GB1586137A

GB1586137A - Electrophotographic developer

Info

Publication number: GB1586137A
Application number: GB25060/78A
Authority: GB
Original assignee: Mita Industrial Co Ltd
Current assignee: Kyocera Mita Industrial Co Ltd
Priority date: 1977-07-01
Filing date: 1978-05-31
Publication date: 1981-03-18
Also published as: NL185962B; JPS5413342A; FR2396338B1; JPS5748781B2; IT1098351B; NL185962C; IT7825242A0; NL7807145A; FR2396338A1; DE2828890C2; DE2828890A1

Description

(54) ELECTROPHOTOGRAPHIC DEVELOPER (71) We, MITA INDUSTRIAL COMPANY LIMITED, a Japanese Body Corporate of 5, Miyabayashi-cho, Higashi-ku, Osaka. Japan do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a toner for use in electrophotography. More particularly. the invention relates to a two-component type developer for electrophotography in which substantially all of toner particles are controlled so as to have a positive charge polarity and which has excellent stability and charge durabilitv characteristics.

The two-component type developer of this invention is advantageously used for developing an electrostatic latent image formed by known means on a photosensitive surface for the electrophotography using a magnetic brush, transferring an image of toner particles on the photosensitive surface to a transfer sheet (copving paper) and cleaning the photosensitive surface after the transfer by attracting the toner particles left on the photosensitive surface by the magnetic brush.

In an electrophotographic process using a photosensitive laver comprising a photoconductor such as photoconductive zinc oxide dispersed in an electrically insulating binder medium, the surface of the photosensitive layer is uniformly negativelv charged by corona discharge, the charged photosensitive surface is then exposed to actinic rays imagewise to form a negatively charged electrostatic latent image. and finally. the electrostatic image is developed to a visible positive image by using toner particles. As means for developing electrostatic latent images with toner particles. there are known various methods such as the cascade method, the magnetic brush method and the wet developing method. In order to convert the negativelv charged electrostatic latent images to positive visible images. it is indispensable that the toner particles should be uniformly positively charged.

As an electrophotographic process in which a toner image is transferred onto a plain paper, thexe is known a method in which magnetic brushes are used for both the development and the cleaning of the photosensitive surface bv removal of toner particles.

According to this known method. bv blending toner particles with a magnetic carrier such as iron powder. there is formed a mixture in which the toner particles are positivelv charged and the magnetic carrier is negatively charged. and a magnetic brush composed of this mixture is caused to having sliding contact with a photosensitive surface having an electrostatic latent image formed thereon. whereby a visible image is formed. It is known that this magnetic brush is used for not onlv the development but also cleaning of the photosensitive surface.According to this known technique. a photosensitive surface on which a toner imager has been formed according to the above-mentioned method is caused to fall in contact with a transfer sheet (copying paper). the toner image is transferred onto the transfer sheet bv charging the toner image on the transfer sheet is fixed under application of heat or pressure. the photosensitive surface after the tranfer is caused to fall in contact with the magnetic brush again and the photosensitive surface is cleaned by attracting the toner left on the photosensitive surface bv the magnetic brush.

This method in which the magnetic brush is used for development and cleaning is advantageous in that any particular cleaning zone need not be provided along the moving passage of the photosensitive surface and the toner left on the photosensitive surface can be utilized again for development without scattering thereof. However. in this method. electric characteristics of the toner to be used are limited. First of all. it is required that toner particles to be used should be positively charged strongly and uniformly. Further, in order for toner particles left on the photosensitive surface to be effectively attracted to the magnetic brush, it is required that even after the transfer of the toner image, all the toner particles should be positively charged uniformly for a relatively long time.If the charge is lost even on parts of the toner particles, complete removal of the residual toner becomes impossible, resulting in insufficient charging or exposure of the photosensitive surface and contamination of the background. As a result, it is difficult to form clear and sharp copied images.

As means for controlling the charge polarity of toner particles ot a positive polarity, there is known a method in which an oil-soluble dye as a charge controlling agent (triboelectricity controlling agent) is incorporated in a binder medium constituting the toner particles.

However, oil-soluble dyes which are used as the charge controlling agents are difficult to disperse or dissolve completely or uniformly in the binder resin medium, and therefore, when these oil-soluble dyes are used as the charge controlling agents, it is difficult to control the charge polarity of toner particles so that they have a positive polarity uniformly and to maintain this positive polarity stably for a long time in the toner particles. Accordingly, because of these defects known toners comprising an oil-soluble dye as the charge controlling agent cannot be practically applied to the electrostatic photographic process in which cleaning is performed by magnetic brush, though they may be used for the electrostatic photographic process in which such cleaning mechanism as a fur brush is employed.The defect of insufficient dispersion or dissolution of a charge controlling agent composed of an oil-soluble dye is especially conspicuous when an offset an offsetpreventing agent (parting agent) such as a low-molecular-weight olefin resin is incorporated into a binder resin medium for toner particles.

There has recently been proposed a positively charged toner comprising a 2-vinylpyridine copolymer or a blend thereof with other compatible polymer, in which the 2-vinylpyridine is present in an amount of 5 to 25% by weight based on the total binder (see Japanese Patent Publication No. 27598/76).

This 2-vinylpyridine copolymer is excellent in the property of controlling the charge polarity of toner particles so that they are uniformly positively charged. However, this copolymer is still insufficient in the following points.

When this known 2-vinylpyridine copolymer is used at such a concentration as will enable the magnetic brush to perform the cleaning operation, blocking (cohesion) of toner particles becomes conspicuous because of inherent characteristics of the 2-vinylpyridine copolymer, and therefore, the efficiency of the developing operation is reduced and the development becomes impossible when the toner is used for a long time. Moreover. the heat resistance of this known copolymer is poor and therefore, if the copolymer is incorporated in a large amount, the heat resistance and durability of toner particles are drastically degraded.

As means for eliminating these disadvantages. there may be considered a method in which the content of the 2-vinvlpyridine copolymer in toner particles is reduced. However, since the stability and durability of the charge characteristics of toner particles are significantly influenced by the 2-vinylpyridine content in the toner, it has been confirmed that if the amount of the copolymer is reduced to a level not causing the above problems of the blocking phenomenon and the insufficient heat resistance. complete removal of residual toner particles for cleaning by the magnetic brush is difficult and substantially impossible.

We found that a copolymer of a nitrogen-containing heterocyclic vinyl compound such as 2-vinylpyridine is especially excellent in the property of dissolving or dispersing an oil-soluble dye in other thermoplastic resins and that when this copolymer is incorporated in combination with an oil-soluble dye as a charge controlling agent into toner particles. the positive charge characteristics of the toner particles are synergistically increased and if the resulting developer is used. cleaning by a magnetic brush can be accomplished very effectively.

In accordance with this invention. there are provided toner particles for use in electrophotographv. which particles are positively chargeable and comprise a coloring agent. a binder resin and. as charge controlling agent. and oil-soluble dye and a copolymer resin derived from a nitrogen-containing heterocvclic vinyl compound. the copolymer resin being present in an amount of ().2 to 1()C/e by weight. preferably ().5 to A.56/c by weight, as the nitlogen-containint heterocyclic vinyl compound based on the total amount of resins in the toner particles and the oil-soluble dye being present in an amount of I to 7C/c by weight.

preferably 1.5 to 5% bv weight. based on the total amount of resins in the toner particles.

As the nitrogen-containing heterocyclic vinyl compound for use in preparing the copolymer resin of the charge-controlling agent. there can be mentioned a known nitroeen-containing heterocyclic compound having one hydrogen atom substituted by an ethylnically unsaturated group. especially a monomer represented by the following general formula:

wherein Rl represents hydrogen or alkyl of up to 4 carbon atoms (hereinafter referred to as "lower alkyl group") and Y represents a nitrogen-containing heterocyclic residue.

As specific examples of such vinyl monomer, there can be mentioned 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, 2-isopropenylpyridine, 3-isopropenylpyridine 2vinylquinoline, 2-isopropenylquinoline, 2-vinylthiazole, vinylcarbazole, vinylsuccinic imide, vinylphthalic imide, vinyl-el-caprolactam and vinylpyrrolidone. Among these monomers, vinylpyridines, especially 2-vinylpyridine, are preferred.

The nitrogen-containing heterocyclic vinyl compound is copolymerised with at least one other ethylenically unsaturated monomer copolymerizable therewith to provide the copolymer resin. As such comonomer, there can be mentioned, for example. aromatic vinyl compounds such as styrene, a-methylstyrene and vinyl-toluene, vinyl halides such as vinyl chloride, vinylidene chloride and vinyl fluoride, vinyl esters such as vinyl formate, vinyl acetate and vinyl propionate. acrylic monomers such as acrylic acid. methacrylic acid, maleic anhydride, fumaric acid, itaconic acid, acrylonitrile. methacrylonitrile, acrylamide, methyl acrylate, ethyl acrylate. 2-ethylhexyl acrylate, monoethyl maleate. methyl methacrylate and 2-ethylhexyl methacrylate. vinyl ethers such as methyl vinyl ether and ethvl vinyl ether. vinyl ketones such as methylvinyl ketone and methylisopropenyl ketone. and monoand di-olefins such as ethylene. propylene and butadiene. These comonomers may be used singly or in the form of a mixture of two or more of them. Aromatic vinyl monomers and acrylic monomers are especially preferred.

From the viewpoint of the fixing property of toner particles. it is preferred that the monomer composition and molecular weight of the copolymer resin that is used in the charge controlling agent be determined so that the softening point of the copolymer is 70 to 1800C.. especially 80 to 160 C.. as measured according to the method of JIS 2531-1960. As regards the monomer composition in the copolymer it is preferred that the amount of the nitrogen-containing heterocyclic vinyl compound is 1 to 40% by weight. especiallv 5 to 25% by weight. based on the copolymer. though the preferred monomer composition differs to some extent according to the kind of the copolymer.

It is preferred that the weight average molecular weight of the copolymer resin that is used in the charge controlling agent be 5.000 to 100.000. especially 20.000 to 50.000.

Any known oil-soluble dye capable of controlling the charge polarity of toner particles to a positive polarity can be used in this invention. Preferablv these oil-soluble dyes have a primary. secondary or tertiary amino group or a quaternary ammonium group and they are basic dyes.

Suitable examples of the oil-soluble dyes include Oleosol Blue G (C.l. Solvent Blue 11).

Oriental Oil Blue K (C. I. Solvent Blue 12). Orient Oil Blue BO (C. I. Solvent Blue 25).

Sudan Blue II (C. I. Solvent Blue 35). Sumiplast Blue OA (C. I. Solvent Blue 36). Zapon Fast Blue FLE (C. I. Solvent Blue 55). Aizen Spilon Blue (C. I. Solvent Blue 73).

Sumiplast Green G (C. I. Solvent Green 3). Orient Oil Black HBB (C. I. Solvent Black 3).

Nigrosine Base (C. I. Solvent Black 7. Aizen Spilon Black BH (C. I. Solvent Black 22).

Aizen Spilon Black GSH (C. I. Solvent Black 23). Victoria Blue (C. I. Solvent Blue 2).

Orient Oil Yellow GG (C. I. Solvent Yellow 2). Zapon Fast Yellow CGG (C. I. Solvent Yellow 15). Aizen Spilon Yellow GRH (C. I. Solvent Yellow 61). Iketon Yellow GR Extra (C. I. Solvent Orange l). Aizen Spilon Orange GRH (C. 1. Solvent Orange 37). Aizen Spilon Fair Red BH (C. I. Solvent Red 81). Aizen Spilon Pink BH (C. I. Solvent Red 82).

Aizen Spilon Red BEH (C. I. Solvent Red 83). Orient Oil Violet #730 (C. I. Solvent Violet 13) and Aizen Spilon Violet RH (C. I. Solvent Violet 21).

Among the foregoing dyes. Oil Black. Spilon Black and Nigrosine Base are especially preferred for use in this invention.

In this invention it is important that the above-mentioned oil-soluble dye should be used in combination nvith the above-mentioned vinyl compound nitrogen-containing heterocyclic copolymer resin of the as the charge controlling agent of the toner particles. More specifically. as illustrated in Comparative Example 3 given hereinafter. a toner comprising an oil-soluble dye (Spirit Black AB) in an amount of 15cue by weight based on the total resins in toner particles has a capacity of being positively charged. but when the toner image left on the photosensitive surface after the transfer is removed for cleaning by the magnetic brush, a considerable amount of the toner is not attracted by the magnetic brush but is left on the photosensitive surface.Accordingly, it is apparent that the use of such oil-soluble dye alone is still insufficient in the property of maintaining the charge characteristic of the toner stably. Further, as illustrated in Comparative Example 4 given hereinafter, a toner comprising a 2-vinylpyridine copolymer in an amount of 48% by weight as the 2-vinylpyridine monomer based on the total resin components of the toner has a capacity of being positively charged, but it is difficult to completely remove the residual toner by attracting it by the magnetic brush and the toner is insufficient in the stability and durability of the positive charge characteristic.Still further, in this toner comprising the 2vinylpyridine copolymer alone as the charge controlling agent, the toner particles have an increased tendency to agglomerate and cohere to one another in a developer tank and such troubles as contamination of the background are often caused by falling of agglomerated toner particles.

In contrast, when the 2-vinylpyridine copolymer and oil-soluble dye are incorporated in combination according to this invention, even if the amounts of them are reduced to about 1/2 of the above-mentioned amounts. respectively, it is possible to maintain the positive charge characteristic of the toner stably and therefore, it is possible to completely remove all the toner particles left on the photosensitive surface by attracting them by the magnetic brush. Namely, according to this invention, the copolymer of the nitrogen-containing heterocyclic vinyl compound to be used as one component of the charge controlling agent has an ability to dissolve or disperse the oil-soluble dye to be used as the other component of the charge controlling agent, and the copolymer per se is well dispersed in the binder resin medium.Accordingly, a strong and uniform positive charge characteristic can be imparted to toner particles and this characteristic can be maintained in stable manner.

Any known binder resins can be used in this invention so far as it is compatible with the copolymer resin of the nitrogen-containing heterocyclic vinyl compound or it is capable of dispersing the copolymer therein.

Thermoplastic resins and thermosetting resins in the form of uncured products of precondensates can be used as the binder resin, As suitable examples of the binder resin, there can be mentioned. in the order of importance. from the viewpoints of electric characteristics of toner particles, facility of molding of a developer composition into toner particles and the fixing property of toner particles, aromatic vinyl resins. acrylic resins.

polyvinyl resins. polyvinyl acetal resins. polyester resins, epoxy resins. phenolic resins, petroleum resins and olefin resins. Of course. the binder resin that can be used in this invention is not limited to these resins.

As the aromatic vinyl resin. there can be mentioned homopolymers and copolymers of monomers represented by the following general formula:

wherein R2 represents hydrogen or lower alkyl. R3 represents lower alkyl lower alkoxv.

nitro amino halogen or other substituent. and n is (). l or 2, and copolymers of these monomers with other ethvlenicallv unsaturated monomers (exclusive of nitrogencontaining heterocyclic vinyl monomers). As the monomer represented by the above general formula (2). there can be mentioned. for example. styrene. a-methylstyrene, vinyltoluene (o-. p- or m-methylstvrene). o-. p- or m-ethvlstvrene tert-butvlstvrene.

cyclohexylstyrene. phenylstyrene. methoxystyrene. ehlorostyrene: nitrostyrene and ami nostvrene.

As the monomer copolymerizable with such aromatic vinyl monomer. there can be mentioned. for example. vinyl esters such as vinyl acetate. vinyl formate and vinyl propionate. ethylenically unsaturated carboxvlic acids such as acrylic acid. methacrylic acid, maleic anhydride. fumaric acid. crotonic acid and itaconic acid. esters of these carboxylic acids such as ethyl acrylate. methyl methacrylate. 7-ethvlhexvl acrylate and 3-hydroxyethyl acrylate. amides of these carboxylic acids such asacrviamide and methacrvlamide.

ethylenically unsaturated nitriles such as acrvlonitrile and methacrylonitrile, vinyl esters such as vinylmetbyl ether and vinylisobutyl ether. vinyl ketones such as vinylmethyl ketone and vinyihexyl ketone. olefins such as ethylene. propylene and 4-methylpentene, and diolefins such as butadiene and isoprene.

The above-mentioned aromatic vinyl copolymers may be so-called random, block or graft copolymers. Suitable examples of the copolymers include a styrene/butadiene copolymer, a vinyltoluene/butadiene copolymer, a styrene/acrylate copolymer. a vinyltoluene/acrylate copolymer, a styrene/acrylate/butadiene copolymer, vinyltoluene/acrylate/butadiene copolymer and styrene/ethylene copolymer.

It is preferred that the content of the aromatic vinyl monomer units in the aromatic vinyl resin that may be used in this invention is at least 15 mole %, especially at least 50 mole %.

The acrylic resin that may be used in this invention includes homopolymers and copolymers of acrylic acid, acrylic acid esters, acrylamide, acrylonitrile, methacrylic acid and methacrylic acid esters. As suitable examples, there can be mentioned, for example, a poly(acrylic acid ester), a poly(methacrylic acid ester), an acrylate/methacrylate copolymer and an acrylate/vinyl acetate copolymer.

As the polyvinyl acetal resin, there can be used polymers obtained by acetalizing a saponified vinyl acetate polymer, such as polyvinyl butyral and polyvinyl formal.

As the epoxy resin, there can be used bis- and trisepoxy compounds prepared by reacting a polyhydric phenol, polyhydric alcohol or resol type phenolic resin with an epihalohydrin.

A typical instance of the epoxy resin is a bis-epoxy compound represented by the following general formula:

wherein R4 represents a residue of a dihydric phenol. especially a residue of bis-2,2-(4hydroxyphenyl)propane.

These epoxy resins can be used singly or in the form of a mixture with a reactive resin such as a polyvinyl acetal resin. a phenolic resin or an acrylic resin.

As the polvester resin, there can be used. for example, saturated polvester resins having a relatively low softening point. such as ethylene/vutylene terephthalate/isophthalate copolymers and ethylene/butylene terephthalate/isophthalate/adipate copolymers. maleic acid resins, namely resins prepared from a rosin-maleic anhydride adduct and a polyhydric alcohol. and alkvd resins.

As the phenolic resin. there can be used. for example, resol type phenolic resins obtained by condensing phenol. o-. m- or p-cresol. bisphenol A. p-tert-butyl phenol or p-phenyl phenol with formaldehyde in the presence of an alkali catalyst. and products obtained by modifying these phenolic resins with rosin or xylene resin.

In general, it is preferred that the molecular weight of the binder resin be relatively low.

namelv in the range of from 500 to 15.000. especially 1,000 to 10.000. Further. it is ordinarily preferred that the softening point of the binder resin be 70 to 180"C.. especially 80 to 1600C.

A coloring pigment or dye or an extender pigment can be used in this invention. The oil-soluble dye that is used as the charge controlling agent has a function as the coloring agent. In this invention. however. other coloring pigments can be used in addition to such oil-soluble dye. Examples of these coloring agents are as follows: Black Pigs7lents Carbon black. acetylene black, lamp black. aniline black and black triiron tetroxide.

Yellow Pigiiieiits Chrome yellow. zinc Yellow. cadmium yellow. vellow iron oxide. Mineral Fast Yellow.

nickel titanium Yellow. naples yellow. Naphthol Yellow S. Hansa Yellow G. Hansa Yellow lOG. Benzidine Yellow G. Benzidine Yellow GR. Quinoline Yellow Lake. Permanent Yellow NCG and Tartrazine Lake.

Orange Pig//le/lts Chrome orange. molvbdenum orange. Permanent Orange GTR. Pyrazolone Orange.

Vulcan Orange. Indanthrene Brilliant Orange RK. Benzidine Orange G. Indanthrene Brilliant Orange GK.

Red pignle/lts Red iron oxide. cadmium red. red lead. mercurv sulfide. cadmium. Permanent Red AR.

Lithol Red. Pvrazolone Red. Watchung Red calcium salt. Lake Red D. Brilliant Carmine 6B. Eosine Lake. Rhodamine Lake B. Alizarine Lake and Brilliant Carmine 3B.

Violet Pigments Manganese violet, Fast Violet B and Methyl Violet Lake.

Blue Pigments Prussian blue. cobalt blue, Alkali Blue Lake, Victoria Blue Lake, Phthalocyanine Blue.

metal-free Phthalocyanine Blue. partially chlorinated Phthalocyanine Blue, Fast Sky Blue and Indanthrene Blue BC.

Creel Pigments Chrome green, chromium oxide, Pigment Green B, Malachite Green Lake and Fanal Yellow Green G.

White Pigments Zinc flower, titanium oxide. antimony white and zinc sulfide.

Exteti der Pigments Baryte powder. barium carbonate. clay, silica. white carbon, talc and alumina white.

In this invention, it is preferred that the oil-soluble dye as the charge controlling agent be chosen so that its hue is similar to the hue of the coloring pigment used. For example, when carbon black is employed. it is preferred to choose a black dve. Of course. in this invention, there may be adopted a method in which a blue oil soluble dye is combined with carbon black to impart a bluish black hue to toner particles.

In this invention. it is very important that the copolymer of the nitrogen-containing heterocyclic vinyl compound should be incorporated in an amount of 0.2 to 1OC/c by weight.

especially 0.5 to 4.5Cic by weight. as the nitrogen-containing heterocyclic vinyl monomer based on the total resins and the charge controlling dye should be incorporated in an amount of 1 to 7% bv weight. especially 1.5 to 5% by weight. based on the total resins.

When the amount of the copolymer of the nitrogen-containing heterocvclic vinyl compound is below the above range. it is difficult to dissolve or disperse the dye uniformly in the toner and the positive charge characteristic or the stabilitv or durability thereof becomes insufficient. If the amount of the copolymer is above the above-mentioned range.

the blocking tendency becomes conspicuous in toner particles and such troubles as falling of agglomerated toner particles are caused. Further. the heat resistance or durability of the toner particles becomes insufficient. and because of increased moisture-absorbing tendency. electric characteristics of the toner are rather degraded. If the amount of the oil-soluble dye is below the above range. the svnergistic effect of improving the positive charge characteristic or the stability or durability thereof, intended in this invention. cannot be attained. If the amount of the dye exceeds the above range. it is difficult to dissolve or disperse all the dye uniformly in the toner and it also is difficult to impart a strong positive charge uniformly to all the toner particles.

In this invention. optimum results are obtained when the amount of the nitrogencontaining heterocyclic vinyl monomer (A) is 1.0 to 3.5C/c bv weight based on the total resins of the toner and the amount of the oil soluble dye (B) is 1.5 to DCic by weight based on the total resins of the toner. and in this case. it is most preferred that the weight ratio of (B)/(A) be in the range of from 0.5 to 3.

The positively chargeable toner of this invention is especially advantageouslv applied to a method in which toner particles are fixed on a transfer sheet bv using a heater fixing roll on which an offset-preventing liquid is not coated. It is known that by incorporating a parting substance (offset-preventing agent) such as parting substance (offset-preventing agent) such as low-molecular-weight polyethylene or polypropylene into toner particles. a toner image can be fixed without occurrence of the offset phenomenon bv a heating developing roll.

However. since such low-moleculal--\veight olefin resin has such a property that it is negatively charged. a conventional toner comprising such olefin resin is still insufficient in the positive charge characteristic or the stability or durability thereof. Accordingly. this toner cannot be applied at all to the method in which the toner left on the photosensitive surface after the transfer is removed for cleaning bv attracting it by a magnetic brush.

lii contrast. when the copolymer of the nitrogen-containing heterocyclic vinyl compound and oil-soluble dve are incorporated in combination as the charge controlling agent according to this invention. even when such parting substance havig a negative charge characteristic is incorporated into toner particles. a high positive charge polarity can be maintained uniformly throughout the toner particles and the toner can be effectively applied to the method in which the residual toner can be removed from the photosensitive surface by the cleaning action of the magnetic brush.

In the toner particles of this invention. anv of known parting substances can be used. For example. as the lo'v-molecular-wei'ht olefin resin. there can be mentioned homopolymers and copolymers of olefins represented by the following general formula:

wherein Rl represents hydrogen or lower alkyl, such as ethylene, propylene, butene-1, pentene-1 and 4-methylpentene-1, and polymers obtained by modifying these homopolymers and copolymers. As the homopolymer, there can be mentioned, for example, polyethylene, polypropylene and polybutene-1, and as the copolymer, there can.be mentioned, for example, an ethylene copolymer.As the modified polymer, there can be mentioned, for example, an oxidized polyethylene obtained by oxidizing polyethylene and acrylate-grafted polyethylene and maleic anhydride-modified polypropylene obtained by grafting or terminal-treating an olefin homopolymer or copolymer such as mentioned above with maleic anhydride or an acrylic acid ester. It is preferred that the number average molecular weight of such low-molecular-weight olefin resin be 500 to 15,000, especially 1,000 to 10,000.

As the parting substance, there can be used a so-called silicone oil such as polydimethylsiloxane, liquid paraffin, paraffin wax, higher fatty acids and derivatives thereof.

Such parting substance can be incorporated in an amount of 1 to 25% by weight, preferably 3 to 15% by weight, based on the total resins without substantial degradation of the positive charge characteristic of toner particles or the stability or durability thereof.

The toner particles of this invention can be prepared by kneading the respective components at a temperature melting each resin component and shaping the kneaded composition into particles. It it preferred that the oil soluble dye be dissolved or dispersed in advance into the copolymer of the nitrogen-containing heterocyclic vinyl compound.

When a parting substance is incorporated into the toner, it is preferred that the parting substance be added last and the kneading be then conducted.

The kneading operation can be carried out by using known kneading means such as a hot roll, a mixer or a kneader. The kneading temperature and time are ordinarily chosen within a range of 100 to 2000C. and a range of 20 to 240 minutes, respectively, so that the respective components are uniformly dispersed and mixed without occurrence of substantial decomposition of each resin component Shaping of the kneaded composition into particles can easily be accomplished by cooling the kneaded composition to room temperature or a lower temperature. pulverizing the cooled composition by a pulverizer such as a jet mill. a ball mill. a pin mill or a vibrating mill. and classifying the resulting particles according to need.

As another method. there can be mentioned a method in which the respective components of the toner particles are stirred in a high speed stirrer under such conditions as will generate friction heat to melt or soften each resin component. whereby toner particles in which the respective components are integrated with one another can be obtained.

Still further. toner particles can be directly obtained from a molten mixture of the respective components by such means as spray granulation or centrifugal granulation.

Still in addition. toner particles can be prepared according to a method comprising dissolving or dispersing the respective components in an aromatic solvent such as toluene or a volatile solvent such as an alcohol. an ether or a ketone. spraving the resulting liquid composition into a drying atmosphere and a thus forming dried toner particles.

In this invention. it is preferred that the number average particle size of the toner particles be in the range of from 2 to 80 bi. especially from 5 to SOti. though the preferred range of the particle size varies to some extent depending on the preparation process or the -intended use. Moreover. it is preferred that the particle size distribution of the toner particles be such that particles having a size larger than SOit occupy less than 20C/c of the total particles and particles having a size smaller than 5ç occupy less than 15% of the total particles.

It is preferred that the shape of the toner particles be substantially spherical. However.

even if the toner particles have an amorphous shape such as a shape resembling that of sand particles. pulverized particles or granules or they are sharplv angled particles. an excellent flowahilitv and a high blocking resistance (reduced tendency to agglomerate) can be maintained in accordance with this invention.

The toner particles of this invention can be advantageously used in an electrophotog raphic process in which the toner particles are used together with magnetic carrier such as iron powder to provide a two-component developer an electrostatic latent image formed on the photosensitive surface for electrophotopraphy is developed bv a magnetic brush of the developer. the toner particle image formed on the photosensitive surface is transferred onto a transfer sheet (copying paper), and the toner particles left on the photosensitive surface after the transfer removed by the magnetic brush to clean the photosensitive surface. The developer of this invention is excellent in the. positive charge characteristic and the stability and durability thereof, and the tendency of toner particles to agglomerate is remarkably reduced.As will be apparent to those skilled in the art, these advantages can be similarly attained when the toner particles of this invention are used in a developing method in which a carrier composed of glass beads is employed.

This invention will now be described in detail by reference to the following Examples.

Example 1 75 Parts by weight qf a styrene resin (Piccolastic D-125 manufactured by Esso Standard Oil) and 17 parts by weight of a 2-vinylpyridine/styrene/methyl methacrylate copolymer (copolymerization molar ratio = 10/65/25) were kneaded with 6 parts by weight of carbon black (Special Black IV manufactured by Degussa Co.) and 2 parts by weight of an oil-soluble dye (Oil Black HBB manufactured by Orient Chemical) by using a heated three-roll mill. The kneaded composition was cooled and roughly pulverized to a size of 1000 to 3000y by a rough pulverizer (Rotoplex Cutting Mill manufactured by ALPINE Co.). Then, the roughly pulverized composition was finely pulverized to 1 to 40 by a jet mill (Super-Sonic Jet Mill manufactured by Nippon Pneumatic Mfg.Co.) and classified by a classifying machine (Multi-Plex Labor--ZZ-Sebter A 100 MZR manufactured by ALPINE Co.) to collect a toner having a particle size of 5 to 25p. A developer was formed by mixing 5 parts by weight of the so obtained toner with 95 parts by weight of an iron powder carrier (KMPF-402S manufactured by Mitsubishi Kasei), and the copying operation was carried out by using this developer in an electrocopying machine (Copystar 251R manufactured by Mita Industrial Co.; zinc oxide master paper is used as the photosensitive plate). Clear and sharp positive images free of fogging were obtained.

In the copying machine 251R a system using a magnetic brush for cleaning is adopted as the cleaning system. It was found that the developer was very suitable for this cleaning system. More specifically. even if the developer concentration was relatively high, no insufficient cleaning took place and the surface of the master could be cleaned sufficiently.

Example 2 In the same manner as described in Example 1. a toner having a particle size of 5 to 25uke was prepared from 70 parts by weight of a styrene resin (Piccolastic D-125). 19 parts by weight of a 2-vinylpyridine/styrene copolymer (copolymerization molar ratio = 20/80), 4 parts by weight of a carbon black (Special Black IV manufactured by Degussa Co.) and 2 parts by weight of an oil-soluble dye (Oil Black HBB). A developer was formed by mixing 5 parts by weight of the so prepared toner with 95 parts by weight of an iron powder carrier.

and the copying operation was carried out by using the so prepared developer in an electrocopving machine (Copvstar 251R). Clear and sharp positive images free of fogging were obtained. It was found that the toner had a very good adaptability to the cleaning operation.

Example 3 In the same manner as described in Example 1. a toner having a particle size of 5 to 25 it was prepared from 75 parts by weight of an acrylic resin (Dianearl BR-lü5 manufactured by Mitsubishi Rayon). 15 parts by weight of a 2-vinylpyridine/2-ethvlhexyl acrylate copolymer (copolymerization molar ratio = 30/70). 3 parts by weight of a high-melting-point wax (Sazol Wax Hl manufactured by Sazol Co.). 6 parts by weight of carbon black (Carbon Black #30 manufactured bv Mitsubishi Kasei) and 1 part bv weight of an oil-soluble dye (Oleosol Blue G manufactured by Sumitomo Chemical).A developer was formed bv mixing 5 parts by weight of the so prepared toner with 95 parts by weight of an iron powder carrier. The copying operation was carried out by using the so prepared developer in an electrocopying machine (Copystar 251R). Clear and sharp positive images free of fogging were obtained.When a plain copying paper and a tracing paper. each having a toner image transferred thereon. were passed between a "Teflon"-coated roller ("Teflon" is a Registered Trade Mark) and a silicone rubber roller. which had pressing contact with each other. while maintaining the surface temperature of the "Teflon"-coated roller at 170 to 19()"C.. it was found that the toner images could be effectively fixed without occurrence of the offset phenomenon.

E.n,llle 4 lii the same manner as described in Example 1. a toner having a particle size of 5 to 25 it was prepared from 68 parts by weight of a styrene resin (Piccolastic D-150). 17 parts bv weight of another styrene resin ( Himer SMB-73 manufactured by Sanyo Kasei ). 10 parts by weight of a 2-vinylpyridine/methyl acrylate copolymer (copolymerization molar ratio = 25/75), 3 parts by weight of carbon black (Carbon Black MA-100 manufactured by Mitsubishi Kasei), 1 part by weight of an oil-soluble dye (Oil Black HBB) and 1 part by weight of another oil-soluble dye (Spilon Black GMH Special manufactured by Hodogaya Chemical).A developer was formed by mixing 5 parts by weight of the so prepared toner with 95 parts by weight of an iron powder carrier, and the copying operation was carried out by using the so prepared developer in an electrocopying machine (Copystar 251R). Clear and sharp positive images free of fogging were obtained. It was found that the toner had a very good adaptability to the cleaning operation according to the magnetic brush cleaning method.

Example 5 In the same manner as described in Example 1. a toner having a particle size of 5 to 25,u was prepared from 60 parts by weight of an epoxy resin (AER-667 manufactured by Asahi Kasei), 5 parts by weight of gilsonite (Barber Gilsonite Selects manufactured by American Gilsonite Company), 25 parts by weight of a 2-vinylpyridine/styrene copolymer (copolymerization molar ratio = 15/85), 4 parts by weight of a low-molecular-weight polyethylene (San-Wax 171P manufactured by Sanyo Kasei). 4 parts by weight of carbon black (Carbon Black #30) and 2 parts by weight of an oil-soluble dye (Zapon Fast Blue FLE manufactured by BASF).A developer was formed by mixing 5 parts by weight of the so prepared toner with 95 parts by weight of an iron powder carrier, and the copying operation was carried out by using the so prepared developer in an electrocopying machine (Copystar 251R). Clear and sharp positive images free of fogging were obtained. It was found that the toner had a very good adaptability to the cleaning operation according to the magnetic brush cleaning method.

When a plain copying paper and a tracing paper. each having a toner image transferred thereon, were passed through between a Teflon-coated roller and a silicone rubber roller, which had pressing contact with each other. while maintaining the surface temperature of the Teflon-coated roller at 160 to 2üü C.. it was found that the toner images could be effectively fixed without occurrence of the offset phenomenon.

Example 6 In the same manner as described in Example 1. a toner having a particle size of 5 to 25u was prepared from 59 parts bv weight of a styrene resin (Piccolastic D-I50). 30 parts by weight of a 2-vinylpyridne/styrene/2-ethylhexyl acrylate copolymer (copolvmerization molar ratio = 10/65/25). 3 parts by weight of a high-melting-point wax (PW Powder M-201O manufactured bv Tovo Ink). 5 parts by weight of carbon black (Carbon Black #30) and 3 parts by weight of an oil-soluble dye (Nigrosine Base LK manufactured by BASF).A developer was formed by mixing 5 parts bv weight of the so prepared toner with 95 parts bv weight of an iron powder carrier. and the copying operation was carried out bv using the so prepared developer in an electrocopying machine (Copvstar 251R). Clear and sharp positive images free of fogging were obtained. It was found that the toner had a very good adaptability to the cleaning operation according to the magnetic brush cleaning method.

When a plain copying paper and a tracing paper. each having a toner image transferred thereon. were passed through between a Teflon-coated roller and a silicone rubber roller, which had pressing contact with each other. while maintaining the surface temperature of the Teflon-coated roller at 160 to 2000C.. it was found that the toner images could be effectively fixed without occurrence of the offset phenomenon.

Co,t2parafli'e Example I In the same manner as described in Example 1. a toner having a particle size of 5 to 2DLt was prepared from 92 parts bv weight of a styrene resin (Piccolastic D-l25). 6 parts by weight of carbon black (Special Black IV) and 2 parts by weight of an oil-soluble dye (Oil Black HBB). A developer was formed by mixing 5 parts bv weight of the so prepared toner with 95 parts bv weight of an iron powder carrier. The copying operation was carried out by using the so prepared developer in an electrocopying machine Copystar 251R). Fogging was caused. and cleaning according to the magnetic brush cleaning method was impossible.

Co/7lparatil e Exaiiiple 2 In the same manner as described in Example l. a toner having a particle size of 5 to 25 it was prepared from 7() parts by weight of a styrene resin (Piccolastic D-l25). 21 parts by weight of a r-vinvlp vr idine/stvrene copolymer (copolymerization molar ratio = 20i80) and 4 parts bv weight of carbon black. A developer was formed by mixing 5 parts bv weight of the so prepared toner with 95 parts by weight of an iron powder carrier.The copying operation was carried out by using the so prepared developer in an electrocopying machine (Copvstar 251R). A reversed image was formed and such troubles as fogging and insufficient transfer were caused. Further. the image density was low, and cleaning according to the magnetic brush cleaning method was impossible.

Comparatilte Example 3 In the same manner as described in Example 1. a toner having a particle size of 5 to 25u was prepared from 69 parts by weight of an acrylic resin (Dianearl BR-lû5), 10 parts by weight of a 2-vinylpyridine/2-ethylhexyl acrylate copolymer (copolymerization molar ratio = 30/70). 6. parts bv weight of carbon black (Carbon Black #30) and 15 parts by weight of an oil-soluble dye (Oleosol Blue G). A developer was formed bv mixing 5 parts bv weight of the so prepared toner with 95 parts by weight of an iron powder carrier.The copying operation was carried out bv using the so prepared toner in an electrocopying machine (Copystar 251R). Occurrence of the fogging phenomenon was conspicuous. and cleaning according to the magnetic brush cleaning method was impossible.

Comparative Example 4 In the same manner as described in Example 1. a toner having a particle size of 5 to 25 ti was prepared from 20 parts bv weight of an epoxy resin (AER-667). 5 parts bv weight of gilsonite (Barber Gilsonite Selects). 69 parts by weight of a 2-vinvlpvridine/stvrelle copolymer (copolvmerization molar ratio = 70/30). 4 parts bv weight of carbon black (Carbon Black #3û) and 2 parts by weight of an oil-soluble dye (Zapon Fast Blue FLE). A developer was formed by mixing 5 parts by weight of the so prepared toner with 95 parts by weight of an iron powder carrier.The copying operation was carried out by using the so prepared developer in an electrocopying machine (Copystar 25IR). Occurrence of fogging was conspicuous. and cleaning according to the magnetic brush cleaning method was impossible. Further. the fiowability of the toner was bad and agglomeration of toner particles was conspicuous.

WHAT WE CLAIM IS: 1. Toner particles for use in electrophotography. which particles are positively chargeable and comprise a coloring agent. a binder resin and. as charge controlling agent.

an oil-soluble dye and a copolymer resin derived from a nitrogen-containing heterocvclic vinyl compound. the copolymer resin being present in an amount of 0.2 to 10% by weight as the nitrogen-containing heterocyclic vinyl compound based on the total amount of resins in the toner particles and the oil-soluble dye being present in an amount of l to 7 by weight based on the total amount of resins in the toner particles.

2. Toner particles according to claim I wherein the copolymer resin is derived from a nitrogen-containing heterocyclic vinyl compound of the general formula:

wherein R1 represents hydrogen or alkyl of up to 4 carbon atoms. and N. represents a nitrogen-containing heterocvclic residue. with other ethylenically unsaturated monomer.

3. Toner particles according to claim 2 wherein the nitrogeil-colltaillilly heterocyclic vinyl compound is -vin!lpvridine.

4. Toner particles according to claim 1. 2 or 3 wherein the copolymer resin has a softening point of 70 to 18 C (measured in accordance with JIS 2531-1960).

5. Toner particles according to any one of the preceding claims wherein the copolymer resin contains units derived from the nitrogen-containing heterocyclic vinyl compound in an amount of 1 to 4 . by weight based on the weight of the copolymer resin.

6. Toner particles according to an! one of the preceding claims wherein the oil-soluble dye is a dye having a primary. sec ondary or tertiary amino group or a quaternary ammonium group.

7. Toner particles according to any one of the preceding claims wherein the binder resin is an aromatic vinyl resin or an acrylic resin.

8. Toner particles according to an; one of the preceding claims wherein the copolymer resin is present in an amount of (1.5 to 4.5% b! weight as the nitrogen-containing heterocyclic vinyl compound based on the total amount of resins and the oil-soluble dye is present in an amount of 1.5 to '. by weight based on the total amount of resins.

9. Toner particles according to an! one of the preceding claims which also comprise a parting substance.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. 251R). A reversed image was formed and such troubles as fogging and insufficient transfer were caused. Further. the image density was low, and cleaning according to the magnetic brush cleaning method was impossible. Comparatilte Example 3 In the same manner as described in Example 1. a toner having a particle size of 5 to 25u was prepared from 69 parts by weight of an acrylic resin (Dianearl BR-lû5), 10 parts by weight of a 2-vinylpyridine/2-ethylhexyl acrylate copolymer (copolymerization molar ratio = 30/70). 6. parts bv weight of carbon black (Carbon Black #30) and 15 parts by weight of an oil-soluble dye (Oleosol Blue G). A developer was formed bv mixing 5 parts bv weight of the so prepared toner with 95 parts by weight of an iron powder carrier.The copying operation was carried out bv using the so prepared toner in an electrocopying machine (Copystar 251R). Occurrence of the fogging phenomenon was conspicuous. and cleaning according to the magnetic brush cleaning method was impossible. Comparative Example 4 In the same manner as described in Example 1. a toner having a particle size of 5 to 25 ti was prepared from 20 parts bv weight of an epoxy resin (AER-667). 5 parts bv weight of gilsonite (Barber Gilsonite Selects). 69 parts by weight of a 2-vinvlpvridine/stvrelle copolymer (copolvmerization molar ratio = 70/30). 4 parts bv weight of carbon black (Carbon Black #3û) and 2 parts by weight of an oil-soluble dye (Zapon Fast Blue FLE). A developer was formed by mixing 5 parts by weight of the so prepared toner with 95 parts by weight of an iron powder carrier.The copying operation was carried out by using the so prepared developer in an electrocopying machine (Copystar 25IR). Occurrence of fogging was conspicuous. and cleaning according to the magnetic brush cleaning method was impossible. Further. the fiowability of the toner was bad and agglomeration of toner particles was conspicuous. WHAT WE CLAIM IS:

1. Toner particles for use in electrophotography. which particles are positively chargeable and comprise a coloring agent. a binder resin and. as charge controlling agent.

10. Toner particles according to claim 9 wherein the parting substance is a low

molecular-weight olefin resin, a polysiloxane oil. a paraffin wax or a higher fatty acid or a derivative thereof.

11. Toner particles according to claim 9 or 10 wherein the parting substance is present in an amount of 1 to 259 by weight based on the total amount of resins in the toner particles.

12. Toner particles according to claim 1 substantially as described in any one of the Examples.

13. A two-component electrophotographic developer comprising positively charged toner particles as claimed in any one of the preceding claims. and carrier particles.