GB1570239A - Electrically insulating magnetic toner for developing an electrostatic latent image - Google Patents

Description

(54) AN ELECTRICALLY INSULATING MAGNETIC TONER FOR DEVELOPING AN ELECTROSTATIC LATENT IMAGE (71) We, KONISHIROKU PHOTO IN DUSTY Co. LTD., a Corporation organized and existing under the laws of Japan, of 10,1,3, Muromachi, Nihonbashi, C7huo-ku, Tokyo, 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:: The present invention relates to a magnetic toner for developing an electrostatic latent image in electrophotography, electrostatic recording or electrostatic printing, and in detail a transferable, one-component, elec trically insulating magnetic toner for de veloping an electrostatic image, said toner making a main component of only toner particles and containing no carrier and a process for the preparation thereof.

Methods of developing an electrostatic charge are roughly divided into liquid de veloping methods, using a developer in which various pigments or dyestuffs are finely dispersed in an insulating organic liquid, and dry methods, such as a cascade method or magnetic brush method, using a developer in which a carrier consisting of iron powders or glass beads is mixed with finely crushed electroscopic powder, called a toner, in which colorants such as carbon black are contained in dispersion in natural or synthetic resins, and a fur brush method, an impression method, a powder cloud method and an open chamber method, using a developer consisting only of said toner without a carrier mixed.The present invention relates to a developer of the type using a developer consisting only of a toner without a carrier mixed, among the latter dry developing methods and a process for the preparation thereor.

Generally, in a two-component developer, when a toner and a carrier are agitated mechanically, triboelectricity occurs be tween the toner and the carrier, the carrier is charged to a polarity, the toner has an electric charge of polarity opposite the carrier and a latent electrostatic image can be developed. Generally the toner is subjected to mechanical wear due to shearing force or impact strength it receives during its mechanical movement within a developing device, and after development of several thousand times it gets deteriorated. And when relative humidity is high, frictional electric charging properties and fluidity characteristic of a lot of carrier particles are adversely affected, and, for instance, the value of triboelectric charge of a certain type of carrier substance varies with relative humidity. This is undesirable for use in a device of electrophotography.

In order that these defects may be eliminated, a one-component developer making a main component of only a toner and containing no carrier has been proposed. For instance, in U.S. Patent 3,639,245 has been disclosed the so-called electrically conductive toner, in which ferromagnetic fine particles, such as ferrosoferric oxide, a thermoplastic resin, such as an epoxy resin, and electrically conductive carbon black are combined. Said magnetic toner could eliminate the above defects of a two-component developer, but on the other hand, since said magnetic toner is electrically conductive, part or the whole of a powder image consisting of the same magnetic toner is disturbed and a good transferred image is not obtained, when transferring is conducted onto the paper with the use of a most universal and easily controllable corona discharger.

The Applicant, on making research to develop a transferable magnetic tone, has completed a developer of only a toner making a main component of a resin and a ferromagnetic substance, the ferromagnetic substance being fine particles having triboelectric tendency against said resin and being uniformly dispersed in the resin and comprising toner particles formed so that magnetic substance fine powders 'are 'sub stantially exposed from the resinous surface on the toner particle surface and further being electrically insulating as the whole.

Said developer of only a toner has no defects of the conventional two-component developer consisting of a toner and a carrier and is electrically insulating as the whole toner, and consequently it has enabled the transferring onto paper, which was regarded as the defect of an electrically conductive, magnetic toner. A magnetic toner prepared by a general crushing and granulating method has the defect that if it is used for a transfer type copying machine conducting repeated development and transferring, it caused the pollution of an electrophotosensitive material and with small amounts of copies the sensitized body becomes unusuable.

That is, it causes decrease in sensitivity of the electrophotosensitive material, decrease in transferring efficiency, blushing of transferring, and occurrence of transfer bleeding. It is because fine particles of 1 micron or below in particle diameter which have occurred at the time of crushing are mixed within the magnetic toner said fine particles comprising not only particles having properties as the toner but also particles free of properties as the toner, namely particles of the resin, the ferromagnetic substance and the pigment or dye. Said fine particles of about 1 micron or below sticking onto this electrophotosensitive material adhere to the magnetic toner surface so strongly that they cannot be separated by classifying procedures.Further, in the magnetic toner as crushed, the shapes of particles are fine powders of indeterminate forms and the ferromagnetic powders on the toner particle surface are in the state where they are protruded from the resin. Therefore, frictional electric charging between said magnetic toner particles occurs partly strongly and partly weakly. In consequence, said magnetic toner is poor in fluidity as a developer, causes much blushing and produces only dim copies. And when relative humidity is high, an electric charge caused by mutual friction is liable to leak and what is more, fluidity gets deteriorated, and hence, an image obtained after transferring becomes the much dimmer one which is low in image concentration and has bleeding wholly.

And as a defect of a granulating method of a spray drying type, when liquid drops formed bv spraying drv the liquid evapor- ates faster on the surface and the resin starts being solidified from the surface of the liquids drops; consequently, the interior is apt to become caverous and the vapor which has evaporated late from the interior is ant to make the resinous film prwiously solidified porous. In consequence, the thus resulted powder substance is weak in mechanical strength, and when it is used in a developing device of the copying machine, the particle size varies, becoming the cause of trouble.Further, another defect is that since owing to dispersion of pigments, it is impossible to obtain a stable dispersion solution by an ordinary method of dispersion, it becomes a developer having a nonuniform electric charge after drying.

Still further, on copying in great numbers, developing becomes impossible. And in order to obtain a stable dispersion solution of pigments, there is need to use more or less ionic or nonionic surfactants, and after drying the surfactants inevitably remain on the surface of the powder substance. In consequence, the particles are apt to absorb moisture in the air and the fluidity of the powder substance remarkably deteriorates.

This also causes its malfunction as a toner in the developing device. Further another defect is that since a great amount of solvent must be completely evaporated, energy consumption is great and costs of solvent recovery become extremely high. And since a magnetic toner contains a feeler (magnetic substance) in the resin, melting viscosity is relatively raised and fixing properties deteriorates. If in order to improve the fixing properties, a resin having a low softening point is used as a toner, the object is attained with respect to a question of fixing properties, but on the other hand, come out problems that blocking occurs during the preservation or toner filming is caused on the surface of an electrophoto sensitive material.

The present invention provides a magnetic toner, for developing an electrostatic latent image, comprising particles comprising a thermoplastic resin and a powdered ferromagnetic substance, said toner comprising at least one additive selected from metallic soaps; fatty acids, amides or alcohols having at least 8 carbon atoms; lubricating hydrocarbons; and lubricating esters, said additive having a content gradient such that the content is higher at the surface than in the interior of said toner particles, and said toner having a character such that an electrostatic charge necessary to form an electrostatic latent image can be obtained by mutual friction of said toner particles and said toner particles have an electric resistance of 1414cm.

The present invention also provides a process for the preparation of a magnetic toner as defined above, which comprises the steps of mixing the compound selected from metallic soaps, fatty acids, fatty amides, alcohols, lubricating hydrocarbons and lubricating esters; the thermoplastic resin, and the powdered ferro magnetic substance kneading, crushing to form particles and heat-treating at a temperature range higher than the softening point of the thermoplastic resin.

It has been found that pollution of an electrophotosensitive material of the magnetic toner, occurs when fine particles about 1 micron or below in particle diameter are adhered to, or mixed with, the toner particles. It is found that when this magnetic toner is treated, for instance, in a hot gas current of a temperature higher than the softening point of the constituting resin, fine particles 1 micron or below in particle diameter electrically or physically sticking to the toner surface can be substantially eliminated.During the heat-treatment the above mentioned additive leaches out on to the magnetic toner resinous surface and exhibits a concentration gradient such that the content is higher at the surface than in the interior of said toner particles and at the same time, said fine particles 1 micron or below in particle diameter are easily fused in the additive on the softened toner resinous surface or in the resin and, after cooling, are tightly held. In consequence, pollution of the electrophotosensitive material disappears, resulting in a developer having a good durability. Further, it becomes possible to prevent toner filming on the sensitized body to the utmost and use the electrophotosensitive material repeatedly.And it is found that since the additive leaches out on to the magnetic toner resinous surface, it becomes possible to use a resin having a low softening point as a thermoplastic resin to be used as a binder, and it is possible to provide a one-component magnetic toner excellent in fixing properties, and what is more, it is also possible in view of the above fact to prevent blocking at temperatures of a storage container or copying machine.

Further, it is found that since an additive to be used in the present invention has an electric charging property proper for developing, it is excellent in gradation, antiblushing and transferring and can easily provide a clear image and said toner particles made spherical have very excellent effects in fluidity and cleaning properties. As for thermoplastic resins to be used as a binder. styrene-type resins, epoxy-type resins and polyester-type resins (hereinafter called the resin used in the present invention) can bring a clear copy excellent in image-forming properties as compared with other resins.

A resin used in the present invention is the one having a softening point of preferably 50 to 2000C and most preferably 70 to 150"C.

Said thermoplastic resins have the advantage that thev are excellent in crushability and apt to fuse fine particles 1 micron or below in particle diameter, which are liberated among toner particles. These resins have very fine characteristics that the occurrence of fine particle 1 micron or below in particle diameter is very rare in crushing and owing to low melting viscosity even in the steps of heat-treatment on comparison with other resins, they are fully melted even in instantaneous heat-treatment to fuse fine particles 1 micron or below in particle diameter and they become easily spherical. The amount of additive is preferably 0.1 to 65% by weight, most preferably 0.2 to 20% by weight, based on the weight of the magnetic toner.The magnetic toner according to the invention because of the electric resistance of 10l4Qcm. or above, is an insulating magnetic toner for developing a latent elec trostatic image in which generally, in a given measuring method, the dark decay factor (V-leak) or potential of a toner de veloped on an electrophotosensitive material is less than 50% .The dark decay factor of potential is calculated as follows: Development of a given area is conducted on a zinc oxide sensitized paper and photoirradiation is spontaneously given to the extent that a latent image is not perfectly but almost erased to produce a toner potential, and after interception, dark decay is recorded for a short time (within one minute) by putting a phototransparency-type electrometer (point A in Fig. 2, time = t1).Then, if whole surface irradiation is given at point B, the remaining latent image is completely erased, and hence, potential rise up to point C and later continues to drop. Then, if curve ABCD is obtained, a curve parallel to curve AB is drawn from point C, intersecting with time tl at point E. Potential V1 at point E is an initial potential of the toner layer when there is no latent image, and there is substantially no potential decay due to photoirradiation. Let potential at t (3 minutes later than t1) be V2 and V1 - V2 x x 100% V2 indicates the decay factor of potential.

As a magnetic substance usable in the present invention, it is desirable that it be a substance strongly magnetized by the magnetic field in its direction, preferably black in color, dispersed well in resin, chemically stable and that fine particle type 1 micron or below in particle diameter be easily obtained. Thus, magnetite (ferrosoferric oxide) is most desirable.As typical magnetic or magnetizable materials, are usable metals such as cobalt, iron and nickel an alloy of metals such as aluminum, cobalt, copper, iron, lead, magnesium, nickel, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium manganese, selenium, titanium, tungsten and vanadium and the mixture thereof; a metal compound containing metal oxides such as aluminum oxide, iron oxide, copper oxide, nickel oxide, zinc oxide, titanium oxide and magnesium oxide; a refractcry nitride such as vanadium nitride and chromium nitride; carbides such as tungsten carbide and silica carbide; and ferrites and the mixture thereof. In these ferromagnetic substances, the one having an average particle diameter of 0.1-1 micron is desirable and the amount contained in a toner is preferably 35 to 60 parts by weight based on 100 parts by weight of the toner.

As a resin, styrene-type resins, epoxytype resins and polyester-type resins are preferable.

For example, as styrene-type resin, a homopolymer of styrene, or a copolymer of a monomer of vinyl series with styrene will do. In monomers for forming these copolymers, are listed p-chlorostyrene, vinylnaphthalene and unsaturated olefins of ethylene series such as ethylene, propylene, butylene, isobutylene and butadiene, vinylhalides such as vinyl chloride, vinyl bromide and vinyl fluoride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate; a,!ssunsatur- ated aliphatic monocarboxylic acid esters such as methyl acrylate, ethyl acrylate, nbutyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, ethyl i chloro- acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate and dialkylaminoethyl methacrylate; acrylonitrile; acrylamides; vinyl ethers such as vinylmethyl ether, vinylethyl ether and vinylisobutyl ether; vinylketones such as vinylmethylketone, vinylhexylketone and methylisopropenyl ketone; N-vinyl compounds such as N-vinyl pyrrole. N-vinyl carbazole, Nvinyl indole and N-vinylpyrrolidine; and proper styrene-type resins in which one or more of them can be copolymerized with a styrene monomer, has a weight average molecular weight of 3,000 or above. And thermoplastic resins in which styrene-type resins are mixed with other resins can be used as a toner resinous component in the present invention.

And in polyester resins, as diols and dicarboxylic acids constituting their components, are listed the following: For instance. as for dicarboxylic acids, are listed succinic acid, phthalic acid, isophthalic acid. terephthalic acid, maleic acid, maleic anhydride, fumaric acid, fumaric anhydride. trans-hexahvdroterephtharic acid, diphenyl-p.pl-dicarboxylic acid, benzo phenone-4.41-dicarboxvlic acid. naphthalene 2,7-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid. 1,2-diDhenoxvethane-p,pl- dicarboxylic acid, 1,3-diphenoxypropane p,pWcarboxylic acid, 1 ,4-diphenoxybutane- p,pl-dicarboxylic acid and the one similar to those.

As diols are listed ethylene glycol, 1,3propylenediol, trimethylene glycol, tetra methylene glycol, 1,4-butylene diol, 1,5pentylene glycol, hexamethylene glycol, heptamethylene glycol, octamethylene glycol, nonamethylene glycol, decamethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol p-di(hydroxymethyl)-benzene, cis- and trans-quinitol, hydroquinone di CP-hydroxethyl) ether, 4,41-dihyroxy-bisphenyl, bis-(4-hydroxyphenyl) methane, bis (4-hydroxyphenyl) diphenylmethane, bis (hydroxyphenyl) ether and bis(hydroxyphenyl) sulfone.

Suitable polyhydric alcohols usable as an optional branch-forming agent in said polyesters are a polyhydric alcohol containing 3 to 15 carbon atoms and 3 to 8 hydroxyl groups. As typical polyhydric alcohols are listed sugar alcohols such as glucose, fructose, ribose, maltose, lactose, anhydrous sugar alcohols, monosaccharides and disaccharides and the alkylene oxide derivatives thereof. Of these polyhydric alcohols, are desirable sorbitol, 1,2,3,6-hexanetetrol, 1 .4-sorbitan, pentaerythritol, tripentaerythritol, 1,2,Sbutanetriol 1 2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl 1 ,2,4-butanetriol, trimethylolethane, tri methyloipropane and 1,3,5-trihydroxymethylbenzene and mixtures thereof.

Polycarboxylic acids or the esters thereof usable as an optional branch-forming agent in said polyesters, are acids and esters having 3 to 60 carbon atoms and 3 to 8 carboxyl groups. As typical polycarboxylic acids and the esters thereof are listed 1,2,4- benzenetricarboxylic acid, 1,2.5,-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7, - naphthalene tricarboxylic acid, 1,2,4-naphthalenetri carboxylic acid, 1,2,4-butanetricarboxylic acid, 12,5-hexanetricarboxylic acid, 1,3-dicarboxyl - 2 - methylene carboxylpropane, 1,3 - dicarboxyl - 2 - methylenecarboxylpropane, 1,3 - dicarboxyl - 2 - methyl - 2methylenecarboxylpropane, tetra(methylene- carboxyl) methane, 1,2,7,8,-octanetetracarboxylic acid, and mixtures thereof. These branch-forming agents are employed to lower the melting point of polyesters. Many conventional polyesters have a softening point of about 200"C, and are inappropriate as a resin to be mixed with a toner for use in electrophotography. By introduction of branches to them using a branch-forming agent, the one having a lower melting point and a high Tg is obtained. The content of the branches is preferably 10 molo/o of below.

As epoxy-type resins usable in the present invention are exemplified the following typical ones commerically available.

Epikote (Registered Trade Mark) 1002, 1004, 1007 DX-55 (made by Shell Chemical), Araldite (Registered Trade Mark) 6084, 7072, 7097, 6097 (made by CUBA) Eposerm CE-80 made by Mitsubishi Chemical), EPX 43 (made by Asahi Denka), AER 664, 667 (made by Asahi Chemical) and so forth.

As other resins to be mixed with the thermoplastic resin used in the present invention are listed a homopolymer obtained by polymerizing the monomers of vinyl naphthalene, vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride, vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate, uyl-unsaturated aliphatic monocarboxylic acid esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloro-ethyl acrylate, phenyl acrylate, methyl n-chloro acrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate, acrylonitrile, methacrylonitrile, acrylamides, vinyl ethers such as vinyl methyl ether, vinylisobutyl ether and vinylethyl ether, vinyl ketones such as vinyl methylketone, and N-vinyl compounds such as Nvinylpyrrole, N-vinylcarbazole, N-vinylindole and N-vinylpyrrolidine, or a copolymer obtained by combining more than one of these monomers, or non-vinyl-type thermoplastic resins such as rosin-modified phenolformaldehyde resins, oil-modified epoxy resins, polyurethane resins, cellulosic resins and polyether resins.

As fatty acids having at least 8 carbon atoms to be added in the present invention, are listed the following typical examples: Lauric acid, myristic acid, palmitic acid, stearic acid, arachic acid, behenic acid, lignoceric acid, selacholeic acid, and mixtures thereof can be mentioned.

As metallic soaps to be used in the present invention, are listed the following typical examples: Metal salts of stearic acid with zinc, cadmium, barium, lead, iron, nickel, cobalt, copper, aluminium, or magnesium; lead dibasic stearate (PbO); metal salts of oleic acid with zinc, magnesium, iron, cobalt, copper, lead, or calcium; metal salts of palmitic acid with aluminium, or calcium; lead caprylate; lead caproate; zinc linoleate; cobalt linoleate; calcium ricinoleate; metal salts of ricinoleic acid with zinc or cadmium; and mixtures thereof can be mentioned.

As fatty amides to be added to the toner of the present invention, are preferable fatty amides and bis-fatty amide compounds, having a melting point of 60"C or above.

The following are typical examples: As fatty amides are listed lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, arachic acid amide, behenic acid amide, oleic acid amide, linolic acid amide, linolenic acid amide, gadoleic acid amide, erucic acid amide or selacholeic acid amide; as bis-fatty amides are listed bis-lauric acid amide, bis-myristic acid amide, bis-palmitic acid amide, or bisstearic acid amide; as alkylene bis-fatty amides are listed 1 C10H21CO--NH--(CH2)5--NH--OCC10H21 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 C17H35CO--NH--CH2--N H--OCC17H35 7 C17H35CO--NH--(CH2)2-NH-OCC15H31 8 C23H47CO--NH--CH2--NH--OCC15H31

As alcohols having at least 8 carbon atoms to be added in the present invention either monohydric alcohols or polyhydric alcohols will do; for instance, lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, arakyl alcohol, on behenyl alcohol.

As fatty esters usable in the present invention can be used esters of fatty acids and monohydric alcohols, esters of fatty acids and polyhydric alcohols, partial esters of fatty acids and polyhydric alcohols. In the present invention, these fatty esters or their partial saponified products may be used singly or the mixture consisting of the composition obtained by blending various types of fatty esters or the mixture consisting of the composition obtained by blending fatty esters and their partial saponified products can be used. In the present invention, the ones commercially available as fatty esters or their partial saponified products can be effectively used and many commercially available ones have a composition of the mixtures mentioned above.

Lubricating hydrocarbons usable in the present invention can be natural paraffin microwax, synthetic paraffin, or chlorinated hydrocarbons.

The mixing ratio of additives usable in the present invention is generally 0.1 to 65% by weight, and most preferably 0.2 to 20% by weight, based on the total weight af the toner. If it is too much in amounts, it is difficult to obtain a good image and appropriate conditions in developing, and if it is too little in amounts, it becomes difficult to attain the initial object. Optional appropriate pigments or dyestuffs are in use as colorants in the one-component toner of the present invention.For instance, carbon black, nigrosine dye, aniline blue, calcooil blue, chrome yellow, ultramarine blue, du Pont oil red, quinoline yellow, methylene blue, chloride phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and the mixture thereof are used, and their amounts which enable clear coloring on a visible image by development are caused tci be contained in the magnetic toner.

Optionally the magnetic toner con contain 0.01 to 1.0 parts by weight of hydrophobic silica powder based on 100 parts by weight of said magnetic toner.

Then, a process for the preparation of a magnetic toner for developing a latent elect trostatic image in the present invention will be described below.

Fig. 1 is a flowchart of an electrically insulating magnetic toner in the present invention. Fig. 1 is a schematic diagram showing one example of an apparatus for preparing an insulating magnetic toner in the present invention. Fig. 2 shows the relationships between the time and the potential of a toner layer in case the dark decay factor of potential is measured.

The process for the preparation of a magnetic toner composed of a thermoplastic resin and ferromagnetic fine particles as a main component in the present invention is characterized by causing at least one additive selected from metallic soaps, fatty acids, amides alcohols having at least 8 carbon atoms, lubricating esters and lubricating hydrocarbons, for instance, in an amount from 0.1 to 65% by weight, preferably 0.2-20% by weight based on the weight of the magnetic toner; after mixing, kneading and crushing, heat4reating said magnetic toner at a temperature higher and preferably higher by 30"C than the softening point of the thermoplastic resin so that said toner particle surface turns to a state in which it is leached out with said additive.

One method of preparing the electrically insulating magnetic toner of the present invention are that first, a thermoplastic resin, magnetic substance powders, an additive used in the present invention and, if necessary, dyestuffs and pigmetns are mixed well, heated, melted, kneaded and crushed so that an average particle size of, for example, 10 to 20 microns is obtained. This crushing and granulating method has the very good advantage that the production cost is cheap, powder substance treatment is very easy, and it is very advantageous in a problem of environmental pollution.

And, for instance, this magnetic toner can be prepared by spray drying methods disclosed in U.S. Patent 3.338,991.

Then, the fine particles crushed can be spray introduced with air jet nozzles into a device forming hot gas current heated to a temperature higher than a softening point of the thermoplastic resin. The thus obtained specimen is classified into products.

One example of a device for forming said hot gas current is shown in Fig. 1. The open air is entered from air inlet 2 by operating blower 1, heated via heater 3 to à temperature higher than a softening point of the thermoplastic resin and introduced into hot gas curtent-forming device 6. At the same time, specimen 5 is introduced from air jet nozzle 4 into hot gas currentforming device 6 and spontaneously heattreated with hot gas Current 7. The toner particles heat-treated with collector S and air are separated from each other and products 10 are gathered into pot 9. On the other hand, air enters into back filter 11 through blower 1. In the preparing process of the present invention, any type of device, which forms hot gas current can be used.

As temperature conditions of heat-treatment, a temperature higher than a softening point of the thermoplastic resin will be enough and most preferably a temperature 30"C higher than the softening point brings a good result.

The hot gas current in the present invention is meant to denote a state in which a gas heated to a given temperature moves at a given speed, and the heat-treatment in the present invention a form in which a specimen to be treated is in motion at random in said hot gas current and moves together with the hot gas current as the whole system.

And the softening point of resin cannot be accurately determined, but, as one guideline, is defined by the softening point JIS K2531 (ASTM E-28-58T) meausred by the ring and ball test.

The thus obtained magnetic toner, because of no use of a carrier and of onecomponent type, has no defects of the conventional two-component developer, is electrically insulating as the whole magnetic toner particles to obtain clear copies on the transfer paper and what is more, there does not occur blocking during the storage of a toner, pollution of the electrophotosensitive material, or occurrence of blushing, and it is an electrically insulating magnetic toner for developing an electrostatic charge, which is excellent in durability and can guarantee a stable developing action only by supplementing a toner.

Then, with reference to the examples of the present invention and controls, the function and effect of this magnetic toner will be described below. Parts in the examples and the controls are parts by weight unless otherwise stated.

Control 1 Fifty parts of Hymer-SBM-73 (styrenetype resin made by San-yo Chemical), 50 parts of Mapico Black BL-500 (ferrosoferric oxide made by Chitan Kogyo), 2.5 parts of Peerless-155 (carbon black made by Columbia Carbon) and 1 part of Oil Black BS (charge controlling agent made by Orient Chemical) were mixed, and a ballmill was applied for about 24 hours, kneaded with heat roll and after cooling, crushed to prepare a toner having an average particle size of about 15 ecum. To this obtained toner was added R-972 powders of 0.2% by weight (made by Aerosil Co.) as a fluidizing agent to make a specimen. A developing device was mounted on an electrophotocopying machine of U-BIX (Registered Trade Mark) 800 type of Konishiroku Photo Industry Co.

Ltd. and filled with said speciments and repeatedly developing and transferring were conducted on a zinc sensitized material. As a result, a blushing of high concentration occurred and images stopped coming out with about 10 copies and remarkable filming occurred on the master. The one obtained by adding to said toner 5% by weight of zinc stearate, kneading and crushing it showed the same result.

Control 2 Fifty parts of Hymer-SBM-73, 50 parts of Mapico Black BL-500, 2.5 parts of Peerless155, and 1 part of Oil Black BS were mixed and a ballmill was applied for about 24 hours. Then, the mixture was kneaded with a hot roll and, after cooling, was crushed.

Said powder toner was blown into a commercially available spray dryer experimental device (Mobilemyer made by Niro, Inc.) with the use of core jet nozzles and heattreated instantaneously with a blown-in hot air of 250"C prepare a toner. Said toner was classified with a classifier to obtain a toner having an average particle diameter of 15 ,am and to the obtained toner were added 0.2% by weight silica powders as a fluidizing agent to make a specimen. The developing device described in Control 1 was filled with said toner and repeatedly, developing and transferring were conducted.

As an initial image, clear images with no transfer Blurring were obtained, but after 2000 copies a slight fog occurred and the clearance dropped as compared with the initial image. And the surface of the zinc oxide electrophotosensitive material was slightly stained. The value of V leak of this toner was 36%, Control 3 Thirty-five parts of Epikote 1004 (epoxytype resin made by Shell Chemical}, 65 parts of Mapico Black (ferrosoferric oxide male by Columbia Carbon) were dispersed in a mixed solvent of 70 parts of toluene and 30 parts of acetone and after the solids content was made 60% and the mixture was dispersed for 32 hours in a porcelain ballmill, said mixed solvent was further added to adjust the solid content of 20% and granulation was conducted by a spray drying device of rotary disc type.The thus obtained black toner particles having an average particle diameter of about 10 microns were developed and transferred with a device described in Control 1. The image developed on the electrophotosensitive material was an image having a very good gradation, but with transferred image, a big blurring occurred. And the pollution of the zinc oxide electrophotosensitive material was terrible. The value of V leak of this toner was 75.6%.

Example 1 Thirty-three parts of Hymer-SBM-73, 50 parts of Mapico Black BL-500, 2.5 parts of Peerless-155, 1 part of zinc stearate and 1 part of behenyl alcohol were thoroughly kneaded with a pressure kneader. The resulting mixture was roughtly crushed after cooling and further finely crushed with a jet mill. Then said crushed toner was blown into a spray dryer experimental device with the use of air jet nozzles and specimens each were instantaneously heat-treated at each hot air temperature of 100"C, 125"C, 1500C, 175"C, 200"C and 250"C to prepare insulating magnetic toner.Each toner thus prepared was classified with a classifier so as to obtain a toner having an average particle size of 15 microns and to the obtained toner was added 0.2% by weight of silica powders as a fluidizing agent to obtain specimens Nos. 1-6. And . separately control specimen No. 7 similar to specimens Nos. 1-6 was prepared in the same way as above except by an instantaneous heat-treatment at 400"C with said spray dryer. Further, control specimen No.

8 similar to specimens Nos. 1-6 was prepared execept with no heat-treatment. In Table 1 are given (1) the values obtained by measuring the content of fine particles 1 micron or below in particle diameter within those specimens with a Centrifugal Photo Sediment meter (made by Seishin Kigyo), (2) the number of sheets copiable at a time when repeatedly developing and trans ferring were carried out on the zinc oxide electrophotosensitive material with 5,000 sheets being aimed at and (3) the values of image evaluation classified to three stages of O--excellent, X-poor and A-slightly poor.

Table 1 (1) (2) (3) Average- Content of No. of Heating particle particle 1 copiable Specimen temperature dia. y or below sheet Image No. ( C) (microns) (%) (sheet) evaluation No. 1 100 14 0.10 200 0 No. 2 125 14 0.05 1,000 0 No. 3 150 15 0 3,500 0 No. 4 175 16 0 5,000 0 No. 5 200 14 0 5,000 0 No. 6 250 15 0 5,000 0 No. 7 400 18 0 400 A No. 8 - 13 1.2 10 X Note. Nos. 2-6 are specimens prepared by the process of the present invention.

Example 2 A recipe of 50 parts of Hymer-ST-95 (polystyrene made by San-yo Chemical), 50 parts of Mapico Black BL-500, 2.5 parts of Peerless-155, 1 part of stearyl alcohol and 2 parts of 15Q C microparaffin was treated the same as Control 2 and developing and transferring were repeatedly conducted and even after copying of 20,000 sheets, images as clear as the initial image were obtained.

The value of V leak was 8.9%.

Example 3 Fifty parts of Chemitylen PEB-4 (polyester resin made by San-yo Chemical), 50 parts of Mapico Black BL-500, 2 parts of Peerless-155, 1.5 parts of stearic acid amide, l part of Rytol (made by Sanwa Yushi) were treated the same as specimen No. 4 in Example 1 was. A selenium sensitized photosensitive material was mounted, instead of a zinc oxide one, on a U-BIX 2000 R copying machine made by Konishiroku Photo Industry Co Ltd. and repeatedly developing and transferring were conducted and even after 50,000 copies, a clear image the same as the initial image was obtained.

And even after 50.000 copies, several hundred thousand copies could be thought to be guaranteed. The value of V leak was 6.7%.

Example 4 A toner prescribed from 25 parts of Hymer-UP-1 10 (polyester resin made by San-yo Chemical), 25 parts of Picolastick E100 (polystyrene made by Esso Standard), 50 parts of Mapico Black BL-500, 2.5 parts of Peerless-155, 2 parts of NAA-222 (a mixture of behenic, stearic, arachidic and palmitic acids, made by Nippon Yushi) and 1 part of Oil Black, was treated the same way as specimen No. 5 in Example 1 was.

Repeatedly developing and transferring were conducted with a U-BIX 2000 R copying machine made by Konishiroku Poto Industry Co. Ltd.; even after 20,000 copies, as clear an image as the initial image was obtained.

The value of V leak was 15.1% Example 5 A toner prescribed from 45 parts of Epikote 1004 (epoxy resin made by Shell Chemical), 55 parts of Mapico Black BL500, 2.5 parts of Peerless-155, 3 parts of a bisamide of the formula C17H25=CO NH-CH2-NH#)CC17H3 (made by Nippon Hydrogen Industrial) and 1 part of Rikemarl B-100 (a fatty acid ester made by Riken Vitamin Oil) was treated the same as specimen No. 6 in Example 1 was. Repeatedly developing and transferring were conducted with a U-BIX 2000 R type copying machine of Konishiroku Photo Industry Co. Ltd. and even after 30,000 copies, as clear an image as the initial image was obtained. The value of V leak was 4.6%.

Example 6 A recipe of 40 parts of Epikote 1004, 60 parts of Mapico Black BL- 100, 2 parts of Oil Black BS, 6 parts of zinc stearate and 2 parts of stearic acid was treated the same as the specimen in Control 2 was except that a heating temperature was made 3000 C.

Repeatedly developing and transferring were conducted and even after 10,000 copies, changes of an image were not recognized.

The value of V leak was 43.3 %.

Having regard to the provisions of Section 9 of the Patents Act 1949, attention is directed to the claims of British Patent Application No. 23623/77 (Serial No.

1,505,596).

WHAT WE CLAIM IS:- 1. A magnetic toner, for developing an electrostatic latent image, comprising particles comprising a thermoplastic resin and a powdered ferromagnetic substance, said toner comprising at least one additive selected from metallic soaps; fatty acids, amides or alcohols having at least 8 carbon atoms; lubricating hydrocarbons; and lubricating esters, said additive having a content gradient such that the content is higher at the surface than in the interior of said toner particles, and said toner having a character such that an electrostatic charge necessary to form an electrostatic latent image can be obtained by mutual friction of said toner particles and said toner particles have an electric resistance of 10'4rim. or above 2.A magnetic toner as claimed in Claim 1 wherein said thermoplastic resin comprises at least one styrene-type resin, polyester-type resin and/or, epoxy-type resin, or a mixture thereof with a different thermoplastic resin compatible therewith.

3. A toner as in Claim 2 wherein said styrene-type resin is a homopolymer of a styrene monomer or a copolymer of a styrene monomer with a vinyl-type comonomer.

4. A magnetic toner as claimed in Claim 3 wherein said vinyl-type comonomer is pchlorostyrene, an unsaturated olefin of the ethylene series, a vinyl halide, a vinyl ester, an a,ss-unsaturated aliphatic monocarboxylic acid ester, acrylonitrile, an acrylamide, a vinyl ether, an N-vinyl compound, of a mixture thereof.

5. A magnetic toner as claimed in Claim 2 wherein said polyester resins are a poly mer of a diol and a dicarboxylic acid.

6. A magnetic toner as clamied in Claim 2 or Claim 5 wherein said polyester resins incorporate a proportion of a branch-form ing agent selected from polyhydric alcohols having 3 to 15 carbon atoms and 3 to 8 hydroxyl groups and polycarboxylic acids having 3 to 60 carbon atoms and 3 to 8 carboxyl groups, or the esters thereof.

7. A magnetic toner as claimed in Claim 2 wherein said different compatible thermo plastic resin is derived from vinyl naphthal ene, a vinyl halide, a vinyl ester, and a,,B- unsaturated aliphatic monocarboxylic acid ester, acrylonitrile or an acrylamide, a vinyl ether, a vinyl ketone, a homopolymer or copolymer of an N-vinyl compound, a rosin modified phenolformaldehyde resin, an oil modified epoxy resin, a cellulosic resin or a polyether resin.

8. A magnetic toner as claimed in any preceding Claim wherein the softening point of said thermoplastic resin is 70 to 1500C.

9. A magnetic toner as claimed in any preceding Claim wherein said magnetic substance is cobalt, iron, nickel, an alloy or oxide thereof, ferrite or a mixture thereof.

10. A magnetic toner as claimed in any preceding Claim wherein said magnetic sub stance has an average particle diameter of 0.1 to 1 micron and the content thereof in the magnetic toner is 35 to 60 parts by weight, based on 100 parts by weight of the magnetic toner.

11. A magnetic toner claimed in any preceding Claim wherein the content of the additive is 0.2 to 20% by weight, based on the total weight of the toner.

12. A magnetic toner as claimed in any preceding Claim wherein the magnetic toner consists substantially of particles made spherical.

13. A magnetic toner as claimed in any preceding Claims wherein said magnetic toner contains 0.01 to 1.0 parts by weight of hydrophobic silica powder based on 100 parts by weight of said magnetic toner.

14. A magnetic toner as claimed in any preceding Claim wherein the decay factor of potential of the magnetic toner developed on a sensitized substance is less than 50% in a given measuring method.

15. A process for the preparation of a magnetic toner according to any of the preceding Claims which comprises the steps of mixing the additive selected from metallic soaps, fatty acids, fatty amides, alcohols, lubricating hydrocarbons and lubricating esters; the thermoplastic resin, and the powdered ferro magnetic substance knead ing, crushing to form particles and heat treating at a temperature range higher than the softening point of the thermoplastic resin.

16. A process as claimed in Claim 15 wherein the heat-treatment method employs a hot gas current.

17. A process as claimed in Claim 15 or 16 wherein hydrophobic silica powder is mixed with said crushed particles before heat-treatment.

18. A magnetic toner as claimed in Claim 1 substantially as hereinbefore des cribed and with reference to any of Examples 1 to 6.

19. A process as claimed in Claim 15 substantially - as hereinbefore described and with reference to any of Examples 1 to 6.

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

Claims (19)

**WARNING** start of CLMS field may overlap end of DESC **. directed to the claims of British Patent Application No. 23623/77 (Serial No. 1,505,596). WHAT WE CLAIM IS:-

1. A magnetic toner, for developing an electrostatic latent image, comprising particles comprising a thermoplastic resin and a powdered ferromagnetic substance, said toner comprising at least one additive selected from metallic soaps; fatty acids, amides or alcohols having at least 8 carbon atoms; lubricating hydrocarbons; and lubricating esters, said additive having a content gradient such that the content is higher at the surface than in the interior of said toner particles, and said toner having a character such that an electrostatic charge necessary to form an electrostatic latent image can be obtained by mutual friction of said toner particles and said toner particles have an electric resistance of 10'4rim. or above

2.A magnetic toner as claimed in Claim 1 wherein said thermoplastic resin comprises at least one styrene-type resin, polyester-type resin and/or, epoxy-type resin, or a mixture thereof with a different thermoplastic resin compatible therewith.

3. A toner as in Claim 2 wherein said styrene-type resin is a homopolymer of a styrene monomer or a copolymer of a styrene monomer with a vinyl-type comonomer.

4. A magnetic toner as claimed in Claim 3 wherein said vinyl-type comonomer is pchlorostyrene, an unsaturated olefin of the ethylene series, a vinyl halide, a vinyl ester, an a,ss-unsaturated aliphatic monocarboxylic acid ester, acrylonitrile, an acrylamide, a vinyl ether, an N-vinyl compound, of a mixture thereof.

5. A magnetic toner as claimed in Claim 2 wherein said polyester resins are a poly mer of a diol and a dicarboxylic acid.

6. A magnetic toner as clamied in Claim 2 or Claim 5 wherein said polyester resins incorporate a proportion of a branch-form ing agent selected from polyhydric alcohols having 3 to 15 carbon atoms and 3 to 8 hydroxyl groups and polycarboxylic acids having 3 to 60 carbon atoms and 3 to 8 carboxyl groups, or the esters thereof.

7. A magnetic toner as claimed in Claim 2 wherein said different compatible thermo plastic resin is derived from vinyl naphthal ene, a vinyl halide, a vinyl ester, and a,,B- unsaturated aliphatic monocarboxylic acid ester, acrylonitrile or an acrylamide, a vinyl ether, a vinyl ketone, a homopolymer or copolymer of an N-vinyl compound, a rosin modified phenolformaldehyde resin, an oil modified epoxy resin, a cellulosic resin or a polyether resin.

8. A magnetic toner as claimed in any preceding Claim wherein the softening point of said thermoplastic resin is 70 to 1500C.

9. A magnetic toner as claimed in any preceding Claim wherein said magnetic substance is cobalt, iron, nickel, an alloy or oxide thereof, ferrite or a mixture thereof.

10. A magnetic toner as claimed in any preceding Claim wherein said magnetic sub stance has an average particle diameter of 0.1 to 1 micron and the content thereof in the magnetic toner is 35 to 60 parts by weight, based on 100 parts by weight of the magnetic toner.

11. A magnetic toner claimed in any preceding Claim wherein the content of the additive is 0.2 to 20% by weight, based on the total weight of the toner.

12. A magnetic toner as claimed in any preceding Claim wherein the magnetic toner consists substantially of particles made spherical.

13. A magnetic toner as claimed in any preceding Claims wherein said magnetic toner contains 0.01 to 1.0 parts by weight of hydrophobic silica powder based on 100 parts by weight of said magnetic toner.

14. A magnetic toner as claimed in any preceding Claim wherein the decay factor of potential of the magnetic toner developed on a sensitized substance is less than 50% in a given measuring method.

15. A process for the preparation of a magnetic toner according to any of the preceding Claims which comprises the steps of mixing the additive selected from metallic soaps, fatty acids, fatty amides, alcohols, lubricating hydrocarbons and lubricating esters; the thermoplastic resin, and the powdered ferro magnetic substance knead ing, crushing to form particles and heat treating at a temperature range higher than the softening point of the thermoplastic resin.

16. A process as claimed in Claim 15 wherein the heat-treatment method employs a hot gas current.

17. A process as claimed in Claim 15 or 16 wherein hydrophobic silica powder is mixed with said crushed particles before heat-treatment.

18. A magnetic toner as claimed in Claim 1 substantially as hereinbefore des cribed and with reference to any of Examples 1 to 6.

19. A process as claimed in Claim 15 substantially - as hereinbefore described and with reference to any of Examples 1 to 6.