GB2109572A - Encapsulated toner for development of electrostatic images - Google Patents

Abstract

A toner for development of electrostatic images, containing a fluid hardenable under an oxygen- containing atmosphere or a mixture of a liquid substance and a wax encapsulated within a capsule of a vinyl type resin is found to have good charging characteristics and can also be well fixed by the pressure fixation method onto a paper with good storability.

Description

SPECIFICATION Toner for development of electrostatic images This invention relates to a toner for development of electrostatic images formed in electrophotography, electrostatic printing, electrostatic recording, etc.

In recent years, for formation of a visible image based on an image information, there has widely been utilized the method in which such an image is formed via an electrostatic image. An electrostatic image is developed by utilization of its electrostatic attraction force with a toner as developer to form a toner image, which toner image is usually transferred onto a transfer paper, etc., followed by fixing, to obtain a visible image.

Accordingly, a toner for development of electrostatic image is required to have suitable charging characteristics to achieve good development with sufficient image density and also to have sufficient fixing characteristic onto a transfer paper, etc.

In the prior art, use is made widely of powdery toners comprising thermoplastic resins as binders having incorporated colorants such as carbon black, etc. They are charged to develop electrostatic images and the resultant toner images are transferred onto, for example, transfer papers, followed by fixing by heating with a heating roller, etc. When such a heating fixation method is employed, it will take a considerable time before the fixer is heated to a desired temperature to be set and a large amount of energy is required for heating. Further, there may be also the trouble such as the danger of fire when jamming of papers occurs. Moreover, to ensure achievement of fixing, it is necessary to satisfy severe conditions with respect to temperature conditions and others.

Under the situation as described above, investigations have recently been made about so called microcapsules for use as the toner for development of electrostatic images. This microcapsule type of toner is a powdery material having a fluid core material containing a colorant encapsulated within a microparticulate resin capsule. Fixing of the toner image formed with this toner may be conducted by applying a pressure on the capsule by means of a pressure roller, etc. to cause so to speak rupture of the capsule, thereby effecting release of the fluid core material contained therein. Thus, no heating is required or only slight heating may sufficiently be used according to this method, and the problems of the heating fixation as described above can advantageously be alleviated to a great extent.

However, in the microcapsule type toner of the prior art, the resin to be used for formation of the capsule is limited in species and therefore it is difficult to obtain sufficient charging characteristics, thus giving only poor developing characteristic. Further, although a fluid core material can be fixed onto a transfer paper, etc. primarily through the pressure applied, the toner is generally secured onto the transfer paper only in the state wherein a part of the toner is merely inserted between the fibers of the transfer paper. As a consequence, on occurrence of rubbing between papers or application of friction with fingers of a man, the fixed toner may become peeled off or dropped off to result ultimately in the drawbacks of low durability and storability of the visible images formed.

The present invention has been accomplished in view of the state of the art as described above.

An object of the present invention is to provide a microcapsule type toner for development of electrostatic image which can possess good charging characteristics and also great durability or storability of the visible images formed.

The specific feature of the toner according to the present invention resides in encapsulation of a fluid core material hardenable in an oxygen-containing atmosphere or a fluid core material comprising mixture of a liquid substance and a wax within a capsule comprising a vinyl type resin.

The present invention is now to be described in detail below.

The toner of the present invention comprises a capsule, which is formed by a resin prepared by polymerization of a vinyl type polymerizable monomer, and a fluid core material having the property to be hardened when left to stand in contact with an oxygen-containing atmosphere, typically air, or a fluid core material which is a mixture of a liquid substance and a wax encapsulated within said capsule.

Within the fluid core material, or further within the wall fiim of the capsule, there is generally incorporated a colorant. Also, when a magnetic toner is to be made, magnetic powders are incorporated in place of or together with the colorant. It is also possible to incorporate various additives, if desired.

As the aforesaid vinyl type polymerizable monomer, there may be employed styrenes such as styrene, p-chlorostyrene, tu-methylstyrene, t-butylstyrene, etc.; (t-methylene aliphatic mono-carboxylic acid esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, stearyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, etc.; vinyl nitriles such as acrylonitrile, methacrylonitrile, etc,; vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, etc.; vinyl pyridines such as 2-vinyl pyridine, 4vinyl pyridine, etc.;N-vinylcyclic compounds such as N-vinyl-pyrrolidone; vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, methyl isopropenyl ketone, etc,; unsaturated hydrocarbons such as ethylene, propylene, isobutylene, butadiene, isoprene, etc.; halo-containing unsaturated hydrocarbons such as chloroprene, etc.; and other mono-functional vinyl type monomers, either as a single species or as a combination of two or more species.

Other than the mono-functional monomers as set forth above, it is also possible to use poly functional vinyl type monomers. As such poly-functionai monomers, there may be employed polyhydric alcohol methacrylates such as ethyleneglycol dimethacrylate, diethyleneglycol dimethacrylate, triethyleneglycol dimethacrylate, tetraethyleneglycol dimethacrylate, neopentylglycol dimethacrylate, dipropyleneglycol dimethacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, pentaerythrytol tetramethacrylate, etc.; polyhydric alcohol acrylates such as diethyleneglycol diacrylate, triethyleneglycol diacrylate, neopentylglycol diacrylate, trimethylolpropane triacrylate, trimethylolethane triacrylate, pentaerythrytol tetraacrylate, etc.; polyfunctional vinyl benzenes such as divinylbenzene; and others, either as a single species or as a combination of two or more species.Further, these poly-functional monomers may also be used in combination with the mono-functional monomers as already described.

When the above polyfunctional monomer is used, the resultant polymer is crosslinked and the toner finally obtained can be favorably improved in durability. Of course, such a crosslinked polymer may be obtained by use of other crosslinking agents.

In the present invention, the core material to be encapsulated within the capsule as described above is (a) a fluid substance hardenable under an oxygen-containing atmosphere or (b) a mixture of a liquid substance and a wax.

According to one mode (a) of the invention, there is employed a fluid substance which can be hardened under an oxygen-containing atmosphere, typically air (this substance is hereinafter referred to as hardenable fluid). Examples of such a hardenable fluid are esters of unsaturated fatty acids such as linoleic acid, linolenic acid, oleic acid, elaidic acid, eleostearic acid, linolenelaidic acid, gadoleic acid, erucic acid, arachidonic acid, clupanodonic acid, c-licanic acid, etc.; drying or semi-drying vegetable oils such as linseed oil, perilla oil, tung oil, hempseed oil, kapok oil, poppy seed oil, sesame oil, rice bran oil, safflower oil, soybean oil, corn oil, rapeseed oil, sunflower oil, cottonseed oil, etc; drying or semidrying animal oils and fats such as cuttlefish oil, salmon oil, saury oil, tallow, mutton tallow, etc.; synthetic drying oils such as copolymers of acetylene and butadiene, dicyclopentadiene oligomers (e.g.

"Quinton", produced by Nippon Zeon Co.); and so on.

Further, as a modification of the mode (a), it is also possible to add a wax as described hereinafter in detail with respect to the mode (b) to the above hardenable fluid. In this case, a wax may be incorporated in the hardenable fluid at a proportion which can sufficiently retain the hardenable fluid onto the paper after fixation, generally 1 to 30% by weight, preferably 5 to 1 5% by weight, based on the hardenable fluid.

According to the alternative mode (b) of the invention, there is employed a fluid core material comprising a mixture of a liquid substance and a wax.

As the liquid substance which is one component of the fluid core material in this mode (b), there may be included high molecular substances which are liquid, as exemplified by polybutene, polychloroprene, polybutadiene, polyester, acrylate or oligomer of acrylate, oligomer of styrene type monomer, oligomer of copolymer of styrene with alkyl acrylate or alkyl methacrylate, etc.; liquid substances conventionally used as plasticizers such as chlorinated paraffin, epoxidized soybean oil, epoxidized triglyceride, adipic acid type polyester, octylepoxy stearate, trioctyl trimellitate, dipentaerythritol ester, adipic acid ester, dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, triphenyl phosphate, etc.; vegetable oils such as olive oil, Tsubaki (camellia) oil, etc.; silicone oil; mineral oil; petroleum type liquid substances such as asphalt, gilsonite, etc.; liquid high molecular substance such as (Z-pinene resin, P-pinene resin, epoxy resin, c-pinene phenol resin, dipentene resins; and other liquid substances.

As the wax to be used as the component together with the above liquid substance in the fluid core material of the mode (b), there may be employed one suitably selected from natural waxes and synthetic waxes. As natural waxes, there may be mentioned vegetable waxes such as carnauba wax, Ouri-Curi wax, candelilla wax, sugar cane wax, Japan wax, bran wax, etc.; animal waxes such as bees wax, bleached bees wax, whale wax, shellac wax, lanolin, etc.; and mineral waxes such as montan wax, ozocerite, ceresin, etc.

There may also suitably be employed waxes as enumerated below which can be industrially produced. All the names of products having an asterisk (*) are trade names or trademarks (The same applies throughout the present specification).

1) Paraffin waxes "Sazol Wax H 1 *" (produced by Sazol Marketing Co.) "Sazol Wax A 1*" (produced by Sazol Marketing Co.) "Sazol Wax A 2*" (produced by Sazol Marketing Co.) "Microcrystalline Wax #220*" (produced by Mobil Oil Co.) "1 700 Microparaffin*,, (produced by Nippon Sekiyu Co.) "Suntite A*", "Suntite B*", "Suntite C*" (produced by Seiko Kagaku Co.) "22-Tritetracontanone*,, (produced by Tokyo Kasei Co.) "1350 Paraffin*", "No. 1 Separate Paraffin*", "1 500 Microparaffin*,, (produced by Nippon Sekiyu Co.) "Shell 1350 Paraffin Wax*" (produced by Shell Oil Co.) "Ample Wax*" (produced by Hodogaya Kagaku Co.) 2) Fatty acid esters, partially saponified products thereof These are fatty acid esters having melting points of about 50-1 300C or partially saponified products thereof, including esters obtained by reacting saturated or unsaturated aliphatic alcohols with saturated or unsaturated fatty acids, and the saponified products thereof obtained by partial saponification of these esters with hydroxides of metals such as sodium, calcium, magnesium, lead, aluminum, barium, zinc, etc.As the fatty acid as the starting component, there may be employed either lower or higher fatty acids, as exemplified by valeric acid, caproic acid, enanthic acid, caprylic acid, peralgonic acid, caprylic acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, nonadecylic acid, arachidic acid, behenic acid, lignoceric acid, cerotic acid, montanic acid, merissinic acid, hentriacontanoic acid, dotriacontanoic acid, tetratriacontanoic acid, hexatriacontanoic acid, octatriacontanoic acid, linderic acid, lauroleic acid, Tsuznic acid, myristoleic acid, zoomaric acid, petroselinic acid, oleic acid, elaidic acid, vaccenic acid, gadoleic acid, erucic acid, brassidic acid, selacholeic acid, linoleic acid, linolenic acid, eleostearic acid, linoelaidic acid, parinaric acid, arachidonic acid, glutaric acid, adipic acid, pimellic acid, suberic acid, azelaic acid, sebacic acid, and other dicarboxylic acids having 9 to 1 9 methylene groups. As the other starting component of aliphatic alcohols, there may be included either lower or higher alcohols similarly as fatty acids which may also be monohydric or polyhydric alcohols, as exemplified by methyl alcohol, ethyl alcohol, propyl alcohol, butyi alcohol, amyl alcohol, caproyl alcohol, caprylyl alcohol, capryl alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, arachyl alcohol, behenyl alcohol, carnaubyl alcohol, ceryl alcohol, myricyl alcohol, lacceryl alcohol, allyl alcohol, crotyl alcohol, 2 butenol- 1 ,2-pentenol-1, 2-pentenol- 1, 3-hexenol-1, 2-heptenol-1, 1 0-undecenol- 1, 11-dodecenol-1, 1 2-tridecenol-1, oleyl alcohol, elaidyl alcohol, linoleyl alcohol, linolenyl alcohol, ethyleneglycol, propyleneglycol, trimethyleneglycol, 1 ,3-butanediol, 1 ,4-butanediol, 2,3-butanediol, 2-butene-1 ,4-diol, 1,5-pentanediol, 2,4-pentanediol, 1,6-hexanediol, 2,5-hexanediol, 2-methyl-1 3-pentanediol, 2,4heptane-diol, 2-ethyl- 1 ,3-hexa nediol, 2-ethyl-2-butyl- 1 ,3-propa nediol, hexadecane- 1 ,2-diol, octadecane-1 ,2-diol, eicosane-1 ,2-diol, docosane-1,2-diol, tetracosane-1 ,2-diol, diethyleneglycol, triethyleneglycol, tetraethyleneglycol, dipropyleneglycol, glycerine, pentaerythritol, sorbitol, and so on.

These fatty acid esters or partially saponified products thereof may be used individually as a single species or alternatively as a mixture comprising a composition of various fatty acid esters or a mixture comprising a composition of fatty acid esters and partially saponified products thereof. In the present invention, commercially available fatty acid esters or partially saponified products thereof can effectively be used. Most of these commercially available products have the compositions of mixtures as mentioned above. Representative commercial products are enumerated below.

Lower alcohol esters of fatty acids "Butyl stearate" (produced by Kawaken Fine Chemical Co.); "Butyl stearate" (produced by Kao Sekken Co.) Polyhydric alcohol esters of fatty acids "Nissan Castor Wax*" (produced by Nippon Yushi Co., Glycerol tri-1 ,2-hydroxystearate); "Diamond Wax*,, (produced by Shinnippon Rika Co.); "Himako*,, (produced by Kawaken Fine Chemical Co.) Higher alcohol esters of fatty acids "Spermaceti*" (produced by Nippon Yushi Co., cetyl palmitate) "Hoechst Wax*" (produced by Hoechst Japan Co., ethyleneglycol ester of montanic acid); "Hoechst Wax-OP*,, (produced by Hoechst Japan Co., partially saponified product of butyleneglycol ester of montanic acid);; Partial ester of fatty acid and polyhydric alcohol "Monogly-M*,, (produced by Nippon Yushi Co., rr-glycerol monostearate); "Fatty acid monoglyceride R-60*,, (produced by Matsumoto Yushi Seiyaku Co., stearic acid monoglyceride); "Fatty acid monoglyceride R-80*,, (produced by Matsumoto Yushi Seiyaku Co., oleic acid-stearic acid monoglyceride); "Rikemal-S-200*,, (produced by Riken Vitamine Oil Co., glycerine stearate); "Rikemal-B-1 00*" (produced by Riken Vitamine Oil Co., glycerine monobehenate); "Rikemaí-S-300*" (produced by Riken Vitamine Oil Co., sorbitane monostearate); "Rikemal-PS-100*,, (produced by Riken Vitamine Oil Co., propleneglycol monostearate);; "ATMUL-T-95*,, (produced by Kao Atlas Co., high purity monoglyceride) Mixed system esters "VLTN-4*,, (produced by Kawaken Fine Chemical Co.); "VLT-L*,, (produced by Kawaken Fine Chemical Co.); "K-3 Wax*" (produced by Kawaken Fine Chemical Co.); "Ricewax*,, (produced by Noda Wax Co.) 3) Alkylene-bis-fatty acid amides Alkylene-bis-fatty acid amide compounds having melting points of 1 00-1 800C may be employed, of which typical examples are set forth below.

1. C10H21CO-NH-(CH2)5-NH-0CC10H21 2. C11H23CO-NH-(CH2)4-NH-OCC11H23 3. C13H27CO-NH-(CH2)2-NH-OCC18H37 4. C10H21CO-NH-(CH2)2-NH-OCC14H29 5. C15H31CO-NH-(CH2)2-NH-OCC15H31 6. C17H35C0-NH-CH2-NH-0CC17H35 7. C17H35CO-NH-(CH2)2-NH-OCC15H31 8. C23H47CO-NH-CH2-NH-OCC15H31

14. C17H31CO-NH-(CH2)3-NH-OCC17H31 As commercially available alkylene-bis-fatty acid amide compounds, there may be mentioned the following products.

"Bisamide*,, (produced by Nitto Kagaku Co.); "Plastflowf*" (produced by Nitto Kagaku Co.); "Diad 200 Bis*" (produced by Nippon Suiso Co.); "Rublon E*,, (produced by Nippon Suiso Co.); "Alflow-H 50S*" (produced by Nippon Yushi Co.); "Alflow-V 60*" (produced by Nippon Yushi Co.); "Amide-6L*,, (produced by Kawaken Fine Chemical Co.); "Amide-75*,, (produced by Kawaken Fine Chemical Co.); "Amide-6H*,, (produced by Kawaken Fine Chemical Co.); "Armowax-EBS*,, (produced by Lion Armor Co.); "Hoechst Wax C*" (produced by Hoechst Co.); "Nobko Wax-22DS*" (produced by Nobko Chemical Co.); "Advawax-280*" (produced by Advance Co.); "Kao Wax-EB*,, (produced by Kao Sekken Co.); ; "Baricin-285*" (produced by Baker Castor Oil Co.) 4) Higher fatty acids As higher fatty acids, there may be included lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, ricinoleic acid, arachic acid, behenic acid, lignoceric acid, selacholeic acid, etc., and mixtures thereof.Commercially available higher fatty acids may include, for example, "F-3*,,, "VLZ-200*,, (produced by Kawaken Fine Chemical Co.); "Powdery stearic acid with marks of Sakura, Matsu, Take and Tsubaki, respectively", "Tallow Kyokudo*", "NAA 222*", "NAA 221*" (produced by Nippon Yushi Co.);Lunac S-40*", "Lunac S-90*", "Lunac S-30*", "Lunac 855*", "Lunac 895*", Lunac 1095*", "MY-85*", "MY-95*", "P-85*,,, "P-95*,,, "S-10*", "S-20*", "T-S-4*", "T-S-2*", "T D-2*,,, "T-D-4*", "Kao Wax M-80*,,, "Kao Wax M-85 Powder*", "Kao Wax M-SS*,, (produced by Kao Sekken Co.).

The waxes as mentioned above have melting points of 50 to 1 800C, preferably 50 to 100 C.

When a wax with a melting point of lower than 500C is employed, the visible images formed are liable to be sticky and no good fixing characteristic can be obtained. On the contrary, when a wax with too high a melting point is used, it is difficult to effect homogeneous mixing with a liquid substance, whereby fixing characteristic is also lowered.

The amount of a wax to be added may be at a proportion relative to said liquid substance so as to retain said substance sufficiently onto a paper, generally 1 to 30% by weight, preferably 5 to 15% by weight, based on the liquid substance.

As colorants, there may be employed carbon black, Nigrosine dye* (C.l. No. 504158), Aniline Blue* (C.l. No. 50405), Calcooil Blue* (C.l. No. azoec Blue 3), Chrome Yellow* (C.l. No. 14090), Ultramarine Blue* (C.l. No. 77103), Du Pont Oil Red* (C.l. No. 26105), Quinoline Yellow* (C.l. No.

47005), Methylene Blue Chloride* (C.l. No.52015), Phthalocyanine Blue* (C.l. No. 74160), Malachite Green Oxalate* (C.l. No. 42000), Lamp Black* (C.l. No. 77266), Rose Bengal* (C.l. No. 45435), mixtures thereof and others. These colorants are required to be incorporated at proportions enough to form visible images of sufficient density, generally in an amount of 1 to 20 parts by weight based on 100 parts by weight of toner.

As the aforesaid magnetic materials, there may be employed metals or alloys exhibiting strong magnetic property such as iron, cobalt, nickel, etc. or compounds containing these elements, typically ferrite, magnetite, or alloys which contain no strong magnetic element but exhibits strong magnetic property when subjected to suitable heat treatment, such as alloys of the type called as Whisler alloys containing manganese and copper (e.g. manganese-copper-aluminum, manganese-copper-tin, etc.), chromium dioxide, etc. These magnetic materials may be dispersed uniformly in the fluid core material in the form of micropowders with average particle sizes of 0.1 to 1 micron. The content of such magnetic materials may range from 20 to 70 parts by weight, preferably 40 to 70 parts by weight per 100 parts by weight of a toner.

In case when a polymerizable monomer is to be polymerized in the presence of these magnetic materials, polymerization reaction may be affected by the oil absorption content of said magnetic materials. For example, when a magnetic material with an oil absorption content in excess of 35% is used, monomers may be adsorbed thereon in large amounts, whereby no smooth progress of polymerization can be effected or other inconveniences may be caused. Accordingly, the aforesaid magnetic material is desired to have an oil absorption content of 35% or less, particularly preferably 10 to 30%.

Such magnetic materials are commercially available, as exemplified by "Toda Color EPT-SOD*,, (22-26), "Toda Color EPT-1000*" (17), "Toda Color MRM-B-450 A*" (27) (produced by Toda Kogyo Co.); "MAPICO BLACK BL-100*" (26), "MAPICO BLACK BL-SP*,, (25), "MAPICO BLACK BL-200*" (27), "MAPICO BLACK RB-BL*,, (22) (produced by Titanium Kogyo Co.); and others (the numerals in the bracket indicate oil adsorption contents, unit:%).

The aforesaid oil absorption contents may be measured according to the method as described in Japanese Industrial Standard (JIS) K 5101-1 9. That is, S (g) of a magnetic material is sampled on a glass plate (250x250x5 mm), and linseed oil is added dropwise in small quantities on the center of the sample and sufficiently kneeded with the sample by means of a spatula for each addition. This operation of addition and kneading of linseed oil is repeated until the whole sample is made into a putty-like mass capable of stand-up in convolution with a steel spatula. The amount of linseed added to this point is determined (H ml) and the oil absorption content G is calculated by the following formula: H G= x 100 (%) S The toner of the present invention may preferably be produced according to, for example, the following procedure.That is, a liquid or solid vinyl type polymerizable monomer is mixed with a hardenable fluid or a mixture of a liquid substance and a wax to prepare a solution and then, optionally with addition of a polymerization initiator, a crosslinking agent, etc., the resultant solution is mixed with a colorant, followed by suspension of the monomeric mixture in minute particles in a dispersion medium. The particle sizes of the dispersed minute particles can be controlled by, for example, regulation of the rotation number of the stirrer of a homomixer used for suspension of the particles, while monitoring the particle sizes and the degree of dispersion by, for example, microscopic observation.

Thus, while the monomeric mixture of the aforesaid monomer with a hardenable fluid or a mixture of a liquid substance and a wax is suspended in a dispersion medium, the system is placed under polymerization reaction conditions to polymerize the aforesaid monomer according to the in situ polymerization. In the in situ polymerization, polymerized products of the monomer are migrated with the progress of polymerization from the inner portions of said dispersed minute particles to the surface sides thereof to result in formation of capsules of the polymer, having encapsulated a hardenable fluid or a mixture of a liquid substance or a wax therein, to provide the toner of the invention.

The thus prepared toner particles contain a colorant which is incorporated within the capsule wall films of the polymer. Unaltered monomers may also remain in the fluid core material, but it will cause no problem at all.

In the above process, the monomeric mixture as a whole is lipophilic in nature. This is because the monomer used is a vinyl type which is lipophilic and hence a lipophilic material is preferred as a hardenable fluid or a mixture of a liquid substance and a wax. Accordingly, as the dispersion medium in the polymerization system, there may be employed water or a hydrophilic liquid. And, it is practically necessary to have a dispersion stabilizer mixed in this dispersion medium, whereby the monomeric mixture can be maintained to be stably suspended during the polymerisation reaction.

As the dispersion stabilizer, there may be effectively used water-soluble macromolecular substances such as gelatin, gelatin derivatives, polyvinyl alcohol, polystyrene sulfonic acid, hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxymethyl cellulose sodium, sodium polyacrylate, etc.; surfactants with HLB values of 10 or more such as anionic surfactants, nonionic surfactants, cationic surfactants, etc.; hydrophilic colloidal substances such as colloidal silica, alumina, tricalcium phosphate, ferric hydroxide, titanium hydroxide, aluminum hydroxide, etc.; and so on. Of course, it is possible to use two or more kinds of these stabilizers in combination or to use an appropriate aid at the same time.

In the aforesaid polymerization reaction system, there may also be employed a polymerization initiator, if desired. Typical examples of such an initiator may include organic peroxides such as benzoyl peroxide, lauroyl peroxide, etc. and azobis type polymerization initiators such as azobisisobutyronitrile, azobisvaleronitrile, etc. The polymerization initiator may be employed in an amount of 0.1 to 10% by weight, preferably 0.2 to 5% by weight, based on the monomer component in the aforesaid monomeric mixture. Further, the toner of the present invention can be produced according to other methods such as the coacervation method and the drying-in-liquid method.

The toner of the present invention, when it contains minute powders of a magnetic material, may be used as the so called one-component system developer or, when it contains no magnetic material powder, as the two-component system developer in admixture with a carrier comprising iron powders, glass beads, etc.

When minute magnetic material powders are to be incorporated to make a magnetic toner, the toner may be treated similarly as in case of the colorant. However, since they are in themselves low in affinity for an organic substance such as the aforesaid monomer, it is better to use a so called coupling agent such as titanium coupling agents, silane coupling agents, lecithin, etc. together with the minute magnetic material powders or pre-treat the minute magnetic material powders with such a coupling agent before use, whereby the minute magnetic material powders can be dispersed uniformly.

The toner of the present invention has the constitution as described above and, because its capsule is formed of a vinyl type resin, it is possible to select said resin from a wide scope of resins with respect to kinds, compositions, etc. Accordingly, charging characteristics adapted for use conditions can easily and surely be obtained to result in good developing characteristics enabling formation of visible images of high quality.

The microcapsule type toner is pressed during fixing procedure by means of a pressure roll under a pressure of, for example, 1 0-30 Kg/cm, whereby its capsule is ruptured to release a fluid core material contained therein. When the material forming the core material is a hardenable fluid, the hardenable fluid is exposed to the air once it has been fixed on a transfer paper, etc. As the result, the hardenable fluid will be hardened with lapse of time to be secured more firmiy to the fibers of the transfer paper simultaneously with consolidation of the hardened product per se. Therefore, the visible images formed will not easily be peeled off or falled off by friction with other materials to be enriched in durability and excellent in storability.

When the core material is a mixture of a liquid substance and a wax, good fixing may be effected on a paper such as a transfer paper, etc. This may be considered to be due to the fact that a wax, which is a relatively soft material, can be readily pressed into between fibers of a paper to be retained therein, and the liquid substance is retained via the wax. In fact, even when the liquid substance employed may have a low viscosity and be penetrable alone to the backside of the paper, it can be mixed with a wax to prevent assuredly generation of strike through or show through. As the result, the image can be well fixed and beautiful with the paper being prevented from any remaining contamination. And, it is also possible to use a liquid substance as constituent of a core material which has not been available in the prior art because of its too low viscosity.

Further, the resin forming the capsule may be crosslinked to increase the mechanical strength of the toner, thus giving a developer with small deterioration with improvement of the stability of the toner to heat, whereby the anti-blocking property of the toner can be improved to suppress agglomeration during storage for a long term.

In fixing of the toner image with the use of the toner of the present invention, only pressure may be applied, but more or less of heat may also be applied at the same time. By doing so, when a hardenable fluid is contained in the core material released by rupture of the capsule and penetrated into between fibers through its fluidity, hardening of the fluid can be positively accelerated to achieve good fixation.

In the toner of the present invention, when it has a large thickness of capsule wall, higher pressure is required for fixing, while mechanical strength is decreased to lower stability when it has a small thickness. Accordingly, in preparation of the toner of the present invention according to the method as described above, the proportion of a monomer in the monomeric mixture is controlled to 5 to 60% by weight, preferably 10 to 50% by weight. The proportion of a hardenable fluid or a mixture of a liquid substance and a wax as fluid core material may be 90 to 10% by weight, preferably 80 to 15% by weight, based on the monomeric mixture.

The toner of the present invention may have particle sizes, which are not particularly limited, but generally have average particle sizes of 5 to 50 1jim, preferably 10 to 30 Hm.

The present invention is described in further detail by the following Examples, by which the present invention is not limited.

Example 1 Styrene (polymerizable monomer) 50 g Ethyleneglycol dimethacrylate (crosslinking monomer) 100 g Lauroyl peroxide (polymerization initiator) 7.5 g Soybean oil (hardenable fluid) 150 g Minute magnetic material powders "MAPICO BLACK BL-1 00*" (water absorption content: 26%) 300 g Lecithin (coupling agent for magnetic material) lOg The above materials were thoroughly mixed under stirring to prepare a monomeric mixture.Into 3000 ml of water having dispersion stabilizers of 20 g of colloidal calcium phosphate and 0.2 g of sodium dodecylbenzenesulfonate dispersed therein, the above monomeric mixture was dispersed by means of a stirrer homo-jetter at 5000 r.p.m. for about 30 minutes to make the average particle size of the dispersed particles 10-1 5 u by observation with an optical microscope. The resultant dispersion was charged into a four-necked flask and the temperature of the system was raised to 750C while under stirring at 300 r.p.m., at which temperature polymerization was initiated and the reaction was conducted at the same temperature for 10 hours. Then, hydrochloric acid was added to decompose and dissolve the dispersion stabilizers, followed by filtration of the solid.The solid product was washed with water and dried to prepare a magnetic toner according to the present invention, having an average particle size of 12,u. This is called as "Sample 1".

Example 2 Following the procedure of Example 1, except for using neopentylglycol dimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer, there was prepared a magnetic toner according to the present invention. This is called as "Sample 2".

Example 3 Following the procedure of Example 1, except for using trimethylopropane trimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer, there was prepared a magnetic toner according to the present invention. This is called as "Sample 3".

Example 4 Following the procedure of Example 1, except for using linseed oil in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as "Sample 4".

Example 5 Following the procedure of Example 1, except for using trimethylopropane trimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer and linseed oil in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as "Sample 5".

Example 6 Following the procedure of Example 1, except for using a mixture of equal amounts of linseed oil and a synthetic drying oil "Quinton 0580*" (produced by Nippon Zeon Co.) in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as Sample 6".

Example 7 Following the procedure of Example 1, except for using trimethylopropane trimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer and a mixture of equal amounts of linseed oil and a synthetic drying oil "Quinton 0580*" (produced by Nippon Zeon Co.) in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as "Sample 7".

Example 8 Following the procedure of Example 1, except for using perilla oil in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as Sample 8".

Example 9 Following the procedure of Example 1, except for using trimethylopropane trimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer and perilla oil in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as Sample 9".

Example 10 Following the procedure of Example 1, except for using perilla oil in place of soybean oil as hardenable fluid and "MAPICO BLACK BL-250*,, (oil absorption content: 43%) as minute magnetic material powders, there was prepared a magnetic toner according to the present invention. This is called as "Sample 10".

Example 11 Following the procedure of Example 1, except for using trimethylopropane trimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer, perilla oil in place of soybean oil as hardenable fluid and "MAPICO BLACK BL-250*,, (oil absorption content: 43%) as minute magnetic material powders, there was prepared a magnetic toner according to the present invention. This is called as "Sample 11".

Comparative example 1 A magnetic toner for comparative purpose was prepared according to the same procedure as in Example 1, except for using a liquid polybutene "Nisseki Polybutene LV-50*,, (produced by Nippon Sekiyu Co.) which is a non-hardenable fluid in place of soybean oil which is a hardenable fluid. This is called as "Comparative sample 1".

Comparative example 2 A magnetic toner for comparative purpose was prepared according to the same procedure as in Example 1, except for using a chlorinated paraffin "Enpara K-45*,, (produced by Ajinomoto Co.) which is a non-hardenable fluid in place of soybean oil which is a hardenable fluid. This is called as "Comparative sample 2".

Experimental example 1 Using each of the thus prepared magnetic toners Samples 1 though 11 and Comparative samples 1 and 2, electrostatic image was developed by means of a modified electrophotographic machine of "U-Bix T*" (produced by Konishiroku Photo Industry Co.) and the toner image was transferred onto a transfer paper of plain paper, followed by fixation by means of a pressure fixer having a line pressure of 1 5 kg/cm, to obtain a visible image. In any case, there was obtained a clear and good visible image.

For each of the images formed with respective toners, presence of peel-off of the toner forming the visible image was tested by friction with the same kind of plain paper three times, namely immediately after formation, after elapse of 24 hours and after elapse of one week. The results are shown in the following Table 1.

Table 1 Immediately after formation After 24 hrs. After 1 week Sample 1 Present Slight None 2 Present Slight None 3 Present Slight None 4 Slight None None 5 Slight None None 6 Slight None None 7 Slight None None 8 None None None 9 None None None 10 Present Slight None 11 Present Slight None Comparative sample 1 Present Present Present 2 Slight Slight Slight As apparently seen from the results in Table 1, the visible image obtained by the toner of the present invention is increased in durability with lapse of time and therefore can give excellent storability.

Example 12 In the formulation of Example 1, minute magnetic material powders and lecithin were omitted and 7 g of acidic carbon black "Morgal L*,, (produced by Cabott Corporation) was added in place thereof, following otherwise the same procedure as in Example 1, to prepare a toner according to the present invention. A developer was prepared by mixing 5 parts by weight of the toner with 100 parts by weight of iron powder carriers coated with styrene-acrylic resin (average particle size: 70--90 pl).

With the use of this developer, a copied image was formed by means of an electrophotographic copying machine "U-Bix V*" modified into the pressure-fixing type, whereby an excellent image with good fixing property was obtained.

Example 13 Styrene (polymerizable monomer) 50 g Neopentylglycol dimethacryiate (crosslinking monomer) 100 g Liquid polybutene "Nisseki Polybutene LV-50*" (produced by Nippon Sekiyu Co.) 150 g Minute magnetic material powders 300 g Lecithin (coupling agent for magnetic material) 39 Carnauba wax 109 The above materials were homogeneously mixed under stirring at 60-700C. In the resultant monomeric mixture, 7.5 g of a polymerization initiator lauroyl peroxide was dissolved.The mixture was dispersed into 3000 ml of water, having dispersion stabilizers of 20 g of colloidai calcium phosphate and 0.2 g of sodium dodecylbenzenesulfonate dispersed therein, by means of a stirrer homo-jetter at 5000 r.p.m. for about 30 minutes to make the average particle size of the dispersed particles 10-1 5 by observation with an optical microscope. The resultant dispersion was charged into a four-necked flask and the temperature of the system was raised to 750C while under stirring at 300 r.p.m., at which temperature polymerization was initiated and the reaction was conducted at the same temperature for 10 hours. Then, hydrochloric acid was added to decompose and dissolve the dispersion stabilizers, followed by filtration of the solid.The solid product was washed with water and dried to prepare a magnetic toner according to the present invention, having an average particle size of 1 2 X. This is called as "Sample 13".

Example 14 Example 1 3 was repeated, except that an adipic acid type polyester "ADK Cizer PN-200*,, (produced by Adeka-Argas Kagaku Co.) was used in place of the liquid polybutene as liquid substance, to prepare a magnetic toner according to the present invention. This is called as "Sample 14".

Example 15 Example 1 3 was repeated, except that a chlorinated paraffin "Enpara K-SD*,, (produced by Ajinomoto Co.) was used in place of the liquid polybutene as liquid substance to prepare a magnetic toner according to the present invention. This is called as "Sample 15".

Example 16 Example 1 3 was repeated, except that ceresin was used in place of carnauba wax as the wax, to prepare a magnetic toner according to the present invention. This is called as "Sample 16".

Example 17 Example 13 was repeated, except that bees wax was used in place of carnauba wax as the wax, to prepare a magnetic toner according to the present invention. This is called as "Sample 17".

Example 18 Example 13 was repeated, except that an adipic acid type polyester "ADK Cizer PN-200*" (produced by Adeka-Argas Kagaku Co.) was used in place of the liquid polybutene as liquid substance and ceresin was used in place of carnauba wax as the wax, to prepare a magnetic toner according to the present invention. This is called as "Sample 18".

Example 19 Example 1 3 was repeated, except that a chlorinated paraffin "Enpara K-SD*,, (produced by Ajinomoto Co.) was used in place of the liquid polybutene as liquid substance and bees wax in place of carnauba wax as the wax, to prepare a magnetic toner according to the present invention. This is called as Sample 19".

Example 20 Example 1 3 was repeated, except that an epoxidized soybean oil "ADK Cizer 0-1 30P+" (produced by Adeka-Argas Kagaku Co.) was used in place of the liquid polybutene as liquid substance, to prepare a magnetic toner according to the present invention. This is called as "Sample 20".

Example 21 Example 1 3 was repeated, except that an epoxidized soybean oil "ADK Cizer 0-1 30P" (produced by Adeka-Argas Kagaku Co.) was used in place of the liquid polybutene as liquid substance and ceresin as the wax in place of carnauba wax, to prepare a magnetic toner according to the present invention.

This is called as "Sample 21".

Comparative examples 3-5 Examples 1 3-1 5 were repeated, respectively, except that carnauba wax was omitted in each case, to prepare three kinds of toners for comparative purpose. These are called as "Comparative sample 3"-"Comparative sample 5", respectively.

Experimental example 2 Using each of the thus prepared magnetic toners Samples 13 through 21 and Comparative samples 3 through 5, electrostatic image was developed by means of a modified electrophotographic machine of "U-Bix T*" (produced by Konishiroku Photo Industry Co.) and the toner image was transferred onto a transfer paper of plain paper, followed by fixation by means of a pressure fixer having a line pressure of 1 5 kg/cm. For each of the thus obtained visible image with the use of each toner, fixing characteristic was tested by rubbing with a plastic eraser until no change was recognized.

Generation of strike through by the toner was also examined. The results are shown in Table 2, in which the marks for the fixing characteristic mean the following: no no peel-off of toner at all; 0: slight peel-off of toner when strongly rubber; A: a part of toner peeled off; X: toner easily peeled off.

Table 2 Fixing characteristic Presence of strike through Sample 13 0 None Sample 14 (i) None Sample 15 G None Sample 1 6 Go None Sample 17 0 None Sample 18 G None Sample 19 0 None Sample 20 0 None Sample 21 G None Comparative sample 3 X Present 4 A Slightly present 5 A Present As can be judged from the results in this Table, it is possible to form excellent visible images which are very excellent in fixing characteristic and completely free from strike through by use of the toner of the present invention.

Example 22 In the formulation of Example 13, minute magnetic material powders and lecithin were omitted and 7 g of acidic carbon black "Morgal L*" (produced by Cabott Corporation) was added in place thereof, following otherwise the same procedure as in Example 13, to prepare a toner according to the present invention. A developer was prepared by mixing 5 parts by weight of the toner with 100 parts by weight of iron powder carriers coated with styrene-acrylic resin (average particle size: 70-90 fly).

With the use of this developer, a copied image was formed by means of an electrophotographic copying machine "U-Bix V*" modified into the pressure-fixing type, whereby there was obtained an excellent image which was good in fixing characteristic without strike through.

Example 23 Styrene (polymerizable monomer) 50 g Ethyleneglycol dimethacrylate (crosslinking monomer) 100 g Soybean oil 150 g Ceresin lOg Minute magnetic material powders 300 g Lecithin (coupling agent for magnetic material) 39 The above materials were homogeneously mixed under stirring at 6070 C. In the resultant monomeric mixture, 7.5 g of a polymerization initiator lauroyl peroxide was dissolved.The mixture was dispersed into 3000 ml of water, having dispersion stabilizers of 20 g of colloidal calcium phosphate and 0.2 g of sodium dodecylbenzenesulfonate dispersed therein, by means of a stirrer homo-jetter at 5000 r.p.m. for about 30 minutes to make the average particle size of the dispersed particles 10-1 5 zt by observation with an optical microscope. The resultant dispersion was charged into a four-necked flask and the temperature of the system was raised to 750C while under stirring at 300 r.p.m., at which temperature polymerization was initiated and the reaction was conducted at the same temperature for 10 hours. Then, hydrochloric acid was added to decompose and dissolve the dispersion stabilizers, followed by filtration of the solid.The solid product was washed with water and dried to prepare a magnetic toner according to the present invention, having an average particle size of 1 2 flt. This is called as "Sample 23".

Example 24 Following the procedure of Example 23, except for using neopentylglycol dimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer, there was prepared a magnetic toner according to the present invention. This is called as "Sample 24".

Example 25 Following the procedure of Example 23, except for using perilla oil in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as "Sample 25".

Example 26 Following the procedure of Example 23, except for using neopentylglycol dimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer and perilla oil as the hardenable fluid in place of soybean oil, there was prepared a magnetic toner according to the present invention. This is called as "Sample 26".

Example 27 Following the procedure of Example 23, except for using linseed oil in place of soybean oil as the hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as "Sample 27".

Example 28 Following the procedure of Example 23, except for using a mixture of equal amounts of perilla oil and a synthetic drying oil "Quinton 0580*" (produced by Nippon Zeon Co.) in place of soybean oil as hardenable fluid, there was prepared a magnetic toner according to the present invention. This is called as "Sample 28".

Example 29 Following the procedure of Example 23, except for using Japan wax in place of ceresin as the wax, there was prepared a magnetic toner according to the present invention. This is called as "Sample 29".

Example 30 Following the procedure of Example 23, except for using neopentylglycol dimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer and Japan wax in place of ceresin as the wax, there was prepared a magnetic toner according to the present invention. This is called as "Sample 30".

Example 31 Following the procedure of Example 23, except for using neopentylglycol dimethacrylate in place of ethyleneglycol dimethacrylate as the crosslinking monomer, perilla oil in place of soybean oil as hardenable fluid and Japan wax in place of ceresin as the wax, there was prepared a magnetic toner according to the present invention. This is called as "Sample 31".

Example 32 Following the procedure of Example 23, except for using perilla oil in place of soybean oil as hardenable fluid and Japan wax in place of ceresin as the wax, there was prepared a magnetic toner according to the present invention. This is called as "Sample 32".

Example 33 Following the procedure of Example 23, except for using bees wax in place of ceresin as the wax, there was prepared a magnetic toner according to the present invention. This is called as "Sample 33".

Example 34 Following the procedure of Example 23, except for using carnauba wax in place of ceresin as the wax, there was prepared a magnetic toner according to the present invention. This is called as "Samp;e 34".

Comparative example 6 A magnetic toner for comparative purpose was prepared according to the same procedure as in Example 23, except for emitting ceresin in the formulation of Example 23 and using a liquid polybutene "Nisseki Polybutene LV-5O*,, (produced by Nippon Sekiyu Co.) which is a non-hardenable fluid in place of soybean oil which is a hardenable fluid. This is called as "Comparative sample 6".

Comparative example 7 A magnetic toner for comparative purpose was prepared according to the same procedure as in Comparative example 6, except for using a chlorinated paraffin "Enpara K-45*,, (produced by Ajinomoto Co.) as non-hardenable fluid in place of the liquid polybutene. This is called as "Comparative sample 7".

Comparative example 8 Ethylene-vinyl acetate copolymer 150 g Minute magnetic material powders 150 g The above materials were kneaded by heating on two rolls, followed by pulverization to prepare a magnetic toner with average particle size of 12,zz for comparative purpose. This is called as "Comparative sample 8".

Experimental example 3 Using each of the thus prepared magnetic toners Samples 23 through 34 and Comparative samples 6 through 8, electrostatic image was developed by means of a modified electrophotographic machine of "U-Bix T*" (produced by Konishiroku Photo Industry Co.) and the toner image was transferred onto a transfer paper of plain paper, followed by fixation by means of a pressure fixer having a line pressure of 1 5 kg/cm. For each of the thus obtained image with the use of each toner, fixing characteristic test was performed by rubbing with a plastic eraser of the image immediately after formation and after elapse of one week. Presence of strike through and show through generated was also examined. The results are shown in Table 3, in which the marks for the fixing characteristic mean the following: no no peel-off of toner at all; 0: slight peel-off of toner when strongly rubbed; A: a part of toner peeled off; X: toner easily peeled off.

Table 3 Presence of Presence of Fixing characteristic strike show Immediately After one Sample no. through through after formation week 23 None None O (i) 24 None None (@ ) 25 None None (i 26 None None 0 0 27 None None 0 0 28 None None O (i) 29 None None O 30 None None G 31 None None O (i) 32 None None O 33 None None O (g 34 None None O Sj Comparative sample 6 Present Present A A 7 Present None O 0 8 None Present X X As can be judged from the results in Table 3, the toner of the present invention can perform good fixing without strike through and show through, and also the visible image is increased in durability with lapse of time to give excellent storability.

Example 35 In the formulation of Example 23, minute magnetic material powders and lecithin were omitted and 7 g of acidic carbon black "MA-8*,, (produced by Mitsubishi Kasei Kogyo Co.) was added in place thereof, following otherwise the same procedure as in Example 23, to prepare a toner according to the present invention. A developer was prepared by mixing 5 parts by weight of the toner with 100 parts by weight of iron powder carriers coated with styrene-acrylic resin (average particle size: 70-90 y).

With the use of this developer, a copied image was formed by means of an electrophotographic copying machine "U-Bix V*,, modified into the pressure-fixing type, whereby there was obtained an excellent image which was good in fixing characteristic without probiems such as strike through.

Claims (30)

Claims

1. A toner for development of an electrostatic image, comprising a fluid core material selected from the group consisting of (a) fluid substances hardenable under an oxygen-containing atmosphere which may optionally be admixed with a wax and (b) mixtures comprising at least one liquid substance and at least one wax encapsulated within a capsule comprising a vinyl type resin.

2. A toner according to claim 1, wherein the fluid core material is a fluid substance hardenable under an oxygen-containing atmosphere.

3. A toner according to claim 2, wherein the fluid substance hardenable under an oxygencontaining atmosphere is admixed with a wax.

4. A toner according to claim 2 or claim 3, wherein the fluid substance hardenable under an oxygen-containing atmosphere is a drying oil or a semi-drying oil of an unsaturated fatty acid ester.

5. A toner according to claim 4, wherein the fluid substance hardenable under an oxygencontaining atmosphere is selected from the group consisting of linoleic acid, linolenic acid, oleic acid, elaidic acid, eleostearic acid, linolenelaidic acid, gadoleic acid, erucic acid, arachidonic acid, clupanodonic acid, c-licanic acid, linseed oil, perilla oil, tung oil, hempseed oil, kapok oil, poppy seed oil, sesame oil, rice bran oil, safflower oil, soybean oil, corn oil, rapeseed oil, sunflower oil, cottonseed oil, cuttlefish oil, salmon oil, saury oil, tallow and mutton tallow.

6. A toner according to claim 3, wherein the wax has a melting point of 50 to 1800 C.

7. A toner according to claim 6, wherein the wax is selected from natural waxes, paraffin waxes, fatty acid esters or partially saponified products thereof, alkylene-bis-fatty acid amides and higher fatty acids.

8. A toner according to claim 3, claim 6 or claim 7, wherein the wax is contained in an amount of 1 to 30% by weight based on the fluid substance hardenable under an oxygen-containing atmosphere.

9. A toner according to claim 8, wherein the wax is contained in an amount of 5 to 15% by weight.

10. A toner according to claim 1, wherein the fluid core material is a mixture of a liquid substance and a wax.

11. A toner according to claim 10, wherein the liquid substance is one selected from the group consisting of polybutene, polychloroprene, polybutadiene, polyester, acrylate or oligomer of acrylate, oligomer of styrene type monomer, oligomer of copolymer of styrene with alkyl acrylate or alkyl methacrylate, chlorinated paraffin, epoxidized soybean oil, epoxidized triglyceride, adipic acid type polyester, octylepoxy stearate, trioctyl trimellitate, dipentaerythritol ester, adipic acid ester, dibutyl phthalate, dioctyl phthalate, tricresyl phosphate, triphenyl phosphate, olive oil, Tsubaki (camellia) oil, silicone oil, mineral oil, asphalt, gilsonite, cr-pinene resin, 13-pinene resin, epoxy resin, n-pinene phenol resin and dipentene resin.

12. A toner according to claim 10 or claim 11, wherein the wax has a melting point of 50 to 1800C.

1 3. A toner according to claim 12, wherein the wax is selected from natural waxes, paraffin waxes, fatty acid esters or partially saponified products thereof, alkylene-bis-fatty acid amides and higher fatty acids.

14. A toner according to any of claims 10 to 13, wherein the wax is contained in an amount of 1 to 30% by weight based on the fluid substance hardenable under an oxygen-containing atmosphere.

1 5. A toner according to claim 14, wherein the wax is contained in an amount of 5 to 15% by weight.

16. A toner according to any of claims 1 to 15, wherein the vinyl type resin is a polymer of at least one monomer selected from the group consisting of styrenes, ,I-methylenealiphatic monocarboxylic acid ester, vinyl nitriles, vinyl ethers, vinyl pyridines, N-vinyl cyclic compounds, vinyl ketones, halo-containing olefins, olefins and polyacrylates or polymethacrylates of polyols.

1 7. A toner according to claim 1 6, wherein the polymer is crosslinked.

1 8. A toner according to any of claims 1 to 17, wherein there is incorporated a colorant.

19. A toner according to claim 18, wherein the colorant is carbon black.

20. A toner according to any of claims 1 to 19, wherein there are incorporated magnetic powders.

21. A toner according to claim 20, wherein the magnetic powders are magnetite powders.

22. A process for producing a toner for development of an electrostatic image, which comprises dispersing oil droplets comprising a polymerizable vinyl monomer and a liquid substance in an aqueous system to be suspended therein and then polymerizing said polymerizable monomer to form a polymer insoluble in said liquid substance, whereby outer walls of suspended particles are formed to coat said liquid substance.

23. A process according to claim 22, wherein the liquid substance is hardenable under an oxygen-containing atmosphere.

24. A process according to claim 22 or 23, wherein a wax is further dispersed in the oil droplets.

25. A process according to any of claims 22 to 24, wherein a colorant is further dispersed in the oil droplets.

26. A process according to any of claims 22 to 25, wherein magnetic material powders are further dispersed in the oil droplets.

27. A process according to claim 26, wherein the magnetic material has an oil absorption content of not more than 35%.

28. A process according to claim 27, wherein the oil absorption content is within the range of from 10 to 30%.

29. A process according to any of claims 26 to 28, wherein the magnetic material powders are pre-treated with a coupling agent.

30. A process according to any of claims 26 to 28, wherein a coupling agent is added to the oil droplets.