obtained mixture was subjected to polymerization reaction at the temperature of 700C for a period of 7 hours, thus completing the reaction.The reaction produce was then cooled, treated with a dilute hydrochloric acid solution to decompose and remove the tricalcium phosphate, and then washed repeatedly to thereby obtain a resin having the Tg of 520C and the Mw of 250, 000.

EXAMPLE 10 95 parts of styrene, 5 parts of n-butyl methacrylate, 5 parts of Carbon Black #30, 5 parts of 2,2' azobis-(2,4-dimethyl valeronitrile), one part of n-dodecyl mercaptan, 30 parts of the resin synthesized in Synthesis Example - 1, 3.5 parts of polypropyrene PP-660 (manufactured by Shin-etsu Chemical Industry Co., Ltd.), and one part of Aerosyl R-972 were taken to be sufficiently mixed and dispersed by means of a sand stirrer.Subsequently there were prepared 700 ml of an aqueous solution containing tricalcium phosphate in the quantity of 3% by weight, NL-R in 0.04% by weight, ammonium molybdate in 0.06% by weight and sodium nitrite in 0.1% by weight to the above monomer and the resin, and to the solution with stirring by means of a TK Homogenizer at the rate of 5,000 r.p.m. was added the above-prepared dispersed mixture. When desired particle sizes were observed to have been obtained, the stirring was replaced with the normal stirring rate of 200 r.p.m. by means of a normal stirrer to perform polymerization reaction at 650C for a period of 7 hours, thus completing the reaction.

The reaction product was cooled, treated with a dilute aqueous hydrochloric acid solution to decompose and remove the tricalcium phosphate, washed repeatedly, and then dried to thereby obtain a toner of the present invention having the average particle diameter of 1 2,u. The obtained toner was in the substantially globular form and the ratio between the longer particle diameter (a) and the shorter particle diameter (b) was in the range of 1.00 S a/b = < 1.05. The toner particle sizes were in the range of from 1 to 30ym and those toner particles within the range of the principal particle size + 3ym determined by the measurement by means of a coulter counter was 74% by weight.The toner had the Tg of 600C, Mw/Mn of 20.0, Mw of 80,000 and softening point (Tm) of 1 350C.

5 parts of the toner obtained and 95 parts of iron powder carried were mixed to prepare a developer.

The obtained developer was used to develop an electrostatic latent image formed by the ordinary electrophotographic process, and the thus developed toner image was transferred onto a transfer paper sheet, which was then fused to be fixed by being brought into pressed contact at 160--1700C with a fixing roller coated on the surface thereof with EFP, whereby a satisfactory fixation was carried out.

In order to examine whether or not the fusedly fixed toner image is transferred onto the surface of the fixing roller to bring about an offset phenomenon, after the fixing operation, a plain transfer paper sheet with no toner image was brought into pressed contact with the fixing roller in the same condition as in the above to thus observe the occurrence of the offset phenomenon of the toner on the transfer paper sheet.

As the result, no stain due to the offset phenomenon was observed. In addition, tests were made on the coiling of transfer paper sheets around the foregoing fixing roller, but where the toner of the present invention was used, no coiling-around-the-roller phenomenon was observed.

Further, image tests were made on the toner, using an electrophotographic copier U-Bix V, and the results showed that the resolution was 7 lines/mm, fog was 0.02, the change in the quantity of charge at the time of successive copying operations was as small as in the range of from 20.5yc/g in the initial stage to 21.0,uc/g after copying 10,000 sheets, and the image densities were not deteriorated.

SYNTHESIS EXAMPLE -- 2 A resin having the Tg of 52.50C and Mw of 350,00Q was produced in quite the same manner as in Synthesis Example - 1 with the exception that 1.0 part of lauryl peroxide was used and polymerization reaction took place at the temperature of 650C.

EXAMPLE 11 A toner was synthesized in the same manner as in Example 10 with the exception that 20 parts of the resin obtained in the above Synthesis Example - 2 was used in place of the resin of Synthesis Example 1 in Example 10, and as the result, the thus obtained toner had the Tg of 61 OC, Mw/Mn of 25.0, Mw of 85,000 and Tm of 1 370C. The obtained toner was in the substantially globular form with the ratio between the longer particle diameter (a) and the shorter particle diameter (b) in the range of 1.00 S a/b S 1.05.The toner particle sizes determined by means of a coulter counter were in the range of from 1 to 29cm, and those particle sizes within the principal particle size + 3ym was 77% by weight.

This toner was used to produce a developer in the same manner as in Example 10, and the obtained toner was subjected to tests for examining both offset phenomenon and coiling-around-theroller phenomenon of the toner, and as the result, none of these phenomena were observed.

And, image tests were made on the toner, using the U-Bix V and the results showed that the resolution was 7 lines/mm, fog was 0.02, the change in the quantity of charge at the time of successive copying operations was as small as in the range of from 21yc/g in the initial stage to 22yc/g after copying 1 0,000 sheets, and the image densities were not deteriorated. And further, a blocking test was made on the toner in an incubation cabinet kept at the temperature of 500C, but no caking phenomenon was observed.

SYNTHESIS EXAMPLE-3 A resin having the Tg of 750C and Mw of 270,000 was obtained in quite the same manner as in Synthesis Example - 1 with the exception that 90 parts of styrene and 10 parts of butyl acrylate were used.

Control 2 A toner was produced in the same manner as in Example 10 with the exception that 40 parts of the resin of the foregoing Synthesis Example -- 3, 80 parts of styrene and 20 parts of n-butyl methacrylate were used in place of the resin of Synthesis Example - 1 in Example 10, then the toner having the Tg of 550C, Mw/Mn of 150, Mw of 100,000, and Tm of 1 550C was obtained. The obtained toner was evaluated in the same manner as in Example 10, then the evaluation showed that the toner brought about an offset phenomenon, coiling-around-the-roller phenomenon, and unthorough fixation.

In addition, a blocking test was made on the toner in an incubation cabinet kept at the temperature of 500C, then the toner was found caking.

Claims

1. A toner for developing electrostatic latent image which comprises particles of a coloring agent and a resin, having a ratio of longer diameter/shorter diameter from 1.00 to 1.05, the particle size being from 1 to 30 microns, and at least 70% by weight of the particles having a size within the range of the mean particle size + 3 microns.

2. A toner as claimed in Claim 1, wherein the resin comprises at least 60 weight %, based on the total resin weight, of a polymer of s 3-unsaturated ethyleneic monomer, having a weight average molecular weight of at least 80,000.

3. A toner as claimed in Claim 2, wherein the polymer is a homopolymer of an a-methylene aliphatic monocarboxylic acid ester or a copolymer of an aromatic vinyl compound with an a-methylene aliphatic monocarboxylic acid ester.

4. A toner as claimed in Claim 3, wherein the aromatic vinyl compound is a styrene.

5. A toner as claimed in any preceding Claim, wherein said toner has a softening point of up to 1 500C and a glass transition point of at least 450C.

6. A toner as claimed in any preceding Claim, wherein the resin comprises a polymer having a ratio of weight average molecular weight/number average molecular weight ratio of at least 3.5.

7. A toner as claimed in Claim 6, wherein the polymer contains both a high molecular weight component and a low molecular weight component.

8. A toner as claimed in Claim 7, wherein the high molecular weight component comprises 5 to 50% by weight of the polymer, and has a weight average molecular weight of at least 150,000.

9. A toner as claimed in Claim 8, wherein the high molecular weight component has a weight average molecular weight of from 200,000 to 500,000.

10. A toner as claimed in any of Claims 7 to 9, wherein the high molecular weight component has a glass transition point of from 300C to 700 C.

11. A toner as claimed in any of Claims 7 to 10, wherein the lower molecular weight component has a weight average molecular weight of up to 1 50,000.

12. A toner as claimed in Claim 11 , wherein the lower molecular weight component has a weight average molecular weight of from 10,000 to 150,000.

13. A toner as claimed in Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 11.