GB2070036A - A toner composition for electrophotography and a method for manufacturing the same - Google Patents

Abstract

A toner composition for electrophotography comprises (a) spherically shaped polymer grains containing a polymer which has been prepared by polymerizing an aqueous suspension of a monomer which is, when dispersed in water, capable of being charged in a first polarity, in the presence of an inorganic dispersing agent which is, when dispersed in water, capable of being charged in the opposite polarity to said first polarity, with (b) a coloring agent incorporated in said polymer grains. The composition can be charged in the first polarity by incorporating an anionic or cationic monomer in the aqueous suspension, or by incorporating a sparingly soluble organic amine. Suitable dispersing agents are silica and bentonite (negative) and Al2O3 (positive). The toner compositions have good resistance to humidity and do not exhibit the so-called offset and twinning phenomena.

Description

SPECIFICATION A toner composition for electrophotography and a method for manufacturing the same The present invention relates to a toner composition for electrophotography, electrostatic printing and an electrostatic recording method and a method for manufacturing such toner.

Generally, an electrostatic image formed on a photoconductive plate is developed by the use of colored powder, toner and thus formed toner image is fixed directly thereon or after being transferred onto a transfer paper or the like. As a fixing method, among others, heat-fixing method is well known and used from a practical point of view, and in particular, a contact type heat-fixing method by the use of a pair of heat-fixing rollers is widely utilized because of its high heat efficiency with relatively low temperature and because according to this method, fixing at high speed becomes possible.

In the contact type heat-fixing method, however, there is often occurred a so-called "off-set" phenomenon, wherein melted or haif-melted toner adheres to the surface of the heat-fixing roller and thus deposited toner is thereafter transferred onto the paper coming into contact with it succeedingly.

This off-set phenomenon tends to occur when viscoelasticity of the toner is not proper and, especially, when it is too small.

Meanwhile, toner is usually vigorously agitated before it is used for development. This agitation is necessary in order to induce the toner to bear electric charge. However, such vigorous agitation of the toner often crushes toner grains into finer powder. This is harmful for the formation of the good toner image since, for example, the fine powder tends to adhere to the surface of the carrier grains, which are subject to the agitation together with the toner before development, or to the surface of a photoconductive plate, on which the electrostatic image is formed. Thus such adhesion of the toner on the carrier grains or photoconductive plate causes deterioration of the carrier in its durability or socailed "grey background".

Further, the conventional method of preparing toner has its own demerit that since a crushing and puiverizing means is used to get a powder of a grain size that satisfies the requirement for toner (usually between 1 and 50 ,u), the product toner has a very wide distribution of grain sizes and, therefore, it must furpher undergo a classification step to obtain toner for practical use, which complicates the preparing process for a higher cost.

Meanwhile, as a method that does not include any crushing and pulverizing step but prepares fine polymer powder directly, it is known to disperse and suspend a polymerizable monomer in water for the suspension polymerization. In this method the polymerizable monomer is dispersed by agitation into fine particles, which are polymerized as they are, when it is essential to prevent these particles from rejoining for the stabilization of the dispersed and suspended phase. For this purpose, a dispersing agent is used.

Those that are generally used for such dispersing agent are grossly classified into two categories, one including water soluble polymers and the other including fine powder of inorganic compounds haldly soluble in water. For example, the former category includes gelatin, starch, polyvinyl alcohol, etc.

while the latter includes fine powder of salts hardly soluble in water, such as barium sulfate, calcium sulfate, barium carbonate, calcium carbonate, magnesium caronate and calcium phosphate, inorganic high polymers, such as talc, clay, silicic acid and diatorn earth, and metal oxides.

However, even under the presence of a dispersing agent as above cited in the suspension polymerization system, it is very hard to keep fine particles of the polymerizable monomer in the stabilized state of dispersion till the polymerization reaction completes, for as the polymerization proceeds and these fine particles gain in viscosity, their sticking forces grow so much that they are no more prevented from joining even under agitation. Therefore, the polymer is produced in larger grain sizes, so any polymer powder having grain sizes preferable for use as toner becomes unavailable.

Though a method is known to add to the reaction system a dispersing agent as described above together with a type of dispersing aid such as glycol or glycerin to increase the viscosity of the medium and thereby prevent fine particles from joining or with another type of dispersing aid or electrolyte such as sodium chloride or sodium sulfate to increase the interfacial tension between water and fine particles, no remarkable effect can be achieved with it. The present invention has been made with the above background.

Accordingly, it is the primary object of the present invention to provide toner for the development of electrostatic latent images which is composed of spherically shaped polymer grains containing a coloring agent and thereby endowed with an excellent anti-offset property and shock resistance as well as favorable fluidity and keeping quality so it may always exhibit excellent developing and fixing performances.

It is another object of the present invention to provide toner for the development of electrostatic latent images which is composed of substantially spherical cross-linked polymer grains containing a coloring agent uniformly with their sizes preferably ranging from 1 to 50 u.

It is another object of the present invention to provide toner for the development of electrostatic latent images which is composed of substantially spherical polymer grains containing a coloring agent uniformly and further loaded with a polyolefin of a lower molecular weight, their grain size being within a y9ref--raLie range of 1 to 50 M for toner.

It is another object of the present invention to provide a very easy method of preparing toner for the development of electrostatic latent images composed of spherically shaped polymer grains containing a coloring agent and other additives.

It is another object of the present invention to provide a method not including any crushing and pulverizing step and yet capable of directly preparing toner for the development of electrostatic latent images, said toner having a desirable grain size.

Thus the present invention relates, more specifically, to a toner composition for electrophotography comprising (a) spherically shaped polymer grains containing a polymer which has been prepared by polymerizing a monomer which is, when dispersed in water, capable of being charged in the first polarity, in the form of aqueous suspension and in the presence of an inorganic dispersing agent which is, when dispersed in water, capable of being charged in the opposite polarity to said first polarity, and (b) a coloring agent being incorporated in said polymer grains.

According to one preferable embodiment of the present invention, above-mentioned polymerization of the monomer is conducted in the presence of a cross-linking agent.

According to one other preferable embodiment of the present invention, said polymerization is conducted in the presence of a so-called "anti-offset" agent, which can effectively prevent the occurrence of the off-set phenomenon.

According to still further preferable embodiment of the present invention, said polymerization is conducted in the presence of any mixture of above-mentioned cross-linking agent, anti-offset agent and coloring agent as well as, if necessary, other known additives for the toner, such as so-called charge controlling agent.

According to still further preferable embodiment of the present invention, said polymerization is conducted so that toner particles prepared by a method of the present invention may have an average diameter of 1 to 50 microns.

The method of preparing toner according to the present invention will be described more fully below. First, a composition for polymerization, which is capable of being charged in either positive or negative, when dispersed in water in a form of particles, is prepared. This composition which is a mixture composed of a polymerizable monomer component, and coloring agent, preferably together with a cross-linking agent for the monomer and/or an anti-offset agent, can be made chargeable in water by using an ionic monomer or a non-ionic monomer together with an ionic substance which can confer an ionic nature on said non-ionic monomer. Meanwhile, the above composition may contain a polymerization initiator for the above polymerizable monomer component and a charge control agent as additives, if necessary.Further, in case the final product is a single component type magnetic toner, a magnetic powder is added. The above polymerizable composition is put into water together with an inorganic dispersing agent that is charged to the opposite polarity to particles into which the former is dispersed, and the mixture is dispersed for suspension under agitation. Under continued agitation or after agitation, the suspended system is subjected to a condition at which the polymerizable monomer component are polymerized. Toner for the development of electrostatic latent images composed of a spherically shaped polymer grains is thus prepared.

In the above process, the agitation for the dispersion and suspension can be achieved by a homo mixer, homogenizer, or the like, which is usually driven at a rate of 1 ,000 to 6,000 r.p.m. The temperature for the polymerization is set to 55 to 1200C, though the polymerization proceeds more uniformly at lower temperatures.

As polymeric monomers that can be used in the present invention, styrene monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, -methylstyrene, p-ethylstyrene, 2,4dimethylstyrene, p-n-butylstyrene, p-tert-butylstyrene, p-n-hexylstyrene, p-n-octylstyrene, p-nnonylstyrene, p-n-decylstyrene, p-n-dodecylstyrene, p-methoxystyrene, p-phenylstyrene, pchlorostyrene and 3,4-dichlorostyrene etc. are given as a preferable one.In addition to this, ethylene unsaturated monoolefin such as ethylene, propylene, butylene and isobutylene etc., vinyl halide such as vinyl chloride, vinylidene chloride, vinyl bromide and vinyl fluoride etc., vinylester such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate etc., a-methylene aliphatic monocarboxylic acid ester such as acrylic acid methyl, acrylic acid ethyl, acrylic acid n-butyl, acrylic acid isobutyl, acrylic acid propyl, acrylic acid n-octyl, acrylic acid dodecyl, acrylic acid lauryl, acrylic acid 2-ethylhexyl, acrylic acid stearyl, acrylic acid 2-chloroethyl, acrylic acid phenyl, -chloroacrylic acid methyl, metacrylic acid methyl, metacrylic acid ethyl, metacrylic acid propyl, metacrylic acid n-butyl, metacrylic acid isobutyl, metacrylic acid n-octyl, metacrylic acid dodecyl, metacrylic acid lauryl, metacrylic acid 2-ethyl hexyl, metacryiic acid stearyl, metacrylic acid phenyl, metacrylic acid dimethyl amino ethyl and metacrylic acid diethylaminoethyl etc., acrylic acid derivative or metacrylic acid derivative such as acrylonitrile, metacrylonitrile, acryloamido etc., vinylether such as vinylmethylether, vinylethylether and vinylisobutylether etc., vinylketone such as vinylmethylketone, vinylhexylketone and methylisopropenylketone etc., N-vinyl compound such as N-vinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrolidone etc., vinylnaphthalene and others are given, for example. These monomers can be used either independently or in combination of plural monomers and further, the combination that has polymerization and gives copolymers is also possible.

In the present invention, it is preferable to effect the aforementioned polymerization in the presence of a cross-linking agent which is a compound having two or more polymerizable double bonds in it, of which examples are given as such aromatic divinyl compounds as divinyl benzene, divinyl naphthaiene and the derivatives thereof, e.g.; diethylene carboxylic acid type esters such as diethylene glycol arcylate, diethylene glycol methacrylate, triethylene glycol methacrylate, trimethylol propane triacrylate, allylmethacrylate, t-butylaminoethyl methacrylate, tetraethylene glycol dimethacrylate, 1,3butanediol dimethacrylate, ethyleneglycoi dimethacrylate, and tetramethylolmethane tetraacrylate; every divinyl compound such as N,N-divinyl aniline, divinyl ether, divinyl sulfide and divinyl sulfone; and compounds having three or more vinyl radicals; every of which can be used singly or mixedly. The mixing ratio of the cross linking agents against polymeric monomers is within the range of 0.00520% by weight, preferably 0.15% by weight.

Further in the present invention, it is preferable to use a low molecular polyolefin for the purpose of further improving the anti-offset property of the toner. As the low molecular polyolefin compound, those having relatively low melting point and a weight average molecular weight of 1 ,000 to 45,000 can be mentioned. Especially those having softening point of 100 to 1 800 C, and more preferably, 130 to 1 600C can suitably be used.

As concrete examples of such polyolefin, polyethylene, polypropylene, polybutylene or the like can be given and among these, polypropylene is particularly preferable.

In low molecular polyolefin to be used for the prevention of offset in the present invention, low molecular olefin copolymer is included. Such low molecular olefin copolymer is an olefin copolymer wherein only olefin is contained as monomer component, or is an olefin copolymer wherein the one other than olefin is contained as monomer component and the molecular weight thereof is relatively small.

Olefin as monomer component includes, ethylene, propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, nonene-1 and decene-1 and their isomer wherein the position of unsaturated bond is different for example and 3-methyl-1 -butene, 3-methyl-2-pentene, 3-propyl-5-methyl-2-hexene etc. having branch chains made of alkyl group for example and all other olefins therein.

As a monomer other than olefin that makes up copolymer together with olefin, vinylether such as vinylmethylether, vinyl-n-butylether and vinylphenylether etc. for example, vinylester such as vinylacetate and vinylbutylate for example, haloolefins such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, vinyl chloride, vinylidene chloride and tetrachloroethylene etc. for example, ester acrylate or ester methacrylate such as methylacrylate, ethylacrylate, n-butylacrylate, methylmethacrylate, ethylmethacrylate, n-butylmethacrylate, stearylmethacrylate, N,N dimethylaminoethylmethacrylate and t-butylaminoethylmethacrylate etc. for example, derivative acrylate such as acrylonitrile and N,N-dimethylacrylamide etc. for example, organic acid such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid etc., and various other compound such as diethylefumarate and -pinene can be mentioned.

Consequently, low molecular olefin copolymer that can be used in the present invention as low molecular polyolefin includes olefin copolymer made of only olefin that contains at least 2 kinds of above-mentioned olefin as monomer component, such as ethylene-propylene copolymer, ethylenebutenecopolymer, ethylene-pentene copolymer, propylene-butene copolymer, propylene-pentene copolymer, ethylene-3-methyl- 1 -butene copolymer and ethylene-propylene-butene copolymer etc. for example, or oiefin copolymer containing at least one kind of above-mentioned olefin and at least one kind of monomer other than above-mentioned olefin as monomer component such as ethylenevinylacetate copolymer, ethylene-vinylmethylether copolymer, ethylene-vinyl chloride copolymer, ethylene-methylacrylate copolymer, ethylene-methylmethacrylate copolymer, ethylene-acrylic acid copolymer, propylene-vinylacetate copolymer, propylene-vinylethylether copolymer,propylene- ethylacrylate copolymer, propylene-methacrylic acid copolymer, butene-vinylmethylether copolymer, butene-rnethylmethacrylate copolymer, pentene-vinylacetate copolymer, hexene-vinylbutylate copolymer, ethylene-propylene-vinylacetate copolymer and ethylene-vinylacetate-vinylmethylether copolymer etc. for example.

In case of olefin copolymer containing monomer other than olefin as its monomer component among low molecular olefin copolymer mentioned above, the one containing much olefin component therein is preferable. The reason for this is that in such copolymers, the releasing property is generally low, causing less effect as an offset prevention agent when the containing amount of olefin is small and there is a tendency that the characteristics such as fluidity and image forming property etc. of the toner obtained are deteriorated. Therefore, in case of aforesaid copolymers, the one containing much olefin is more desirable and particularly the one containing olefin component of more than about 50 mol% is advantageous as an offset prevention agent to be used in the present invention.

When using polyolefin having its average molecular weight of less than 1,000, the softening point of toners being obtained thereby is lowered and cohesion of toner grains is apt to occur and accordingly stains on photosensitive substance or carrier become more serious when the aforesaid toners are applied to electrophotographic process, and on the other hand, when the average molecular weight thereof is over 45,000, the softening point of toners thus obtained becomes too high, so that it is impossible to obtain an offset prevention effect successfully.

Polyolefin serving as the abovementioned offset preventive is to be used at the ratio of 1-20 parts by weight, preferably 3-15 parts by weight against 100 parts of monomers of polymerized composite. When the ratio is less than 1 part by weight, the offset prevention effect becomes insufficient and unreliable, and when over 20 parts thereof, the fluidity of the toners thus obtained will become lower.

Further in the present invention, metallic salts of fatty acids such as zinc salt, barium salt, lead salt, cobalt salt, calcium salt and magnesium salt of stearic acid; zinc salt, manganese salt, iron salt and lead salt of oleic acids; and zinc salt, cobalt salt and magnesium salt of palmitic acids; and, higher fatty acids having more than 1 7 carbon atom numbers, higher alcohols having the same as above, esters of polyhydric alcohol, natural or synthesized paraffins, fatty acid esters and the partially saponified matters thereof, alkylene bis fatty acid amido such as ethylene bis stearoylamido, and other matters effective for offset prevention, can be used jointly with the aforesaid polyolefins having a low molecular weight.

The application of the aforementioned polyolefin compound to the toner composition itself has been heretofore known, however, in the known method where polymer and coloring agent are fused and kneaded at high temperature to make a mixture, in which the coloring agent is dispersed in the polymer, and then thus prepared mixture is ground or crushed into fine powders, there is a great disadvantage that because of rather poor miscibility of the polyolefin with the polymer, it has been rather difficult to incorporate the polyolefin into the polymer at high concentration, or uniformly.

As the result of this fact, higher proportion of the polyolefin often exist on the surface of the polymer grains than in the grain, which leads to poor fluidity of the toner and which is the cause of socalled "toner-filming" phenomenon, and thereby proper development with satisfactory image quality becomes difficult. Due to such a problem it has been difficult to use the polyolefin compound in such an amount as to sufficiently prevent the off-set phenomenon. Also, this fact has made it difficult to solve so-called "twinning" problem in which the transfer paper winds around a fixing-roller.

According to the present invention, however, these disadvantages can be greatly improved since in the present invention the polyolefin compound can be incorporated at higher proportion and uniformly in the polymer grains. In this respect it is more preferable in the present invention that the low molecular polyolefin compound is made present at the time of polymerizing the monomer of the invention.

As for the coloring agents to be used for the present invention, any suitable pigment or dye may optionally be used, for example, they are given as carbon black, nigrosine dye (C.l. No. 50415B), aniline blue (C.l. No. 50405), chalcoil blue (C.l. No. azoee blue 3), chrome yellow (C.l. No. 14090), ultramarine blue (C.l. No. 77103), Du Pont oil red (C.l. No. 26105), Orient oil red #330 (C.l. No. 60505), quinoline yellow (C.l. No. 47005), methylene blue chloride (C.l. No.52015), phthalocyanine blue (C.I. No. 74160), malachite green oxalate (C.I. No. 42000), lamp black (C.l. No. 77266), rose bengal (C.l. No. 45435), oil black and azo oil black, each of which may be used singly or by mixing with each other. The coloring agents may be held in toners which are as the ultimate product, at such a ratio that the coloring agent can be held in at about 320% by weight of the toner. And in the case that magnetic powders of which are described hereinafter are to be utilized, the magnetic powders may be utilized as a coloring agent.

Further in the present invention, a so-called "single-component" type magnetic toner may also be obtainable by incorporating in the polymer component of the toner suitable magnetic substances. The magnetic substance in this invention means a substance which is capable of being strongly magnetized in a magnetic field and which has, more preferably, in black and chemically stable. In the present invention it is preferable that the magnetic substance is in the form of fine powders having the average grain size of less than 1 micron, and in the above-mentioned respects magnetite (triiron tetraoxide) is more preferable.As examples of such magnetic substances, metals such as cobalt, iron and nickel; metallic alloys or mixtures of, for example, aluminium, cobalt, copper, iron, magnesium, nickel, tin, zinc, antimony, berylium, bithmuth, cadmium, calcium, manganese, selenium, titanium, tungsten and vanadium; metallic compound including metal oxide such as aluminium oxide, iron oxide, copper oxide, nickel oxide, zinc oxide, titanium oxide and magnecium oxide; refractory nitride such as vanadium nitride and chromium nitride; carbide such as silica carbide; and ferrite and a mixture thereof can be mentioned. It is preferable that fine powders of the aforementioned magnetic substance have the average grain diameter of 0.01 to 1 micron.The magnetic substance may be incorporated into the toner at the proportion of 50 to 300 parts by weight based on 100 parts by weight of polymer component of the toner, preferably 50 to 200 parts by weight, and particularly, 90 to 1 50 parts by weight based on the polymer component of the toner.

In the present invention, the ionic substance that is used to charge the polymerizable composition to either polarity when it is dispersed in water in a form of particles may be adequately chosen from the following cationic and anionic substances: A) CATIONIC SUBSTANCES (1) Cationic Polymerizable Monomers Nitrogen containing polymerizable monomers including dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, 2hydroxy-3-acryloxypropyltrimethylaminoethyl chloride, 2-hydroxy-3 methacryloxypropyltrimethylammonium chloride, acrylamide, diacetonacrylamide, N-n butoxyacrylamide, N-vinylcarbazole, vinylpyridine, and 2-vinylimidazole.

(2) Organic Amines Hardly Soluble in Water i) Primary aliphatic amines, for example, ones having seven or more carbon atoms in their molecule, such as heptylamine, octylamine and dodecylamine.

ii) Secondary aliphatic amines, for example, ones whose boiling point is 800C or higher, such as dipropylamine, diisopropylamine, dibutylamine, diamylamine and didodecylamine.

iii) Tertiary aliphatic amines, for example, ones whose boiling point is 80"C or higher, such as triethylamine, tripropylamine, tributylamine, triamylamine, n-dodecyldimethylamine and n tetradecyldimethylamine.

iv) Aromatic amines including aniline, methylaniline, dimethylaniline, ethylaniline, diethylaniline, toluidine, dibenzylamine, tribenzylamine, diphenylamine, triphenylamine and naphthylamine.

It is noted, however, that aliphatic amines are used in an acidic aqueous medium.

B) ANIONIC SUBSTANCES (1) Anionic Polymerizable Monomers 2-acrylamido-2-methylpropanesulfonic acid, N-methylolacrylamide, acrylic acid, methacrylic acid, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate, polypropylene glycol monomethacrylate, polyethylene glycol monomethacrylate, tetrahydrofurfuryl methacrylate, and acid phosphoxyethy methacrylate, etc.

However, it is noted that the above ionic substances must be able to coexist within particles of the polymerizable monomer component formed by its dispersion into water and for this reason water soluble organic amines cannot be used for them. However, ionic polymerizable monomers, even if water soluble, are applicable since they are copolymerized to form part of polymer grains without entering the aqueous phase as the polymerization proceeds.

The polymerizable composition may be loaded with these ionic substances in a proportion of 0.1 wt-% or more and preferably 0.2 wt-% or more to its polymerizable monomer constituent. It is not necessary to impose any particular upper limit to such proportion. However, even if the proportion is raised above 5 wt-%, no additional effects are exhibited though their use at such condition is never prohibited.

For the inorganic dispersing agent used in the present invention, which is chargeable to the opposite polarity to dispersed particles of the polymerizable composition when dispersed in water, anionic colloidal silica (SiO2) and bentonite (SiO2)/(A12O3), cationic aluminium oxide (A1203), etc. may be cited.

The inorganic dispersing agent can exhibit its effect more fully in a very small quantity when a smaller grain size is used. For example, colloidal silica "Aerosil" (supplier: Degussa), whose primary grains have a means grain size of 40 to 70 m,u, shows a pH of 3.6 to 4.3 when added in water at a concentration of 4 wt-% while "Aluminium Oxide C" (supplier: Degussa), which is a product of high purity and whose primary grains are very fine 20 y in the mean grain size, has its isoelectric point at pH = 9, being used at a neutral or acidic pH. These inorganic dispersing agents are used in a proportion of 0.1 wt-% or more and preferably 0.2 wt-% or more to the polymerizable monomer component. It is not necessary to impose an upper limit to this proportion.However, even if the proportion is raised above 2 wt-%, no additional effects are exhibited in stabilizing the polymerization and making the grain size very fine though the use of such condition is never prohibited.

As for polymerizing initiators which may be used for the present invention, any of ordinary use may be utilized within appropriate temperature range. As the examples, benzoyl peroxide, 2,2'- azobisisobutylonitrile, 2,2'-azobis-(2,4-dibutylvaleronitrile), lauryl peroxide, orthochloro benzoyl peroxide and orthomethoxy benzoyl peroxide can be mentioned.

According to the present invention, therefore, when the polymerizable composition containing a monomer component and a coloring agent, preferably together with a cross-linking agent and/or antioffset agent, is dispersed in water in the form of suspension, the dispersed particles formed are charged either positive or negative at their interfaces depending on ionic nature of the monomer or the ionic substance used. Meanwhile, the inorganic dispersing agent is charged either negative or positive, namely, to the opposite polarity to the dispersed particles of the above polymerizable composition. As a result, particles of the inorganic dispersing agent is strongly bound to these dispersed particles by ionic bonds, so the surface of the latter particles is covered with the inorganic dispersing agent.At this state, the dispersed particles are very stable in water, so they do not join even when they gain in their tackiness at the initial and middle stages of the polymerization.

As described above, the inorganic dispersing agent is ionically bound to the surface of the dispersed particles of the polymerizable composition. Therefore, by contrast to the conventional dispersing agent which is just adsorbed on, the surface of dispersed particles or present between them to prevent them from rejoining the present dispersing agent sticks inseparably to the surface of the dispersed particles by stronger forces, so once it sticks to the surface, it does not separate from that surface. Further, since the whole surface of the dispersed particles are coated with the agent, these particles are fully prevented from joining throughout the polymerization.

Beside, since dispersed particles, once formed, do not join at all as mentioned above, a mechanical agitation of the polymerizable composition in water to disperse into fine particles positively gives polymer grains having a desirable grain size for toner, namely, between 1 and 50,u. The dispersion of the polymerizable composition into particles may be effected immediately before or simultaneously at the start of the polymerization since the dispersed phase will be maintained almost as it is throughout the polymerization. Toner of a desirable grain size can be prepared by using a shearing force between 103 to 106 dyne/cm2 in the above agitation.

Also in the present invention, the polymerization can be effected under either ordinary or high pressure.

Though the scope of the present invention is never limited theoretically, the mechanism of the chemical stabilization of dispersed particles as mentioned above could be explained as follows: (1) Both bentonite (SiO2/AI203) and silica contain silanol groups, though in very small quantities, which dissociate into SiO- group and H+ ions. Namely, bentonite and colloidal silica are anionic dispersing agents that are charged negative in water. Therefore, they are ionically strongly bound to the dispersed particles of the polymerizable composition that are charged positive in the same aqueous medium due to a cationic polymerizable monomer or the like so the surface of dispersed particles is fully covered while the inorganic dispersing agent that adheres to such form a layer of hydration around these particles for the remarkable stabilization thereof.Therefore dispersed particles are prevented from rejoining even when the monomer component gets tackier at the initial and middle stages of its polymerization.

(2) Aluminium oxide (Al203) has its isoelectric point at pH = 9, being a cationic dispersing agent that is charged positive at a neutral or acidic pH. Therefore, it is ionically bound to dispersed particles of the polymerizable composition that are charged negative.

A fact that the above dispersed particles of the polymerizable composition are so constructed that the inorganic dispersing agent is strongly bound to their surface has been proved by observing the electrophoretic behavior of these particles. Namely, it was found that in case an anionic inorganic dispersing agent is used, the sample shows an electrophoretic move toward the anode, indicating the negative charging of the electrophoretic surface of the particles (or the surface of these particles as they are dried). In contrast, in case a cationic inorganic dispersing agent is used, the sample shows an electrophoretic move towards the cathode, indicating the positive charging of the electrophoretic surface of the particles.

The dispersed particles of the polymerizable composition that are formed by the mechanical agitation are stabilized as described above while the polymerizable monomer component contained therein is polymerized. As a result, polymer particles as obtained upon completion of the polymerization are individually spherical in shape and uniform in the distribution of their grain size, being practically applicable as it is for toner.

According to the present invention, therefore, toner that contains necessary components is made available practically by a single-step process that does not include any crushing and polverizing step or any complicated process step.

Further according to the present invention the following technical advantages will be attainable.

(1) Owing to the spherical shape of the toner particles, the toner shows improved fluidity.

(2) Because of uniform presence of the low molecular polyolefin in the toner particles improved anti-offset and anti-winding properties are obtainable to the toner.

(3) Owing to the round shape of the toner particles and by the effect of the cross-linking agent.

The toner particles are less liable to be pulverized by agitation; the deterioration of carrier or photoconductive plate will effectively be prevented.

(4) Toner having improved moistureproof characteristics and, therefore, improved storability can be obtained.

The present invention is further illustrated with reference to the following examples, in which it is noted that the term "parts by weight" is abbreviated by "parts".

EXAMPLE 1 [Composition for Polymerization] Styrene 300 parts Ferrosoferric oxide powder "Mapico Black BL-500" 200 parts (Supplier: Titan Kogyo K.K.) Methylene blue chloride (charge controlling agent) 1 part Diethylaminoethyl methacrylate 1.5 parts Benzoyl peroxide 1 part A composition for polymerization was prepared as shown above. Meanwhile, 1.5 parts of colloidal silica "Aerosil 200" (Supplier: Degussa) was put into a 2 liter separable flask and distilled water was added thereto.Then the above composition was added to the solution and the mixture was heated up to 900C and kept at this temperature under agitation using an agitator "Micro Atitor" (Supplier: Shimazu Seisakusho) driven at a rate 1000 r.p.m. 1 5 minutes after temperature reached 900 C, the size of the dispersed particles was found to range from 1 5 to 20 microns. A polymerization reaction was thus conducted for 6 hours, but no substantial change in the size of the particles was observed till the end of the polymerization reaction. After the completion of the polymerization, solid grains were separated by filtration and dried to give toner for single component type developer, having an average grain size of 1 7 microns. This toner is hereinafter referred to as Sample 1.

EXAMPLE 2 Toner was prepared in the same manner as Example 1 except that, in this example, 2.0 parts of triethylene glycol methacrylate had been added to the composition for polymerization of Example 1.

This toner is herein referred to as Sample 2.

EXAMPLE 3 Toner was prepared in the same manner as Example 1 except that, in this example, a mixed solution prepared by adding 1 5 parts of a lower molecular weight polypropylene "VISCOL 550P" (Supplier: Sanyo Kasei Co., Ltd.) to 300 parts of styrene and heating the mixture at 1 500C under agitation was used instead of 300 parts of styrene in Example 1. This toner is herein referred to as Sample 3.

EXAMPLE 4 Toner (Sample 4) was prepared in the same manner as Example 3 except that, in this example, 2.0 parts of triethylene glycol methacrylate had been added to the composition of Example 3.

EXAMPLE 5 Toner (Sample 5) having an average grain size of 1 7 microns was prepared in the same manner as Example 2 except that, in this example, 200 parts of "Mapico Black BL- 100" (Supplier: Titan Kogyo K.K.), 300 parts of methyl methacrylate, 0.5 parts of tetramethylolmethane tetraacrylate, 2 parts of N-nbutoxyacrylamide and 2 parts of colloidal silica "Aerosil 380" (Supplier: Degussa) were used for the ferrosoferric oxide powder, olymerizable monomer component, cross-linking agent, ionic substance and dispersing agent respectively.

EXAMPLE 6 Toner (Sample 6) was prepared in the same manner as Example 5 except that, in this example, the same stylene-polypropylene mixture used in Example 3 was used instead of 300 parts of styrene in Example 5, and 0.5 parts of tetramethlolmethane tetraacrylate was omitted from the composition of Example 5.

EXAMPLE 7 Toner (Sample 7) was prepared in the same manner as Example 6 except that, in this example, 0.5 parts of tetramethylolmethane tetraacrylate had been added to the composition of Example 6.

EXAMPLE 8 Toner (Sample 8) was prepared in the same manner as Example 2 except that in this example, 100 parts of "Mapico Black BL-100' and 100 parts of "Mapico Black BL-500" were used for ferrosoferric oxide powder, 250 parts of styrene and 50 parts of n-butyl methacrylate for the polymerizable monomer component, 4 parts of diethylaminoethyl methacrylate for the ionic substance, 2 parts of triethylene glycol methacrylate for the cross-linking agent and 4 parts of colloidal silica for the inorganic dispersing agent.

EXAMPLE 9 Toner (Sample 9) was prepared in the same manner as Example 8 except that, in this example, as polymerizable monomer component, 220 parts of styrene and 80 parts of n-butyl methacrylate, as the inorganic ionic substance 4 parts of colloidal silica "Aerosil 200" was used and as the low molecular polyolefin compound 10 parts of polypropylene "VISCOL 550P" had been added thereto but tryethylene glycol methacrylate was omitted from the composition.

EXAMPLE 10 Toner (Sample 9) was prepared in the same manner as Example 9 except that, in this example, 2 parts of ethylene glycol methacrylate had been added to the composition of Example 9.

EXAMPLE 11 [Composition for Polymerization] Methyl methacrylate 250 parts Ferrosoferric oxide powder "Mapico Black BL-l 00" 150 parts Ferrosoferric oxide powder "Toda Color EPT-1000" 100 parts (Supplier: Toda Kogyo) Nigrosine base "EX" -- charge control agent 0.5 parts (Supplier: Orient Chemical Industries) Dicocoamine 3 parts Azobisisobutyronitrile 1 part A composition for polymerization was prepared in the above formulation. Meanwhile, 3 parts of colloidal silica "Aerosil Mox 170" (Supplier: Degussa) were put into a 2 liter separable flask and distilled water was added thereto.The above polymerizable composition was added to the solution and the mixture was heated up to 800C and kept at this temperature under agitation using an agitator "TK Homomixer" (Supplier: Tokushu Kika Kogyo) driven at a rate of 3,000 r.p.m. 30 minutes after the temperature was elevated, the size of the dispersed particles was found to range from 10 to 15 microns.

Thereafter, a polymerization reaction of 6 hours was conducted under agitation using an ordinary agitator driven at a rate of 100 r.p.m. to complete the polymerization, when no change was observed in the size of these particles. After the completion of polymerization, solid grains were separated by filtration and dried to give a single component type toner having a mean grain size of 1 3 microns.

"Sample 11" was thus prepared.

EXAMPLE 12 Another single component type toner (Sample 12) having an average size of 13 microns was prepared by repeating the same procedure as in Example 11 except that 2.0 parts of cross-linking agent, trimethylolpropane trimethacrylate, had been added to the composition thereof.

EXAMPLE 13 Toner (Sample 13) was prepared in the same manner as Example 11 except that, in this example a mixed solution prepared by adding 10 parts lower molecular weight polyolefin "VISCOL 550P" to 250 parts of methyl methacrylate and heating the mixture for processing at 1 5000 under agitation was used instead of 250 parts of methyl methacrylate of Example 11.

EXAMPLE 14 Toner (Sample 14) was prepared in the same manner as Example 13 except that, in this example, 2.0 parts of triethylenepropane methacrylate had been added to the composition.

EXAMPLE 1 5 Another single component type toner (Sample 1 5) also having a mean grain size of 13 microns or was prepared by repeating the same procedure as in Example 12 except that in this example, 250 parts of "Toda Color EPT-1000" for the ferrosoferric oxide, 200 parts of methyl methacrylate and 50 parts of n-butyl methacrylate for the polymerizable monomer component, 3 parts of diethylene glycol methacrylate for the cross-linking agent, 1.5 parts of dodecylamine for the ionic substance- and 1.5 parts of colloidal silica "Aerosil 200" for the agent were used instead of the respective components agent of the composition of Example 12.

EXAMPLE 16 Toner (Sample 16) was prepared in the same manner as Example 1 5 except that, in this example, 160 parts of methyl methacrylate and 90 parts of n-butyl methacrylate for the polymerizable monomer component and 40 parts of polypropylene "Viscol 550P" was added to and the cross-linking agent was omitted from the composition.

EXAMPLE 17 Another toner (Sample 1 7) was prepared in the same manner as Example 1 6 except that, in this example, the same cross-linking agent in the same amount as in Example 15 was added to the composition.

EXAMPLE 18 Another single component type toner (Sample 18) also having an average grain size of 13 microns was prepared in the same manner as Example 12 except that in this example, 100 parts of "Mapico Black BL-500" and 1 50 parts of "Toda Colour EPT-1000" were used for the ferrosoferric oxide powder, 225 parts of styrene and 25 parts of methyl acrylate for the polymerizable monomer, and 30 parts of trimethylolpropane for the cross-linking agent, 5 parts of dimethylaminoethyl methacrylate for the ionic substance and 5 parts of colloidal silica "Aerosil Mox 170" for the inorganic dispersing agent were used instead of the respective component of the composition of Example 12.

EXAMPLE 1 9 Another single component type toner (Sample 19) was prepared in the same manner as Example 1 8 except that in this example 240 parts of styrene and 10 parts of methyl acrylate was used for the polymerizable monomer component, 20 parts of polypropylene "Viscol 550P" for the low molecular weight polyolefin was added to and the cross-linking agent was omitted from the composition.

EXAMPLE 20 Another single component type toner (Sample 20) was prepared in the same manner as Example 1 9 except that in this example, 30 parts of trimethylolpropane triacrylate for the cross-linking agent had been added to the composition.

EXAMPLE 21 [Composition for Polymerization] Styrene 400 parts Methyl methacrylate 50 parts n-butyl methacrylate 50 parts "Carbon Black MA-600" (Supplier: Mitsubishi Chemical Industries) 1 5 parts "Azo Oil Black (R)" -Charge Control Agent 1 part (Supplier: National Aniline, Inc.) Dodecylamine 2 parts Lauroyl peroxide 2 parts A composition for polymerization was prepared in the above formulation. Meanwhile, 2 parts of colloidal silica "Aerosil 380" was put into a 2 liter separable flask and distilled water was added thereto.

The above composition was then added to the solution and the mixture was heated up to 800C and kept at this temperature under agitation using a Micro Agitor driven at a rate of 1000 r.p.m. 15 minutes after the temperature was elevated, the size of the dispersed particles was found to range from 1 5 to 20 microns. A polymerization reaction of 6 hours was thus conducted but no change in the size of these particles till the completion of polymerization was observed. After the polymerization, solid grains were separated by filtration and dried to give toner for two component type developer having an average grain size of 17 microns. Sample 21 was thus prepared.

EXAMPLE 22 A two-component type toner (Sample 22) was prepared in the same manner as Example 21 except that, in this example, 25 parts of diethylene glycol methacrylate for the cross-linking agent had been added to the composition thereof.

EXAMPLE 23 Toner (Sample 23) was prepared in the same manner as Example 21 except that, in this example, instead of the polymerizable monomer component (styren, methyl methacrylate and n-butylmethacrylate) a mixture prepared by adding 30 parts of lower molecular weight polypropylene "Viscol 550P" to a mixture of 400 parts of styrene, 50 parts of methyl methacrylate and 50 parts of n-butyl methacrylate and heating the resultant mixture for processing at 1 5000 under agitation was used.

EXAMPLE 24 Toner (Sample 24) was prepared in the same manner as Example 23 except that, in this example, 25 parts of diethylene glycol methacrylate had been added to the composition thereof.

EXAMPLE 25 Another two component type toner (Sample 25) was prepared in the same manner as Example 21 except that, in this example, 40 parts of "Raven 1250" (Supplier: Colombian) was used for the carbon black, 400 parts of styrene, 50 parts of methyl methacrylate, and 10 parts of triethylene glycol methacrylate for the cross-linking agent, 3 parts of methacrylic acid for the ionic substance, and 3 parts of "Aluminium Oxide C" (Supplier: Degussa) for the inorganic dispersing agent were used instead of respective components for the composition of Example 22.

EXAMPLE 26 Another two component type toner (Sample 26) was prepared in the same manner as Example 25 except that, in this example, 40 parts of polypropylene "Viscol 550P" for the low molecular polyolefin was added to and 2 parts of triethylene glycol was omitted from the composition thereof.

EXAMPLE 27 Another two component type toner (Sample 27) was prepared in the same manner as in Example 26 except that in this example, 2 parts of triethylene glycol methacrylate for the cross-linking agent had been added to the composition thereof.

EXAMPLE 28 Another two component type toner (Sample 28) was prepared in the same manner as Example 22 except that in this example 20 parts of "Monarch 1100" (Supplier: Gabbot) was used for the carbon black, 450 parts of styrene, 40 parts of r-butyl methacrylate and 10 parts of n-butyl acrylate for the polymerizable monomer component, and 20 parts of tetramethylolmethane tetraacrylate for the cross linking agent, 5 parts of colloidal silica "Aerosil 200" for the inorganic dispersing agent were used instead of the respective components of the composition thereof.

EXAMPLE 29 Another two component type toner (Sample 29) was prepared in the same manner as Example 28 except that in this example, 25 parts of "Viscol 550P" for the low molecular polyolefin was added to and the cross-linking agent (2 parts of triethylene glycol methacrylate) was omitted from the compostion thereof.

EXAMPLE 30 Another two component type toner (Sample 30) was prepared in the same manner as Example 29 except that in this example, 20 parts of tetramethylolmethane tetraacrylate for the cross-linking agent had been added to the composition thereof.

EXAMPLE 31 [Composition for Polymerization] Styrene 450 parts n-butyl acrylate 50 parts "Carbon Black #2300" (Supplier: Mitsubishi Chemical Industries) 25 parts "Oil Black BW" - charge control agent 0.5 parts (Supplier: Orient Chemical Industries) Diethylaminoethyl methacrylate 4 parts 2,2'-azobis-(2,4-dimethylvaleronitri le) 2 parts A composition for polymerization was prepared in the above formulation. Meanwhile, 4 parts of colloidal silica "Aerosil 200" were put into a 2 liter separable flask and distilled water was added thereto.The above composition was then added to the solution and the resultant mixture was heated up to 650C and kept at this temperature under agitation using a TK Homo Mixer (Supplier: Tokushu Kika Kpgyo, Inc.) driven at a rate of 3000 r.p.m. 30 minutes after the temperature was elevated, the size of dispersed particles was found to range from 10 to 1 5 microns. Thereafter, a polymerization reaction was conducted for 6 hours, a polymerization reaction was conducted for 6 hours under agitation using an ordinary agitator driven at a rate of 100 r.p.m. After the completion of the polymerization, no change in the size of these particles was observed. After the completion of the polymerization, solid grains were separated by filtration and dried to give a two component type toner having an average grain size of 13 microns. Sample 31 was thus prepared.

EXAMPLE 32 Another two component type toner (Sample 32) was prepared in the manner as Example 31 except that in this example 2.5 parts of trimethylolpropane triacrylate for the cross-linking agent had been added to the composition thereof.

EXAMPLE 33 Toner (Sample 33) was prepared in the same manner as Example 32 except that, in this example, a mixture prepared by adding 25 parts of lower molecular weight polypropylene "Viscol 550P" to a mixture of 450 parts of styrene and 50 parts of n-butyl acrylate and heating the resultant mixture for processing at 1 500C under agitation was used instead of the polymerizable monomer components of the composition thereof and trimethylolpropane triacrylate (cross-linking agent) had been omitted therefrom.

EXAMPLE 34 Toner (Sample 34) was prepared in the same manner as Example 33 except that, in this example, 2.5 parts of trimethylolpropane triacrylate had been added to the composition thereof.

COMPARATIVE EXAMPLE Cross-linked polymer grains having an average grain size of 1 7 microns were prepared in the same manner as Example 22 except that, in this comparative example, the carbon black and charge control agent were omitted from the formulation of the composition for polymerization. A mixture of 100 parts of these cross-linked polymer grains, 3 parts of "Carbon Black MA-600" and 0.2 parts of charge control agent "Azo Oil Black (R)" was then fused and kneaded. The resultant lump was crushed and pulverized.

The powder thus made available was classified to give a two component type toner having an average grain size of 7 microns. Comparative Sample was thus prepared.

Using thus prepared Sample toners 1 to 34 and Comparative Sample, the following tests were conducted.

1) An offset test (with respect of Sample 1 to 20): First, in the offset test, individual samples were used to develop electrostatic latent images formed with a PPC "U-Bix T" unit (Supplier: Konishiroku Photo Industry) and toner images thus made available were transferred to copy papers of 64 g/m2. The transferred toner images were fixed on the papers by passing the papers and images through a fixing unit composed of a pair of rollers, or a hot roller whose surface was coated with teflon (tetrafluoroethylene supplied by Du Pont) and a pressure roll whose surface was coated with silicon rubber "KE-1300 RTV" (Supplier: Shinetsu Chemical Industry), at a linear speed of 1 50 mm/sec. After fixing of individual toner images, some plain copy papers were treated by the same method under the same condition to see if their surface got soiled due to offset phenomena.The above test procedures were repeated by setting the temperature of the above hot roll to various levels to determine the temperature at which offset phenomena appeared. The results are shown in Table 1.

TABLE 1 Offset Occurring Sample No. Temperature (OC) 1 130 2 200 3 190 4 240 5 200 6 190 7 240 8 200 9 190 10 240 11 125 12 200 13 190 14 240 15 200 16 190 17 240 18 200 19 190 20 240 As shown in Table 1, the incorporation of the cross-linking agent and/or low molecular weight polyolefin improves the anti-offset property of the sample.

2) A winding test (with respect of Sample 3,4, 6, 7, 9, 10, 13, 14, 16, 17, 19 and 20): Further, the same device and copy papers were used under the same conditions as in the offset test to form and fix a 3 cm wide strip of black toner image toward the leading edge of individual copy papers with the temperature of the fixing unit set to various levels so as to determine the minimum of temperatures at which winding of copy papers do not occur.

As a result to all the Samples No. winding occurred above 1700 C.

3) An offset test (with respect to Samples 21 to 34).

In this test, the same procedure as in 1) was applied except that a ccp "U-Bix V" (Supplier: Konishiroku Photo Industry Co., Ltd.) unit was used in the test and 5 parts of each test sample was mixed with 95 parts of iron powder carrier to prepare a developer.

Results of the test is shown in Table 2.

TABLE 2 Offset Occurring Sample No. Temperature (OC) 21 130 22 200 23 190 24 240 25 200 26 190 27 240 28 200 29 190 30 240 31 135 32 200 33 190 34 240 As clearly understood from Table 2, similar results as those of Samples 1 to 20 were obtained with respect to the toner for two component type developer.

4) Further, in the same manner as in 1) except that the same developers and CCP unit as in the 3) the winding test was conducted with respect to Samples 23, 24, 26, 27, 29, 30, 33 and 34.

As a result, no winding failure was observed to all the samples when the temperature of hot roller was set above 1 700C or higher.

5) A fluidity test (with respect to Samples 21 to 34 and Comparative Sample): Further, in the fluidity test, 50 g of individual Samples and Controls was taken to estimate the time for it to drop a prescribed distance by a powder tester (Supplier: Hosokawa Tekkosho). Results are given in Table 3. These results indicated including the crushing and pulverizing step showed a remarkably low fluidity since its toner grains were not spherical.

6) A copy test (with respect to Samples 1 to 34 and Comparative Sample): In this test, Samples 1 to 34 gave sharp and excellent copy images and even in the 20,000th copy, there was no sign of toner soiling was observed with both on the hot roller fixing unit and on the photoconductor and the copy image was as good as that of the first copy. In contrast thereto when the Comparative Sample was used, copy images were soiled in a so-called "sweeped pattern" and in the 1,000th copy and there observed substantial grey background in copy images and the hot roller too, was found soiled and the photoconductor showed toner filming.

TABLE 3 Sample No. Drop Time (sec.) 21 25.8 22 25.5 23 25.8 24 26.0 25 26.8 26 26.2 27 26.4 28 25.2 29 25.6 30 25.4 31 27.1 32 27.2 33 26.6 34 26.8 Comparative 35.0

Claims (24)

1. A toner composition for electrophotography which comprises (a) spherically shaped polymer grains containing a polymer which has been prepared by polymerizing an aqueous suspension of a monomer which is, when dispersed in water, capable of being charged in a first polarity, in the presence of an inorganic dispersing agent which is, when dispersed in water, capable of being charged in the opposite polarity to said first polarity, and (b) a coloring agent incorporated in said polymer grains.

2. A toner composition as claimed in Claim 1, wherein the polymer grains have been obtained by polymerizing the monomer in the presence of a cross-linking agent.

3. A toner composition as claimed in Claim 1 or 2 wherein the polymer grains have been obtained by polymerizing the monomer in the presence of a low molecular polyolefin having a weight average molecular weight of 1,000 to 45,000.

4. A toner composition as claimed in any preceding Claim wherein the polymer grains have an average diameter of 1 to 50 microns.

5. A toner composition as claimed in any preceding Claim wherein the polymer grains are charged to the first polarity by incorporating a cationic or anionic substance in the polymerizable mixture.

6. A toner composition as claimed in Claim 5 wherein the cationic substance is a cationic polymerizable monomer or an organic amine that is sparingly soluble in water.

7. A toner composition as claimed in Claim 5 wherein the anionic substance is an anionic polymerizable monomer.

8. A toner composition as claimed in any of Claims 1 to 6 wherein the inorganic dispersing agent is anionic colloidal silica or bentonite.

9. A toner composition as claimed in any of Claims 1 to 5 or 7 wherein the inorganic dispersing agent is cationic aluminium oxide.

10. A toner composition as claimed in Claim 1 and substantially as hereinbefore described with reference to any of Examples 1 to 34.

11. A method for manufacturing a toner composition for electrophotography which comprises polymerizing an aqueous suspension of a monomer which is, when dispersed in water, capable of being charged in a first polarity, in the presence of an inorganic dispersing agent which is, when dispersed in water, capable of being charged in the opposite polarity to said first polarity.

12. A method as claimed in Claim 11, wherein polymerization is effected in the presence of a cross-linking agent.

1 3. A method as claimed in Claim 12, wherein the cross-linking agent is present in an amount of 0.005 to 20 percent by weight based on said monomer.

14. A method as claimed in any of Claims 11 to 13, wherein polymerization is effected in the presence of a low molecular polyolefin having weight average molecular weight of 1,000 to 45,000.

1 5. A method as claimed in Claim 14, wherein the low molecular polyolefin is present in an amount of 1 to 20 percent by weight based on said monomer.

16. A method as claimed in any of Claims 11 to 1 5, wherein the aqueous suspension is formed with agitation at a shearing force of 103 to 106 dyn/cm2.

1 7. A method as claimed in Claim 16, wherein the agitation is effected at the initial stage of polymerization.

18. A method as claimed in any of Claims 11 to 17, wherein polymerization is effected in the presence of a coloring agent.

19. A method as claimed in any of Claims 11 to 18, wherein the polymer grains are charged to the first polarity by incorporating a cationic or anionic substance in the polymerizable mixture.

20. A method as claimed in Claim 19, wherein the cationic substance is a cationic polymerizable monomer or an organic amine that is sparingly soluble in water.

21. A method as claimed in Claim 19, wherein the anionic substance is an anionic polymerizable monomer.

22. A method as claimed in any of Claims 11 to 20, wherein the inorganic dispersing agent is anionic colloidal silica or bentonite.

23. A method as claimed in any of Claims 11 to 19 or 21, wherein the inorganic dispersing agent is cationic aluminium oxide.

24. A toner as claimed in Claim 11 and substantially as hereinbefore described with reference to any of Examples 1 to 34.